Method for removing Hg residues on surface of wafer

Abstract

The invention relates to a method for removing Hg residues on the surface of a wafer. The method comprises the following steps that the wafer subjected to an MCV test is soaked in an SPM solution to be cleaned for the first time; and putting the wafers cleaned for the first time into an SC1 solution one by one for megasonic cleaning to obtain cleaned wafers. According to the method, megasonic cleaning is carried out on the wafers subjected to MCV testing one by one at a time, Hg residues and other impurities can be effectively removed, meanwhile, cross contamination between batches can be avoided, and the defects that in the prior art, groove type soaking adopted frequently is poor in precision, impurities are prone to being left on the surfaces of the cleaned wafers, cleaning is not thorough, and cross contamination is prone to being caused are overcome; the cleaning method provided by the invention realizes high-uniformity and low-pollution cleaning effects, and is suitable for an advanced process.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for removing Hg residue from the surface of a wafer. Background Technology

[0002] With the booming development of industries such as semiconductors, LEDs, and solar energy, product applications are becoming increasingly widespread. Driven by ever-expanding global demand, major semiconductor companies are continuously expanding their new factories and increasing production capacity to meet market demands. However, during wafer production, each process must be monitored to ensure stability and yield, in order to produce the products customers require. Therefore, while meeting market demand, it is essential to realistically consider the costs of testing wafers required for wafer production.

[0003] Mercury-probe Capacitance-Voltage (MCV) is a non-destructive electrical characterization technique based on Schottky barrier transient capacitance spectroscopy. It is used to quantitatively extract the net doping concentration (Nd–Na) and its longitudinal distribution in wide-bandgap or narrow-bandgap semiconductor epitaxial layers or substrates, and can indirectly assess process-induced defects, metal contamination, and carrier compensation. Its physical model is based on the Poisson equation and Debye shielding theory. By applying a DC reverse bias (V) to the mercury droplet-semiconductor junction and simultaneously recording the high-frequency (typically 1MHz) small-signal capacitance C(V), the doping concentration at different depths x is inferred using the Mott-Schottky relation. By scanning the bias voltage (up to ±200V), a depletion depth range of 0.1–5µm can be covered, achieving nanometer-scale longitudinal resolution. To suppress the effects of interface states and leakage currents, mercury-indium alloying or liquid mercury micro-jet technology is typically used, coupled with a temperature-controlled probe station (25–200°C) for variable-temperature CV to separate doping from deep-level responses. This testing method offers advantages such as non-destructive testing, speed, high sensitivity, and depth resolution.

[0004] However, this testing method inevitably causes mercury contamination on the silicon wafer surface: the MCV equipment uses a Hg probe to measure the doping concentration of the SiC epitaxial layer, resulting in Hg residue and other impurities. The residual Hg and other impurities may also introduce cross-contamination into subsequent processes, thereby affecting the processing and use of subsequent wafers.

[0005] Existing technologies mainly use SPM cleaning or a combination of SPM and two-fluid cleaning to remove residual Hg. Although this method can remove Hg from the surface, it leaves residues at test points, and the cleaning effect is not ideal, which will still affect the subsequent processing and use of the wafer.

[0006] Therefore, how to clean the residual Hg and other impurities on the surface of silicon carbide wafers after MCV testing, and achieve a clean and contamination-free surface with high purity, has become an urgent problem to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a method for removing Hg residue from the surface of wafers. The method described in this invention employs a wafer-by-wafer cleaning approach with mega-acoustic cleaning, which can effectively remove Hg residue while avoiding cross-contamination between batches.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for removing residual Hg from the surface of a wafer, the method comprising the following steps:

[0010] After MCV testing, the wafers are immersed in SPM solution for the first cleaning; the wafers after the first cleaning are then placed one by one into SC1 solution for mega-sonic cleaning to obtain the cleaned wafers.

[0011] The SPM solution and SC1 solution described in this invention are two chemical cleaning solutions used to remove different types of contaminants. The SPM solution can remove organic contaminants and some metal contaminants; the SC1 solution can remove particulate contaminants (such as SiO2 particles and dust), and slightly removes organic contaminants and some metal ions.

