Method for etching a pi structure sheet for preventing damage to an oxygen-silicon substrate

Abstract

The application belongs to the technical field of semiconductor, and particularly relates to an etching method of PI structure piece for preventing damage of silicon-oxygen substrate. In the etching of the PI structure piece, F-based gas is used for main etching in the early stage, and when the PI film thickness is only 10% left, the process gas is switched from F-based gas to O2. Since O2 can have combustion reaction with the PI film and the PR film, but has no reaction with the silicon-oxygen substrate, when the process gas is switched from F-based gas to O2 for etching, the selectivity ratio of the PI film to the silicon-oxygen substrate is extremely high, the etching of the PI film with 10% H left can be completed without damaging the silicon-oxygen substrate, so that the PI structure piece has perfect appearance, the silicon-oxygen substrate is rarely over-etched or even not over-etched, the over-etching problem of the silicon-oxygen substrate under the PI structure piece is solved, and the micro-groove appearance problem is also solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor, and particularly relates to an etching method of PI structure piece for preventing damage of silicon oxide substrate. BACKGROUND

[0002] The advent and development of 5G communication technology have put forward higher requirements for the CD (Critical Dimension, simply referred to as CD, feature size), etching angle and aspect ratio of etching of the semiconductor industry, and the etching research of these morphological features is completed through the etching of PI (Polyimide, simply referred to as PI, polyimide) structure piece.

[0003] The PI structure piece is composed of a silicon oxide substrate, a PI film and a PR (Photo Resist, simply referred to as PR, photoresist) film. The silicon oxide substrate is located at the lowermost layer as a substrate, the second layer is the PI film, and the uppermost layer is the PR film. The PR film is developed through photolithography, so that the PI structure piece has a certain structure. The compositions of the PI film and the PR film are both hydrocarbons, the molecular compositions are similar, and the selection ratio is approximately 1:1. Therefore, when the PI structure piece is etched, a PR film with sufficient thickness is needed to maintain the mask pattern of the PR film.

[0004] The mainstream etching method of the PI structure piece is etching based on F-based gas, which has a big problem: F-based gas can cause over-etching of the silicon oxide substrate. This is because F-based gas not only has good etching effect on the PI film and the PR film, but also maintains good etching performance on the silicon oxide substrate. This leads to the fact that when F-based gas is used to etch the PI structure piece, after the trench etching of the PI film is completed, the remaining F-based gas will etch the silicon oxide substrate of the PI structure piece, resulting in a large loss of the silicon oxide substrate of the PI structure piece. SUMMARY

[0005] The purpose of the present application is to overcome the deficiencies in the prior art and provide an etching method of PI structure piece for preventing damage of silicon oxide substrate. In the etching process of the PI structure piece, the process gas is switched from F-based gas which has good etching performance on the PR film, the PI film and the silicon oxide substrate to a process gas which has a larger selection ratio on the silicon oxide, so as to complete the etching of the PI film and reduce the over-etching phenomenon of the silicon oxide substrate.

[0006] To achieve the above technical purposes, the technical scheme adopted by the embodiments of the present application is as follows:

[0007] An etching method of PI structure piece for preventing damage of silicon oxide substrate, the PI structure piece sequentially comprises a PR film, a PI film and a silicon oxide substrate from top to bottom, and comprises the following steps:

[0008] Step S1, a process gas with a pressure of 5-20 mT is introduced into the etching reaction chamber, the process gas includes F-based gas and auxiliary gas, the F-based gas generates F-based plasma under the action of a TCP (Transformer Coupled Plasma, TCP for short) radio frequency power source;

[0009] Step S2, the concentration of the ionized F-based plasma is controlled at 10 9 -10 12 cm ⁻3 , and a double helix vortex is formed under the action of the TCP radio frequency power source;

[0010] Step S3, the double helix vortex formed by the F-based plasma moves to the PI film in the PI structure piece under the traction of a Bias radio frequency generator with a power of 100-300 W;

[0011] Step S4, the PI film reacts with the charged ions in the F-based plasma to form an etching trench;

[0012] Step S5, when the OES (Optical Emission Spectroscopy, OES for short) device captures that the thickness of the PI film is only 10% H, the process gas is switched, and the process gas is switched to O2 or a mixed gas of O2 and N2, wherein H is the thickness of the PI film;

[0013] Step S6, the O2 or the mixed gas of O2 and N2 in the etching reaction chamber maintains a pressure of 5-20 mT, and O plasma is generated under the action of the TCP radio frequency power source;

[0014] Step S7, the concentration of the ionized O plasma is controlled at 10 9 -10 12 cm ⁻3 , and a double helix vortex is formed under the action of the TCP radio frequency power source;

[0015] Step S8, the double helix vortex formed by the O plasma moves to the PI film under the traction of a Bias radio frequency generator with a power of 100-300 W;

[0016] Step S9, the O plasma and the PI film occur a combustion reaction, and the etching of the remaining 10% H of the PI film is completed.

