JP4578887B2 - Etching method and etching apparatus - Google Patents

Description

  The present invention relates to an etching method and an etching apparatus for etching a silicon substrate by converting an etching gas and a protective film forming gas into plasma.

  Conventionally, as a method for etching a silicon substrate, after placing the silicon substrate on a base, while applying a bias voltage to the base, the etching gas is turned into plasma to etch the silicon substrate, and a protective film is formed. A method is known in which a gas is turned into plasma and a protective film forming process for forming a protective film on a structure surface formed by the etching is alternately and repeatedly performed to etch a silicon substrate.

  When the etching gas is turned into plasma, ions, electrons, radicals, etc. are generated, and the radicals chemically react with silicon atoms, or ions move toward the silicon substrate (base) due to the bias voltage generated at the base. The silicon substrate is etched by the collision. Thereby, a groove (hole) having a predetermined width and depth is formed in the silicon substrate. Incidentally, most of the ions irradiated to the silicon substrate are incident perpendicularly to the surface of the silicon substrate and collide with the bottom surface of the groove.

  On the other hand, when the protective film forming gas is turned into plasma, ions, electrons, radicals, etc. are generated like the etching gas, and a polymer is generated from these radicals, and the generated polymer is deposited on the side wall and bottom surface of the groove. Thus, a protective film that does not react with radicals generated from the etching gas is formed.

  According to this etching method, during the etching process, the protective film is removed by ion irradiation and the etching by radical and ion irradiation proceeds on the bottom surface of the groove with a large amount of ion irradiation, while ions are formed on the side wall of the groove with a small amount of ion irradiation. Only the removal of the protective film by irradiation is advanced to prevent the side wall from being etched, and during the protective film forming process, the protective film can be formed by re-depositing the polymer on the bottom surface and the side wall. By alternately repeating the etching process and the protective film forming process, a new sidewall of the groove formed by the etching process is immediately protected by the protective film formed by the protective film forming process, and Etching can proceed only in the depth direction.

  However, in the etching method described above, some of the ions irradiated to the silicon substrate are bent in the moving direction due to collision with gas molecules, charge-up of the silicon substrate surface, etc., and obliquely with respect to the silicon substrate surface. Since it enters and collides with the upper side wall of the groove, the protective film on the upper side wall is more easily removed than the bottom side. When the protective film is removed and the side wall surface is exposed, the exposed part is etched by ion irradiation or radicals. Therefore, each time the above processes are repeated, the etching of the upper part of the side wall also proceeds. As shown in the drawing, there is a problem that the upper opening of the groove is widened, or the upper side wall of the groove is in an arcuate shape as shown in FIG.

  In particular, in the case of etching a silicon substrate having a high aspect ratio (depth is deeper than the opening width of the groove), it is necessary to repeat each of the above treatments by the amount of the deeper groove. Such a problem appears remarkably. In FIGS. 6 and 7, symbol K indicates a silicon substrate, symbol T indicates a groove, and symbol M indicates a mask.

  Therefore, in order to solve such a problem, an etching method as disclosed in Japanese Patent Application Laid-Open No. 2000-299310 has been proposed, and this etching method includes the above-described etching process and protective film forming process. After removing the etching process alternately repeating a certain number of times and the protective film formed by the protective film formation process from the surface of the groove, the surface hardly reacts with radicals generated from the etching gas and is irradiated by ion irradiation. Also, an oxide film forming step for forming an oxide film that is difficult to be etched is alternately repeated.

  In the oxide film formation process, a mixed gas of argon and oxygen is turned into plasma to generate oxygen ions, oxygen radicals, and argon ions, and a bias voltage is applied to the base to form a protective film with oxygen ions and oxygen radicals. Chemical reaction with the atoms to be bombarded, or argon ions collide with the silicon substrate to remove the protective film formed on the surface of the groove and to expose the surface, and to convert only oxygen gas into plasma Then, oxygen ions and oxygen radicals are generated, and an oxide film forming process for forming an oxide film on the surface of the groove exposed by the protective film removing process is performed by the generated oxygen ions and oxygen radicals.

  In the etching method configured as described above, the protective film is formed on the oxide film by alternately repeating the etching process and the oxide film forming process, and the sidewall of the groove is formed of two layers of the protective film and the oxide film. Since it can be protected by a film, even if the protective film is removed during the etching process and the oxide film may be exposed, the oxide side wall is effectively prevented from being etched by the oxide film. Can do. Thereby, it is possible to prevent the upper side wall of the groove from having a shape as shown in FIGS. 6 and 7, and to obtain a highly accurate etching shape.

JP 2000-299310 A

  By the way, in carrying out the etching method as described above, after a silicon substrate is carried into a processing chamber having a closed space and placed on a base, a predetermined gas (etching gas, A protective film forming gas, a mixed gas of argon and oxygen, oxygen gas) is supplied, and the gas in the processing chamber is appropriately converted into plasma, and the above-described processes (etching process, protective film forming process, protective film removing process, and oxide film forming) Process).

  However, when performing a series of processes for etching a silicon substrate in this way, if four kinds of gases are replaced in the processing chamber, the gas substituting property in the processing chamber is not constant when the gases are replaced. Since the gas components in the processing chamber are different for each cycle and the state of the generated plasma changes for each cycle, there is a problem that the variation in etching shape generated for each silicon substrate is large.

  Further, it is necessary to connect four supply pipes, a supply pipe for supplying an etching gas, a supply pipe for supplying a protective film forming gas, a supply pipe for supplying argon gas, and a supply pipe for supplying oxygen gas, to the processing chamber. There is also a problem that the device configuration becomes complicated.

