Optimization method of wafer regeneration chemical mechanical polishing process

Abstract

The invention discloses an optimization method for a wafer regeneration chemical mechanical polishing process. The optimization method comprises the steps of wet etching pretreatment, multi-stage CMP polishing, dynamic parameter adjustment and polishing solution control. According to the invention, the structure is reasonable, the condition of particles on the surface of the regenerated wafer is greatly improved by adjusting CMP parameters, and meanwhile, the cost of the grinding fluid of 60 nm and the cost of the grinding fluid of 90 nm are different, so that the cost of the grinding fluid of 60 nm is extremely high. And the grinding time is shortened by 60nm, so that the cost improvement is promoted. The improvement degree of the roughness of the surface of the silicon wafer is reduced to be within 0.1 nm from 0.2 nm.

Description

Technical Field

[0001] The present invention relates to an optimization method for a wafer regeneration chemical mechanical polishing process. Background Art

[0002] The wafer regeneration polishing process is formed by combining the polishing process and the CMP process. The polishing process uses a three-platen rough polishing operation, and the CMP process uses a three-platen fine polishing operation, which may cause microscopic scratches on the silicon wafer surface, such as pits and scratches, as well as uneven roughness or subsurface defects. This type of defect appears as removable shallow pits and micro-scratches after being scanned by a measuring device.

[0003] Whether this type of defect is removed in the wafer regeneration process is crucial. If the residual incoming damage layer on the surface is not completely removed, the clustered particles caused by these scratches will have an adverse impact on the subsequent processing process. For example, there are metal ions in the scratched pits, and these metal ions will diffuse to the furnace tube and the clean wafer during the high-temperature furnace tube process, contaminating the equipment and the characteristics of the wafer itself, resulting in a decrease or even damage to the performance in the final electrical test.

[0004] In the actual wafer regeneration operation process of the above process, due to the problem of the front and back matching of the polishing process, the surface particles of the operation product exceed the limit. The high-specification production rate of the product after CMP does not exceed 30%, the particle size is about 100, and the surface roughness is 0.2 nm.

[0005] Glossary of Terms

[0006] Q-time: The time when the wafer waits for the start of the next process after completing one process.

[0007] Haze: A microscopic defect existing on the wafer surface, which can reflect the surface roughness to a certain extent.

[0008] CMP: The process for achieving wafer surface planarization. Summary of the Invention

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

[0010] To achieve the above purpose, the present invention provides the following technical solution: An optimization method for a wafer regeneration chemical mechanical polishing process, including 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 - 60 seconds;

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

[0013] Among them, in the medium polishing stage (P1), a polishing liquid with a particle size of 60 - 90 nm and a non - woven polishing pad with grooves are used; in the fine polishing stages (P2, P3), a polishing liquid with a particle size ≤ 60 nm and a non - woven polishing pad without grooves are used;

[0014] (3) Dynamic parameter adjustment:

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

[0016] In the P2 and P3 stages, the rotation speed ratio of the platen to the spindle is controlled to be 1.1 - 1.5;

[0017] (4) Polishing liquid control:

[0018] In the medium polishing stage (P1), the operation time of the polishing liquid with a 60 - nm particle size is shortened, and the operation time of the polishing liquid with a 90 - nm particle size is extended;

[0019] The pH value of the polishing liquid is maintained at 8 - 12, and the polishing temperature is 20 - 40 °C.

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

[0021] Preferably, in step (2), the polishing liquid in the medium polishing stage (P1) is 7310 - type polishing liquid, and the polishing liquids in the fine polishing stages (P2, P3) are 8100 - type polishing liquids.

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

[0023] Preferably, in step (3), the rotation speed ratio of the platen to the spindle is 1.2.

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

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

[0026] A pretreatment module for performing the wet etching pretreatment described in any one of claims 1 - 6;

[0027] A multi - stage polishing module, configured to be sequentially connected 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 surface are adjusted according to claims 1 to 5;

[0028] A control unit, used for real - time monitoring and adjusting the proportion, pH value, and temperature of the polishing liquid.

[0029] Preferably, a regenerated wafer is prepared by the above - mentioned method, with a surface roughness ≤ 0.1 nm, a particle density ≤ 30 particles per wafer, and the cluster density of LPDN defects reduced by more than 50%.

