Optimization method for chemical mechanical polishing process parameters of wafer and chemical mechanical polishing method

Abstract

The invention relates to an optimization method for chemical mechanical polishing process parameters of a wafer and a polishing method, which are characterized in that the wafer is polished by a chemical mechanical polishing machine through a polishing process, and a polishing result 1 is measured; changing at least one of the parameters of the polishing process, polishing the wafer by using a chemical mechanical polishing machine, and measuring a polishing result 1 '; comparing the polishing result 1 with the polishing result 1 '; if the polishing result 1'is not superior to the polishing result 1, continuously changing the parameters until the polishing result 1 'is superior to the polishing result 1; if the polishing result 1'is superior to the polishing result 1, subsequent steps are directly carried out; on the basis, other parameters in the polishing process are changed, and the polishing process with the multiple optimized parameters is obtained; and the operation is repeated until the polishing process with the optimized target parameters is obtained. The parameters of the chemical mechanical polishing process are systematically optimized, the scientificity and rationality of parameter setting of the polishing process are improved, and the polishing quality is improved.

Description

Technical Field

[0001] The present invention relates to a method for optimizing chemical mechanical polishing process parameters for a wafer and a chemical mechanical polishing method, and in particular to a method for optimizing chemical mechanical polishing process parameters for a silicon carbide wafer and a chemical mechanical polishing method, and belongs to the technical field of semiconductor manufacturing. Background Art

[0002] Silicon carbide (SiC) is a material with extremely high hardness, good thermal conductivity, high temperature resistance and corrosion resistance. It is widely used in high-power semiconductors, optoelectronic devices, aerospace, automotive industry and other fields. The superior properties of silicon carbide make it an ideal material for the preparation of high-performance electronic devices, especially under high temperature, high frequency and high pressure environments. In order to achieve the best performance of these devices, the surface of silicon carbide wafers must have extremely low roughness and high flatness, which requires advanced polishing technology. Since the hardness of silicon carbide material is very close to that of diamond, its polishing is quite challenging.

[0003] The key challenges of silicon carbide polishing mainly include the following points: First, the high hardness and wear resistance of silicon carbide make it difficult to remove silicon carbide materials in a short time by traditional mechanical polishing methods, and the polishing tools and materials are severely worn; second, silicon carbide has very stable chemical inertness, and it is difficult to effectively remove the material through chemical reactions during chemical polishing; finally, silicon carbide usually has a variety of crystal structures, such as 4H-SiC and 6H-SiC, and their polishing performance reactions are different and require special treatment.

[0004] In order to overcome the above challenges, the main technologies for silicon carbide polishing are mechanical polishing, chemical mechanical polishing, ion beam polishing, magnetic fluid polishing, laser-assisted polishing, etc. The principle of mechanical polishing is to physically grind the silicon carbide surface on the polishing pad using abrasive particles to remove the uneven surface material.

[0005] Mechanical polishing is a simple process with low equipment requirements and is easy to achieve large-area polishing. However, the polishing efficiency is low and it is easy to produce surface defects such as scratches and cracks. It is usually used for rough polishing and subsequent fine processing is required to obtain a more precise surface.

[0006] The principle of chemical mechanical polishing is to soften the material surface through the chemical agent in the polishing liquid, and then remove it mechanically by the abrasive to achieve a more efficient polishing effect. It can effectively reduce the surface roughness, quickly remove the material, and has good compatibility with different crystal structures to obtain a high-quality surface, but its process is complicated, chemical polishing is also costly, and the polishing time is relatively long.

[0007] The principle of ion beam polishing is to use high-energy ion beams to bombard the surface of silicon carbide to remove tiny uneven areas. It is mainly used for ultra-precision surface processing. It can achieve atomic-level flatness and produce extremely low surface roughness, but the equipment is very expensive, the processing speed is slow, and there may be modification or damage to the surface atomic layer.

[0008] The principle of magnetic fluid polishing is to use the abrasive contained in the magnetic fluid to polish the material under the control of the magnetic field. The shape and flow of the fluid can be precisely controlled by the magnetic field to achieve uniform surface treatment. It can accurately control the distribution of polishing pressure, reduce scratches and wear, and the surface finish after polishing is high, but the equipment cost is high, the process is complex, and the preparation of the polishing fluid and the control of the magnetic field are required to be high.

[0009] The principle of laser-assisted polishing is to heat the silicon carbide surface through laser to soften or melt it locally, and then polish it through mechanical means to improve the material removal efficiency. It can effectively remove materials, and laser heating softens the material, which reduces the difficulty and time of polishing, but the equipment technology requirements are high, and the control of laser power parameters is crucial, which may cause thermal damage to the material.

