JP6082639B2 - Plasma etching method - Google Patents

Description

  The present invention relates to a plasma etching method for a silicon substrate, and more particularly to a plasma etching method for forming a tapered etching structure having a predetermined taper angle on a silicon substrate.

  In recent years, a semiconductor device having a so-called super junction structure has attracted attention as a power control semiconductor device having both high withstand voltage and low on-resistance. The super junction structure is a structure in which n-conducting portions and p-conducting portions are alternately arranged. This structure is formed as follows, for example. That is, first, an n conductivity type layer is formed on a substrate by epitaxial growth, and then a trench is formed in the n conductivity type epitaxial layer using a plasma etching method. Thereafter, a p-conductivity type layer is formed in the trench by epitaxial growth, so that the n-conductivity part and the p-conductivity part are arranged alternately.

  In the semiconductor device having the super junction structure, the on-resistance can be reduced as the widths of the n-conducting part and the p-conducting part are reduced, and the withstand voltage is increased as the thickness of each part is increased. Can be high. However, for example, if the width of the trench formed in the n-conductivity type epitaxial layer is narrowed to narrow the width of the p-conductivity type portion, the trench is formed when the p-conduction type layer is formed in the trench by epitaxial growth. A p-conductivity type epitaxial layer is formed first in the opening. Therefore, there is a problem that the trench opening is blocked, the p-conductive type epitaxial layer is not formed in the entire trench, and a void is generated at the center of the trench.

  In order to solve the above problem, for example, a semiconductor device and a method for manufacturing the semiconductor device disclosed in Japanese Patent Laid-Open No. 2008-305927 have been proposed.

  In this semiconductor device, n conductivity type portions and p conductivity type portions are alternately arranged, the n conductivity type portion has a tapered shape whose diameter is increased toward the substrate side, and the p conductivity type portion is a substrate. The taper shape is reduced in diameter toward the side. Then, this semiconductor device uses a plasma etching method to form a tapered trench having a reduced diameter from the opening toward the bottom and having a straight side wall surface in the n-conductivity type epitaxial layer. A p-conductivity type epitaxial layer is formed therein. Thus, by forming the shape of the trench into a tapered shape having a wider opening than the bottom, when forming the p conductivity type epitaxial layer, the p conductivity type epitaxial layer is formed in the entire trench faster than the trench opening is blocked. A layer can be formed, and voids can be prevented from occurring in the center of the trench.

JP 2008-305927 A

  Incidentally, in recent years, in order to further increase the breakdown voltage and the on-resistance of a semiconductor device, it is required to further narrow the pitch interval between the n conductivity type portion and the p conductivity type portion. However, as described above, the trench formed by the above-described conventional method is reduced in diameter toward the bottom and the side wall surface has a linear taper shape, and the taper angle is increased in order to reduce the pitch interval. The opening becomes small and the generation of voids cannot be suppressed. That is, with the conventional trench shape, the pitch interval cannot be narrowed while suppressing the generation of voids.

  Therefore, as a shape of the trench that can suppress the generation of voids and can further reduce the pitch interval, a shape in which the taper angle gradually increases toward the bottom has been proposed. With such a shape, even if the taper angle at the bottom is increased and the pitch interval is narrower than before, the taper angle gradually decreases toward the opening, so the opening should be widened as before. Can do. However, a method for forming such a trench with high accuracy has not been proposed.

  Therefore, the inventors of the present application repeatedly perform a first etching process for etching a silicon substrate, a protective film forming process for forming a protective film on the etching structure surface, and a second etching process for removing the protective film on the bottom surface of the etching structure. As a result of extensive research on a method for forming a trench having the above-described shape, a trench formed with the processing time in the first etching process and the second etching process, the pressure in the processing chamber, and the power applied to the base. As a result of finding a correlation with the shape of the substrate and further researching it, a trench having a predetermined taper shape is formed by gradually changing the processing time, the pressure in the processing chamber, and the power applied to the base. I got the knowledge that.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of forming an etching structure (trench) having a predetermined taper shape whose diameter is reduced from the opening toward the bottom.

To achieve the above object, the present invention provides:
A method of etching a silicon substrate placed on a base in a processing chamber to form an etching structure on the silicon substrate,
An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process A2 for forming a protective film on the silicon substrate, plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. In the plasma etching method provided with the first processing step A that repeats at least two cycles or more, with the processing including the etching processing A3 to be performed as one cycle,
In the first processing step A,
The bias potential applied in the etching process A3 is made larger than the bias potential applied in the etching process A1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process A1 and the etching process A3 may at least gradually reduce the processing time or the processing chamber according to the repetition of the cycle. The present invention relates to a plasma etching method configured to gradually decrease the internal pressure or gradually decrease the base applied power.

  According to this etching method, first, a silicon substrate having a mask having an opening on the surface is placed on a base, and etching processing A1, protective film formation processing A2, and etching processing A3 are performed on the silicon substrate. The first processing step A including at least two cycles in which the above is repeated is performed.

