Quartz etching method based on C4F6 mixed gas

Abstract

The invention relates to a quartz etching method based on a C4F6 (hexafluoro-2-butyne) mixed gas. According to the method, the developed quartz glass substrate is etched through a special etching gas ratio and etching parameters, and the photoresist on the quartz glass substrate is removed, so that the quartz glass device is obtained. The method is applied to micro-nano machining and integrated circuit processes, and replacement of original etching technologies based on CHF3 mixed gas and the like is achieved. According to the method, the high etching selection ratio is achieved while it is guaranteed that the etching speed is high and the etching dip angle perpendicularity is good, and etching of materials such as quartz and silicon oxide can be effectively achieved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing application technology, specifically relating to a quartz etching method based on a C4F6 mixed gas. Background Technology

[0002] Quartz possesses superior properties such as high temperature resistance, low coefficient of thermal expansion, excellent light transmittance, good electrical insulation, and corrosion resistance. Its superior performance and wide range of end-use applications make it a key raw material in the semiconductor industry. Devices based on quartz materials are widely used in optical communication and photonics integration, MEMS and sensors, as well as advanced packaging and interconnects.

[0003] In the field of optical communication, quartz transmission gratings can replace volume holographic gratings (VPHGs) to solve their problems of narrow bandwidth and high ultraviolet absorption, thereby improving the performance of telescopes and spectrometers. In the field of sensors, quartz resonators utilize the piezoelectric effect to achieve a stable conversion from mechanical vibration to electrical oscillation, offering advantages such as high frequency stability and miniaturized packaging. In the field of advanced packaging, through-hole quartz (TGV) achieves three-dimensional interconnection by etching metal filling into a glass substrate, breaking through the limitations of traditional two-dimensional wiring and offering advantages such as small package size, low power consumption, and high speed.

[0004] Wet etching is a relatively fast method for etching quartz glass, but its isotropic nature makes it difficult to achieve structures with steep sidewalls and high aspect ratios. Dry etching, on the other hand, offers advantages such as anisotropy and controllable etching processes. Therefore, dry etching techniques for quartz have always been a hot research topic. However, although the main component of quartz is SiO2, it is crystalline silicon dioxide, unlike SiO2 deposited on silicon wafers. Silicon and oxygen atoms in quartz exhibit a highly ordered and tightly packed periodic arrangement in three-dimensional space. This regular structure makes the chemical bonds (Si-O bonds) very strong and stable, requiring higher energy to break. Therefore, under the same conditions, etching quartz is more difficult.

[0005] C4F6 (including hexafluoro-2-butyne, hexafluorobutadiene, and hexafluorocyclobutene), taking the preparation of hexafluoro-2-butyne as an example, is mainly generated as a byproduct during the hydrogenation and dechlorination of 2,3-dichloro-1,1,1,4,4,4-hexafluoro-2-butene (CFO-1316) to prepare 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336). CFO-1316 is a highly toxic byproduct in the production of fluorochemical products and is a substance whose production and emission are restricted by the state. Converting CFO-1316 into C4F6 is a more environmentally friendly exhaust gas treatment method (patent number: 202111039241.3), and applying C4F6 to the dry etching field of the micro-nano processing industry is conducive to further improving the economic benefits of enterprises and achieving sustainable development.

[0006] To further optimize the etching effect of dry etching of quartz, researchers have proposed various gas combination schemes and different mask selections. Quan Xueling et al. (Patent No.: 202111014187.7) designed a method for fabricating fine micro / nano glass structures based on CHF3, C2F6, C4F8, or CF4 gases. However, this method has a relatively low etching selectivity when using photoresist as a mask, making it impossible to etch structures with high aspect ratios. Liu Jian et al. (Patent No.: 202210848946.8) proposed a deep etching process for quartz crystals using CF4 as the etching gas and CHF3 as the protective gas. However, this process uses Ni as a hard mask, is complex, and was only tested at a large linewidth of around 30µm, without mentioning the etching effect at small linewidths. Daniel et al. (Patent No.: 201310734714.0) proposed an etching method for high aspect ratio vertical glass vias based on SF6 gas. However, this method uses metal or semiconductor as a hard mask, the overall process is very complex, and the requirements for processing equipment are also very high, which is not conducive to large-scale production. Summary of the Invention

