JP2012142495A - Plasma etching method and plasma etching apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma etching method and a plasma etching apparatus with which it becomes possible to form a pattern having a high aspect ratio and a uniform inner diameter.SOLUTION: With the plasma etching method according to the present invention, a substrate W, on whose surface a mask pattern is formed, is placed in a vacuum chamber 21, a plasma of a gas introduced into the vacuum chamber 21 is generated, the substrate W is etched using the plasma while applying a high-frequency electric field to the substrate W, and a frequency of the high-frequency electric field is changed in accordance with advancement of the etching of the substrate W. As a result, it becomes possible to change directivity of the etching (between isotropic etching and anisotropic etching). Through switching between a frequency, at which the isotropic etching is performed, and a frequency at which the anisotropic etching is performed, it becomes possible to form a pattern having a uniform inner diameter by suppressing enlargement and reduction of the pattern.

Description

  The present invention relates to a plasma etching method and a plasma etching apparatus for converting an etching gas into a plasma by a high frequency electric field.

  There is a plasma etching method as a substrate processing process used for semiconductor manufacturing or the like. In this method, an etching gas introduced into a vacuum chamber is turned into plasma and reacts with a substrate to be processed (hereinafter referred to as a substrate) to etch the substrate. An etching mask or the like is formed on the substrate and is patterned by etching.

  Here, plasma etching may be highly isotropic depending on the type of substrate or etching gas, etching conditions, and the like. In such a case, when a pattern having a high aspect ratio (deep in the depth direction) is formed on the substrate, it is necessary to prevent etching in the side wall direction (direction perpendicular to the depth direction). This is because the initial hole diameter is expanded with the progress of etching in the depth direction. Various plasma etching methods corresponding to this point have been proposed.

  For example, Patent Document 1 discloses an etching method and an etching apparatus in which a protective film is formed on a sidewall of a pattern formed by etching to form a high aspect ratio pattern. Magnetic Neutral Loop Discharge (NLD) type plasma etching apparatus is used, and ions in the plasma are sputtered by a high frequency electric field applied along the magnetic neutral line (region where the magnetic field is zero). It is drawn into the target and etching or sputtering proceeds.

WO2006 / 003962 Publication

However, in the etching method and the etching apparatus described in Patent Document 1, the frequency of the high-frequency electric field for drawing ions in plasma into the substrate is the same during the etching process.
Here, when the frequency of the high-frequency electric field is high, the selectivity between the etching mask and the substrate is high, the etching rate is high, and the isotropy of etching is high. For this reason, the inner wall of the pattern may be eroded with the progress of etching, and the pattern inner diameter may be expanded. Further, when the frequency of the high frequency electric field is low, the etching anisotropy is large, while the selectivity between the etching mask and the substrate is small, and the etching rate is also small. For this reason, as the etching proceeds, the number of ions reaching the deep part of the pattern decreases, and the pattern inner diameter may be reduced. As described above, it is difficult to form a pattern having a constant inner diameter from the opening to the bottom particularly in a pattern having a high aspect ratio.

  In view of the circumstances as described above, an object of the present invention is to provide a plasma etching method and a plasma etching apparatus capable of forming a pattern having a uniform inner diameter while having a high aspect ratio.

A plasma etching method according to an embodiment of the present invention includes disposing a substrate having a mask pattern formed on a surface in a vacuum chamber.
Plasma of the gas introduced into the vacuum chamber is generated.
The substrate is etched using the plasma while a high frequency electric field is applied.
The target material installed in the vacuum chamber is sputtered by the plasma, and a protective film is formed on the side wall portion of the etching pattern formed on the substrate.
The frequency of the high-frequency electric field is changed according to the progress of etching on the substrate.

A plasma etching apparatus according to an aspect of the present invention includes a vacuum chamber, a stage, a plasma generation unit, a first high-frequency power source, a second high-frequency power source, and a control unit.
The stage supports a substrate disposed in the vacuum chamber.
The plasma generating means converts the gas introduced into the vacuum chamber into plasma.
The first high-frequency power supply applies a high-frequency electric field having a first frequency to the stage.
The second high-frequency power source applies a high-frequency electric field having a second frequency higher than the first frequency to the stage.
The control means controls connection of the first high-frequency power source to the stage and connection of the second high-frequency power source to the stage.

