A process for reducing haze in orientation polished wafers

Abstract

The present application relates to the technical field of semiconductor silicon wafer polishing, in particular to a process for reducing wafer fog of crystal direction polished wafer, comprising the following steps: after the crystal direction silicon wafer is pasted on the ceramic carrier, the wafer is loaded into the polishing equipment, rough polishing is carried out, fine polishing is carried out by using PUP polishing cloth with service time not more than 10 hours, and cleaning is carried out. Through the synergistic control of pasting and fixing, rough polishing, fine polishing, cleaning and detection feedback, the cumulative service time of PUP material polishing cloth in the fine polishing stage is limited within 10 hours, combined with cloth time record, cloth surface state judgment, activation treatment before fine polishing and subsequent detection feedback mechanism, local uneven grinding and residue adsorption caused by fiber collapse, micropore blockage and cloth surface hardening of the polishing cloth can be effectively avoided, the generation probability of wafer fog defects is reduced from the source, the process prevention and active control of wafer fog defects are realized, the surface flatness, cleanliness and polishing consistency of the silicon wafer can be improved, and the stability and product yield of subsequent photoetching, etching and device manufacturing processes can be improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor silicon wafer polishing technology, and more particularly to a process for reducing haze on crystal-oriented polished wafers. Background Technology

[0002] In semiconductor silicon wafer processing, chemical mechanical polishing (CMP) is a key step in obtaining a high flatness and low-damage surface. For silicon wafers with specific crystal orientations, especially 111-oriented wafers, due to their dense atomic arrangement and relatively low surface chemical activity, the chemical etching rate during polishing is slow. Material removal is more likely to be a combination of localized selective removal and mechanical grinding, which can easily lead to the formation of submicroscopic rough areas or residual adsorption areas on the silicon wafer surface, resulting in wafer haze defects.

[0003] The defects of film fog are somewhat concealed and are not easily identified in a timely manner during routine visual inspection. If they flow into subsequent photolithography, etching or device manufacturing processes, they may affect the uniformity of photoresist coating, exposure energy distribution, etching uniformity and device electrical performance, thereby causing fluctuations in the chip's critical dimensions, increased leakage risk, reduced product consistency and decreased yield.

[0004] Current silicon wafer polishing processes typically employ a combination of rough and fine polishing to achieve surface leveling. However, given the tendency of 111-oriented silicon wafers to develop wafer haze, existing processes focus primarily on polishing pressure, rotation speed, time, and polishing fluid parameters. They lack targeted control over factors such as the condition of the polishing cloth during fine polishing, cumulative usage time, cloth pore blockage, fiber collapse, and residual adsorption. Especially when the fine polishing cloth is used for an extended period, problems such as fiber compaction, micropore blockage, cloth hardening, and decreased localized liquid carrying capacity can easily occur on the cloth surface. This makes it difficult to maintain uniform mechanical and chemical action during the fine polishing stage, thereby inducing or exacerbating wafer haze defects. Summary of the Invention

[0005] To address the technical problems existing in the prior art, embodiments of the present invention provide a process for reducing haze in crystal-oriented polished wafers. The technical solution is as follows: A process for reducing haze on crystal-oriented polished wafers includes the following steps: S1. The silicon wafer to be polished is attached to a ceramic carrier through a wax layer to form a wafer assembly; S2. Install the wafer carrier assembly onto the polishing equipment, so that the surface of the crystal-oriented silicon wafer to be polished faces the polishing cloth; S3. Perform rough polishing on the crystal-oriented silicon wafer to remove the damaged layer on the surface of the crystal-oriented silicon wafer; S4. The crystal-oriented silicon wafer after rough polishing is subjected to fine polishing. The fine polishing process uses PUP material polishing cloth, and the cumulative usage time of the PUP material polishing cloth is controlled to be no more than 10 hours. S5. After the fine polishing process, the crystal-oriented silicon wafer is cleaned to remove wax residue, polishing fluid residue and particle residue on the surface of the crystal-oriented silicon wafer. The crystal orientation silicon wafer includes at least a 111 crystal orientation silicon wafer. Before or during the fine polishing process, the PUP material polishing cloth is recorded for application time and its usage status is determined. When the cumulative usage time of the PUP material polishing cloth exceeds a preset application time threshold or the cloth surface status does not meet the preset conditions, the fine polishing process is stopped using the PUP material polishing cloth.

