JP2626618C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for holding a sample in a vacuum processing apparatus, and more particularly to a method for holding and holding a substrate by electrostatic attraction. . 2. Description of the Related Art Vacuum processing of a sample, for example, an apparatus for processing using plasma (hereinafter abbreviated as plasma processing), for example, one of important applications of a dry etching apparatus is a semiconductor integrated circuit. There is formation of a fine pattern in the manufacture of a micro solid device. This fine pattern is usually formed by dry etching using a pattern drawn by exposing and developing a polymer material called a resist applied on a semiconductor substrate (hereinafter abbreviated to “substrate”) as a mask as a mask. It is performed by transferring to. [0003] At the time of such dry etching of the substrate, the mask and the substrate are heated by heat of chemical reaction with the plasma or impact incident energy such as ions or electrons in the plasma. Therefore, when sufficient heat radiation cannot be obtained, that is, when the temperature of the substrate is not properly controlled, the mask is deformed or deteriorated, and a correct pattern cannot be formed.
A disadvantage arises in that it is difficult to remove the mask from the substrate after the dry etching. In order to eliminate these inconveniences, the following techniques have been conventionally used and proposed. Hereinafter, these conventional techniques will be described. As a first example of the prior art, for example, as shown in Japanese Patent Publication No. 56-53853, a sample table to which an output of a high-frequency power supply is applied is cooled with water, and a work piece is formed on the sample table. A substance is placed via a dielectric film, and a DC voltage is applied to the sample stage to apply a potential difference to the dielectric film via plasma. In some cases, the thermal resistance between the workpiece and the sample stage is reduced to effectively cool the workpiece. As a second example of the prior art, for example, as disclosed in JP-A-57-145321, a gas gas is blown from the back surface of a wafer and the wafer is directly cooled by the gas gas. is there. As a third example of the prior art, for example, EJ Egerton et al., Solid State Te
25, No. 8, pp. 84-87 (1982-8), an electrode which is a water-cooled sample stage and an outer periphery which is mounted on the electrode and which is mechanically clamped. GHe with a pressure of about 6 Torr between the substrate and the substrate pressed and fixed
To reduce the thermal resistance between the electrode and the substrate, thereby effectively cooling the substrate. [0007] However, these prior arts are not sufficiently considered in terms of effective cooling of a sample and influence of a gas flowing on the back surface of a substrate on a process. However, there were the following problems. In the first prior art, even if the above-described operation is performed, the contact portion between the material to be processed and the sample stage is still small, and there is a slight gap when viewed microscopically. . Also,
A process gas enters this gap, and this gas becomes a thermal resistance. In a general dry etching apparatus, a material to be processed is usually etched by a process gas pressure of about 0.1 Torr, and a gap between the material to be processed and the dielectric film becomes smaller than an average free path length of the process gas. Therefore, the decrease in the gap due to the electrostatic attraction force
There is almost no change in terms of thermal resistance, and the effect is increased by the increase in the contact area. Therefore, a large electrostatic attraction force is required to reduce the thermal resistance between the material to be processed and the sample stage and to cool the material to be processed more effectively. For this reason, such a technique has the following problems. (1) Since the material to be processed is less likely to be detached from the sample table, it takes time to transport the material to be processed after the etching process is completed, or the material to be processed is damaged. (2) In order to generate a large electrostatic attraction force, it is necessary to apply a large potential difference between the dielectric film and the material to be processed. That is, since the damage to the elements in the substrate is increased, the yield is deteriorated. In the fine processing of a thin gate film, which is demanded as the integration degree of the integrated circuit is increased, the yield is further deteriorated. In the second prior art, the cooling efficiency of the wafer can be improved by using a gas gas having excellent heat conductivity such as helium gas (hereinafter, abbreviated as GHe). However, such a technique has the following problems. (1) Since a large amount of gaseous gas flows into the etching chamber instead of staying on the cooling surface side of the wafer, even an inert gas such as GHe has a large effect on the process. Can not. In the third prior art, even if the outer periphery of the substrate is fixed by a clamp, the GHe