[0017] Further, the F-based gas in step S1 is derived from one or more of CF4, CHF3, and C4F8, and the volume flow rate of the F-based gas is 60-100 sccm.

[0018] Further, the auxiliary gas in step S1 includes Ar, and further includes O2 or N2 (O2 can promote the generation of more F radicals, and Ar or N2 mainly plays a role in maintaining the plasma atmosphere), wherein the volume flow rate of Ar is 10-40 sccm, the volume flow rate of O2 is 10-20 sccm, and the volume flow rate of N2 is 10-30 sccm.

[0019] Further, in the PI structure sheet, the thickness H of the PI film is 1-2 μm, and the thickness of the PR film is 2-3 μm.

[0020] When the process gas is O2, the volume flow rate of O2 is 30-60 sccm.

[0021] When the process gas is a mixed gas of O2 and N2, the volume flow rate of O2 in the mixed gas is 30-60 sccm, and the volume flow rate of N2 is 50-140 sccm.

[0022] Further, in steps S1 and S2, the power of the TCP radio frequency power supply is 700-1000 W.

[0023] In steps S6 and S7, the power of the TCP radio frequency power supply is 500-900 W.

[0024] The technical scheme provided by the embodiment of the application has the following beneficial effects:

[0025] The original F radical one-step etching method is optimized to a two-step etching method of F radical etching first and O2 etching later. The PI structure sheet is etched mainly by F radicals in the early stage, and when the PI film thickness is only 10% H, the process gas is switched from F radical gas to O2 or a mixed gas of O2 and N2 for etching. O2 can have a combustion reaction with the PI film and the PR film, but has substantially no reaction with the oxygen-silicon substrate. The addition of N2 can dilute the concentration of O2, so that O2 is more uniformly distributed and the speed of the combustion reaction is more easily controlled. Therefore, when the process gas is switched from F radical gas to O2 for etching, the selectivity of the PI film / oxygen-silicon substrate is greatly improved, so that the PI film can be etched to a thickness of 10% H without damaging the oxygen-silicon substrate. In this way, the PI structure sheet can be etched to a perfect shape, and the oxygen-silicon substrate is over-etched little or not at all. The problem of over-etching of the oxygen-silicon substrate of the PI structure sheet is solved, and the problem of micro-groove shape is also solved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a scanning electron microscope image of the PI structure sheet after etching of the PI film in Example 1.

[0027] Figure 2is a scanning electron microscope image of a PI structure piece after etching of the PI film in Example 2.

[0028] Figure 3 is a scanning electron microscope image of a PI structure piece after etching of the PI film in Example 3.

[0029] Figure 4 is a scanning electron microscope image of a PI structure piece after etching of the PI film in Comparative Example 1.

[0030] Figure 5 is a scanning electron microscope image of a PI structure piece after etching of the PI film in Comparative Example 2.

[0031] Figure 6 is a scanning electron microscope image of a PI structure piece after etching of the PI film in Comparative Example 3.

[0032] BRIEF DESCRIPTION OF DRAWINGS DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be given below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and should not be used to limit the present application.

[0034] Example 1

[0035] An etching method of a PI structure piece for preventing damage to a silicon oxide substrate, comprising the following steps:

[0036] Step S1, a process gas with a total pressure of 5 mT (mtorr, mT for short) is introduced into an etching reaction chamber, the process gas comprising an F-based gas (derived from CF4) and a mixed gas of O2 and Ar, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source with a power of 700 W;

[0037] The volume flow rate of the F-based gas is 60 sccm, the volume flow rate of O2 is 10 sccm, and the volume flow rate of Ar is 10 sccm;

[0038] Step S2, the concentration of the ionized F-based plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 700 W;

[0039] Step S3, the double helix vortex formed by the F-based plasma moves towards the PI film under the traction of a Bias radio frequency generator with a power of 100 W;

[0040] Step S4, the PI film reacts with the charged ions in the F-based plasma to form an etching trench;

