Alkaline polishing solution for low-germanium-content silicon-germanium wafer and preparation method thereof

Abstract

The application provides a low-germanium-component silicon germanium wafer alkaline polishing liquid and a preparation method thereof. The low-germanium-component silicon germanium material is Si 1‑X Ge X , wherein x<=0.5. The polishing liquid has a pH value of 9.0-12.0 and comprises, in percentage by mass, 0.5%-3.0% of colloidal silica abrasive, 0.1%-1.5% of corrosion accelerator A, 0.01%-0.2% of selectivity enhancer B, a pH regulator and the rest of deionized water. The corrosion accelerator A is a cyclic secondary amine compound, and the selectivity enhancer B is a polymer containing a sulfonic acid group. The low-germanium-component silicon germanium surface is mildly activated by the cyclic secondary amine, and the interface lubrication and TEOS selective protection are formed by the polymer containing the sulfonic acid group, so that the low-germanium-component silicon germanium wafer is chemically mechanically polished at a high removal rate, a high selectivity ratio and a low defect.

Description

Technical Field

[0001] This invention relates to the field of chemical mechanical polishing technology for semiconductor wafers, and particularly to an alkaline polishing solution for silicon-germanium wafers with low germanium content and its preparation method. Background Technology

[0002] As Moore's Law evolves, traditional silicon-based CMOS devices are gradually approaching their physical limits. Introducing silicon-germanium (SGR) materials into PMOS channels, leveraging their high hole mobility and stress engineering properties, has become an important technological path for continuing to improve device performance. Especially in 3nm and below GAA (Gate All Around) structures and FinFET (Fin Field-Effect Transistor) structures, SGR materials can be used as core functional materials such as PMOS channels, strain-relaxation buffer layers (SRB), and GAA sacrificial layers.

[0003] In the integration process of silicon-germanium devices, chemical mechanical polishing (CMP) is a crucial step in achieving global planarization of the wafer surface, controlling material removal thickness, and providing a smooth surface for subsequent photolithography and etching steps. Unlike high-germanium-content silicon-germanium materials, when the germanium content is ≤50%, the surface chemistry of silicon-germanium materials is closer to that of polycrystalline silicon, exhibiting a dense, chemically inert SiO2 natural oxide layer. x It is mainly composed of silicon and may contain a silicon-rich residual layer formed after selective dissolution of germanium, which has strong resistance to alkaline corrosion.

[0004] Existing alkaline polishing slurries still have the following problems when used for polishing silicon-germanium materials with low germanium content: Firstly, the dense SiO₂ on the surface of silicon-germanium with low germanium content. x The passivation layer is difficult to activate effectively, and conventional alkaline polishing solutions are unable to break through the surface barrier, resulting in a low material removal rate that is difficult to meet the requirements of mass production efficiency. Secondly, the strong coordinating organic amines introduced to improve the removal rate, such as ethylenediamine and triethanolamine, have a more intense and uneven effect on the low-germanium silicon-germanium surface that is more like polycrystalline silicon. This can easily cause localized excessive corrosion, resulting in orange peel texture, pitting, and hazy defects after polishing, making it difficult to consistently meet the surface roughness standards. Third, while existing alkaline amine systems promote silicon-germanium corrosion, they may cause unexpected loss of the TEOS oxide layer due to chemical erosion or abrasive adhesion, resulting in a low SiGe / TEOS removal selectivity. In addition, there are problems such as reaction product redeposition and abrasive scratches.

[0005] To this end, an alkaline polishing solution for silicon-germanium wafers with low germanium content and its preparation method are proposed. Summary of the Invention

[0006] In view of this, the present invention provides an alkaline polishing slurry for silicon-germanium wafers with low germanium content and a method for preparing the same, in order to solve or alleviate the technical problems existing in the prior art, and at least provide a beneficial alternative.

[0007] The technical solution of this invention is implemented as follows: an alkaline polishing solution for low-germanium-content silicon-germanium wafers, wherein the low-germanium-content silicon-germanium material in the low-germanium-content silicon-germanium wafer is Si. 1-x Ge x Where x≤0.5, preferably x≤0.3.