Inevitably flows into the vacuum processing chamber, and therefore has the same problems as the above-mentioned problems in the second prior art, and further has the following problems. (1) Since the outer periphery of the substrate is pressed by the mechanical clamping means to fix the substrate to the electrode, the substrate is deformed to a convex shape at a middle height in the peripheral support state by the gas pressure of the flowing GHe. For this reason, the gap amount between the back surface of the substrate and the electrode increases, and accordingly, the heat conduction characteristics between the substrate and the electrode deteriorate. Therefore, the cooling of the substrate cannot be performed sufficiently effectively. (2) Since the electrodes are provided with mechanical clamping means for pressing and fixing the outer periphery of the substrate, the area for manufacturing elements in the substrate is reduced, and the uniformity of plasma is hindered. During the operation of the mechanical clamping means, there is a risk that reaction products adhered to the mechanical clamping means fall off the mechanical clamping means and generate dust,
Substrate transport becomes extremely complicated, resulting in an increase in the size of the apparatus and a decrease in reliability. An object of the present invention is to provide a sample holding method for holding and holding a substrate without requiring a large electrostatic holding force, as a sample holding method of a vacuum processing apparatus using an electrostatic holding force. is there. Means for Solving the Problems Supplying a heat transfer gas to a gap between the back surface of the sample held by suction and the sample table,
While reducing the pressure difference between the processing gas pressure in the vacuum processing chamber and the heat transfer gas pressure on the back surface of the sample as long as the thermal resistance between the sample and the sample stage is sufficiently reduced,
It is characterized in that the electrostatic attraction force is reduced within a range where the floating of the sample is prevented. According to a feature of the present invention, the area of the adsorption portion electrostatically adsorbed to the insulating film on the back surface of the sample is determined by the difference between the gas pressure of the heat transfer gas and the pressure of the vacuum processing chamber. In order to prevent the air from rising, the pressure is selected based on the required electrostatic attraction force determined by the pressure difference between the gas pressure of the heat transfer gas and the pressure of the vacuum processing chamber. The area of the portion where the sample is adsorbed on the sample table by the electrostatic attraction force is preferably at least 1/5 of the area of the back surface of the sample. A large electrostatic attraction is achieved by reducing the pressure difference between the processing gas pressure in the vacuum processing chamber and the heat transfer gas pressure on the back surface of the sample within the range allowed by the thermal resistance between the sample and the sample stage. It is possible to suppress an increase in the amount of gap between the back surface of the sample and the sample table without requiring force. For example, when the pressure of the heat transfer gas is 1 Torr and the pressure of the vacuum processing chamber 10 is 0.1 Torr, the required electrostatic attraction force for preventing the sample from floating from the lower electrode 20 is about 1.3 g / cm @ 2. Therefore, the area of the adsorption section is selected to be about 1/5 of the area of the back surface of the sample. According to the present invention, the effect of cooling the sample can be reduced even if the electrostatic attraction force is reduced, as compared with the conventional technology in which the contact area between the sample and the lower electrode is increased by electrostatic adsorption to reduce the thermal resistance. Is sufficiently obtained. Since the electrostatic attraction force is small, it is easy to separate the sample from the lower power, and it is possible to shorten the transport time of the sample after the etching process,
Sample damage can be prevented. Further, since the electrostatic attraction force may be small, the potential difference applied to the sample is small, and damage to elements in the sample can be reduced. Therefore, there is no fear that the yield is deteriorated even in the fine processing of the thin gate film. Examples of apparatuses for performing vacuum processing of a sample, for example, plasma processing, include a dry etching apparatus, a plasma CVD apparatus, and a sputtering apparatus. In this embodiment, a dry etching apparatus is taken as an example. Will be described. An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic configuration of a dry etching apparatus. On the bottom wall of the vacuum processing chamber 10 in this case, a lower electrode 20 serving as a sample stage is electrically insulated and provided airtight through an insulator 11. An upper electrode 40 is provided in the vacuum processing chamber 10 so as to have a discharge space 30 and face the lower electrode 20 in the vertical direction. In this case, an insulator 60 is buried in the surface of the lower electrode 20 corresponding to the back surface of the substrate 50 corresponding to the periphery of the back surface of the substrate 50. The lower electrode 20 inside the insulator 60 has a groove 21 that forms a heat transfer gas supply path.
The groove 21 communicates with the discharge space 30 when the substrate 50 is not placed. In addition, a groove (not shown) for gas dispersion connected to the groove 21 is formed in the insulator 60. The lower electrode 20 has a gas supply passage 23a and a gas discharge passage 23b formed in communication with the groove 21. In the lower electrode 20, a coolant channel 22 is formed. The lower electrode 20 communicates with the refrigerant flow path 22 and has a refrigerant supply path 24 a and a refrigerant discharge path 2.
