Method for reducing wafer defects through surface modification

Abstract

The invention provides a method for reducing wafer defects through surface modification, which comprises the following steps: providing a wafer, and carrying out first wet etching on the silicon surface of the wafer; performing oxidation treatment on the silicon surface of the wafer to reduce the surface roughness; then cleaning the silicon surface by using a standard cleaning solution 1 to remove particle contamination possibly brought in the previous technical process; and carrying out second wet etching on the silicon surface of the wafer. According to the method, in the thinning process of the wafer, oxidation treatment on the silicon surface of the wafer is inserted between the two times of wet etching on the surface of the silicon wafer, so that the roughness of the silicon surface of the wafer is reduced, the thickness uniformity of the thinned wafer is further improved, and surface defects can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for reducing wafer defects through surface modification. Background Art

[0002] The last step of the back-side illumination (BSI) thinning process requires the use of tetramethylammonium hydroxide (TMAH) solution to etch the EPI Si to the target thickness (depending on the target thickness of different products, usually in the range of 2 to 7um, the average thickness of each wafer is allowed to fluctuate within a range of less than 0.06um, and the in-plane thickness range does not exceed 0.18um. The process requirements are very demanding.

[0003] In order to reduce the impact of different Si thickness after chemical mechanical polishing of the previous Si layer, TMAH etching has adopted automatic process control (APC) to control the process. However, because the etching rate of TMAH solution on epitaxy (EPI) Si is affected by temperature and oxygen concentration, even if the temperature of the solution in the tank is strictly controlled, the actual temperature of the solution reaching the wafer surface in each working chamber is still uncontrollable. In addition, even if the solution replacement cycle has been controlled within 6 hours, the difference in etching rate between the initial and final stages causes the actual average thickness of the wafer to still fluctuate greatly. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for reducing wafer defects by surface modification, so as to solve the problem of uneven wafer thickness caused by etching rate differences in the wafer thinning process in the prior art.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides a method for reducing wafer defects by surface modification, which at least comprises:

[0006] Step 1: providing a wafer, and performing a first wet etching on the silicon surface of the wafer;

[0007] Step 2: Oxidizing the silicon surface of the wafer to reduce the surface roughness; then cleaning the silicon surface with a standard cleaning solution 1 to remove particle contamination that may be introduced during the previous process;

[0008] Step three: performing a second wet etching on the silicon surface of the wafer.

[0009] Preferably, the etchant for the first wet etching in step one is tetramethylammonium hydroxide.

[0010] Preferably, in step one, an automatic process control system is used to monitor the thickness of the epitaxial layer of the wafer before the first wet etching.

[0011] Preferably, in step 2, the silicon surface of the wafer is oxidized using O3 to reduce surface roughness.

[0012] Preferably, the concentration of O3 in step 2 is at the ppm level; and the oxidation treatment time is no more than 1 min.

[0013] Preferably, the standard cleaning solution 1 in step 2 is SC1.

[0014] Preferably, the time for cleaning the silicon surface in step 2 is no more than 1 minute.

[0015] Preferably, the etchant for the second wet etching in step three is tetramethylammonium hydroxide.

[0016] Preferably, in step three, an automatic process control system is used to monitor the thickness of the epitaxial layer of the wafer before the second wet etching.

[0017] As described above, the method of surface modification to reduce wafer defects of the present invention has the following beneficial effects: the present invention adopts an oxidation treatment of the silicon surface of the wafer between two wet etchings of the silicon wafer surface in the wafer thinning process to reduce the roughness of the silicon surface of the wafer, thereby improving the thickness uniformity of the wafer after thinning, which can effectively reduce surface defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Shown is a flow chart of the method for reducing wafer defects by surface modification of the present invention;

[0019] Figure 2 Shown is a defect distribution diagram of a wafer surface after a thinning process in the prior art;

[0020] Figure 3 The defect distribution diagram of the wafer surface after step three of the present invention is completed is shown. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] See also Figures 1 to 3It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0023] The present invention provides a method for reducing wafer defects by surface modification, such as Figure 1 As shown, Figure 1 The flowchart of the method for reducing wafer defects by surface modification of the present invention is shown, and the method comprises at least the following steps:

[0024] Step 1: providing a wafer, and performing a first wet etching on the silicon surface of the wafer;

[0025] The present invention further comprises that the etchant for the first wet etching in step 1 of this embodiment is tetramethylammonium hydroxide (TMAH). In step 1, the silicon surface of the wafer to be subjected to the backside illumination (BSI) thinning process is first wet-etched.