[0008] The low-germanium-content alkaline polishing slurry for silicon-germanium wafers has a pH value of 9.0-12.0 and comprises the following components by mass percentage: 0.5%-3.0% colloidal silica abrasive, preferably 1.0%-2.0%; corrosion accelerator A, preferably 0.3%-1.0%; selective enhancer B, preferably 0.01%-0.2%; pH adjuster as needed; and the balance being deionized water.

[0009] The average particle size of the colloidal silica abrasive is 30-80 nm, preferably 50-70 nm. If the particle size is too small, the mechanical removal efficiency is insufficient; if the particle size is too large, it easily causes scratches and defects on the wafer surface. The colloidal silica abrasive is uniformly dispersed in an alkaline polishing slurry for low-germanium silicon-germanium wafers to provide a stable and controllable mechanical polishing effect.

[0010] Corrosion promoter A is a cyclic secondary amine compound selected from at least one of morpholine, piperidine, and N-methylpiperazine, preferably morpholine or piperidine. Compared with commonly used chain primary amines, the lone pair electrons on the nitrogen atom in the cyclic secondary amine molecule are affected by the steric hindrance of the ring structure, resulting in a milder coordination ability and basicity. This characteristic enables it to undergo a slow and uniform hydroxylation reaction with the low-germanium silicon-germanium surface, which is predominantly polycrystalline silicon, to generate a loosely textured, controllable-thickness hydrated oxide layer. This hydrated oxide layer ensures the contribution of chemical corrosion to the material removal rate while avoiding surface defects such as orange peel texture and pitting caused by localized severe reactions.

[0011] Selectivity enhancer B is a polymer containing sulfonic acid groups, selected from at least one of poly(sodium 4-styrene sulfonate) or sodium polyethylene sulfonate, preferably poly(4-styrene sulfonate), with a weight-average molecular weight of 50-100 kDa. The polymer containing sulfonic acid groups exhibits strong negative charge under alkaline conditions, generating electrostatic repulsion between the negatively charged silica abrasive particles and the TEOS oxide layer surface, thereby forming a hydrated lubricating film between the abrasive and the TEOS surface. This hydrated lubricating film can inhibit the mechanical removal of the TEOS oxide layer by the abrasive, improving the selectivity of silicon-germanium materials for TEOS removal; it can also reduce the adhesion of abrasive particles to the wafer surface, reducing scratches and particle residue defects on the polished surface. Furthermore, the long-chain structure of the polymer can physically adsorb and protect the microscopic depressions on the silicon-germanium surface, promoting preferential removal of protrusions and thus improving planarization efficiency.

[0012] The pH adjuster is potassium hydroxide or tetramethylammonium hydroxide, and the pH value of the alkaline polishing solution for low-germanium silicon-germanium wafers is preferably 9.5-10.5. This weakly alkaline range can activate the corrosion-promoting effect of cyclic secondary amines while avoiding excessive erosion of the silicon-germanium surface due to excessively high pH value.

[0013] Furthermore, 0.005%-0.05% of a nonionic surfactant can be added to the low-germanium-content silicon-germanium wafer alkaline polishing slurry. The preferred nonionic surfactant is fatty alcohol polyoxyethylene ether. The nonionic surfactant improves the wetting and spreading properties of the polishing slurry on the wafer surface, enhancing the uniformity of the polishing removal within the wafer.

[0014] This invention also provides a method for preparing an alkaline polishing solution for silicon-germanium wafers with low germanium content, comprising the following steps: S1. Add 80%-90% of the formula amount of deionized water to a clean container. Under stirring conditions, add the formula amount of corrosion accelerator A and selective enhancer B in sequence, and continue stirring until completely dissolved to obtain a mixed solution. S2. Under continuous stirring, slowly add the formula amount of colloidal silica abrasive mother liquor to the mixed solution obtained in step S1. The solid content of the colloidal silica abrasive mother liquor is 30%. After the addition is completed, continue stirring for 10-20 minutes to make the abrasive particles evenly dispersed. S3. Use a pH adjuster to adjust the pH of the solution obtained in step S2 to the target range of 9.0-12.0, then add deionized water to the total amount of the formula, and continue stirring for 20-30 minutes to obtain the low germanium content silicon-germanium wafer alkaline polishing solution.