  In addition, the resist mask has a problem that it is not practical for etching a high aspect ratio silicon substrate because the mask is easily removed by reaction with oxygen radicals and the selection ratio of the mask to silicon is low.

  The present invention has been made in view of the above circumstances, and provides an etching method and an etching apparatus capable of obtaining a highly accurate etching shape and suppressing variations in the etching shape of each silicon substrate. For that purpose.

To achieve the above object, the present invention provides:
A method of etching a silicon substrate placed on a base in a processing chamber, wherein an etching gas is supplied into the processing chamber and high-frequency power is applied to a coil disposed near the outside of the processing chamber. Applying the etching gas into plasma and applying high frequency power to the base, etching process for etching the silicon substrate, supplying a protective film forming gas into the processing chamber, and supplying the coil to the coil Including a first protective film forming step of forming a protective film on the silicon substrate by applying high-frequency power to plasma the protective film forming gas, and starting from the etching step or the first protective film forming step The etching process and the first protective film forming process are alternately and repeatedly performed,
The first protective film forming step is a silicon substrate etching method in which each processing time to be repeatedly performed is a fixed time each time or is set to vary within a fixed time each time,
Similarly to the first protective film forming step, the protective film forming gas is supplied into the processing chamber, and a high frequency power is applied to the coil to convert the protective film forming gas into plasma, thereby forming the protective film. The processing time is set to a time that is not less than 3 times and not more than 45 times the predetermined time as compared to the first protection film forming step, or the protection film forming gas in the processing chamber is formed. A second protective film forming step is performed, which is performed under a condition where the pressure is set high, and forms a protective film having a higher etching resistance than the protective film formed in the first protective film forming step,
The etching process and the first protective film forming process are repeatedly performed a predetermined number of times, then the second protective film forming process is performed, and then the etching process and the first protective film forming process are performed again. The present invention relates to an etching method characterized in that the process is repeatedly performed.

And this etching method can implement this suitably with the following etching apparatuses.
That is, this etching apparatus
A processing chamber having an enclosed space;
A base disposed on the lower side in the processing chamber and on which a silicon substrate is placed;
Base power supply means for applying high frequency power to the base;
Etching gas supply means for supplying an etching gas into the processing chamber;
Protective film forming gas supply means for supplying a protective film forming gas into the processing chamber;
Flow rate adjusting means for adjusting the flow rates of the etching gas and the protective film forming gas supplied into the processing chamber by the etching gas supply means and the protective film forming gas supply means;
A coil disposed near the outside of the processing chamber;
Coil power supply means for applying high-frequency power to the coil to turn the etching gas and protective film forming gas supplied into the processing chamber into plasma,
The base power supply means, a control means for controlling the coil power supply means and the flow rate adjusting means, a high-frequency power is applied to the base, and the etching gas supply means or Lae Tchingugasu into the processing chamber supplies, supplying an etching step of etching the silicon substrate by plasma the etching gas by applying a high frequency power to said coil, said protective film forming gas supplying means or RaTamotsu Mamorumaku forming gas into the processing chamber to together, and a to that control means executes the first protective film forming step of forming a protective film high-frequency power is applied by plasma the protective film forming gas to the silicon substrate to the coil,
The control means starts from the etching step or the first protective film forming step, and repeatedly performs the etching step and the first protective film forming step alternately, and repeatedly performs each first protective film formation. The process is configured to be performed at a certain time each time or at a processing time varied within a certain time each time,
The control means further supplies the protective film forming gas into the processing chamber and applies high frequency power to the coil to convert the protective film forming gas into plasma, as in the first protective film forming step. In this process, the protective film is formed, and the processing time is set to be not less than 3 times and not more than 45 times the predetermined time compared to the first protective film forming process, or the processing chamber is formed. A second protective film forming step of forming a protective film having a higher etching resistance than the protective film formed in the first protective film forming step, under the condition that the pressure of the protective film forming gas inside is set high And repeatedly performing the etching step and the first protective film forming step a predetermined number of times, then performing the second protective film forming step, and then again, Etching process Configured repeatedly to continue running the first protective film forming step.

  According to this etching apparatus, after the silicon substrate is placed on the base in the processing chamber, the etching process and the first protective film forming process are started from the etching process or the first protective film forming process. Repeated alternately. Each of the repeated first protective film forming steps may be performed at a constant processing time each time or may be performed at a processing time varied within the predetermined time each time.

  In the etching process, under the control of the control means, the etching gas whose flow rate is adjusted by the flow rate adjusting means is supplied into the processing chamber from the etching gas supply means for a predetermined time, and the high frequency is supplied by the coil power supply means and the base power supply means. Electric power is applied to the coil and the base, respectively.

  When high frequency power is applied to the coil, a magnetic field is formed in the processing chamber, and the electric field induced by the magnetic field causes the etching gas supplied into the processing chamber to be a plasma containing ions, electrons, radicals, and the like. The Further, when high frequency power is applied to the base, a bias voltage is generated between the base and the plasma.

  The radicals chemically react with the silicon atoms to etch the silicon substrate, and the ions move toward the silicon substrate (base) side by the bias voltage and collide with each other to etch the silicon substrate. Thereby, a groove (hole) having a predetermined width and depth is formed in the silicon substrate. Incidentally, most of the ions moving toward the silicon substrate are incident perpendicularly to the silicon substrate surface and collide with the substrate surface.

  On the other hand, in the first protective film forming step, as in the etching step, the protective film forming gas whose flow rate is adjusted under the control of the control means is supplied from the protective film forming gas supply means into the processing chamber for a predetermined time (the predetermined time or The high frequency power is applied to the coil by the coil power supply means.