[0041] Step S5, when the thickness of the PI film is only 10% H, the OES device captures, wherein H is the thickness of the PI film, H = 2 μm, switches the process gas, and the process gas is switched to a mixed gas of O2 and N2, the volume flow rate of O2 is 30 sccm, and the volume flow rate of N2 is 50 sccm;

[0042] Step S6, the mixed gas of O2 and N2 in the etching reaction chamber maintains a pressure of 5 mT, and O plasma is generated under the action of a TCP radio frequency power source with a power of 500 W;

[0043] Step S7, the concentration of ionized O plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source;

[0044] Step S8, the double helix vortex formed by O plasma moves to the PI film under the traction of a Bias radio frequency generator with a power of 100 W;

[0045] Step S9, O plasma and PI film have a combustion reaction, and the etching of the remaining 10% H PI film is completed, and the scanning electron microscope graph of the PI structure piece after etching is shown in Figure 1 .

[0046] Example 2

[0047] An etching method of a PI structure piece for preventing damage to an oxygen-silicon substrate, comprising the following steps:

[0048] Step S1, a process gas with a total pressure of 12 mT is introduced into the etching reaction chamber, and the process gas includes F-based gas (from CF4) and mixed gas of O2 and Ar, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source with a power of 900 W;

[0049] The volume flow rate of the F-based gas is 80 sccm, the volume flow rate of O2 is 20 sccm, and the volume flow rate of Ar is 30 sccm;

[0050] Step S2, the concentration of ionized F-based plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 900 W;

[0051] Step S3, the double helix vortex formed by the F-based plasma moves to the PI film under the traction of a Bias radio frequency generator with a power of 200 W;

[0052] Step S4, the PI film is reacted with the charged ions in the F-based plasma to form an etching trench;

[0053] Step S5, when the thickness of the PI film is only 10% H, the OES device is switched to a mixed gas of O2 and N2, the volume flow rate of O2 is 50 sccm, and the volume flow rate of N2 is 100 sccm, where H is the thickness of the PI film, H = 2 μm;

[0054] Step S6, the mixed gas of O2 and N2 in the etching reaction chamber maintains a pressure of 12 mT, and O plasma is generated under the action of a TCP radio frequency power source with a power of 700 W;

[0055] Step S7, the concentration of the ionized O plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 700 W;

[0056] Step S8, the double helix vortex formed by the O plasma moves to the PI film under the traction of a Bias radio frequency generator with a power of 200 W;

[0057] Step S9, the O plasma and the PI film undergo a combustion reaction, and the etching of the remaining 10% H of the PI film is completed, and the scanning electron microscope image of the PI structure piece after etching is shown in Figure 2 .

[0058] Example 3

[0059] An etching method of a PI structure piece for preventing damage to an oxygen-silicon substrate, comprising the following steps:

[0060] Step S1, a process gas with a total pressure of 20 mT is introduced into an etching reaction chamber, the process gas includes F-based gas (derived from CF4) and a mixed gas of O2 and Ar, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source with a power of 1000 W;

[0061] The volume flow rate of the F-based gas is 100 sccm, the volume flow rate of O2 is 20 sccm, and the volume flow rate of Ar is 40 sccm;

[0062] Step S2, the concentration of the ionized F-based plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 1000 W;

[0063] Step S3, the double helix vortex formed by the F-based plasma moves to the PI film under the traction of the Bias radio frequency generator with a power of 300 W;

[0064] Step S4, the PI film reacts with the charged plasma in the F-based plasma to form an etching groove;

[0065] Step S5, when the OES device captures the PI film with a thickness of only 10% H, H is the thickness of the PI film, H = 2 μm, the process gas is switched, and the process gas is switched to a mixed gas of O2 and N2, the volume flow rate of O2 is 60 sccm, and the volume flow rate of N2 is 140 sccm;

[0066] Step S6, the mixed gas of O2 and N2 in the etching reaction chamber maintains a pressure of 20 mT, and O plasma is generated under the action of the TCP radio frequency power source with a power of 900 W;

[0067] Step S7, the ionization generated O plasma concentration is controlled at 10 10 cm ⁻3 , and a double helix vortex is formed under the action of the TCP radio frequency power source with a power of 900 W;

[0068] Step S8, the double helix vortex formed by the O plasma moves to the PI film under the traction of the Bias radio frequency generator with a power of 300 W;

[0069] Step S9, the O plasma and the PI film have a combustion reaction, and the etching of the remaining 10% H PI film is completed, and the scanning electron microscope image of the PI structure piece after etching is shown in Figure 3 .