[0006] As a further aspect of the present invention, in step S1, the amount of wax applied to the crystal-oriented silicon wafer is 0.7±0.2mL / wax wafer, and the wax application speed is 1500~2500rpm; during the bonding process, the vacuum degree of the wax-coating rotating part is -20.0~-30.0KPa, the bonding main vacuum degree is 100~150Pa, and the holding time is 5~15s.

[0007] As a further aspect of the present invention, the ceramic carrier is an alumina ceramic carrier or a silicon carbide ceramic carrier; before the crystal-oriented silicon wafer is attached to the ceramic carrier, the bearing surface of the ceramic carrier is subjected to flatness detection and cleanliness treatment to ensure that the bearing surface meets the flatness requirements for attachment, thereby reducing the local polishing difference caused by attachment warping.

[0008] As a further aspect of the present invention, in step S3, the polishing pressure of the rough polishing process is 1–5 kg / cm². 2 The fixed plate speed is 50±5 rpm, the polishing head speed is 50±5 rpm, and the coarse polishing time is 5 to 45 min. The dilution rate of the polishing slurry used for coarse polishing is 1:30, the pH value is 11.00±0.10, the flow rate of the polishing slurry is 2.0±0.5 L / min, and the service life of the polishing slurry circulation is no more than 10 hours.

[0009] As a further aspect of the present invention, the polishing pressure of the fine polishing process is 1-5 kg / cm. 2 The fixed plate speed is 30±5 rpm, the polishing head speed is 30±5 rpm, the fine polishing time is 8~10 min, and the fine polishing temperature is 30.0~40.0℃; the dilution rate of the fine polishing solution used for fine polishing is 1:20, and the flow rate of the fine polishing solution is 0.5±0.2L / min.

[0010] As a further aspect of the present invention, the cloth time record includes recording the cumulative usage time, number of processing batches, and number of processed pieces of the PUP material polishing cloth since its first participation in fine polishing treatment; When the cumulative usage time reaches 8 hours but is less than 10 hours, the PUP material polishing cloth will be marked as a warning state, and the frequency of cloth cleaning or repair will be increased. When the cumulative usage time reaches 10 hours, the PUP material polishing cloth is prohibited from being used for fine polishing of the crystal-oriented silicon wafer.

[0011] As a further aspect of the present invention, before step S4, the PUP material polishing cloth undergoes a pre-polishing activation treatment, the pre-polishing activation treatment comprising: The PUP material polishing cloth is rinsed with deionized water and cleaning agent to remove residual particles and polishing liquid crystals from the cloth surface; Subsequently, the PUP material polishing cloth is pre-wetted and pre-rotated under low pressure conditions to keep the micropores of the PUP material polishing cloth open and form a stable liquid-holding state.

[0012] As a further aspect of the present invention, after step S5, the crystal-oriented silicon wafer is subjected to wafer haze detection and surface roughness detection, and the fine polishing control parameters for subsequent batches are adjusted according to the detection results. When the haze value or surface roughness exceeds the preset standard, the allowable cumulative usage time of the PUP material polishing cloth in subsequent batches will be reduced by 0.5 to 2 hours, or the frequency of the pre-polishing activation treatment of the PUP material polishing cloth will be increased, so as to form a closed-loop control of haze defects.

