JP5913830B2 - Etching method of silicon substrate - Google Patents

Description

The present invention, an etching method for silicon substrate, relates to how to etch particular silicon substrate anisotropically.

  Conventionally, fluorine-containing gases such as sulfur hexafluoride gas have been frequently used for plasma etching for patterning a silicon substrate. In plasma etching using a fluorine-containing gas, a silicon substrate is etched by reacting fluorine radicals in plasma with silicon to form highly volatile silicon fluoride. In addition, in the plasma etching, positive ions in the plasma are attracted to the surface of the silicon substrate to promote collision between positive ions containing fluorine and silicon, thereby etching the silicon substrate. Thus, according to plasma etching using a fluorine-containing gas, a silicon substrate is formed by isotropic etching due to reaction between silicon and fluorine radicals and anisotropic etching due to collision between silicon and positive ions. It is etched effectively.

  In recent years, for example, as described in Patent Document 1, in a semiconductor device in which a plurality of silicon substrates in which elements or the like are formed are stacked, a through silicon via (TSV) penetrating the silicon substrate in the stacking direction is It is being used for electrical connection between silicon substrates. Plasma etching using a fluorine-containing gas as described above is also used to form a silicon through hole in which such a silicon through electrode is embedded.

JP-T-2007-513493

  By the way, the thickness of each silicon substrate constituting the semiconductor device is several tens μm to several hundreds μm. Since a through hole having a diameter of several μm or less is formed on such a silicon substrate, the aspect ratio of the through hole is several tens to several hundreds.

  As described above, when the silicon substrate is etched using the plasma of the fluorine-containing gas, the etching using positive ions proceeds with anisotropic etching in the thickness direction of the silicon substrate while using radicals. According to the conventional etching, isotropic etching of the silicon substrate proceeds. Therefore, especially when the through hole having a high aspect ratio as described above is formed, the etching in the radial direction of the through hole is a desired region as the etching in the depth direction of the through hole proceeds. It will progress more than that.

  Such a problem is not limited to the case where a through-hole is formed in a silicon substrate, but generally occurs in a case where a recess including a trench extending in the thickness direction is formed in the silicon substrate. .

The present invention has been made in view of the above circumstances, and its object is to provide an etching how the silicon substrate capable of enhancing the machining accuracy of a recess formed in the silicon substrate.

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

The invention according to claim 1 is an etching method of a silicon substrate for forming a recess extending in a thickness direction of the silicon substrate, wherein a plasma of fluorine-containing gas is supplied to the silicon substrate, and the silicon substrate An etching step for forming the recess, and a protective film forming step for supplying a plasma of boron-containing gas to the silicon substrate to form a protective film containing boron and silicon on the inner wall surface of the recess , An etching step and a protective film forming step are simultaneously performed to form the protective film made of a silicon boride compound containing fluorine as the protective film, and using the fluorine-containing gas plasma, among the a bottom wall portion formed of the recess by etching said silicon substrate exposed in the bottom wall of said recess to form said recess The gist of the door.

  According to the first aspect of the present invention, when the recess extending in the thickness direction is formed on the silicon substrate, the etching step for forming the recess by the fluorine-containing gas plasma and the silicon by the boron-containing gas plasma are used. And a protective film forming step for forming a protective film made of a compound containing boron and boron on the inner wall surface of the recess. As a result, the vertical component contained in the etchant and the component that travels in the direction intersecting the vertical component reach the bottom wall surface of the recess, so that the removal of the protective film and the etching of the silicon substrate proceed. become. On the other hand, since the component that travels in the direction intersecting the vertical component included in the etchant reaches the side wall surface of the recess, the formed protective film is maintained, and the silicon substrate is hardly etched. Therefore, it is possible to prevent the side wall surface of the recess from being etched in a direction perpendicular to the formation direction of the recess beyond the opening while maintaining the progress of etching on the bottom wall surface of the recess. As a result, the processing accuracy of the recess can be increased.

In the first aspect of the invention, the etching of the silicon substrate by the fluorine-containing gas plasma and the formation of the protective film by the boron-containing gas plasma are simultaneously performed. Therefore, since the protective film is formed simultaneously with the progress of etching on the silicon substrate, the side wall surface of the recess that is difficult to be exposed to the vertical component contained in the etchant is not easily exposed to the etchant during the formation of the recess. Become. On the other hand, the bottom wall surface of the recess that is easily exposed to the vertical component of the etchant is preferentially etched. Therefore, it is possible to prevent the side wall surface of the recess from being etched in a direction perpendicular to the direction in which the recess is formed beyond the opening thereof, thereby improving the processing accuracy of the recess.

