JP4459877B2 - Etching method and etching apparatus - Google Patents

Description

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

  Conventionally, as an etching method of a silicon substrate, after placing the silicon substrate on a base, the etching gas is turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas There is known a method of etching a silicon substrate by alternately and repeatedly executing a protective film forming process for forming a protective film on a silicon substrate by converting the plasma into a plasma.

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

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

  According to this etching method, during the etching process, removal of the protective film by ion irradiation and etching by radical and ion irradiation proceed on the bottom surface of the groove where ion irradiation is high, and ion irradiation occurs on the side wall of the groove where ion irradiation is low. Only the removal of the protective film by means of this prevents the side wall from being etched, and during the protective film forming process, the polymer is deposited again on the bottom surface and the side wall to form the protective film. As a result, a new sidewall of the groove formed by the etching process is immediately protected by the protective film formed by the protective film forming process, and etching proceeds only in the depth direction of the groove.

  However, some of the ions irradiated onto the silicon substrate are bent in the direction of movement due to collisions with gas molecules, charge-up on the silicon substrate surface, etc. Since the protective film on the upper side of the side wall is more easily removed than on the bottom side, the exposed part is etched by ion irradiation or radicals when the protective film is removed and the side wall surface is exposed. As each process is repeated, the etching of the upper portion of the sidewall also proceeds. For this reason, in the above etching method, as shown in FIG. 7, the upper opening of the groove is in a widened shape, or as shown in FIG. 8, the upper part of the side wall of the groove is in a circular shape, An accurate etching shape could not be obtained.

  In particular, in the case of etching a silicon substrate having a high aspect ratio (the depth is deeper than the opening width of the groove), it is necessary to repeat each of the processes more than the depth of the groove, Such a problem appears remarkably. In FIGS. 7 and 8, symbol K indicates a silicon substrate, symbol T indicates a groove, and symbol M indicates a mask.

  Therefore, in order to solve such a problem, an etching method as disclosed in Japanese Patent Application Laid-Open No. 2000-299310 has been proposed, and this etching method includes the above-described etching process and protective film forming process. It is difficult to react with radicals generated from the etching gas on the side wall and bottom surface after removing the protective film and the like formed by the protective film formation process alternately from the etching step that repeats a certain number of times from the side wall and bottom surface of the groove. In addition, an oxide film forming step for forming an oxide film that is difficult to be etched by ion irradiation is alternately repeated.

  In the oxide film forming step, a mixed gas of argon and oxygen is converted into plasma to generate oxygen ions, oxygen radicals, and argon ions, and a protective film is formed by applying a bias potential to the base. Chemical reaction with atoms or collision of argon ions with the silicon substrate to remove the protective film formed on the surface of the groove, and a protective film removing process to expose the surface, and oxygen gas alone is converted into plasma to produce oxygen It comprises an oxide film forming process in which ions and oxygen radicals are generated and an oxide film is formed on the surface of the groove exposed by the protective film removal process by the generated oxygen ions and oxygen radicals.

  According to such an etching method, the etching process and the oxide film forming process are alternately repeated, so that the protective film is formed on the oxide film, and the sidewall of the groove is a two-layer film of the protective film and the oxide film. Since the protective film is protected, even when the protective film is removed during the etching process, the oxide film effectively prevents the etching of the sidewall of the groove.

JP 2000-299310 A

  However, in the etching method disclosed in Japanese Patent Laid-Open No. 2000-299310, the protective film is not formed during the etching process in the etching process immediately after the execution of the oxide film forming process, and the sidewall must be protected only by the oxide film. Problem The side wall of the groove formed before the first oxide film forming process is executed, and the side wall of the groove newly formed before the next oxide film forming process is executed after the execution of the oxide film forming process Is not protected by the oxide film, the protective film is removed during the etching process, and the oxide film is exposed. If the oxide film is removed, only the protective film is formed until the oxide film is formed again. There is a problem that the side wall of the groove has to be protected, and the protection of the side wall is insufficient. In addition, when the side wall is protected only by the oxide film, the protection is insufficient (weak). This oxide film is formed on the surface layer portion of the side wall unlike the protective film deposited on the side wall surface. This is because the etching of the sidewall cannot be completely prevented.