1 is a schematic configuration diagram of a plasma etching apparatus according to a first embodiment. It is a flowchart which shows the operation example of a plasma etching apparatus. It is a timing chart which shows the operation example of a plasma etching apparatus. It is a figure explaining the frequency of the high frequency applied to a board | substrate. It is a figure which shows the influence of the frequency of the high frequency on a pattern shape. It is a schematic block diagram of the plasma etching apparatus by 2nd Embodiment.

A plasma etching method according to an embodiment of the present invention includes disposing a substrate having a mask pattern formed on a surface thereof in a vacuum chamber.
Plasma of the gas introduced into the vacuum chamber is generated.
The substrate is etched using the plasma while a high frequency electric field is applied.
The target material installed in the vacuum chamber is sputtered by the plasma, and a protective film is formed on the side wall portion of the etching pattern formed on the substrate.
The frequency of the high-frequency electric field is changed according to the progress of etching on the substrate.

According to the plasma etching method, the protective film is formed by sputtering on the pattern formed by etching, and the side wall direction of the pattern is prevented from being etched.
In addition, by changing the frequency of the high-frequency electric field applied during etching, the etching directivity (isotropic or anisotropic) can be changed. By switching between the frequency at which etching is isotropic and the frequency at which etching is anisotropic, expansion and reduction of the pattern can be suppressed, and a pattern having a uniform inner diameter can be formed.

  The etching step includes a first step of etching with the high-frequency electric field having a first frequency, and a second step of etching with the high-frequency electric field having a second frequency higher than the first frequency after the first step. And a third step of etching with the high-frequency electric field having a third frequency lower than the second frequency after the second step.

  According to the above configuration, high processing accuracy can be obtained by etching at the first frequency with high etching anisotropy at the etching start stage. Next, the inner diameter of the pattern is prevented from being reduced by etching with the second frequency having high isotropic etching. In the etching end stage, the inner diameter of the pattern is prevented from being expanded by etching again with the third frequency having high etching anisotropy.

  The substrate may be a silicon substrate or a quartz substrate.

  According to the above configuration, it is possible to form a pattern with a uniform inner diameter on a silicon substrate or quartz substrate with a high aspect ratio.

  The first frequency and the third frequency may be the same.

  The first frequency may be 1.0 MHz, and the second frequency may be 13.56 MHz.

A plasma etching apparatus according to an embodiment of the present invention includes a vacuum chamber, a stage, a plasma generating unit, a first high frequency power source, a second high frequency power source, and a control unit.
The stage supports a substrate disposed in the vacuum chamber.
The plasma generating means converts the gas introduced into the vacuum chamber into plasma.
The first high-frequency power supply applies a high-frequency electric field having a first frequency to the stage.
The second high-frequency power source applies a high-frequency electric field having a second frequency higher than the first frequency to the stage.
The control means controls connection of the first high-frequency power source to the stage and connection of the second high-frequency power source to the stage.

  The control means connects the first high-frequency power source and the stage at the start of etching, connects the second high-frequency power source and the stage as the etching progresses, and connects the first high-frequency power source and the stage as the etching progresses. Connect the high frequency power supply and the above stage.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a plasma etching apparatus 20 applied to the plasma etching method according to the first embodiment of the present invention. The illustrated plasma etching apparatus 20 is configured as an NLD (magnetic neutral loop discharge) type plasma etching apparatus, and has an etching function on the substrate surface and a protective film on the side wall portion of the etching pattern on the substrate surface. It has the function to form.

  In FIG. 1, reference numeral 21 denotes a vacuum chamber, in which a vacuum chamber (plasma chamber) including a plasma forming space 21a is formed. A vacuum pump such as a turbo molecular pump (TMP) is connected to the vacuum chamber 21, and the inside of the vacuum chamber 21 is evacuated to a predetermined degree of vacuum.

  A plasma forming space 21 a is partitioned around a cylindrical wall 22 that constitutes a part of the vacuum chamber 21. The cylindrical wall 22 is made of a transparent insulating material such as quartz. On the outer peripheral side of the cylindrical wall 22, a plasma generating high-frequency coil (antenna) 23 connected to the first high-frequency power source RF1 and three magnetic coil groups 24 (24A) arranged on the outer peripheral side of the high-frequency coil 23 are provided. , 24B, 24C) are arranged respectively.