[0012] This invention employs mega-acoustic cleaning of wafers after MCV testing, one wafer at a time, which effectively removes Hg residue and other impurities while avoiding cross-contamination between batches. In contrast, the tank immersion method commonly used in existing technologies has relatively low precision, leaving impurities on the wafer surface after cleaning, resulting in incomplete cleaning and easy cross-contamination. The cleaning method of this invention achieves a highly uniform and low-contamination cleaning effect, making it suitable for advanced processes.

[0013] This invention first uses SPM solution to remove Hg beads from the surface after testing, and then uses SC1 solution (on a single-unit machine) while simultaneously activating megasonic cleaning to effectively remove impurities at the test points. The megasonic generator outputs megasonic waves, which are transmitted downwards and come into contact with the cleaning solution through the quartz lower housing. The megasonic wave energy is transferred to the wafer surface through the cleaning solution, thereby effectively removing impurities at the test points. In contrast, tank cleaning requires a large amount of cleaning solution, with all wafers sharing a single tank of cleaning solution, which easily leads to cross-contamination. Furthermore, the megasonic wave distribution is uneven, resulting in low efficiency and difficulty in meeting cleaning cleanliness requirements.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] The mega-sound cleaning process involves placing the wafer in a single-wafer cleaning station.

[0016] Preferably, the rotation speed of the single-piece cleaning table during mega-sound cleaning is 250rpm-350rpm, for example, it can be 250rpm, 280rpm, 300rpm, 220rpm or 350rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] Preferably, the flow rate of the single-piece cleaning station during mega-sound cleaning is 0.8L / min-1.2L / min, for example, it can be 0.8L / min, 0.9L / min, 1.0L / min, 1.1L / min or 1.2L / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the first cleaning includes soaking in SPM1 solution and SPM2 solution in sequence.

[0019] Preferably, the SPM1 solution and the SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water.

[0020] After removing Hg beads from the surface using SPM solution, the reaction relationship between mercury and concentrated sulfuric acid is: Hg + 2H2SO4(conc.) = HgSO4 + SO2 + 2H2O.

[0021] Preferably, the volume ratio of sulfuric acid, hydrogen peroxide and water is (4-5):1:(1-2), for example, it can be 4:1:1, 4.5:1:1, 5:1:1, 4:1:2, 4.5:1:2 or 5:1:2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] Preferably, the mass concentration of the sulfuric acid is 92%-98%, for example, it can be 92%, 93%, 94%, 95%, 96%, 97% or 98%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the soaking time in SPM1 solution and SPM2 solution is independently 5 min to 15 min, for example, 5 min, 8 min, 10 min, 12 min, 14 min or 15 min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the temperature during the first cleaning is 115℃-135℃, for example, it can be 115℃, 118℃, 120℃, 122℃, 125℃, 128℃, 130℃, 132℃ or 135℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] Preferably, the wafer is dried after the first cleaning is completed.

[0026] Preferably, after the first cleaning and before the mega-sound cleaning, the process also includes immersing the wafer in water and spraying it with pure water.

[0027] Preferably, the temperature of the immersion water is 40℃-60℃, for example, it can be 40℃, 42℃, 45℃, 48℃, 50℃, 52℃, 55℃, 58℃ or 60℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the soaking time in the water is 30s-60s, for example, it can be 30s, 35s, 40s, 45s, 50s, 55s or 60s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the SC1 solution comprises ammonia, hydrogen peroxide, and water.

[0030] Preferably, the volume ratio of ammonia, hydrogen peroxide and water in the SC1 solution is 1:(1-2):(4-7), for example, it can be 1:1:4, 1:1:5, 1:1:6, 1:1:7, 1:2:4, 1:2:5, 1:2:6 or 1:2:7, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the mass concentration of the ammonia water is 20%-40%, for example, it can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38% or 40%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the mass concentration of hydrogen peroxide is 20%-40%, for example, it can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38% or 40%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the power of the megaphonic cleaning is 10W-25W, for example, it can be 10W, 12W, 15W, 18W, 20W, 22W or 25W, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] This invention further controls the power of mega-acoustic cleaning in the single-piece cleaning station to 10W-25W. If the power of mega-acoustic cleaning is too low, it can effectively impact the wafer surface and peel off smaller, more adherent Hg beads; if the power of mega-acoustic cleaning is too high, it may cause substrate damage and increase particle redeposition.

