Monitoring and cleaning method for improving utilization rate of target material in magnetron sputtering coating
By monitoring, cleaning and removing tumors during magnetron sputtering coating, the problem of degradation of surface uniformity of the target material and nodules is solved, extending the service life of the target material and improving the coating quality.
Patent Information
- Application Number
- CN202411669855.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-21
- Publication Date
- 2025-02-25
AI Technical Summary
During magnetron sputtering coating, the uniformity of the target surface and nodding problems lead to low target utilization, which increases costs and affects the coating quality.
By monitoring the square resistance value of the film, if it exceeds 480Ω/□, the target material will be cleaned and removed, including pre-cleaning, water washing, polishing and drying steps to extend the service life of the target material.
It extends the utilization rate of the target material, improves the stability of the target material during long-term use, reduces the difficulty of control, and reduces the dependence on new target material.
Smart Images
Figure CN119506807A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of sputtering target materials in vacuum sputtering coating technology, and specifically, it shows a monitoring and cleaning method for improving the utilization rate of target materials in magnetron sputtering coating. Background Art
[0002] Sputtering coating in PVD technology refers to the process of bombarding the surface of the target material with particles (such as argon ions) that have acquired functions under vacuum conditions, so that the atoms on the target surface gain enough energy to escape. Filling argon (Ar) gas under vacuum conditions and glow discharging the argon gas under high voltage can ionize argon (Ar) atoms into argon ions (Ar+). At this time, introducing a magnetic field on the surface of the cathode target can use the electromagnetic field to constrain electrons, extend the electron path, increase the probability of ionization of argon atoms, and achieve stable discharge under low pressure. The coating method based on this principle is called magnetron sputtering coating. Under the action of the magnetic field force, argon ions are accelerated to bombard the cathode target made of plating material, and the target material will be sputtered out and deposited on the surface of the workpiece. PVD technology has achieved a reduction in preparation temperature, process time, manufacturing cost, and an increase in yield.
[0003] At the same time, some reaction gases, such as phosphine, can be introduced into the magnetron sputtering coating process. These reaction gases are added to the argon plasma and are excited, ionized or ionized together with the Ar atoms to form active groups. These activated groups reach the substrate surface together with the target atoms to form the corresponding doped film and realize in-situ doping. Therefore, in the preparation of solar cell PN junction, the coating method based on PVD technology can be used to prepare high-quality n-type polysilicon passivation film, that is, n+poly layer.
[0004] Figure 1The figure shows the principle diagram of magnetron sputtering. The main components in the vacuum chamber 1 are the magnetron sputtering target 2 and the silicon wafer substrate 3. The silicon wafer substrate 3 and the target 2 are facing each other, the silicon wafer substrate 3 is grounded, and the target 2 is connected to a negative voltage, that is, the silicon wafer substrate 3 is at a positive potential relative to the target 2, so the direction of the electric field is from the silicon wafer substrate 3 to the target 2. The permanent magnet 4 used to generate the magnetic field is set on the back of the target 2. The magnetic field lines point from the N pole of the permanent magnet 4 to the S pole, and form a closed space with the cathode target surface. The target 2 and the permanent magnet 4 are cooled by cooling water 5. After the vacuum chamber 1 is evacuated for leak detection, argon gas is filled into the vacuum chamber 1 to 0.1-1Pa, and then a voltage is applied to the positive and negative poles to make the gas glow discharge and form plasma. The argon ions in the argon plasma 6 move toward the cathode target under the action of the electric field force, and are accelerated under the action of the magnetic field Lorentz force when passing through the cathode dark area, bombarding the target, and sputtering out target atoms and secondary electrons. From the law of conservation of momentum, we know that: m1v1+m2v2+…=m1v1ˊ+m2v2ˊ+…, where m represents the mass of the particle, and v is the velocity of each particle at the moment. When high-speed particles (v1) bombard the stationary (v2=0) atoms on the surface of the target, the target atoms will obtain a very high speed (v2ˊ>>0).
