CN113290426B - Method for improving polishing thickness uniformity of wafer - Google Patents

Abstract

The invention relates to the field of semiconductor production and processing, and specifically discloses a method for improving the uniformity of wafer polishing thickness, comprising the following steps: using a polishing head to polish a plurality of test wafers arranged in a ring to obtain polished test wafers; Obtain thickness data at different positions of each test wafer after polishing; determine pressure values at different positions of the polishing head according to the thickness data; determine the shape of the calibration pad according to the pressure values at different positions of the polishing head; The pad is placed between the polishing head and the polishing disc; polishing is performed on the wafer to be processed on the polishing disc. Determine the pressure distribution at different positions of the polishing head according to the thickness data at different positions of the test wafer, and then determine the shape of the calibration pad, and adjust the pressure uniformity of the polishing head by adding the calibration pad.

Description

Method for improving wafer polishing thickness uniformity

technical field

The invention relates to the field of semiconductor production and processing, and specifically discloses a method for improving the uniformity of wafer polishing thickness.

Background technique

In the field of semiconductor material production and processing, the thickness uniformity of wafer processing is an important parameter to measure the quality of wafer processing, and the thickness uniformity will directly affect the subsequent epitaxy use of the wafer and the quality of the device. Among them, the polishing process is the last link in the processing of semiconductor wafer materials, and the uniformity of the polishing thickness will directly affect whether the wafer product can finally meet the shipping standards. Therefore, various parameters must be strictly controlled during the polishing process to ensure the final polishing quality. In actual production, due to the long-term wear and tear of the polishing head of the chemical polishing machine or the accuracy of the polishing head itself, the pressure of the polishing head is often uneven during production, which in turn results in a large deviation in the thickness of the polished wafer. The on-chip TV3 (the thickness variation of three points in a single chip) is too large, which seriously affects the final product shipment. Therefore, how to solve the problem of wafer polishing thickness uniformity caused by uneven pressure of the polishing head has become an urgent problem to be solved at present.

SUMMARY OF THE INVENTION

The present invention aims to solve the above-mentioned technical problems in the related art at least to a certain extent. To this end, the present invention proposes a method for improving the uniformity of wafer polishing thickness, which solves at least one of the above-mentioned technical problems.

In order to achieve the above object, a first aspect of the present invention provides a method for improving the uniformity of wafer polishing thickness, comprising the following steps:

Using a polishing head to polish a plurality of test wafers arranged in a ring to obtain polished test wafers;

Obtain thickness data at different positions of each test wafer after polishing;

Determine pressure values at different positions of the polishing head according to the thickness data;

Determine the shape of the calibration pad according to the pressure values at different positions of the polishing head;

placing the determined calibration pad between the polishing head and the polishing disc;

Polish the wafer to be processed on the polishing pad.

In addition, the method for improving the uniformity of wafer polishing thickness of the present invention may also have the following additional technical features:

According to some embodiments of the present invention, the different points of the polishing head are a first point, a second point, and a third point on the test wafer.

According to some embodiments of the present invention, the first point, the second point and the third point are located on the same line segment, and the line segment coincides with the line segment where the diameter of the test wafer is located.

According to some embodiments of the present invention, the distances between two adjacent points are equal.

According to some embodiments of the present invention, the first point is located inside the third point, the second point is located in the middle of the first point and the third point, and the second point is the where the center of the test wafer is located.

According to some embodiments of the present invention, if the thickness data of the first point, the second point, and the third point on all the test wafers increase sequentially, the central pressure value of the polishing head is determined greater than the surrounding pressure value of the polishing head;

According to the central pressure value of the polishing head being greater than the surrounding pressure value of the polishing head, it is determined that the shape of the calibration pad is annular.

According to some embodiments of the present invention, if the thickness data of the third point, the second point, and the first point on all the test wafers increase sequentially, the center pressure of the polishing head is determined The value is less than the surrounding pressure value of the polishing head;

According to the central pressure value of the polishing head being less than the surrounding pressure value of the polishing head, it is determined that the shape of the calibration pad is circular.

According to some embodiments of the present invention, if the thickness data of all or at least some of the points on the test wafer on one side are smaller than the thickness data of all points on the test wafer on the other side, the pressure on one side of the polishing head is determined value is greater than the pressure value on the other side;

According to the pressure value of one side of the polishing head is greater than the pressure value of the other side, it is determined that the shape of the calibration pad is a semicircle.

