JP6110530B2 - Plasma etching equipment - Google Patents

Description

  The present invention relates to a plasma etching apparatus capable of reducing greenhouse gas emissions without reducing etching processing characteristics in a plasma etching process in which an etching step and a protective film forming step are alternately repeated. .

  When microelectromechanical systems (MEMS), through-silicon vias (TSV), etc. are formed using a silicon substrate (for example, a single crystal silicon substrate) as a base material, the silicon substrate is dug to a depth of several tens to several hundreds of micrometers. It is necessary to perform etching.

In such deep etching, an etching step of plasma-etching a silicon substrate using SF ₆ having excellent etching characteristics as an etching gas, and C ₄ F ₈ (IPCC (Interventional Panel on Climate Change) _4th as a deposition gas) are used. Protective film formation for forming a protective film on the side wall of the silicon substrate constituting the side surface of the recess formed by etching using the global warming potential (GWP) 10300) described in the next evaluation report A plasma etching method in which steps are alternately repeated is widely employed (see, for example, Patent Document 1).

Japanese Patent No. 4090492

  By the way, when the silicon substrate is deeply etched using the plasma etching method, the plasma etching process time (total time required for the plasma etching process in which the etching step and the protective film forming step are alternately repeated) is: When a semiconductor integrated circuit (circuit element layer) is formed, it is longer than the time for etching the silicon substrate (for example, the time for forming a groove for element isolation).

Therefore, using conventional plasma etching method, when forming a MEMS and TSV like, it is necessary to long-term use of SF ₆ is a greenhouse gas (etching gas) and _C 4 _{F 8} (deposition gas).
For this reason, when the conventional plasma etching method was used, there existed a problem of promoting the global warming.

  Therefore, the present invention provides a plasma etching process that can reduce greenhouse gas emissions without deteriorating etching processing characteristics in a plasma etching process in which an etching step and a protective film forming step are alternately repeated. An object is to provide an apparatus.

In order to solve the above-described problem, according to the invention according to claim 1, a chamber accommodating a susceptor on which silicon is placed, and an etching gas for etching the silicon into the chamber via an etching gas supply line As an etching gas supply source for supplying a gas containing SF ₆ as a plasma generator, a plasma generation unit disposed around the chamber, and 2, 3, 3, 3 which is a deposition gas in the chamber via a deposition gas supply line A plasma etching apparatus comprising: a deposition gas supply source for supplying tetrafluoropropene;

  According to the second aspect of the invention, there is provided a chamber for accommodating a susceptor on which silicon is placed, and an etching for supplying an etching gas for plasma etching the silicon into the chamber via an etching gas supply line. A gas supply source, a plasma generating unit that is disposed around the chamber and converts the etching gas into plasma, and covers the sidewall of the silicon exposed by the plasma etching in the chamber via a deposition gas supply line A plasma etching apparatus comprising: a deposition gas supply source that supplies 2,3,3,3-tetrafluoropropene, which is a deposition gas for forming a sidewall protective film, is provided.

  According to a third aspect of the present invention, there is provided the plasma etching apparatus according to the first or second aspect, wherein the etching gas and the deposition gas can be alternately and repeatedly supplied into the chamber. Is done.

  Moreover, according to the said invention, etching gas is made into plasma, the etching step which plasma-etches silicon, and 2,3,3,3-tetrafluoropropene (molecular formula; CF3-CF = CH2) is used as a deposition gas. A plasma etching method is provided, wherein the silicon is processed by alternately performing a sidewall protection film forming step of forming a protection film covering the sidewall of the silicon exposed by the plasma etching. Is done.

Further, according to the invention, as the etching gas, characterized by using a gas containing SF _6, the plasma etching method is provided.

Further, according to the invention, the flow rate of the 2,3,3,3-tetrafluoropropene is in the range of 0.2 to 0.9 times the flow rate of the SF _6. An etching method is provided.

Further, according to the invention, the flow rate of the 2,3,3,3-tetrafluoropropene is in the range of 0.4 to 0.6 times the flow rate of the SF _6. An etching method is provided.

  According to the invention, there is provided a plasma etching method characterized in that a MEMS is formed by using a single crystal silicon substrate as the silicon and processing the single crystal silicon substrate.

  Further, according to the invention, plasma etching is characterized in that a single crystal silicon substrate is used as the silicon, and the single crystal silicon substrate is processed to form a through-hole penetrating the single crystal silicon substrate. A method is provided.

According to the present invention, by using 2,3,3,3-tetrafluoropropene having a global warming potential as small as 4 as a deposition gas, a protective film that covers the side wall of silicon exposed by plasma etching is formed. Compared with the case where a protective film is formed using C ₄ F ₈ , which is a conventional deposition gas, greenhouse gas emissions can be reduced.