[0035] Preferably, the temperature during megaphonic cleaning is 45℃-65℃, for example, it can be 45℃, 48℃, 50℃, 52℃, 55℃, 58℃, 60℃, 62℃ or 65℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] Preferably, the megaphonic cleaning time is 70s-120s, for example, it can be 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s or 120s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] This invention further controls the megasonic cleaning time to 70s-120s. If the megasonic cleaning time is too short, it will be difficult to effectively peel off the Hg beads with strong adhesion.

[0038] As a preferred embodiment of the method described in this invention, the method includes the following steps:

[0039] (1) After the MCV test, the wafer is immersed in SPM1 solution at 115℃-135℃ for 5min-15min, then immersed in SPM2 solution for 5min-15min, then immersed in water at 40℃-60℃ for 30s-60s, then sprayed with pure water and dried.

[0040] The SPM1 solution and SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water in a volume ratio of (4-5):1:(1-2);

[0041] (2) Place the dried wafers from step (1) in a single-wafer cleaning station and immerse them one by one in the SC1 solution. Perform mega-sonic cleaning for 70s-120s at a power of 10W-25W to obtain the cleaned wafers.

[0042] The SC1 solution comprises ammonia, hydrogen peroxide, and water in a volume ratio of 1:(1-2):(4-7).

[0043] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0044] Compared with the prior art, the present invention has at least the following beneficial effects:

[0045] This invention employs mega-acoustic cleaning of wafers after MCV testing, one wafer at a time. This effectively removes Hg residue and other impurities while avoiding cross-contamination between batches. In contrast, the tank immersion method commonly used in existing technologies has relatively low precision, leaving impurities on the wafer surface after cleaning, resulting in incomplete cleaning and cross-contamination. The cleaning method of this invention achieves a highly uniform and low-contamination cleaning effect, making it suitable for advanced processes. Attached Figure Description

[0046] Figure 1 This is a Candela 8520 Scan image of the cleaned wafer from Embodiment 1 of the present invention;

[0047] Figure 2 This is a Candela 8520 Scan image of the cleaned wafer from Comparative Example 1 of this invention. Detailed Implementation

[0048] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0049] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0050] Example 1

[0051] This embodiment provides a method for removing residual Hg from the surface of a wafer, the method comprising the following steps:

[0052] (1) After the MCV test, the wafer was immersed in SPM1 solution at 125°C for 10 min, then immersed in SPM2 solution for 10 min, then immersed in water at 50°C for 50 s, then sprayed with pure water and dried.

[0053] The SPM1 solution and SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water in a volume ratio of 5:1:1, wherein the sulfuric acid has a mass concentration of 98% and the hydrogen peroxide has a mass concentration of 30%.

[0054] (2) Place the dried wafers from step (1) into a single-wafer cleaning station, and immerse each wafer in SC1 solution. Perform mega-sonic cleaning for 90 seconds at a power of 20W to obtain the cleaned wafers.

[0055] The SC1 solution comprises ammonia, hydrogen peroxide, and water in a volume ratio of 1:1:5, with the ammonia having a mass concentration of 30% and the hydrogen peroxide having a mass concentration of 30%.

[0056] Example 2

[0057] This embodiment provides a method for removing residual Hg from the surface of a wafer, the method comprising the following steps:

[0058] (1) After the MCV test, the wafer was immersed in SPM1 solution at 115℃ for 15 min, then immersed in SPM2 solution for 15 min, then immersed in water at 40℃ for 60 s, then sprayed with pure water and dried.

[0059] The SPM1 solution and SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water in a volume ratio of 5:1:2, wherein the sulfuric acid has a mass concentration of 96% and the hydrogen peroxide has a mass concentration of 35%.

[0060] (2) Place the dried wafers from step (1) into a single-wafer cleaning station, and immerse each wafer in SC1 solution. Perform mega-sonic cleaning for 120 seconds at a power of 15W to obtain the cleaned wafers.