  Further, if the protective film removal process is performed and the protective film is removed in advance before the execution of the oxide film forming process, the removal of the protective film in the protective film removing process is incomplete. Oxygen ions and oxygen radicals generated by the treatment chemically react with the protective film and are consumed for removal of the protective film. Therefore, unevenness is generated in the formed oxide film, and the surface of the groove is made 2 of the oxide film and the protective film. If the protective film cannot be protected by the film of the layer and the protective film is removed, there is a problem that the side wall of the groove is etched. Note that if the protective film removal process is performed for a long time, the protective film can be reliably removed, but if this is done, the etching rate will decrease.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an etching method and an etching apparatus that can more reliably prevent etching of a sidewall of a groove.

To achieve the above object, the present invention provides:
A method of etching a silicon substrate placed on a base,
An etching process that turns the etching gas into plasma and applies a bias potential to the base to etch the silicon substrate;
A first protective film forming process for converting oxygen gas into plasma to form a first protective film as an oxide film on the silicon substrate;
The present invention relates to an etching method characterized in that a protective film forming gas is converted into plasma and a second protective film forming process for forming a second protective film on the first protective film is sequentially repeated.

And this etching method can implement this suitably with the following etching apparatuses.
That is, this etching apparatus
A processing chamber having an enclosed space;
A base disposed on the lower side in the processing chamber and on which a silicon substrate is placed;
Base power supply means for applying high frequency power to the base;
A gas supply unit configured to supply an etching gas, an oxygen gas, and a protective film forming gas into the processing chamber, and to adjust a supply flow rate of the etching gas, the oxygen gas, and the protective film forming gas;
A coil disposed near the outside of the processing chamber;
Coil power supply means for applying high frequency power to the coil to turn the etching gas, oxygen gas and protective film forming gas in the processing chamber into plasma,
Control means for controlling the base power supply means, coil power supply means and gas supply means,
The control means controls the gas supply means to adjust the supply flow rates of the etching gas, oxygen gas, and protective film forming gas supplied into the processing chamber, thereby bringing the etching gas into the processing chamber. An etching process for supplying and etching the silicon substrate; a first protective film forming process for supplying the oxygen gas into the processing chamber to form a first protective film as an oxide film on the silicon substrate; and the protective film A formation gas is supplied into the processing chamber and a second protective film forming process for forming a second protective film on the first protective film is sequentially and repeatedly performed, and at least during the etching process, the base power It is comprised so that high frequency electric power may be applied to the said base by a supply means.

  According to this etching apparatus, first, the silicon substrate is placed on the base in the processing chamber. Next, under the control of the control means, an etching gas whose flow rate is adjusted is supplied from the gas supply means into the processing chamber, and high-frequency power is supplied to the coil and the base by the coil power supply means and the base power supply means, respectively. Applied.

  When a high frequency power is applied to the coil, a magnetic field is formed in the processing chamber, and an etching gas in the processing chamber is changed to plasma containing ions, electrons, radicals, and the like by an electric field induced by the magnetic field. Further, when high frequency power is applied to the base, a potential difference (bias potential) is generated between the base and the plasma.

  The radicals chemically react with the silicon atoms to etch the silicon substrate, and the ions move toward the base (silicon substrate) side by the bias potential and collide with each other to etch the silicon substrate. As a result, a groove (hole) having a predetermined width and depth is formed in the silicon substrate, and the etching process is performed in this way. Incidentally, most of the ions irradiated to the silicon substrate are incident perpendicularly to the surface of the silicon substrate and collide with the bottom surface of the groove.

  When the etching gas is supplied for a predetermined time, the supply of the etching gas is stopped under the control of the control means, and the oxygen gas whose flow rate is adjusted is supplied from the gas supply means into the processing chamber. Similarly to the etching gas supply, high-frequency power is applied to the coil by the coil power supply means, but the application of the high-frequency power to the base by the base power supply means is stopped.

  Like the etching gas, the oxygen gas supplied into the processing chamber is converted into plasma containing oxygen ions, electrons, oxygen radicals, and the like by the electric field, and the oxygen ions and oxygen radicals chemically react with silicon atoms. The first protective film, which is an oxide film that does not easily react with radicals generated from the etching gas and that is difficult to be etched by ion irradiation, is formed on the side walls and the bottom surface of the groove. Is executed.