4b are formed. The gas supply path 23a is connected to a conduit 70a connected to a gas source (not shown), and the gas discharge path 23b is connected to one end of the conduit 70b. The conduit 70a is provided with a mass flow controller (hereinafter abbreviated as MFC) 71, and the conduit 70b
Is provided with an adjustment valve 72. The other end of the conduit 70b is connected to the exhaust conduit 12 connecting the vacuum processing chamber 10 and the vacuum pump 80. A conduit 90a connected to a refrigerant source (not shown) is connected to the refrigerant supply path 24a, and a refrigerant discharge pipe 90b is connected to the refrigerant discharge path 24b. The lower electrode 20 is connected to a high-frequency power supply 101 via a matching box 100 and a DC power supply 103 via a high-frequency cutoff circuit 102. The vacuum processing chamber 10, the high-frequency power supply 101, and the DC power supply 103 are each grounded. The upper electrode 40 has a processing gas discharge hole (not shown) that opens into the discharge space 30.
And a processing gas flow path (not shown) communicating with the processing gas discharge hole.
In the processing gas flow path, a conduit (not shown) connected to a processing gas supply device (not shown)
Are connected. Next, an example of a detailed structure of the lower electrode 20 of FIG. 1 will be described with reference to FIGS. In FIG. 2 and FIG. 3, the gas supply path 23a shown in FIG. 1 is formed by a conduit 25a in this case, and the conduit 25a in this case is centered on the substrate mounting position center of the lower electrode 20 as an axis. It is provided movably up and down. Outside the conduit 25a, the conduit 25b is provided by forming the gas discharge passage 23b shown in FIG. Outside the conduit 25b, FIG.
The conduit 25c is provided by forming the refrigerant supply path 24a shown in FIG. Conduit 25c
A conduit 25d is formed outside the refrigeration line, forming the refrigerant discharge passage 24b shown in FIG. The upper end of the conduit 25b is connected to the upper electrode plate 26, and the upper end of the conduit 25d is connected to the upper electrode plate receiver 27 below the upper electrode plate 26. An empty space 28 is formed at the upper end of the conduit 25b by the upper electrode plate 26, the upper electrode plate receiver 27, and the conduit 25b. A dividing plate 29 is formed in the vacant space 28 so as to form the refrigerant passage 22, and the upper end of the conduit 25 c is connected to the dividing plate 29. In this case, on the surface of the electrode upper plate 26 on which the substrate (not shown) is placed, in this case, a radial heat transfer gas dispersion groove 21a and a circumferential heat transfer gas dispersion groove 21b are provided. A plurality of sections are formed. The grooves 21a and 21b for dispersing the heat transfer gas are connected to the conduits 25a and 25b. An insulator 60 is provided on the surface of the electrode upper plate 26 on which the substrate is mounted. In this case, the insulating film is coated. In FIGS. 2 and 3, reference numeral 110 denotes an electrode cover for protecting the surface of the electrode upper plate 26 where the substrate is not placed, and reference numeral 111 denotes a portion for protecting the lower electrode 20 other than the surface of the electrode upper plate 26. The insulating cover 112 is a shield plate. Further, at the upper end of the conduit 25a, pins 113 for supporting the substrate from the back side when the substrate is mounted on the electrode upper plate 26 and when the substrate is detached from the electrode upper plate 26, in this case, three pins at 120 ° intervals. This is installed. Further, the depth of the grooves 21 a and 21 b is determined by adjusting the depth of the grooves 21 a and 21 b
If the gap between the bottom surface of the heat transfer gas (hereinafter abbreviated as groove space) becomes longer than the average free path length of the heat transfer gas, the heat transfer effect of the heat transfer gas is reduced. It is preferable to select the depth of the grooves 21a and 21b so as to be equal to or less than the average free path length of the heat transfer gas. The area of a portion of the back surface of the substrate that is electrostatically attracted to the insulating film (hereinafter, abbreviated as an attracting portion) is determined by the pressure difference between the gas pressure of the heat transfer gas and the pressure of the vacuum processing chamber 10. Lower electrode 2
In order to prevent the floating from zero, the selection is made based on the required electrostatic attraction force determined by the differential pressure between the gas pressure of the heat transfer gas and the pressure of the vacuum processing chamber 10. For example, when the pressure of the heat transfer gas is 1 Torr and the pressure of the vacuum processing chamber 10 is 0.1 Torr, the required electrostatic attraction force for preventing the substrate from floating from the lower electrode 20 is about 1.3 g / cm @ 2. Therefore, the area of the suction portion is selected to be about 1/5 of the rear surface area of the substrate. In the dry etching apparatus of FIGS. 1 to 3 configured as described above,
After being transported into the vacuum processing chamber 10 by a known transport device (not shown), it is placed on the lower electrode 20 with its outer peripheral portion corresponding to the insulator 60. Lower electrode 2
After the mounting of the substrate 50 on the gas flow path, the processing gas supplied from the processing gas supply device to the gas flow path via the conduit is discharged into the discharge space 30 from the gas discharge hole of the upper electrode 40 after flowing through the gas flow path. Is done. After adjusting the pressure in the vacuum processing chamber 10, high-frequency power is applied to the lower electrode 20 from the high-frequency power supply 101, and a glow discharge occurs between the lower electrode 20 and the upper electrode 40. The processing gas in the discharge space 30 is turned into plasma by the glow discharge, and the etching of the substrate 50 is started by the plasma.
