Method for planarizing front surface of copper CMP (Chemical Mechanical Polishing)

Abstract

The invention provides a method for planarizing the front surface of copper CMP (Chemical Mechanical Polishing), which comprises the following steps of: providing a wafer which is subjected to a copper filling process; forming a first sacrificial layer with a first thickness on the surface of the wafer; coating a first layer of photoresist on the surface of the first sacrificial layer; performing planarization reverse etching for the first time, removing the first layer of photoresist, and etching a part of the first sacrificial layer; forming a second sacrificial layer with a second thickness on the surface of the first sacrificial layer; coating a second layer of photoresist on the surface of the second sacrificial layer; and second-time planarization reverse etching is carried out. A step-by-step gradual method is adopted, higher etching precision is guaranteed through multiple times of planarization reverse etching, the surface local planarization quality is improved, the problem of MEMS structure deformation at the sunken position is avoided, and the final yield is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor manufacturing, and in particular relates to a method for planarizing a copper CMP front surface. Background Art

[0002] Some semiconductor devices, such as infrared emitters, require copper filling and copper CMP (chemical mechanical polishing) processes due to the need to pass large currents. In order to ensure device quality, the wafer needs to be surface flattened before the copper CMP process. Flattening reverse etching is a commonly used flattening method. A sacrificial layer is filled in the low-lying steps or holes on the surface. The etching rate of the high part is faster than the etching rate of the low part in dry etching, so that the height difference between the two is finally reduced to achieve the flattening effect. However, there is still a problem of poor local flattening. When performing the copper CMP process, in order to remove the copper at the lowest part of the step, the time of the CMP process needs to be increased. When the copper CMP process is performed under the condition of poor flattening, obvious graphic depressions are generated locally after the copper CMP process, and the MEMS (micro-electromechanical system) structure in some depressions is severely deformed, affecting the subsequent yield rate.

[0003] Based on the above problems, it is urgent to provide a method for planarizing the copper CMP front surface to ensure the final yield. Summary of the invention

[0004] The present invention aims to solve all or part of the problems of the above-mentioned prior art and provides a method for planarizing the surface before copper CMP. The wafer that has completed copper filling is planarized before CMP. The planarization process adopts a step-by-step method. Through multiple planarization reverse etchings, higher etching accuracy is guaranteed, the quality of local surface planarization is improved, the problem of MEMS structure deformation in the recess is avoided, and the final yield is guaranteed.

[0005] The present invention provides a method for planarizing the front surface of copper CMP, comprising the following steps: providing a wafer, the wafer having completed a copper filling process; forming a first sacrificial layer with a first thickness on the surface of the wafer; coating a first layer of photoresist on the surface of the first sacrificial layer; performing a first planarization reverse etching, removing the first layer of photoresist, and etching a portion of the first sacrificial layer; forming a second sacrificial layer with a second thickness on the surface of the first sacrificial layer; coating a second layer of photoresist on the surface of the second sacrificial layer; and performing a second planarization reverse etching. A step-by-step planarization method is adopted, and etching accuracy is improved through multiple planarization reverse etchings, the quality of local surface planarization is improved, the problem of MEMS structure deformation in the recess is avoided, and the final yield is guaranteed.

[0006] The lowest point of the first sacrificial layer is higher than the highest point of the original surface of the wafer, ensuring that the target flatness can be achieved.

[0007] The sum of the first thickness and the second thickness is in the range of 3-8 μm, so as to avoid the problem of being easily damaged due to being too thin or being difficult to etch uniformly due to being too thick.

[0008] In the first planarization reverse etching, the first sacrificial layer is etched to a thickness of 10% of the thickness of the first layer of photoresist removed. The first sacrificial layer is properly etched to make the remaining surface of the first sacrificial layer relatively flat, while avoiding excessive etching to damage the material, thereby improving the consistency and reliability of the production process.