  When the oxygen gas is supplied for a predetermined time, the supply of the oxygen gas is stopped under the control of the control means as described above, and then the protective film forming gas whose flow rate is adjusted from the gas supply means is supplied into the processing chamber. To be supplied. Similarly to the supply of oxygen gas, high-frequency power is applied to the coil by the coil power supply means, and the application of high-frequency power to the base by the base power supply means is stopped.

  Like the etching gas and oxygen gas, the protective film forming gas supplied into the processing chamber is changed to plasma containing ions, electrons, radicals, and the like by the electric field, and a polymer is generated from the radicals to form the groove. Deposited on the side wall and bottom surface (on the first protective film). As a result, a second protective film that does not react with radicals generated from the etching gas is formed on the first protective film, and thus the second protective film forming process is performed.

  When the protective film forming gas is supplied for a predetermined time and the supply of the protective film forming gas is stopped, the etching gas is supplied again to perform the etching process, and the etching process and the first protective film forming process as described above are performed. The second protective film forming process is sequentially repeated.

  In this way, by sequentially repeating the etching process, the first protective film forming process, and the second protective film forming process, the first and second protective films formed by the ion irradiation are formed on the bottom surface of the groove where the ion irradiation is frequently performed during the etching process. And etching by radical and ion irradiation proceeds, and only the removal of the second protective film by ion irradiation proceeds on the side wall of the groove with less ion irradiation, and the etching of the side wall is prevented. In some cases, the first protective film is formed on the side wall and bottom surface of the trench newly formed by the etching process, and in the second protective film forming process, the first protective film formed by the first protective film forming process is formed. The polymer is deposited again on the top to form a second protective film.

  Therefore, the new side wall of the groove formed by the etching process is immediately protected by the first and second protective films formed by the first and second protective film forming processes, and the etching proceeds only in the depth direction of the groove. To do.

  Note that some of the ions irradiated to the silicon substrate are incident on the silicon substrate surface from an oblique direction and collide with the upper portion of the sidewall of the groove due to collision with gas molecules or charge-up of the silicon substrate surface. The second protective film on the upper side is easier to remove than the bottom side, but even if it is completely removed, the first protective film hardly reacts with the radicals generated from the etching gas as described above. In addition, the first protective film effectively prevents the etching of the side walls of the grooves because it is difficult to be etched even by ion irradiation.

  Thus, according to the etching method and the etching apparatus according to the present invention, the etching process, the first protective film forming process, and the second protective film forming process are sequentially repeated. The new side wall can be immediately protected by the first and second protective films formed by the first and second protective film forming processes, and even if the first protective film is removed by the etching process, One protective film can be immediately re-formed, and the sidewall of the groove can always be protected by two protective films of the first protective film and the second protective film during the etching process.

  In addition, by performing the first protective film forming process after the etching process, the second protective film can be completely removed by the etching process, or the first protective film can be formed on the surface of the groove in a substantially removed state. In addition, oxygen ions and oxygen radicals generated by the first protective film formation process are not spent on the chemical reaction with the second protective film, and the first protective film is uniformly formed to protect the sidewalls of the trenches for the first protection. It can be reliably protected by a two-layer protective film of the film and the second protective film. Further, it is not necessary to perform a protective film removing process for removing the protective film (second protective film) as in the conventional etching method described above, which is efficient.

  In this way, the sidewall of the groove can be reliably protected by the two protective films of the first protective film and the second protective film, so that the upper opening of the groove has a widened shape, or the upper portion of the sidewall of the groove. Can be effectively prevented from being formed in an arcuate shape, and even a shape with a high aspect ratio exceeding 40 can be etched with high accuracy.

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

  As shown in FIG. 1, an etching apparatus 1 of this example includes a processing chamber 11 having a closed space, and a base 12 on which a silicon substrate K to be etched is placed. An exhaust device 14 for decompressing the inside of the processing chamber 11, a gas supply device 20 for supplying an etching gas, oxygen gas and protective film forming gas into the processing chamber 11, and an etching gas and oxygen supplied into the processing chamber 11. A plasma generator 30 that converts the gas and the protective film forming gas into plasma, and a first high-frequency power source 13 that applies a high-frequency power to the base 12 to generate a potential difference (bias potential) between the base 12 and the plasma. And a control device 40 that controls operations of the exhaust device 14, the gas supply device 20, the plasma generation device 30, the first high-frequency power source 13, and the like.