For example, when SF ₆ excellent in etching processing characteristics is used as an etching gas, it is possible to reduce greenhouse gas emissions while suppressing the deterioration of etching processing characteristics and improving productivity.

  That is, according to the present invention, etching processing characteristics and productivity can be improved, and greenhouse gas emissions can be reduced.

It is sectional drawing which shows the principal part of the plasma etching apparatus used when performing the plasma etching method which concerns on embodiment of this invention. It is sectional drawing (the 1) for demonstrating the plasma etching method which concerns on embodiment of this invention, Specifically, it is sectional drawing which shows the single crystal silicon substrate in which the resist mask which has an opening part was formed. is there. It is sectional drawing (the 2) for demonstrating the plasma etching method which concerns on embodiment of this invention, Specifically, a recessed part is formed in the single crystal silicon substrate in which the resist mask which has an opening part was formed. It is sectional drawing for demonstrating the step to do. FIG. 6 is a cross-sectional view (No. 3) for explaining the plasma etching method according to the embodiment of the present invention, specifically, a step of forming a protective film covering the side wall of the recess formed in the step shown in FIG. It is sectional drawing for demonstrating. FIG. 6 is a cross-sectional view (No. 4) for explaining the plasma etching method according to the embodiment of the present invention, specifically, on a single crystal silicon substrate located below a recess formed in the step shown in FIG. It is sectional drawing for demonstrating the step which forms a recessed part. FIG. 6 is a cross-sectional view (No. 5) for explaining the plasma etching method according to the embodiment of the present invention, specifically, a cross-section schematically showing a state in which a through-hole penetrating a single crystal silicon substrate is formed. FIG. The cross-sectional SEM photograph of the hole aiming at the aperture diameter of 30 micrometers formed in the single crystal silicon wafer of a comparative example and the hole diameter aiming at 50 micrometers is shown. It is a cross-sectional SEM photograph of the hole aiming at the aperture diameter of 30 micrometers formed in the single crystal silicon wafer of Examples 1-4, and the hole diameter aiming at 50 micrometers.

  Embodiments to which the present invention is applied will be described below in detail with reference to the drawings. The drawings used in the following description are for explaining the configuration of the embodiment of the present invention, and the size, thickness, dimensions, etc. of each part shown in the drawings are different from the dimensional relationship of an actual plasma etching apparatus. There is a case.

(Embodiment)
FIG. 1 is a cross-sectional view showing a main part of a plasma etching apparatus used when performing a plasma etching method according to an embodiment of the present invention. In FIG. 1, some components of plasma etching apparatus 10 (specifically, chamber 11, susceptor 12, etching gas supply source 14, deposition gas supply source 15, etching gas supply line 17, deposition gas supply line 18, and exhaust gas) Line 22 only) is illustrated.

  First, the configuration of the plasma etching apparatus 10 used when performing the plasma etching method according to the present embodiment (in other words, the plasma etching method in which the etching step and the protective film forming step are alternately repeated) will be described. Then, the plasma etching method according to the present embodiment will be described.

  Referring to FIG. 1, a plasma etching apparatus 10 includes a chamber 11, a susceptor 12, a plasma generator 13, an etching gas supply source 14, a deposition gas supply source 15, an etching gas supply line 17, and a deposition gas supply line. 18 and an exhaust gas line 22.

  The chamber 11 is a reaction chamber in which a plasma etching process is performed. The chamber 11 has an upper wall 11A and a lower wall 11B that are arranged to face each other. During the plasma etching process, the chamber 11 is evacuated.

  The susceptor 12 is accommodated in the chamber 11. The susceptor 12 is disposed on the lower wall 11B of the chamber 11. The susceptor 12 has a substrate mounting surface 12a on which a single crystal silicon substrate 25, which is silicon (an object to be etched), is mounted.

  Hereinafter, a case where a single crystal silicon substrate 25 (more specifically, a single crystal silicon wafer) is used as silicon processed by the plasma etching method according to the present embodiment will be described as an example.

The plasma generating unit 13 includes a coil 13-1 and a high frequency power source 13-2. The coil 13-1 is disposed around the chamber 11 and is connected to the high frequency power source 13-2. The high frequency power supply 13-2 is arranged outside the chamber 11.
The plasma generator 13 has a function of converting the etching gas supplied from the etching gas supply source 14 into plasma.

  The etching gas supply source 14 is connected to one end of the etching gas supply line 17. The etching gas supply source 14 supplies the etching gas into the chamber 11 via the etching gas supply line 17 when performing the etching step.

As an etching gas, an etching gas containing SF ₆ may be used. As described above, by using a gas containing SF ₆ having excellent etching characteristics as the etching gas, the single crystal silicon substrate 25 can be processed into a good shape (in other words, the deterioration of the etching characteristics is suppressed). it can.).