  The protective film forming gas supplied into the processing chamber is a plasma containing ions, electrons, radicals, and the like by the electric field, as with the etching gas, and a polymer is generated from the radicals to form sidewalls and bottom surfaces of the grooves. To deposit. Thereby, a protective film that does not react with radicals generated from the etching gas is formed on the side wall and the bottom surface.

  As described above, by alternately repeating the etching process and the first protective film forming process, in the etching process, removal of the protective film by ion irradiation and etching by radical and ion irradiation proceed on the bottom surface of the groove where ion irradiation is frequently performed. On the other hand, on the side wall of the groove with less ion irradiation, only the removal of the protective film by ion irradiation proceeds to prevent the side wall from being etched, and in the first protective film forming step, polymerization is performed on the bottom surface and the side wall. Since the protective film is formed by depositing again, the new sidewall of the groove formed in the etching process is immediately protected by the protective film formed in the first protective film forming process, and only in the depth direction of the groove. Etching progresses.

  By the way, as described above, most of the ions irradiated to the silicon substrate are incident perpendicularly to the surface of the silicon substrate and collide with the bottom surface of the groove, but some of the ions collide with gas molecules. Since the movement direction is bent due to the charge-up of the silicon substrate surface, it enters the silicon substrate surface from an oblique direction and collides with the side wall on the upper side of the groove, so the protective film on the upper side of the side wall is removed from the bottom side. It is easy to be done. When the protective film is removed and the sidewall surface is exposed, the exposed portion is etched by ion irradiation and radicals. Therefore, each time the above steps are repeated, the etching of the upper portion of the sidewall also proceeds, and the upper portion of the groove. It becomes a shape in which the opening is widened or the shape of the upper side wall of the groove is in a circular shape, so that a highly accurate etching shape cannot be obtained.

Therefore, in this onset bright constitutes prior Symbol to further execute a second protective film forming step of forming etch-resistant high protective film than the protective film formed by the first protective film forming step, further The etching process and the first protective film forming process are repeatedly performed a predetermined number of times, and then the second protective film forming process is performed. Thereafter, the etching process and the first protective film forming process are performed again. And are repeatedly executed.

  Thereby, in the second protective film forming step, a protective film having a higher etching resistance (hard to be removed) than the protective film formed in the first protective film forming step is formed on the bottom surface and side wall of the groove, that is, Compared to the first protective film forming step, a thick protective film or a dense protective film having a high film density can be formed. Therefore, the etching step and the first protective film forming step Is repeated, the protective film on the upper side wall of the groove is removed and the side wall surface is effectively prevented from being etched, and a highly accurate etching shape can be obtained.

  The control means repeats the etching process and the first protective film forming process a predetermined number of times and then executes the first protective film forming process to be executed next. The second protective film forming step may be executed instead of the forming step, and then the etching step and the first protective film forming step may be repeatedly executed again in this way. Also, the same effect as described above can be obtained.

In addition, the processing condition in the second protective film forming step for obtaining a protective film having high etching resistance is that the processing time is longer than that in the first protective film forming step, or the protection in the processing chamber is performed. the pressure of the film forming gas is high.

In this case, the protective film having a larger thickness can be formed by supplying the protective film forming gas into the processing chamber for a longer time than the first protective film forming step . Also, the pressure of the protective film deposition gas in the processing chamber by supplying a first protective film formed becomes higher as the protective film forming gas processing chamber than step, protected by generating more radicals Formation of a film can be promoted (deposition rate can be increased), and a protective film with a thicker film and better film quality can be formed. Thereby, it is possible to more effectively prevent the surface of the upper side wall of the groove from being etched, and a highly accurate etching shape can be obtained.

Incidentally, pre-Symbol processing time in the second protective film forming step, preferably not more than 45 times more than three times the predetermined time in the first protective film forming step.

  This is because if the time is shorter than three times, the protective film to be formed is insufficient (thin), and the protective film is immediately formed even though the thicker protective film is formed in the second protective film forming step. This is because the sidewall surface is etched and the surface of the sidewall is etched. On the contrary, if the time is longer than 45 times, the protective film to be formed is too thick (too thick), the etching rate is reduced, This is because it becomes difficult to remove the protective film on the side wall bottom side, and the groove width on the bottom side becomes small. For this reason, a protective film having an appropriate thickness can be formed within the above range, that is, the thickness of the protective film to be formed can be balanced with the thickness of the protective film to be removed. An accurate etching shape can be obtained.

  In addition, the control means supplies high frequency power to the base by the base power supply means at least during the execution of the second protective film formation process of the first protective film formation process and the second protective film formation process. It is preferable to be configured to be applied. In this way, even when the second protective film forming step is performed, a bias voltage can be generated between the base and the plasma, and ions can collide with the silicon substrate (protective film). As a result, the ions efficiently reach the bottom and side walls of the groove where the polymer is difficult to deposit, and the action of such ions can improve the quality of the protective film formed on the bottom and side walls of the groove. An accurate etching shape can be obtained.

  In this case, the control means includes the base power so that the high frequency power applied to the base when the second protective film forming step is performed is higher than that when the first protective film forming step is performed. More preferably, the supply means is configured to be controlled, and in this way, a protective film with better film quality can be formed as compared with the first protective film forming step, and therefore more accurate. An etched shape can be obtained.

Thus, according to the etching method and the etching apparatus according to the present invention, when the etching process and the first protective film forming process are repeated a predetermined number of times, the second protective film forming process or the first protective film forming process is performed. Instead of performing the second protective film forming process, the etching process and the first protective film forming process are continuously repeated, and in the second protective film forming process, the first protective film forming process is performed. Since the protective film having high etching resistance is formed on the bottom and side walls of the groove, it is possible to effectively prevent the upper part of the side wall of the groove from being etched, and the shape of the high aspect ratio is Can be etched with high accuracy.

