High-selection-ratio etching solution for SiGe laminations with different germanium contents and use method of high-selection-ratio etching solution

Abstract

The invention provides a high-selection-ratio etching solution for SiGe laminations with different germanium contents and a use method, and the high-selection-ratio etching solution comprises the following components in percentage by mass: 0.1 to 20 percent of quaternary ammonium hydroxide, 0.00001 to 1 percent of oxidant, 0.0001 to 10 percent of inhibitor, 0.5 to 40 percent of solvent and the balance of water. The etching solution disclosed by the invention has a high etching rate for low-germanium-content SiGe, and is extremely slow in etching for high-germanium-content SiGe, so that the etching selection ratio of low-germanium / high-germanium SiGe is up to 60. The etching solution provided by the invention is suitable for a microelectronic device to selectively remove SiGe with low germanium content from SiGe laminations with different germanium contents.

Description

Technical Field

[0001] This invention relates to the field of electronic chemicals, and more specifically to a high selectivity etching solution for SiGe stacks with different germanium contents and its application method. Background Technology

[0002] The increasing precision and three-dimensionality of semiconductor manufacturing technology have placed extremely high demands on the fabrication of device structures. In advanced devices such as gate-all-around transistors (GAAs) and three-dimensional memories, silicon-germanium (SiGe) materials, with their tunable lattice constant and etch selectivity, have become a key element in constructing multilayer stacked structures. It is noteworthy that in certain specific device designs, such as stacked structures composed of 20% germanium SiGe and 40% germanium SiGe, the process objective does not follow the traditional convention of "etching the high-germanium content layer and retaining the low-germanium content layer." Instead, it requires achieving a reverse selective etching process—selectively and completely removing the low-germanium content (e.g., 20%) SiGe sacrificial layer while perfectly preserving the high-germanium content (e.g., 40%) SiGe functional layer. This unique requirement presents a significant challenge to existing wet etching techniques.

[0003] The need for this "reverse" high selectivity etching stems from optimizing the physical properties of specific device structures. In the design of high-performance GAA transistors or novel memories, SiGe layers with varying germanium contents are not merely sacrificial layers; they are often integral to the device's functional structure, playing a crucial role in regulating channel stress and optimizing carrier mobility. For example, in a 20SiGe / 50SiGe stack, the high-germanium-content SiGe layer (50% Ge) might be designed as the device's channel layer, significantly improving p-type device performance due to its higher hole mobility and other properties; while the low-germanium-content SiGe layer (20% Ge) might serve as a sacrificial or buffer layer. By selectively etching the low-germanium-content layer while retaining the high-germanium-content layer, device designers gain unprecedented freedom to achieve band structures or stress states difficult to obtain using conventional methods, thereby overcoming performance bottlenecks. This design approach breaks with conventional understanding of etching selectivity and is one of the key processes driving further performance improvements in advanced semiconductor devices.

[0004] However, achieving this goal faces inherent materials science challenges. Chemically, the higher the germanium (Ge) content, the stronger the chemical activity of the SiGe alloy, and the faster its etching rate in common wet or dry etching environments. This makes achieving a high selectivity ratio—etching low-Ge-content SiGe while retaining high-Ge-content SiGe—extremely difficult, as it requires overcoming the inherent properties of the material itself. Existing wet etching technologies, including traditional formulations based on components such as hydrogen peroxide, hydrofluoric acid, and nitric acid, mostly focus on enhancing the etching rate of high-germanium-content SiGe, and cannot meet this specific reverse selective etching requirement.