The invention according to claim 2 is the method for etching a silicon substrate according to claim 1, wherein the fluorine-containing gas is a sulfur hexafluoride gas, the boron-containing gas is boron trifluoride, and the etching step. And the step of forming the protective film simultaneously, only the plasma of the sulfur hexafluoride gas and the plasma of the boron trifluoride gas are supplied to the silicon substrate.
Invention of claim 3, in the etching method for silicon substrate according to claim 1, when performing said etching step and the protective film forming step simultaneously, at least one of the plasma in the plasma and a rare gas of oxygen gas The gist is to further supply the silicon substrate.
The invention described in claim 4 is the silicon substrate etching method according to any one of claims 1 to 3, further comprising a step of removing the protective film by a cleaning process using an RCA method. And

Diagram showing a schematic configuration of a dry etching apparatus as an embodiment of etching apparatus divorced substrate. (A)-(c) The figure which showed one Embodiment of the etching method of the silicon substrate in this invention in order of the process of an etching process. (A) SEM image showing the shape of a recess formed under the process conditions of Example 1 (b) SEM image showing the shape of a recess formed under the process conditions of Example 2. (A)-(f) The figure which showed other embodiment of the etching method of the silicon substrate in this invention in order of the process of an etching process.

Hereinafter will be described with reference to FIGS. 1 and 2 An embodiment of an etch how the silicon substrate of the present invention. First, a dry etching apparatus as an embodiment of a silicon substrate etching apparatus will be described with reference to FIG.

[Dry etching equipment]
As shown in FIG. 1, a quartz window 12 that seals the opening of the vacuum chamber 11 is fixed to a cylindrical vacuum chamber 11 of the dry etching apparatus 10. In a space formed by the vacuum chamber 11 and the quartz window 12, a substrate stage 13 that holds the substrate S is installed. A bias high-frequency power source 15 that outputs, for example, 13.56 MHz high-frequency power is connected to the stage electrode 14 disposed in the substrate stage 13 via a bias matching unit 16 including a capacitor that applies a bias voltage to the substrate S. It is connected. The bias matching unit 16 matches the output impedance of the bias high frequency power supply 15 with the input impedance of the load and applies a bias voltage to the substrate S when the bias high frequency power supply 15 outputs.

  A high frequency antenna 21 including an upper antenna 21 a and a lower antenna 21 b is disposed on the outer surface side of the quartz window 12. Each of the antennas 21a and 21b included in the high-frequency antenna 21 has, for example, a spiral shape that is wound twice and a half in the circumferential direction of the substrate S, and a power input portion 21c that is an end portion on the center side of the spiral, It is connected to the power output unit 21d which is the outer end.

  For example, an antenna high-frequency power source 22 that outputs a high-frequency power of 13.56 MHz is connected to the power input unit 21 c of the high-frequency antenna 21 via an input-side variable capacitor 23 and an antenna matching unit 24. An output side variable capacitor 25 is connected to the power output unit 21 d of the high frequency antenna 21. The antenna matching unit 24 matches the output impedance of the antenna high frequency power supply 22 with the input impedance of the load when the antenna high frequency power supply 22 is output. Further, the input-side variable capacitor 23 and the output-side variable capacitor 25 make the amounts of current flowing through the power input unit 21c side and the power output unit 21d side of the high-frequency antenna 21 substantially equal when performing the etching process. Thereby, the by-product attached to the inner surface of the quartz window 12 is easily sputtered over the entire inner surface.

  A magnetic field coil 26 that forms a magnetic neutral line in the vacuum chamber 11 is disposed on the outer periphery of the quartz window 12. The magnetic field coil 26 includes an upper coil 26a, a middle coil 26b, and a lower coil 26c. A current supply unit 27 that outputs a current for forming the magnetic neutral line is connected to the magnetic field coil 26. More specifically, the upper stage supply part 27a is connected to the upper stage coil 26a, the middle stage supply part 27b is connected to the middle stage coil 26b, and the lower stage supply part 27c is connected to the lower stage coil 26c. Among the current supply units 27, the upper supply unit 27a and the lower supply unit 27c output currents in the same direction to the upper coil 26a and the lower coil 26c, respectively, and the middle supply unit 27b includes the other supply units 27a and 27c. The magnetic neutral line is formed in the vacuum chamber 11 by outputting a current in the opposite direction to the middle coil 26b.