[0007] To address the poor performance of existing dry etching techniques when etching quartz, a quartz etching method based on a C4F6 (hexafluoro-2-butyne) mixed gas is proposed. This method can be used for etching dielectric materials such as silicon oxide and quartz. Applied to micro / nano fabrication and integrated circuit processes, this method replaces previous etching techniques based on CHF3 mixed gases. While maintaining a fast etching rate and good etching tilt perpendicularity, this method also achieves a high etching selectivity, effectively etching materials such as quartz and silicon oxide.

[0008] Traditional methods using gases like CHF3, CF4, and SF6 as the primary etching gases are suitable for etching conventional silicon dioxide thin films. However, due to the different chemical structures of quartz and silicon dioxide films—quartz is non-conductive and its etching rate is higher than that of silicon dioxide films—directly using gases like CHF3 requires a hard mask to achieve high aspect ratio morphologies, making the process complex. The C4F6 used in this invention forms a fluorocarbon film during etching, protecting the photoresist and thus enabling the acquisition of high aspect ratio morphologies on glass substrates without the need for a hard mask.

[0009] However, using only C4F6, especially at high flow rates, can lead to deposition effects, while reducing the flow rate results in a slower etching rate. This invention addresses this by introducing O2, which reduces film formation and avoids deposition effects. Simultaneously, introducing Ar and increasing the RF power enhances the physical bombardment intensity of Ar on the sample surface, disrupting the thin film formed thereon. Through the combined action of O2 and Ar, this invention achieves high aspect ratio etching by reducing film formation while maintaining a high etching rate.

[0010] The objective of this invention can be achieved through the following methods: This invention relates to the application of a C4F6 mixed gas in quartz etching, characterized in that the C4F6 mixed gas is an oxygen-containing etching gas or an oxygen-free etching gas; Oxygen-based etching gases include C4F6, O2, and Ar; Oxygen-free etching gases include C4F6 and Ar.

[0011] As one embodiment of the present invention, the volume ratio of C4F6, O2 and Ar in the C4F6 mixed gas is 5~20:0~10:40~100.

[0012] As one embodiment of the present invention, when the C4F6 mixed gas is C4F6, O2, and Ar, the flow rates of each component during etching are 5~20 sccm for C4F6, 5~10 sccm for O2, and 40~100 sccm for Ar, with an RF power of 150W~300W; when the C4F6 mixed gas is C4F6 and Ar, the flow rates of each component during etching are 5~6 sccm for C4F6 and 40~100 sccm for Ar, with an RF power of 200W~300W.

[0013] As one embodiment of the present invention, a more preferred embodiment is that when the C4F6 mixed gas is C4F6, O2, and Ar, the flow rates of each component during etching are 10~20 sccm for C4F6, 8~10 sccm for O2, and 40~80 sccm for Ar, and the RF power is adjusted to 150W~200W. When the C4F6 mixed gas is C4F6 and Ar, the flow rates of each component during etching are 5~6 sccm for C4F6 and 80~100 sccm for Ar, with the RF power adjusted to 250W~300W. More preferably, the flow rates are 5 sccm for C4F6 and 90~100 sccm for Ar, with the RF power adjusted to 290W~300W.

[0014] As one embodiment of the present invention, the C4F6 used in the present invention is hexafluoro-2-butyne.

[0015] This invention relates to a quartz etching method based on a C4F6 (hexafluoro-2-butyne) mixed gas, comprising the following steps: S1. Spin-coat photoresist onto the surface of a quartz glass substrate, transfer the pattern to be processed onto the photoresist on the substrate surface, and obtain the developed quartz glass substrate. S2. Set the etching gas ratio and etching parameters, and perform etching treatment on the developed quartz glass substrate. After etching treatment, remove the photoresist on the quartz glass substrate to obtain the etched quartz glass device. The etching gases include C4F6, O2, and Ar; the volume ratio is 5~20:0~10:40~100.