[0005] Currently, no publicly available wet etchant can reliably achieve high selectivity etching of low-germanium-content SiGe relative to high-germanium-content SiGe. This technological gap severely restricts the design flexibility and performance optimization space of advanced semiconductor devices based on silicon-germanium materials. Therefore, there is an urgent need to develop a novel etchant composition that can effectively solve the problem of reverse selective etching in low-germanium-content SiGe and high-germanium-content SiGe stacked structures, achieving efficient and uniform removal of the low-germanium-content SiGe sacrificial layer while maintaining an extremely low etching rate for the high-germanium-content SiGe functional layer, silicon dioxide, and related dielectric materials, to meet the needs of next-generation high-performance, multi-dimensional semiconductor device manufacturing. Summary of the Invention

[0006] To address the problems in the prior art, the main objective of this invention is to provide a high-selectivity etchant and its application method for SiGe stacks with varying germanium contents. The high-selectivity etchant of this invention utilizes the synergistic effect of quaternary ammonium hydroxide, oxidant, inhibitor, and solvent to precisely control the etching behavior by adjusting component concentration and temperature, thereby achieving efficient removal of SiGe with low germanium content.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A high selectivity etchant for SiGe stacks with different germanium contents comprises, by mass fraction, 0.1-20 wt% quaternary ammonium hydroxide, 0.00001-1 wt% oxidant, 0.0001-10 wt% inhibitor, 0.5-40 wt% solvent, and the balance being water.

[0008] Preferably, the quaternary ammonium hydroxide is R4NOH, wherein R is four identical or different aliphatic or aromatic groups selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, and 2-hydroxyethyltrimethylammonium hydroxide.

[0009] More preferably, the high selectivity etching solution comprises 0.5-10 wt% quaternary ammonium hydroxide, 0.0001-0.1 wt% oxidant, 0.001-5 wt% inhibitor, 1-30 wt% solvent, and the balance being water.

[0010] Preferably, the oxidant is an iodine-containing oxidant or a persulfate.

[0011] Preferably, the iodine-containing oxidant is selected from one or more of periodic acid (H5IO6), iodic acid, 2-iodobenzoic acid (IBX), Des Martin periodane (DMP), and diacetoxyiodobenzene (PIDA); The persulfate is selected from ammonium persulfate (NH4)2S2O8.

[0012] Preferably, the inhibitor is selected from one or more of the following: n-octylphosphonic acid, phenylphosphonic acid, 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotris(methylenephosphonic acid) (ATMP), ethylenediaminetetra(methylenephosphonic acid) (EDTMP), N,N-bis(phosphonomethyl)glycine, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), and polyethyleneimine-phosphonic acid derivatives.

[0013] Preferably, the solvent is selected from one or more of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), propanol, isopropanol, propylene glycol, butanol, butyl diethylene glycol, cyclohexane, acetonitrile, dimethylformamide, and sulfolane.

[0014] More preferably, the high selectivity etching solution comprises 0.5-10 wt% quaternary ammonium hydroxide, 0.0001-0.1 wt% oxidant, 0.001-5 wt% inhibitor, 1-30 wt% solvent, and the balance being water.

[0015] A second aspect of the present invention provides a method for using the high selectivity etchant to remove low-germanium-content SiGe in SiGe stacks with different germanium contents, comprising the following steps: S1. Etching of SiGe stacked structures with different germanium contents using an etching solution; S2. After etching is complete, the etching solution is removed from the structural sheet, thus completing the low germanium content SiGe etching.

[0016] Preferably, the etching temperature in step S1 is 10℃-100℃ and the etching time is <24h.

[0017] More preferably, the etching temperature in step S1 is 25-80°C and the etching time is 1-60 min.

[0018] Preferably, before etching, the microelectronic device structure is cleaned with an aqueous solution containing 0.5 wt% HF at room temperature for 30-240 seconds, preferably 60 seconds, more preferably 30 seconds. After etching, the etching solution can be easily removed from the microelectronic device by rinsing, washing, or other removal steps. For example, the etching solution can be removed by rinsing with a rinsing solution such as deionized water or an organic solvent, and / or by drying (e.g., spin drying, N2, steam drying, etc.).

[0019] Preferably, the etching rate of the etching solution on SiO2 is <2 Å / min; more preferably, the etching rate is <1 Å / min.

