Method for reducing plasma damage

Abstract

The invention discloses a method for reducing plasma damage, which comprises the following steps of: after a PECVD (Plasma Enhanced Chemical Vapor Deposition) deposition process is finished, carrying out two steps of surface plasma treatment: firstly, using O2 / He as surface treatment gas, and simultaneously introducing high frequency of first power to carry out surface treatment on a PECVD film; 2, O2 / He is used as surface treatment gas, and meanwhile radio frequency of second power is introduced to conduct surface treatment on the PECVD thin film; the second power is lower than the first power. According to the method, after a deposition process is completed, two-step double-frequency (low power + lower power) radio frequency is introduced to be combined with O2 / He to serve as surface treatment gas; the first step of low-power plasma surface treatment can be rapidly compounded with redundant electrons or positive ions left on the surface of the silicon wafer, and the second step of lower-power plasma surface treatment can be further compounded with redundant electrons or positive ions left on the surface of the silicon wafer, so that plasma damage is reduced.

Description

Technical Field

[0001] The invention relates to the field of semiconductor manufacturing, and in particular to a method for reducing plasma damage. Background Art

[0002] The plasma process uses the extra energy of plasma to reduce the process temperature, but the resulting directional ion bombardment of the silicon wafer surface will cause charging of the surface of the silicon wafer insulation layer film.

[0003] The mechanism or cause of charging / plasma damage is: In the PECVD process, HF (high frequency 13.56 MHz) is usually used to provide moderate plasma density and moderate ion energy, such as Figure 1 As shown, in the first RF cycle, there is a positive bias in the cavity, which attracts electrons from the plasma, and in the second RF cycle, the cavity is negatively biased, which attracts positive ions from the plasma. In uniform plasma, the flux of electrons in the first cycle is equal to that of positive ions in the second cycle, and they will soon recombine. In non-uniform plasma, the flux of electrons in the first cycle is not equal to that of positive ions in the second cycle, and there will be excess electrons or positive ions left on the surface of the silicon wafer. When the surface of the silicon wafer is an insulating film, a charging phenomenon will be formed. This phenomenon is summarized in Table 1 below. These excess electrons or positive ions are transmitted through the conductor (metal or polysilicon) under the insulating film and directly affect the device.

[0004]

[0005] Table 1 If the charged insulating layer is connected to a conductive film (metal, poly, etc.), the performance of the thin oxide (i.e., gate dielectric layer) under these conductors may be severely degraded by this charging, that is, the oxide will completely short-circuit or fail prematurely.

[0006] Traditional methods to reduce plasma damage include changing the design of the process chamber, changing the process parameters during deposition, etc. However, changing the design of the process chamber is often costly and will also bring about additional particles, poor film thickness uniformity, and other problems. Changing the process gas and parameters during deposition will also change the film quality. At the same time, attempts have also been made to perform ordinary plasma treatment on the film surface, but in actual processes, such as Figure 2 As shown in the figure, the common surface plasma one-step treatment method needs to be further improved for the specific plasma damage of the dual-frequency (HF / LF) PECVD process. Multi-point Vs (surface voltage) test was performed, and the standard deviation Vs-stdev of Vs still has room for improvement. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for reducing plasma damage.

[0008] To solve the above problems, the present invention provides a method for reducing plasma damage, comprising the following process steps: After the PECVD deposition process, a two-step surface plasma treatment is performed: Step 1: Use O2 / He as the surface treatment gas and introduce a high frequency of the first power to perform surface treatment on the PECVD film; Step 2: Use O2 / He as the surface treatment gas and introduce a second power radio frequency to perform surface treatment on the PECVD film; The second power is lower than the first power.

[0009] Furthermore, in the first and second steps, O2 / He is used as the surface treatment gas, and the gas flow rate is set according to the gas flow rate of the PECVD deposition process.

[0010] Furthermore, the gas flow rates, wherein the O2 flow rate is 500-4000 sccm, and the He flow rate is 500-5000 sccm; appropriately increasing the He flow rate by 10-50%, can improve plasma damage to a certain extent.

[0011] Furthermore, in the first step, the first power introduced is 100-250W.

[0012] Furthermore, in the first step, the frequency of the high frequency is 13.65 MHz.

[0013] Furthermore, in the first step, the surface treatment time is 3 to 30 seconds.

[0014] Furthermore, in the second step, the second power introduced is 10-100W.

[0015] Furthermore, in the second step, the surface treatment time is 3 to 30 seconds.

[0016] Furthermore, before the two-step surface plasma treatment process, a process stabilization step and a deposition process are also included; after the two-step surface plasma treatment process, a process gas extraction step is also included.

[0017] The method for reducing plasma damage of the present invention is to introduce a two-step dual-frequency (low power + lower power) radio frequency combined with O2 / He as a surface treatment gas after the deposition process is completed; the first step of low-power plasma surface treatment will quickly recombine with excess electrons or positive ions remaining on the surface of the silicon wafer, and the second step of lower-power plasma surface treatment will further recombine with excess electrons or positive ions remaining on the surface of the silicon wafer, thereby reducing plasma damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram showing that in the deposition process, in the first RF cycle, the process chamber is forward biased to attract electrons from the plasma, while in the second RF cycle, the chamber is negatively biased to attract positive ions from the plasma.

[0019] Figure 2 This is a schematic diagram of the treatment results of a common surface plasma one-step treatment method. A multi-point Vs (surface voltage) test was performed to obtain the standard deviation of Vs, Vs-stdev.

[0020] Figure 3 It is a schematic diagram of the radio frequency power curve in the two-step processing process of the present invention.