  Further, unlike the conventional etching method described above, it is not necessary to exchange various types of gases in the processing chamber, and a series of processes for etching a silicon substrate can be performed by alternately replacing only two types of gases. Therefore, the gas replacement property in the processing chamber can be further stabilized, and the gas components in the processing chamber can be made substantially the same for each cycle. As a result, the state of the generated plasma can be made substantially constant for each cycle, and the variation in the etching shape generated for each silicon substrate can be reduced.

  Furthermore, it is only necessary to connect only two supply pipes, ie, a supply pipe for supplying an etching gas and a supply pipe for supplying a protective film forming gas, to the processing chamber. Therefore, it is not necessary to connect many supply pipes so that the structure of the etching apparatus can be simplified. Further, the resist mask is removed by oxygen radicals, and there is no possibility that the mask selection ratio is lowered.

  Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view partially showing a schematic configuration of an etching apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an etching apparatus 1 of this example includes a processing chamber 11 having a closed space, and a base on which a silicon substrate K to be etched is placed, which is disposed on the lower side of the processing chamber 11. 12, a decompression device 14 for decompressing the inside of the processing chamber 11, a gas supply device 20 for supplying an etching gas and a protective film forming gas into the processing chamber 11, and a plasma of the etching gas and the protective film forming gas in the processing chamber 11 A plasma generator 30 to be converted, a first high-frequency power source 13 for applying a high-frequency power to the base 12 to generate a bias voltage between the base 12 and the plasma, a gas supply device 20, and a plasma generator 30 And a control device 40 that controls the operation of the first high-frequency power source 13 and the like.

  The decompression device 14 includes an exhaust pipe 15 connected to the lower portion of the processing chamber 11 and a vacuum pump 16 connected to the exhaust pipe 15, and the pressure in the processing chamber 11 is reduced by the vacuum pump 16.

The gas supply device 20 includes a supply pipe 21 connected to the upper end portion of the processing chamber 11 and gas cylinders 22 and 23 connected to the supply pipe 21 via flow rate adjustment mechanisms 24 and 25. The gas whose flow rate has been adjusted by 25 is supplied from the gas cylinders 22 and 23 into the processing chamber 11. The gas cylinder 22 is filled with SF ₆ gas for etching, and the gas cylinder 23 is filled with C ₄ F ₈ gas for forming a protective film.

  The plasma generating apparatus 30 includes a coil 31 disposed on the outer peripheral upper side of the processing chamber 11 and a second high-frequency power source 32 that applies high-frequency power to the coil 31. By applying electric power, a magnetic field is formed in the processing chamber 11, and the gas in the processing chamber 11 is turned into plasma by an electric field induced by the magnetic field.

The control device 40 controls the flow rate adjusting mechanisms 24 and 25 to adjust the flow rates of SF ₆ gas and C ₄ F ₈ gas supplied from the gas cylinders 22 and 23 into the processing chamber 11, and A base power control unit 42 that controls the first high frequency power supply 13 to adjust the high frequency power applied to the base 12, and a coil that controls the second high frequency power supply 32 to adjust the high frequency power applied to the coil 31. And a power control unit 43.

  2 and 3, the control device 40 performs an etching process for etching the silicon substrate K and a protective film forming process for forming a protective film on the silicon substrate K (the first protective film forming process and the second protective film forming process). The protective film forming process is performed, and the etching process and the first protective film forming process are alternately and repeatedly performed while the etching process and the first protective film forming process are alternately performed. When the process is repeatedly executed a predetermined number of times (4 and 8 in FIGS. 2 and 3), the first protective film formation process to be executed next (fifth and tenth times) Instead of the first protective film forming process, the second protective film forming process is executed, and thereafter, the etching process and the first protective film forming process are repeatedly executed again. In the figure, symbol E indicates an etching processing time zone, symbol D1 indicates a first protective film forming processing time zone, and symbol D2 indicates a second protective film forming processing time zone.

  In addition, the control device 40 executes the etching process and the first protective film forming process every time for a predetermined processing time set for the etching process and the first protective film forming process, respectively, and the second protective film forming process. Is executed every time with a processing time set for the second protective film forming process of 3 to 45 times the processing time in the first protective film forming process.

  The controller 40 is configured to execute the first protective film forming process and the second protective film forming process in this way, as described later, in the second protective film forming process. This is because a protective film having higher etching resistance than that of the protective film formed by the first protective film forming process is formed.

As shown in FIGS. 2A and 2B, the flow rate control unit 41 controls the flow rate adjusting mechanisms 24 and 25 to supply SF ₆ gas and C supplied from the gas cylinders 22 and 23 into the processing chamber 11. by varying the flow rate of ₄ F ₈ gas, while supplying only SF ₆ gas in the etching process time E, supplies only _C 4 _{F 8} gas in the protective film forming process at the time D1, D2.

Further, the flow rate control unit 41 determines that the supply flow rate V _D1 of the C ₄ F ₈ gas during the second protective film formation process D2 is the supply flow rate during the first protective film formation process D1 as shown in FIG. The pressure of C ₄ F ₈ gas supplied into the processing chamber 11 during the second protective film forming process D2 is higher than that during the first protective film forming process D1 so as to be higher than V _D2. Next, the flow rate adjusting mechanism 25 is controlled.

As shown in FIG. 3A, the base power control unit 42 applies the first high frequency power so as to apply a predetermined high frequency power to the base 12 during the etching process E and the second protective film formation process D2. The power supply 13 is controlled. The high frequency power applied during the second protective film formation process D2 is set to _WP2, and is set higher than that during the first protective film formation process D1 (zero applied power).