[0020] Preferably, the etching selectivity of the etching solution for low germanium content SiGe / high germanium content SiGe is >20, and more preferably, the etching selectivity is >50.

[0021] This invention allows for the adjustment of the SiGe removal rate by controlling etching conditions, such as component content and temperature; and the adjustment of the etching selectivity ratio of low-germanium-content SiGe / high-germanium-content SiGe by combining different inhibitors.

[0022] Preferably, the solvent is miscible with water at a ratio of at least 1:1 (wt) at 20°C and ambient pressure.

[0023] A third aspect of the present invention provides the application of the etching solution in a composite semiconductor device comprising SiGe stacks with varying germanium contents.

[0024] In the etching solution of this invention, quaternary ammonium hydroxide acts as the etchant and also serves as an alkaline medium, creating an optimal environment for the adsorption of organophosphonic acid inhibitors while exhibiting an extremely low etching rate for SiO2. The oxidant (such as an iodine-containing oxidant and persulfate) is responsible for slightly oxidizing the SiGe surface, forming a controllable oxide layer (such as GeO2 / SiO2). Subsequently, organophosphonic acid inhibitor molecules preferentially and firmly adsorb onto the newly formed GeO2 on the high-germanium-content SiGe surface, forming a dense protective film that effectively prevents further etching. For low-germanium-content SiGe (such as 20% Ge), its surface oxide layer properties are closer to SiO2, resulting in weaker inhibitor adsorption and an inability to form effective protection, allowing the quaternary ammonium hydroxide and other components to effectively etch it. Through the synergistic effect of the etchant, oxidant, and inhibitor, this invention achieves an etching selectivity ratio of >20 for low-germanium-content SiGe and >50 for high-germanium-content SiGe. Meanwhile, the alkaline environment and inhibitor properties in the formulation also ensure that the etching rate of silicon dioxide (SiO2) is extremely low (<2Å / min, preferably <1Å / min), which can effectively protect the key SiO2 structures such as the isolation layer and gate dielectric layer in the device, avoid damage to the electrical performance of the device during the etching process, and significantly improve the yield of finished products.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves selective and efficient removal of low-germanium-content SiGe in SiGe stacks with different germanium contents by controlling the concentration of quaternary ammonium hydroxide and the type and content of inhibitors, combined with etching temperature to precisely control the etching behavior. Under optimized conditions, the etching selectivity ratio of low-germanium / high-germanium SiGe is as high as 60.

[0026] 2. Compared with traditional fluorine-containing or strong acid etching systems, the etching solution of this invention uses a weakly alkaline, low-concentration oxidant and a biodegradable phosphonic acid inhibitor, which reduces corrosiveness and toxicity and conforms to the trend of green manufacturing. Detailed Implementation

[0027] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0028] The term "silicon-germanium layer" or "SiGe layer" as used in this invention corresponds to a layer comprising or composed of a silicon-germanium alloy known in the art and represented by the formula SixGey, where x + y = 1.00. 20SiGe here refers to SiGe with y = 0.20, i.e., a germanium content of 20%.

[0029] Preparation and etching methods: (1) Preparation: Weigh the corresponding raw materials according to the components and contents in the table below by percentage calculation to prepare different selective etching solutions, with water as the balance; (2) Etching conditions: 50℃, 300r / min stirring and soaking for 1-30min; (3) Etched test pieces: SiGe stacks with different germanium contents, namely 50SiGe and 20SiGe.

[0030] The components and test data of each embodiment and comparative example are shown in Tables 1-3.

[0031] Table 1. Etching solution component ratios and test data for different oxidants

[0032] As shown in Table 1, in the alkaline etching solution, the selectivity of Comparative Example 1 (without oxidant) was only 4, while the selectivity of Example 1 with 0.01% H5IO6 added was as high as 44, which is superior to organic high-valent iodine oxidants such as IBX (29) and DMP (33). This is because periodic acid can react with periodate (IO4) under alkaline conditions (pH>12). - It exists stably in its oxidizing form and has stronger oxidizing power than other organic iodine oxidants (such as IBX or DMP). In addition, periodic acid decomposes slowly in alkaline media, maintaining its oxidizing power for a longer period, thus ensuring the stability and selectivity of the etching process.