  In the first processing step A, first, an etching gas is supplied into a processing chamber whose inside is maintained at a predetermined pressure to be converted into plasma, and a predetermined bias potential is applied to the base to convert the etching gas into plasma. An etching process A1 is performed in which the silicon substrate is etched by a chemical reaction with an etching species such as sputtering or radicals (hereinafter referred to as “etching species”) by ions generated by the above. Thereby, an etching structure having a predetermined width and depth is formed in the silicon substrate.

  Then, after this etching process A1 is performed on the silicon substrate for a predetermined time, a protective film forming gas is supplied into the processing chamber and converted into plasma, and the protective film such as radicals generated by converting the protective film forming gas into plasma is formed. A protective film forming process A2 is performed in which a protective film is formed on the silicon substrate by a formation type (hereinafter referred to as “protective film formation type”). Thereby, the inner wall surface of the etching structure formed on the silicon substrate by the etching process A1 is protected.

  Then, after the protective film formation process A2 is performed on the silicon substrate for a predetermined time, an etching gas is supplied into the processing chamber whose interior is maintained at a predetermined pressure to be turned into plasma, and a predetermined bias potential is applied to the base. Then, the etching process A3 for removing the protective film formed on the bottom of the etching structure by sputtering with ions is performed. Since the main purpose of the etching process A3 is to remove the protective film by sputtering with ions, a bias potential stronger than that of the etching process A1 is applied to the base in the etching process A3. Yes. Further, the etching process A3 is performed so that the silicon substrate exposed by removing the protective film is not excessively etched and the protective film is not left as a residue.

  Then, the etching process A1, the protective film forming process A2, and the etching process A3 are repeated for a predetermined cycle. At that time, in at least one of the etching processing A1 and the etching processing A3, at least the processing time is reduced, the pressure in the processing chamber is reduced, or the base is applied according to the repetition of the cycle. Reduce power.

  In this way, by repeating the etching process A1, the protective film forming process A2, and the etching process A3, in the etching process A1, an etching structure having a predetermined width and depth is formed on the silicon substrate, and the protective film forming process is performed. In A2, a protective film is formed on the side wall and bottom surface of the etching structure formed in the etching process A1, and in the etching process A3, the protective film on the bottom surface of the etching structure with a large amount of ion irradiation is removed by sputtering with ions. In the process A1, the bottom surface of the etching structure from which the protective film has been removed by the etching process A3 is etched. In this way, etching proceeds in the depth direction of the etching structure.

  In the etching process A1, the shorter the processing time, the shorter the contact time between ions and etching species and the silicon substrate, so the etching amount in the width direction and the depth direction decreases, and the pressure in the processing chamber is small. The time for the etching species to stay in the processing chamber becomes shorter. Accordingly, the amount of etching in the width direction and the depth direction decreases, and the smaller the base applied power, the weaker the sputtering by ions, so the amount of etching in the width direction and the depth direction decreases.

  Furthermore, in the etching process A3, it is removed by reducing the processing time in order to shorten the time during which the protective film is sputtered by ions, or by reducing the power applied to the base in order to weaken the sputtering by ions. The amount of protective film is reduced. Further, the amount of etching of the silicon substrate in the depth direction by ions is also reduced.

  Accordingly, in at least one of the etching process A1 and the etching process A3, at least the processing time is gradually shortened for each cycle, or the pressure in the processing chamber or the power applied to the base is gradually decreased for each cycle. By doing so, a balance is achieved between the etching in the width direction, the etching in the depth direction and the amount of the protective film to be removed, and the width of the formed etching structure is gradually narrowed as the number of cycles increases. . The process for gradually shortening the process time, the process for gradually reducing the pressure in the process chamber, and the process for gradually decreasing the power applied to the base may be performed by one of these three processes. It is possible to perform two of the three processes, or to perform all three processes.

  In the process of gradually shortening the processing time, the process of gradually decreasing the pressure in the processing chamber, and the process of gradually decreasing the power applied to the base as the cycle is repeated, the amount of change between the cycles is constant. By doing so, it is possible to form an etching structure in which the side wall has a substantially linear taper shape. Note that the taper angle of the taper shape depends on the amount of change between cycles. For example, if the amount of change is small, an etching structure having a larger taper angle value is formed. An etching structure with a smaller angle value is formed. Alternatively, when the amount of change between cycles is gradually reduced, a tapered etching structure in which the diameter reduction rate gradually decreases from the opening toward the bottom is formed.

  Thus, according to the plasma etching method of the present invention, it is possible to form an etching structure having a predetermined taper shape whose diameter is reduced from the opening toward the bottom.

  The “tapered shape” as used in the present application means that the opening width is wider than the bottom width in the etching structure, and the entire side wall is a straight line or a curve that bulges inward. In the present application, an angle (complementary angle) formed by the bottom surface and the side wall of the etching structure is defined as a “taper angle”. Further, “the value of the taper angle is larger” means that “the value of the taper angle is closer to 90 °”.