According to some embodiments of the present invention, the test wafer or the wafer to be processed is selected from any one of silicon wafer, sapphire wafer, silicon carbide wafer, gallium nitride, and gallium arsenide; the material of the calibration pad is For polyurethane or cerium oxide.

According to some embodiments of the present invention, the step of polishing the wafer to be processed on the polishing disc includes: setting the polishing pressure to 350-550 g/cm ² ; setting the rotational speed of the upper polishing head to 35-40 rpm/min; Set 40-45rpm/min, set the temperature to 20-50°C, set the polishing time to 60-90min, and use 20-30% concentration alumina polishing solution for polishing, and set the removal amount to 7-10μm.

Compared with the prior art, the present invention has the following beneficial effects:

Determine the pressure distribution at different positions of the polishing head according to the thickness data at different positions of the test wafer, and then determine the shape of the calibration pad, adjust the pressure uniformity of the polishing head by adding the calibration pad, and cooperate with the appropriate polishing process parameters to ensure that the wafer is fully aligned. The disc thickness is uniform and the TV3 (thickness variation at three points within a single chip) within a single chip is small.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained according to the structures shown in these drawings without creative efforts.

FIG. 1 is a schematic structural diagram 1 of a polishing disc with wafers attached to Embodiments 1-3 of the present invention;

FIG. 2 is a schematic structural diagram 2 of a polishing disc with wafers in Embodiments 1-3 of the present invention;

3 is a schematic structural diagram of a ring-shaped calibration pad in Embodiment 1 of the present invention;

4 is an exploded view of the polishing equipment in Embodiment 1 of the present invention;

5 is a schematic structural diagram of a semicircular calibration pad in Embodiment 2 of the present invention;

FIG. 6 is a schematic structural diagram of a circular calibration pad in Embodiment 3 of the present invention.

The realization, functional characteristics and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Detailed ways

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be more thoroughly understood, and will fully convey the scope of the present disclosure to those skilled in the art.

Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments, and are not intended to limit the protection scope of the present invention.

Example 1

Assume that the polishing head number of the machine is 1#, as shown in Fig. 1-2, firstly, put the polishing disc 2 with 7 test wafers 1 attached to the polishing head 3 to prepare for polishing operation. Wherein, there is no calibration pad 4 between the polishing head 3 and the polishing disc 2, and the conventional polishing process is used to carry out the polishing operation. The process parameters are set as follows: the polishing pressure is set to 350g/cm ² ; the rotation speed of the upper polishing head is set to 35rpm/min; The rotating speed of the disc is set to 40 rpm/min; the temperature is set to 20° C., the polishing time t is 90 min, and polishing is carried out with a 20% concentration alumina polishing solution, and the set removal amount is 7 μm. After polishing, take out the polishing disk 2 and rinse the test wafer 1 on the polishing disk 2, and measure the thickness data of the entire disk of the test wafer 1 and the TV3 in the single chip, wherein, the specific experimental results are shown in Table 1 below:

Table 1: The thickness of the test wafer 1 and the TV3 in a single chip

It should be noted that the first point, the second point and the third point on the test wafer 1 correspond to the inner, middle and outer points on the wafer 1 respectively. According to FIG. 2 , the first point and the second point And the third point is located on the line segment where the diameter of the test wafer 1 is located, the second point is where the center of the test wafer is located, and the distance between two adjacent points is equal.

It can be seen from Table 1 that after polishing the 1# polishing head, measuring the thickness of the entire test wafer 1 and the TV3 in a single wafer, it can be seen that the first point (inside) and the second point (middle) on all test wafers ), the thickness data of the third point (outside) increases in turn, that is to say, the thickness of the entire disk of wafer 1 is thick on the outside and thin on the inside, and then it can be determined that the center pressure of the polishing head is too large, and the surrounding pressure If it is too small, the central pressure value of the polishing head is greater than the surrounding pressure value of the polishing head. At this time, the shape of the calibration pad 4 can be determined to be annular according to the pressure distribution of the polishing head, as shown in FIG. 3 .

Next, as shown in FIG. 4, the calibration pad 4 determined as shown in FIG. 3 is placed between the polishing head 3 and the polishing disc 2; the conventional polishing process is used to perform the polishing operation, and the process parameters are set as follows: polishing pressure Set 350g/cm ² ; set the rotational speed of the upper polishing head to 35 rpm/min; set the rotational speed of the lower disc to 40 rpm/min; set the temperature to 20° C., set the polishing time t to 90 min, and use 20% concentration of alumina polishing solution for polishing, The removal amount was set to 7 μm.