[0005] As sputtering continues, the target surface is constantly eroded, and the surface uniformity gradually decreases until the film quality drops below the process standard. At this time, the target needs to be replaced. However, in fact, there is still a lot of surplus target at this time. In order to enhance the utilization rate of the target, the existing technology is to design the target into a cylindrical shape and rotate it at a constant speed during sputtering, so that different positions of the target can be bombarded by functional particles, thereby extending the service life of the target. Figure 2 Schematic diagram shown.
[0006] The target material needs to be energized to form an electric field with the silicon wafer substrate, so the target material needs a certain conductivity, and the conductivity will affect the sputtering rate of the silicon target material during the sputtering process. Specifically:
[0007] a) Generally speaking, silicon targets with low resistivity are more easily sputtered, and the sputtering rate is relatively high, because under the action of the electric field, electrons can be conducted more quickly in the target to form plasma, making it easier for atoms on the surface of the target to be sputtered out. On the contrary, silicon targets with high resistivity have a relatively slow sputtering rate, which may affect the efficiency of coating and production time.
[0008] b) When current passes through the silicon target, Joule heat will be generated due to its certain resistance. The silicon target with higher resistivity will generate relatively less Joule heat under the same current because the current conduction is difficult and the energy loss is small. The Joule heating effect is relatively obvious for the silicon target with lower resistivity.
[0009] c) Changes in resistivity will also affect the stress distribution inside the silicon target.
[0010] In the process of sputtering coating, target nodule is a common but difficult problem.
[0011] (1) First, a long sputtering process will cause local overheating of the target surface. When the temperature of certain areas of the target is too high, it is easy to cause material aggregation and crystallization, thus gradually forming nodules.
[0012] (2) There are impurity particles in the sputtering environment, which may adhere to the surface of the target. Over time, these impurities continue to accumulate and eventually form nodules.
[0013] In the prior art, the treatment methods for target nodules are either to replace new target materials or to use a rotating target material for sputtering. Replacing new target materials will increase costs, and some target materials actually have surplus for use, so direct recycling is a waste; while using a rotating target material for sputtering, the target material will still produce mechanical fatigue during continuous use, and the service life of the target material will not be greatly improved.
[0014] Based on the above analysis, the inventors of the present application have designed a monitoring and cleaning method that can improve the utilization rate of the target material so as to recycle the target material. Summary of the invention
[0015] The purpose of the present invention is to provide a monitoring and cleaning method for improving the utilization rate of target materials in magnetron sputtering coating, reducing costs, avoiding waste of target materials, and meeting scientific research and production needs.
[0016] The technical solution is as follows:
[0017] A monitoring and cleaning method for improving the utilization rate of target materials in magnetron sputtering coating is characterized in that, in the process of manufacturing solar cells, sputtering coating is performed on the target based on PVD technology, and then the sheet resistance of the thin film is monitored. If the sheet resistance of the manufactured thin film exceeds 480Ω / □, the target material is taken out of the cavity and the target material is cleaned in the following steps:
[0018] Step 1: Pre-cleaning: Immerse the loaded target in a pre-cleaning tank with DIW, add appropriate amounts of KOH solution and H2O2 solution according to a certain ratio, and clean at 60°C for 120s;
[0019] Step 2: Water washing: clean the target with DIW at room temperature for 100 seconds;
[0020] Step 3: Polishing: Add DIW into the alkaline polishing tank, and add appropriate amount of KOH solution and polishing agent to polish the surface of the target material. The polishing temperature is 65°C and the polishing time is 300s.
[0021] Step 4: Water washing: clean the target with DIW at room temperature for 100 seconds.
[0022] Step 5: Drying: Place the target material in a drying tank and introduce nitrogen gas at 90°C to dry the target material;
[0023] After the target material is loaded into the cavity for secondary use, the square resistance of the produced film continues to be monitored. If the square resistance of the produced film exceeds 480Ω / □ again, the target material is taken out of the cavity again and the target material is cleaned again according to steps 1 to 5 as above. In the polishing process of step 3, the polishing time is changed to 450s.
[0024] Preferably, in step 1, during the cleaning process, the target material is rotated at a uniform speed of 3 to 5 revolutions per second to achieve uniform cleaning and effectively remove dirt on the surface of the target material.