  In the plasma etching method of the present invention, the second processing step B may be performed after the first processing step A is performed. Similar to the first processing step A, the second processing step B includes at least two cycles that repeat the etching processing B1, the protective film formation processing B2, and the etching processing B3. Of the etching processing B1 and the etching processing B3, The at least one process is configured to at least gradually reduce the process time, gradually decrease the pressure in the process chamber, or gradually decrease the power applied to the base according to the repetition of the cycle. In addition, the amount of change between cycles in these processes is constant and is set to be smaller than the amount of change between cycles in the first processing step A. Also in the second processing step B, the bias potential applied in the etching process B3 is set larger than the bias potential applied in the etching process B1.

  In this way, the side wall surface is substantially straight below the tapered etching structure having a substantially straight side wall surface or the tapered etching structure in which the diameter reduction rate gradually decreases from the opening toward the bottom. It is possible to further form an etching structure having a taper angle larger than that of the etching structure formed in the first processing step A.

  In at least one of the etching process B1 and the etching process B3 in the second processing step B, at least the processing time in the first cycle is set to be shorter than the processing time in the last cycle of the first processing step A. Alternatively, the pressure in the processing chamber in the first cycle is preferably set to be equal to or lower than the pressure in the processing chamber in the last cycle of the first processing step A. The processing time in the first cycle is set to be equal to or shorter than the processing time in the last cycle of the first processing step A, and the pressure in the processing chamber in the first cycle is set to the processing chamber in the last cycle of the first processing step A. You may make it below the inside pressure.

  Here, when the etching process B1, the protective film formation process B2, and the etching process B3 are repeatedly performed to form an etching structure on the silicon substrate, the depth of the etching structure becomes deep (for example, the aspect ratio of the etching structure is 10). And a depth that is larger than that), ions and etching species are difficult to enter the bottom of the etching structure and the etching is weakened, and the naturally formed etching structure is in the tapered shape formed in the second processing step B. The taper shape has a taper angle equal to or smaller than the taper angle. Therefore, in order to obtain an etching shape in a direction in which the degree of perpendicularity is maintained, it is necessary to obtain the degree of perpendicularity in a direction opposite to the method used in the first processing step A and the second processing step B.

  Therefore, when the etching structure formed in the first processing step A or the second processing step B has a predetermined depth or more, the third processing is performed after the first processing step A or the second processing step B is performed. It is preferable to carry out step C. The third processing step C includes at least two cycles in which the etching process C1, the protective film forming process C2, and the etching process C3 are repeated. At least one of the etching process C1 and the etching process C3 is performed as described above. As the cycle repeats, at least the processing time is gradually extended, the pressure in the processing chamber is gradually increased, or the base applied power is gradually increased. Also in the third processing step C, the bias potential applied in the etching process C3 is made larger than the bias potential applied in the etching process C1.

  In this case, as the number of cycles in the third processing step C increases, etching proceeds in a direction in which the width of the etching structure gradually increases, and as a result, the width of the formed etching structure gradually increases. Can be made narrower.

  Before the first processing step A, an initial step P including a process of isotropically etching the silicon substrate by supplying an etching gas into the processing chamber and converting it into plasma may be further performed. . In this way, the silicon substrate is isotropically etched to form an etching structure in which the portion directly under the mask is undercut. Therefore, by performing each processing step after performing the initial step P, the width of the opening is larger than the width of the mask opening without forming a mask having a different opening width, and from the opening. A tapered etching structure having a diameter reduced toward the bottom can be formed. In the first processing step A performed after the initial step P is performed, the protective film formation processing A2, the etching processing A3, and the etching processing A1 are performed so as not to continuously perform the processing for etching the silicon substrate. It is preferable to repeatedly perform each treatment on the silicon substrate in order.

Note that the etching process in the initial process P is a process of making SF ₆ gas into plasma and isotropically etching the silicon substrate, and making SF ₆ gas and O ₂ gas into plasma and etching the silicon substrate isotropically. It is preferable to include at least any one of the processes and the process of making SF ₆ gas, C ₄ F ₈ gas and O ₂ gas into plasma and isotropically etching the silicon substrate.

The etching gas is preferably a fluorine-based gas. Examples of the fluorine-based gas include sulfur hexafluoride (SF ₆ ) gas. Further, the protective film forming gas is preferably a perfluorocarbon gas or a hydrofluorocarbon gas, and the perfluorocarbon gas can be exemplified by C ₄ F ₈ gas, and the hydrofluorocarbon gas can be CHF ₃ . It can be illustrated.

  As described above, according to the plasma etching method of the present invention, an etching structure having a predetermined taper shape whose diameter is reduced from the opening to the bottom can be formed, and a complicated shape can be formed with one mask. An etched structure can be formed.

It is sectional drawing which showed schematic structure of the plasma etching apparatus used for implementation of the plasma etching method concerning one Embodiment of this invention. It is explanatory drawing for demonstrating the process in which the etching structure in the initial process P forms. It is explanatory drawing for demonstrating the process in which the etching structure in the 1st process process A forms. It is the figure which showed typically the change of the pressure in the etching process A1 of the 1st process process A. FIG. It is explanatory drawing for demonstrating the process in which the etching structure in the 2nd process process B forms. It is explanatory drawing for demonstrating the process in which the etching structure in the 3rd process process C forms. It is sectional drawing which showed the etching structure formed with the plasma etching method which concerns on one Embodiment. It is the table | surface which put together the etching conditions in the experiment to which the plasma etching method which concerns on one Embodiment is applied. The change of processing time, pressure, and applied power when performing processing that gradually shortens the processing time, processing that gradually decreases the pressure in the processing chamber, and processing that gradually decreases the power applied to the base is schematically shown. FIG. It is sectional drawing which showed the etching structure formed by the plasma etching method which concerns on other embodiment.