  The deposition gas supply source 15 is connected to one end of the deposition gas supply line 18. The deposition gas supply source 15 supplies deposition gas necessary for forming a protective film into the chamber 11 via the deposition gas supply line 18 when performing the protective film formation step.

As the deposit gas, 2,3,3,3-tetrafluoropropene having a global warming potential as low as 4 may be used.
In this way, by using 2,3,3,3-tetrafluoropropene as the deposit gas when forming the protective film, C ₄ F ₈ which is a conventional deposit gas and has a global warming potential of 10300 can be obtained. The amount of greenhouse gas emissions can be reduced compared to the case of using it.

  The etching gas supply line 17 has one end connected to the etching gas supply source 14 and the other end connected to the upper wall 11 </ b> A of the chamber 11. The other end of the etching gas supply line 17 passes through the upper wall 11A of the chamber 11. The etching gas supply line 17 is a line for supplying an etching gas into the chamber 11.

  The deposition gas supply line 18 has one end connected to the deposition gas supply source 15 and the other end connected to the upper wall 11 </ b> A of the chamber 11. The other end of the deposition gas supply line 18 passes through the upper wall 11A of the chamber 11. The deposition gas supply line 18 is a line for supplying deposition gas into the chamber 11.

One end of the exhaust gas line 22 is connected to the lower wall 11 </ b> B of the chamber 11. One end of the exhaust gas line 22 passes through the lower wall 11B of the chamber 11. The other end of the exhaust gas line 22 is connected to an abatement apparatus (not shown) via a dry pump (not shown).
The exhaust gas line 22 is a line for discharging the etching gas, the deposition gas, each dissociated species, and the reaction product from the chamber 11.

  2 to 6 are cross-sectional views for explaining the plasma etching method according to the embodiment of the present invention. Specifically, FIG. 2 is a cross-sectional view illustrating a single crystal silicon substrate on which a resist mask having an opening is formed. FIG. 3 is a cross-sectional view for explaining a step of forming a recess in a single crystal silicon substrate on which a resist mask having an opening is formed.

  FIG. 4 is a cross-sectional view for explaining a step of forming a protective film covering the side wall of the recess formed in the step shown in FIG. FIG. 5 is a cross-sectional view for explaining the step of forming the recess in the single crystal silicon substrate located below the recess formed in the process shown in FIG. FIG. 6 is a cross-sectional view schematically showing a state in which a through hole penetrating the single crystal silicon substrate is formed.

Next, with reference to FIGS. 1-6, the plasma etching method of this Embodiment which performs an etching step and a protective film formation step alternately and repeatedly is demonstrated.
Hereinafter, in the present embodiment, a case where the through hole 38 (see FIG. 6) penetrating the single crystal silicon substrate 25 is processed by using the plasma etching method of the present embodiment will be described as an example.

First, in the step shown in FIG. 2, a substrate 30 with a resist mask is prepared. The substrate 30 with a resist mask is formed by the following method, for example.
A conductor in which a circuit element layer 41 (for example, an element such as a transistor and a through hole 38 is exposed on the front surface 25b of the single crystal silicon substrate 25 that is not thinned (a surface located on the opposite side of the back surface 25a) by a known technique. A multilayer wiring structure including 42) is formed (see FIG. 6).

  Next, the single crystal silicon substrate 25 is thinned from the back surface 25a side of the single crystal silicon substrate 25 using, for example, a backside grinder. The thickness of the thinned single crystal silicon substrate 25 can be set to, for example, 50 to 400 μm.

Next, a resist mask 31 having an opening 31A is formed on the back surface 25a of the thinned single crystal silicon substrate 25 by photolithography. At this time, the opening 31A is formed so as to expose the back surface 25a of the single crystal silicon substrate 25 corresponding to the formation region of the through hole 38 shown in FIG. Thereby, the substrate 30 with a resist mask shown in FIG. 2 is formed.
When the thickness of the single crystal silicon substrate 25 is 50 μm, the opening diameter of the opening 31A can be set to 400 μm, for example.

Next, the substrate 30 with a resist mask shown in FIG. 2 is carried into the chamber 11 of the plasma etching apparatus 10 shown in FIG. 1, and then the substrate 30 with a resist mask is fixed to the substrate mounting surface 12 a of the susceptor 12.
At this time, the substrate 30 with the resist mask is fixed so that the side on which the resist mask 31 is formed becomes the upper surface side. Next, the inside of the chamber 11 is evacuated by a dry pump (not shown).