  The exhaust device 14 includes an exhaust pipe 15 connected to the lower portion of the processing chamber 11, a vacuum pump 16 connected to the exhaust pipe 15, and a flow rate adjusting mechanism 17 that adjusts the flow rate of gas flowing through the exhaust pipe 15. Thus, the gas inside the processing chamber 11 is exhausted to the outside by the vacuum pump 16, whereby the pressure in the processing chamber 11 is reduced to a predetermined pressure.

The gas supply device 20 includes a supply pipe 21 connected to the ceiling portion of the processing chamber 11 and gas cylinders 22, 23, and 24 connected to the supply pipe 21 via flow rate adjusting mechanisms 25, 26, and 27. Gases whose flow rates are adjusted by the adjusting mechanisms 25, 26, and 27 are supplied into the processing chamber 11 from the gas cylinders 22, 23, and 24. The gas cylinder 22 is filled with SF ₆ gas for etching, the gas cylinder 23 is filled with O ₂ gas for forming the first protective film, and the gas cylinder 24 is filled with C ₄ for forming the second protective film. F ₈ gas is filled.

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

As shown in FIG. 2, the control device 40 includes an etching process E for etching the silicon substrate K, a first protective film forming process D1 for forming a first protective film as an oxide film on the silicon substrate K, and a first protective film. The second protective film forming process D2 for forming the second protective film on the film is repeatedly performed for a predetermined time sequentially, and the gas cylinders 22, 26 are controlled by controlling the flow rate adjusting mechanisms 25, 26, 27. The supply flow rate control unit 41 for adjusting the flow rates of SF ₆ gas, O ₂ gas and C ₄ F ₈ gas supplied into the processing chamber 11 from the flow control units 23 and 24 and the flow rate adjustment mechanism 17 are controlled by the vacuum pump 17. An exhaust flow rate control unit 42 that adjusts the flow rate of gas exhausted from the inside of the processing chamber 11, a base power control unit 43 that controls the first high frequency power supply 13 to adjust the high frequency power applied to the base 12, 2 by controlling the high frequency power supply 32 and a coil power controller 44 to adjust the high frequency power applied to the coil 31.

As shown in FIG. 2, the supply flow rate controller 41 changes the flow rates of SF ₆ gas, O ₂ gas, and C ₄ F ₈ gas supplied from the gas cylinders 22, 23, and 24 into the processing chamber 11. SF ₆ gas is supplied when the etching process E is executed, O ₂ gas is supplied when the first protective film forming process D 1 is executed, and C ₄ F ₈ gas is supplied when the second protective film forming process D 2 is executed.

  The exhaust flow rate controller 42 controls the exhaust flow rate so that the pressure inside the processing chamber 11 becomes a predetermined pressure when the etching process E, the first protective film forming process D1, and the second protective film forming process D2 are performed. The base power controller 43 controls the first high frequency power supply 13 so that a predetermined high frequency power is applied to the base 12 during the execution of the etching process E, the first protective film forming process D1, and the second protective film forming process D2. The coil power control unit 44 controls the second high frequency power so that a predetermined high frequency power is applied to the coil 31 when the etching process E, the first protective film forming process D1, and the second protective film forming process D2 are performed. The power source 32 is controlled.

FIG. 3 shows the amount of undercut formed on the silicon substrate K when the etching process E, the first protective film forming process D1 and the second protective film forming process D2 are sequentially repeated, and the plasma O ₂ gas. Is a graph showing the relationship with the ashing rate of the resist, and from this graph, if the ashing rate is 5000 (か ら / min) or higher, that is, the processing capability corresponding to the ashing rate of 5000 (Å / min) or higher is shown. It can be seen that if the 1 protective film forming process D1 is performed, an undercut amount is small and a highly accurate etching shape can be obtained.

Originally, the film thickness of the first protective film, the formation rate of the first protective film by plasma O ₂ gas, etc. should be compared with the undercut amount, but the resist is different from the formation of the first protective film. Similarly, since it is removed by the action of plasmatized O ₂ gas, it can be determined simply by replacing the formation speed and film thickness of the first protective film with the ashing rate.

  In order to set the ashing rate to 5000 (Å / min) or more, for example, the pressure inside the processing chamber 11 is about 0.4 Pa to 1.0 Pa, and the high frequency power applied to the coil 31 is about 2200 W to 2800 W. It is necessary to be a degree. For this reason, when the first protective film formation process D1 is performed, the exhaust flow rate control unit 42 is configured so that the pressure inside the processing chamber 11 is about 0.4 Pa to 1.0 Pa, and the coil power control unit 44 is configured so that the high-frequency power applied to the coil 31 is about 2200W to 2800W.