  Current is supplied to the magnetic coil 24A and the magnetic coil 24C in the same direction, and current is supplied to the magnetic coil 24B in the opposite direction to the other magnetic coils 24A and 24C. As a result, in the plasma formation space 21a, the magnetic neutral line 25 having a magnetic field of zero is continuously formed in an annular shape. And the induction plasma electric field (high frequency electric field) along the magnetic neutral line 25 is formed by the high frequency coil 23, and discharge plasma is formed.

In particular, in the NLD plasma etching apparatus, the formation position and size of the magnetic neutral wire 25 can be adjusted by the magnitude of the current flowing through the magnetic coils 24A to 24C. That is, when the currents flowing through the magnetic coils 24A, 24B, and 24C are I _A , I _B , and I _C , respectively, when I _A > I _C , the formation position of the magnetic neutral wire 25 is lowered to the magnetic coil 24C side, On the other hand, when I _A <I _C , the formation position of the magnetic neutral wire 25 goes up to the magnetic coil 24A side. Also, when gradually increasing the current I _B flowing through the intermediate magnetic coil 24B, at the same time when the ring diameter of the magnetic neutral line 25 becomes small, it becomes gentle gradient of the magnetic field at the position of the zero magnetic field. By utilizing these characteristics, it is possible to optimize the plasma density distribution.

  On the other hand, a stage 26 for supporting a semiconductor wafer (silicon (Si) substrate) W is installed in the vacuum chamber 21. The stage 26 is made of a conductor and is connected to the control unit 36. The stage 26 incorporates a heating source such as a heater for heating the substrate W to a predetermined temperature. The control unit 36 is connected to the second high frequency power supply RF2 (1.0 MHz) via the capacitor 27 and to the third high frequency power supply RF3 (13.56 MHz) via the capacitor 35. The control unit 36 switches which of the second high frequency power source RF2 and the second high frequency power source RF3 is connected to the stage 26. The control unit 36 is controlled by, for example, a computer that outputs a switching signal.

  The frequency of the second high-frequency power supply RF2 is not limited to 1.0 MHz, and the etching anisotropy becomes large under the etching conditions employed, that is, within the frequency range where the physical process is dominant as will be described later. Is possible. Further, the frequency of the third high frequency power supply RF3 is not limited to 13.56 MHz, and is within a frequency range in which etching isotropic is increased under the employed etching conditions, that is, within a frequency range in which a chemical process is dominant as will be described later. Is possible.

  A top plate 29 is installed above the plasma forming space 21a. The top plate 29 is configured as a counter electrode of the stage 26, and is connected to the fourth high-frequency power source RF4 via the capacitor 28. A target (sputtering target) 30 for forming a substrate by sputtering is attached to the surface of the top plate 29 on the plasma forming space 21a side. In the present embodiment, the target 30 is made of a fluororesin such as polytetrafluoroethylene (PTFE), but other synthetic resin materials, or silicon, carbon, silicon carbide, silicon oxide, nitriding A silicon material etc. are applicable.

  In the vicinity of the top plate 29, a gas introduction pipe 31 for introducing a process gas into the vacuum chamber 21 is installed. In the present embodiment, the process gas includes an etching gas, a sputtering gas, and a cleaning gas described later.

The operation of the plasma etching apparatus 20 will be described.
FIG. 2 is a flowchart showing an example of the operation of the plasma etching apparatus 20.
As shown in the figure, the plasma etching apparatus 20 performs etching (ST101, 203, etc.), sputtering (ST102, ST203, etc.), and cleaning (ST201, ST301). After removing the surface of the substrate W by etching and forming a protective film by sputtering alternately for a plurality of cycles (50 to 100 cycles), the deposit is removed by cleaning, and etching and sputtering are performed again. As a result, a predetermined pattern is formed. The number of executions of etching and sputtering can be set as appropriate, and the number of times etching and sputtering are repeated during cleaning is also arbitrary.