As shown in FIG. 3B, the coil power control unit 43 applies the second high frequency power source 32 so as to apply a predetermined high frequency power to the coil 31 during the etching process E and the protective film formation process D1 and D2. To control. Incidentally, the high-frequency power applied to the second protective film forming process when D2 is set to W _C2, the high-frequency power applied to the first protective film forming process at the time D1 is set higher than the W _C3.

According to the etching apparatus 1 of the present example configured as described above, first, the silicon substrate K is placed on the base 12 in the processing chamber 11. Next, SF ₆ gas whose flow rate is adjusted by the flow rate adjusting mechanism 24 under the control of the control device 40 is supplied from the gas cylinder 22 into the processing chamber 11, and high-frequency power is supplied from the high-frequency power sources 13 and 32 to the base 12. And applied to the coil 31, respectively.

The SF ₆ gas supplied into the processing chamber 11 is converted into plasma containing ions, electrons, F radicals, etc. by the electric field formed by the coil 31 to which high frequency power is applied, and the F radicals chemically react with silicon atoms. Then, the silicon substrate K is etched, and the ions move toward the silicon substrate K (base 12) side by the bias voltage generated between the base 12 to which the high frequency power is applied and the plasma, and collide with each other. The substrate K is etched. Thereby, a groove (hole) having a predetermined width and depth is formed in the silicon substrate K. Most of the ions moving toward the silicon substrate K are incident on the surface of the silicon substrate K perpendicularly and collide with the surface of the substrate K.

When the SF ₆ gas is supplied for a predetermined time, under the control of the control device 40, the supply of the SF ₆ gas is stopped by the flow rate adjustment mechanism 24 and the flow rate is adjusted by the flow rate adjustment mechanism 25. ₄ F ₈ gas is supplied from the gas cylinder 23 into the processing chamber 11. In addition, the high frequency power is applied to the coil 31 by the second high frequency power supply 32 as in the case of supplying SF ₆ gas, but the application of the high frequency power to the base 12 by the first high frequency power supply 13 is stopped.

Like the SF ₆ gas, the C ₄ F ₈ gas supplied into the processing chamber 11 is converted into plasma containing ions, electrons, radicals, and the like by the electric field, and a polymer is generated from the radicals, and the grooves Deposit on the sidewalls and bottom. Thereby, a fluorocarbon film (protective film) that does not react with the F radicals is formed on the side wall and the bottom surface.

When the C ₄ F ₈ gas is supplied for a predetermined time, the supply of the C ₄ F ₈ gas is stopped by the flow rate adjusting mechanism 25, and then the SF ₆ gas is supplied again to perform an etching process. The etching process and the protective film forming process (first protective film forming process) are alternately and repeatedly executed.

  As described above, by alternately repeating the etching process and the first protective film forming process, the protective film is removed by ion irradiation and the etching is performed by F radical and ion irradiation at the bottom surface of the groove where ion irradiation is frequently performed. On the other hand, on the side wall of the groove with less ion irradiation, only the removal of the protective film by ion irradiation proceeds and the side wall is prevented from being etched, and during the first protective film forming process, the bottom surface and Since the polymer is deposited again on the side wall to form the protective film, the new side wall of the groove formed by the etching process is immediately protected by the protective film formed by the first protective film forming process, and the depth of the groove is increased. Etching proceeds only in the vertical direction.

  By the way, as described above, most of the ions irradiated to the silicon substrate K are incident on the surface of the silicon substrate K perpendicularly and collide with the bottom surface of the groove. Since the movement direction is bent due to collision, charge-up of the surface of the silicon substrate K, etc., it is incident on the surface of the silicon substrate K from an oblique direction and collides with the upper side wall of the groove. It is easier to remove than the bottom side. When the protective film is removed and the sidewall surface is exposed, the exposed portion is etched by ion irradiation and F radicals. Therefore, the etching of the upper portion of the sidewall also proceeds each time the above processes are repeated. As shown in FIG. 7, the groove has a shape in which the upper opening of the groove is widened, or as shown in FIG.

  Therefore, in the etching apparatus 1 of this example, when the etching process and the first protective film forming process are repeatedly performed a preset number of times, the first protection film is formed when the first protective film forming process to be performed next is performed. The second protective film forming process is executed in place of the film forming process, and then the etching process and the first protective film forming process are repeatedly performed again, and the second protective film forming process is performed. In the processing, the processing conditions are different from those of the first protective film formation processing.

Specifically, the processing condition of the second protective film forming process is that the processing time is longer than that of the first protective film forming process (a process that is not less than 3 times and not more than 45 times the processing time in the first protective film forming process). In time), the supply flow rate of the C ₄ F ₈ gas supplied into the processing chamber 11 is increased, the pressure of the C ₄ F ₈ gas in the processing chamber 11 is increased, and the high frequency power applied to the base 12 and the coil 31 Is set high.

  Thereby, in the second protective film forming process, a protective film having a higher etching resistance (hard to be removed) than the protective film formed in the first protective film forming process is formed on the bottom surface and side wall of the groove, that is, Compared to the first protective film forming process, a thick protective film or a dense protective film with a high film density can be formed. Therefore, the etching process and the first protective film forming process Is repeated, the protective film on the upper side wall of the groove is removed and the side wall surface is effectively prevented from being etched, and even a high aspect ratio shape can be etched with high accuracy. .

In addition, by supplying the C ₄ F ₈ gas at a flow rate higher than that of the first protective film formation process, it is possible to generate more radicals and promote the generation of the protective film (increase the film formation rate). A protective film with better film quality can be formed, and by increasing the pressure of the C ₄ F ₈ gas in the processing chamber 11 higher than that in the first protective film forming process, more radicals can be formed in the same manner. It is possible to promote the generation of the protective film (increase the film formation speed) and to form a protective film with a thicker film and better film quality, and moreover than the first protective film forming process. By applying high high frequency power to the coil 31, the plasma density of the C ₄ F ₈ gas can be increased, radicals and the like can be generated efficiently, and a protective film can be generated efficiently. Thick and It is possible to form a good protective film quality. Thereby, it is possible to more effectively prevent the surface of the upper side wall of the groove from being etched, and a highly accurate etching shape can be obtained.