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

[0031] 1. The particle density is reduced from 100 particles per wafer to ≤ 30 particles per wafer;

[0032] 2. The surface roughness is reduced from 0.2 nm to ≤ 0.1 nm;

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

[0034] 4. The cost of single - pass CMP is saved by 10% (from 30 yuan to 27 yuan). Detailed implementation manners

[0035] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] The present invention provides a technical solution: an optimization method for a chemical - mechanical polishing process of wafer regeneration, including 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 - 60 seconds;

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

[0039] Among them, in the medium - polishing stage (P1), a polishing liquid with a particle size of 60 - 90 nm and a non - woven polishing pad with grooves are used; in the fine - polishing stages (P2, P3), a polishing liquid with a particle size ≤ 60 nm and a non - woven polishing pad without grooves are used;

[0040] (3) Dynamic parameter adjustment:

[0041] In the medium polishing stage (P1), the polishing pressure is increased to 10 - 15 kPa, and the rotational speed is increased to 40 - 60 revolutions per minute; in the fine polishing stages (P2, P3), the polishing pressure is adjusted to 8 - 12 kPa, and the rotational speed is increased to 30 - 50 revolutions per minute;

[0042] In the P2 and P3 stages, the ratio of the platen speed to the head speed is controlled to be 1.1 - 1.5;

[0043] (4) Polishing liquid control:

[0044] In the medium polishing stage (P1), the operation time of the 60 nm particle size abrasive slurry is shortened, and the operation time of the 90 nm particle size abrasive slurry is extended;

[0045] The pH value of the polishing liquid is maintained at 8 - 12, and the polishing temperature is 20 - 40 °C.

[0046] Among them, the technical improvement includes several aspects: adjustment of the polishing process steps, innovation of the relative proportion of the polishing liquid, and control of the silicon wafer surface morphology:

[0047] 1. Adjustment of the polishing process steps: Before CMP, the reclaimed wafers will be pre-treated by wet etching. The natural oxide layer on the surface is removed by diluted acidic liquids such as HF. However, when proceeding from this process step to the next process step, the Q-time should be effectively controlled: if the Q-time is too long, a relatively thick natural oxide layer is likely to form again, which cannot be removed and improved. Generally, the best effect is achieved when the soaking time is controlled within 30S - 60S. Note that the soaking time should not be too long to prevent over-etching on the silicon wafer surface: the surface of the over-etched silicon wafer turns black or shows a matte morphology. It is easy to misjudge during the surface inspection in the next process, resulting in an unmatched process route.

[0048] After completing the above steps, the next preparation work includes the implementation of the multi-stage CMP stage. During the CMP operation, the polishing operation needs to be carried out in three stages. The flow of these three polishing operations is medium polishing, fine polishing, and then fine polishing again. In the medium polishing stage, the particle size of the abrasive slurry used is 90 nm or 60 nm, and a non-woven polishing pad with grooves is used in combination. In the fine polishing stage, the particle size of the abrasive slurry is adjusted to 60 nm, and a non-woven polishing pad without grooves is used. It should be noted that the processes adopted in the P2 and P3 stages are the same. In the P1 stage, the main task is to process and repair the surface of the incoming wafers and the shallow scratches and subsurface defects generated during the middle polishing process, reducing the impact of the surface defects of the incoming silicon wafers on the particles after the CMP process. And in this stage, the rough surface after rough polishing will be repaired and improved, and the roughness is reduced from 0.2 nm to within 0.1 nm.

[0049] According to the scanning results of the KLA equipment after the operation, the following conclusions can be drawn: there are many LPDN particles, which are mainly due to the failure to effectively remove the small scratch defects of the incoming materials, and these defects are not properly dispersed, but appear in the form of clusters. Therefore, on the CMP parameter side, the pressure and speed in each disk process need to be adjusted synchronously to improve this situation. Specifically, the purpose of optimizing the process can be achieved by increasing the pressure and reducing the speed, or reducing the pressure and increasing the speed. Such adjustments will help reduce the clustering of particles and improve the quality of the product.

[0050] In the process of optimizing the CMP (chemical mechanical polishing) process, we made detailed adjustments to the key process parameters. Specifically, the process pressure of the P1 disk was significantly increased from the original 8kpa to 12kpa. This adjustment is to enhance the overall removal efficiency during the CMP process, thereby effectively improving and correcting the LPDN (local particle density non-uniformity) defects at the incoming material end. In addition, we also adjusted the process pressure of the P2 and P3 disks, increasing the pressure from 8kpa to 10kpa, in order to achieve the same effect.