Next, in the step shown in FIG. 3, the single crystal silicon substrate 25 is isotropically dry-etched through the resist mask 31 to form a recess 33 that becomes a part of the through hole 38 (see FIG. 6).
Specifically, an etching gas containing SF ₆ is made into plasma by inductively coupled plasma (ICP), and silicon is plasma-etched (specifically, isotropic dry etching using F-based radicals). Then, the recess 33 is formed (etching step).
Thus, by using a gas containing SF ₆ as an etching gas when performing isotropic dry etching, the recess 33 can be processed into a good shape.
The depth of the recess 33 when the back surface 25a of the single crystal silicon substrate 25 is used as a reference can be set to 1 μm, for example.

Next, in the step shown in FIG. 4, the side surface 33 a of the recess 33 exposed by plasma etching (in other words, the silicon (single crystal silicon substrate 25) exposed by plasma etching) and the single crystal silicon substrate 25 are exposed. A protective film 34 is formed to cover the surface of the resist mask 31 (the surface including the upper surface 31a of the resist mask 31 and the side surface 31b of the opening 31A) (protective film forming step).
At this stage, the protective film 34 exposes the bottom surface 33 b of the recess 33.

Specifically, the protective film 34 that exposes the bottom surface 33b of the recess 33 is formed by the following method.
First, using 2,3,3,3-tetrafluoropropene as a deposition gas, from the inner surface 33c of the recess 33 exposed by plasma etching (the surface formed by the side surface 33a and the bottom surface 33b) and the single crystal silicon substrate 25 A protective film 34 is formed to cover the exposed surface of the resist mask 31. At this stage, the bottom surface 33 b of the recess 33 is covered with the protective film 34.

Next, the protective film 34 formed on the bottom surface 33b of the recess 33 is selectively removed by anisotropic dry etching using a gas containing SF ₆ as an etching gas.
Thereby, the protective film 34 that covers the side surface 33a of the recess 33 and exposes the bottom surface 33b of the recess 33 is formed.

Thus, the protective film 34 covering the side surface 33a of the recess 33 exposed by plasma etching is formed using 2,3,3,3-tetrafluoropropene having a global warming potential as small as 4 as the deposition gas. Thus, compared with the case where a protective film is formed using C ₄ F ₈ (global warming potential; 10300), which is a conventional deposition gas, the emission of greenhouse gases can be reduced.

  Further, by using 2,3,3,3-tetrafluoropropene as a deposition gas, a protective film having a low reactivity with F radicals (in other words, difficult to be etched) due to film formation with a high C (carbon) ratio. 34 can be formed.

Thereby, the thickness of the protective film 34 formed using 2,3,3,3-tetrafluoropropene can be made thinner than the protective film formed using C ₄ F ₈ .
C ₄ The thickness of the protective film 34 required to obtain a protective film performance equivalent formed using F ₈ is, C ₄ F ₈ 1 /. 4 to the thickness of the protective film formed by using the It may be about 1/2.

Further, by using 2,3,3,3-tetrafluoropropene as the deposition gas, the time for forming the protective film 34 (film formation time) is the same as the case of using C ₄ F ₈ as the deposition gas, or It becomes possible to make it shorter than the case of using C ₄ F ₈ .
Accordingly, it is possible to shorten the plasma etching processing time in which the etching step and the protective film forming step are alternately repeated, so that productivity can be improved.

Further, by using a gas containing SF ₆ as an etching gas when performing anisotropic dry etching (etching for removing the protective film 34 formed on the bottom surface 33b of the recess 33), the bottom surface 33b of the recess 33 is formed. The formed protective film 34 can be selectively removed with high accuracy.

The flow rate of 2,3,3,3-tetrafluoropropene, for example, may be set within a range of 0.2-0.9 times the flow rate of SF _6. Thus, it is possible to obtain the same etching performance as that of C ₄ F ₈ as the deposition gas.

It is preferred that 2,3,3,3 flow of tetrafluoropropene, for example, set within a range of 0.4 to 0.6 times the flow rate of SF _6.
As a result, a good etching shape can be obtained, and even when the same etching step is used, the time required for forming the protective film is shortened, so that the etching rate of the single crystal silicon substrate 25 can be increased. Therefore, productivity can be improved.

Next, in the process shown in FIG. 5, single crystal silicon located below the recess 33 by isotropic dry etching using the protective film 34 as a mask (radical etching by plasma using a gas containing SF ₆ as an etching gas). By etching the substrate 25, a recess 36 having the same shape as the recess 33 and having an inner surface 36c composed of a side surface 36a and a bottom surface 36b is formed (etching step).

  At this time, since the resist mask 31 and the side surface 33a of the recess 33 are covered with the protective film 34, they are not etched. Thereby, it is possible to suppress the opening diameter of the recess 33 shown in FIG. 3 from being increased by the isotropic dry etching, and to reduce the film thickness of the resist mask 31 (in other words, the opening diameter of the opening 31A is increased). , The thickness of the resist mask 31 is reduced).