  In addition, since the processing time of the second protective film forming process is set to a processing time that is three to 45 times the processing time in the first protective film forming process, a protective film with an appropriate thickness can be formed, The thickness of the protective film to be formed and the thickness of the protective film to be removed can be balanced, and a highly accurate etching shape can be obtained.

  It should be noted that such a range is that if the time is shorter than three times, the protective film formed is insufficient (thin), and a thicker protective film is formed in the second protective film formation process. Regardless, the protective film is removed immediately and the side wall surface is etched. Conversely, if the time is longer than 45 times, the protective film is formed too much (too thick) and the etching rate is increased. This is because it is difficult to remove the protective film on the bottom side of the side wall of the groove and the width of the groove on the bottom side becomes small.

  Further, in the second protective film formation process, the high frequency power is applied to the base 12, and the high frequency power higher than that in the first protective film formation process (zero applied power) is applied. A highly accurate etching shape can be obtained. This is because a bias voltage is generated between the base 12 and the plasma to cause the ions to collide with the silicon substrate K (protective film), so that the ions are also efficiently applied to the bottom and side walls of the groove where the polymer is difficult to deposit. This is because the film quality of the protective film formed on the bottom surface and the side wall of the groove can be improved by the action of the ions as compared with the first protective film forming process.

  In addition, unlike the conventional etching method described above, it is not necessary to replace various types of gases in the processing chamber 11, and a series of processes for etching the silicon substrate K is performed by alternately replacing only two types of gases. Therefore, the gas replacement property in the processing chamber 11 can be made more stable, and the gas components in the processing chamber 11 can be made substantially the same for each cycle. Thereby, the state of the generated plasma can be made substantially constant for each cycle, and the variation in the etching shape that occurs for each silicon substrate K can be reduced.

Further, only two supply pipes, that is, a supply pipe for supplying an etching gas (SF ₆ gas) and a supply pipe for supplying a protective film forming gas (C ₄ F ₈ gas) may be connected to the processing chamber 11. Since it is not necessary to connect many supply pipes in order to supply various kinds of gases into the processing chamber 11 as in the prior art, the apparatus configuration of the etching apparatus 1 can be simplified. Further, the resist mask is removed by oxygen radicals, and there is no possibility that the mask selection ratio is lowered.

Incidentally, in the etching process, the processing time is 8 seconds, the pressure in the processing chamber 11 is 2 Pa, the high frequency power applied to the coil 31 is 1.8 kW, the high frequency power applied to the base 12 is 25 W, The supply flow rate of SF ₆ gas is 300 ml / min, and in the first protective film forming process, the processing time is 3 seconds, the pressure in the processing chamber 11 is 2.67 Pa, and the high frequency power applied to the coil 31 is 1 0.5 kW, the high frequency power applied to the base 12 is 0 W, the supply flow rate of the C ₄ F ₈ gas is 180 ml / min, and the processing time is 6 seconds, 9 seconds, 15 at the time of the second protective film forming process. Seconds, 30 seconds, 60 seconds, 90 seconds, 120 seconds, 150 seconds or 300 seconds, the pressure in the processing chamber 11 is 2.67 Pa, the high frequency power applied to the coil 31 is 1.5 kW, Apply The first protective film is formed after alternately repeating the etching process and the first protective film forming process for a predetermined time under the condition that the high-frequency power is 20 W and the supply flow rate of C ₄ F ₈ gas is 180 ml / min. The second protective film forming process is performed instead of the process, and then the silicon substrate having a mask opening width of 5 μm is etched by alternately repeating the etching process and the first protective film forming process again for a predetermined time. As a result, the results shown in FIG. 4 were obtained for the relationship between the processing time of the second protective film forming process and the groove depth, the upper groove width, and the bottom groove width.

  As shown in FIG. 4, when the processing time of the second protective film forming process is 6 seconds, the groove width is wide as a whole, and when it is 150 seconds, the bottom groove width is reduced and a residue is generated at the bottom of the groove. However, at 300 seconds, the bottom groove width could not be measured due to residue. Also from this result, as a preferable range of the processing time in the second protective film forming process, a time (9 seconds to 135 seconds) that is not less than 3 times and not more than 45 times the processing time (3 seconds) in the first protective film forming process. It can be said that it is in the range. In FIG. 4, the upper groove width is the portion indicated by symbol a in FIG. 6, and the bottom groove width is the portion indicated by symbol b in FIG. 6.

  As mentioned above, although one Embodiment of this invention was described, the specific aspect which this invention can take is not limited to this at all.

  In the above example, for example, as illustrated in FIG. 2, the etching process and the first protective film forming process are alternately and repeatedly started from the etching process. However, the present invention is not limited to this. As shown in FIG. 5A, the first protective film forming process D1 and the etching process E may be alternately and repeatedly started from the first protective film forming process D1.

  In this case as well, if the first protective film formation process D1 and the etching process E are repeatedly performed a predetermined number of times, the first protection film formation process D1 to be executed next is executed. The second protective film forming process D2 is executed instead of the film forming process D1, and thereafter, the first protective film forming process D1 and the etching process E are repeatedly executed again.

  Even in this case, the same effect as described above can be obtained, and a protective film is formed on the surface of the silicon substrate K by the first protective film forming process D1 before the first etching process E is performed. Therefore, it is possible to effectively prevent the side wall of the groove formed by the first etching process E from being etched.

