Method for effectively removing copper contamination in 12-inch silicon substrate body

Abstract

The invention discloses a method for effectively removing copper contamination in a 12-inch silicon substrate body. The method comprises the following steps: (1) preheating an oven to 100-180 DEG C; (2) placing the to-be-processed silicon wafer in an oven, accurately and slowly heating the oven to 180-350 DEG C, and carrying out long-time heat preservation at the temperature for 6-10 hours; (3) precisely and slowly cooling to 50 DEG C, opening a door, cooling to room temperature, and then taking out the silicon wafer; (4) putting the silicon wafer into pure water containing ozone to passivate the silicon wafer, and curing copper stains separated out by baking on the surface; and (5) removing a passivation film on the surface of the silicon wafer by using a hydrofluoric acid solution. Through the method provided by the invention, on the premise of not introducing other metal contamination and not consuming thermal budget of the silicon wafer, the copper metal contamination of the silicon substrate can be effectively removed, so that the copper content in the silicon wafer body is 1t; and the method is suitable for the preparation process of substrates with high metal requirements such as 12-inch large-size silicon wafers and the like, and is also suitable for the reprocessing preparation process of recycled wafers.

Description

Technical Field

[0001] The invention relates to a method for effectively removing copper contamination in a 12-inch silicon substrate, belonging to the technical field of semiconductor materials. Background Art

[0002] With the development of semiconductor technology, silicon substrate polishing wafers are gradually developing towards larger sizes. With the increase in size, the quality parameters of silicon substrate polishing wafers are becoming more and more stringent, among which metal control is the top priority. Among them, many important properties of copper are different from other 3d transition metals, and copper exists in silicon in an interstitial state. Due to the small ion radius of copper and the weak interaction with the lattice, copper has an extremely high diffusion rate in silicon. The diffusion of other impurities needs to overcome the elastic and electrostatic effects between the lattice atoms, making it the most difficult to control fast-diffusion metal.

[0003] Copper contamination can significantly reduce device yields in semiconductor manufacturing, including structural defects in the oxide-polysilicon gate structure, as well as increased leakage current and reduced minority carrier lifetime at the PN junction, resulting in current breakdown and device failure.

[0004] In order to suppress and solve the contamination problem of metal copper, gettering is usually used in the preparation process of silicon substrate polishing wafers. The gettering process mainly includes three steps: release, diffusion and capture of metal impurities. In order to ensure the effectiveness of gettering, the binding energy of capture must be higher than the release energy and diffusion activation energy, so as to ensure that the captured impurity atoms will not be released again and return to the device working area. In addition, since metal silicon compounds are not stable at high temperatures, the impurity atoms will dissolve and reprecipitate each time the silicon wafer is reheated, so gettering is a dynamic process and unstable. In addition, gettering requires artificial defects or damage in the body (internal gettering) or on the surface (external gettering) of the silicon wafer. Among them, internal gettering has high requirements for the crystal material itself, and the process of artificially creating internal gettering points requires very high temperatures and a long thermal history, while external gettering requires artificial damage and defects on the surface of the silicon wafer, which is also not suitable for large-size and double-sided polished silicon wafers, especially recycled wafers. For copper precipitation, if there is no gettering, its precipitation is more likely to occur on the surface of the silicon wafer, because the free surface contains atomic steps and the growth of precipitation is not constrained by the lattice.

[0005] Therefore, how to effectively and efficiently remove copper contamination in the silicon substrate has become a problem that all substrate and IC manufacturers are very concerned about. Summary of the invention

[0006] The purpose of the present invention is to provide a method for effectively removing copper contamination in a 12-inch silicon substrate. Based on the diffusion characteristics of Cu in silicon, precise temperature and time processing is performed in the entire process of silicon wafer heat treatment to ensure that Cu can be fully removed. The method is suitable for the process of polishing silicon substrates of 12 inches and below, and can effectively remove copper contamination in the silicon substrate without introducing contamination of other heavy metals and affecting the total thermal budget of the silicon wafer. The method is particularly suitable for the processing of recycled wafers.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for effectively removing copper contamination in a 12-inch silicon substrate comprises the following steps: (1) Preheat the oven to 100-180°C. The preheating temperature rises quickly, and this process mainly provides a higher diffusion rate for Cu. (2) Place the silicon wafer to be processed in an oven, and slowly and accurately heat the oven to 180-350°C, and keep it at this temperature for a long time, with the holding time being 6-10 hours; (3) Slowly and accurately cool down to 50°C, open the door and cool to room temperature before taking out the silicon wafer; (4) Place the silicon wafer in pure water containing ozone to passivate the silicon wafer and solidify the copper contamination precipitated by baking on the surface; (5) Use hydrofluoric acid solution to remove the passivation film on the surface of the silicon wafer.

[0008] Preferably, in step (2), the heating rate is 0.5-1°C / min, and the heating rate is precisely controlled to be slow. This process takes a long time, and during this process, Cu atoms will not produce silicon-copper compounds. The binding energy on the silicon wafer surface is large, and Cu mainly diffuses to the silicon wafer surface. After reaching a specific temperature (180-350°C), the temperature is kept constant. At this temperature, Cu combines with Si to form Cu3Si, and no other copper-silicon compounds are produced at this stage. Cu3Si is relatively easy to oxidize, and it will be oxidized in step (4).

[0009] Preferably, in step (2), the temperature fluctuation during the insulation process is less than 1°C.

[0010] Preferably, in step (3), the cooling rate is 0.5-1°C / min. The slow cooling process is divided into several stages to prevent the Cu that has diffused to the surface from rapidly diffusing into the interior of the silicon wafer.