[0070] Example 4

[0071] An etching method of a PI structure piece for preventing damage to an oxygen-silicon substrate, which is different from example 1 in that the ionization generated F-based plasma concentration in step S2 is controlled at 10 9 cm ⁻3 ; the ionization generated O plasma concentration in step S7 is controlled at 10 9 cm ⁻3 , and the remaining conditions and parameters are the same as those in example 1.

[0072] Example 5

[0073] An etching method of a PI structure piece for preventing damage to an oxygen-silicon substrate, which is different from example 1 in that the ionization generated F-based plasma concentration in step S2 is controlled at 10 12 cm ⁻3 ; the ionization generated O plasma concentration in step S7 is controlled at 10 12 cm⁻3 The rest of the conditions and parameters are the same as in Example 1.

[0074] Comparative Example 1

[0075] An etching method of a PI structure piece, comprising the following steps:

[0076] Step S1, a process gas with a pressure of 5mT is introduced into the etching reaction chamber, the process gas is a mixed gas of O2 and N2, the volume flow rate of O2 is 30sccm, and the volume flow rate of N2 is 50sccm, and O plasma is generated under the action of a TCP radio frequency power source with a power of 500W;

[0077] Step S2, the concentration of the ionized O plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 500W;

[0078] Step S3, the double helix vortex formed by the O plasma moves to the PI film in the PI structure piece under the traction of a Bias radio frequency generator with a power of 100W, an etching groove is formed, and the etching is stopped after the PI film with a thickness of H=2μm is etched completely, and the scanning electron microscope image of the PI structure piece after etching is shown in Figure 4 .

[0079] Comparative Example 2

[0080] An etching method of a PI structure piece, comprising the following steps:

[0081] Step S1, a process gas with a pressure of 5mT is introduced into the etching reaction chamber, the process gas includes a F-based gas (from CF4) and a mixed gas of O2 and Ar, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source with a power of 700W;

[0082] The volume flow rate of the F-based gas is 60sccm, the volume flow rate of O2 is 10sccm, and the volume flow rate of Ar is 10sccm;

[0083] Step S2, the concentration of the ionized F-based plasma is controlled to be 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 700W;

[0084] Step S3, the double helix vortex formed by the F-based plasma moves to the PI film in the PI structure piece under the traction of a Bias radio frequency generator with a power of 100W;

[0085] Step S4, the PI film reacts with the charged ions in the F-based plasma to form an etching groove;

[0086] Step S5, when the thickness of the PI film is only 10% H, H is the thickness of the PI film, H = 2 μm, the process gas is switched, the process gas includes F-based gas (derived from CF4) and mixed gas of O2 and N2, the volume flow rate of the F-based gas is 60 sccm, the volume flow rate of O2 is 10 sccm, and the volume flow rate of N2 is 10 sccm;

[0087] Step S6, the pressure in the etching reaction chamber is maintained at 5 mT, and plasma is generated under the action of a TCP radio frequency power source with a power of 700 W;

[0088] Step S7, the ionized F-based plasma concentration is controlled at 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 700 W;

[0089] Step S8, the double helix vortex formed by the F-based plasma moves to the PI film under the traction of a Bias radio frequency generator with a power of 100 W;

[0090] Step S9, the F-based plasma and the PI film have a combustion reaction, and the etching of the remaining 10% H of the PI film is completed, and the scanning electron microscope image of the PI structure piece after etching is shown in Figure 5 .

[0091] Comparative Example 3

[0092] An etching method of a PI structure piece, comprising the following steps:

[0093] Step S1, a process gas with a total pressure of 5 mT is introduced into the etching reaction chamber, the process gas includes F-based gas (derived from CF4) and mixed gas of O2 and N2, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source with a power of 700 W;

[0094] The volume flow rate of the F-based gas is 60 sccm, the volume flow rate of O2 is 10 sccm, and the volume flow rate of N2 is 10 sccm;

[0095] Step S2, the ionized F-based plasma concentration is controlled at 10 10 cm ⁻3 , and a double helix vortex is formed under the action of a TCP radio frequency power source with a power of 700 W;

[0096] Step S3, the double helix vortex formed by F-based plasma moves to the PI film under the traction of the Bias radio frequency generator with a power of 100 W, forms an etching groove, and etches the PI film with a thickness of H=2 μm completely. The scanning electron microscope (SEM) image of the PI structure sheet after etching is shown in Figure 6 .