  Further, as shown in FIG. 5B, starting from the etching process E, the etching process E and the first protective film forming process D1 are alternately and repeatedly performed, and the etching process E and the first protective film formation are performed. After the process D1 is repeatedly executed a predetermined number of times, the second protective film forming process D2 is executed, and then the etching process E and the first protective film forming process D1 are repeatedly executed again. May be.

  Further, as shown in FIG. 5C, the first protective film forming process D1 and the etching process E are alternately and repeatedly started from the first protective film forming process D1, and the first protective film is formed. After the film forming process D1 and the etching process E are repeatedly performed a predetermined number of times, the second protective film forming process D2 is performed, and then the first protective film forming process D1 and the etching process E are continuously repeated again. It may be configured to execute.

  Even if the etching process E and the first protective film forming process D1 are alternately repeated as shown in FIGS. 5B and 5C, the same effect as described above can be obtained.

  Further, the number of times the second protective film forming process is executed in the series of processes for etching the silicon substrate K is not limited at all, and may be executed only once. Further, as in the above example, the second protective film formation process may be executed randomly rather than periodically (periodically).

  In the above example, the processing time of the etching process and the first protective film forming process is set to a fixed processing time, but the processing time is not limited to this, and is changed each time within a fixed time (for example, the first processing time) The processing times of the first etching process and the first protective film forming process are 10 seconds and 4 seconds, respectively, the processing times of the second etching process and the first protective film forming process are 8 seconds and 3 seconds, respectively. The processing time of the third etching process and the first protective film forming process may be 6 seconds and 2 seconds, respectively). In this case, the processing time of the second protective film forming process is set to be not less than 3 times and not more than 45 times the predetermined time of the first protective film forming process (the longest processing time in the first protective film forming process). .

  Further, the high frequency power applied to the coil 31 and the high frequency power applied to the base 12 are set to be lower even if the etching process is set to be higher than the second protective film forming process. Either way is fine. Furthermore, in the above example, the high-frequency power applied to the base 12 during the first protective film forming process is zero, but a predetermined high-frequency power may be applied. Even in this case, it is preferable that the high frequency power applied to the base 12 during the second protective film forming process is set higher than the predetermined high frequency power.

It is sectional drawing which showed the schematic structure of the etching apparatus which concerns on one Embodiment of this invention with a partial block diagram. SF ₆ is a timing chart showing a control state of the supply flow rate of the gas, and _C 4 _{F 8} gas. It is a timing chart which shows the control state of the high frequency electric power applied to a base and a coil. It is the figure which showed the relationship between the processing time of a 2nd protective film formation process, and groove depth, upper groove width, and bottom part groove width. It is explanatory drawing which showed the execution order of the etching process which concerns on other embodiment of this invention, a 1st protective film formation process, and a 2nd protective film formation process. It is explanatory drawing for demonstrating the problem of the conventional etching method. It is explanatory drawing for demonstrating the problem of the conventional etching method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching device 11 Processing chamber 12 Base 13 1st high frequency power supply 14 Decompression device 16 Vacuum pump 20 Gas supply device 22, 23 Gas cylinder 24, 25 Flow rate adjusting mechanism 30 Plasma generator 31 Coil 32 2nd high frequency power supply 40 Control device 41 Flow rate Control unit 42 Base power control unit 43 Coil power control unit

Claims (8)