[0025] Preferably, in step 3, during the polishing process, the target material rotates at a constant speed of 3 to 5 revolutions per second, thereby achieving uniform polishing, reducing the risk of sputtering and spraying, and improving safety, and effectively removing oxides during the target material polishing process.
[0026] Preferably, the water washing process of step 2 is consistent with that of step 4, and the DIW washing is an overflow immersion washing method. In order to ensure the cleaning effect, the excess water in the cleaning tank is directly discharged, and the pollutants and impurities are also taken out to avoid these pollutants and impurities from contaminating the target material again, which can ensure the stability and consistency of the cleaning effect and improve the quality and reliability of the target cleaning.
[0027] Preferably, in step 1, KOH accounts for 0.4% and H2O2 solution accounts for 0.6%. A small amount of KOH and H2O2 is used to wash away oil impurities on the surface of the target.
[0028] Preferably, in step 3, KOH accounts for 1.8-2.0%, and polishing agent accounts for 0.5-1.0%. A small amount of KOH and polishing agent is used to remove the oxide layer and pollutants on the surface of the target material to obtain a smooth surface.
[0029] Compared with the prior art, the beneficial effect of the present invention is that by monitoring the square resistance of the prepared thin film, the target material is cleaned and detumored at an appropriate time, so that the surface of the target material becomes smooth again, thereby extending the utilization rate of the target material, improving the stability of the target material during long-term use, and reducing the control difficulty. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 This is a schematic diagram of the current principle of magnetron sputtering;
[0031] Figure 2 It is a simplified schematic diagram of the prior art using a rotating target;
[0032] Figure 3 The following is a monitoring data diagram of the sheet resistance of a thin film prepared by using the same silicon target material under the prior art for 1000 hours with other parameters unchanged;
[0033] Figure 4 This is a graph showing the monitoring data of the sheet resistance of a thin film prepared by using the target material tumor removal monitoring and cleaning method according to an embodiment of the present invention for 1100 hours with the same target material and other parameters unchanged;
[0034] Relevant marks in the accompanying drawings: 1-vacuum chamber, 2-target material, 3-silicon wafer substrate, 4-permanent magnet, 5-cooling water, 6-argon plasma, 7-cathode, 8-anode. DETAILED DESCRIPTION
[0035] Example:
[0036] Take the silicon target material used in the preparation of the n+poly layer of solar cells as an example: the silicon target material can be cleaned with an alkaline solution. - +H2O→SiO3 2- +H2, silicon is corroded in alkaline solution, and the lattice direction of the nodule area is inconsistent, the specific surface area is large, and the reaction rate is faster than that of the other areas. Therefore, after cleaning with alkaline solution, the target material is flat again.
[0037] like Figure 3 As shown in Figure 1, the sheet resistance monitoring data of the thin film prepared by the same silicon target material under continuous use for 1000 hours with other parameters unchanged. It can be clearly seen that when the current, gas flux and other conditions are not changed, the sheet resistance of the prepared film gradually increases, which means that the doping performance gradually deteriorates, the resistance increases, and the film performance deteriorates.
[0038] Use existing equipment such as a scanning four-probe square resistance tester (FPP230A) to monitor the battery square resistance. After the target has been used for 700 hours, when the battery square resistance exceeds 480Ω / □, remove the target from the chamber, replace it with a new target, and clean and remove the old target.
[0039] Take out the old target from the chamber and clean it as follows:
[0040] Step 1, pre-cleaning: mainly to remove residual organic matter and ensure the cleanliness of the target surface, immerse the loaded target in a pre-cleaning tank with DIW (deionized water), add appropriate amount of KOH solution and H2O2 solution according to a certain ratio (KOH accounts for 0.4%, H2O2 solution accounts for 0.6%), and clean at 60°C for 120s. During the cleaning process, the target rotates at a constant speed of 3 to 5 rpm;
[0041] Step 2, water washing: the target material is cleaned with DIW at room temperature for 100s. The DIW cleaning is an overflow immersion cleaning method.