[0013] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: This invention, through the coordinated control of steps such as attachment and fixing, rough polishing, fine polishing, cleaning, and inspection feedback, limits the cumulative usage time of the PUP material polishing cloth in the fine polishing stage to within 10 hours. Combined with cloth usage recording, cloth surface condition judgment, pre-polishing activation treatment, and subsequent inspection feedback mechanisms, it effectively avoids uneven grinding and residue adsorption caused by fiber collapse, micropore blockage, and cloth surface hardening, thus reducing the probability of wafer haze defects at the source. Compared with existing technologies that rely on post-processing rework or scrapping, this invention achieves process prevention and proactive control of wafer haze defects, improving silicon wafer surface flatness, cleanliness, and polishing consistency, reducing rework frequency and material loss, shortening production cycle time, reducing overall manufacturing costs, and improving the stability and product yield of subsequent photolithography, etching, and device manufacturing processes. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0015] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0016] Please see Figure 1This invention provides a technical solution: a process for reducing haze on crystal-oriented polished wafers, comprising the following steps: S1. The silicon wafer to be polished is attached to a ceramic carrier through a wax layer to form a wafer assembly; S2. Install the wafer carrier assembly onto the polishing equipment, so that the surface of the silicon wafer to be polished faces the polishing cloth. S3. Perform rough polishing on the crystal-oriented silicon wafer to remove the damaged layer on the surface of the crystal-oriented silicon wafer; S4. Perform fine polishing on the crystal-oriented silicon wafers after rough polishing. The fine polishing process uses PUP material polishing cloth, and the cumulative usage time of the PUP material polishing cloth is controlled to be no more than 10 hours. S5. After fine polishing, the crystal-oriented silicon wafer is cleaned to remove wax residue, polishing fluid residue and particle residue on the surface of the crystal-oriented silicon wafer. Among them, the crystal orientation silicon wafers include at least 111 crystal orientation silicon wafers, and before or during the fine polishing process, the polishing time of the PUP material polishing cloth is recorded and the usage status is determined. When the cumulative usage time of the PUP material polishing cloth exceeds the preset polishing time threshold or the cloth surface status does not meet the preset conditions, the fine polishing process of the PUP material polishing cloth is stopped.

[0017] Specifically, the silicon wafer to be processed can be a 111 crystal orientation silicon wafer, or other specific crystal orientation silicon wafers that are prone to hazy defects during polishing.

[0018] In the fine polishing stage, the polishing cloth is no longer simply replaced based on batch number or experience. Instead, the cumulative working state of the PUP material polishing cloth is controlled as a key variable affecting wafer haze generation. By confirming whether the polishing cloth is still in a suitable state for processing silicon wafers before or during fine polishing, it is possible to avoid using polishing cloths with surface hardening, pore blockage, or uneven grinding performance to continue processing silicon wafers, thereby reducing the probability of forming submicroscopic rough areas and residual adsorption areas after fine polishing.

[0019] As a further embodiment of the present invention, in S1, the wax coating amount of the crystal-oriented silicon wafer is 0.7±0.2mL / wax wafer, the wax coating rotation speed is 1500~2500rpm; during the bonding process, the vacuum degree of the wax coating rotation part is -20.0~-30.0KPa, the bonding main vacuum degree is 100~150Pa, and the holding pressure time is 5~15s.

[0020] Specifically, the wax application process not only connects the silicon wafer to the ceramic carrier but also directly affects the uniformity of force during subsequent polishing. Insufficient wax application can lead to insufficient adhesion in certain areas, causing slight displacement or localized lifting of the silicon wafer during polishing. Excessive wax application can result in uneven wax layer thickness, causing variations in the support on the back of the silicon wafer and consequently leading to localized removal deviations during front-side polishing. By controlling the wax application amount, spin coating speed, vacuum adsorption level, and holding pressure time, a continuous and relatively uniform support layer is formed between the silicon wafer and the ceramic carrier. This ensures that the silicon wafer maintains a stable planar support state during subsequent rough and fine polishing stages, reducing the risk of edge fogging, localized fogging, or ring-shaped fogging caused by poor adhesion.

[0021] As a further aspect of the present invention, the ceramic carrier is an alumina ceramic carrier or a silicon carbide ceramic carrier; before the crystal-oriented silicon wafer is attached to the ceramic carrier, the bearing surface of the ceramic carrier is subjected to flatness testing and cleanliness treatment to ensure that the bearing surface meets the flatness requirements for attachment, so as to reduce the local polishing difference caused by attachment warping.

