Method for etching high selectivity silicon oxide

Abstract

The application relates to the field of semiconductor manufacturing technology, in particular to an etching method of high-selectivity silicon oxide, which comprises the following steps: placing a silicon oxide sample with a titanium nitride mask in a reaction ion etching device, and pumping the reaction chamber to a basic vacuum; introducing a CHF3 and O2 mixed reaction gas into the reaction chamber, and starting a radio frequency power source to excite plasma; by controlling the reaction gas and process parameters, the CHF3 gas is decomposed to generate low-energy fluorocarbon groups under the action of the plasma; the low-energy fluorocarbon groups do not etch or have low etching on the titanium nitride mask, and the low-energy fluorocarbon groups react with the silicon oxide to generate volatile products, so that the etching of the high-selectivity silicon oxide is carried out, and the etching is stopped until the target depth is reached. By controlling the etching reaction gas and process parameters to generate low-energy fluorocarbon groups, high etching rate is realized while the high selectivity is ensured, and the requirements of high selectivity and high etching rate for semiconductor manufacturing are met.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to an etching method for silicon oxide with high selectivity. Background Technology

[0002] With the continuous advancement of semiconductor manufacturing processes, the demand for high-precision, high-selectivity etching processes is increasing. Silicon oxide, as a commonly used dielectric material in semiconductor devices, has its etching process selectivity directly impacting device performance and reliability. Traditional silicon oxide etching methods often struggle to simultaneously meet the requirements of high selectivity and high etching rate, especially when using titanium nitride as a mask, where the selectivity is often low, leading to severe mask loss and affecting the precise control of the device structure. Furthermore, existing technologies also suffer from uneven etching rates and poor sidewall morphology control, limiting further miniaturization and integration of semiconductor devices.

[0003] To address the issue of low selectivity in existing silicon oxide etching processes, several patent documents have been published. For example, patent document (CN114783867A) discloses a silicon oxide etching method that achieves deep silicon etching by cyclically executing deposition and etching steps up to a set number of cycles. This patent can etch deep silicon structures with high aspect ratios, high absolute depths, perpendicular sidewall angles, and smooth sidewalls within the silicon oxide layer exposed by the mask layer. However, the process of this patent is relatively complex, requiring multiple cycles, which increases process time and cost. Patent document (CN101372311A) discloses a high aspect ratio silicon oxide etching process that uses an inductively coupled plasma etching system with reaction gases including C4F8, H2, and He, and employs specific process parameters. This patent can significantly improve the etching rate of silicon oxide and the selectivity of the etching mask, while also meeting the etching requirements for sidewall perpendicularity. However, this patent does not consider the special process requirements when using titanium nitride as a mask.

[0004] Therefore, there is an urgent need to develop a high-selectivity silicon oxide etching method that can meet the requirements of high selectivity while maintaining a high etching rate and good sidewall morphology, thereby improving the manufacturing precision and reliability of semiconductor devices. Furthermore, this method should be simple, low-cost, and easy to implement to meet the needs of large-scale production. Summary of the Invention

[0005] The purpose of this invention is to provide a high-selectivity etching method for silicon oxide to solve the technical problems existing in the prior art and achieve high-selectivity etching of silicon oxide with a titanium nitride mask.

[0006] This invention provides an etching method for silicon oxide with high selectivity, comprising the following steps: S1. Place the silicon oxide sample with the titanium nitride mask in the reactive ion etching equipment and evacuate the reaction chamber to a basic vacuum. S2. Introduce a mixture of CHF3 and O2 reaction gas into the reaction chamber, turn on the radio frequency power supply to excite the plasma, and control the reaction gas and process parameters to decompose the CHF3 gas under the action of the plasma to produce low-energy fluorocarbon groups. S3. Low-energy fluorocarbon groups do not etch or etch very little on the titanium nitride mask. The low-energy fluorocarbon groups react with silicon oxide to generate volatile products, thereby performing etching of silicon oxide with high selectivity until the target depth is reached and the etching stops.

[0007] Preferably, the reaction chamber is evacuated to a basic vacuum level ≤ 5 × 10⁻⁶. -5 Torr maintains the vacuum state of the reaction chamber for no less than 5 minutes.

[0008] Preferably, the O2 content in the mixed reaction gas is 2%-6%. CHF3 gas decomposes under plasma to produce low-energy fluorocarbon groups, which react chemically with silicon oxide to form volatile products such as SiF4. The addition of O2 helps regulate the concentration and energy distribution of free radicals in the plasma, while preventing the formation of carbon deposits. By precisely controlling the proportions of these gases and process parameters, etching selectivity and rate can be optimized. Too low an O2 content makes it difficult to generate sufficient amounts of active fluorine radicals (F·), resulting in insufficient etching ability for SiO2. Simultaneously, the fluorocarbon polymers produced by CHF3 decomposition exacerbate the problem, leading to deterioration of the etching profile, pattern deformation, and potentially particle contamination. Too high an O2 content significantly reduces etching selectivity and also causes roughness and deformation of the silicon oxide sidewalls.