  An exhaust part 31 that exhausts the fluid in the vacuum chamber 11 is connected to an exhaust port 11 a formed through the vacuum chamber 11. The exhaust unit 31 includes, for example, a pressure adjustment valve that adjusts the pressure in the vacuum chamber 11 and various vacuum pumps.

An etching gas supply unit 32 that supplies sulfur hexafluoride (SF ₆ ) gas as a fluorine-containing gas used for etching the substrate S to the vacuum chamber 11 is connected to the gas supply port 11 b formed through the vacuum chamber 11. Has been. The etching gas supply unit 32 is a mass flow controller connected to a cylinder storing sulfur hexafluoride gas, and adjusts the flow rate of the sulfur hexafluoride gas supplied into the vacuum chamber 11.

The gas supply port 11b is connected to a protective film forming gas supply unit 33 for supplying boron trifluoride (BF ₃ ) gas as a boron-containing gas for forming a protective film on the substrate S to the vacuum chamber 11. Yes. The protective film forming gas supply unit 33 is a mass flow controller connected to a cylinder storing boron trifluoride gas, and adjusts the flow rate of boron trifluoride gas supplied into the vacuum chamber 11.

  When the etching process is performed on the substrate S, the exhaust gas flow rate of the exhaust unit 31, the flow rate of the sulfur hexafluoride gas supplied from the etching gas supply unit 32, and the three fluorine gas supplied from the protective film forming gas supply unit 33. The inside of the vacuum chamber 11 is set to a predetermined pressure by the flow rate of the boron fluoride gas.

  The dry etching apparatus 10 includes a control unit that controls driving of the bias high-frequency power source 15, the antenna high-frequency power source 22, the current supply unit 27, the exhaust unit 31, the etching gas supply unit 32, and the protective film forming gas supply unit 33. 41 is mounted.

  The control unit 41 stores the amount of power to be supplied to the stage electrode 14 as one of the process conditions, and outputs a drive signal corresponding to the amount of power to the bias high-frequency power source 15. The control unit 41 stores the amount of power to be supplied to the high-frequency antenna 21 as one of the process conditions, and outputs a drive signal corresponding to the amount of power to the antenna high-frequency power source 22. Further, the control unit 41 stores a current value to be supplied to the magnetic field coil 26 as one of the process conditions, and outputs a drive signal corresponding to the current value to the current supply unit 27. In addition, the control unit 41 stores the exhaust flow rate of the exhaust unit 31 as one of the process conditions, and outputs a drive signal for exhausting the fluid in the vacuum chamber 11 to the exhaust unit 31 at the flow rate. The control unit 41 stores the supply flow rate of the sulfur hexafluoride gas as one of the process conditions, and outputs a drive signal for supplying the sulfur hexafluoride gas at the flow rate to the etching gas supply unit 32. To do. In addition, the control unit 41 stores the supply flow rate of boron trifluoride gas as one of the process conditions, and supplies a drive signal for supplying the boron trifluoride gas at the flow rate to the protective film forming gas supply unit 33. Output to.

  Based on such process conditions, the control unit 41 drives the etching gas supply unit 32 and the protective film formation gas supply unit 33, while the antenna high-frequency power source 22, the current supply unit 27, and the bias high-frequency power source 15 are connected. To drive. Thereby, the plasma using sulfur hexafluoride gas and the plasma using boron trifluoride gas are simultaneously supplied to the substrate S, thereby forming a recess extending in the thickness direction of the substrate S. And the formation of the protective film on the side wall surface of the recess are simultaneously performed.

  In the present embodiment, the high frequency antenna 21, the antenna high frequency power supply 22, the magnetic field coil 26, and the current supply unit 27 constitute a plasma generation unit.

[Silicon substrate etching method]
Of the operations of the dry etching apparatus 10, an embodiment of the silicon substrate etching method implemented by the dry etching apparatus 10 will be described below with reference to FIGS. 2 and 3. As shown in FIG. 2A, the substrate S to be subjected to the etching process includes a support substrate 51 made of silicon oxide or the like, a silicon substrate 52 laminated on the support substrate 51, and the silicon substrate 52. And a resist pattern 53 having an opening 53a corresponding to the shape of the recess to be formed. Such a substrate S is carried into the dry etching apparatus 10 and placed on the substrate stage 13.