[0061] The SC1 solution comprises ammonia, hydrogen peroxide, and water in a volume ratio of 1:1:4, with the ammonia having a mass concentration of 35% and the hydrogen peroxide having a mass concentration of 35%.

[0062] Example 3

[0063] This embodiment provides a method for removing residual Hg from the surface of a wafer, the method comprising the following steps:

[0064] (1) After the MCV test, the wafer was immersed in SPM1 solution at 135℃ for 5 minutes, then immersed in SPM2 solution for 5 minutes, then immersed in water at 60℃ for 30 seconds, and then sprayed with pure water and dried.

[0065] The SPM1 solution and SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water in a volume ratio of 5:1:2, wherein the sulfuric acid has a mass concentration of 98% and the hydrogen peroxide has a mass concentration of 20%.

[0066] (2) Place the dried wafers from step (1) into a single-wafer cleaning station and immerse them one by one in the SC1 solution. Perform mega-sonic cleaning for 70 seconds at a power of 25W to obtain the cleaned wafers.

[0067] The SC1 solution comprises ammonia, hydrogen peroxide, and water in a volume ratio of 1:2:7, with the ammonia having a mass concentration of 20% and the hydrogen peroxide having a mass concentration of 20%.

[0068] Example 4

[0069] This embodiment provides a method for removing Hg residue from the surface of a wafer. The only difference from Embodiment 1 is that the power of the megaphonic cleaning in step (2) is 5W.

[0070] Example 5

[0071] This embodiment provides a method for removing Hg residue from the surface of a wafer. The only difference from Embodiment 1 is that the power of the megaphonic cleaning in step (2) is 30W.

[0072] Example 6

[0073] This embodiment provides a method for removing Hg residue from the surface of a wafer. The only difference from Embodiment 1 is that the time for mega-sonic cleaning in step (2) is 50 seconds.

[0074] Comparative Example 1

[0075] This comparative example provides a method for removing Hg residue from the surface of a wafer. The only difference from Example 1 is that it uses an SC1 tank cleaning method. The method includes the following steps:

[0076] The wafer from step (1) of Example 1 was immersed in SC1 solution at 50°C for 10 minutes, then sprayed with pure water and dried. SC1 cleaning was performed under the condition that the tank power was 800W to obtain the cleaned wafer.

[0077] Test method: The cleaned wafers obtained in the examples and comparative examples were inspected by Candela 8520 Scan. The test results are shown in Table 1 below. OK means that there is no obvious cross-shaped map in the Candela scan, and NG means that there is a cross-shaped map in the Candela scan.

[0078] Example 1: The surface of the cleaned wafer was inspected using a Candela 8520 Scan, and the inspection results are as follows. Figure 1 As shown, from Figure 1 As can be seen from the data, the candela scan does not show a clear fork-shaped map.

[0079] Comparative Example 1: The cleaned wafer surface was inspected using a Candela 8520 Scan, and the inspection results are as follows. Figure 2 As shown, from Figure 2 As can be seen from this, the Candela scan has a distinct fork-shaped map.

[0080] Table 1

[0081]

[0082] The test results show that:

[0083] (1) As can be seen from Examples 1-3, the present invention uses mega-sound cleaning to clean the wafers after MCV testing one wafer at a time, which can effectively remove Hg residue and other impurities while avoiding cross-contamination between batches. In contrast, the tank immersion method commonly used in the prior art has weak precision, and impurities are easily left on the surface of the wafers after cleaning, resulting in incomplete cleaning and easy cross-contamination. The cleaning method of the present invention achieves a cleaning effect with high uniformity and low contamination, and is suitable for advanced processes.

[0084] (2) By comparing Example 1 with Example 4-5, it can be seen that the present invention further controls the power of mega-sonic cleaning in the single-piece cleaning station to 10W-25W. If the power of mega-sonic cleaning is too small, it can effectively impact the wafer surface and peel off smaller, more adherent Hg beads; if the power of mega-sonic cleaning is too large, it may cause substrate damage and increase particle redeposition.