[0016] As one embodiment of the present invention, in step S1, before spin coating the photoresist, the quartz glass substrate to be processed is cleaned and then placed in a nitrogen oven for drying.

[0017] In one embodiment of the present invention, in step S1, the photoresist includes AZ5214 photoresist.

[0018] As one embodiment of the present invention, in step S1, the pattern to be processed is transferred by selecting a suitable conventional photolithography method according to the minimum line width of the pattern to be processed, and transferring the pattern onto the photoresist on the substrate surface.

[0019] In one embodiment of the present invention, in step S1, the flow rate of the etching gas is 70-105 sccm. The reaction gas is a mixture of C4F6 (5~20 sccm), O2 (0~10 sccm), and Ar (40~100 sccm), and the proportion of each gas is adjustable, including other proportions such as 2:1:4 and 1:0:20.

[0020] As one embodiment of the present invention, in step S2, the etching process is performed using an inductively coupled reactive ion etching (ICP-RIE) machine.

[0021] As one embodiment of the present invention, in step S2, the etching parameters are: ICP power 800W~1400W, chamber pressure 3mTorr~6mTorr, and process temperature 10~20℃.

[0022] In one embodiment of the present invention, the etching process in step S2 takes 10-20 minutes. The linewidth during etching is 800 nm - 2 μm.

[0023] As one embodiment of the present invention, in step S2, the photoresist on the quartz glass substrate is removed by wet etching to obtain the quartz glass device structure.

[0024] After a C4F6 gas mixture is introduced into the chamber, the strong electric field induces inelastic collisions of electrons, generating highly chemically active plasma containing ions, electrons, and free radicals. Taking hexafluoro-2-butyne as an example, when its flow rate is high (greater than 8 sccm) and no O2 is introduced, a deposition effect is observed. This is because, on the one hand, excess hexafluoro-2-butyne collides with active free radicals (such as active fluorine atoms, CF3), deactivating them and causing free radical annihilation, thus reducing etching performance. On the other hand, excess hexafluoro-2-butyne also combines with high-energy electrons to form negative ions, suppressing plasma intensity and reducing the generation of active fluorine atoms, thereby reducing etching performance and resulting in an overall deposition effect.

[0025] To limit this deposition effect, there are generally two solutions. One is to add an appropriate amount of O2, which reacts with excess CF4 and C4F6, reducing their content to insufficient for film deposition and fundamentally solving the film formation problem. The advantage of this method is a relatively fast etching rate; however, it also has drawbacks. O2 reacts with the photoresist, causing it to be rapidly consumed, reducing the selectivity of the etching process and hindering deep etching. The other method is to add an appropriate amount of Ar and increase the RF power, thereby enhancing the physical bombardment intensity of Ar on the sample surface and destroying the fluorocarbon film. Although this method has a relatively slow etching rate, it can achieve a higher etching selectivity.

[0026] In fact, the molecular structure of hexafluoro-2-butyne itself determines that it possesses both etching and deposition capabilities. The molecular structure of hexafluoro-2-butyne is CF3-C≡C-CF3. When the chemical bonds break, CF3-C≡C-CF3 is generated, which has etching capabilities. x Ionic groups and active fluorine atoms react with SiO2 to generate gaseous SiF4 (silicon tetrafluoride), which is then removed by a vacuum system, thus etching the quartz. At the same time, the broken C≡C (carbon-carbon triple bond) also forms dangling bonds and combines with some CF2 groups to form (CF2) on the sample surface. nType of polymer film.

[0027] The etching principle of CHF3 (trifluoromethane) gas mentioned in the comparative example is similar to that of C4F6. The chemical structure of CHF3 contains one CH bond and three CF bonds. During the reaction, the active fluorine atoms generated by the breaking of the CF bonds react with SiO2 to generate gaseous SiF4 (silicon tetrafluoride), which is then removed by the vacuum system, thus etching the quartz. The broken CH bonds form carbon radicals, which react with the unreacted CF bonds... x The groups polymerize on the sidewalls and the surface of the non-etched areas of the bottom layer to form (CF2). n C4F6 is a type of polymer film. However, compared to C4F6, CHF3 exhibits a weaker deposition film-forming effect. This is because CH is more stable than C≡C. The energy required for C≡C to break into C=C and CC is lower than that required for CH to break. Therefore, C4F6 is more likely to exhibit deposition film-forming phenomena.