[0009] Preferably, the process parameters include: reaction chamber temperature, reaction chamber pressure, radio frequency power supply power, and radio frequency power supply frequency.

[0010] Preferably, the temperature of the reaction chamber is controlled at 25~30℃. This temperature is the optimal temperature for the reaction of low-energy particles under the process conditions. If it is too high, the sidewall products will decompose, resulting in insufficient protection. If it is too low, it will not be enough for the fluorine-based and silicon oxide to react under the process conditions, which will seriously affect the etching efficiency.

[0011] Preferably, the pressure in the reaction chamber is controlled at 90~100 mTorr.

[0012] Preferably, the radio frequency power (RF power) is controlled between 180 and 200 W. The selection of RF power directly affects plasma density and ion energy. An appropriate power setting can ensure a sufficient etching rate while avoiding excessive damage to the mask material.

[0013] The reaction chamber pressure, power, and other parameters used in this invention can better obtain low-energy fluorocarbon groups. Too high a power will reduce the selectivity, while too low a power will result in insufficient reaction. Similarly, increasing the reaction chamber pressure will result in insufficient reaction, while decreasing the pressure will reduce the selectivity.

[0014] Preferably, the frequency of the radio frequency power supply is controlled at 13.56MHz.

[0015] Preferably, the process parameters adopt a dynamic adjustment strategy to adapt to the natural changes in reaction conditions during the etching process and maintain the stability of the etching rate and selectivity.

[0016] Preferably, in the dynamic adjustment strategy, the O2 content is increased while the RF power supply is reduced. Specifically, the O2 content is increased (from 2.5% to 6%) to ensure sufficient reactive ions in the deep trench etching to maintain the reaction, while the power is reduced (from 200W to 180W) to maintain a high selectivity.

[0017] Preferably, the etching depth is monitored in real time during the etching process using an endpoint detection system (e.g., an optical emission spectroscopy detection system, a laser interferometry detection system, etc.). Specifically, the endpoint detection system can acquire characteristic signals during the etching process in real time to dynamically monitor the etching depth; when the detection signal reaches the target depth, the flow of the CHF3 and O2 mixed reaction gas is stopped, the RF power supply is turned off, and the vacuum system is kept running for a preset time to remove the residual reaction products in the chamber. Then, the vacuum is broken and the sample is removed, completing the etching process.

[0018] Preferably, after etching is completed, the etching morphology and dimensional accuracy are inspected using an optical microscope and a profilometer.

[0019] Preferably, the etching selectivity ratio of the silicon oxide and titanium nitride mask is (95-120):1.

[0020] The high-selectivity silicon oxide etching method provided by this invention is particularly suitable for semiconductor manufacturing processes requiring high-precision pattern transfer, such as shallow trench isolation and dielectric layer windowing applications. The etched structure obtained by this method exhibits excellent sidewall morphology and dimensional control accuracy, meeting the high-precision pattern transfer requirements of advanced semiconductor devices. Simultaneously, this method results in extremely low mask material loss, significantly extending mask lifespan and reducing manufacturing costs.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: (1) By controlling the etching reaction gas and process parameters, the present invention can effectively regulate the distribution of active groups in the plasma, especially promote the generation of low-energy fluorocarbon groups. Low-energy fluorocarbon groups have high selectivity for silicon oxide, but have very weak etching effect on titanium nitride masks. By utilizing the high chemical etching activity of low-energy fluorocarbon groups on silicon oxide and the low etching effect on titanium nitride masks, high selectivity etching of silicon oxide with titanium nitride masks can be achieved, effectively reducing mask loss and improving the precise control capability of device structure.

[0022] (2) By controlling the etching reaction gas and process parameters, the present invention generates low-energy fluorocarbon groups, thereby achieving a high etching rate while ensuring a high selectivity, which meets the requirements of semiconductor manufacturing for high selectivity and high etching rate.

[0023] (3) By controlling the etching reaction gas and process parameters, the present invention optimizes the plasma characteristics during the etching process, improves the sidewall morphology, and enhances the etching quality.

[0024] (4) By controlling the etching reaction gas and adjusting the process parameters, the present invention eliminates the need for a complex cyclic execution process, reducing process complexity and cost, and is beneficial for large-scale production applications.

[0025] (5) The process equipment used in this invention has low requirements, low cost, and is easy to implement, and has good prospects for industrial application. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the etching method for high selectivity silicon oxide provided by the present invention. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 like Figure 1 As shown, this embodiment provides an etching method for silicon oxide with high selectivity, as detailed below: At a process temperature of 25°C, the pressure in the reaction chamber was maintained at 100 mTorr. The plasma was excited using 200 W of RF power, and 200 sccm of CHF3 and 4 sccm of O2 were introduced as reaction gases.