According to the etching apparatus 1 of the present example configured as described above, after the silicon substrate K is placed on the base 12 in the processing chamber 11, the control by the control apparatus 40 is performed so as to perform the etching process E. The SF ₆ gas whose flow rate is adjusted by the flow rate adjusting mechanism 25 is supplied from the gas cylinder 22 into the processing chamber 11, and predetermined high frequency power is applied to the base 12 and the coil 31 by the high frequency power sources 13 and 32, respectively. The

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

When the SF ₆ gas is supplied for a predetermined time, the supply of the SF ₆ gas is stopped by the flow rate adjusting mechanism 25 under the control of the control device 40 to perform the first protective film formation process D1, and the flow rate adjustment is performed. The O ₂ gas whose flow rate is adjusted by the mechanism 26 is supplied from the gas cylinder 23 into the processing chamber 11. At this time, predetermined high frequency power is applied to the coil 31 and the base 12 by the high frequency power sources 13 and 32, respectively, in the same manner as when SF ₆ gas is supplied.

Like the SF ₆ gas, the O ₂ gas supplied into the processing chamber is converted into plasma containing oxygen ions, electrons, oxygen radicals, and the like by the electric field, and these oxygen ions and oxygen radicals chemically react with silicon atoms. As a result, an oxide film (first protective film) that does not easily react with F radicals and is not easily etched by ion irradiation is formed on the side wall and bottom surface of the groove. Since ions move toward the silicon substrate K side by the bias voltage, an oxide film is efficiently formed.

Then, when the O ₂ gas is supplied for a predetermined time, the flow adjustment is performed after the supply of the O ₂ gas is stopped by the flow adjustment mechanism 26 under the control of the control device 40 in order to perform the second protective film formation process D2. The C ₄ F ₈ gas whose flow rate is adjusted by the mechanism 27 is supplied from the gas cylinder 24 into the processing chamber 11. Also at this time, predetermined high frequency power is applied to the coil 31 and the base 12 by the high frequency power sources 13 and 32, respectively, as in the case of supplying SF ₆ gas or O ₂ gas.

The C ₄ F ₈ gas supplied into the processing chamber 11 is made into a plasma containing ions, electrons, radicals, and the like by the electric field, like SF ₆ gas and O ₂ gas, and a polymer is generated from the radicals. Depositing on the first protective film on the sidewall and bottom of the groove. Thereby, a fluorocarbon film (second protective film) that does not react with F radicals is formed on the first protective film.

Then, when the C ₄ F ₈ gas is supplied for a predetermined time and the supply of the C ₄ F ₈ gas is stopped by the flow rate adjusting mechanism 27 under the control of the control device 40, the etching gas is supplied again and the etching process E is performed. The silicon substrate K is etched by sequentially repeating the etching process E, the first protective film forming process D1, and the second protective film forming process D2 as described above.

  When the etching process E, the first protective film forming process D1, and the second protective film forming process D2 are executed, the exhaust gas flow rate is adjusted by the flow rate adjusting mechanism 17 under the control of the control device 40, and the pressure in the processing chamber 11 is increased. Is adjusted to a predetermined pressure.

  As described above, the etching process E, the first protective film formation process D1, and the second protective film formation process D2 are sequentially repeated, so that the first and second ion irradiations are performed on the bottom surface of the groove where the ion irradiation is large. The removal of the second protective film and the etching by the F radical and ion irradiation proceed, and only the removal of the second protective film by the ion irradiation proceeds on the side wall of the groove with less ion irradiation to prevent the etching of the side wall. At the time of the first protective film forming process D1, the first protective film is formed on the side wall and the bottom surface of the groove newly formed by the etching process E, and at the time of the second protective film forming process D2, the first protective film forming process is performed. The polymer is deposited again on the first protective film formed in D1, and a second protective film is formed.

  Therefore, the new side wall of the groove formed by the etching process E is immediately protected by the first and second protective films formed by the first and second protective film forming processes D1 and D2, and in the depth direction of the groove. Only the etching proceeds.