At the same time, a DC voltage is applied to the lower electrode 20 from the DC power supply 103. When the etching process of the substrate 50 by the plasma is started, the lower electrode 20 is formed by the self-bias voltage generated by the plasma processing process and the DC power supply 103.
The substrate 50 is electrostatically attracted to the lower electrode 20 and fixed by the DC voltage applied to the substrate 50. Thereafter, a heat transfer gas, for example, a processing gas is supplied to the grooves 21a and 21b from the gas source via the MFC 71 and the gas supply path 23a in order. At this time, the processing gas is supplied in a controlled amount by operating the MFC 71 and the adjustment valve 72, and in some cases, the processing gas can be used in a space on the back surface of the substrate. Thereby, the thermal resistance between the lower electrode 20 and the substrate 50, which are cooled by the refrigerant flowing through the refrigerant flow path 22, for example, water or low-temperature liquefied gas, is reduced, and the substrate 50 is effectively cooled. Thereafter, as the etching is approached, the supply of the processing gas to the grooves 21a and 21b is stopped. With the completion of the etching, the supply of the processing gas to the discharge space 30, the DC voltage to the lower electrode 20, and the high frequency The application of power is stopped. Thereafter, the electrostatic attraction force generated on the substrate 50 is subsequently released. In this case, the static electricity is removed by the contact of the electrically grounded pins 113 with the substrate 50, and the operation of the pins 113 causes the substrate 50 to be removed. It is removed from the lower electrode 20. afterwards,
The substrate 50 is carried out of the vacuum processing chamber 10 by a known transfer device. The static electricity can also be removed by stopping the application of the DC voltage and then stopping the application of the high-frequency power. As described above, according to the present embodiment, the following effects can be obtained. (1) Since the substrate can be fixed to the lower electrode using not only the outer periphery of the back surface of the substrate but also other portions of the back surface, deformation of the substrate due to the gas pressure of the processing gas as a heat transfer gas is prevented. Thus, it is possible to suppress an increase in the amount of gap between the lower electrode and the back surface of the substrate fixed to the lower electrode. Therefore, it is possible to prevent deterioration of the heat conduction characteristic between the substrate and the lower electrode, and it is possible to efficiently cool the substrate. (2) Since at least the outer periphery of the back surface of the substrate is adsorbed, the processing gas, which is a heat transfer gas, is suppressed from flowing into the vacuum processing chamber at the adsorption section. Less and can be used for all processes. (3) Compared with the conventional technology in which the contact area between the substrate and the lower electrode is increased by electrostatic adsorption to reduce the thermal resistance, in this embodiment, the magnitude of the electrostatic adsorption force is larger than that of the processing gas. The pressure may be large enough to prevent the substrate from rising due to the pressure difference between the pressure and the pressure in the vacuum processing chamber.The pressure difference between the processing gas pressure and the plasma pressure is determined by the difference between the back surface of the substrate and the lower electrode. Even if the electrostatic attraction force is reduced, the effect of cooling the substrate can be sufficiently obtained by reducing the thermal resistance within the range permitted by the thermal resistance. (4) Since the electrostatic attraction force is small, it is easy to separate the substrate from the lower power, and it is possible to shorten the transport time of the substrate after the etching process and prevent the substrate from being damaged. (5) Since the electrostatic attraction force may be small, the potential difference applied to the substrate is small, and damage to elements in the substrate can be reduced. Therefore, there is no fear that the yield is deteriorated even in the fine processing of the thin gate film. (6) Since the substrate is fixed to the lower electrode by an electrostatic attraction force without using a mechanical clamping means, it is possible to prevent a reduction in an element manufacturing area in the substrate and to maintain good plasma uniformity. Also, there is no danger of generating dust when the substrate is placed on the lower electrode and when the substrate is removed from the lower electrode, and further, the substrate can be easily transported, and as a result, the size of the apparatus can be suppressed. In addition, reliability can be improved. FIG. 4 shows another example of the dry etching apparatus embodying the present invention. The outside of the vacuum processing chamber 10 and the discharge space 30 are connected to the top wall of the vacuum processing chamber 10 and the upper electrode 40. Thus, an optical path 120 is formed. A light-transmitting window 121 is provided hermetically outside the optical path 120 outside the vacuum processing chamber 10. Vacuum processing chamber 1 corresponding to translucent window 121
A thermometer 122, for example, an infrared thermometer 122, is provided outside the apparatus. The output of the infrared thermometer 122 is sent to the process control computer 1 via the amplifier 123.
