JP5100075B2 - Plasma etching method - Google Patents

Description

  The present invention relates to a plasma etching method including a step of etching an object to be processed using plasma.

  In recent years, semiconductor devices have been required to have higher integration, and therefore, it is required to form finer patterns. In order to satisfy these requirements, in the photolithography process, it is necessary to form a thin resist film on the semiconductor wafer during pattern formation by dry etching in order to obtain high resolution corresponding to a fine pattern. is there. However, if the resist film is made thinner corresponding to the fine pattern, the etching selectivity of the film to be etched with respect to the resist film cannot be ensured sufficiently, and it is difficult to form a fine pattern with high accuracy. It was.

  Therefore, a three-layer resist is used as a technique for solving the above inconvenience. As an example of a three-layer resist, a lower resist film made of an organic material is formed thickly on a base layer, which is a film to be etched, for planarization, and a silicon oxide film by, for example, SOG (Spin On Grass) is formed thereon. An inorganic material film such as the above is formed as an intermediate layer, and an upper resist film (photosensitive resist film) is further formed thereon.

  In such a three-layer resist, first, the upper layer upper resist film is patterned by a photolithographic technique, then the intermediate layer is etched using the patterned upper layer resist film as a mask, and the pattern of the upper layer resist film is formed. Transfer to the intermediate layer. Next, using the upper resist film and the intermediate layer as a mask, the lower resist film is etched (dry development), and the pattern of the upper resist film and the intermediate layer is transferred to the lower resist film. At this time, the upper resist film formed thinner than the lower resist film disappears during the etching, and the etching of the lower resist film is completed using the intermediate layer as a mask. In this way, the finally patterned lower resist film and intermediate layer remain. Then, the underlying layer is etched using a laminated structure mask composed of the lower resist film and the intermediate layer.

In this series of etching steps, a dry development step, i.e., when etching the lower resist film as a mask the upper resist film and the intermediate layer, O ₂ -based etching gas containing O ₂ gas has been used ( For example, Patent Documents 1 to 3).
JP 2002-93778 A (Claim 3 etc.) JP 2002-110443 A (Claim 4 etc.) JP 2004-71768 A (Claim 1 etc.)

When dry development is performed using an O ₂ -based etching gas, it is difficult to etch the lower resist film vertically, and there is a difficulty in controlling the etching shape. Further, when a pattern having a wide opening area is dry-developed, there is a problem that a reaction product during etching adheres and deposits as a residue on the surface of the base layer that should be exposed in the opening after dry development. there were. In dry development using O ₂ -based etching gas plasma, there is a trade-off relationship between the control of the etching shape and the suppression of residues, and no actual etching conditions that can satisfy these two requirements have been found. Met.

Therefore, the present invention provides a plasma etching method capable of simultaneously controlling the etching shape and suppressing residues when dry developing the lower resist film of the three-layer resist using plasma of an O ₂ -based etching gas. It is to be.

In order to solve the above-described problem, a first aspect of the present invention is that an upper layer lower than the underlayer is formed with a lower organic material film, an intermediate layer made of an inorganic material, and an upper organic material film, and the intermediate layer For the object to be processed in which the layer and the upper organic material film are patterned,
In the processing chamber of the plasma etching apparatus, a mixed gas containing CH ₄ gas and O ₂ gas is used as an etching gas, and the flow rate ratio of the CH ₄ gas to the total gas flow rate is set to 40 to 60 %. There is provided a plasma etching method including a step of transferring a pattern of the intermediate layer to the lower organic material film by etching the lower organic material film using the material film and the intermediate layer as a mask.

In the first aspect, the plasma etching apparatus is preferably a capacitively coupled plasma etching apparatus that generates a plasma by forming a high-frequency electric field between a pair of upper and lower electrodes facing each other. In this case, a high frequency for plasma formation of 500 to 1000 W may be applied to the upper electrode and a high frequency for ion attraction of 100 to 300 W may be applied to the lower electrode. Alternatively, a high frequency of plasma formation of 500 to 1000 W and ions may be applied to the lower electrode. You may apply 100-300W of drawing high frequency.
Further, a high frequency for plasma formation can be applied to the upper electrode or the lower electrode at a power density of 0.94 to 1.88 W / cm ² .

The second aspect of the present invention operates on a computer, when executed, controls the flop plasma etching apparatus as a plasma etching method of the first aspect is performed, to provide a control program.