When the substrate S is carried into the vacuum chamber 11, the etching gas supply unit 32 supplies sulfur hexafluoride gas into the vacuum chamber 11 at a flow rate of, for example, 56 sccm, and the protective film forming gas supply unit 33 Boron fluoride gas is supplied into the vacuum chamber 11 at a flow rate of 224 sccm, for example. In performing anisotropic etching on the silicon substrate 52, the flow rate of boron trifluoride gas is 80% or more and 90% or less with respect to the total flow rate of sulfur hexafluoride gas and boron trifluoride gas. It is more preferable that only be included. Next, the high frequency power supply 22 for antenna outputs high frequency power to the high frequency antenna 21 and the current supply unit 27 supplies current to the magnetic field coil 26, whereby the sulfur hexafluoride gas and trifluoride are introduced into the vacuum chamber 11. Plasma using boron gas is generated. The bias high-frequency power supply 15 outputs high-frequency power to the stage electrode 14, whereby a negative bias voltage is applied to the stage electrode 14.

As a result, positive ions contained in the plasma, particularly positive ions containing fluorine, are attracted to the surface of the substrate S by the bias voltage, so that the openings 53a of the resist pattern 53 are formed as shown in FIG. A recess 54 extending in the thickness direction of the silicon substrate 52 is formed. At this time, in addition to the positive ions containing fluorine, positive ions containing boron and radicals containing boron are also supplied to the silicon substrate 52 from the openings of the resist pattern 53. These positive ions and radicals containing boron form _a silicon boride compound (Si _a B _b F _c ) having _a vapor pressure low enough to adhere to the substrate S and containing fluorine. Therefore, a protective film 55 made of a silicon boride compound is formed on the inner wall surface of the recess 54 formed in the silicon substrate 52.

  Although both the positive ion containing fluorine and the radical containing fluorine reach the bottom wall surface 54a of the concave portion 54, the radical containing fluorine reaches the side wall surface 54b of the concave portion 54. Positive ions containing fluorine are hardly reached. Therefore, since the silicon substrate 52 is exposed by removing the protective film 55 on the bottom wall surface 54 a of the recess 54, the etching that extends in the thickness direction of the silicon substrate 52 proceeds. On the other hand, in the side wall surface 54 b of the recess 54, the protection of the side wall surface 54 b by the protective film 55 is maintained, so that the silicon substrate 52 is not easily etched, so that the direction is perpendicular to the thickness direction of the silicon substrate 52. Etching becomes difficult to proceed.

  Then, when etching using plasma generated using sulfur hexafluoride gas and boron trifluoride gas is continued, as shown in FIG. 2C, the protective film 55 is formed on substantially the entire side wall surface 54b of the recess 54. Will be formed. As described above, according to the present embodiment, the etching in the direction perpendicular to the thickness of the silicon substrate 52 does not easily proceed, so that the processing accuracy of the recess 54 formed in the silicon substrate 52 can be increased. Incidentally, the protective film 55 attached to the side wall surface 54b of the concave portion 54 can be removed by a cleaning process using, for example, the RCA method.

  The process conditions for forming the recess 54 include an output value of the antenna high frequency power supply 22 of 800 W to 1200 W, an output value of the bias high frequency power supply 15 of 50 W to 150 W, and the pressure in the vacuum chamber 11. It is preferable that it is 6 Pa or more and 7 Pa or less.

  As described above, according to the silicon substrate etching method and the silicon substrate etching apparatus in the above embodiment, the following effects can be obtained.