[0028] The main chemical reaction formulas involved in the above etching process are as follows:

[0029]

[0030]

[0031]

[0032]

[0033]

[0034] Among them, (1) is the core reaction for etching SiO2. Atomic fluorine (F•) attacks silicon atoms, breaking the Si-O bond and forming highly volatile silicon tetrafluoride (SiF4) gas that escapes. Oxygen is usually released in the form of O2 (it may also form other oxygen-containing products such as CO, CO2, COF2); (2) represents CF x Free radicals (especially CF2 and CF3) can polymerize on surfaces to form fluorocarbon polymer films (-(CF2)). n - (3) indicates part of CF x Free radicals (especially CF3) can react with surface oxygen to generate volatile oxygen-containing fluorocarbon compounds (such as COF2); (4), (5), and (6) are the main electrolytic pathways of C4F6 under electron bombardment.

[0035] Compared with the prior art, the present invention has the following beneficial effects: (1) Dry etching of glass usually requires a hard mask and the process is complicated. This invention provides a glass etching solution with high selectivity that does not require a hard mask and uses photoresist as a mask.

[0036] (2) When dry etching glass uses photoresist as a mask, the etching selectivity is relatively low and high aspect ratio etching cannot be achieved. This invention provides a quartz etching scheme with a high aspect ratio (aspect ratio greater than 4:1) and a quartz etching rate exceeding 220nm / min.

[0037] (3) Existing etching gases for glass are usually CHF3, SF6 and other gases, which cause serious environmental pollution. This invention provides a solution for etching glass with environmentally friendly gas C4F6. Attached Figure Description

[0038] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the etching process; Figure 2 The image shown is an electron microscope image of the quartz obtained in Example 1. Figure 3 The image shown is an electron microscope image of the quartz obtained in Example 2. Figure 4 The image shown is an electron microscope image of the quartz obtained in Example 3. Figure 5 The image shown is an electron microscope image of the quartz obtained in Example 4. Figure 6 The image shown is an electron microscope image of quartz obtained in Comparative Example 3. Figure 7 The electron microscope image of quartz obtained in Comparative Example 4; Figure 8 The image shows an electron microscope image of quartz obtained in Comparative Example 1. Figure 9 This is an electron microscope image of quartz obtained in Comparative Example 2. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0040] This invention solves the problem of low selectivity of glass to photoresist in the field of dry etching technology in the micro-nano fabrication industry, and proposes a glass etching scheme with high selectivity, high aspect ratio and no need for hard masks. This invention provides an effective and efficient application method for C4F6 generated in the fluorochemical industry, realizes the recycling and reuse of products containing toxic gases in the fluorochemical industry, and is conducive to sustainable development.

[0041] Example 1 This embodiment relates to a dry etching method using a gas mixture containing C4F6, such as... Figure 1 As shown, this method is used to etch quartz crystals.

[0042] The quartz glass substrate to be processed is cleaned by bombarding it with oxygen plasma for 3 minutes to remove any possible stains on the surface. Then it is placed in a nitrogen oven and baked at 120°C for 15 minutes. After baking, photoresist (AZ5214) is spin-coated onto the surface of the quartz glass substrate. Then, an MA8 lithography machine is used with a 365nm light source and an exposure dose of 150mj / cm². After exposure, an automatic developer is used with a developer solution of 2.38% TMAH and a development time of 1 minute to transfer the pattern to the photoresist on the surface of the quartz substrate, thus obtaining the sample.

[0043] The sample was fed into the etching chamber, and all process parameters were set. A mixed gas (70 sccm) was introduced, in which the ratio of C4F6, O2, and Ar was 2:1:4. The ICP power was 1000W, the RF power was 150W, the chamber pressure was 6mTorr, the process temperature was 20℃, and the etching time was 15min.