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

  First, an etching apparatus 1 used for implementing a plasma etching method according to an embodiment of the present invention will be described. As shown in FIG. 1, the etching apparatus 1 includes a processing chamber 11 having a closed space, a base 15 that is disposed in the processing chamber 11 so as to be movable up and down, and on which a silicon substrate K is placed, and the base. The raising / lowering cylinder 18 that raises and lowers the table 15, the gas supply device 20 that supplies the etching gas and protective film forming gas into the processing chamber 11, and the etching gas and protective film forming gas supplied into the processing chamber 11 are turned into plasma. The plasma generation device 25, a high frequency power supply 30 that supplies high frequency power to the base 15, and an exhaust device 35 that reduces the pressure in the processing chamber 11.

  The processing chamber 11 includes an upper chamber 12 and a lower chamber 13 having internal spaces communicating with each other. The upper chamber 12 is formed smaller than the lower chamber 13. The base 15 is composed of an upper member 16 on which the silicon substrate K is placed and a lower member 17 to which the elevating cylinder 18 is connected, and is disposed in the lower chamber 13.

The gas supply apparatus 20, as the etching gas, a SF ₆ gas supply unit 21 for supplying the SF ₆ gas, as a protective film forming _gas, and _C 4 _{F 8} gas supply unit 22 for supplying C 4 _{F 8} gas, O and _{O 2} gas supply unit 23 for supplying ₂ gas, one end is connected to the upper surface of the upper chamber 12, the other end branched SF ₆ gas supply unit _21, C 4 _{F 8} gas supply unit 22 and the _{O 2} gas A supply pipe 24 connected to each of the supply sections 23, and the SF ₆ gas supply section 21, the C ₄ F ₈ gas supply section 22, and the O ₂ gas supply section 23 into the processing chamber 11 through the supply pipe 24. ₆ gas, C ₄ F ₈ gas and O ₂ gas are supplied. Note that the etching gas is not limited to SF ₆ gas, and other fluorine-based gases such as CF ₄ , NF ₃ , and IF ₅ can be used. Further, the protective film forming gas is not limited to C ₄ F ₈ gas, and other perfluorocarbon gas such as C ₅ F ₈ or hydrofluorocarbon gas such as CHF ₃ or CH ₂ F ₂ may be used. it can.

The plasma generation device 25 is a device that generates so-called inductively coupled plasma (ICP), and includes a plurality of annular coils 26 that are vertically arranged on the outer peripheral portion of the upper chamber 12, and a high frequency applied to the coils 26. The high frequency power supply 27 is configured to supply power, and the high frequency power is supplied to the coil 26 by the high frequency power supply 27, so that the SF ₆ gas, C ₄ F ₈ gas, and O ₂ gas supplied into the upper chamber 12 are converted into plasma. Turn into.

The high frequency power supply 30 supplies high frequency power to the base 15 to give a bias potential between the base 15 and the plasma, and plasma of SF ₆ gas, C ₄ F ₈ gas and O ₂ gas. The ions generated by the conversion are made incident on the silicon substrate K placed on the base 15.

  The exhaust device 35 includes a vacuum pump 36 for exhausting gas, and an exhaust pipe 37 having one end connected to the vacuum pump 36 and the other end connected to a side surface of the lower chamber 13. A vacuum pump 36 exhausts the gas in the processing chamber 11 and maintains the inside of the processing chamber 11 at a predetermined pressure.

  Next, a method of plasma etching the silicon substrate K using the etching apparatus 1 configured as described above to form the etching structure shown in FIG. 7 will be described with reference to FIGS. The etching structure shown in FIG. 7 has a shape that is reduced in diameter from the opening toward the bottom, and includes three portions with different taper angles θ (θ1 <θ2 <θ3). Further, P, A, B, and C in FIG. 7 indicate portions of the etching structure formed in the initial process P, the first processing process A, the second processing process B, and the third processing process C, respectively. 2, 3, 5, and 6 are for explaining the process of forming the etching structure in the initial process P, the first process process A, the second process process B, and the third process process C, respectively. It is explanatory drawing.

  First, when plasma etching the silicon substrate K, the silicon substrate K is subjected to mask formation processing.

  After the mask formation process, the mask M is formed on the surface of the silicon substrate K by, for example, vapor deposition (chemical vapor deposition (CVD) or physical vapor deposition (PVD)), photoresist coating, or the like. Then, a predetermined mask pattern having an opening in the mask M is formed (see FIG. 2A). Examples of the mask M include a resist mask, an oxide film, a metal mask, and a laminated film.

  Next, a plasma etching process is performed on the silicon substrate K on which the mask M is formed.