A third aspect of the present invention is a computer-readable storage medium storing a control program that runs on a computer,
Wherein the control program, when executed, controls the flop plasma etching apparatus as a plasma etching method of the first aspect is performed, a computer-readable storage medium.

According to a fourth aspect of the present invention, there is provided a processing chamber for performing a plasma etching process on an object to be processed;
A support for placing the object to be processed in the processing chamber;
Exhaust means for depressurizing the processing chamber;
Gas supply means for supplying a processing gas into the processing chamber;
A controller for controlling the plasma etching method of the first aspect to be performed in the processing chamber;
A plasma processing apparatus is provided.

According to the plasma etching method of the present invention, a mixed gas containing CH ₄ gas and O ₂ gas is used as an etching gas , and the flow rate ratio of CH ₄ gas to the total gas flow rate is set to 40 to 60%. When dry developing the lower organic material film of the layer resist, the controllability of the etching shape can be secured and the generation of residues in the large opening pattern can be suppressed.
Therefore, the plasma etching method of the present invention is suitable as an etching process in the manufacturing process of a semiconductor device that is being miniaturized, and can be advantageously used for manufacturing a highly reliable semiconductor device.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view showing a plasma etching apparatus that can be suitably used for carrying out the present invention. The plasma etching apparatus 1 is configured as a capacitively coupled parallel plate plasma etching apparatus in which electrode plates face each other in parallel in the vertical direction and a plasma forming power source is connected to one of them.

  The plasma etching apparatus 1 has a chamber 2 as a processing container formed into a cylindrical shape made of aluminum whose surface is ceramic sprayed, for example, and the chamber 2 is grounded for safety. In the chamber 2, a semiconductor wafer (hereinafter simply referred to as "wafer") W made of, for example, silicon and having a predetermined film formed thereon is horizontally mounted, and also functions as a lower electrode. 3 is provided in a state supported by the support member 4. This support member 4 is supported by a support base 6 of a lifting device (not shown) via an insulating plate 5 such as ceramic, and the susceptor 3 can be lifted and lowered by this lifting mechanism. The atmospheric portion at the lower center of the support base 6 is covered with a bellows 7, and the inside of the chamber 2 and the atmospheric portion are separated.

  A refrigerant chamber 8 is provided inside the support member 4. In the refrigerant chamber 8, for example, a refrigerant such as Galden is introduced and circulated through the refrigerant introduction pipe 8 a, and the cold heat is supplied to the susceptor 3. Then, heat is transferred to the wafer W through this, whereby the processing surface of the wafer W is controlled to a desired temperature. Further, even if the chamber 2 is held in a vacuum, a heat transfer medium such as He is provided on the back surface of the wafer W as the object to be processed so that the wafer W can be effectively cooled by the refrigerant circulating in the refrigerant chamber 8. A gas passage 9 for supplying gas or the like is provided, and the cold heat of the susceptor 3 is effectively transmitted to the wafer W through this heat transfer medium, and the temperature of the wafer W can be controlled with high accuracy.

  The susceptor 3 is formed in a disc shape having a convex upper central portion, and an electrostatic chuck 11 having an electrode 12 interposed between insulating materials is provided on the susceptor 3. By applying a direct current voltage from the direct current power source 13, the wafer W is electrostatically adsorbed by, for example, Coulomb force. An annular focus ring 15 for improving the uniformity of etching is disposed on the periphery of the upper end of the susceptor 3 so as to surround the wafer W placed on the electrostatic chuck 11.

  Above the susceptor 3, a shower head 21 that functions as an upper electrode is provided in parallel with the susceptor 3. The shower head 21 is supported on the upper portion of the chamber 2 via an insulating material 22, and has a large number of discharge holes 23 on the surface 24 facing the susceptor 3. The surface of the wafer W and the shower head 21 are separated from each other by about 30 to 90 mm, for example, and this distance can be adjusted by the lifting mechanism.

A gas inlet 26 is provided in the center of the shower head 21, and a gas supply pipe 27 is connected to the gas inlet 26. Further, a valve 28 is connected to the gas supply pipe 27 through a valve 28. A processing gas supply system 30 for supplying an etching gas is connected. The processing gas supply system 30 includes, for example, a CO gas supply source 301 and an O ₂ gas supply source 302, as shown in FIG. 2, and a mass flow controller 311 and a valve 312 are connected to piping from these gas sources, respectively. Is provided. FIG. 3 shows another configuration example of the processing gas supply system 30. In this example, the processing gas supply system 30 includes a CH ₄ gas supply source 303 and an O ₂ gas supply source 304, and piping from these gas sources includes: A mass flow controller 311 and a valve 312 are provided.