[0051] We have also made important adjustments in terms of rotation speed. The process speed of P2 and P3 disks has been increased from 40 rpm to 50 rpm. This increase will help improve polishing efficiency and uniformity. In the final stage of polishing, we changed the previous practice of maintaining the same rotation speed for the disk surface and disk head, and instead adopted a differentiated rotation speed strategy with a disk surface and disk head speed ratio of 1.2. The purpose of this adjustment is to reduce LPDN defects that may be caused by increased temperature during the polishing process. In the previous process, the rotation speed of the disk surface and disk head was the same, resulting in many overlapping motion trajectories, which would make the polishing temperature too high, causing removable particles to adhere to the surface of the silicon wafer, affecting the polishing quality. By implementing differentiated rotation speeds, the temperature of the polishing area can be effectively reduced, reducing the adhesion of particles, thereby improving the particle situation on the surface of the silicon wafer and improving the quality of the final product.

[0052]

[0053] 2. Control of the relative proportion of polishing liquid: During the adjustment of the relative proportion of polishing liquid, the operating time of the 60nm and 90nm grinding liquids of the P1 disk was adjusted at the same time. Specifically, the grinding time of the 60nm grinding liquid was shortened, and at the same time, the operating time of the 90nm grinding liquid was correspondingly increased. Through this adjustment, the amount of silicon wafer surface removal can be indirectly increased. This operation is to achieve the effect of improving the surface granularity of the silicon wafer, thereby improving the overall quality of the silicon wafer.

[0054] 3. By carefully controlling the pH value range of the polishing liquid, that is, maintaining it between 8 and 12, and at the same time ensuring that the polishing temperature is kept within the appropriate range of 20°C to 40°C, the surface roughness of the silicon wafer can be effectively reduced to an extremely low level below 0.1 nm. The precise control of the pH value and the appropriate adjustment of the polishing temperature have a decisive impact on the corrosion rate of the polishing liquid on the silicon wafer surface. During this process, potential defects such as LPDN (local point defects) will be magnified, and once these defects occur, it is difficult to repair or improve them through further processing in the subsequent chemical mechanical polishing (CMP) stage.

[0055] To further improve the quality and effect of silicon wafer polishing, it is mainly achieved by adjusting the CMP polishing process. The specific measures include: A. Pretreating the silicon wafer to remove the natural oxide layer on the surface and create a clean starting surface for the subsequent polishing steps; B. Implementing a multi-stage polishing strategy, combining medium polishing and fine polishing to ensure that the surface of the silicon wafer reaches the required smoothness; C. Making detailed adjustments to the polishing process parameters to ensure that after polishing, the surface particle size and roughness of the regenerated wafer are significantly improved, thus meeting higher quality standards.

[0056]

[0057] A wafer regeneration CMP process equipment includes:

[0058] A pretreatment module for performing the wet etching pretreatment described in any one of claims 1 to 6;

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

[0060] A control unit for real-time monitoring and adjusting the polishing liquid ratio, pH value, and temperature.

[0061] A regenerated wafer prepared by the above method, having a surface roughness ≤ 0.1 nm, a particle density ≤ 30 particles per wafer, and a cluster density of LPDN defects reduced by more than 50%.

[0062] Example 1: Basic process implementation

[0063] Step 1: Wet etching pretreatment

[0064] Immerse the regenerated wafer in diluted hydrofluoric acid (HF:H2O = 1:50) for 40 seconds, and control the Q-time within 5 minutes;

[0065] Step 2: Multi-stage CMP polishing

[0066] Stage P1: Use polishing liquid type 7310 (particle size 90 nm), grooved non-woven polishing pad, pressure 12 kPa, rotation speed 50 revolutions per minute;

[0067] Stage P2: Use polishing liquid type 8100 (particle size 60 nm), non-grooved polishing pad, pressure 10 kPa,

[0068] rotation speed 40 revolutions per minute;

[0069] Stage P3: Parameters are the same as P2, the rotation speed ratio of the disk surface to the disk head is 1.2;

[0070] Step 3: Polishing liquid control

[0071] Adjust the operation time ratio of the 90 nm grinding liquid in Stage P1 to 70%, pH = 10.5, temperature 30 °C. Effect: Particle density 28 pieces per wafer, roughness 0.09 nm, LPDN clusters reduced by 55%.