  Next, in the process shown in FIG. 6, the process shown in FIG. 4 (in other words, the protective film forming step) and the process shown in FIG. 5 (in other words, the etching step) described above are alternately performed. Then, a through hole 38 exposing the surface 42a of the conductor 42 constituting the circuit element layer 41 is formed.

According to the plasma etching method of this embodiment, the etching gas containing SF ₆ excellent in etching processing characteristics is turned into plasma, and silicon is plasma-etched, so that deterioration in etching processing characteristics can be suppressed.

Further, as the deposition gas, 2,3,3,3-tetrafluoropropene having a global warming potential as small as 4 is used to form the protective film 34 covering the side surfaces 33a and 36a of the recesses 33 and 36 exposed by plasma etching. By doing so, compared with the case where a protective film is formed using C ₄ F ₈ (global warming potential; 10300), which is a conventional deposition gas, it is possible to reduce greenhouse gas emissions.

  That is, according to the plasma etching method of the present invention, greenhouse gas emissions can be reduced without deteriorating the etching processing characteristics.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and within the scope of the present invention described in the claims, Various modifications and changes are possible.

For example, in the present embodiment, the gas containing SF ₆ is described as an example of the etching gas, but a gas such as IF ₅ , NF ₃ , or F ₂ may be used instead of SF ₆ .

In this embodiment, as an example, the case where the through-hole 38 is formed in the single crystal silicon substrate 25 using the plasma etching method of this embodiment has been described as an example. The plasma etching method can also be applied when forming MEMS (Micro Electro Mechanical Systems), which is a device in which mechanical element parts, sensors, actuators, and electronic circuits are integrated on a single silicon substrate. The same effect can be obtained.

(Comparative Example 1)
First, a single crystal silicon wafer (diameter 200 mm) that is silicon was prepared. Next, a resist mask having a plurality of openings having different opening diameters (including opening diameters of 30 μm and 50 μm) is formed on the surface of the single crystal silicon wafer by a photolithography technique. Produced.

Next, in place of the deposition gas supply source 15 provided in the plasma etching apparatus 10 shown in FIG. 1, the same as the plasma etching apparatus 10 except that a deposition gas supply source (not shown) for supplying C ₄ F ₈ as a deposition gas is provided. A plasma etching apparatus B (not shown) having a different structure was prepared.
Next, the evaluation sample A was fixed to the substrate mounting surface of the susceptor of the plasma etching apparatus, and then the chamber 11 was evacuated.

Table 1 shows the optimized plasma etching conditions (specifically, the conditions of the etching step and the conditions of the protective film forming step) of Comparative Example 1 when processing the evaluation sample A.
Table 1 shows plasma etching conditions in which the flow rate is optimized in consideration of side wall protection when SF ₆ is used as the etching gas and C ₄ F ₈ is used as the deposition gas.
As shown in Table 1, in Comparative Example 1, the flow rate of C ₄ F ₈ was 450 sccm, and the protective film formation time was 3.8 seconds. The protective film formation time is a processing time in one protective film formation step, and is an optimized time in consideration of the side wall protection.

Next, using the conditions in Table 1, the etching step and the protective film forming step were repeated 19 times.
At this time, as shown in Table 1, in the etching step of Comparative Example 1, SF ₆ which is a gas excellent in etching processing characteristics is used, and in the protective film forming step of Comparative Example 1, the global warming potential is 10300 as a deposition gas. And high C ₄ F ₈ were used.

Table 2 shows the etching rate of the single crystal silicon wafer at the time of the plasma etching and the usage amount (total usage amount) of the deposition gas (in this case, C ₄ F ₈ ) used in the plasma etching treatment.
Here, “the etching rate of the single crystal silicon wafer” means the etching rate of the single crystal silicon when the single crystal silicon is etched through the resist mask having a width of 50 μm.

Referring to Table 2, in Comparative Example 1, the etching rate of the single crystal silicon wafer was 36.5 μm / min, and the amount of deposition gas (in this case, C ₄ F ₈ ) was 4.83 g.
FIG. 7 shows a cross-sectional SEM photograph of a hole having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm formed in the single crystal silicon wafer of the comparative example.

Example 1
Evaluation sample A was produced by the same method as described in Comparative Example 1. Next, the evaluation sample A was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the chamber 11 was evacuated.

Table 3 shows the plasma etching conditions (specifically, the conditions of the etching step and the conditions of the protective film forming step) of Example 1.
In Example 1, SF ₆ was used as the etching gas, and 2,3,3,3-tetrafluoropropene was used as the deposition gas.

