A method for optimizing a wafer reconditioning chemical mechanical polishing process

Abstract

The application discloses a kind of optimization methods of wafer regeneration chemical mechanical polishing process, including steps wet etching pretreatment, multistage CMP polishing, dynamic parameter adjustment and polishing liquid control;The application is reasonable in structure, and the surface particle condition of regenerated wafer is greatly improved by adjusting CMP parameters.Simultaneously, because 60nm and 90nm grinding fluid cost is not one:60nm grinding fluid cost is extremely high.Shorten the grinding time of 60nm to promote the improvement of cost.The improvement degree of the roughness of the silicon wafer surface in the application: reduce to 0.1nm within 0.2nm.

Description

Technical Field

[0001] This invention relates to an optimized method for a wafer regeneration chemical mechanical polishing process. Background Technology

[0002] The wafer regeneration polishing process is formed by combining polishing and CMP processes. The polishing process uses a three-pane rough polishing operation, while the CMP process uses a three-pane fine polishing operation. This may cause micro-scratches on the silicon wafer surface, such as pits, scratches, etc., as well as uneven roughness or subsurface defects. These types of defects are shown to be removable shallow pits and micro-scratches when scanned by measuring equipment.

[0003] In wafer regeneration processes, the removal of this type of defect is crucial. If the residual damage layer from the incoming material is not completely removed, the clusters of particles caused by these scratches will adversely affect subsequent processing. For example, if metal ions are present in the scratch pits, these ions can diffuse into the furnace tube and clean wafer during the high-temperature furnace tube process, contaminating the equipment and the characteristics of the wafer itself, leading to performance degradation or even damage during electrical testing.

[0004] In actual wafer regeneration operations, the above process resulted in excessive particle size on the surface of the finished product due to issues with the matching of polishing processes before and after the polishing. The high-specification yield of the CMP-processed product was no more than 30%, with approximately 100 particles and a surface roughness of 0.2 nm.

[0005] Glossary

[0006] Q-time: The time a wafer waits for the next process to begin after completing one process.

[0007] Haze: A type of microscopic defect that exists on the surface of a wafer, which can reflect the surface roughness to some extent.

[0008] CMP: a process for planarizing the surface of a wafer. Summary of the Invention

[0009] The purpose of this invention is to provide an optimized method for wafer regeneration chemical mechanical polishing process to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution: an optimized method for wafer regeneration chemical mechanical polishing process, comprising the following steps:

[0011] (1) Wet etching pretreatment: Immerse the regenerated wafer in a diluted acidic solution to remove the natural oxide layer on the surface, and control the immersion time to be 30 to 60 seconds;

[0012] (2) Multi-stage CMP polishing: intermediate polishing (P1 stage), fine polishing (P2 stage) and secondary fine polishing (P3 stage) are performed in sequence;

[0013] The intermediate polishing stage (P1) uses an abrasive slurry with a particle size of 60-90 nm and a grooved non-woven polishing pad; the fine polishing stages (P2, P3) use an abrasive slurry with a particle size ≤60 nm and a grooveless non-woven polishing pad.

[0014] (3) Dynamic parameter adjustment:

[0015] In the intermediate polishing stage (P1), the polishing pressure is increased to 10-15 kPa and the rotation speed is increased to 40-60 rpm; in the fine polishing stage (P2, P3), the polishing pressure is adjusted to 8-12 kPa and the rotation speed is increased to 30-50 rpm.

[0016] During stages P2 and P3, the ratio of the control disc speed to the disc head speed is controlled to be 1.1 to 1.5.

[0017] (4) Polishing slurry control:

[0018] In the intermediate polishing stage (P1), shorten the working time of the 60nm particle size polishing slurry and extend the working time of the 90nm particle size polishing slurry.

[0019] Maintain the pH of the polishing solution at 8–12 and the polishing temperature at 20–40℃.

[0020] Preferably, the acidic solution in step (1) is diluted hydrofluoric acid (HF), and the interval (Q-time) between the wet etching process and the start of the CMP process does not exceed 10 minutes.