[0022] Specifically, ceramic carriers are preferably made of ceramic materials with high rigidity, low thermal deformation, and good chemical corrosion resistance. Both alumina ceramics and silicon carbide ceramics can provide stable support for silicon wafers under polishing pressure and reduce the impact of carrier deformation on wafer flatness. Before attaching the silicon wafer, the bearing surface of the ceramic carrier should be cleaned, dried, and its surface condition checked to remove residual wax, particles, dried polishing fluid, or other foreign matter. When there are local bumps or contaminants on the bearing surface of the ceramic carrier, tiny support high points will form after the silicon wafer is attached, causing the corresponding area to bear abnormal pressure during polishing. By checking the condition of the ceramic carrier before attachment, the attachment interface is more stable, reducing localized uneven polishing caused by carrier surface abnormalities from the source.

[0023] As a further aspect of the present invention, in S3, the polishing pressure of the rough polishing process is 1-5 kg / cm. 2 The fixed plate speed is 50±5 rpm, the polishing head speed is 50±5 rpm, and the coarse polishing time is 5 to 45 min. The dilution rate of the polishing slurry used for coarse polishing is 1:30, the pH value is 11.00±0.10, the flow rate of the polishing slurry is 2.0±0.5 L / min, and the service life of the polishing slurry circulation is no more than 10 hours.

[0024] Specifically, the rough polishing stage is mainly used to remove the mechanical damage layer and larger-scale surface undulations formed in the previous processing, providing a relatively uniform substrate state for subsequent fine polishing. If insufficient material is removed during rough polishing, the residual damage layer will continue to affect surface uniformity in the fine polishing stage; if the rough polishing is too strong, it may exacerbate micro-damage on the silicon wafer surface and increase the load on subsequent fine polishing. By limiting the rough polishing pressure, platen speed, polishing head speed, processing time, and polishing slurry state, the rough polishing stage balances removal efficiency and surface stability. Maintaining the pH value of the polishing slurry within a slightly alkaline range is beneficial for moderate chemical reactions on the silicon wafer surface, while simultaneously cooperating with mechanical grinding to remove the damage layer; limiting the slurry's cycle life reduces the impact of particle agglomeration, reaction product accumulation, or chemical activity decay in aged slurry on polishing uniformity.

[0025] As a further aspect of the present invention, the polishing pressure for fine polishing is 1–5 kg / cm². 2 The fixed plate speed is 30±5 rpm, the polishing head speed is 30±5 rpm, the fine polishing time is 8~10 min, and the fine polishing temperature is 30.0~40.0℃; the dilution rate of the fine polishing solution used for fine polishing is 1:20, and the flow rate of the fine polishing solution is 0.5±0.2L / min.

[0026] Furthermore, the fine polishing stage is used to microscopically level the surface of the silicon wafer after rough polishing and reduce residual defects, which is a key step in controlling wafer haze defects. Compared with rough polishing, fine polishing uses a lower mechanical speed and a shorter processing time, allowing the silicon wafer surface material to be removed in a gentler and more uniform manner. For 111 crystal orientation silicon wafers, their crystal plane chemical reactivity is relatively low. If the mechanical action of fine polishing is too strong, it is easy to form fine scratches or local grinding differences; if the chemical action is insufficient, it may lead to the residue of reaction products and fine particles. This embodiment controls the fine polishing pressure, speed, temperature, fine polishing solution dilution ratio, and supply flow rate to maintain a stable liquid film state and a uniform material removal state at the polishing interface, thereby reducing haze defects caused by local dry friction, residue accumulation, or uneven removal.

[0027] As a further aspect of the present invention, the cloth time record includes recording the cumulative usage time, number of processing batches, and number of processed pieces of PUP material polishing cloth since its first participation in fine polishing treatment; When the cumulative usage time reaches 8 hours but is less than 10 hours, the PUP material polishing cloth will be marked as a warning state, and the frequency of cloth cleaning or repair will be increased. When the cumulative usage time reaches 10 hours, the PUP material polishing cloth shall not be used for fine polishing of crystal-oriented silicon wafers.