[0015] The present invention also provides a chemical mechanical polishing method for silicon-germanium wafers with low germanium content, wherein the above-mentioned alkaline polishing solution for silicon-germanium wafers with low germanium content is used for chemical mechanical polishing, the polishing pressure is 1.0-2.0 psi, preferably 1.5 psi; the polishing head speed is 80-100 rpm, preferably 87 rpm; the polishing disk speed is 85-100 rpm, preferably 93 rpm; the polishing solution flow rate is 100-300 ml / min, preferably 150-200 ml / min; and the polishing pad is a rigid polyurethane polishing pad.

[0016] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention uses cyclic secondary amine corrosion promoters to gently activate the surface of low-germanium silicon-germanium, enabling the surface of low-germanium silicon-germanium to undergo a slow and uniform hydroxylation reaction, forming a loose and controllable thickness hydrated oxide layer. This reduces the risk of orange peel texture, pitting, and fogging defects caused by localized excessive corrosion while maintaining a high SiGe removal rate.

[0017] Second, this invention introduces a polymer containing sulfonic acid groups as a selective enhancer. Under alkaline conditions, the strong negative charge of the sulfonic acid groups forms an electrostatic repulsion and hydration lubrication effect between the silica abrasive particles and the TEOS oxide layer surface, suppressing the unintended removal of the TEOS oxide layer, stabilizing and improving the SiGe / TEOS removal selectivity ratio, and reducing abrasive particle adhesion, scratches, and particle residue defects.

[0018] Third, this invention forms a polishing mechanism that combines mild activation, interface lubrication and selective protection through the synergistic effect of corrosion promoter A and selective enhancer B. This enables low-germanium silicon-germanium wafers to have a high removal rate, low surface roughness, high selectivity and low LPD defect level during alkaline chemical mechanical polishing, making them suitable for planarization requirements in advanced complementary metal-oxide-semiconductor manufacturing processes. Detailed Implementation

[0019] This invention provides an alkaline polishing solution for low-germanium-content silicon-germanium wafers, wherein the low-germanium-content silicon-germanium material in the low-germanium-content silicon-germanium wafer is Si. 1-x Ge x Where x ≤ 0.5, preferably x ≤ 0.3. The TEOS oxide layer refers to the silicon oxide layer formed by the TEOS process. MRR is the material removal rate, Sq / RMS is the surface roughness, and LPD is the optical spot defect.

[0020] The method for preparing the low-germanium-content alkaline polishing solution for silicon-germanium wafers of the present invention includes the following steps: S1. Add 80%-90% of the formula amount of deionized water to a clean container. Under stirring conditions, add the formula amount of corrosion accelerator A and selective enhancer B in sequence, and continue stirring until completely dissolved to obtain a mixed solution. S2. Under continuous stirring, slowly add the formula amount of colloidal silica abrasive mother liquor to the mixed solution obtained in step S1. The solid content of the colloidal silica abrasive mother liquor is 30%. After the addition is completed, continue stirring for 10-20 minutes to make the abrasive particles evenly dispersed. S3. Use a pH adjuster to adjust the pH of the solution obtained in step S2 to the target range of 9.0-12.0, then add deionized water to the total amount of the formula, and continue stirring for 20-30 minutes to obtain the low germanium content silicon-germanium wafer alkaline polishing solution.

[0021] When performing chemical mechanical polishing using the low-germanium-content silicon-germanium wafer alkaline polishing slurry of the present invention, the polishing pressure is 1.0-2.0 psi, preferably 1.5 psi; the polishing head speed is 80-100 rpm, preferably 87 rpm; the polishing disc speed is 85-100 rpm, preferably 93 rpm; the polishing slurry flow rate is 100-300 ml / min, preferably 150-200 ml / min; and the polishing pad is a rigid polyurethane polishing pad.