[0072] Example 2: Q-time and acidic solution optimization

[0073] Step 1: Wet etching pretreatment

[0074] Use phosphoric acid (H3PO4:H2O = 1:30) to replace HF, soaking time 50 seconds, Q-time compressed to 3 minutes;

[0075] Step 2: Multi-stage CMP parameters

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

[0077] Step 3: Polishing liquid control

[0078] pH = 11, temperature 25 °C, the operation time ratio of the 90 nm grinding liquid in Stage P1 is 80%.

[0079] Effect: Particle density 25 pieces per wafer, roughness 0.08 nm, oxide layer residual 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 revolutions per minute; P2 / P3 pressure 12 kPa, rotation speed 50 revolutions per minute;

[0085] Step 3: Polishing Liquid Control

[0086] pH = 8.5, temperature 40°C, add 0.1% surfactant (sodium dodecyl sulfate).

[0087] Effect: Roughness 0.07 nm, surface Haze value reduced by 20%, applicable to high-end logic chip regeneration.

[0088] Example 4: Low-cost Process Adaptation

[0089] Step 1: Wet Etching Pretreatment

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

[0091] Step 2: CMP Parameters

[0092] P1 pressure 8 kPa, rotation speed 30 revolutions per minute; P2 / P3 pressure 8 kPa, rotation speed 30 revolutions per minute;

[0093] Step 3: Polishing Liquid Control

[0094] pH = 9, temperature 20°C, grinding liquid reuse rate increased to 50%.

[0095] Effect: Particle density 35 pieces per wafer, roughness 0.12 nm, single-polishing cost reduced to 25 yuan, applicable to low-end memory regeneration.

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

Claims

1. A method for optimizing a wafer regeneration chemical mechanical polishing process, characterized in that: The following steps are involved: (1) Wet etching pretreatment: Immerse the regenerated wafer in a diluted acid solution to remove the natural oxide layer on the surface, and control the immersion time to 30 to 60 seconds; (2) Multi-stage CMP polishing: intermediate polishing (P1 stage), fine polishing (P2 stage) and secondary fine polishing (P3 stage) are performed in sequence; The intermediate polishing stage (P1) uses a grinding liquid with a particle size of 60 to 90 nm and a non-woven polishing pad with grooves; the fine polishing stages (P2 and P3) use a grinding liquid with a particle size of ≤60 nm and a non-woven polishing pad without grooves; (3) Dynamic parameter adjustment: In the intermediate polishing stage (P1), the polishing pressure is increased to 10-15 kPa, and the 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 speed is increased to 30-50 rpm; In the P2 and P3 stages, the speed ratio of the disk surface to the disk head is controlled to be 1.1 to 1.5; (4) Polishing liquid control: In the intermediate polishing stage (P1), the operation time of the 60nm particle size polishing liquid is shortened, and the operation time of the 90nm particle size polishing liquid is prolonged; Maintain the pH value of the polishing liquid at 8-12 and the polishing temperature at 20-40°C.

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

3. The method for optimizing a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that: The grinding liquid in the intermediate polishing stage (P1) in step (2) is 7310 type polishing liquid, and the grinding liquid in the fine polishing stage (P2, P3) is 8100 type polishing liquid.

4. The method for optimizing a wafer regeneration chemical mechanical polishing process according to claim 1, characterized in that: 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 stage (P2, P3) is 10 kPa, and the rotation speed is 40 rpm.

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

2.

6. The method for optimizing 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°C.

7. A wafer regeneration CMP process equipment, characterized in that: include: A pre-processing module, used to perform the wet etching pre-processing according to any one of claims 1 to 6; The multi-stage polishing module is configured to sequentially connect a medium polishing disc (P1), a fine polishing disc (P2) and a secondary fine polishing disc (P3), and the pressure and speed parameters of each disc surface are adjusted according to claims 1 to 5; Control unit, used to monitor and adjust polishing liquid ratio, pH value and temperature in real time.

8. A regenerated wafer, characterized in that: The method according to any one of claims 1 to 6 is adopted for preparation, wherein the surface roughness is ≤0.1 nm, the particle density is ≤30 particles / piece, and the cluster density of LPDN defects is reduced by more than 50%.

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