That is, in Example 1, in place of the _C 4 _{F 8} is a deposition gas of Comparative Example 1, it differs greatly for the use of lower 2,3,3,3 global warming potential.
As shown in Table 3, in Example 1, the flow rate of 2,3,3,3-tetrafluoropropene was 100 sccm, and the protective film formation time was 3.8 seconds.

  Next, using the conditions shown in Table 3, the etching step and the protective film forming step were repeated 19 times.

Also, the etching rate of the single crystal silicon wafer at the time of the plasma etching, the amount of deposit gas used in the plasma etching process (in this case, 2,3,3,3-tetrafluoropropene) (the total amount used), Are shown in Table 2.
Referring to Table 2, in Example 1, the etching rate of the single crystal silicon wafer was 35.4 μm / min, and the amount of deposition gas (2,3,3,3-tetrafluoropropene in this case) was 0.61 g. there were.

FIG. 8 is a cross-sectional SEM photograph of a hole having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm formed in the single crystal silicon wafers of Examples 1 to 4. In FIG. 8, with the resist mask removed by ashing, a scanning electron microscope (S-4700, manufactured by Hitachi High-Technologies Corporation) was used to observe a cross section of the single crystal silicon wafer in which the holes were formed.
Referring to FIG. 8, it was confirmed that the hole having the opening diameter of 30 μm and the hole having an opening diameter of 50 μm in Example 1 had a shape in which the upper part was slightly expanded, but had no problem. .

(Example 2)
Evaluation sample A was produced by the same method as described in Comparative Example 1. Next, the evaluation sample A was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the chamber 11 was evacuated.

Table 4 shows the plasma etching conditions (specifically, the conditions of the etching step and the conditions of the protective film forming step) of Example 2.
In Example 2, SF ₆ having the same flow rate as that of Example 1 was used as an etching gas, and 2,3,3,3-tetrafluoropropene increased by 100 sccm as compared with Example 1 was used as a deposition gas.

  As shown in Table 4, in Example 2, the flow rate of 2,3,3,3-tetrafluoropropene was 200 sccm, and the protective film formation time was 2.0 seconds.

  Next, using the conditions shown in Table 4, the etching step and the protective film forming step were repeated 22 times.

Also, the etching rate of the single crystal silicon wafer at the time of the plasma etching, the amount of deposit gas used in the plasma etching process (in this case, 2,3,3,3-tetrafluoropropene) (the total amount used), Are shown in Table 2.
Referring to Table 2, in Example 2, the etching rate of the single crystal silicon wafer was 40.0 μm / min, and the amount of deposition gas (in this case, 2,3,3,3-tetrafluoropropene) was 0.73 g. Met.

FIG. 8 shows a cross-sectional SEM photograph of a hole having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm formed in the single crystal silicon wafer of Example 2.
Referring to FIG. 8, it was confirmed that the holes of Example 2 having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm are substantially straight and can be processed into a favorable shape.

(Example 3)
Evaluation sample A was produced by the same method as described in Comparative Example 1. Next, the evaluation sample A was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the chamber 11 was evacuated.

Table 5 shows the plasma etching conditions (specifically, the conditions of the etching step and the conditions of the protective film forming step) of Example 3.
In Example 3, SF ₆ having the same flow rate as that of Example 2 was used as an etching gas, and 2,3,3,3-tetrafluoropropene increased by 100 sccm as compared with Example 2 was used as a deposition gas.

  As shown in Table 5, in Example 3, the flow rate of 2,3,3,3-tetrafluoropropene was 300 sccm, and the protective film formation time was 1.0 second.

  Next, using the conditions shown in Table 5, the etching step and the protective film forming step were repeated 23 times.

Also, the etching rate of the single crystal silicon wafer at the time of the plasma etching, the amount of deposit gas used in the plasma etching process (in this case, 2,3,3,3-tetrafluoropropene) (the total amount used), Are shown in Table 2.
Referring to Table 2, in Example 3, the etching rate of the single crystal silicon wafer was 42.6 μm / min, and the amount of deposition gas (2,3,3,3-tetrafluoropropene in this case) was 0.59 g. Met.

FIG. 8 shows a cross-sectional SEM photograph of a hole having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm formed in the single crystal silicon wafer of Example 3.
Referring to FIG. 8, it was confirmed that the shape of the hole of Example 3 targeted for an opening diameter of 30 μm and the shape of a hole targeted for an opening diameter of 50 μm are substantially straight and can be processed into a favorable shape.

Example 4
Evaluation sample A was produced by the same method as described in Comparative Example 1. Next, the evaluation sample A was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the chamber 11 was evacuated.

Table 6 shows the plasma etching conditions (specifically, the conditions of the etching step and the conditions of the protective film forming step) of Example 4.
In Example 4, SF ₆ having the same flow rate as that of Example 3 was used as an etching gas, and 2,3,3,3-tetrafluoropropene increased by 150 sccm from Example 3 was used as a deposition gas.