  A part of ions moving toward the silicon substrate K are incident on the surface of the silicon substrate K from an oblique direction and collide with the upper part of the side wall of the groove due to collision with gas molecules or charge up of the surface of the silicon substrate K. Therefore, the second protective film on the upper side of the side wall is easier to remove than the bottom side, but even if it is completely removed, the first protective film hardly reacts with the F radical as described above. In addition, the first protective film effectively prevents the etching of the side walls of the grooves because it is difficult to be etched even by ion irradiation.

  Thus, according to the etching apparatus 1 of the present example, the etching process E, the first protective film forming process D1, and the second protective film forming process D2 are sequentially repeated. The new side walls can be immediately protected by the first and second protective films formed by the first and second protective film forming processes D1 and D2, and the first protective film is removed by the etching process E. In this case, the first protective film can be immediately re-formed. When the etching process E is performed, the sidewall of the groove is always protected by the two protective films of the first protective film and the second protective film. Can do.

  In addition, by performing the first protective film forming process D1 after the etching process E, the second protective film is completely removed by the etching process E, or the first protective film is applied to the surface of the groove in the almost removed state. The oxygen ions and oxygen radicals generated in the first protective film formation process D1 are not consumed for the chemical reaction with the second protective film, and the first protective film is uniformly formed to form the grooves. The side wall can be reliably protected with the two protective films of the first protective film and the second protective film. Further, it is not necessary to perform a protective film removing process for removing the protective film (second protective film) as in the conventional etching method described above, which is efficient.

  In this way, the side wall of the groove can be reliably protected with the two protective films of the first protective film and the second protective film, so that the upper opening of the groove is widened (see FIG. 7). It is possible to effectively prevent the upper portion of the side wall of the groove from being formed into a shape that is arcuate (see FIG. 8), and even with a high aspect ratio shape with an aspect ratio exceeding 40, it is highly accurate. It can be etched.

  Further, the first protective film forming process D1 is performed under the condition that the ashing rate is 5000 (min / min) or more, so that a highly accurate etching shape can be obtained and the first protection is efficiently performed. A film can be formed, and the etching rate can be increased.

Incidentally, as an example, during the etching process E, the processing time is 10 seconds, the pressure in the processing chamber 11 is 2 Pa, the high-frequency power applied to the coil 31 is 2200 W, and the high-frequency power applied to the base 12 is When the supply flow rate of 40 W, SF ₆ gas is 300 ml / min, and the first protective film forming process D1, the processing time is 3 seconds, the pressure in the processing chamber 11 is 0.6 Pa, and the coil 31 is applied. When the high frequency power is 2500 W, the high frequency power applied to the base 12 is 20 W, the supply flow rate of O ₂ gas is 100 ml / min, and the second protective film forming process D 2, the processing time is 5 seconds, and 2Pa the pressure in 11, and 1500W RF power applied to the coil 31, and 20W of the high-frequency power applied to the base _12, the supply flow rate of C 4 _{F 8} gas 200m When the silicon substrate K is etched for a predetermined time under the condition of / min, even if the aspect ratio is 50, the shape shown in FIGS. 7 and 8 is not obtained, and a highly accurate etching shape is obtained. The etching rate was 5 μm / min.

  On the other hand, as a comparative example, an etching process (corresponding to the etching process E) and a protective film forming process (corresponding to the second protective film forming process D2) are alternately performed as in the etching method of Japanese Patent Application Laid-Open No. 2000-299310. After 43 times, an oxide film forming process (oxide film removing process and oxide film forming process) (corresponding to the first protective film forming process D1) is performed for 10 minutes, and the etching process and the protective film forming process are performed again. Are alternately repeated 43 times (this condition is defined as condition 1), and the etching process (corresponding to the etching process E) and the protective film forming process (corresponding to the second protective film forming process D2) are alternately performed 21 After repeating the oxide film forming process (oxide film removing process and oxide film forming process) (corresponding to the first protective film forming process D1) for 10 minutes, the etching process and the protective film type The process is alternately repeated 21 times, and then the oxide film forming process is performed for 10 minutes. Thereafter, the etching process and the protective film forming process are alternately repeated 21 times (this condition is condition 2). When the silicon substrate K is etched, an etching shape as shown in FIG. 4 (a shape in which the upper portion of the side wall is etched) is obtained under any conditions, and the etching rate is 1.55 μm / min (conditions). 1) and 1.59 μm / min (in the case of condition 2).