[0028] The condition of PUP polishing cloth is not entirely dependent on whether it reaches a scrapped state, but is also related to its cumulative processing time, number of pieces processed, number of batches processed, and type of products processed. As the usage time increases, the fiber structure on the surface of the polishing cloth will gradually compact, and the residual polishing fluid and silicon powder particles in the micropores will also gradually increase, causing changes in its liquid retention capacity and microscopic contact state.

[0029] Furthermore, a tiered management system is implemented, with an early warning system in place before the polishing cloth reaches its lifespan limit. This allows operators to proactively clean, repair, or check the cloth surface, preventing it from continuing to process oriented silicon wafers for extended periods while nearing failure. Once the polishing cloth reaches the end of its lifespan, it is no longer used for fine polishing of oriented silicon wafers, even if there is no obvious damage to its appearance. This ensures that different batches of silicon wafers achieve relatively consistent polishing interface conditions during the fine polishing stage.

[0030] As a further aspect of the present invention, before step S4, the PUP material polishing cloth undergoes a pre-polishing activation treatment, which includes: The PUP material polishing cloth is rinsed with deionized water and cleaning agent to remove residual particles and polishing liquid crystals from the cloth surface; Subsequently, the PUP material polishing cloth was pre-wetted and pre-rotated under low pressure conditions to keep the micropores of the PUP material polishing cloth open and form a stable liquid-holding state.

[0031] Furthermore, the PUP material polishing cloth is activated before fine polishing, which can be used to restore or improve the wetting state and micropore open state of the polishing cloth surface. Since the polishing cloth may have residual polishing liquid residue, silicon powder, cleaning agent residue or other fine particles on its surface after the previous processing, if it is directly put into the next batch of fine polishing, the residue may form local obstruction or secondary scratches on the silicon wafer surface.

[0032] Furthermore, before fine polishing, the cloth surface is rinsed with deionized water and cleaning agent, and the polishing cloth is fully wetted by low-pressure pre-rotation, allowing the fine polishing solution to be more evenly distributed on the polishing interface. This activation treatment, combined with polishing cloth life management, reduces cloth residue on the surface and minimizes material removal differences caused by localized dry or clogged areas on the cloth surface, thereby further improving the fog control effect.

[0033] As a further aspect of the present invention, after S5, wafer haze detection and surface roughness detection are performed on the crystal-oriented silicon wafer, and the fine polishing control parameters of subsequent batches are adjusted according to the detection results. When the haze value or surface roughness exceeds the preset standard, the allowable cumulative usage time of PUP material polishing cloth in subsequent batches will be reduced by 0.5 to 2 hours, or the frequency of pre-polishing activation treatment of PUP material polishing cloth will be increased to form a closed-loop control of haze defects.

[0034] Furthermore, after fine polishing and cleaning, the silicon wafers can be quality-confirmed using wafer haze detection equipment, surface roughness detection equipment, or appearance inspection equipment, and the results can be used for process adjustments in subsequent batches. If the detection results show an increase in wafer haze levels or a deterioration in surface roughness, even if it has not exceeded the product scrap standard, it can be used as a signal of changes in polishing cloth condition or process window shift. In this case, the allowable usage time of PUP material polishing cloth in subsequent batches can be appropriately shortened, or the frequency of pre-polishing activation treatment, cloth cleaning, and finishing can be increased. Through this feedback method, the terminal detection results can be linked with the front-end fine polishing control parameters, forming a preventive closed-loop management of wafer haze defects, rather than simply reworking or scrapping after defects occur.