  As shown in Table 6, in Example 4, the flow rate of 2,3,3,3-tetrafluoropropene was 450 sccm, and the protective film formation time was 0.8 seconds.

  Next, using the conditions in Table 6, the etching step and the protective film forming step were repeated 23 times.

Also, the etching rate of the single crystal silicon wafer at the time of the plasma etching, the amount of deposit gas used in the plasma etching process (in this case, 2,3,3,3-tetrafluoropropene) (the total amount used), Are shown in Table 2.
Referring to Table 2, in Example 4, the etching rate of the single crystal silicon wafer was 35.5 μm / min, and the amount of deposition gas (in this case, 2,3,3,3-tetrafluoropropene) was 0.72 g. Met.

FIG. 8 shows a cross-sectional SEM photograph of a hole having an opening diameter of 30 μm and a hole having an opening diameter of 50 μm formed in the single crystal silicon wafer of Example 4.
Referring to FIG. 8, it was confirmed that the hole with the opening diameter of 30 μm and the hole with an opening diameter of 50 μm in Example 4 had a shape with a slightly expanded bottom, but had no problem. .

(Summary of results of Comparative Example 1 and Examples 1 to 4)
From the cross-sectional SEM photograph of the comparative example shown in FIG. 7 and the cross-sectional SEM photographs of Examples 1 to 4 shown in FIG. 8, the flow rate of 2,3,3,3-tetrafluoropropene, which is the deposition gas, is changed to the flow rate of SF ₆ ( In this case, it is confirmed that an etching shape (refer to FIG. 7) equivalent to the case where C ₄ F ₈ is used as the deposition gas can be obtained by setting within a range of 0.2 to 0.9 times (500 sccm). did it.

In addition, by setting the flow rate of 2,3,3,3-tetrafluoropropene, which is the deposition gas, within the range of 0.4 to 0.6 times the flow rate of SF ₆ (in this case, 500 sccm), a substantially straight shape It was confirmed that the excellent holes defined as above could be formed.

Moreover, from the results of Examples 1 to 4 shown in Table 2, it was confirmed that the protective film formation time can be shortened as the flow rate of 2,3,3,3-tetrafluoropropene, which is a deposition gas, increases.
From the results of Comparative Example 1 and Examples 1 to 4 shown in Table 2, by using 2,3,3,3-tetrafluoropropene as the depogas, the depogas of Comparative Example 1 (specifically, C ₄ F ₈ It was confirmed that the amount of depot gas used can be greatly reduced and the amount of greenhouse gas emissions can be significantly reduced compared with the case of using).

Moreover, from the results of Examples 1 to 4 shown in Table 2, it was confirmed that the etching rates of Examples 1 and 4 were slower than the etching rates of Examples 2 and 3.
The reason why the etching rate of Example 1 is slow is that the protective film forming step is long.

Further, the reason why the etching rate of Example 4 is slow is that 2,3,3,3-tetrafluoropropene is a highly polymerizable gas, and therefore, when the decomposition is insufficient due to a large flow rate, unbonded It is thought that the etching rate does not occur because the polymerization including the portion occurs, the protective film is thick, and the F radicals of the etchant are consumed in the many unbonded portions existing in the film during the etching step.
From the results of Examples 1 to 4 shown in Table 2, it was confirmed that the etching rates of Examples 2 and 3 were about 10% faster than the etching rates of Examples 1 and 4.

To summarize the above results, the flow rate of 2,3,3,3-tetrafluoropropene, which is the depogas, is set within a range of 0.2 to 0.9 times the flow rate of SF ₆ (in this case, 500 sccm). It was confirmed that an etching shape (not shown) equivalent to the case of using C ₄ F ₈ as the deposition gas can be obtained and the amount of deposition gas used can be reduced.

In addition, by setting the flow rate of 2,3,3,3-tetrafluoropropene, which is the deposition gas, within the range of 0.4 to 0.6 times the flow rate of SF ₆ (in this case, 500 sccm), a substantially straight shape As a result, it was confirmed that productivity could be improved by reducing the amount of deposition gas used, reducing the amount of deposition gas used, and improving (faster) the etching rate.

(Comparative Example 2)
First, a single crystal silicon wafer (diameter 200 mm, thickness 725 μm), which is silicon, was prepared. Next, an evaluation sample B was produced by forming a resist mask having a plurality of openings with an opening diameter of 20 μm on the surface of the single crystal silicon wafer by photolithography.

  Next, the evaluation sample B was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the inside of the chamber 11 was evacuated.