In both cases of conditions 1 and 2, the etching time is 9 seconds, the pressure in the processing chamber 11 is 2 Pa, the high frequency power applied to the coil 31 is 2200 W, and the base 12 The high frequency power applied to the substrate is 60 W, the supply flow rate of SF ₆ gas is 300 ml / min, the processing time is 5 seconds, the pressure in the processing chamber 11 is 2 Pa, and the coil 31 is applied to the coil 31. The high frequency power to be applied is 1500 W, the high frequency power applied to the base 12 is 20 W, the supply flow rate of C ₄ F ₈ gas is 200 ml / min, and the pressure in the processing chamber 11 is 2 Pa during the oxide film formation treatment. The high frequency power applied to the coil 31 was 2200 W, the high frequency power applied to the base 12 was 20 W, and the supply flow rate of O ₂ gas was 40 ml / min. In FIG. 4, symbol K indicates a silicon substrate, symbol T indicates a groove, and symbol M indicates a mask. The same applies to FIGS. 5 and 6 described later.

Further, as Reference Example 1, the processing gas supply sequence in this example (etching process E performed by supplying SF ₆ gas, first protective film forming process D 1 performed by supplying O ₂ gas, and C ₄ F ₈ gas) The order of execution of the second protective film forming process D2 performed by supplying the gas is replaced with the order of SF ₆ gas, C ₄ F ₈ gas and O ₂ gas, and the etching process using SF ₆ gas and the protection using C ₄ F ₈ gas are performed. When the silicon substrate K is etched by sequentially repeating the film formation process and the oxygen plasma process using O ₂ gas, an etching shape as shown in FIGS. 5A and 5B (a shape in which the upper portion of the sidewall is etched) is obtained. Further, the etching rates were 1.27 μm / min (in the case of FIG. 5A) and 0.95 μm / min (in the case of FIG. 5B).

In the etching process using SF ₆ gas, the processing time is 9 seconds, the pressure in the processing chamber 11 is 2 Pa, the high frequency power applied to the coil 31 is 2200 W, and the high frequency power applied to the base 12 is 60 W. The supply flow rate of SF ₆ gas is 300 ml / min, and when the protective film is formed by C ₄ F ₈ gas, the processing time is 5 seconds, the pressure in the processing chamber 11 is 2 Pa, and the coil 31 is applied. The high-frequency power is 1500 W, the high-frequency power applied to the base 12 is 20 W, the supply flow rate of C ₄ F ₈ gas is 200 ml / min, and the processing time is 5 seconds or 10 when oxygen plasma treatment with O ₂ gas is performed. Second, the pressure in the processing chamber 11 is 2 Pa, the high frequency power applied to the coil 31 is 800 W, the high frequency power applied to the base 12 is 20 W, and the O ₂ gas The supply flow rate was 40 ml / min. FIG. 5 (a) shows the result when the processing time of oxygen plasma treatment using O ₂ gas is 5 seconds, and FIG. 5 (b) shows the processing time when oxygen plasma processing using O ₂ gas is 10 seconds. Shows the results.

The etching as a reference example 2, alternately supplying SF ₆ gas and O ₂ gas, the silicon substrate K as sequentially repeating the etching process and the O ₂ gas by oxidation film (protective film) formation process by SF ₆ gas As a result, an etching shape as shown in FIG. 6A (a shape in which etching progressed isotropically) and an etching shape as shown in FIG. 6B (a shape in which the upper portion of the side wall was etched), The etching rate was 0.7 μm / min (in the case of FIG. 6B).

In the etching process using SF ₆ gas, the processing time is 9 seconds or 3 seconds, the pressure in the processing chamber 11 is 2 Pa, the high-frequency power applied to the coil 31 is 2200 W, and the high-frequency power applied to the base 12. The power is 60 W, the supply flow rate of SF ₆ gas is 300 ml / min, and when the oxide film is formed by O ₂ gas, the processing time is 9 seconds, the pressure in the processing chamber 11 is 2 Pa, and the coil 31 is applied. The high frequency power to be applied was 2200 W, the high frequency power applied to the base 12 was 20 W, and the supply flow rate of O ₂ gas was 40 ml / min. FIG. 6A shows the result when the processing time of the etching process using SF ₆ gas is 9 seconds, and FIG. 6B shows the result when the processing time of the etching process using SF ₆ gas is 3 seconds. Is shown.