[0044] When using AZ5214 photoresist and employing the etching method designed in this embodiment, an etching depth of approximately 3.5 μm was achieved at an 860 nm linewidth, with an aspect ratio of 4.07. Simultaneously, a quartz etching rate of 235 nm / min was achieved, with a quartz-to-photoresist selectivity of 2.96 and a tilt angle of 82.3°. The results are as follows... Figure 2 As shown, H2 is the photoresist thickness, H1 is the etching depth, and V1 is the aperture width.

[0045] The same method was used to adjust the proportions of the mixed gas, as shown in Table 1 below: Table 1

[0046] Example 2 The etching parameters in this example are the same as those in Example 1.

[0047] The etching depth was approximately 33.317 μm with a linewidth of 2 μm, achieving a photoresist selectivity of 2.95. A quartz etching rate of 221.1 nm / min was also achieved at a tilt angle of 76.9°. The results are as follows... Figure 3 As shown, H1 is the photoresist thickness, H2 is the etching depth, and V2 is the aperture width.

[0048] Example 3 This embodiment relates to a dry etching method using a gas mixture containing C4F6 for etching quartz crystals.

[0049] The sample was fed into the etching chamber, and various process parameters were set. The ratio of C4F6, O2, and Ar mixed gas (105 sccm) was 5:0:100, the ICP power was 1000W, the RF power was 300W, the chamber pressure was 5mTorr, the process temperature was 20℃, and the etching time was 10min.

[0050] When using AZ5214 photoresist and employing the etching method designed in this embodiment, an etching depth of approximately 2.092 μm was achieved with a linewidth of 2 μm, resulting in a photoresist selectivity of 7.28. Simultaneously, a quartz etching rate of 209.2 nm / min was achieved at an angle of 84.6°. The results are as follows... Figure 4 As shown, H1 is the photoresist thickness, Cursor Height is the etching depth, and V1 is the aperture width.

[0051] Example 4 Except for the etching time being extended to 15 minutes, the other etching parameters in this example are the same as those in Example 3.

[0052] The etching depth was approximately 2.411 μm with a linewidth of 1 μm, achieving a photoresist selectivity of 6.4. A quartz etching rate of 160.7 nm / min was also achieved at an angle of 86.7°. The results are as follows... Figure 5 As shown, H3 is the thickness of the photoresist, H4 is the etching depth, and V1 is the aperture width.

[0053] Comparative Example 1 This comparative example relates to a dry etching method using a gas mixture containing CHF3 for etching quartz crystals.

[0054] The sample was fed into the etching chamber, and the various process parameters were set. The ratio of CHF3, O2, and Ar mixed gas was 80:0:35, the ICP power was 1000W, the RF power was 300W, the chamber pressure was 6mTorr, the process temperature was 20℃, and the etching time was 5min.

[0055] When using AZ5214 photoresist and employing the etching method designed in this embodiment, an etching depth of approximately 1.787 μm was achieved with a linewidth of 1.2 μm, resulting in a photoresist selectivity of only 1.8. Simultaneously, a quartz etching rate of 357.4 nm / min was achieved at an angle of approximately 83°. The results are as follows... Figure 8 As shown, H1 is the photoresist thickness, H2 is the etching depth, and V1 is the aperture width.

[0056] Comparative Example 2 This comparative example relates to a dry etching method using a gas mixture containing CHF3. The steps are basically the same as in Example 1, except that C4F6 is replaced with CHF3.

[0057] After using this etching method, the result is as follows Figure 9 As shown, after observing the experimental results, it was found that the photoresist had been completely etched, indicating that the etching selectivity of CHF3 gas was poor; at this time, the etching depth was measured to be about 801 nm and the tilt angle was about 61°.

[0058] Comparative Example 3 Except for adjusting the C4F6 gas flow rate to 8 sccm and the RF power to 150 W, the other etching parameters in this example are the same as in Example 3. The results are as follows: Figure 6 As shown, a fluorocarbon film is deposited on the surface of the quartz glass substrate without etching.