Then, the CO gas / O ₂ gas or the CH ₄ gas / O ₂ gas as the etching gas is supplied from each gas supply source of the processing gas supply system 30 through the gas supply pipe 27 and the gas inlet 26 to the shower head 21. It reaches the inner space and is discharged from the gas discharge hole 23.

  An exhaust pipe 35 is connected near the bottom of the side wall of the chamber 2, and an exhaust device 36 is connected to the exhaust pipe 35. The exhaust device 36 includes a vacuum pump such as a turbo molecular pump, and is configured so that the chamber 2 can be evacuated to a predetermined reduced pressure atmosphere, for example, a predetermined pressure of 1 Pa or less. Further, a loading / unloading port 37 for the wafer W and a gate valve 38 for opening and closing the loading / unloading port 37 are provided on the side wall of the chamber 2, and the wafer is passed through the loading / unloading port 37 with the gate valve 38 opened. W is transported between adjacent load lock chambers (not shown).

  A high frequency power supply 40 is connected to the shower head 21 that functions as an upper electrode, and a matching unit 41 is interposed in the power supply line. The high frequency power supply 40 supplies high frequency power having a frequency of, for example, 60 MHz to the shower head 21 that is the upper electrode, and generates a high frequency electric field for plasma formation between the shower head 21 that is the upper electrode and the susceptor 3 that is the lower electrode. Form. The shower head 21 is connected to a low pass filter (LPF) 42.

  A high frequency power supply 50 is connected to the susceptor 3 functioning as the lower electrode, and a matching unit 51 is interposed in the power supply line. The high-frequency power supply 50 supplies high-frequency power having a frequency of, for example, 2 MHz to the susceptor 3 that is the lower electrode, and draws ions in the plasma toward the wafer W, thereby realizing highly anisotropic etching. The susceptor 3 is connected to a high pass filter (HPF) 16.

  Each component of the plasma etching apparatus 1 is connected to and controlled by a process controller 60 having a CPU. The process controller 60 includes a user interface 61 including a keyboard that allows a process manager to input commands to manage the plasma etching apparatus 1, a display that visualizes and displays the operating status of the plasma etching apparatus 1, and the like. It is connected.

  Further, the process controller 60 has a storage unit 62 in which a recipe in which a control program for realizing various processes executed by the plasma etching apparatus 1 is realized under the control of the process controller 60 and processing condition data is stored. It is connected.

  Then, if desired, an arbitrary recipe is called from the storage unit 62 by an instruction from the user interface 61 and is executed by the process controller 60, so that a desired one in the plasma etching apparatus 1 is controlled under the control of the process controller 60. Is performed. The recipe may be stored in a computer-readable storage medium such as a CD-ROM, a hard disk, a flexible disk, or a flash memory, or may be a dedicated line from another device. It is also possible to transmit and use it as needed.

Next, an outline of dry development of a multilayer resist performed using the plasma etching apparatus 1 configured as described above will be described with reference to FIGS. First, as shown in FIG. 4, for example, a lower resist film 102 made of an organic material, silicon oxide (SiO ₂ ), etc., on a base layer 101 made of silicon oxide (SiO ₂ ) or the like as a final etching target. An SOG film 103 made of an inorganic material and an upper resist film 104 made of an organic material such as polymethacrylate resin are sequentially formed. Here, the upper resist film 104 is formed thinner than the lower resist film 102. The upper resist film 104 is patterned by a photolithography technique. Although not shown here, an antireflection film may be provided between the SOG film 103 and the upper resist film 104.

Next, the SOG film 103 is etched using an etching gas containing a fluorocarbon-based gas such as CF ₄ and the upper resist film 104 as a mask, and the pattern of the upper resist film 104 is changed to the SOG film 103 as shown in FIG. Transcript to.

Next, the lower resist film 102 is etched and dry developed using the upper resist film 104 and the SOG film 103 as a mask. For the dry development, the capacitively coupled parallel plate plasma etching apparatus 1 is preferably used. At this time, a carbon-containing compound gas and an O ₂ gas are introduced into the chamber 2 as an etching gas at a specific gas flow ratio, and predetermined high-frequency power is supplied to the shower head 21 as the upper electrode and the susceptor 3 as the lower electrode, respectively. Is applied to form a high frequency electric field between the electrodes to excite the plasma of the etching gas, and the lower resist film 102 is etched by the plasma.