[0085] (3) By comparing Example 1 and Example 6, it can be seen that the present invention further controls the time of megasonic cleaning to 70s-120s. If the time of megasonic cleaning is too short, it will be difficult to effectively peel off the Hg beads with strong adhesion.

[0086] (4) As can be seen from Example 1 and Comparative Example 1, the present invention uses mega-sound cleaning of wafers one by one (one wafer at a time) to avoid cross-contamination between batches. In contrast, the tank immersion method commonly used in the prior art has low precision, and impurities are easily left on the surface of the wafers after cleaning, resulting in incomplete cleaning and easy cross-contamination. The cleaning method of the present invention achieves a cleaning effect with high uniformity and low contamination, and is suitable for advanced processes.

[0087] In summary, the present invention employs mega-acoustic cleaning of wafers after MCV testing on a wafer-by-wasp (one wafer at a time), which can effectively remove Hg residue and other impurities while avoiding cross-contamination between batches. In contrast, the tank immersion method commonly used in the prior art has low precision, and impurities are easily left on the wafer surface after cleaning, resulting in incomplete cleaning and easy cross-contamination. The cleaning method of the present invention achieves a highly uniform and low-contamination cleaning effect, and is suitable for advanced processes.

[0088] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for removing residual Hg from the surface of a wafer, characterized in that, The method includes the following steps: After MCV testing, the wafers are immersed in SPM solution for the first cleaning; the wafers after the first cleaning are then placed one by one into SC1 solution for mega-sonic cleaning to obtain the cleaned wafers.

2. The method according to claim 1, characterized in that, The speed of the mega-sound cleaning is 250rpm-350rpm; Preferably, the flow rate of the megasonic cleaning is 0.8 L / min to 1.2 L / min.

3. The method according to claim 1 or 2, characterized in that, The SC1 solution comprises ammonia, hydrogen peroxide, and water; Preferably, the first cleaning includes soaking in SPM1 solution and SPM2 solution in sequence; Preferably, the SPM1 solution and the SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water; Preferably, the volume ratio of sulfuric acid, hydrogen peroxide and water is (4-5):1:(1-2).

4. The method according to any one of claims 1-3, characterized in that, The volume ratio of ammonia, hydrogen peroxide and water in the SC1 solution is 1:(1-2):(4-7).

5. The method according to claim 3 or 4, characterized in that, The soaking time in SPM1 solution and SPM2 solution is independently 5 min-15 min.

6. The method according to any one of claims 1-5, characterized in that, The temperature during the first cleaning was 115℃-135℃.

7. The method according to any one of claims 1-6, characterized in that, After the first cleaning and before the mega-sound cleaning, the process also includes immersing the wafer in water and spraying it with pure water. Preferably, the soaking temperature is 40℃-60℃; Preferably, the soaking time is 30s-60s.

8. The method according to any one of claims 1-7, characterized in that, The power of the mega-sound cleaning is 10W-25W.

9. The method according to any one of claims 1-8, characterized in that, The temperature during mega-sound cleaning is 45℃-65℃; Preferably, the megaphonic cleaning time is 70s-120s.

10. The method according to any one of claims 1-9, characterized in that, The method includes the following steps: (1) After the MCV test, the wafer is immersed in SPM1 solution at 115℃-135℃ for 5min-15min, then immersed in SPM2 solution for 5min-15min, then immersed in water at 40℃-60℃ for 30s-60s, then sprayed with pure water and dried. The SPM1 solution and SPM2 solution each independently comprise sulfuric acid, hydrogen peroxide, and water in a volume ratio of (4-5):1:(1-2), wherein the sulfuric acid has a mass concentration of 92%-98%. (2) Place the dried wafers from step (1) in a single-wafer cleaning station and immerse them one by one in the SC1 solution. Perform mega-sonic cleaning for 70s-120s at a power of 10W-25W to obtain the cleaned wafers. The SC1 solution comprises ammonia, hydrogen peroxide, and water in a volume ratio of 1:(1-2):(4-7), wherein the mass concentration of the ammonia is 20%-40% and the mass concentration of the hydrogen peroxide is 20%-40%.

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