[0035] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should 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 process for reducing haze on crystal-oriented polished wafers, characterized in that, Includes the following steps: S1. The silicon wafer to be polished is attached to a ceramic carrier through a wax layer to form a wafer assembly; S2. Install the wafer carrier assembly onto the polishing equipment, so that the surface of the crystal-oriented silicon wafer to be polished faces the polishing cloth; S3. Perform rough polishing on the crystal-oriented silicon wafer to remove the damaged layer on the surface of the crystal-oriented silicon wafer; S4. The crystal-oriented silicon wafer after rough polishing is subjected to fine polishing. The fine polishing process uses PUP material polishing cloth, and the cumulative usage time of the PUP material polishing cloth is controlled to be no more than 10 hours. S5. After the fine polishing process, the crystal-oriented silicon wafer is cleaned to remove wax residue, polishing fluid residue and particle residue on the surface of the crystal-oriented silicon wafer. The crystal orientation silicon wafer includes at least a 111 crystal orientation silicon wafer. Before or during the fine polishing process, the PUP material polishing cloth is recorded for application time and its usage status is determined. When the cumulative usage time of the PUP material polishing cloth exceeds a preset application time threshold or the cloth surface status does not meet the preset conditions, the fine polishing process is stopped using the PUP material polishing cloth.

2. The method for reducing haze on a crystal orientation polished wafer according to claim 1, characterized in that: In step S1, the wax coating amount of the crystal-oriented silicon wafer is 0.7±0.2mL / wax wafer, and the wax coating rotation speed is 1500~2500rpm; during the bonding process, the vacuum degree of the wax coating rotation part is -20.0~-30.0KPa, the bonding main vacuum degree is 100~150Pa, and the holding pressure time is 5~15s.

3. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, The ceramic carrier is an alumina ceramic carrier or a silicon carbide ceramic carrier; before the crystal-oriented silicon wafer is attached to the ceramic carrier, the bearing surface of the ceramic carrier is subjected to flatness detection and cleanliness treatment to ensure that the bearing surface meets the flatness requirements for attachment, so as to reduce the local polishing difference caused by attachment warping.

4. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, In step S3, the polishing pressure for the rough polishing process is 1–5 kg / cm². 2 The fixed plate speed is 50±5 rpm, the polishing head speed is 50±5 rpm, and the coarse polishing time is 5 to 45 min. The dilution rate of the polishing slurry used for coarse polishing is 1:30, the pH value is 11.00±0.10, the flow rate of the polishing slurry is 2.0±0.5 L / min, and the service life of the polishing slurry circulation is no more than 10 hours.

5. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, In step S4, the polishing pressure for the fine polishing process is 1–5 kg / cm². 2 The fixed plate speed is 30±5 rpm, the polishing head speed is 30±5 rpm, the fine polishing time is 8~10 min, and the fine polishing temperature is 30.0~40.0℃; the dilution rate of the fine polishing solution used for fine polishing is 1:20, and the flow rate of the fine polishing solution is 0.5±0.2L / min.

6. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, The cloth usage record includes the cumulative usage time, number of processing batches, and number of processed pieces of the PUP material polishing cloth since its first participation in fine polishing. When the cumulative usage time reaches 8 hours but is less than 10 hours, the PUP material polishing cloth will be marked as a warning state, and the frequency of cloth cleaning or repair will be increased. When the cumulative usage time reaches 10 hours, the PUP material polishing cloth is prohibited from being used for fine polishing of the crystal-oriented silicon wafer.

7. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, Before step S4, the PUP material polishing cloth undergoes a pre-polishing activation treatment, which includes: The PUP material polishing cloth is rinsed with deionized water and cleaning agent to remove residual particles and polishing liquid crystals from the cloth surface; Subsequently, the PUP material polishing cloth is pre-wetted and pre-rotated under low pressure conditions to keep the micropores of the PUP material polishing cloth open and form a stable liquid-holding state.

8. The method for reducing haze on a crystal-oriented polished wafer according to claim 1, characterized in that, After step S5, the crystal-oriented silicon wafer is subjected to wafer haze detection and surface roughness detection, and the fine polishing control parameters for subsequent batches are adjusted based on the detection results. When the haze value or surface roughness exceeds the preset standard, the allowable cumulative usage time of the PUP material polishing cloth in subsequent batches will be reduced by 0.5 to 2 hours, or the frequency of the pre-polishing activation treatment of the PUP material polishing cloth will be increased, so as to form a closed-loop control of haze defects.

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