  RF2 etching (ST101, ST302, etc.) means etching that proceeds in a state where a high frequency power supply RF2 is connected to the stage 26 and a high frequency of the frequency (1.0 MHz) of the high frequency power supply RF2 is applied to the stage 26. RF3 etching (ST201 or the like) means etching that proceeds in a state where the high frequency power supply RF3 is connected to the stage 26 and a high frequency of the frequency (13.56 MHz) of the high frequency power supply RF3 is applied to the stage 26. In FIG. 2, the frequency is changed before and after cleaning, but the present invention is not limited to this. For example, step 103 can be RF3 etching.

Etching and sputtering will be described.
FIG. 3 is a timing chart showing an operation example of the plasma etching apparatus 20 according to the present embodiment. In FIG. 3, A is the power application timing of the first high frequency power supply RF1 supplied to the high frequency coil 23, B is the power application timing of the second high frequency power supply RF2 supplied to the stage 26, and C is supplied to the stage 26. The power application timing of the third high frequency power supply RF3, D represents the power application timing of the fourth high frequency power supply RF4 supplied to the top plate 29, and E represents the pressure inside the vacuum chamber 21, respectively. In this example, the etching processing pressure (process gas introduction amount) is set higher than that of sputtering.

  A mask pattern is formed in advance on the surface of the substrate W. This mask pattern includes an etching mask such as an organic resist or a metal mask. In the etching and sputtering, an annular magnetic neutral wire 25 is formed in the plasma forming space 21a by the magnetic coil group 24. Further, by applying power from the first high frequency power supply RF1 to the high frequency coil 23, the annular magnetic neutral wire 25 is formed. Along with this, an inductively coupled plasma is formed.

In the etching, the etching gas (SF ₆ and Ar mixed gas) introduced into the vacuum chamber 21 is turned into plasma in the plasma formation space 21a, and the substrate W on the stage 26 is etched by the generated ions and radicals. To do. At this time, the substrate bias is turned on by applying power from the second high-frequency power source RF2 or the third high-frequency power source RF3, ions are accelerated to the stage 26 side, and radical products on the substrate W are sputtered to remove the etching property. Increase. That is, the fluorine radicals react with silicon to form radical products, which are removed by the sputtering action of ions in the plasma, whereby the etching process of the substrate W proceeds. Switching between the second high-frequency power source RF2 and the third high-frequency power source RF3 will be described later.

  After the etching process is performed for a predetermined time, the etching gas remaining in the vacuum chamber 21 is exhausted. Then, sputtering is started by introducing a process gas (Ar) for forming the protective film into the vacuum chamber 21. The introduced process gas is turned into plasma in the plasma forming space 21a. At this time, the substrate bias (RF2 or RF3) is turned off, and instead, the top plate bias is turned on when power is supplied from the fourth high frequency power supply (RF4). As a result, the target 30 placed on the top plate 29 is sputtered by ions in the plasma, and the sputtered material adheres to the surface of the substrate W and the etching pattern formed by the above-described etching. As described above, the polymer layer functioning as a protective film is formed on the bottom and side walls of the etching pattern.

  Here, the sputtered particles knocked out from the target 30 pass through the NLD plasma formed in the plasma forming space 21a and reach the substrate. At this time, the sputtered particles are decomposed and re-excited in a high-density plasma region where the annular magnetic neutral line 25 is formed, thereby forming a film form similar to a chemical vapor deposition method (CVD method) and the surface of the substrate. Isotropically incident. Therefore, the step film (protective film) of the etching pattern obtained by this embodiment has high coverage and excellent in-plane uniformity.

As a sputtering process gas, for example, by using a mixed gas of Ar and a fluorocarbon-based gas (C ₄ F ₈ , CHF ₃ or the like), the reaction gas in the process gas is converted into plasma in the plasma formation space 21a, and its radical The product is deposited on the substrate surface to form a polymer layer that functions as a protective film. Furthermore, by using the above mixed gas as the process gas, it is possible to improve the sputtering rate (deposition rate) as compared with the case where only Ar gas is used as the process gas.