A method of etching a silicon substrate placed on a base in a processing chamber, wherein an etching gas is supplied into the processing chamber and high-frequency power is applied to a coil disposed near the outside of the processing chamber. Applying the etching gas into plasma and applying high frequency power to the base, etching process for etching the silicon substrate, supplying a protective film forming gas into the processing chamber, and supplying the coil to the coil Including a first protective film forming step of forming a protective film on the silicon substrate by applying high-frequency power to plasma the protective film forming gas, and starting from the etching step or the first protective film forming step The etching process and the first protective film forming process are alternately and repeatedly performed,
The first protective film forming step is a silicon substrate etching method in which each processing time to be repeatedly performed is a fixed time each time or is set to vary within a fixed time each time,
Similarly to the first protective film forming step, the protective film forming gas is supplied into the processing chamber, and a high frequency power is applied to the coil to convert the protective film forming gas into plasma, thereby forming the protective film. The processing time is set to a time that is not less than 3 times and not more than 45 times the predetermined time as compared to the first protection film forming step, or the protection film forming gas in the processing chamber is formed. A second protective film forming step is performed, which is performed under a condition where the pressure is set high, and forms a protective film having a higher etching resistance than the protective film formed in the first protective film forming step,
The etching process and the first protective film forming process are repeatedly performed a predetermined number of times, then the second protective film forming process is performed, and then the etching process and the first protective film forming process are performed again. An etching method characterized in that the process is repeatedly performed. A method of etching a silicon substrate placed on a base in a processing chamber, wherein an etching gas is supplied into the processing chamber and high-frequency power is applied to a coil disposed near the outside of the processing chamber. Applying the etching gas into plasma and applying high frequency power to the base, etching process for etching the silicon substrate, supplying a protective film forming gas into the processing chamber, and supplying the coil to the coil Including a first protective film forming step of forming a protective film on the silicon substrate by applying high-frequency power to plasma the protective film forming gas, and starting from the etching step or the first protective film forming step The etching process and the first protective film forming process are alternately and repeatedly performed,
The first protective film forming step is a silicon substrate etching method in which each processing time to be repeatedly performed is a fixed time each time or is set to vary within a fixed time each time,
Similarly to the first protective film forming step, the protective film forming gas is supplied into the processing chamber, and a high frequency power is applied to the coil to convert the protective film forming gas into plasma, thereby forming the protective film. The processing time is set to a time that is not less than 3 times and not more than 45 times the predetermined time as compared to the first protection film forming step, or the protection film forming gas in the processing chamber is formed. A second protective film forming step is performed, which is performed under a condition where the pressure is set high, and forms a protective film having a higher etching resistance than the protective film formed in the first protective film forming step,
After the etching process and the first protective film forming process are repeatedly performed a predetermined number of times, the first protective film forming process is performed, and then the first protective film forming process is performed instead of the first protective film forming process. (2) An etching method characterized in that the protective film forming step is performed, and then the etching step and the first protective film forming step are repeatedly performed again. Among the first protective film forming step and the second protective film forming step, when the run of at least the second protective film forming step, claims 1, characterized in that so as to apply a high frequency power to the base, or d etching two methods described. 4. The etching method according to claim 3 , wherein the high-frequency power applied to the base during execution of the second protective film forming step is set higher than that during execution of the first protective film forming step. A processing chamber having an enclosed space;
A base disposed on the lower side in the processing chamber and on which a silicon substrate is placed;
Base power supply means for applying high frequency power to the base;
Etching gas supply means for supplying an etching gas into the processing chamber;
Protective film forming gas supply means for supplying a protective film forming gas into the processing chamber;
Flow rate adjusting means for adjusting the flow rates of the etching gas and the protective film forming gas supplied into the processing chamber by the etching gas supply means and the protective film forming gas supply means;
A coil disposed near the outside of the processing chamber;
Coil power supply means for applying high-frequency power to the coil to turn the etching gas and protective film forming gas supplied into the processing chamber into plasma,
The base power supply means, a control means for controlling the coil power supply means and the flow rate adjusting means, a high-frequency power is applied to the base, and the etching gas supply means or Lae Tchingugasu into the processing chamber supplies, supply an etching step of etching the silicon substrate by plasma the etching gas by applying a high frequency power to said coil, said protective film forming gas supplying means or RaTamotsu Mamorumaku forming gas into the processing chamber to together, and a to that control means executes the first protective film forming step of forming a protective film high-frequency power is applied by plasma the protective film forming gas to the silicon substrate to the coil,
The control means starts from the etching step or the first protective film forming step, and repeatedly performs the etching step and the first protective film forming step alternately, and repeatedly performs each first protective film formation. In a silicon substrate etching apparatus configured to perform the process at a certain time each time or at a processing time varied within a certain time each time,
In the process of forming the protective film by supplying the protective film forming gas into the processing chamber and converting the protective film forming gas into plasma, as in the first protective film forming process. Then, compared with the first protective film forming step, the processing time is set to a time not less than 3 times and not more than 45 times the predetermined time, or the pressure of the protective film forming gas in the processing chamber is set high. And a second protective film forming step for forming a protective film having a higher etching resistance than that of the protective film formed in the first protective film forming step. The etching process and the first protective film forming process are repeatedly performed a predetermined number of times, then the second protective film forming process is performed, and then the etching process and the first protective film forming process are performed again. Continue Etching apparatus characterized by comprising configured to perform return. A processing chamber having an enclosed space;
A base disposed on the lower side in the processing chamber and on which a silicon substrate is placed;
Base power supply means for applying high frequency power to the base;
Etching gas supply means for supplying an etching gas into the processing chamber;
Protective film forming gas supply means for supplying a protective film forming gas into the processing chamber;
Flow rate adjusting means for adjusting the flow rates of the etching gas and the protective film forming gas supplied into the processing chamber by the etching gas supply means and the protective film forming gas supply means;
A coil disposed near the outside of the processing chamber;
Coil power supply means for applying high-frequency power to the coil to turn the etching gas and protective film forming gas supplied into the processing chamber into plasma,
The base power supply means, a control means for controlling the coil power supply means and the flow rate adjusting means, a high-frequency power is applied to the base, and the etching gas supply means or Lae Tchingugasu into the processing chamber supplies, supplying an etching step of etching the silicon substrate by plasma the etching gas by applying a high frequency power to said coil, said protective film forming gas supplying means or RaTamotsu Mamorumaku forming gas into the processing chamber to together, and a to that control means executes the first protective film forming step of forming a protective film high-frequency power is applied by plasma the protective film forming gas to the silicon substrate to the coil,
The control means starts from the etching step or the first protective film forming step, and repeatedly performs the etching step and the first protective film forming step alternately, and repeatedly performs each first protective film formation. In a silicon substrate etching apparatus configured to perform the process at a certain time each time or at a processing time varied within a certain time each time,
As in the first protective film forming step , the control means supplies the protective film forming gas into the processing chamber and applies high frequency power to the coil to convert the protective film forming gas into plasma. A process of forming the protective film, wherein the processing time is set to be not less than 3 times and not more than 45 times the predetermined time as compared to the first protective film forming process, or in the processing chamber A second protective film forming step of forming a protective film having a higher etching resistance than that of the protective film formed in the first protective film forming step by carrying out under a condition in which the pressure of the protective film forming gas is set high; The first and second protective film forming steps are repeatedly performed a predetermined number of times, and then the first protective film forming step to be executed next is performed. For protective film formation process Ete executing the second protective film forming step, and thereafter, again, the etching process and the etching apparatus characterized by comprising configured to repeatedly execute continue the first protective film forming step. The control means causes the base power supply means to apply high frequency power to the base at least during the execution of the second protective film formation process among the first protective film formation process and the second protective film formation process. et etching apparatus according to claim 5 or 6, characterized by comprising configured to. The control means controls the base power supply means so that a high-frequency power applied to the base during execution of the second protective film formation step is higher than that during execution of the first protective film formation step. 8. The etching apparatus according to claim 7 , wherein the etching apparatus is configured as described above.

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