After polishing, take out the polishing disc 2 and rinse the wafer to be processed on the polishing disc 2, and measure the entire disc thickness data of the wafer to be processed and the TV3 in the single chip, wherein, the specific experimental results are shown in the following table 2:

Table 2: The thickness of the whole wafer and the TV3 in a single chip after using the ring calibration pad

It can be seen from Table 2 that the thickness deviation of the entire wafer has been significantly improved, and the thickness deviation of a single wafer is very small, which is less than or equal to 3 μm, indicating that the pressure of the 1# polishing head on the polishing head after the pad is placed on the pad has been significantly improved. Wafer polishing thickness uniformity.

Example 2

Assume that the polishing head number of the machine is 2#, as shown in Figure 1-2, firstly, put the polishing disc 2 with 7 test wafers 1 attached to the polishing head 3 to prepare for polishing operation. Wherein, there is no calibration pad 4 between the polishing head 3 and the polishing disc 2, and the conventional polishing process is used to carry out the polishing operation. The process parameters are set as follows: the polishing pressure is set to 550g/cm ² ; the rotation speed of the upper polishing head is set to 35rpm/min; The disc rotation speed was set to 40 rpm/min; the temperature was set to 50° C., the polishing time t was 60 min, and polishing was carried out with 20% concentration alumina polishing solution, and the set removal amount was 7 μm. After polishing, take out the polishing disk 2 and rinse the test wafer 1 on the polishing disk 2, and measure the thickness data of the entire disk of the test wafer 1 and the TV3 in the single chip, wherein, the specific experimental results are shown in Table 3 below:

Table 3: The thickness of the test wafer 1 and the TV3 in a single chip

It can be seen from Table 3 that the thickness data of three points or at least one point on the test wafer 1 on one side are smaller than the thickness data of the three points on the test wafer 1 on the other side, that is to say, the entire disk of the test wafer 1 The thickness is thick on one side and thin on the other side (the first, second, and third sheets are thinner, and the fourth, fifth, and sixth sheets are thicker), so it can be determined that the pressure on one side of the polishing head is too large and the pressure on the other side is too small. In addition, due to the uneven pressure of the polishing head, the TV3 of a single piece fluctuates greatly. At this time, the shape of the calibration pad 4 can be determined to be a semicircle according to the pressure distribution of the polishing head, as shown in FIG. 5 .

Next, place the determined calibration pad 4 between the polishing head 3 and the polishing disc 2; use a conventional polishing process to perform the polishing operation, and set the process parameters as follows: the polishing pressure is set to 550g/cm ² ; the rotation speed of the upper polishing head is Set 35rpm/min; set the lower disk speed to 40rpm/min; set the temperature to 50°C, set the polishing time t to 60min, and polish with 20% concentration alumina polishing solution, and set the removal amount to 7μm. After polishing, take out the polishing disk 2 and rinse the wafer to be treated on the polishing disk 2, and measure the thickness data of the entire disk of the wafer to be treated and the TV3 in the single chip, wherein, the specific experimental results are shown in Table 4 below:

Table 4: Thickness of the whole wafer and TV3 in a single wafer after using the semicircular calibration pad

It can be seen from Table 4 that the thickness deviation of the entire wafer has been significantly improved, and the thickness deviation of a single wafer is very small, all less than or equal to 3 μm, indicating that the 2# polishing head has significantly improved the pressure on the polishing head after the semicircular calibration pad is placed on the pad. , greatly improving the uniformity of wafer polishing thickness.

Example 3

Assume that the polishing head number of the machine is 3#, as shown in Figure 1-2, firstly, put the polishing disc 2 with 7 test wafers 1 attached to the polishing head 3 to prepare for polishing operation. Wherein, there is no calibration pad 4 between the polishing head 3 and the polishing disc 2, and the conventional polishing process is used to carry out the polishing operation. The set process parameters are as follows: the polishing pressure is set to 500g/cm ² ; the rotation speed of the upper polishing head is set to 35rpm/min; The rotating speed of the disc is set to 40 rpm/min; the temperature is set to 30° C., the polishing time t is 70 min, and polishing is carried out with 20% concentration alumina polishing solution, and the set removal amount is 7 μm. After polishing, take out the polishing disk 2 and rinse the test wafer 1 on the polishing disk 2, and measure the thickness data of the entire disk of the test wafer 1 and the TV3 in the single chip, wherein, the specific experimental results are shown in Table 5 below:

Table 5: The thickness of the test wafer 1 and the TV3 in a single chip

It can be seen from Table 5 that the thickness data of the third point (outside), the second point (middle), and the first point (inside) on all test wafers increase in turn, that is to say, the wafer The thickness of the entire disk is thin on the outside and thick on the inside, so it can be determined that the central pressure of the polishing head is too small, the surrounding pressure is too large, and the central pressure value of the polishing head is smaller than the surrounding pressure value of the polishing head. At this time, the shape of the calibration pad 4 can be determined to be circular according to the pressure distribution of the polishing head, as shown in FIG. 6 .