In this plasma etching process, first, the silicon substrate K is carried into the etching apparatus 1 and placed on the upper member 16 of the base 15. Next, the silicon substrate K is isotropically etched (initial step P). Specifically, in the initial process P, the SF ₆ gas, the C ₄ F ₈ gas and the O ₄ gas are supplied from the SF ₆ gas supply unit 21, the C ₄ F ₈ gas supply unit 22 and the O ₂ gas supply unit 23 into the processing chamber 11. _Two gases are supplied at a predetermined flow rate, and high frequency power is applied to the coil 26 by the high frequency power source 27. Note that the pressure in the processing chamber 11 is reduced to a predetermined pressure by the exhaust device 35.

As a result, SF ₆ gas, C ₄ F ₈ gas, and O ₂ gas supplied into the processing chamber 11 are converted into plasma, and the formation and removal of the protective film are performed in parallel, while the SF ₆ gas is converted into plasma. The generated etching species (for example, fluorine radicals) chemically react with silicon atoms, whereby the silicon substrate K is isotropically etched (see FIG. 2B). By performing the initial process P for a predetermined time, as shown in FIG. 2C, a taper-shaped etching structure is formed in which the portion directly under the mask M is also etched.

  Next, a first processing step A and a second processing step B in which a cycle of repeating the protective film formation processing A2, B2, C2, etching processing A3, B3, C3 and etching processing A1, B1, C1 is performed a plurality of times on the silicon substrate K. And the 3rd processing process C is carried out one by one.

Specifically, in the first processing step A, first, a protective film forming process A2 is performed. In the protective film formation process A2, the _C 4 _{F 8} gas into the processing chamber 11 from the _C 4 _{F 8} gas supply unit 22 is supplied at a predetermined flow rate, a high-frequency power is applied to the coil 26 by the high frequency power source 27, also, The exhaust device 35 exhausts the gas in the processing chamber 11 so that the pressure in the processing chamber 11 becomes a predetermined pressure. Thereby, a protective film is formed on the inner wall of the etching structure formed in the initial step P.

Next, an etching process A3 is performed. In this etching process A3, said SF ₆ gas is supplied at a predetermined flow rate from the SF ₆ gas supply unit 21 into the processing chamber 11, a high-frequency power is applied to the coil 26 and the base 15 by a high frequency power source 27 and 30, also The gas in the processing chamber 11 is exhausted by the exhaust device 35 so that the pressure in the processing chamber 11 becomes a predetermined pressure.

Thus, SF ₆ gas supplied into the processing chamber 11 into a plasma, by fluorine ions generated by the plasma of the SF ₆ gas is incident to the silicon substrate K, etching structure bottom protective film is removed .

Next, after performing the etching process A3 for a predetermined time, the etching process A1 is performed for a predetermined time. In the etching process A1, the high-frequency power applied to the base 15 is lowered, the inside of the processing chamber 11 is adjusted to a predetermined pressure, and fluorine ions generated by the plasma formation of SF ₆ gas enter the silicon substrate K, or the like The silicon substrate K is etched by the chemical reaction of the etching species generated by the plasma formation of SF ₆ gas with silicon atoms (see FIG. 3A).

  Subsequently, after the protective film formation process A2 and the etching process A3 are performed under the same conditions as described above, the etching process A1 is performed in which the processing time is shortened and the pressure in the processing chamber 11 is reduced. That is, the etching process A1 is performed while shortening the processing time compared to the etching A1 in the previous cycle and reducing the pressure in the processing chamber 11. Thus, by shortening the processing time and decreasing the pressure in the processing chamber 11, the etching amount in the etching structure width direction and depth direction is reduced, as shown in FIG. 3B. Etching into a shape narrower than the previous cycle.

  Thereafter, similarly, the protective film forming process A2 and the etching process A3 are performed under the same conditions as described above, and in the etching process A1, the processing time is gradually shortened so that the amount of change between cycles is constant, and the processing chamber 11 These series of processes are repeated a certain number of times under the condition that the internal pressure is gradually reduced.

  In this example, when the pressure in the processing chamber 11 is gradually reduced, the amount of change (ΔP) between the cycles at the start of each cycle of the etching process A1 is set to be constant, In one cycle, the pressure is gradually decreased as time passes (see FIG. 4A). For example, the amount of change (ΔP) between the cycles is constant. In addition, the same pressure may be maintained in one cycle (see FIG. 4B).

  As a result, as shown in FIG. 3C, a tapered etching structure with a taper angle of θ1 is formed.

  Next, the second processing step B is performed. In the second processing step B, first, the protective film formation processing B2 is performed similarly to the first processing step A to form a protective film on the inner wall of the etching structure formed in the first processing step A, and then etching is performed. Processing B3 is performed to remove the protective film at the bottom of the etching structure, and then etching processing B1 is performed to etch the silicon substrate K. At this time, the processing time in the etching process B1, the pressure in the processing chamber 11 and the power applied to the base are made equal to or lower than the processing time, the pressure in the processing chamber 11 and the power applied to the base in the final cycle of the first processing step A. Preferably it is done. By doing so, the width of the etching structure opening formed in the second processing step B is narrower than the width of the bottom of the etching structure formed in the first processing step A, and the etching structure has a reduced diameter. Become.