[0022] Example 1 This embodiment provides an alkaline polishing slurry that uses a single cyclic secondary amine as a corrosion promoter.

[0023] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% morpholine; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0024] The preparation steps are as follows: Add 80 wt% of the formula amount of deionized water to a clean container, and add 0.5 wt% of morpholine under stirring, stirring until completely dissolved. Then, slowly add 1.0 wt% of colloidal silica abrasive while continuously stirring, and after stirring evenly, adjust the pH value to 10.0 using potassium hydroxide solution, add deionized water to the total formula amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 1.

[0025] Example 2 This embodiment provides an alkaline polishing solution using a combination of cyclic secondary amines and polymers containing sulfonic acid groups.

[0026] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% morpholine; 0.05 wt% sodium poly(4-styrene sulfonate); pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0027] The preparation steps are as follows: Add 80 wt% of the formulated amount of deionized water to a clean container. While stirring, add 0.5 wt% morpholine and 0.05 wt% poly(4-styrene sulfonate) sequentially, stirring continuously until completely dissolved. Then, slowly add 1.0 wt% colloidal silica abrasive while continuously stirring. After stirring evenly, adjust the pH to 10.0 using potassium hydroxide solution, add deionized water to the total formulated amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 2.

[0028] Example 3 This embodiment provides an alkaline polishing solution using optimized component concentrations and amine types.

[0029] The specific formula is as follows: 1.5 wt% colloidal silica abrasive with an average particle size of 50 nm; 0.5 wt% piperidine; 0.08 wt% sodium polyvinyl sulfonate; pH adjusted to 9.8 with potassium hydroxide; the remainder is deionized water.

[0030] The preparation steps are as follows: Add 80 wt% of the formulated amount of deionized water to a clean container. While stirring, add 0.5 wt% piperidine and 0.08 wt% sodium polyvinyl sulfonate sequentially, stirring continuously until completely dissolved. Then, slowly add 1.5 wt% colloidal silica abrasive while continuously stirring. After stirring evenly, adjust the pH to 9.8 using potassium hydroxide solution, add deionized water to the total formulated amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 3.

[0031] Example 4 This embodiment provides an alkaline polishing solution suitable for silicon-germanium materials with lower germanium content.

[0032] The specific formula is as follows: 1.2 wt% colloidal silica abrasive with an average particle size of 70 nm; 0.6 wt% N-methylpiperazine; 0.06 wt% sodium poly(4-styrene sulfonate); pH adjusted to 10.2 with potassium hydroxide; the remainder is deionized water.

[0033] The preparation steps are as follows: Add 80 wt% of the formulated amount of deionized water to a clean container. While stirring, add 0.6 wt% N-methylpiperazine and 0.06 wt% sodium poly(4-styrenesulfonate) sequentially, stirring continuously until completely dissolved. Then, slowly add 1.2 wt% colloidal silica abrasive while continuously stirring. After stirring evenly, adjust the pH to 10.2 using potassium hydroxide solution, add deionized water to the total formulated amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 4.

[0034] Example 5 This embodiment provides an alkaline polishing slurry that uses a combination of cyclic secondary amines as corrosion promoters.

[0035] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.3 wt% morpholine; 0.3 wt% piperidine; 0.05 wt% sodium polyvinyl sulfonate; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0036] The preparation steps are as follows: Add 80 wt% of the formulated amount of deionized water to a clean container. While stirring, add 0.3 wt% of morpholine, 0.3 wt% of piperidine, and 0.05 wt% of sodium polyvinyl sulfonate sequentially, stirring continuously until completely dissolved. Then, slowly add 1.0 wt% of colloidal silica abrasive while continuously stirring. After stirring evenly, adjust the pH to 10.0 using potassium hydroxide solution, add deionized water to the total formulated amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 5.

[0037] Example 6 This embodiment provides an alkaline polishing liquid with the addition of trace amounts of nonionic surfactants based on an optimized formula.