  After performing the sputtering for a predetermined time, the above-described etching is performed again. This initial stage of etching is spent on removing the protective film covering the bottom of the etching pattern. Thereafter, the etching process of the bottom of the etching pattern exposed by removing the protective film is resumed. At this time, ions in the plasma are incident on the substrate in the vertical direction by the substrate bias action. For this reason, the number of ions reaching the protective film covering the side wall of the etching pattern is less than the number of ions reaching the bottom of the etching pattern. Therefore, during the etching, the protective film covering the side wall portion of the etching pattern remains without being completely removed. As a result, contact between the sidewall portion of the etching pattern and the fluorine radical is avoided, and erosion due to etching of the sidewall portion of the etching pattern is prevented.

  As described above, a pattern is formed by alternately performing etching and sputtering a plurality of times. Here, the frequency of the high frequency applied to the substrate W is changed by switching the high frequency power source connected to the stage 26 during etching to either the second high frequency power source RF2 or the third high frequency power source RF3 by the control unit 36. Change to optimize etching characteristics.

FIG. 4 is a diagram for explaining the frequency of the high frequency applied to the substrate by the plasma etching apparatus 20 according to the present embodiment.
FIG. 4A shows how the frequency is changed as the etching progresses.
As shown in the figure, the second high frequency power supply RF2 (1.0 MHz) is used in the portion near the opening, that is, the etching start stage, and the third high frequency power supply RF3 (13.56 MHz) is used in the intermediate stage. The second high-frequency power source RF2 (1.0 MHz) is used again in the back portion, that is, in the end stage.
FIG. 4B shows the use frequency of the formed pattern for each etching depth.

FIG. 5 is a diagram illustrating the influence of high frequency on the pattern shape.
FIG. 5A is a conceptual diagram of a pattern when the frequency of the high frequency is only 1.0 MHz during etching. As shown in the figure, in the pattern, the diameter decreases from the opening toward the tip, and the film thickness of the etching mask M decreases.

  FIG. 5B is a conceptual diagram of a double pattern in which the frequency of the high frequency is only 13.56 MHz during etching. As shown in the figure, the pattern is expanded by etching the side wall, while the thickness of the etching mask M is hardly reduced.

  Selectivity, directivity, and etching rate can be increased as influences of high-frequency frequencies during etching on etching characteristics. As described above, the plasma of the etching gas is dissociated into radicals and ions by a high-frequency electric field, the generated radicals react with the substrate W (chemical process), and the ions collide with the substrate W to remove radical products (physical). The process proceeds as a result. The frequency of the high frequency affects the degree of plasma dissociation and the incident energy of ions incident on the substrate W. For this reason, whether the chemical process or the physical process is dominant depends on the frequency of the high frequency, and the etching characteristics change.

  A high frequency (13.56 MHz) with a high frequency has a higher degree of plasma dissociation and a larger contribution of chemical processes than a low frequency (1.0 MHz), whereas a low frequency has a higher incident frequency of ions than a high frequency. The contribution of physical processes is large.

The selectivity is the ratio between the etching rate of the etching mask M and the substrate W. Ideally, only the substrate W is etched and the etching mask M is not etched, but in many cases, the etching mask M is also etched. When the selectivity is high, the difference in etching rate is large, that is, the etching mask M is difficult to be etched, and when the selectivity is low, the difference in etching rate is small, that is, the etching mask M is easily etched.
If the etching mask M is lost before the formation of the pattern is completed, the region to be masked on the substrate W is also etched, so it is preferable that the selectivity is high.

  In the plasma etching apparatus 20 according to the present embodiment, the selectivity is small when the frequency is 1.0 MHz, and the selectivity is large when the frequency is 13.56 MHz. This is because the progress of etching by the chemical process is more dominant than the physical process, and the material (chemical composition) of the substrate W and the etching mask M is different. Therefore, the etching rate is increased at 13.56 MHz where the contribution of the chemical process is large. This is because the difference is large.

  Directivity means whether etching proceeds isotropically or anisotropically. In the plasma etching apparatus 20 according to the present embodiment, a protective film for protecting the side wall portion of the pattern is formed. However, if the etching is highly isotropic, the protective film on the side wall portion is also removed and a high aspect ratio is removed. The pattern cannot be formed.

  In the plasma etching apparatus 20 according to the present embodiment, the anisotropy is large when the frequency is 1.0 MHz, and the isotropic property is large when the frequency is 13.56 MHz. This is because the incidence of ions (physical process) is highly anisotropic, and the reaction between the radical and the substrate W (chemical process) is highly isotropic.