  Subsequently, after the protective film forming process B2 is performed under the same conditions as described above, the base applied power is reduced after performing the process of reducing the base applied power, that is, the etching process B3 in the previous cycle. Then, the etching process B3 is performed.

  After performing the etching process B3 for a predetermined time, after performing a process with a shortened process time, that is, an etch process B1 with a shorter process time than the etch process B1 of the previous cycle is performed.

  Thus, by reducing the base application power in the etching process B3, the amount of the protective film to be removed is reduced and the etching amount in the depth direction is reduced. On the other hand, by reducing the pressure in the processing chamber 11 in the etching process B1, the etching amount in the width direction and the depth direction of the etching structure is decreased, and as a result, etching is performed in a shape narrower than the previous cycle ( (See FIG. 5 (a)).

  Thereafter, similarly, the protective film forming process B2 is performed under the same conditions as described above, and the etching process B3 is performed under the condition that the base application power is gradually decreased so that the change amount between cycles is constant, and the etching process B1 is performed. The processing time is gradually shortened so that the amount of change between cycles is constant, and the series of processing is repeated a certain number of times. The amount of change between cycles in the second processing step B so that the taper angle θ2 of the etching structure formed in the second processing step B is larger than the taper angle θ1 of the etching structure formed in the first processing step. Is smaller than the amount of change between cycles in the first processing step A.

  As a result, as shown in FIG. 5B, a tapered etching structure having a taper angle of θ2 (> θ1) is formed below the etching structure formed in the first processing step.

  Here, when the etching structure reaches a predetermined depth (for example, a depth at which the aspect ratio of the etching structure is larger than 10), it becomes difficult for fluorine ions and etching species to enter the bottom of the etching structure, and the etching gradually weakens. Therefore, the naturally formed etching structure becomes a tapered shape having a taper angle θ3 ′ equal to or smaller than the taper angle θ2 (see FIG. 5B). Therefore, when the taper angle of the etching structure to be formed is larger than the taper angle of the etching structure that is naturally formed, the processing that shortens the processing time, the processing that reduces the pressure in the processing chamber 11, and the base application Even if any of the processes with reduced power is performed, the target etching structure cannot be formed.

  Therefore, in the plasma etching method of this example, after the second processing step B is performed, the third processing step C is performed. In the third processing step C, first, a protective film formation processing C2 is performed on the silicon substrate K, and a protective film is formed on the inner wall of the etching structure formed in the second processing step B. Next, the etching process C3 is performed to remove the protective film at the bottom of the etching structure, and then the etching process C1 is performed to etch the silicon substrate K.

  Subsequently, after the protective film forming process C2 is performed under the same conditions as described above, after the process of increasing the base applied power is performed, that is, the base applied power is increased compared to the etching process C3 of the previous cycle. The etched etching process C3 is performed. Then, after performing the etching process C3 for a predetermined time, the etching process C1 is performed under the same conditions as described above.

  Thereafter, similarly, the protective film forming process C2 and the etching process C1 are performed under the same conditions as described above, and the etching process C3 is performed by gradually increasing the base applied power so that the amount of change between cycles is constant. Above, a series of these processes is repeated a certain number of times.

  As described above, in the etching process C3, the base applied power is gradually increased to increase the amount of the protective film to be removed, and the amount of etching in the depth direction is increased, so that it is naturally formed. An etching structure having a taper angle θ3 (> θ2) larger than the taper angle θ3 ′ of the etching structure is formed (see FIG. 6).

  Thus, as shown in FIG. 7, an etching structure is formed in which the opening is wide, the side walls are three different taper angles, and the diameter is reduced from the opening toward the bottom.

  Incidentally, the inventors of the present application performed an experiment in which the plasma etching method of the present embodiment was applied to perform etching on a silicon substrate on which a resist mask was formed. FIG. 8 is a table summarizing the etching conditions in each processing step.

  In this experiment, in the first processing step A, the processing time of the etching process A1 is gradually shortened from 8.0 seconds to 4.0 seconds, and the pressure in the processing chamber is gradually decreased from 10.0 Pa to 4.0 Pa. It was made to decrease. In the first processing step A, a cycle in which the protective film formation processing A2, the etching processing A3, and the etching processing A1 are sequentially repeated was performed five times.

In the second process step B, while gradually reduced the processing time of the etching grayed process B1 from 4.0 seconds to 0.5 seconds, gradually decreases the base power applied in the etching process B3 from 50W to 30W I did it. In the second treatment step B, the cycle was performed 40 times.

  Further, in the third processing step C, the base application power in the etching process C3 is gradually increased from 50 W to 65 W. In the third treatment step C, the cycle was performed 150 times.

  As a result, the silicon substrate K was formed with an etching structure having a wide opening and having three different taper angles on the side wall. The taper angles of the etching structures formed in the first, second, and third processing steps were 86 °, 87 °, and 88 °, respectively.

  As described above, according to the plasma etching method according to the present embodiment, in the etching process A1 in the first process step A, the processing time is gradually reduced and the process is performed under the condition in which the pressure in the processing chamber is gradually decreased. In addition, in the etching process B3 in the second process step B, the base applied power is gradually decreased, and in the etching process B1, the process is performed under the condition that the process time is gradually shortened. An etching structure having a predetermined taper angle can be formed.