Examples of the carbon-containing compound gas used for the dry development include CO gas, CH ₄ gas, C ₂ H ₆ gas, C ₃ H ₈ gas, and the like. Among these, CO gas and CH ₄ gas are exemplified. Is preferred. Since these carbon compound-containing gases are so-called deposition gases that easily generate reaction products during etching, the reaction products adhere to the side walls of the lower resist film 102 during etching, and a protective film is formed. The progress of side etching is suppressed by this protective film. As a result, occurrence of undercut below the mask is avoided. Further, when etching the base layer 101 for the purpose of narrowing the opening width / opening diameter of trenches, holes and the like formed in the base layer 101 as needed, compared with the upper resist film 104 patterned by the photolithography technique. It is also possible to form the side wall of the lower resist film 102 serving as a mask in a tapered shape. Such controllability of the etching shape is obtained by selecting the flow ratio of the carbon-containing compound gas and the O ₂ gas within a specific range.

The flow rate ratio of the carbon-containing compound gas to the total gas flow for controlling the etching shape for the lower resist film 102 is preferably 40 to 99%.
A more preferable etching gas flow ratio varies depending on the type of the carbon-containing compound gas. For example, when CO gas and O ₂ gas are used as the etching gas, the flow rate ratio of the CO gas to the total gas flow rate is preferably 50 to 99%. When the ratio of the CO gas flow rate to the total gas flow rate is less than 50%, side etching proceeds, an undercut is formed immediately below the SOG film 103 as an etching mask, and the etching shape is difficult to control. On the other hand, if the ratio of the CO gas flow rate to the total gas flow rate exceeds 99%, there is a risk of etch stop.

Also, when using CH ₄ gas and _{O 2} gas as the etching gas, it is desirable that the flow rate of CH ₄ gas to the total gas flow rate 40 to 60%. When the ratio of CH ₄ gas to the total gas flow rate is less than 40%, side etching proceeds, undercuts are formed immediately below the SOG film 103 as an etching mask, and it becomes difficult to control the etching shape. On the other hand, if the ratio of the CH ₄ gas flow rate to the total gas flow rate exceeds 60%, the amount of deposits increases, etching does not proceed, and etch stop often occurs, so that it becomes difficult to control the etching shape. Further, when a large opening pattern is etched, there arises a problem that the reaction product becomes an etching residue and is deposited on the surface of the base film 101 that should be exposed.

In addition, in order to generate plasma of the etching gas in the chamber 2, for example, 500 to 1000 W (power density; 0.94 to 1.88 W / cm ² ) is used as the high frequency power applied to the shower head 21 that is the upper electrode. preferable. Here, the power density means a value obtained by dividing the high-frequency power applied to the upper electrode by the total area of the surface area of the silicon focus ring 15 and the surface area of the wafer W (hereinafter, the same meaning). In the plasma etching apparatus 1 of FIG. 1, the power density was calculated by setting the outer diameter of the focus ring 15 to 260 mm and the outer diameter of the wafer W to 200 mm.
When the high-frequency power applied to the shower head 21 is less than 500 W, the plasma density becomes small, so that the etching rate of the lower resist film 102 made of an organic material may be extremely reduced. There arises a problem that an object becomes an etching residue and is deposited on the surface of the base film 101 that should be exposed.

  Moreover, as high frequency electric power applied to the susceptor 3 which is a lower electrode, 100-300W is preferable, for example. If the high frequency power applied to the susceptor 3 is less than 100 W, the etching rate may be extremely reduced, or side etching or etching residue may occur. If it exceeds 300 W, the etching rate becomes too fast. The problem arises that precise control becomes difficult.

  In the dry development process for etching the lower resist film 102, since the upper resist film 104 is formed thinner than the lower resist film 102, the upper resist film 104 is consumed while the lower resist film 102 is being etched. Removed. Therefore, the etching of the lower resist film 102 is completed using only the SOG film 103 as a mask. In this way, the patterns of the upper resist film 104 and the SOG film 103 are transferred to the lower resist film 102, and as shown in FIG. 6, a mask in which the lower resist film 102 and the SOG film 103 are laminated on the base layer 101. A pattern is formed.

  Next, the underlying layer 101 is etched using the patterned lower resist film 102 and the SOG film 103 as a mask, thereby forming a recess 110 such as a target trench or hole in the underlying layer 101 as shown in FIG. Can be formed.