[0010] In general, chemical mechanical polishing is the main development direction of silicon carbide polishing at present, especially in high-precision surface treatment. As a key fine polishing step after rough polishing, its processing method and polishing process parameters have a crucial influence on the surface of the chip and the performance of the device.

[0011] Although chemical mechanical polishing can achieve a high degree of flattening of the surface of silicon carbide, its equipment process parameters are very complicated (the common chemical polishing process can be found in CN102049734A), and the preparation of the polishing liquid also requires long-term experiments to obtain a suitable formula. Most of the traditional polishing equipment process parameters rely on the personal experience of engineers or are set according to the parameters of other equipment manufacturers. Although relatively stable process parameters can be found within a certain range, there are still problems such as uneven polishing surface, low polishing efficiency, and large parameter errors. Later, people began to adopt the method of designing experiments to ensure the stability of the process, but the process and steps of the experiment are often calculated manually, and the previous experimental experience has not been effectively utilized. There is no complete process parameter library, which makes it impossible to find the changing trend of various indicators of silicon carbide. Moreover, the performance and optional parameter range of chemical mechanical polishers of different manufacturers and models are different, so there is currently no polishing parameter that can be applied to different chemical mechanical polishers. Summary of the invention

[0012] In view of the deficiencies of the prior art, one of the objects of the present invention is to provide a method for optimizing process parameters of chemical mechanical polishing of wafers; a second object of the present invention is to provide a chemical mechanical polishing method for wafers.

[0013] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0014] A method for optimizing chemical mechanical polishing process parameters for a wafer comprises the following steps:

[0015] S1, polishing the wafer using a chemical mechanical polisher in a polishing process, and measuring a polishing result 1;

[0016] Wherein, the polishing process includes at least 2 parameters;

[0017] S2, changing at least one of the parameters of the polishing process, polishing the wafer using a chemical mechanical polisher, and measuring the polishing result 1';

[0018] Compare polishing result 1 and polishing result 1';

[0019] S3, if the polishing result 1' is not better than the polishing result 1, continue to change the parameters changed in S2, and repeat S2-S3 until the polishing result 1' is better than the polishing result 1. At this time, the polishing process corresponding to the polishing result 1' is the polishing process after the relevant parameters are optimized;

[0020] If the polishing result 1' is better than the polishing result 1, the polishing process corresponding to the polishing result 1' is used as the polishing process with optimized relevant parameters, and S4 is directly performed;

[0021] S4, based on the polishing process after the relevant parameters determined in S3 are optimized, changing at least one of the other parameters in the polishing process, repeating S2-S3, and obtaining a polishing process after multiple parameters are optimized;

[0022] S5, repeat S4 until a polishing process with all target parameters optimized is obtained;

[0023] In each step, the chemical mechanical polishing machine used is the same machine or the same model, and the wafers used are the same type of wafers.

[0024] Furthermore, the parameters of the polishing process include several of the disk rotation speed W, pressure head rotation speed w, pressure P, polishing liquid flow F, whether the polishing liquid circulates, whether the polishing head swings, and ambient temperature.

[0025] Further, S2, changing the pressure head speed w and pressure P in the polishing process, using a chemical mechanical polisher to polish the wafer, and measuring the polishing result 1';

[0026] Compare polishing result 1 and polishing result 1';

[0027] S3, if the polishing result 1' is not better than the polishing result 1, continue to change the pressure head speed w and the pressure P in S2, and repeat S2-S3 until the polishing result 1' is better than the polishing result 1. At this time, the polishing process corresponding to the polishing result 1' is the polishing process after the pressure head speed w and the pressure P are optimized;

[0028] If the polishing result 1' is better than the polishing result 1, the polishing process corresponding to the polishing result 1' is used as the polishing process after the pressure head speed w and the pressure P are optimized, and S4 is directly performed;

[0029] S4, based on the polishing process after the pressure head speed w and pressure P determined in S3 are optimized, the large disk speed W in the polishing process is changed, and S2-S3 are repeated to obtain the polishing process after the pressure head speed w and pressure P, and the large disk speed W are optimized;

[0030] S5. Repeat S4 until a polishing process is obtained in which the pressure head speed w, the pressure P, the disk speed W and whether the polishing head swings are all optimized.

[0031] Further, the polishing result includes one or more indicators of the thickness difference of the wafer before and after polishing, the polishing rate (i.e., the rate of change of the thickness of the wafer during the polishing process, usually in um / h), the surface defect state of the polished surface, and the life of the polishing liquid. Optionally, the surface defect state of the polished surface can be visually inspected under the irradiation of a strong light. Optionally, the power of the strong light is ≥20W.