(1) The etching of the silicon substrate 52 by plasma using sulfur hexafluoride gas and the formation of the protective film 55 by plasma using boron trifluoride gas are performed simultaneously. Therefore, since the protective film 55 is formed simultaneously with the progress of the etching on the silicon substrate 52, the side wall surface 54b of the recess 54 that is not easily exposed to the vertical component contained in the etchant is formed while the recess 54 is being formed. Less likely to be exposed to etchants. On the other hand, the bottom wall surface 54a of the recess 54 that is easily exposed to the vertical component of the etchant is preferentially etched. Therefore, the side wall surface 54b of the recess 54 can be prevented from being etched in a direction perpendicular to the direction in which the recess 54 is formed beyond the opening thereof, and as a result, the processing accuracy of the recess 54 can be improved.
[Example]
[Example 1]
A resist pattern having an opening having a diameter of 2 μm was formed on a silicon substrate having a diameter of 200 mm. And the recessed part was formed in the silicon substrate with the plasma using the sulfur hexafluoride gas and the boron trifluoride gas which were produced | generated on the following process conditions.
・ Sulfur hexafluoride gas flow rate 56sccm
・ Flow rate of boron trifluoride gas 224sccm
(Flow rate of boron trifluoride gas in the total gas flow rate: 80%)
・ Output value of high frequency power supply for antenna 1000W
・ Output value of high frequency power supply for bias 100W
・ Pressure inside vacuum chamber 6Pa
Etching rate 3.25 μm / min
According to the etching of the silicon substrate under the above process conditions, it was confirmed that anisotropic etching as shown in FIG.
[Example 2]
From the conditions of Example 1, recesses were formed in the silicon substrate under process conditions in which only the flow rate of sulfur hexafluoride gas and the flow rate of boron trifluoride gas were changed as follows.
・ Sulfur hexafluoride gas flow rate 28sccm
・ Flow rate of boron trifluoride gas 252sccm
Etching rate: 2.4 μm / min
(Flow rate of boron trifluoride gas in the total gas flow rate: 90%)
According to the etching of the silicon substrate under the above process conditions, it was confirmed that anisotropic etching as shown in FIG. 3B is possible. Thus, it was recognized that anisotropic etching of the silicon substrate was possible when the flow rate of boron trifluoride gas in the total flow rate of the gas was 80% or more and 90% or less.
[Comparative example]
From the conditions of Example 1, recesses were formed in the silicon substrate under process conditions in which only the flow rate of sulfur hexafluoride gas and the flow rate of boron trifluoride gas were changed as follows.
・ Sulfur hexafluoride gas flow rate 280sccm
・ Flow rate of boron trifluoride gas 0sccm
According to the etching of the silicon substrate under the above process conditions, it was recognized that the etching is isotropic.

[Other Embodiments]
In addition, each said embodiment can also be suitably changed and implemented as follows.
The frequency of the high frequency power output from the bias high frequency power supply 15 can be arbitrarily changed within a range in which the silicon substrate 52 can be etched.

  The frequency of the high frequency power output from the antenna high frequency power supply 22 can be arbitrarily changed within a range where the silicon substrate 52 can be etched.

  The dry etching apparatus 10 includes the magnetic field coil 26 and the current supply unit 27 that supplies power to the magnetic field coil 26, but these may be omitted.

  The dry etching apparatus 10 is a so-called inductively coupled plasma etching apparatus that forms plasma in the vacuum chamber 11 using the high frequency antenna 21. Not limited to this, a so-called capacitive coupling type dry etching apparatus having an electrode at a position facing the substrate stage 13 in the vacuum chamber 11 may be used.

  The substrate S that is an object to be etched was a laminate in which a support substrate 51 made of silicon oxide or the like, a silicon substrate 52, and a resist pattern 53 were laminated in this order. The substrate S is not limited to this, as long as the substrate S includes the silicon substrate 52. For example, the substrate S may include a multilayer wiring layer and various insulating layers stacked on the silicon substrate 52.

  In place of the resist pattern 53, a patterned hard mask made of silicon oxide, silicon nitride or the like may be used.

  A rare gas such as argon (Ar) gas, helium (He) gas, neon (Ne) gas, or xenon (Xe) gas may be mixed as a dilution gas with the gas used for plasma generation.

  -When forming the recessed part 54, it was made to use sulfur hexafluoride gas and boron trifluoride gas. In addition to this, oxygen gas may be used. As a result, the following effects can be obtained.

  (2) On the inner wall surface of the recess 54, a silicon oxide film is also formed in addition to a protective film made of a compound containing silicon and boron. Since the silicon substrate 52 has a higher selectivity of the sulfur hexafluoride gas to the plasma than the silicon oxide film, the silicon oxide film also functions as a protective film in addition to the protective film containing silicon boride. Therefore, the side wall surface 54b of the recess 54 can be further suppressed from being etched in a direction perpendicular to the direction in which the recess 54 extends.

  The ratio of boron trifluoride gas to the total flow rate of sulfur hexafluoride gas and boron trifluoride gas may not be 80% or more and 90% or less. If boron trifluoride gas is included in the gas for etching the silicon substrate, the silicon substrate is in a direction perpendicular to the thickness direction compared to the case of etching using only sulfur hexafluoride gas. Etching can be suppressed.