[0038] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.8 wt% morpholine; 0.10 wt% sodium poly(4-styrene sulfonate); 0.02 wt% fatty alcohol polyoxyethylene ether; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0039] The preparation steps are as follows: Add 80 wt% of the formulated amount of deionized water to a clean container. While stirring, add 0.8 wt% morpholine, 0.10 wt% poly(4-styrene sulfonate) and 0.02 wt% fatty alcohol polyoxyethylene ether sequentially, and continue stirring until completely dissolved. Then, slowly add 1.0 wt% colloidal silica abrasive while continuously stirring. After stirring evenly, adjust the pH to 10.0 using potassium hydroxide solution, add deionized water to the total formulated amount, and continue stirring for 30 minutes to obtain the polishing solution of Example 6.

[0040] Comparative Example 1 This comparative example provides a pure abrasive alkaline polishing slurry without any additives.

[0041] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; pH value adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0042] The preparation steps are as follows: Add 80wt% of the formula amount of deionized water to a clean container, slowly add 1.0wt% of colloidal silica abrasive under stirring conditions, stir evenly, adjust the pH value to 10.0 with potassium hydroxide solution, add deionized water to the total formula amount, and continue stirring for 30 minutes to obtain the polishing liquid of Comparative Example 1.

[0043] Comparative Example 2 This comparative example provides an alkaline polishing slurry with added conventional chain-like primary amines.

[0044] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% ethylenediamine; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0045] The preparation steps are as follows: Add 80 wt% of the formula amount of deionized water to a clean container, and add 0.5 wt% of ethylenediamine under stirring, stirring until completely dissolved. Then, slowly add 1.0 wt% of colloidal silica abrasive while continuously stirring, and after stirring evenly, adjust the pH value to 10.0 using potassium hydroxide solution, add deionized water to the total formula amount, and continue stirring for 30 minutes to obtain the polishing solution of Comparative Example 2.

[0046] Comparative Example 3 This comparative example provides a polishing fluid that uses a common nonionic polymer without sulfonic acid groups as an additive.

[0047] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% morpholine; 0.05 wt% polyethylene glycol with a weight-average molecular weight of 60 kDa; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0048] The preparation steps are the same as in Example 2, except that poly(4-styrene sulfonate) is replaced with polyethylene glycol of equal mass and molecular weight.

[0049] Comparative Example 4 This comparative example provides a polishing fluid using a polymer with extremely low molecular weight sulfonic acid groups.

[0050] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% morpholine; 0.05 wt% poly(4-styrene sulfonate) with a weight-average molecular weight of 20 kDa; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0051] The preparation steps are the same as in Example 2, except that the molecular weight of polymer B is adjusted.

[0052] Comparative Example 5 This comparative example provides a polishing fluid using an ultra-high molecular weight polymer containing sulfonic acid groups.

[0053] The specific formula is as follows: 1.0 wt% colloidal silica abrasive with an average particle size of 60 nm; 0.5 wt% morpholine; 0.05 wt% poly(4-styrene sulfonate) with a weight-average molecular weight of 200 kDa; pH adjusted to 10.0 with potassium hydroxide; the remainder is deionized water.

[0054] The preparation steps are the same as in Example 2, except that the molecular weight of polymer B is adjusted.

[0055] Test case 1. Material Removal Rate (MRR) Test: The material removal rate (MRR) was calculated using a high-precision electronic balance via the weight difference method. The sensitivity of the high-precision electronic balance was 0.1 mg. The calculation formula is as follows: MRR=Δm / (ρ×S×t) Where Δm is the difference in material mass before and after polishing, ρ is the material density, S is the polishing area, and t is the polishing time. Simultaneously, a spectral ellipsometry is used to monitor thickness changes for calibration.

[0056] 2. Surface roughness test: The surface roughness Sq / RMS was tested using atomic force microscopy (AFM). Five points were taken at the center and edge of the wafer surface, with a test range of 10 μm × 10 μm, and the arithmetic mean was taken.