[0011] Preferably, in step (4), the concentration of ozone in pure water is 10-15 mg / L, and the immersion time of the silicon wafer is controlled at 5-10 min.

[0012] Preferably, in step (5), the mass percentage concentration of hydrofluoric acid in the hydrofluoric acid solution is 0.5-1.5%.

[0013] ICP-MS was used to test the Cu metal on the surface of the silicon wafer treated by the method. The test was repeated twice, with an interval of 7 days between the two tests. The Cu content was <1E8atoms / cm -2 .

[0014] Compared with the prior art, the present invention has the following beneficial effects: The method of the present invention bakes the copper contamination to the surface by baking for a long time at a low temperature, and then removes the contamination after solidification through a special cleaning process, thereby achieving the purpose of removing the copper contamination, while not introducing other metal contamination and not consuming the thermal budget of the silicon wafer. The method of the present invention can effectively remove the copper metal contamination of the silicon substrate without introducing other metal contamination and not consuming the thermal budget of the silicon wafer, so that the copper content in the silicon wafer body is less than 1E8, which is suitable for the substrate preparation process with high metal requirements such as 12-inch large-size silicon wafers, and is also suitable for the reprocessing preparation process of recycled wafers.

[0015] The method of the present invention is also applicable to the manufacturing process of small-size (6 / 8 inch) silicon substrates with strict requirements on metal contamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a process flow chart for effectively removing copper contamination at low temperature. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but is not intended to limit the protection scope of the present invention.

[0018] like Figure 1 As shown, the method of the present invention is as follows: preheating the oven to a certain temperature, then placing the silicon wafer to be processed in the oven, accurately and slowly heating the oven to a certain temperature, and keeping the temperature for a long time at this temperature. The temperature fluctuation during the keeping temperature should be small, then accurately and slowly cooling, opening the door to cool to room temperature and then taking out the silicon wafer; then using ozone to passivate the silicon wafer, solidifying the copper contamination precipitated by baking on the surface, and finally using hydrofluoric acid solution to remove the passivation film on the surface of the silicon wafer to achieve the purpose of removing copper contamination.

[0019] Example 1 Take 10 12-inch silicon substrate polished wafers, of which 5 (group 1) introduced 1E14 copper contamination, and the other 5 (group 2) were not treated. The two groups of silicon wafers were treated separately using the above method, wherein the initial temperature was 100°C, the heating rate was 0.5°C / min, the holding temperature was 200°C, the holding time was 8h, the cooling rate after baking was 0.5°C / min, the unpacking temperature was 50°C, and the surface of the silicon wafer that was cooled to room temperature was oxidized and passivated using ozone, and then the oxide film was removed using a hydrofluoric acid solution with a mass percentage concentration of 1%. The copper content in the two groups of silicon wafers was tested again using ICP-MS, and both were below the 1E8 level (Cu content <1E8atoms / cm -2 ). The test was repeated 7 days apart, and the copper content in both groups of silicon wafers was below 1E8.

[0020] Example 2 Take 10 12-inch recycled wafers that have undergone the copper diffusion process for IC manufacturing. The copper content in the test body is all at the order of 1E13. Use the above method to treat the silicon wafers respectively, where the initial temperature is 100℃, the heating rate is 0.5℃ / min, the holding temperature is 250℃, the holding time is 6h, the cooling rate after baking is 0.5℃ / min, the unpacking temperature is 50℃, and ozone is used to oxidize and passivate the surface of the silicon wafer that has been cooled to room temperature. Then, a hydrofluoric acid solution with a mass percentage concentration of 1% is used to remove the oxide film. ICP-MS is used again to test the copper content in the silicon wafer, which is all below the order of 1E8. Repeat the test at an interval of 7 days, and the copper content in the 10 silicon wafers is all below the order of 1E8.

Claims

1. A method for effectively removing copper contamination from a 12-inch silicon substrate, characterized in that: The following steps are involved: (1) Preheat the oven to 100-180℃; (2) Place the silicon wafer to be processed in an oven, and slowly and accurately heat the oven to 180-350°C, and keep it at this temperature for a long time, with the holding time being 6-10 hours; (3) Slowly and accurately cool down to 50°C, open the door and cool to room temperature before taking out the silicon wafer; (4) Place the silicon wafer in pure water containing ozone to passivate the silicon wafer and solidify the copper contamination precipitated by baking on the surface; (5) Use hydrofluoric acid solution to remove the passivation film on the surface of the silicon wafer.

2. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1, characterized in that: In the step (2), the heating rate is 0.5-1°C / min.

3. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1 or 2, characterized in that: In the step (2), the temperature fluctuation during the insulation process is less than 1°C.

4. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1 or 2, characterized in that: In the step (3), the cooling rate is 0.5-1°C / min.

5. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1 or 2, characterized in that: In step (4), the concentration of ozone in pure water is 10-15 mg / L, and the immersion time of the silicon wafer is controlled at 5-10 min.

6. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1 or 2, characterized in that: In step (5), the mass percentage concentration of hydrofluoric acid in the hydrofluoric acid solution is 0.5-1.5%.

7. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 1 or 2, characterized in that: ICP-MS was used to test the Cu content on the surface of the silicon wafer treated by the method. After repeated testing, the Cu content was less than 1E8 atoms / cm -2 .

8. The method for effectively removing copper contamination in a 12-inch silicon substrate according to claim 7, characterized in that: The test was repeated twice, with an interval of 7 days between the two tests, and the Cu content was <1E8atoms / cm -2 .

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