A command signal input to the MFC 71 and calculated by the process control computer 124 is input to the MFC 71. In addition, the same devices and the like as those in FIG. According to this embodiment, the following effects can be further obtained. (1) The supply amount of the processing gas is adjusted while measuring the temperature of the substrate, that is, the MFC that supplies GHe is connected to the process control computer, and the MFC that supplies GHe between the substrate temperature and the supply amount of GHe obtained in advance. By controlling the supply amount of GHe from the relationship, the substrate temperature can be maintained at a constant temperature. Such control is particularly effective at the time of dry etching of the Al-Cu-Si material, and the residue of the material to be etched can be reduced by controlling the temperature to a high temperature within a range where the photoresist is not damaged. (2) When the plasma pressure is high, there is also a process in which the etching rate increases as the temperature of the substrate increases. In such a case, the temperature of the substrate exceeds a predetermined temperature. In this case, it is possible to reduce the etching time while flowing GHe to increase the cooling effect and prevent the photoresist from being damaged. In the embodiment described above, the electrostatic attraction force is used for the substrate attraction, but it is also possible to use the vacuum attraction force in a process in which the plasma gas pressure is high. Alternatively, the positive electrode and the negative electrode may be alternately arranged on the lower surface of the insulator to apply electrostatic attraction to the substrate. Further, in the case where overetching is further performed after the base material starts to be exposed, the supply of GHe is stopped at the time when the base material starts to be exposed, and a DC voltage is reversely applied to the lower electrode. With this configuration, the electrostatic force remaining on the substrate at the end of the etching can be further reduced, so that the substrate is not damaged at the time of unloading the substrate, and the time required for unloading the substrate can be shortened. However, in this case, it is necessary to control so that the temperature of the substrate during etching is reduced by the temperature rise during over-etching. Further, a gas having good heat conductivity such as hydrogen gas or neon gas may be used as the heat transfer gas in addition to GHe. The present invention has a similar effect in controlling the temperature of a sample that is placed and held on another substrate substrate to be cooled and subjected to vacuum processing. As described above, according to the present invention, compared with the prior art in which the contact area between the sample and the lower electrode is increased by electrostatic adsorption to reduce the thermal resistance, Even if the adsorption force is reduced, the effect of cooling the sample can be sufficiently obtained. Since the electrostatic attraction force is small, the sample can be easily detached from the lower power, and the transport time of the sample after the etching process can be shortened, and the sample can be prevented from being damaged. Further, since the electrostatic attraction force may be small, the potential difference applied to the sample is small, and damage to elements in the sample can be reduced. Therefore, there is no fear that the yield is deteriorated even in the fine processing of the thin gate film.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing an example of a dry etching apparatus embodying the present invention. FIG. 2 is a detailed plan view of a lower electrode of FIG. 1; FIG. 3 is a sectional view taken along line AA of FIG. 2; FIG. 4 is a configuration diagram showing another example of the dry etching apparatus embodying the present invention. DESCRIPTION OF SYMBOLS 10 ... Vacuum processing chamber, 20 ... Lower electrode, 21, 21a, 21b ... Groove, 22 ... Refrigerant channel, 23a ... Gas supply path, 24a ... Refrigerant supply path, 50 ... Substrate.

Claims (1)

[Claims] The heat transfer gas is supplied to the gap between the back surface of the sample held and adsorbed and held and the sample stage, and the pressure difference between the processing gas pressure in the vacuum processing chamber and the heat transfer gas pressure on the back surface of the sample is supplied. Is reduced in a range where the thermal resistance between the sample and the sample stage is sufficiently reduced, and the electrostatic attraction force is reduced in a range where the floating of the sample is prevented.