[0057] 3. Selectivity ratio test: The selectivity ratio is defined as the ratio of the material removal rate (MRR) of SiGe to the material removal rate (MRR) of TEOS under the same process conditions.

[0058] 4. Surface defect testing: Surface defects LPD is tested using a laser scanning surface inspection instrument. The test measures the total number of particles larger than 0.16μm and scratches on the wafer surface. The laser scanning surface inspection instrument is a KLA-Tencor Surfscan series.

[0059] Experimental Results and Analysis Table 1: Comparison of the effects of different selectivity enhancers

[0060] As shown in Table 1, in Comparative Example 3, using the common dispersant polyethylene glycol, the selectivity ratio was only 3.6:1, indicating that ordinary steric hindrance is insufficient to effectively protect the TEOS oxide layer. In Example 2, after using a polymer containing sulfonic acid groups, the TEOS removal rate decreased from 45 nm / min to 5 nm / min, indicating that the polymer containing sulfonic acid groups was not merely used as a common dispersant, but rather enhanced the interfacial electrostatic repulsion under alkaline conditions through the strong negative charge of the sulfonic acid groups.

[0061] In an environment with pH > 9, the polymer containing sulfonic acid groups is fully ionized, causing the TEOS surface potential to further decrease from approximately -30mV to below -60mV. This electrostatic repulsion is the physical basis for achieving selective protection of TEOS, enabling the TEOS removal rate to be suppressed to below 10nm / min without significantly reducing the SiGe removal rate.

[0062] The results of Comparative Examples 4, 2, and 5 indicate that when the molecular weight of the polymer containing sulfonic acid groups is in the range of 50-100 kDa, the selectivity is highest and the defects are few. Within this molecular weight range, the polymer chains can fully extend in alkaline aqueous solutions, providing sufficient electrostatic repulsion through the sulfonic acid groups and forming a moderately tough interfacial lubricating layer, thus achieving a better selectivity and surface smoothness. When the molecular weight is too low, the polymer chains are too short, resulting in insufficient charge density and hydration film thickness on the TEOS surface, leading to a weak shielding effect against mechanical wear, insufficient protection, and limited improvement in selectivity. When the molecular weight is too high, the system viscosity is too high, which easily causes abrasive particle bridging and flocculation, leading to an increase in LPD value, and excessive steric hindrance hinders entry into the micro-groove region to form effective protection.

[0063] Table 2: Summary of Polishing Performance

[0064] As shown in Table 2, Comparative Example 1, using a pure abrasive alkaline polishing slurry, achieved an MRR of only 38 nm / min and a Sq of 2.15 nm for Si0.7Ge0.3, with a selectivity of only 3.8:1. This indicates that the dense SiO2 on the surface of low-germanium silicon-germanium silicon... x The passivation layer severely hinders chemical corrosion, making it difficult to achieve effective polishing through simple mechanochemical action.

[0065] In Comparative Example 2, the addition of chain-like primary amine ethylenediamine increased the SiGe MRR to 185 nm / min, but the Sq deteriorated to 0.95 nm, and obvious orange peel texture and pitting defects appeared. The selectivity ratio was only 10.3:1, indicating that although highly corrosive organic amines can improve the removal rate, they are easy to sacrifice surface quality and selectivity.

[0066] Compared to Comparative Example 2, in Example 1, after replacing ethylenediamine with an equal concentration of cyclic secondary amine morpholine, the SiGe MRR remained at 162 nm / min, while the Sq improved to 0.48 nm, and the selectivity increased to 13.5:1. This result indicates that the lone pair electrons on the nitrogen atom in the cyclic secondary amine molecule are affected by the steric hindrance of the cyclic structure, resulting in a milder coordination ability and basicity compared to the chain-like primary amine. This allows it to undergo a slow and uniform hydroxylation reaction with the low-germanium-content silicon-germanium surface, forming a loosely textured, controllable-thickness hydrated oxide layer. This ensures the removal rate while reducing surface defects caused by localized, violent reactions.