[0032] Further, the wafer is a silicon carbide wafer, preferably a silicon carbide wafer. Optionally, the size of the silicon carbide wafer is 6 inches.

[0033] The chemical mechanical polishing method for a wafer uses a polishing process in which all target parameters obtained by the optimization method described above are optimized to polish the wafer.

[0034] The optimization method of the present invention can be used to systematically optimize the parameters of the polishing process adopted by a chemical mechanical polisher when polishing a semiconductor wafer, thereby improving the scientificity and rationality of the setting of the polishing process parameters.

[0035] The optimization method of the present invention can optimize the polishing process parameters of the chemical mechanical polisher, which is helpful to improve the precision surface quality of the wafer and enhance the stability of the polishing process. The polishing process optimized by the optimization method of the present invention can significantly improve the polishing efficiency, reduce material loss, improve the smoothness and uniformity of the polished surface, and significantly reduce surface defects. The optimization method of the present invention is suitable for the optimization of the polishing process of different chemical mechanical polishers and semiconductor materials of different specifications, and has good versatility. In addition, the optimization method of the present invention has a complete and simple process and reasonable logic.

[0036] Compared with traditional mechanical grinding, chemical mechanical polishing can achieve nano-scale high-quality surface of silicon carbide wafers through the synergistic effect of chemical polishing solution and mechanical thinning. The present invention optimizes polishing process parameters in a step-by-step manner, which is efficient and helps to more accurately evaluate the impact of relevant polishing process parameters on wafer surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of an optimization method of the present invention.

[0038] Figure 2 This is the flatness characterization test result of the silicon carbide wafer after polishing in S5 of Example 1.

[0039] Figure 3 This is a schematic diagram of the size measurement results of the polished silicon carbide wafer in Example 1.

[0040] Figure 4 This is a schematic diagram of the state of the wafer of Example 1 when being polished on a chemical mechanical polisher.

[0041] In the figure, 1-large plate, 2-polishing pad, 3-silicon carbide wafer, 4-carrying plate, 5-pressure head, 6-infusion tube, 7-polishing liquid. DETAILED DESCRIPTION

[0042] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0043] Example 1

[0044] See also Figure 1 The method for optimizing the chemical mechanical polishing process parameters of a wafer in this embodiment comprises the following steps:

[0045] S1. Using a polishing process, a chemical mechanical polisher is used to polish the wafer (silicon carbide wafer), and a polishing result 1 is measured, see Table 2;

[0046] Among them, the assembly state of the wafer and the chemical mechanical polisher is as follows Figure 4 As shown; the parameters of the polishing process include: the disk speed is set to 51rpm, the pressure head speed range is 42rpm, the pressure setting range is 63kg, the flow setting range is 1.2L / min, the polishing liquid circulation (acidic polishing liquid, self-circulation), the polishing head swings, the wafer and the carrier plate are adhered by a laminating machine, and the experimental temperature is set to 30°C;

[0047] The concentration of sulfuric acid in the polishing liquid is 5wt%, and the concentration of potassium permanganate is 5wt%;

[0048] S2, changing the pressure head speed w (changed to 46 rpm) and the pressure P (changed to 66 kg) in the polishing process, using a chemical mechanical polisher to polish the wafer, and measuring the polishing result 1', see Table 2;

[0049] Compare polishing result 1 and polishing result 1';

[0050] Among them, the setting range of relevant parameters is shown in Table 1.

[0051] Table 1

[0052]

[0053] S3, polishing result 1' is better than polishing result 1, the polishing process corresponding to polishing result 1' is the polishing process after the pressure head speed w and pressure P are optimized, and S4 is directly performed;

[0054] S4, based on the polishing process after the pressure head speed w and pressure P determined in S3 are optimized, the disk speed W in the polishing process is changed (to 57 rpm), and S2-S3 are repeated to obtain the polishing process after the pressure head speed w and pressure P, and the disk speed W are optimized;

[0055] S5. On the basis of the polishing process after the pressure head speed w, pressure P and large disk speed W are optimized as determined by S4, change whether the polishing head in the polishing process swings (to not swinging), repeat S2-S3, and obtain the polishing process after the pressure head speed w, pressure P and large disk speed W are optimized; until the polishing process after the pressure head speed w, pressure P, large disk speed W and whether the polishing head swings are all optimized is obtained.

[0056] In each step, the chemical mechanical polisher used is the same, which is a precision single-sided chemical mechanical polisher produced by Shanghai Zhiling Semiconductor Co., Ltd. The wafer used is a 6-inch silicon carbide wafer; in the relevant steps, the polishing time is 4 hours.