Next, a specific procedure for performing etching (dry development) of the lower resist film 102 using the plasma etching apparatus 1 of FIG. 1 will be described. First, the gate valve 38 is opened, a wafer W having a laminated structure as shown in FIG. 5 is loaded into the chamber 2, placed on the susceptor 3, and then the gate valve 38 is closed.
Next, the susceptor 3 is raised and the distance between the surface of the wafer W on the susceptor 3 and the shower head 21 is adjusted to, for example, about 50 to 60 mm. Then, the inside of the chamber 2 is evacuated through the exhaust pipe 35 by the vacuum pump of the exhaust device 36, the inside of the chamber 2 is reduced to a predetermined pressure, and then a DC voltage is applied from the DC power source 13 to the electrode 12 in the electrostatic chuck 11. Then, the wafer W is electrostatically adsorbed on the electrostatic chuck 11.

Next, CO gas / O ₂ gas or CH ₄ gas / O ₂ gas is introduced into the chamber 1 as an etching gas from the processing gas supply system 30. Then, a high frequency power of 60 MHz, for example, is applied from the high frequency power supply 40 to the shower head 21, thereby generating a high frequency electric field between the shower head 21 as the upper electrode and the susceptor 3 as the lower electrode, Turn into plasma.

  The lower resist film 102 is etched by the etching gas plasma thus generated. At this time, a high frequency power of a predetermined frequency, for example, 2 MHz, is applied from the high frequency power supply 50 to the susceptor 3 which is the lower electrode, and ions in the plasma are drawn to the susceptor 3 side.

  In this way, the lower resist film 102 is etched, and the etching is completed when the pattern of the SOG film 103 is transferred to the lower resist film 102 as shown in FIG. If necessary, overetching of about 10 to 30%, preferably 15 to 20% over time may be performed.

  Other conditions (other than the gas flow rate ratio and high frequency power) when performing etching for dry development on the lower resist film 102 using the plasma etching apparatus 1 are as follows.

Next, test results for confirming the effects of the present invention will be described. In the following test, a Si substrate was used as the base layer 101, and a lower resist film 102 with a film thickness of 306 nm made of an organic material, a SOG film 103 with a film thickness of 106 nm made of silicon oxide (SiO ₂ ), and As the upper resist film 104, a laminate in which an ArF resist having a film thickness of 180 nm was formed was used.
Test example 1
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the stacked body having the same structure as in FIG. 5, and the lower resist film 102 was etched (dry development).
In the etching, the following conditions were set as fixed conditions, and only the flow rate ratio of the etching gas was changed. In addition, 20% overetching was performed over time.

<Fixed conditions>
Pressure = 1.3 Pa (10 mTorr)
Upper electrode RF power (60 MHz) = 1000 W (power density; 1.88 W / cm ² )
Lower electrode RF power (2 MHz) = 200 W
Back pressure (center portion / edge portion) = 1333 Pa / 4666 Pa (10/35 Torr; He gas)
Distance between upper and lower electrodes = 55mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 60 ° C./50° C./20° C.

<Etching gas flow ratio>
CO / O ₂ was used at the following flow ratio.
CO / O ₂ flow ratio = 80/20 mL / min (sccm), 50/50 mL / min (sccm) or 20/80 mL / min (sccm)

After the etching, the etched shape was observed with a transmission electron microscope (TEM) image. First, CD (Critical Dimension) at the center (center portion) and the periphery (edge portion) on the wafer W was measured for a dense region and a sparse region of line & space patterns formed by dry development. There are three measurement sites shown in FIG. That is, the top CD (denoted as CD _t ), middle CD (denoted as CD _m ), and bottom CD (denoted as CD _b ) were measured, and the presence or absence of side etching (occurrence of undercut under the mask) was observed. The results are shown in Table 1.

  In addition, in the above etching conditions, for example, the presence or absence of etching residue was observed in a wide opening simulating the structure of the target pad (PAD) or guard ring (Guard Ring). The results are shown in Table 2.

From Table 1, regardless of the in-plane position of the wafer W and the density of the pattern, the larger the CO / O ₂ flow rate ratio, the smaller the difference in CD _t , CD _m , CD _b , and the occurrence of side etch is suppressed, which is high. It was shown that the etching accuracy can be secured. Moreover, generation | occurrence | production was not confirmed from Table 2 on all the conditions tested about the etching residue of the large opening pattern.