  The etching rate is a rate at which the substrate W is etched in the depth direction. In the plasma etching apparatus 20 according to this embodiment, the etching rate is higher when the frequency is 13.56 MHz than when the frequency is 1.0 MHz. This is because plasma dissociation proceeds as the frequency increases, and as a result, more fluorine radicals are generated.

In FIG. 5A, since the anisotropy of etching is high, ions reaching the bottom decrease as the pattern depth increases, the diameter decreases from the opening toward the tip, and the etching rate is slow. Further, as described above, the remaining film thickness of the etching mask M is small.
In FIG. 5B, since the isotropicity of etching is high, the side wall of the pattern is etched and expanded, and the shape maintaining property of the etching pattern is deteriorated.

  As described above, when the frequency of the high frequency is large (for example, 13.56 MHz), due to the large contribution of the chemical process, the selectivity is large and the etching rate is large, but the etching isotropic is large. In addition, when the frequency of the high frequency is small (for example, 1.0 MHz), due to the large contribution of the physical process, the etching anisotropy is large, while the selectivity is small and the etching rate is small. By using the influence of the high frequency on etching characteristics, the high frequency is switched as the etching progresses.

  At the etching start stage, the high frequency is set to 1.0 MHz (the second high frequency power supply RF2 is used). By making the anisotropy high at 1.0 MHz, it is possible to maintain the processing accuracy of the opening.

  When the etching has progressed to some extent, the high frequency is set to 13.56 MHz (the third high frequency power supply RF3 is used). By setting the isotropic high 13.56 MHz, it is possible to prevent the pattern diameter from shrinking and to improve the etching rate. Further, the etching mask is prevented from being etched.

Further, when the etching progresses, the high frequency is set again to 1.0 MHz. If the frequency is 13.56 MHz, the side wall expands as described above, but the pattern shape can be maintained by changing to 1.0 MHz at an appropriate stage.
In addition, the processing accuracy of the bottom surface of the pattern is high.

  As described above, by switching the frequency at which etching is isotropic and the frequency at which etching is anisotropic, expansion and reduction of the pattern can be suppressed and a pattern with a uniform inner diameter can be formed. At the same time, it is possible to improve all of processing accuracy, etching rate, and etching mask residual film thickness.

  Next, the surface cleaning process of the target 30 according to the present invention will be described.

When the substrate etching process and the protective film forming process are continued, reaction generation related to the etching gas (SF ₆ / Ar), target material (PTFE), substrate material (silicon), etc. generated in the plasma formation space 21a Objects are deposited on the surface of the target 30. This kind of deposited film is sputtered by plasma irradiation and adheres to an etching pattern formed on the surface of the substrate. During the etching, the sputtered matter of the deposited film is deposited on the opening of the etching pattern, thereby preventing the progress of the etching.

  Therefore, in the present embodiment, a cleaning process for cleaning the surface of the target 30 is performed by replacing the atmospheric gas in the vacuum chamber 21 with an oxygen-based gas during or after the etching. In this cleaning step, oxygen-based gas plasma is generated in the vacuum chamber 21 and reaction products adhering to the surface of the target 30 are removed by plasma ashing.

As the process gas used in this cleaning step, any of O ₂ , O ₃ , COx, NOx, H ₂ O, SOx, or a mixed gas thereof is used. Further, a mixed gas of these oxygen-based gas and rare gas may be used. The process pressure is set to the same level as that of etching, and is, for example, 1.0 Pa to 6.0 Pa. The oxygen-based gas plasma is generated using the high-frequency coil 23 and the magnetic coil group 24 connected to the first high-frequency power source RF1.

  FIG. 2 shows an example in which the target 30 is cleaned after etching and sputtering are alternately performed a plurality of times. Each time etching and sputtering are performed for a predetermined cycle (50 to 100 cycles), the surface of the target 30 is cleaned. As described above, the timing for changing the frequency during etching and the timing for cleaning are not related.

(Second Embodiment)
FIG. 6 is a schematic configuration diagram of a plasma etching apparatus 37 according to the second embodiment of the present invention. In the figure, portions corresponding to those of the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the substrate S is composed of a quartz substrate, and the target 38 is composed of a silicon (Si) plate. The top plate 29 is connected to the first high-frequency power source RF1 for the high-frequency coil 23 via the capacitor 28. Thus, bias power is also applied to the top plate 29 while plasma is being formed in the plasma forming space 21a.