[0067] In Example 2, based on Example 1, the introduction of a polymer containing sulfonic acid groups, poly(sodium 4-styrenesulfonate), increased the SiGeMRR to 175 nm / min, further reduced the Sq to 0.14 nm, decreased the TEOS removal rate from 12 nm / min to 5 nm / min, improved the selectivity to 35.0:1, and achieved an LPD of 68 particles. These results indicate that the polymer containing sulfonic acid groups, under alkaline conditions, exhibits strong negative charge through the sulfonic acid groups, generating electrostatic repulsion against the similarly negatively charged silica abrasive particles and the TEOS oxide layer surface. This forms a stable hydrated lubricating film between the abrasive and the wafer surface, achieving interfacial lubrication and selective protection of TEOS.

[0068] Example 3, by optimizing the abrasive particle size, corrosion accelerator type, and polymer concentration, increased the SiGe removal rate to 198 nm / min, reduced the Sq to 0.12 nm, maintained the selectivity at 33.0:1, and reduced the LPD to 42 particles. Example 4 applied the formulation to Si0.8Ge0.2 materials with even lower germanium content, achieving a SiGe removal rate of 145 nm / min, a Sq of 0.11 nm, and a selectivity of 36.3:1, demonstrating the applicability of the synergistic mechanism of this invention to silicon-germanium materials with different low-germanium compositions.

[0069] Example 5 uses a combination of morpholine and piperidine as a corrosion promoter. Through the complementarity of the two cyclic secondary amines in molecular size and adsorption characteristics, the SiGe MRR reaches 215 nm / min, Sq is 0.15 nm, and the selectivity ratio is 35.8:1. Example 6, based on the optimized formulation, adds a trace amount of nonionic surfactant. The SiGe removal rate is 188 nm / min, Sq decreases to 0.09 nm, the selectivity ratio reaches 37.6:1, and the LPD further decreases to 35 particles. This indicates that the addition of surfactant can improve the wetting and spreading properties of the polishing slurry, making the polishing effect more uniform on the wafer surface.

[0070] Based on the above data, this invention achieves efficient and high-quality chemical mechanical polishing (CMP) of low-germanium-content silicon-germanium wafers through the mild activation effect of cyclic secondary amines and the interfacial lubrication and selective protection of polymers containing sulfonic acid groups. For Si0.7Ge0.3 materials, the SiGe MRR can reach 162-215 nm / min; for Si0.8Ge0.2 materials, the SiGe MRR can reach 145 nm / min; the surface area Sq after polishing can be controlled within the range of 0.09-0.15 nm; the SiGe / TEOS selectivity ratio can be stabilized between 33:1 and 38:1; and the LPD (Liquidity Limiting Defect) greater than 0.16 μm can be less than 70 particles / wafer.

[0071] In this embodiment, without departing from the core mechanisms of mild activation, interfacial lubrication, and selective protection of this invention, corrosion promoter A can be any of the following besides morpholine, piperidine, and N-methylpiperazine: other cyclic secondary amines or sterically hindered amines with similar steric hindrance effects, such as N-ethylmorpholine, 2,6-dimethylpiperidine, 1-methylimidazolium, and hexamethylenetetramine. These compounds share the characteristic that the nitrogen atom is sterically shielded by the cyclic structure or adjacent groups, resulting in milder basicity and enabling uniform hydroxylation reactions. Furthermore, chain amines containing ether bonds, such as diethylene glycolamines, can also be used as alternative or supplementary components due to the moderating effect of the ether bond on the activity of the amine group.

[0072] In addition to sodium poly(4-styrene sulfonate) and sodium polyethylene sulfonate, selective reinforcing agent B can also be other water-soluble polymers containing sulfonic acid groups or similar strong anionic groups, such as poly(2-acrylamido-2-methylpropanesulfonic acid) and its copolymers, naphthalene sulfonic acid formaldehyde condensate, lignin sulfonates, etc. All of these polymers can provide a negative charge under alkaline conditions, achieving electrostatic repulsion and interfacial lubrication. Furthermore, polymers containing carboxylic acid groups, such as polyacrylic acid and its copolymers, can also exert similar effects within a specific pH range.