  Comparing the example and the comparative example, it can be seen that according to the etching apparatus 1 of the present example, the silicon substrate K can be etched with high accuracy at a high etching rate. Comparing 1 with Reference Example 2, it can be seen that according to the etching apparatus 1 of this example, the silicon substrate K can be etched at a high etching rate with high accuracy.

The reason why such a result is obtained is that the comparative example is as described in the section “Problems to be solved by the invention”, and the reference example 1 is a protective film made of C ₄ F ₈ gas. Since the oxygen plasma treatment with the O ₂ gas is performed after the formation processing is performed, the protective film formed by the protective film formation processing is removed by oxygen ions and oxygen radicals generated by the oxygen plasma processing, and the SF ₆ gas is used. This is because the protection of the side wall is weakened when the etching process is performed. In Reference Example 2, the oxide film is formed on the surface layer portion of the side wall, unlike the protective film by C ₄ F ₈ gas deposited on the side wall surface. Therefore, the etching of the side wall cannot be completely prevented, and when the surface layer portion of the side wall on which the oxide film is formed is etched, the side wall of the side wall is etched. Since protection is disappears, in order to suppress the etching of the sidewalls is because should reform the oxide film immediately by shortening the processing time by SF ₆ gas.

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

It is sectional drawing which showed the schematic structure of the etching apparatus which concerns on one Embodiment of this invention with a partial block diagram. SF ₆ gas is a timing chart showing a control state of the supply flow rate of _{O 2} gas, and _C 4 _{F 8} gas. The relationship between the amount of undercut formed on the silicon substrate when the etching process, the first protective film forming process, and the second protective film forming process are sequentially repeated, and the ashing rate of the resist by the oxygenated gas It is the shown graph. 6 is a cross-sectional view showing an etching shape obtained in Comparative Example 1. FIG. 6 is a cross-sectional view showing an etching shape obtained in Reference Example 1. FIG. 6 is a cross-sectional view showing an etching shape obtained in Reference Example 2. FIG. It is explanatory drawing for demonstrating the problem of the conventional etching method. It is explanatory drawing for demonstrating the problem of the conventional etching method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Etching device 11 Processing chamber 12 Base 13 1st high frequency power supply 14 Exhaust device 16 Vacuum pump 17 Flow rate adjusting mechanism 20 Gas supply device 22, 23, 24 Gas cylinder 25, 26, 27 Flow rate adjusting mechanism 30 Plasma generating device 31 Coil 32 First 2 High frequency power source 40 Control device 41 Supply flow rate control unit 42 Exhaust flow rate control unit 43 Base power control unit 44 Coil power control unit K Silicon substrate

Claims (2)

A method of etching a silicon substrate placed on a base,
An etching process that turns the etching gas into plasma and applies a bias potential to the base to etch the silicon substrate;
A first protective film forming process for converting oxygen gas into plasma to form a first protective film as an oxide film on the silicon substrate;
An etching method characterized in that a protective film forming gas is converted into plasma and a second protective film forming process for forming a second protective film on the first protective film is sequentially repeated. A processing chamber having an enclosed space;
A base disposed on the lower side in the processing chamber and on which a silicon substrate is placed;
Base power supply means for applying high frequency power to the base;
A gas supply unit configured to supply an etching gas, an oxygen gas, and a protective film forming gas into the processing chamber, and to adjust a supply flow rate of the etching gas, the oxygen gas, and the protective film forming gas;
A coil disposed near the outside of the processing chamber;
Coil power supply means for applying high frequency power to the coil to turn the etching gas, oxygen gas and protective film forming gas in the processing chamber into plasma,
An etching apparatus comprising a control means for controlling the base power supply means, the coil power supply means and the gas supply means,
The control means controls the gas supply means to adjust the supply flow rates of the etching gas, oxygen gas, and protective film forming gas supplied into the processing chamber, thereby bringing the etching gas into the processing chamber. An etching process for supplying and etching the silicon substrate; a first protective film forming process for supplying the oxygen gas into the processing chamber to form a first protective film as an oxide film on the silicon substrate; and the protective film A formation gas is supplied into the processing chamber and a second protective film forming process for forming a second protective film on the first protective film is sequentially and repeatedly performed, and at least during the etching process, the base power An etching apparatus configured to apply high-frequency power to the base by a supply means.

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