[0021] Preferably, the polishing fluid used in the intermediate polishing stage (P1) in step (2) is a 7310 type polishing fluid, and the polishing fluid used in the fine polishing stages (P2, P3) is an 8100 type polishing fluid.

[0022] Preferably, the polishing pressure of the intermediate polishing stage (P1) in step (3) is 12 kPa and the rotation speed is 50 rpm; the polishing pressure of the fine polishing stages (P2, P3) is 10 kPa and the rotation speed is 40 rpm.

[0023] Preferably, the ratio of the rotational speed of the disk surface to that of the disk head in step (3) is 1.2.

[0024] Preferably, the pH value in step (4) is 10-11 and the polishing temperature is 25-35℃.

[0025] Preferably, a wafer regeneration CMP process equipment includes:

[0026] The preprocessing module is used to perform the wet etching preprocessing as described in any one of claims 1 to 6;

[0027] The multi-stage polishing module is configured to be connected in sequence to the intermediate polishing disc (P1), the fine polishing disc (P2), and the secondary fine polishing disc (P3), and the pressure and rotation speed parameters of each disc are adjusted according to claims 1 to 5;

[0028] The control unit is used to monitor and adjust the polishing solution ratio, pH value, and temperature in real time.

[0029] Preferably, a regenerated wafer, prepared by the above method, has a surface roughness ≤0.1nm, a particle density ≤30 particles / wafer, and a reduction of LPDN defect cluster density by more than 50%.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. The particle density has been reduced from 100 particles / tablet to ≤30 particles / tablet;

[0032] 2. Surface roughness decreased from 0.2 nm to ≤0.1 nm;

[0033] 3. The density of LPDN defect clusters is reduced by more than 50%;

[0034] 4. Cost savings of 10% for single-shot CMP (from 30 yuan to 27 yuan). Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0036] This invention provides a technical solution: an optimized method for wafer regeneration chemical mechanical polishing process, comprising the following steps:

[0037] (1) Wet etching pretreatment: Immerse the regenerated wafer in a diluted acidic solution to remove the natural oxide layer on the surface, and control the immersion time to be 30 to 60 seconds;

[0038] (2) Multi-stage CMP polishing: intermediate polishing (P1 stage), fine polishing (P2 stage) and secondary fine polishing (P3 stage) are performed in sequence;

[0039] The intermediate polishing stage (P1) uses an abrasive slurry with a particle size of 60-90 nm and a grooved non-woven polishing pad; the fine polishing stages (P2, P3) use an abrasive slurry with a particle size ≤60 nm and a grooveless non-woven polishing pad.

[0040] (3) Dynamic parameter adjustment:

[0041] In the intermediate polishing stage (P1), the polishing pressure is increased to 10-15 kPa and the rotation speed is increased to 40-60 rpm; in the fine polishing stage (P2, P3), the polishing pressure is adjusted to 8-12 kPa and the rotation speed is increased to 30-50 rpm.

[0042] During stages P2 and P3, the ratio of the control disc speed to the disc head speed is controlled to be 1.1 to 1.5.

[0043] (4) Polishing slurry control:

[0044] In the intermediate polishing stage (P1), shorten the working time of the 60nm particle size polishing slurry and extend the working time of the 90nm particle size polishing slurry.

[0045] Maintain the pH of the polishing solution at 8–12 and the polishing temperature at 20–40℃.

[0046] The technological improvements include several aspects: adjustments to the polishing process steps, innovation in the relative proportions of the polishing slurry, and control over the surface morphology of the silicon wafer.

[0047] 1. Adjustment of Polishing Process Steps: The adjusted process involves wet etching pretreatment of the regenerated wafer before CMP. This pretreatment uses diluted acidic liquids such as HF to remove the natural oxide layer on the surface. However, the Q-time must be effectively controlled between this and the next process step. Excessive Q-time can lead to the re-formation of a thicker natural oxide layer, which cannot be removed. Generally, an immersion time of 30-60 seconds yields the best results. It is important to avoid excessive immersion time to prevent over-etching of the silicon wafer surface. Over-etched wafers may appear black or have a matte finish. This can lead to misjudgment during surface inspection in the next process step, resulting in process route mismatches.