On the other hand, a stage 26 that supports the substrate W is installed inside the vacuum chamber 21. The stage 26 is made of a conductor, and is connected to the second high-frequency power source RF2 via the capacitor 27 and to the third high-frequency power source RF3 via the capacitor 35. The second high frequency power supply RF2 (1.0 MHz) and the third high frequency power supply RF3 (13.56 MHz) are connected by the control unit 36.

As an etching gas for the substrate W made of quartz, a fluorocarbon-based gas such as C ₃ F ₈ , CF ₄ , or CHF ₃ is used. Etching gas plasma is generated in the plasma forming space 21a to etch the substrate W on which the mask pattern is formed. At the time of etching, high frequency power is applied to the target 38, whereby ions in the plasma are drawn into the top plate 29, and the target 38 is sputtered. The sputtered silicon particles react with a part of the etching gas and function to adjust the etchant concentration in the chamber. This makes it possible to perform an appropriate etching process on the substrate W and realize pattern processing with excellent shape controllability.

  In the plasma etching apparatus 37 having such a configuration, as in the first embodiment, any one of processing accuracy, etching speed, and etching mask remaining film thickness can be obtained by changing the frequency of the high frequency in accordance with the progress of etching. Can also be improved.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  In the above-described embodiment, in the etching process, the frequency of the high-frequency power applied to the stage is switched twice. However, the number of times is not limited to two and may be more stages. Further, the frequency of the high frequency may be changed continuously. In addition, the frequency is set to a low frequency at the start of etching, then set to a high frequency, and then set to a low frequency again.

  In the above-described embodiment, two high-frequency power sources having different frequencies connected to the stage are used. However, the present invention is not limited to this, and three or more high-frequency power sources may be used. Alternatively, the oscillation frequency may be variable with a single high-frequency power source. The magnitude of the frequency used from the start to the end of etching, the switching order, the number of times of switching, and the like can be appropriately set according to the required etching accuracy, pattern shape, aspect ratio, and the like.

W substrate M etching mask S substrate RF2 second high frequency power source RF3 third high frequency power source 20 plasma etching device 21 vacuum chamber 30 target 36 control unit 37 plasma etching device 38 target

Claims (7)

A substrate with a mask pattern formed on the surface is placed in a vacuum chamber,
Generating a plasma of the gas introduced into the vacuum chamber;
Etching the substrate using the plasma while applying a high frequency electric field to the substrate,
Sputtering the target material installed in the vacuum chamber with the plasma, forming a protective film on the side wall of the etching pattern formed on the substrate,
A plasma etching method, wherein the frequency of the high-frequency electric field is changed according to the progress of etching on the substrate. The plasma etching method according to claim 1,
The etching step includes
A first step of etching with said high frequency electric field of a first frequency;
After the first step, a second step of etching with the high-frequency electric field having a second frequency higher than the first frequency;
And a third step of etching with the high-frequency electric field having a third frequency lower than the second frequency after the second step. The plasma etching method according to claim 2,
The plasma etching method, wherein the substrate is a silicon substrate or a quartz substrate. The plasma etching method according to claim 3,
The plasma etching method, wherein the first frequency and the third frequency are the same. The first frequency according to claim 4 is 1.0 MHz,
The second frequency is 13.56 MHz. Plasma etching method. A vacuum chamber;
A stage for supporting a substrate disposed in the vacuum chamber;
Plasma generating means for converting the gas introduced into the vacuum chamber into plasma;
A first high frequency power source for applying a high frequency electric field of a first frequency to the stage;
A second high-frequency power source for applying a high-frequency electric field having a second frequency higher than the first frequency to the stage;
A plasma etching apparatus comprising: control means for controlling connection of the first high-frequency power source to the stage and connection of the second high-frequency power source to the stage. The plasma etching apparatus according to claim 6,
The control means connects the first high-frequency power source and the stage at the start of etching, connects the second high-frequency power source and the stage with the progress of etching, and the first high-frequency power source with the progress of further etching. A plasma etching apparatus that connects a high-frequency power source and the stage.

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