[0009] Before coating the second sacrificial layer, the surface of the wafer is cleaned to remove pollutants and particles on the surface of the wafer and to remove residues.

[0010] The second planarization reverse etching removes the second photoresist layer and etches part of the sacrificial layer to a desired thickness, thereby obtaining a desired structure and ensuring a flat surface.

[0011] The first planarization reverse etching and the second planarization reverse etching adopt a dry etching process. The dry etching technology can achieve a faster etching rate for high-position patterns than for low-position patterns, thereby reducing height differences and planarizing the surface.

[0012] The first sacrificial layer and the second sacrificial layer are made of polyimide, which maintains the integrity of the structure during the planarization process and reduces the possible risk of damage.

[0013] The viscosity of the photoresist used is lower than that of the polyimide. When the first photoresist layer and the second photoresist layer are coated, the surfaces of the first sacrificial layer and the second sacrificial layer can be completely covered respectively, and the height difference of the surface parts can be reduced.

[0014] A copper CMP treatment method is also provided, which uses the above method to perform planarization and then performs copper CMP treatment, thereby improving the quality of local surface planarization and avoiding the problem of MEMS structure deformation in the concave part after copper CMP.

[0015] Compared with the prior art, the beneficial effects of the present invention mainly include the following: a method for planarizing the surface before copper CMP is provided, a wafer that has completed copper filling is planarized before CMP, the planarization process adopts a step-by-step method, and higher etching accuracy is ensured through multiple planarization reverse etching, thereby improving the quality of local surface planarization. After the copper CMP is completed, there is no obvious local structural depression, and there is no MEMS structural deformation at the depression, thereby ensuring the final yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A flow chart of a method for planarizing a copper CMP front surface provided by the present invention.

[0018] Figure 2 Plane scan image after the original flattening method.

[0019] Figure 3 This is the SEM image of copper CMP after the original planarization method.

[0020] Figure 4 This is a plane scanned image processed by the flattening method provided by the present invention.

[0021] Figure 5 This is a SEM image of copper CMP after being processed by the planarization method provided by the present invention. DETAILED DESCRIPTION

[0022] The following description and accompanying drawings fully demonstrate specific embodiments of the present invention so that those skilled in the art can practice them. Other embodiments may include structural, logical, electrical, process and other changes. The embodiments represent possible variations only. Unless clearly required, separate components and functions are optional, and the order of operation may vary. The parts and features of some embodiments may be included in or replace the parts and features of other embodiments.

[0023] Before the wafer undergoes the copper CMP process, it needs to undergo surface planarization. The current planarization reverse etching method has the problem of poor local planarization, such as Figure 2 , 3 As shown, after the original planarization method, there are still deep steps on the surface, with the deepest step reaching about 0.8μm; the scanning electron microscope (SEM) image shows that after the copper CMP is completed, the local surface pattern is obviously concave, and the MEMS structure next to the copper column has been bent and deformed.

[0024] Example 1

[0025] In order to solve the above problems, a method for planarizing the front surface of copper CMP is provided, and the specific steps are shown in 1:

[0026] Providing a wafer, wherein the copper filling process has been completed on the wafer;

[0027] A first sacrificial layer with a first thickness is formed on the surface of the wafer; the lowest point of the first sacrificial layer is higher than the highest point of the original surface of the wafer. Ensure that planarization can be achieved to avoid the problem of being fragile due to being too thin or difficult to etch uniformly due to being too thick. The first sacrificial layer is made of polyimide, which maintains the integrity of the structure during the planarization process and reduces the risk of possible damage.

[0028] A first layer of photoresist is coated on the surface of the first sacrificial layer. The viscosity of the photoresist is lower than that of polyimide. When the first layer of photoresist is coated, the surface of the first sacrificial layer can be completely covered and the height difference of the surface part can be reduced, which is conducive to achieving final planarization.