[0042] Step 3, polishing: add DIW to the alkaline polishing tank, and add an appropriate amount of KOH solution and polishing agent (KOH accounts for 1.8-2.0%, and the polishing agent accounts for 0.5-1.0%), and polish the surface of the target material. The polishing temperature is 65°C and the polishing time is 300s. During the polishing process, the target material rotates at a constant speed of 3-5 rpm;
[0043] Step 4, water washing: the target material is cleaned with DIW at room temperature for 100s. The DIW cleaning is an overflow immersion cleaning method.
[0044] Step 5: Drying: Place the target in a drying tank and introduce 90°C nitrogen to dry the target. To prevent the target surface from being oxidized and contaminated by impurities during secondary use, hot nitrogen is used for drying.
[0045] After the target material is loaded into the cavity for secondary use, the square resistance of the produced film continues to be monitored. If the square resistance of the produced film exceeds 480Ω / □ again, the target material is taken out of the cavity again and the target material is cleaned again according to steps 1 to 5 as above. In the polishing process of step 3, the polishing time is changed to 450s.
[0046] like Figure 4 As shown, it is a graph of the monitoring data of the sheet resistance of a thin film prepared by using the target material tumor removal monitoring and cleaning method of this embodiment for 1100 hours with the same target material and other parameters unchanged.
[0047] It can be seen that when the battery square resistance exceeds 480Ω / □ after 800 hours of use, cleaning and nodule removal are carried out at this time; after the cleaning is completed, the target material continues to be used for 975 hours and it is monitored that the battery square resistance exceeds 480Ω / □ again. At this time, a second cleaning and nodule removal is carried out to extend the service life of the target material.
[0048] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.
Claims
1. A monitoring and cleaning method for improving the utilization rate of target materials in magnetron sputtering coating, characterized in that: In the process of manufacturing solar cells, sputtering coating is performed based on PVD technology, and then the sheet resistance of the film is monitored. If the sheet resistance of the film exceeds 480Ω / □, the target is removed from the chamber and cleaned as follows: Step 1: Pre-cleaning: Immerse the loaded target in a pre-cleaning tank with DIW, add appropriate amounts of KOH solution and H2O2 solution according to a certain ratio, and clean at 60°C for 120s; Step 2: Water washing: clean the target with DIW at room temperature for 100 seconds; Step 3: Polishing: Add DIW into the alkaline polishing tank, and add appropriate amount of KOH solution and polishing agent to polish the surface of the target material. The polishing temperature is 65°C and the polishing time is 300s. Step 4: Water washing: clean the target with DIW at room temperature for 100 seconds. Step 5: Drying: Place the target in a drying tank and introduce 90°C nitrogen to dry the target; After the target material is loaded into the cavity for secondary use, the square resistance of the produced film continues to be monitored. If the square resistance of the produced film exceeds 480Ω / □ again, the target material is taken out of the cavity again and the target material is cleaned again according to steps 1 to 5 as above. In the polishing process of step 3, the polishing time is changed to 450s.
2. The monitoring and cleaning method for improving target material utilization in magnetron sputtering coating according to claim 1, characterized in that: In the step 1: during the cleaning process, the target material rotates at a constant speed of 3 to 5 revolutions per second.
3. The monitoring and cleaning method for improving target material utilization in magnetron sputtering coating according to claim 1, characterized in that: In the step 3: during the polishing process, the target material rotates at a constant speed of 3 to 5 revolutions per second.
4. The monitoring and cleaning method for improving target material utilization in magnetron sputtering coating according to claim 1, characterized in that: The water washing process of step 2 is consistent with that of step 4, and the DIW cleaning is performed by overflow immersion cleaning.
5. The monitoring and cleaning method for improving target material utilization in magnetron sputtering coating according to claim 1, characterized in that: In the step 1, the KOH solution accounts for 0.4% and the H2O2 solution accounts for 0.6%.
6. The monitoring and cleaning method for improving target material utilization in magnetron sputtering coating according to claim 1, characterized in that: In the step 3, KOH accounts for 1.8-2.0%, and the polishing agent accounts for 0.5-1.0%.