[0048] After completing the above steps, the next preparatory work includes the implementation of a multi-stage CMP process. The CMP process involves three polishing stages: intermediate polishing, fine polishing, and a final fine polishing. In the intermediate polishing stage, the polishing slurry uses a particle size of 90nm or 60nm, and a grooved non-woven polishing pad is used. In the fine polishing stage, the polishing slurry particle size is adjusted to 60nm, and a non-grooved non-woven polishing pad is used. It is worth noting that the process used in stages P2 and P3 is the same. In stage P1, the main task is to treat and repair the surface of the incoming wafer and the shallow scratches and subsurface defects generated during the intermediate polishing process, reducing the impact of surface defects on the particles after the CMP process. Furthermore, this stage repairs and improves the rough surface after rough polishing, reducing the roughness from 0.2nm to less than 0.1nm.

[0049] Based on the KLA equipment scan results after the operation, the following conclusions can be drawn: there are a large number of LPDN particles. These particles are mainly due to the failure to effectively remove small scratches and defects in the incoming material, and these defects are not properly dispersed, but appear in clusters. Therefore, at the CMP parameter level, the pressure and speed in each disc process need to be adjusted synchronously to improve this situation. Specifically, this can be achieved by increasing pressure and decreasing speed, or decreasing pressure and increasing speed, to optimize the process. Such adjustments will help reduce particle clustering and improve product quality.

[0050] In optimizing the CMP (Chemical Mechanical Polishing) process, we made detailed adjustments to key process parameters. Specifically, the process pressure of disk P1 was significantly increased from 8 kPa to 12 kPa. This adjustment aims to enhance the overall removal efficiency during the CMP process, thereby effectively improving and correcting LPDN (Localized Particle Density Non-uniformity) defects at the incoming material. Furthermore, we also adjusted the process pressure of disks P2 and P3, increasing the pressure from 8 kPa to 10 kPa to achieve the same effect.

[0051] Regarding rotational speed, we also made significant adjustments. The process rotational speed for P2 and P3 pads was increased from 40 rpm to 50 rpm, which helps improve polishing efficiency and uniformity. In the final polishing stage, we changed our previous practice of maintaining the same rotational speed for both the pad and the head, instead adopting a differentiated rotational speed strategy with a 1.2 ratio between the pad and head speeds. This adjustment aims to reduce LPDN defects that may be caused by increased temperature during polishing. In the previous process, the same rotational speed for the pad and head resulted in overlapping motion trajectories, leading to excessively high polishing temperatures. This caused removable particles to adhere to the silicon wafer surface, affecting polishing quality. By implementing differentiated rotational speeds, we can effectively reduce the temperature in the polishing area, reduce particle adhesion, thereby improving the particle condition on the silicon wafer surface and enhancing the quality of the final product.

[0052]

[0053] 2. Polishing Slurry Ratio Control: During the adjustment of the polishing slurry ratio, the working times of the 60nm and 90nm polishing slurries for the P1 disk were also adjusted. Specifically, the polishing time of the 60nm slurry was shortened, while the working time of the 90nm slurry was correspondingly increased. This adjustment indirectly increases the amount of material removed from the silicon wafer surface. This operation aims to improve the surface grain size of the silicon wafer, thereby enhancing the overall quality of the silicon wafer.

[0054] 3. By carefully controlling the pH range of the polishing slurry, maintaining it between 8 and 12, and ensuring the polishing temperature is kept within a suitable range of 20℃ to 40℃, the surface roughness of the silicon wafer can be effectively reduced to an extremely high level below 0.1nm. Precise control of the pH value and appropriate adjustment of the polishing temperature have a decisive impact on the etching rate of the silicon wafer surface by the polishing slurry. During this process, potential defects such as LPDN (Local Point Defects) are amplified, and once these defects occur, they are difficult to repair or improve through further processing in the subsequent chemical mechanical polishing (CMP) stage.