[0033] Table 2. Etching solution formulation ratios and test data for different inhibitors

[0034] As shown in Table 2, compared with Comparative Example 2 (selectivity ratio 9) containing only oxidant, Example 1, with the addition of 0.2% HEDP (monophosphonic acid functional group), increased the selectivity to 44, while multiple phosphonic acid group inhibitors such as ATMP (Example 7, selectivity ratio 57) and EDTMP (Example 8, selectivity ratio 60) were more effective. This indicates that organophosphonic acid inhibitors can effectively inhibit the etching of SiGe with high germanium content, while multidentate phosphonic acids (such as EDTMP containing four phosphonic acid groups) can enhance adsorption strength through multiple coordination sites, achieving a higher selectivity.

[0035] Table 3. Stability of etching solution formulation at 0-4℃

[0036] Table 3 shows the stability data for etching rates with different contents of SiGe and SiO2. After being stored at 0-4℃ for 30 days, the selectivity ratio (e.g., 20SiGe / 50SiGe) of the etching solution remained high, fully meeting the requirements for selective etching, while the etching rate for SiO2 remained below the detection limit (<0.1 Å / min). This indicates that the etching solution has a continuous and reliable protective capability for the critical dielectric layer in electronic devices, effectively preventing damage to the functional layer.

[0037] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A high-selectivity etchant for SiGe stacks with different germanium contents, characterized in that: By mass fraction, it includes 0.1-20 wt% quaternary ammonium hydroxide, 0.00001-1 wt% oxidant, 0.0001-10 wt% inhibitor, 0.5-40 wt% solvent, and the balance is water.

2. The high selectivity etching solution according to claim 1, characterized in that: The quaternary ammonium hydroxide is R4NOH, wherein R is four identical or different aliphatic or aromatic groups selected from one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, ethyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, benzyltriethylammonium hydroxide, and 2-hydroxyethyltrimethylammonium hydroxide.

3. The high selectivity etching solution according to claim 1, characterized in that: The oxidant is an iodine-containing oxidant or a persulfate.

4. The high selectivity etching solution according to claim 3, characterized in that: The iodine-containing oxidant is selected from one or more of periodic acid, iodic acid, 2-iodobenzoic acid, Des Martin periodoyl alkyl, and diacetoxyiodobenzene; the persulfate is selected from ammonium persulfate.

5. The high selectivity etchant according to claim 1, characterized in that: The inhibitor is selected from one or more of the following: n-octylphosphonic acid, phenylphosphonic acid, 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotris(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), N,N-bis(phosphonomethyl)glycine, 2-phosphonobutane-1,2,4-tricarboxylic acid, and polyethyleneimine-phosphonic acid derivatives.

6. The high selectivity etching solution according to claim 1, characterized in that: The solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide, propanol, isopropanol, propylene glycol, butanol, butyl diethylene glycol, cyclohexane, acetonitrile, dimethylformamide, and sulfolane.

7. A method of using the high selectivity etchant according to any one of claims 1 to 6 to remove low-germanium-content SiGe from SiGe stacks with different germanium contents, characterized in that: Includes the following steps, S1. Etching of SiGe stacked devices with different germanium contents using an etching solution; S2. After etching is complete, the etching solution is removed from the microelectronic device, thus completing the low germanium content SiGe etching.

8. The method of use according to claim 7, characterized in that: The etching temperature is 10℃-100℃, and the etching time is <24h.

9. The method of use according to claim 7, characterized in that: Before etching, clean the microelectronic device structure with an aqueous solution containing 0.5 wt% HF at room temperature for 30-240 seconds.

10. The method of use according to claim 7, characterized in that: The etching selectivity of the etching solution for low germanium content SiGe / high germanium content SiGe is >20.

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