Next, using the conditions of Table 1 described above (conditions of Comparative Example 1), the etching step and the protective film forming step were repeated to form a through hole (not shown) covered with the protective film. .
Next, using Quanta SXM manufactured by ULVAC-PHI, the XPS of the protective film formed on the side wall of the through hole of the comparative example 2 (specifically, the side wall located at the center in the depth direction of the through hole) X-ray Photoelectron Spectroscopy) analysis was performed.

Table 7 shows the ratio of C (%), F (%), and F / C of Comparative Example 2 obtained by processing the data acquired from this analysis, and the ratio of CF: CF2: CF3. Show. Table 7 shows the ratio of C (%), F (%), and F / C of Comparative Example 2 and Example 5 and the ratio of CF: CF ₂ : CF ₃ (in other words, the number of fluorine bonded to carbon). Is a table).

(Example 5)
First, an evaluation sample B was produced by the method described in Comparative Example 2. Next, the evaluation sample B was fixed to the substrate mounting surface 12a of the susceptor 12 of the plasma etching apparatus 10 shown in FIG. 1, and then the inside of the chamber 11 was evacuated.

Next, using the conditions of Table 5 described above (the conditions of Example 3), the etching step and the protective film forming step were repeated to form a through hole (not shown) covered with the protective film. .
Next, using Quanta SXM manufactured by ULVAC-PHI, the XPS of the protective film formed on the side wall of the through hole of Example 5 (specifically, the side wall located at the center in the depth direction of the through hole) X-ray Photoelectron Spectroscopy) analysis was performed. The results are shown in Table 7.

(Regarding the results of Comparative Example 2 and Example 5)
Referring to Table 7, in the protective film of Comparative Example 2, the F / C ratio is close to twice, the CF ₂ ratio is about 1.6 times the CF ratio, and the CF ₂ ratio is the CF ₃ ratio. It was confirmed that a polymer mainly composed of CF ₂ was formed.

On the other hand, in the protective film of Example 5, the F / C ratio is lower than the F / C ratio of Comparative Example 2, and the number of carbon-carbon bonds (C—C bonds) is larger than that of CF _2. I understood.
Further, since the ratio of CF ₂ and CF _{3 in} Example 5 is lower than the ratio of CF ₂ and CF ₃ in Comparative Example 2, a carbon-carbon three-dimensional network is formed, and fluorine is partially converted to carbon. It was speculated that it was a combined composition.

  From the above results, by using 2,3,3,3-tetrafluoropropene as the deposition gas, it becomes possible to form a dense protective film having a low reactivity with respect to F radicals. It was confirmed that a thin protective film was sufficient.

  The present invention can be applied to a plasma etching method in which an etching step and a protective film forming step are alternately repeated.

  DESCRIPTION OF SYMBOLS 10 ... Plasma etching apparatus, 11 ... Chamber, 11A ... Upper wall, 11B ... Lower wall, 12 ... Susceptor, 12a ... Substrate mounting surface, 13 ... Plasma generating part, 13-1 ... Coil, 13-2 ... High frequency power supply, DESCRIPTION OF SYMBOLS 14 ... Etching gas supply source, 15 ... Depo gas supply source, 17 ... Etching gas supply line, 18 ... Depo gas supply line, 22 ... Exhaust gas line, 25 ... Single crystal silicon substrate, 25a ... Front surface, 25b ... Back surface, 30 ... Resist mask Substrate, 31 ... resist mask, 31a ... upper surface, 31b ... side surface, 31A ... opening, 33,36 ... concave, 33a, 36a ... side surface, 33b, 36b ... bottom surface, 33c, 36c ... inner surface, 34 ... protective film, 38 ... through hole, 41 ... circuit element layer, 42 ... conductor, 42a ... surface

Claims (3)

A chamber containing a susceptor on which silicon is placed;
An etching gas supply source for supplying a gas containing SF ₆ (excluding 1,3,3,3-tetrafluoropropene) as an etching gas for etching the silicon into the chamber via an etching gas supply line When,
A plasma generator disposed around the chamber;
A plasma etching apparatus comprising: a deposition gas supply source for supplying 2,3,3,3-tetrafluoropropene, which is a deposition gas, through the deposition gas supply line in the chamber. A chamber containing a susceptor on which silicon is placed;
An etching gas supply source for supplying an etching gas (except for 1,3,3,3-tetrafluoropropene) into the chamber via an etching gas supply line;
A plasma generating unit disposed around the chamber and converting the etching gas into plasma;
Depot gas supply for supplying 2,3,3,3-tetrafluoropropene, which is a deposition gas for forming a sidewall protective film that covers the sidewall of the silicon exposed by the plasma etching, into the chamber via a deposition gas supply line And a plasma etching apparatus.   The plasma etching apparatus according to claim 1 or 2, wherein the etching gas and the deposition gas can be alternately and repeatedly supplied into the chamber.