Next, the determined calibration pad 4 is placed between the polishing head 3 and the polishing disc 2; the conventional polishing process is used to perform the polishing operation, and the process parameters are set as follows: the polishing pressure is set to 500g/cm ² ; the rotation speed of the upper polishing head is Set 35rpm/min; set the lower plate speed to 40rpm/min; set the temperature to 30°C, set the polishing time t to 70min, and polish with 20% concentration alumina polishing solution, and set the removal amount to 7μm. After polishing, take out the polishing disc 2 and rinse the wafer to be processed on the polishing disc 2, and measure the entire disc thickness data of the wafer to be processed and the TV3 in the single chip, wherein, the specific experimental results are shown in Table 6 below:

Table 6: Thickness of the whole wafer and TV3 in a single wafer after using the semicircular calibration pad

From Table 6, it can be seen that the thickness deviation of the entire wafer has been significantly improved, and the thickness deviation of a single wafer is very small, which is less than or equal to 3 μm, indicating that the pressure of the 3# polishing head on the polishing head after the pad is placed on the pad has been significantly improved. Wafer polishing thickness uniformity.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (4)

1. a method for improving the uniformity of wafer polishing thickness, is characterized in that, comprises the following steps: Using a polishing head to polish a plurality of test wafers arranged in a ring to obtain polished test wafers; Obtain thickness data at different positions of each test wafer after polishing; Determine pressure values at different positions of the polishing head according to the thickness data; Determine the shape of the calibration pad according to the pressure values at different positions of the polishing head; placing the determined calibration pad between the polishing head and the polishing disc; Polishing the to-be-processed wafer on the polishing disc; The different points of the polishing head are the first point, the second point and the third point on the test wafer; the first point, the second point and the third point are located on the same line segment, and the line segment coincides with the line segment where the diameter of the test wafer is located; The first point is located inside the third point, the second point is located in the middle of the first point and the third point, and the second point is where the center of the test wafer is located ; If the thickness data of the first point, the second point, and the third point on all the test wafers increase sequentially, it is determined that the central pressure value of the polishing head is greater than the surrounding pressure of the polishing head value; according to the central pressure value of the polishing head being greater than the surrounding pressure value of the polishing head, it is determined that the shape of the calibration pad is annular; If the thickness data of the third point, the second point, and the first point on all the test wafers increase sequentially, it is determined that the central pressure value of the polishing head is smaller than the surrounding area of the polishing head pressure value; according to the central pressure value of the polishing head being less than the surrounding pressure value of the polishing head, determine that the shape of the calibration pad is circular; If the thickness data of all or at least some of the first, second and third points on the test wafer on one side is smaller than the first point on the test wafer on the other side, For the thickness data of the second point and all points in the third point, it is determined that the pressure value of one side of the polishing head is greater than the pressure value of the other side; according to the pressure value of one side of the polishing head is greater than the pressure value of the other side , determine that the shape of the calibration pad is a semicircle. 2 . The method for improving the uniformity of wafer polishing thickness according to claim 1 , wherein the distances between two adjacent points are equal. 3 . 3. The method for improving wafer polishing thickness uniformity according to claim 2, wherein the test wafer or the to-be-processed wafer is selected from the group consisting of silicon wafer, sapphire wafer, silicon carbide wafer, gallium nitride, arsenide Any of gallium; the material of the calibration pad is polyurethane or cerium oxide. 4. The method for improving the uniformity of wafer polishing thickness according to any one of claims 1-3, wherein the step of polishing the wafer to be treated on the polishing disc comprises: setting the polishing pressure to 350-550 g/g cm ² ; the rotating speed of the polishing head is set at 35-40 rpm; the rotating speed of the polishing disc is set at 40-45 rpm, the temperature is set at 20-50 ° C, the polishing time is 60-90 min, and the polishing is carried out with a concentration of 20-30% alumina polishing liquid , set the removal amount to 7-10 μm.

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