[0026] In the present invention, the automatic process control system (APC) is used to monitor the thickness of the epitaxial layer of the wafer before the first wet etching in step 1 of the present embodiment. The silicon surface of the wafer in the present invention is the surface of the epitaxial layer.

[0027] Step 2: Oxidizing the silicon surface of the wafer to reduce the surface roughness; then cleaning the silicon surface with a standard cleaning solution 1 to remove particle contamination that may be introduced during the previous process;

[0028] The present invention further comprises that in step 2 of this embodiment, the silicon surface of the wafer is oxidized using O3 to reduce the surface roughness.

[0029] The present invention further comprises that the concentration of O3 in step 2 of this embodiment is at the ppm level; and the time of the oxidation treatment is no more than 1 minute.

[0030] In the present invention, the standard cleaning solution 1 in step 2 of this embodiment is SC1.

[0031] Furthermore, in the present invention, the time for cleaning the silicon surface in step 2 of this embodiment is no more than 1 minute.

[0032] In step 2, the silicon surface of the wafer is oxidized to reduce the surface roughness; after the silicon surface is wet-etched for the first time in step 1, the silicon surface is oxidized. In this embodiment, ozone (O3) is used to oxidize the silicon surface, and the roughness of the oxidized silicon surface is reduced. In this embodiment, the concentration of ozone in the oxidation process of this step is at the ppm level, and the oxidation time does not exceed 1 minute.

[0033] After the oxidation treatment, the silicon surface is then cleaned using standard cleaning solution 1 (SC1) to remove particle contamination that may be brought in during the previous process; that is, the silicon surface after the oxidation treatment is cleaned. The cleaning solution in this embodiment is standard cleaning solution 1, i.e. SC1, which is a common solution in the industry.

[0034] Step three: performing a second wet etching on the silicon surface of the wafer.

[0035] Furthermore, in the present invention, the etchant for the second wet etching in step three of this embodiment is tetramethylammonium hydroxide.

[0036] The present invention further adopts an automatic process control system in step three of this embodiment to monitor the thickness of the epitaxial layer of the wafer before the second wet etching.

[0037] In step 3, the silicon surface of the cleaned wafer is wet-etched for the second time. In this embodiment, the second wet etching uses an automatic process control system (APC) to monitor the thickness of the epitaxial layer of the wafer before the second wet etching. The etchant for the second wet etching is tetramethylammonium hydroxide. By monitoring the thickness of the epitaxial layer before etching twice, the etching thickness range before and after etching can be controlled.

[0038] After two wet etchings, the wafer is thinned, and the silicon surface is oxidized between the two thinning processes to reduce the roughness of the silicon surface, and the pollution caused by the previous process is removed by cleaning, thereby further reducing the probability of defects on the wafer surface in subsequent processes.

[0039] like Figure 2 As shown, Figure 2 Shown is a defect distribution diagram of a wafer surface after a thinning process in the prior art; Figure 3 The defect distribution diagram of the wafer surface after step 3 of the present invention is shown. After comparison, it is found that Figure 2 The number of defects in Figure 3In other words, the method of the present invention has a significant effect in reducing surface defects of wafers. In summary, the present invention inserts an oxidation treatment on the silicon surface of the wafer between two wet etchings of the silicon wafer surface in the wafer thinning process to reduce the roughness of the silicon surface of the wafer, thereby improving the thickness uniformity of the wafer after thinning, and effectively reducing surface defects. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0040] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for reducing wafer defects by surface modification, characterized in that: At least: Step 1: providing a wafer, and performing a first wet etching on the silicon surface of the wafer; Step 2: Oxidizing the silicon surface of the wafer to reduce the surface roughness; then cleaning the silicon surface with a standard cleaning solution 1 to remove particle contamination that may be introduced during the previous process; Step three: performing a second wet etching on the silicon surface of the wafer.

2. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: The etchant for the first wet etching in step 1 is tetramethylammonium hydroxide.

3. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: In step one, an automatic process control system is used to monitor the thickness of the epitaxial layer of the wafer before the first wet etching.

4. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: In step 2, the silicon surface of the wafer is oxidized using O3 to reduce the surface roughness.

5. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: The concentration of O3 in step 2 is at the ppm level; the oxidation treatment time is no more than 1 minute.

6. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: The standard cleaning solution 1 in step 2 is SC1.

7. The method for reducing wafer defects by surface modification according to claim 6, characterized in that: The time for cleaning the silicon surface in step 2 is no more than 1 minute.

8. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: The etchant for the second wet etching in step three is tetramethylammonium hydroxide.

9. The method for reducing wafer defects by surface modification according to claim 1, characterized in that: In step three, an automatic process control system is used to monitor the thickness of the epitaxial layer of the wafer before the second wet etching.

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