Test example 2
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the stacked body having the same structure as in FIG. 5, and the lower resist film 102 was etched (dry development). In the etching, the following conditions were set as fixed conditions, and only the high frequency power applied to the upper electrode and the lower electrode was changed. In addition, 20% overetching was performed over time.

<Fixed conditions>
CO / O ₂ flow rate ratio = 80/20 mL / min (sccm), 50/50 mL / min (sccm)
Pressure = 1.3 Pa (10 mTorr)
Back pressure (center portion / edge portion) = 1333 Pa / 4666 Pa (10/35 Torr; He gas)
Distance between upper and lower electrodes = 55mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 60 ° C./50° C./20° C.

<High frequency power>
Upper electrode RF power (60 MHz) = 500 W (power density; 0.94 W / cm ² ), 1000 W (power density; 1.88 W / cm ² ) or 1500 W (power density; 2.83 W / cm ² )
Lower electrode RF power (2 MHz) = 100 W, 200 W or 300 W

After etching, as in Test Example 1, CD _t , CD _m and CD _b were measured based on the transmission electron microscope (TEM) image, and the presence or absence of generation of etching residues was also observed. The results are shown in Table 3.
Further, similarly to Test Example 1, the observation result of the etching residue when the large opening pattern is formed is shown in Table 4.

Table 3 shows that the etching residue tends to increase when the RF power to the upper electrode is 1500 W regardless of the in-plane position of the wafer W and the pattern density. Etching residue was also generated when the RF power to the lower electrode was 100 W. For CD, the difference between CD _m and CD _b was very small when the RF power to the upper electrode was in the range of 500 to 1500 W (power density 0.94 to 2.83 W / cm ² ) at the optimum flow rate.
Further, from Table 4, it was confirmed that the etching residue of the large opening pattern was generated when the RF power to the upper electrode was 1500 W and when the RF power to the lower electrode was 100 W.

Test example 3
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the stacked body having the same structure as in FIG. 5, and the lower resist film 102 was etched (dry development). In the etching, the following conditions were set as fixed conditions, and only the flow rate ratio of the etching gas was changed. In addition, 20% overetching was performed over time.

<Fixed conditions>
Pressure = 1.3 Pa (10 mTorr)
Upper electrode RF power (60 MHz) = 1000 W (power density; 1.88 W / cm ² )
Lower electrode RF power (2 MHz) = 200 W
Back pressure (center portion / edge portion) = 1333 Pa / 4666 Pa (10/35 Torr; He gas)
Distance between upper and lower electrodes = 55mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 60 ° C./50° C./20° C.

<Etching gas flow ratio>
CH ₄ / O ₂ was used at the following flow ratio.
CH ₄ / O ₂ flow ratio = 80/20 mL / min (sccm), 50/50 mL / min (sccm) or 20/80 mL / min (sccm)

After the etching, the etched shape was observed with a transmission electron microscope (TEM) image. First, CD (Critical Dimension) at the center (center portion) and the periphery (edge portion) on the wafer W was measured for a dense region and a sparse region of line & space patterns formed by dry development. There are three measurement sites shown in FIG. That is, the top CD (denoted as CD _t ), middle CD (denoted as CD _m ), and bottom CD (denoted as CD _b ) were measured, and the presence or absence of side etching (occurrence of undercut under the mask) was observed. The results are shown in Table 5.

  In addition, in the above etching conditions, for example, the presence or absence of etching residue was observed in a wide opening simulating the structure of the target pad (PAD) or guard ring (Guard Ring). The results are shown in Table 6.

From Table 5, regardless of the in-plane position of the wafer W and the density of the pattern, when the CH ₄ / O ₂ flow rate ratio is large, deposits are remarkably generated and etching becomes impossible. Conversely, when the CH ₄ / O ₂ flow rate ratio was small, side etching occurred and the accuracy of the etching shape was lowered. On the other hand, when the CH ₄ / O ₂ flow rate ratio is 50/50 (= 1), the difference in CD _t , CD _m , and CD _b is small, the occurrence of side etching is suppressed, and high etching accuracy is ensured. It was shown that it can be done. Moreover, generation | occurrence | production was not confirmed from Table 6 about all the conditions tested about the etching residue of the large opening pattern.

Test example 4
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the stacked body having the same structure as in FIG. 5, and the lower resist film 102 was etched (dry development). In the etching, the following conditions were set as fixed conditions, and only the high frequency power applied to the upper electrode and the lower electrode was changed. In addition, 20% overetching was performed over time.