  Furthermore, according to the plasma etching method of the present example, an etching structure having a larger opening width than the opening width of the mask M in the initial process P can be formed with a single mask M without forming a plurality of masks M. After the formation, an etching structure having a predetermined taper angle can be formed for each of the processing steps A, B, and C, and a mask forming process needs to be performed a plurality of times when forming an etching structure with a complicated shape. No man-hours can be reduced. In addition, when an etching structure is formed by performing a plurality of mask forming processes, there is a problem that the etching structure becomes a shape different from a desired shape due to mask displacement or the like. By forming the etching structure by the above, occurrence of such a problem can be suppressed.

  Further, in the processing for shortening the processing time, the processing for reducing the pressure in the processing chamber, and the processing for reducing the power applied to the base (hereinafter referred to as “three processings”), the amount of change is set for each processing step. By changing, an etching structure having a plurality of different taper angles can be easily formed.

  Furthermore, in the plasma etching method according to the present embodiment, since the third processing step C in which the base applied power is gradually increased is performed in the etching processing C3, the etching structure has a predetermined depth. Even after reaching this depth, an etching structure having a predetermined taper angle can be formed.

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

  The above example shows an example of the three processes performed in the etching processes A1, B1, C1 and the etching processes A3, B3, C3 in the processing steps A, B, C. It is not something that can be done. That is, according to the etching structure to be formed, for example, in the etching process A3 of the first processing step A, one or more of the three processes may be performed, or the etching in the second processing step B is performed. In the process B1, none of the three processes may be performed.

  In this example, the initial process P is performed. However, the initial process P is not necessarily performed, and is appropriately performed from the processing processes A, B, and C according to the etching structure to be formed. You may make it do. Further, it is not always necessary to perform all of the first, second, and third processing steps A, B, and C. For example, when the etching structure does not reach a predetermined depth, the third processing step C is replaced. Thus, even if the second ′ processing step for performing processing different from the first and second processing steps A and B is performed, an etching structure having three different taper angles can be formed.

  Further, in this example, when the three processes are performed, as shown in FIG. 9A, the change amount dx between cycles is made constant in each of the process steps A and B. As shown in FIG. 9B, the above three processes may be performed so that the change amounts dx1, dx2, dx3 between cycles gradually decrease (dx3 <dx2 <dx1). For example, by performing one of the two processing steps A and B after performing the initial step P, as shown in FIG. 10, the diameter reduction rate is continuously reduced and the side wall is smooth. A tapered etching structure can be formed.

DESCRIPTION OF SYMBOLS 1 Etching apparatus 11 Processing chamber 15 Base 20 Gas supply apparatus 21 SF ₆ Gas supply part 22 C ₄ F ₈ Gas supply part 25 Plasma generation apparatus 26 Coil 27 High frequency power supply 30 High frequency power supply 35 Exhaust apparatus K Silicon substrate M Mask

Claims (12)