[0059] Comparative Example 4 Except for adjusting the C4F6 gas flow rate to 5 sccm, the other etching parameters in this example are the same as those in Comparative Example 3.

[0060] The results are as follows Figure 7 As shown, a fluorocarbon film is deposited on the surface of the quartz glass substrate without etching.

[0061] When adjusting the experimental parameters, the gas ratio was adjusted first. Considering that C4F6 would deposit a fluorocarbon film on the surface of the sample to be etched, we added an appropriate amount of O2 to react with excess CF4 and C4F6, thereby suppressing film formation. However, adding O2 did not achieve a high aspect ratio. To improve the aspect ratio, we initially chose not to add O2. At this time, we reduced the flow rate of C4F6 gas to 5-10 sccm and increased the flow rate of Ar gas to 80-100 sccm. We found that a fluorocarbon film was deposited on the surface of the quartz glass substrate without etching. This was probably due to the excessively high C4F6 gas ratio (Comparative Example 3). After further reducing the C4F6 gas ratio, we found that a thin film still deposited, but the film formation rate decreased, indicating that reducing the gas ratio could effectively suppress film formation (Comparative Example 4). Subsequently, we further adjusted and optimized the parameters. By adjusting the gas ratio and the RF power of the equipment to 250-300W, we finally achieved high selectivity etching of quartz (Examples 3 and 4).

[0062] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. An application of a C4F6 mixed gas in quartz etching, characterized in that, The C4F6 mixed gas is either an oxygen-containing etching gas or an oxygen-free etching gas; Oxygen-based etching gases include C4F6, O2, and Ar; Oxygen-free etching gases include C4F6 and Ar.

2. The application according to claim 1, characterized in that, When the C4F6 mixed gas is C4F6, O2, and Ar, the flow rates of each component during etching are C4F6 5~20 sccm, O2 5~10 sccm, and Ar 40~100 sccm, and the RF power is 150W~300W. When the C4F6 mixed gas is C4F6 and Ar, the flow rates of each component during etching are 5~6 sccm for C4F6 and 40~100 sccm for Ar, and the RF power is 200W~300W.

3. A quartz etching method based on a C4F6 mixed gas, characterized in that, Includes the following steps: S1. Spin-coat photoresist onto the surface of a quartz glass substrate, transfer the pattern to be processed onto the photoresist on the substrate surface, and obtain the developed quartz glass substrate. S2. Set the etching gas ratio and etching parameters, and perform etching treatment on the developed quartz glass substrate to remove the photoresist on the quartz glass substrate and obtain the quartz glass device. The C4F6 mixed gas includes C4F6, O2, and Ar, or C4F6 and Ar; When the C4F6 mixed gas is C4F6, O2, and Ar, the flow rates of each component during etching are 5~20 sccm for C4F6, 5~10 sccm for O2, and 40~100 sccm for Ar, with an RF power of 150W~300W. When the C4F6 mixed gas is C4F6 and Ar, the flow rates of each component during etching are 5~6 sccm for C4F6 and 40~100 sccm for Ar, and the RF power is 150W~300W.

4. The quartz etching method according to claim 3, characterized in that, In step S1, before spin-coating the photoresist, the quartz glass substrate to be processed is cleaned and then placed in a nitrogen oven for drying.

5. The quartz etching method according to claim 3, characterized in that, In step S1, the photoresist includes AZ5214 photoresist.

6. The quartz etching method according to claim 3, characterized in that, In step S2, the etching process is performed using an inductively coupled reactive ion etching (ICD) machine.

7. The quartz etching method according to claim 3, characterized in that, In step S2, the etching parameters are: ICP power 800~1400W, chamber pressure 5mTorr~6mTorr, and process temperature 10~20℃.

8. The quartz etching method according to claim 3, characterized in that, In step S2, the etching process takes 10-20 minutes.

9. The quartz etching method according to claim 3, characterized in that, In step S2, the etching linewidth is 800 nm - 2 μm.

10. The quartz etching method according to claim 3, characterized in that, In step S2, the photoresist on the glass substrate is removed by wet etching to obtain the quartz glass device structure.

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