[0057] The polishing results of each step are shown in Table 2.

[0058] Table 2

[0059]

[0060] PAD refers to the polishing pad. TV5 before and after refers to the difference in wafer thickness before and after polishing. If a wafer is scratched during polishing, it is considered that the life of the polishing liquid has reached its limit.

[0061] Table 3 shows the characterization test results of the surface roughness of the silicon carbide wafer after polishing in S5 (obtained by commissioning a third-party testing agency). It can be seen that the surface roughness of the silicon carbide wafer obtained by the final optimized process is 0.16±0.05nm, and the surface quality is extremely high, which indicates that the optimized polishing process of the present invention has practical reliability and effectiveness.

[0062] Table 3

[0063] Sample name Test items Test Results 6-inch silicon carbide wafer Surface roughness Ra 0.16±0.05nm

[0064] Figure 2 This is the flatness characterization test result of the polished silicon carbide wafer in S5 (obtained by a third-party testing agency). It can be seen from the figure that the polished wafer obtained by the final optimized process has good flatness, with no high points or defects on the surface, which indicates that the surface quality of the silicon carbide wafer after polishing by this process is very good.

[0065] Figure 3 The schematic diagram of the measurement result of the size of the silicon carbide wafer is shown in FIG. As can be seen from the figure, the size of the silicon carbide wafer after polishing is still 6 inches.

[0066] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for optimizing process parameters of chemical mechanical polishing of a wafer, characterized in that: The steps include: S1, polishing the wafer using a chemical mechanical polisher in a polishing process, and measuring a polishing result 1; Wherein, the polishing process includes at least 2 parameters; S2, changing at least one of the parameters of the polishing process, polishing the wafer using a chemical mechanical polisher, and measuring the polishing result 1'; Compare polishing result 1 and polishing result 1'; S3. If polishing result 1' is not better than polishing result 1, continue to change the parameters changed in S2 and repeat S2-S3, until the polishing result 1' is better than the polishing result 1, at which point the polishing process corresponding to the polishing result 1' is the polishing process after the relevant parameters are optimized; If the polishing result 1' is better than the polishing result 1, the polishing process corresponding to the polishing result 1' is used as the polishing process with optimized relevant parameters, and S4 is directly performed; S4, based on the polishing process after the relevant parameters determined in S3 are optimized, changing at least one of the other parameters in the polishing process, repeating S2-S3, and obtaining a polishing process after multiple parameters are optimized; S5, repeat S4 until a polishing process with all target parameters optimized is obtained; In each step, the chemical mechanical polishing machine used is the same machine or the same model, and the wafers used are the same type of wafers.

2. The optimization method according to claim 1, characterized in that: The parameters of the polishing process include the disk rotation speed W, the pressure head rotation speed w, the pressure P, the polishing liquid flow F, whether the polishing liquid circulates, whether the polishing head swings, and the ambient temperature.

3. The optimization method according to claim 2, characterized in that: S2, changing the pressure head speed w and pressure P in the polishing process, using a chemical mechanical polisher to polish the wafer, and measuring the polishing result 1'; Compare polishing result 1 and polishing result 1'; S3, if the polishing result 1' is not better than the polishing result 1, continue to change the pressure head speed w and the pressure P in S2, and repeat S2-S3 until the polishing result 1' is better than the polishing result 1. At this time, the polishing process corresponding to the polishing result 1' is the polishing process after the pressure head speed w and the pressure P are optimized; If the polishing result 1' is better than the polishing result 1, the polishing process corresponding to the polishing result 1' is used as the polishing process after the pressure head speed w and the pressure P are optimized, and S4 is directly performed; S4, based on the polishing process after the pressure head speed w and pressure P determined in S3 are optimized, the large disk speed W in the polishing process is changed, and S2-S3 are repeated to obtain the polishing process after the pressure head speed w and pressure P, and the large disk speed W are optimized; S5. Repeat S4 until a polishing process is obtained in which the pressure head speed w, the pressure P, the disk speed W and whether the polishing head swings are all optimized.

4. The optimization method according to any one of claims 1 to 3, characterized in that: The polishing results include one or more indicators of the thickness difference of the wafer before and after polishing, the polishing rate, the surface defect state of the polishing surface, and the life of the polishing liquid.

5. The optimization method according to any one of claims 1 to 3, characterized in that: The wafer is a silicon carbide wafer, preferably a silicon carbide wafer.

6. A chemical mechanical polishing method for a wafer, characterized in that: The wafer is polished by a polishing process in which all target parameters obtained by the optimization method according to any one of claims 1 to 5 are optimized.

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