[0055] To further improve the quality and effect of silicon wafer polishing, the main approach is to adjust the CMP polishing process. Specific measures include: A. Pre-treating the silicon wafer to remove the natural oxide layer on the surface, creating a clean starting surface for subsequent polishing steps; B. Implementing a multi-stage polishing strategy, combining intermediate and fine polishing to ensure the silicon wafer surface achieves the required smoothness; C. Detailed adjustment of polishing process parameters to ensure that the surface grain size and roughness of the regenerated wafer are significantly improved after polishing, thereby achieving higher quality standards.

[0056]

[0057] A wafer regeneration CMP process equipment, comprising:

[0058] The preprocessing module is used to perform the wet etching preprocessing as described in any one of claims 1 to 6;

[0059] The multi-stage polishing module is configured to be connected in sequence to a medium polishing disc (P1), a fine polishing disc (P2), and a secondary fine polishing disc (P3), and the pressure and rotation speed parameters of each disc are adjusted according to claims 1 to 5;

[0060] The control unit is used to monitor and adjust the polishing solution ratio, pH value, and temperature in real time.

[0061] A regenerated wafer, prepared by the above method, has a surface roughness ≤0.1nm, a particle density ≤30 particles / wafer, and a reduction of LPDN defect cluster density by more than 50%.

[0062] Example 1: Implementation of Basic Process

[0063] Step 1: Wet Etching Pretreatment

[0064] The regenerated wafer was immersed in diluted hydrofluoric acid (HF:H2O = 1:50) for 40 seconds, and the Q-time was controlled at 5 minutes.

[0065] Step 2: Multi-stage CMP polishing

[0066] P1 stage: Use 7310 polishing slurry (particle size 90nm), grooved non-woven polishing pad, pressure 12kPa, rotation speed 50 rpm;

[0067] P2 stage: Using 8100 type polishing slurry (60nm particle size), a grooveless polishing pad, and a pressure of 10kPa.

[0068] Rotational speed 40 revolutions per minute;

[0069] P3 stage: Parameters are the same as P2, the ratio of disc speed to disc head speed is 1.2;

[0070] Step 3: Polishing fluid control

[0071] Adjust the 90nm polishing slurry operation time in stage P1 to 70%, pH=10.5, temperature 30℃. Results: Particle density 28 particles / piece, roughness 0.09nm, LPDN clusters reduced by 55%.

[0072] Example 2: Q-time optimization with acidic solutions

[0073] Step 1: Wet Etching Pretreatment

[0074] Phosphoric acid (H3PO4:H2O=1:30) was used instead of HF, the soaking time was 50 seconds, and the Q-time was compressed to 3 minutes;

[0075] Step 2: Multi-level CMP parameters

[0076] P1 pressure 14 kPa, rotation speed 55 rpm; P2 / P3 pressure 9 kPa, rotation speed 45 rpm;

[0077] Step 3: Polishing fluid control

[0078] pH=11, temperature 25℃, 90nm polishing slurry operation time accounts for 80% of the P1 stage.

[0079] Results: Particle density 25 particles / piece, roughness 0.08nm, residual oxide layer thickness reduced by 30%.

[0080] Example 3: High-precision roughness control

[0081] Step 1: Wet Etching Pretreatment

[0082] HF:H2O = 1:100, soaking time 30 seconds, Q-time ≤ 8 minutes;

[0083] Step 2: CMP Parameters

[0084] P1 pressure 10 kPa, rotation speed 40 rpm; P2 / P3 pressure 12 kPa, rotation speed 50 rpm;

[0085] Step 3: Polishing fluid control

[0086] pH = 8.5, temperature 40℃, with the addition of 0.1% surfactant (sodium dodecyl sulfate).