[0021] Figure 4 It is a process flow chart of the method of the present invention. DETAILED DESCRIPTION

[0022] The following is a specific implementation of the present invention in conjunction with the accompanying drawings, and the technical solutions in the present invention are clearly and completely described, but the present invention is not limited to the following implementations. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. According to the following description and claims, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, which are only used to conveniently and clearly assist in explaining the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] The present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments proposed herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the accompanying drawings, for clarity, the size and relative size of the layers and zones may be exaggerated, and the same reference numerals represent the same elements from beginning to end. In the description of the present application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] The present invention uses the SPV (surface photovoltage) method to test the surface of the plasma film to be evaluated to perform multi-point Vs (surface voltage) testing, and the standard deviation Vs-stdev of Vs directly represents the magnitude of plasma damage to the film. The present invention proposes a new method for reducing plasma damage, which can further improve and reduce plasma damage compared to ordinary one-step surface plasma treatment without changing the process chamber design and deposition process parameters.

[0025] After the PECVD deposition process is completed, the present invention uses a two-step surface treatment process: In the first step, O2 / He is used as the surface treatment gas, and low-power radio frequency HF is introduced to treat the surface of the PECVD film; In the second step, O2 / He is used as the surface treatment gas, and a lower power radio frequency LF is introduced to treat the surface of the PECVD film. Finally, the surface voltage standard deviation (Vs-stdev) that characterizes the plasma damage trend decreases significantly, indicating that the present invention can effectively reduce plasma damage.

[0026] Specifically, taking the dual-frequency (HF+LF) PE-TEOS process as an example, after the PECVD process deposition is completed, O2 / He is used as the reaction gas, and radio frequency is introduced to perform surface treatment on the PECVD film.

[0027] The flow rate of O2 / He gas can be set by referring to the O2 / He in the deposition step.

[0028] The introduced radio frequency is mainly HF (high frequency), and the power will also affect the distribution of surface potential. The radio frequency power of the first step of surface treatment is 100-250W, while the radio frequency power of the second step of surface treatment is lower, at 10-100W.

[0029] In the two-step surface treatment process, the surface O2 / He treatment time of each step is about 3 to 30 seconds. Figure 3 As shown in the figure, after experiments, increasing the processing time will subsequently reach saturation, and its contribution to improving plasma damage is limited.

[0030] After the two-step surface treatment process, the remaining gas in the process chamber is evacuated from the process chamber.

[0031] The mechanism of the method of the present invention for improving plasma damage is: The present invention adds two steps of O2 / He surface treatment under HF (high frequency) plasma after PECVD deposition. The first step of low-power high-frequency plasma surface treatment of 100 to 250W will quickly recombine with the excess electrons or positive ions left on the surface of the silicon wafer, and the second step of lower-power plasma surface treatment of 10 to 100W will further recombine with the excess electrons or positive ions left on the surface of the silicon wafer, thereby reducing plasma damage. Experiments have shown that the two-step surface treatment process of the present invention can effectively reduce plasma damage.

[0032] In the two-step surface treatment process of the present invention, the radio frequency introduced is mainly HF (13.65MHz high frequency), and the power will affect the distribution of the surface voltage that characterizes plasma damage. The first step uses a lower power than the power used in the existing surface treatment process, and the second step uses an even lower power, and the plasma damage will be improved to a certain extent.

[0033] In the processing process, the flow rate of O2 / He gas can be specifically set by referring to the O2 (500-4000sccm) / He (500-5000sccm) in the deposition step. Experiments have shown that an appropriate increase in He (increase of 10%-50%) will improve the distribution of Vs-stdev, that is, the surface potential, and plasma damage will be improved to a certain extent.

[0034] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for reducing plasma damage, characterized in that: The process steps include: After the PECVD deposition process, a two-step surface plasma treatment is performed: Step 1: Use O2 / He as the surface treatment gas and introduce a high frequency of the first power to perform surface treatment on the PECVD film; Step 2: Use O2 / He as the surface treatment gas and introduce a second power high frequency to perform surface treatment on the PECVD film; The second power is lower than the first power.

2. The method for reducing plasma damage according to claim 1, characterized in that: In the first and second steps, O2 / He is used as the surface treatment gas, and its gas flow rate is set according to the gas flow rate of the PECVD deposition process.

3. The method for reducing plasma damage according to claim 2, wherein: The gas flow rates are as follows: O2 flow rate is 500-4000sccm, and He flow rate is 500-5000sccm; by appropriately increasing the He flow rate by 10-50%, the plasma damage can be improved to a certain extent.

4. The method for reducing plasma damage according to claim 1, wherein: In the first step, the first power introduced is 100-250W.

5. The method for reducing plasma damage according to claim 1, wherein: In the first step, the frequency of the high frequency is 13.65 MHz.

6. The method for reducing plasma damage according to claim 1, wherein: In the first step, the surface treatment time is 3 to 30 seconds.

7. The method for reducing plasma damage according to claim 1, characterized in that: In the second step, the second power introduced is 10-100W.

8. The method for reducing plasma damage according to claim 1, wherein: In the second step, the surface treatment time is 3 to 30 seconds.

9. The method for reducing plasma damage according to claim 1, characterized in that: Before the two-step surface plasma treatment process, a process stabilization step and a deposition process are also included; after the two-step surface plasma treatment process, a process gas extraction step is also included.

10. The method for reducing plasma damage according to claim 1, characterized in that: The high frequency of the first power in the first step rapidly recombines with the excess electrons or positive ions remaining on the surface of the silicon wafer, and the second step uses a plasma surface treatment of a second power lower than the first power to further recombine with the excess electrons or positive ions remaining on the surface of the silicon wafer, thereby reducing plasma damage.

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