-An etching process using sulfur hexafluoride gas and a protective film forming process using boron trifluoride gas were performed simultaneously. Not limited to this, as a reference example, as shown in FIG. 4, the etching process and the protective film forming process can be alternately performed. That is, as shown in FIG. 4A, when the substrate S on which the support substrate 61 made of silicon oxide or the like, the silicon substrate 62, and the resist pattern 63 having the opening 63a are stacked in this order is carried into the dry etching apparatus 10. The etching gas supply unit 32 supplies sulfur hexafluoride gas into the vacuum chamber 11. Next, the antenna high-frequency power supply 22 supplies high-frequency power to the high-frequency antenna 21, and the current supply unit 27 supplies current to the magnetic field coil 26, so that plasma using sulfur hexafluoride gas is converted into the vacuum chamber 11. Generated within.

  When the high frequency power supply 15 for bias supplies high frequency power to the stage electrode 14, positive ions containing fluorine drawn into the substrate S and fluorine that has reached the substrate S as shown in FIG. 4B. The silicon substrate 62 exposed from the openings 63a of the resist pattern 63 is etched by radicals containing. Thereby, a recess 64 extending in the thickness direction of the silicon substrate 62 is formed.

When the etching of the silicon substrate 62 is continued for a predetermined time, the etching gas supply unit 32 stops the supply of sulfur hexafluoride gas into the vacuum chamber 11 and the protective film forming gas supply unit 33 operates in the vacuum chamber 11. The supply of boron trifluoride gas into the inside is started. As a result, as shown in FIG. 4C, the silicon boride having a low vapor pressure enough to adhere to the substrate S so as to cover the bottom wall surface 64a and the side wall surface 64b of the recess 64 formed by the previous etching. A protective film 65 made of _a compound (Si _a B _b ) is formed.

When the formation of the protective film 65 on the bottom wall surface 64a and the side wall surface 64b of the recess 64 is continued for a predetermined time, the protective film forming gas supply unit 33 stops supplying the boron trifluoride gas into the vacuum chamber 11. Then, the etching gas supply unit 32 starts supplying sulfur hexafluoride gas into the vacuum chamber 11. 4D, the protective film 65 formed on the bottom wall surface 64a is removed and the silicon substrate 62 is etched in the thickness direction on the bottom wall surface 64a of the recess 64.

  When the etching of the silicon substrate 62 is continued for a predetermined time, the etching gas supply unit 32 stops the supply of sulfur hexafluoride gas into the vacuum chamber 11 and the protective film forming gas supply unit 33 operates in the vacuum chamber 11. The supply of boron trifluoride gas into the inside is started. Thereby, as shown in FIG. 4E, the protective film 65 is formed on the inner wall surface composed of the bottom wall surface 64a and the side wall surface 64b of the recess 64.

  Thus, the etching process for forming the recess 64 extending in the thickness direction of the silicon substrate 62 by the plasma using sulfur hexafluoride gas, and the bottom wall surface 64a and the side wall surface 64b of the recess 64 formed by the etching process are covered. The protective film forming step for forming the protective film 65 is repeated. Thereby, as shown in FIG. 4F, a recess 64 penetrating the silicon substrate 62 is formed. The number of times the etching process and the protective film forming process are repeated is defined by the thickness of the silicon substrate 62, the depth of the recess 64 formed by one etching process, and the like. Thereby, the following effects can be obtained.

  (3) The etching process for forming the recess 64 and the process of forming the protective film 65 on the bottom wall surface 64a and the side wall surface 64b which are the inner wall surfaces of the recess 64 are alternately performed. Therefore, during the etching process, the protective film 65 formed in the previous protective film forming process is attached to the inner wall surface of the recess. Therefore, the protective film 65 is easily maintained during the etching process on the side wall surface 64b of the recess 64 that is difficult to be exposed to the vertical component relative to the bottom wall surface 64a of the recess 64 that is exposed to the vertical component contained in the etchant. . Therefore, it is possible to prevent the side wall surface 64b of the recess 64 from being etched in a direction perpendicular to the direction in which the recess 64 extends beyond the opening, and as a result, the processing accuracy of the recess 64 can be improved.

  As described above, when the etching process and the protective film forming process are alternately performed, oxygen gas may be used in addition to the sulfur hexafluoride gas in the etching process. As a result, the following effects can be obtained.