[0029] Perform the first planarization reverse etching to remove the first layer of photoresist and etch part of the first sacrificial layer; the thickness of the first sacrificial layer etching is 10% of the thickness of the first layer of photoresist removed, and the first sacrificial layer is properly etched to make the surface of the remaining first sacrificial layer after etching relatively flat, while avoiding excessive etching to damage the material, thereby improving the consistency and reliability of the production process. The first planarization reverse etching adopts dry etching, which can achieve a faster etching rate of high graphics than low graphics, reduce height differences, and reduce the unevenness of the material surface after etching.

[0030] A second sacrificial layer is coated on the surface of the first sacrificial layer, and the sum of the first thickness and the second thickness is in the range of 3-8 μm. In this embodiment, the first thickness is equal to the second thickness, and the second sacrificial layer is also made of polyimide.

[0031] A second layer of photoresist is coated on the surface of the second sacrificial layer, and the second layer of photoresist can completely cover the surface of the second sacrificial layer; before coating the second sacrificial layer, the surface of the wafer is cleaned to remove pollutants and particles on the surface of the wafer and remove residues to avoid affecting subsequent processes.

[0032] The second planarization reverse etching is performed to complete the planarization of the wafer. The second planarization reverse etching adopts a dry etching process to etch away the second photoresist layer and partially etch the sacrificial layer to the required sacrificial layer thickness to obtain the required structure and ensure the surface flatness.

[0033] like Figure 4 As shown, the plane scanning image results show that, through the flattening method provided by the present invention, compared with the original method, the deepest step has been reduced from about 0.8 μm to about 0.2 μm, and the surface flatness has been significantly improved.

[0034] Example 2

[0035] This embodiment provides a copper CMP treatment method, which uses the method described in Example 1 to perform a planarization treatment, and then performs a copper CMP treatment. After the copper CMP is completed, the surface step condition is observed by SEM to confirm the planarization effect. Figure 5 As shown in the SEM image, after being processed by the planarization method provided by the present invention and then subjected to copper CMP, the local pattern is slightly concave, and the MEMS structure next to the copper column remains in a straight line.

[0036] The step-by-step surface planarization method provided by the present invention can effectively improve the surface planarization quality. After the copper CMP process is completed, there is no obvious local structural depression on the surface, and there is no MEMS structural deformation at the depression, thereby ensuring the final yield.

[0037] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for planarizing a copper CMP front surface, characterized in that: The steps include: Providing a wafer, wherein the copper filling process has been completed on the wafer; forming a first sacrificial layer having a first thickness on the surface of the wafer; Coating a first layer of photoresist on the surface of the first sacrificial layer; Performing a first planarization reverse etching to remove the first photoresist layer and etch a portion of the first sacrificial layer; forming a second sacrificial layer having a second thickness on a surface of the first sacrificial layer to form a sacrificial layer; Coating a second layer of photoresist on the surface of the second sacrificial layer; Perform a second planarization reverse etching.

2. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: The lowest point of the first sacrificial layer is higher than the highest point of the original surface of the wafer.

3. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: The sum of the first thickness and the second thickness is in the range of 3-8 μm.

4. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: In the first planarization reverse etching, the first sacrificial layer is etched to a thickness of 10% of the thickness of the first photoresist layer removed.

5. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: Before coating the second sacrificial layer, the surface of the wafer is cleaned.

6. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: The second planarization reverse etching removes the second layer of photoresist and etches a portion of the sacrificial layer to a desired thickness.

7. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: The first planarization reverse etching and the second planarization reverse etching adopt a dry etching process.

8. The method for planarizing the copper CMP front surface according to claim 1, characterized in that: The first sacrificial layer and the second sacrificial layer are made of polyimide.

9. The method for planarizing the copper CMP front surface according to claim 8, characterized in that: The photoresist used has a viscosity lower than that of the polyimide.

10. A copper CMP treatment method, characterized in that: The method comprises the following steps: performing a planarization treatment using the method described in any one of claims 1 to 9, and then performing a copper CMP treatment.

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