[0032] In practice, the silicon oxide sample with a titanium nitride mask is first placed on the sample stage of the reactive ion etching (RIE) equipment, ensuring good contact between the sample and the electrode. After evacuating the reaction chamber to a basic vacuum, a mixture of CHF3 and O2 gas is introduced, maintaining a total flow rate of 220 sccm. The RF power supply is turned on, set to 200W, and the plasma is excited at a frequency of 13.56 MHz. By precisely controlling the gas flow ratio and process parameters, a large number of low-energy fluorocarbon groups are generated in the plasma. These low-energy reactive groups preferentially react with silicon oxide to form volatile products such as SiF4, while having almost no etching effect on the titanium nitride mask. The entire etching process continues until the desired etching depth is reached.

[0033] Under these process conditions, the etching rate of silicon oxide reaches 50 nm / min, and the etching selectivity ratio of silicon oxide and titanium nitride masks reaches 100:1.

[0034] Example 2 This embodiment provides a high selectivity silicon oxide etching method. Based on Example 1, the process temperature is adjusted to 30°C, the pressure is adjusted to 90 mTorr, the RF power is adjusted to 180 W, and the CHF3 flow rate is maintained at 200 sccm and the O2 flow rate at 8 sccm.

[0035] In practice, the reaction chamber temperature is controlled at 30±1℃ using a circulating water cooling system. Pressure and intensity are stabilized through the coordinated control of a throttling valve and a vacuum pump. The reduction in RF power slightly decreases the plasma density, but this is compensated for by increasing the O2 flow rate, maintaining a sufficient concentration of active groups. The increased O2 flow rate further helps to reduce the average energy of fluorocarbon groups, thereby improving selectivity for silicon oxide. During etching, the etching depth is monitored in real time using an endpoint detection system to ensure precise process control.

[0036] Under these process conditions, the etching rate of silicon oxide is 45 nm / min, and the etching selectivity ratio of silicon oxide to titanium nitride mask reaches 95:1.

[0037] Example 3 This embodiment also provides an etching method for high selectivity silicon oxide, which adds dynamic adjustment of process parameters based on Embodiment 1. In the initial stage, the same parameter settings as in Embodiment 1 are used. When the etching depth reaches 50% of the target value, the O2 flow rate is gradually increased to 12 sccm, while the RF power is reduced to 180W.

[0038] In practice, a pre-programmed procedure controls the gradual change of gas flow rate and RF power to ensure a smooth transition of process parameters. The dynamic adjustment strategy adapts to natural changes in reaction conditions during etching, maintaining the stability of etching rate and selectivity. Particularly when etching deep trench structures, this method effectively compensates for changes in plasma distribution caused by increased etching depth, ensuring consistent selectivity throughout the etching process. After etching, the etching morphology and dimensional accuracy are inspected using an optical microscope and profilometer to verify the process effectiveness.

[0039] In the dynamic adjustment mode, the etching selectivity ratio for silicon oxide and titanium nitride masks is increased to 120:1.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for etching silicon oxide with high selectivity, characterized in that, Includes the following steps: S1. Place the silicon oxide sample with the titanium nitride mask in the reactive ion etching equipment and evacuate the reaction chamber to a basic vacuum. S2. Introduce a mixture of CHF3 and O2 reaction gas into the reaction chamber, turn on the radio frequency power supply to excite the plasma, and control the reaction gas and process parameters to decompose the CHF3 gas under the action of the plasma to produce low-energy fluorocarbon groups. S3. Low-energy fluorocarbon groups do not etch or etch very little titanium nitride masks. Low-energy fluorocarbon groups react with silicon oxide to generate volatile products, thereby performing etching of silicon oxide with high selectivity until the target depth is reached and etching stops.

2. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, The O2 content in the mixed reaction gas is 2.5%-6%.

3. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, The process parameters include: reaction chamber temperature, reaction chamber pressure, radio frequency power, and radio frequency power frequency.

4. The etching method for high-selectivity silicon oxide according to claim 3, characterized in that, The temperature of the reaction chamber is controlled at 25~30℃, and the pressure of the reaction chamber is controlled at 90~100mTorr.

5. The etching method for high-selectivity silicon oxide according to claim 3, characterized in that, The power of the radio frequency power supply is controlled at 180~200W, and the frequency of the radio frequency power supply is controlled at 13.56MHz.

6. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, The process parameters employ a dynamic adjustment strategy to adapt to the natural changes in reaction conditions during etching, thereby maintaining the stability of the etching rate and selectivity.

7. The etching method for high-selectivity silicon oxide according to claim 6, characterized in that, In the dynamic adjustment strategy, the O2 content is increased while the RF power supply is reduced.

8. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, The etching depth is monitored in real time during the etching process using an endpoint detection system.

9. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, After etching is completed, the etching morphology and dimensional accuracy are inspected using an optical microscope and a profilometer.

10. The etching method for high-selectivity silicon oxide according to claim 1, characterized in that, The etching selectivity ratio of the silicon oxide and titanium nitride masks is (95-120):1.

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