  (4) A silicon oxide film is formed on the bottom wall surface 64a and the side wall surface 64b, which are the inner wall surfaces of the recess 64. Since the silicon substrate 62 has a higher selectivity of the above sulfur hexafluoride gas to plasma than the silicon oxide film, the silicon oxide film functions as a protective film. Therefore, etching of the side wall surface 64b of the recess 64 in a direction perpendicular to the extending direction of the recess 64 can be further suppressed.

  The recesses 54 and 64 formed in the silicon substrates 52 and 62 do not need to penetrate the silicon substrates 52 and 62, and may be recesses extending partway in the thickness direction of the silicon substrates 52 and 62.

-Sulfur hexafluoride gas was used as the fluorine-containing gas. However, the fluorine-containing gas is not limited to NF ₃ , CF ₄ , BF ₃ , PF ₃ , XeF ₂ , IF ₅ , F ₂ , ClF ₃ , COF ₂ , AsF ₃ , SiF ₄ , WF ₆ , and MoF ₆ . Gas may be used. Even when these gases are used, the plasma generated by these gases makes it difficult to etch the silicon boride compound described above, and volatilizes the sputtered residual particles as fluoride having a high vapor pressure. Therefore, the effects according to the above (1) to (4) can be obtained. When the F ₂ gas is used as the fluorine-containing gas, it may be diluted with a rare gas such as Ar.

-Boron trifluoride gas was used as the boron-containing gas. Not limited to this, a gas such as B ₂ H ₆ , BCl ₃ , or BBr ₃ may be used as the boron-containing gas. Even when these gases are used, since the silicon boride compound produced by these gases is difficult to be etched, it is possible to obtain the effects according to the above (1) to (4).

  DESCRIPTION OF SYMBOLS 10 ... Dry etching apparatus, 11 ... Vacuum chamber, 11a ... Exhaust port, 11b ... Gas supply port, 12 ... Quartz window, 13 ... Substrate stage, 14 ... Stage electrode, 15 ... High frequency power supply for bias, 16 ... Matching device for bias , 21 ... high frequency antenna, 21a ... upper antenna, 21b ... lower antenna, 21c ... power input section, 21d ... power output section, 22 ... high frequency power supply for antenna, 23 ... input side variable capacitor, 24 ... antenna matching unit, 25 ... Output-side variable capacitor, 26 ... Magnetic coil, 26a ... Upper coil, 26b ... Middle coil, 26c ... Lower coil, 27 ... Current supply unit, 27a ... Upper supply unit, 27b ... Middle supply unit, 27c ... Lower supply unit, DESCRIPTION OF SYMBOLS 31 ... Exhaust part, 32 ... Etching gas supply part, 33 ... Protective film formation gas supply part, 41 ... Control part, 51, 61 ... Support substrate, 52, 2 ... silicon substrate, 53, 63 ... resist pattern, 53a, 63a ... opening, 54, 64 ... recess, 54a, 64a ... bottom wall surface, 54b, 64b ... side wall surfaces, 55 and 65 ... protective film, S ... substrate.

Claims (4)

A silicon substrate etching method for forming a recess extending in the thickness direction of a silicon substrate,
An etching step of supplying a plasma of fluorine-containing gas to the silicon substrate to form the recesses in the silicon substrate;
A protective film forming step of supplying a plasma of boron-containing gas to the silicon substrate and forming a protective film containing boron and silicon on the inner wall surface of the recess ,
Performing the etching step and the protective film forming step simultaneously to form the protective film made of a silicon boride compound containing fluorine as the protective film, and using the plasma of the fluorine-containing gas, the protective film The etching method of the silicon substrate which etches the part formed in the bottom wall surface of the said recessed part, and the said silicon substrate exposed to the bottom wall surface of the said recessed part, and forms the said recessed part . The fluorine-containing gas is sulfur hexafluoride gas;
The boron-containing gas is boron trifluoride gas;
2. The silicon substrate etching according to claim 1 , wherein when performing the etching step and the protective film forming step simultaneously, only the plasma of the sulfur hexafluoride gas and the plasma of the boron trifluoride gas are supplied to the silicon substrate. Method. The method for etching a silicon substrate according to claim 1 , wherein when the etching step and the protective film forming step are simultaneously performed, at least one of oxygen gas plasma and rare gas plasma is further supplied to the silicon substrate.   The method further includes a step of removing the protective film by a cleaning process using an RCA method.
  The etching method of the silicon substrate as described in any one of Claims 1-3.