<Fixed conditions>
CH ₄ / O ₂ flow rate ratio = 50/50 mL / min (sccm)
Pressure = 1.3 Pa (10 mTorr)
Back pressure (center portion / edge portion) = 1333 Pa / 4666 Pa (10/35 Torr; He gas)
Distance between upper and lower electrodes = 55mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 60 ° C./50° C./20° C.

<High frequency power>
Upper electrode RF power (60 MHz) = 500 W (power density; 0.94 W / cm ² ), 1000 W (power density; 1.88 W / cm ² ) or 1500 W (power density; 2.83 W / cm ² )
Lower electrode RF power (2 MHz) = 100 W, 200 W or 300 W

After the etching, as in Test Example 3, CD _t , CD _m and CD _b were measured based on the transmission electron microscope (TEM) image, and the presence or absence of generation of etching residues was also observed. The results are shown in Table 7.
Further, similarly to Test Example 3, the observation result of the etching residue when the large opening pattern is formed is shown in Table 8.

Table 7 shows that the etching residue tends to increase when the RF power to the upper electrode is 1500 W regardless of the in-plane position of the wafer W and the pattern density. Etching residue was also generated when the RF power to the lower electrode was 100 W. For CD, the difference between CD _m and CD _b was very small when the RF power to the upper electrode was in the range of 500 to 1500 W (power density 0.94 to 2.83 W / cm ² ) at the optimum flow rate. Further, from Table 8, it was confirmed that the etching residue of the large opening pattern was generated when the RF power to the upper electrode was 1500 W and when the RF power to the lower electrode was 100 W.

Test Example 5
Using the plasma etching apparatus 1 of FIG. 1, a plasma etching process was performed on the stacked body having the same structure as in FIG. 5, and the lower resist film 102 was etched (dry development). In the etching, the following conditions were set as fixed conditions, and only the flow rate ratio of the etching gas was changed. In addition, 20% overetching was performed over time.

<Fixed conditions>
Pressure = 1.3 Pa (10 mTorr)
Upper electrode RF power (60 MHz) = 1000 W (power density; 1.88 W / cm ² )
Lower electrode RF power (2 MHz) = 200 W
Back pressure (center portion / edge portion) = 1333 Pa / 4666 Pa (10/35 Torr; He gas)
Distance between upper and lower electrodes = 55mm
Temperature (upper electrode / chamber sidewall / lower electrode) = 60 ° C./50° C./20° C.

<Etching gas flow ratio>
CH ₄ / O ₂ was used at the following flow ratio.
CH ₄ / O ₂ flow ratio = 80/20 mL / min (sccm), 60/40 mL / min (sccm), 50/50 mL / min (sccm), 40/60 mL / min (sccm) or 20/80 mL / min ( sccm)

After the etching, the etched shape was observed with a transmission electron microscope (TEM) image. In this test, the bottom CD (CD _b ) at the center (center portion) and the periphery (edge portion) on the wafer W was measured, and the change was evaluated. The results are shown in Table 9. The relationship between the gas flow rate ratio and _CDb is shown in FIG.

From Table 9 and FIG. 8, it can be seen that CD _b can be controlled by changing the CH ₄ / O ₂ flow rate ratio. In particular, when the CH ₄ / O ₂ flow rate ratio of 40/60 mL / min (sccm) and 60/40 mL / min (sccm) are compared, the flow rate ratio of 40/60 mL / min (sccm) is 40/60 mL / min (sccm). CD _b compared to sccm) has become the largest 20nm narrow. This is considered to be because when the CH ₄ / O ₂ flow rate ratio is 60/40 mL / min (sccm), the CD _b is reduced as a result of the side wall of the lower resist film 102 after etching being formed obliquely in a tapered shape. It is done. Thus, by changing the CH ₄ / O ₂ flow rate ratio in the range of 40/60 to 60/40 mL / min (sccm), the opening width of the lower resist film 102 serving as a mask when the underlayer 101 is etched. / The opening diameter can be adjusted. Therefore, for example, the opening width / opening diameter of the mask (lower resist film 102) when forming the recess 110 in the base layer 101 is larger than the opening width / opening diameter of the upper resist film 104 patterned by photolithography. Small control becomes possible. As shown in Table 9, side etching occurred when the CH ₄ / O ₂ flow rate ratio was 20/80 mL / min (sccm). Further, when the CH ₄ / O ₂ flow rate ratio was 80/20 mL / min (sccm), the amount of deposits (depots) increased and an etch stop occurred.