[0087] Results: Roughness 0.07nm, surface haze value reduced by 20%, suitable for high-end logic chip regeneration.

[0088] Example 4: Low-cost process adaptation

[0089] Step 1: Wet Etching Pretreatment

[0090] Use industrial-grade HF (5% concentration), soaking time 60 seconds, Q-time ≤ 10 minutes;

[0091] Step 2: CMP Parameters

[0092] P1 pressure 8 kPa, rotation speed 30 rpm; P2 / P3 pressure 8 kPa, rotation speed 30 rpm;

[0093] Step 3: Polishing fluid control

[0094] With pH=9 and temperature 20℃, the reusability of the grinding slurry is increased to 50%.

[0095] Results: Particle density of 35 particles / piece, roughness of 0.12nm, single-use cost reduced to 25 yuan, suitable for low-end memory regeneration.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An optimized method for a wafer regeneration chemical mechanical polishing process, characterized in that, Includes the following steps: (1) Wet etching pretreatment: Immerse the regenerated wafer in a diluted acidic solution to remove the natural oxide layer on the surface, and control the immersion time to be 30~60 seconds; (2) Multi-stage CMP polishing: Perform intermediate polishing, fine polishing and secondary fine polishing in sequence; wherein, the intermediate polishing stage uses a polishing slurry with a particle size of 90nm and a grooved non-woven polishing pad; the fine polishing stage and the secondary fine polishing stage use a polishing slurry with a particle size of ≤60nm and a grooveless non-woven polishing pad; (3) Dynamic parameter adjustment: During the intermediate polishing stage, the polishing pressure is increased to 10~15 kPa and the rotation speed is increased to 40~60 rpm; During the fine polishing stage and the secondary fine polishing stage, the polishing pressure is adjusted to 8~12kPa and the rotation speed is increased to 30~50 rpm. During the fine polishing stage and the secondary fine polishing stage, the ratio of the rotation speed of the disc surface to the disc head is controlled to be 1.1~1.5; (4) Polishing fluid control: Adjust the working time of the 90nm polishing slurry to 70%; maintain the pH value of the polishing slurry at 8~12 and the polishing temperature at 20~40℃.

2. The optimized method for a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that, The acidic solution mentioned in step (1) is diluted hydrofluoric acid, and the interval between the wet etching process and the start of the CMP process does not exceed 10 minutes.

3. The optimized method for a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that, The polishing fluid used in the intermediate polishing stage in step (2) is type 7310 polishing fluid, and the polishing fluid used in the fine polishing stage and the second fine polishing stage is type 8100 polishing fluid.

4. The optimized method for a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that, The polishing pressure in the intermediate polishing stage in step (3) is 12 kPa and the rotation speed is 50 rpm; the polishing pressure in the fine polishing stage and the second fine polishing stage is 10 kPa and the rotation speed is 40 rpm.

5. The optimized method for a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that, The ratio of the rotational speed of the disk surface to that of the disk head in step (3) is 1.

2.

6. The optimized method for a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that, The pH value in step (4) is 10~11 and the polishing temperature is 25~35℃.

7. A wafer regeneration CMP process equipment, characterized in that, include: A preprocessing module is used to perform wet etching preprocessing in the optimized method of wafer regeneration chemical mechanical polishing process according to any one of claims 1 to 6; A multi-stage polishing module is configured to sequentially connect an intermediate polishing plate, a fine polishing plate, and a secondary fine polishing plate, and the pressure and rotation speed parameters of each plate are adjusted according to any one of claims 1 to 5 in the optimization method of wafer regeneration chemical mechanical polishing process; The control unit is used to monitor and adjust the polishing solution ratio, pH value, and temperature in real time.

8. A regenerated wafer, characterized in that, Prepared using the method described in any one of claims 1 to 6, the surface roughness is ≤0.1nm, the particle density is ≤30 particles / piece, and the cluster density of local particle density non-uniformity defects is reduced by more than 50%.

Images