[0097] The PI structure sheets used in Examples 1-5 and Comparative Examples 1-3 are the same, the thickness of the PI film H is 2 μm, and the thickness of the PR film is 3 μm. From Figures 1-3 it can be seen that the two-step etching method in Examples 1-3 of the present application can ensure that the PI film is etched completely with 10% H remaining while the oxygen-silicon substrate is not damaged, so as to achieve the purpose of little or no over-etching of the oxygen-silicon substrate while ensuring that the PI structure sheet can be etched to perfect morphology, successfully solve the over-etching problem of the oxygen-silicon substrate of the PI structure sheet, and also solve the micro-groove morphology problem. In Comparative Example 1, only O2 and N2 mixed gas is used for one-step etching, although it can ensure that the oxygen-silicon substrate is not over-etched, but due to the uncontrollable O2 combustion reaction, it will lead to poor morphology angle, as shown in Figure 4 . In Comparative Example 3, F-based gas is used for one-step etching, which cannot avoid the over-etching problem of the oxygen-silicon substrate, as shown in Figure 6 . In Comparative Example 2, although two-step etching is used, F-based gas is used for etching in both steps, which still cannot avoid the over-etching problem of the oxygen-silicon substrate, as shown in Figure 5 .

[0098] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for etching a PI structure sheet for preventing damage of an oxygen-silicon substrate, the PI structure sheet comprising, from top to bottom, a PR thin film, a PI thin film, and an oxygen-silicon substrate, the method comprising: forming a first mask layer on the PI thin film; forming a second mask layer on the first mask layer; and etching the PI structure sheet by using the second mask layer as a mask. The method comprises the following steps: Step S1, introducing process gas with a pressure of 5-20 mT into the etching reaction chamber, wherein the process gas comprises F-based gas and auxiliary gas, and the F-based gas generates F-based plasma under the action of a TCP radio frequency power source; Step S2, the ionized F-based plasma concentration is controlled at 10 9 -10 12 cm ⁻3 , and a double helix vortex is formed under the action of the TCP radio frequency power supply; Step S3, the double helix vortex formed by the F-based plasma moves to the PI film in the PI structure piece under the traction of a Bias radio frequency generator; Step S4, the PI film reacts with charged ions in the F-based plasma to form an etching groove; Step S5, when the thickness of the PI film is only 10% H (H is the thickness of the PI film), the OES device switches the process gas to O2 or a mixture of O2 and N2; Step S6, maintaining the pressure of O2 or the mixture of O2 and N2 in the etching reaction chamber at 5-20 mT, and generating O plasma under the action of a TCP radio frequency power source; The ionized O plasma concentration is controlled at 10 9 -10 12 cm ⁻3 , and a double helix vortex is formed under the action of the TCP radio frequency power supply; Step S8, the double helix vortex formed by the O plasma moves to the PI film under the traction of a Bias radio frequency generator; Step S9, the O plasma and the PI film have a combustion reaction to complete the etching of the remaining 10% H PI film.

2. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In step S1, the F-based gas is derived from one or more of CF4, CHF3, and C4F8.

3. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of an oxygen-silicon substrate. In step S1, the volume flow rate of the F-based gas is 60-100 sccm.

4. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In step S1, the auxiliary gas comprises Ar, and the volume flow rate of Ar is 10-40 sccm.

5. The etching method for preventing damage to the silicon oxide substrate of the PI structure wafer according to claim 4, characterized in that, In step S1, the auxiliary gas further comprises O2 or N2, the volume flow rate of O2 is 10-20 sccm, and the volume flow rate of N2 is 10-30 sccm.

6. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In the PI structure piece, the thickness H of the PI film is 1-2 μm, and the thickness of the PR film is 2-3 μm.

7. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In step S5, when the process gas is O2, the volume flow rate of O2 is 30-60 sccm.

8. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In step S5, when the process gas is a mixture of O2 and N2, the volume flow rate of O2 in the mixture is 30-60 sccm, and the volume flow rate of N2 is 50-140 sccm.

9. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In steps S1 and S2, the power of the TCP radio frequency power source is 700-1000 W. In steps S6 and S7, the power of the TCP radio frequency power source is 500-900 W.

10. The method of claim 1, wherein the PI structure sheet is a PI structure sheet for preventing damage of a silicon substrate. In steps S3 and S8, the power of the Bias radio frequency generator is 100-300 W.

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