  As described above, according to the plasma etching method of the present invention, it is possible to improve the accuracy of the etching shape and suppress the etching residue by selecting the flow ratio of the carbon-containing compound gas and the high frequency power applied to the upper and lower electrodes. become. Therefore, the plasma etching method of the present invention is suitable as an etching process in the manufacturing process of a semiconductor device that is being miniaturized, and can manufacture a highly reliable semiconductor device.

As mentioned above, although embodiment of this invention was described, this invention is not restrict | limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, a parallel plate type plasma etching apparatus that performs etching by applying high-frequency power to the upper and lower electrodes is used, but the present invention is not limited to this, and high-frequency power is applied only to the upper electrode or only the lower electrode. It may be a type of device. In this case, for example, a method of applying both the plasma forming high frequency and the ion drawing high frequency to the lower electrode may be employed. Further, a magnetron RIE plasma etching apparatus using a permanent magnet may be used.
Furthermore, not only the capacitively coupled plasma etching apparatus but also other types of plasma etching apparatuses such as an inductively coupled type can be used.

  The present invention can be suitably used in the process of manufacturing various semiconductor devices such as DRAM (Dynamic Random Access Memory).

Sectional drawing which shows schematic structure of the plasma etching apparatus which can be utilized suitably for implementation of the plasma etching method of this invention. The figure which shows one structural example of a process gas supply system. The figure which shows another structural example of a process gas supply system. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state where the upper resist film was formed in a pattern. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state after etching a SOG film. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state after dry development. It is a mimetic diagram showing the section structure near the surface of a semiconductor wafer, and shows the state after forming a crevice by etching. Graph showing the relationship between the CH ₄ / _{O 2} gas flow rate ratio and the bottom CD.

Explanation of symbols

1: Plasma etching device 2: Chamber (processing vessel)
3: Susceptor (lower electrode)
21: Shower head 30: Processing gas supply system 36: Exhaust device 40: High frequency power supply 50: High frequency power supply 60: Process controller 101: Underlayer 102: Lower layer resist film 103: SOG film 104: Upper layer resist film 110: Concave portion W: Semiconductor Wafer

Claims (8)

The lower layer organic material film, the intermediate layer made of an inorganic material, and the upper organic material film are formed on the upper layer from the lower layer, and the intermediate layer and the upper organic material film are patterned. Against the body
In the processing chamber of the plasma etching apparatus, a mixed gas containing CH ₄ gas and O ₂ gas is used as an etching gas, and the flow rate ratio of the CH ₄ gas to the total gas flow rate is set to 40 to 60 %. A plasma etching method comprising: transferring a pattern of the intermediate layer to the lower organic material film by etching the lower organic material film using the material film and the intermediate layer as a mask. 2. The plasma etching method according to claim 1, wherein the plasma etching apparatus is a capacitively coupled plasma etching apparatus that generates plasma by forming a high-frequency electric field between a pair of upper and lower electrodes facing each other. 3. The plasma etching method according to claim 2 , wherein a high frequency for plasma formation is applied to the upper electrode in a range of 500 to 1000 W, and a high frequency for ion attraction is applied in a range of 100 to 300 W to the lower electrode. 3. The plasma etching method according to claim 2 , wherein a high frequency for plasma formation is applied to the lower electrode at 500 to 1000 W and a high frequency for ion attraction is applied at 100 to 300 W. 4. The plasma etching method according to claim 2 , wherein a high frequency for plasma formation is applied to the upper electrode or the lower electrode at a power density of 0.94 to 1.88 W / cm ² . Running on a computer, when executed, controls the flop plasma etching apparatus as plasma etching method according to any one of claims 1 to 5 is performed, the control program. A computer-readable storage medium storing a control program that runs on a computer,
Wherein the control program, when executed, controls the flop plasma etching apparatus as plasma etching method according to any one of claims 1 to 5 is performed, computer-readable storage medium. A processing chamber for performing a plasma etching process on an object to be processed;
A support for placing the object to be processed in the processing chamber;
Exhaust means for depressurizing the processing chamber;
Gas supply means for supplying a processing gas into the processing chamber;
A control unit that controls the plasma etching method according to any one of claims 1 to 5 to be performed in the processing chamber;
A plasma processing apparatus comprising:

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