[0073] While maintaining the core mechanisms mentioned above, the pH adjuster can be tetramethylammonium hydroxide instead of potassium hydroxide to reduce the risk of potassium ion contamination; the abrasive can be partially or entirely made of surface-modified colloidal silica to enhance dispersion stability.

[0074] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-germanium-content alkaline polishing solution for silicon-germanium wafers, characterized in that: The low-germanium silicon-germanium material in the low-germanium silicon-germanium wafer is Si. 1-x Ge x Where x≤0.5; the pH value of the low-germanium silicon-germanium wafer alkaline polishing solution is 9.0-12.0, and by mass percentage, it comprises the following components: The composition includes 0.5%–3.0% colloidal silica abrasive, 0.1%–1.5% corrosion accelerator A, 0.01%–0.2% selective enhancer B, pH adjuster, and the balance deionized water; wherein corrosion accelerator A is a cyclic secondary amine compound, and selective enhancer B is a polymer containing sulfonic acid groups.

2. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The low-germanium silicon-germanium material is Si. 1-x Ge x , where x≤0.

3.

3. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The colloidal silica abrasive has an average particle size of 30-80 nm, preferably 50-70 nm; the colloidal silica abrasive is uniformly dispersed in the low-germanium silicon-germanium wafer alkaline polishing solution.

4. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The corrosion accelerator A is selected from at least one of morpholine, piperidine, and N-methylpiperazine, preferably morpholine or piperidine.

5. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The selective reinforcing agent B is selected from at least one of poly(4-styrene sulfonate) or sodium polyethylene sulfonate, preferably poly(4-styrene sulfonate), and the weight-average molecular weight of the selective reinforcing agent B is 50-100 kDa.

6. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The pH adjuster is potassium hydroxide or tetramethylammonium hydroxide, and the pH value of the low-germanium silicon-germanium wafer alkaline polishing solution is preferably 9.5-10.

5.

7. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, The low-germanium silicon-germanium wafer alkaline polishing solution also includes 0.005%–0.05% of a nonionic surfactant, wherein the nonionic surfactant is fatty alcohol polyoxyethylene ether.

8. The low-germanium-content alkaline polishing solution for silicon-germanium wafers according to claim 1, characterized in that, By mass percentage, the colloidal silica abrasive is 1.0%–2.0%, the corrosion accelerator A is 0.3%–1.0%, and the selective reinforcing agent B is 0.03%–0.10%.

9. A method for preparing the low-germanium-content alkaline polishing solution for silicon-germanium wafers according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Add 80%-90% of the formula amount of deionized water to a clean container. Under stirring conditions, add the formula amount of corrosion accelerator A and selective enhancer B in sequence, and continue stirring until completely dissolved to obtain a mixed solution. S2. Under continuous stirring, slowly add the formula amount of colloidal silica abrasive mother liquor to the mixed solution obtained in step S1. The solid content of the colloidal silica abrasive mother liquor is 30%. After the addition is completed, continue stirring for 10-20 minutes to make the abrasive particles evenly dispersed. S3. Adjust the pH of the solution obtained in step S2 to 9.0-12.0 using a pH adjuster, then add deionized water to the total amount of the formula, and continue stirring for 20-30 minutes to obtain the low germanium silicon-germanium wafer alkaline polishing solution.

10. A chemical mechanical polishing method for silicon-germanium wafers with low germanium content, characterized in that, The low-germanium-content silicon-germanium wafer is chemically and mechanically polished using the alkaline polishing slurry for silicon-germanium wafers as described in any one of claims 1 to 8; the polishing pressure is 1.0-2.0 psi, preferably 1.5 psi; the polishing head speed is 80-100 rpm, preferably 87 rpm; the polishing disk speed is 85-100 rpm, preferably 93 rpm; the polishing slurry flow rate is 100-300 ml / min, preferably 150-200 ml / min; and the polishing pad is a hard polyurethane polishing pad.

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