A method of etching a silicon substrate placed on a base in a processing chamber to form an etching structure on the silicon substrate,
An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process A2 for forming a protective film on the silicon substrate, plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. In the plasma etching method including the first processing step A that repeats at least three cycles or more, with the processing including the etching processing A3 to be performed as one cycle,
In the first processing step A,
The bias potential applied in the etching process A3 is made larger than the bias potential applied in the etching process A1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process A1 and the etching process A3 may at least gradually reduce the processing time or the processing chamber according to the repetition of the cycle. It is configured to gradually decrease the internal pressure or gradually decrease the base applied power,
In the process of gradually shortening the processing time, the process of gradually decreasing the pressure in the processing chamber, and the process of gradually decreasing the power applied to the base as the cycle is repeated, the amount of change between the cycles gradually increases. A plasma etching method characterized by being made small. An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process C2 for forming a protective film on the silicon substrate, and plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. If the etching structure formed in the first processing step A has a predetermined depth or more, the third processing step C that repeats at least two cycles or more including the processing including the etching processing C3 to be performed is one cycle. 1 After the implementation of process A,
In the third processing step C,
The bias potential applied in the etching process C3 is made larger than the bias potential applied in the etching process C1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process C1 and the etching process C3 is performed by gradually extending at least the processing time or processing chamber according to the repetition of the cycle. 2. The plasma etching method according to claim 1, wherein the internal pressure is gradually increased or the base applied power is gradually increased. A method of etching a silicon substrate placed on a base in a processing chamber to form an etching structure on the silicon substrate,
An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process A2 for forming a protective film on the silicon substrate, plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. In the plasma etching method provided with the first processing step A that repeats at least two cycles or more, with the processing including the etching processing A3 to be performed as one cycle,
In the first processing step A,
The bias potential applied in the etching process A3 is made larger than the bias potential applied in the etching process A1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process A1 and the etching process A3 may at least gradually reduce the processing time or the processing chamber according to the repetition of the cycle. It is configured to gradually decrease the internal pressure or gradually decrease the base applied power,
In the process of gradually shortening the processing time, the process of gradually decreasing the pressure in the processing chamber, and the process of gradually decreasing the power applied to the base as the cycle is repeated, the amount of change between the cycles is constant. So that
Further, an etching gas is supplied into the processing chamber to turn it into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber to turn it into plasma. Then, a protective film forming process B2 for forming a protective film on the silicon substrate, plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to form a protective film formed on the silicon substrate. The second treatment step B that repeats at least two cycles or more is performed after the first treatment step A is performed, with the treatment including the etching treatment B3 for removing as one cycle.
In the second processing step B,
The bias potential applied in the etching process B3 is larger than the bias potential applied in the etching process B1,
At least one of the etching process B1 and the etching process B3 is to at least gradually reduce the processing time, gradually decrease the pressure in the processing chamber, or apply a base according to the repetition of the cycle. while being configured to gradually decrease the power, the amount of change between cycles in these processes is constant and rather smaller than the amount of change between cycles in the first processing step a,
In at least one of the etching process B1 and the etching process B3 in the second processing step B, at least the processing time of the first cycle is set to be equal to or shorter than the processing time in the last cycle of the first processing step A, A plasma etching method , wherein the pressure in the processing chamber of the first cycle is set to be equal to or lower than the pressure in the processing chamber in the last cycle of the first processing step A. An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process C2 for forming a protective film on the silicon substrate, and plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. When the etching structure formed in the second processing step B has a predetermined depth or more, the third processing step C that repeats at least two cycles or more with the processing including the etching processing C3 to be performed as one cycle is performed. 2 After the implementation of processing step B,
In the third processing step C,
The bias potential applied in the etching process C3 is made larger than the bias potential applied in the etching process C1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process C1 and the etching process C3 is performed by gradually extending at least the processing time or processing chamber according to the repetition of the cycle. gradually increasing or, or claim 3 Symbol placement of the plasma etching method, characterized in that it is configured so as to gradually increase the base applied power pressure within. Before the first processing step A,
Wherein by supplying an etching gas into the processing chamber into plasma, either plasma of claims 1 to 4, wherein further comprising isotropically initial step P including the process of etching the silicon substrate Etching method. A method of etching a silicon substrate placed on a base in a processing chamber to form an etching structure on the silicon substrate,
An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process A2 for forming a protective film on the silicon substrate, plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. In the plasma etching method provided with the first processing step A that repeats at least two cycles or more, with the processing including the etching processing A3 to be performed as one cycle,
In the first processing step A,
The bias potential applied in the etching process A3 is made larger than the bias potential applied in the etching process A1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process A1 and the etching process A3 may at least gradually reduce the processing time or the processing chamber according to the repetition of the cycle. It is configured to gradually decrease the internal pressure or gradually decrease the base applied power,
Before the first processing step A,
An initial process P including a process of supplying the etching gas into a processing chamber to form a plasma and isotropically etching the silicon substrate, which is not included in the first processing process A. For a predetermined time ,
In the initial step P, a process gas containing SF ₆ gas and not containing O ₂ gas is turned into plasma to etch the silicon substrate isotropically, and SF ₆ gas, C ₄ F ₈ gas and O ₂ are processed. A plasma etching method characterized by including at least one of a process for converting gas into plasma and isotropically etching the silicon substrate. An etching gas is supplied into the processing chamber and turned into plasma, and a bias potential is applied to the base to etch the silicon substrate, and a protective film forming gas is supplied into the processing chamber and turned into plasma. Protective film formation process C2 for forming a protective film on the silicon substrate, and plasma is generated by supplying an etching gas into the processing chamber, and a bias potential is applied to the base to remove the protective film formed on the silicon substrate. If the etching structure formed in the first processing step A has a predetermined depth or more, the third processing step C that repeats at least two cycles or more including the processing including the etching processing C3 to be performed is one cycle. 1 After the implementation of process A,
In the third processing step C,
The bias potential applied in the etching process C3 is made larger than the bias potential applied in the etching process C1,
In order to form a tapered etching structure on the silicon substrate, at least one of the etching process C1 and the etching process C3 is performed by gradually extending at least the processing time or processing chamber according to the repetition of the cycle. 7. The plasma etching method according to claim 6 , wherein the internal pressure is gradually increased or the base applied power is gradually increased. In the initial step P, SF ₆ gas is plasmatized and the silicon substrate is isotropically etched, SF ₆ gas and O ₂ gas are plasmatized and the silicon substrate is isotropically etched, and _{6. The} plasma according to claim 5 , further comprising at least one of a process of converting SF ₆ gas, C ₄ F ₈ gas, and O ₂ gas into plasma and isotropically etching the silicon substrate. Etching method. The etching gas is, either plasma etching method of claims 1 to 8, wherein the fluorine-based gas. The plasma etching method according to claim 9 , wherein the etching gas is SF ₆ gas. The protective film forming gas, one of the plasma etching method of claims 1 to 10, wherein it is a perfluorocarbon gas or hydrofluorocarbon gas. The plasma etching method according to claim 11 , wherein the protective film forming gas is a C ₄ F ₈ gas.

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