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Silicon Part Reduce The Possibility Of Dirty Stains

Wafer cleaning process is the wire saw machine cutting the finished silicon from the glass from the down, remove the tape, the wafer clean and sort out the level. Cleaning equipment is mainly pre-cleaning machine (degumming machine) and washing machine. The main cleaning process of the pre-washing machine is: feeding - spraying - spraying - ultrasonic cleaning - degumming - water rinse - cutting. The main cleaning process of the washing machine is: feeding - pure water rinse - pure water rinse - alkali washing - alkaline washing - pure water rinse - pure water rinse - pre-dehydration (slow pull) - drying - cutting.

Usually the silicon is divided into A and so on (first grade), B and so on (two) and unqualified pieces, dirty stains belong to B and so on, will reduce the wafer A grade rate. Common stains are mainly divided into three categories: mortar, silica powder residue caused by dirty flakes, oil and watermarks, and dirty stains produced by a variety of factors.

2. Silicon cleaning principle

Cleaning agent is generally two-component products, A agent mainly potassium, corrosion inhibitor, builder composition, B agent is mainly composed of surfactant polymerization. General customers according to the cleaning process directly to the cleaning agent added to pure water, the temperature is usually set between 45-65 ℃, cleaning time of not less than 2 minutes, usually 3-4 minutes. When adding cleaning agent, according to the proportion of water, when encountered grinding polished Silicon Part Silicon Part and recovery of suspended silicon wafer should increase the amount of cleaning agent to ensure the effect of wafer cleaning.

3. Precautions during wafer cleaning

Wafer in the cleaning process, the silicon surface of the cleanliness of a great impact on the surface of the silicon stains will affect the follow-up work.

(1) after the end of the wafer is usually not water, if not timely cleaning, the first silicon into the suspension.

(2) Once the wafer has been placed on the cleaning table, it must be processed immediately to keep the wafer wet throughout the cleaning process.

(3) Silicon Part in the degumming process to keep the surface moist, can not be naturally dry.

(4) the wafer after each cleaning cycle, to thoroughly replace the back of the three cleaning tank of water to prevent contamination of the back of the cleaning of silicon.

(5) Silicon Part in the cleaning process as much as possible to reduce the time in the air to prevent the surface of the wafer to produce flowers.

(6) cleaning staff in the entire cleaning process shall not be directly exposed to the silicon surface, you must wear rubber gloves, in order to avoid fingerprints.

4. Mortar, silicon powder residual dirty tablets cause

(1) the effect of cutting fluid. The main component of the cutting fluid is polyethylene glycol, in addition to fatty acids, fatty acid salts, surfactants, defoamers and water and other ingredients. Excellent performance of the cutting fluid has a good suspension, cooling and easy to clean. Since the mortar is made of silicon carbide and the cutting fluid, the silicon carbide particles are cut during the cutting process. As the steel wire rotates, the silicon carbide particles are wrapped on the surface of the steel wire to grind the silicon block. The cutting fluid has a good suspension to ensure that the silicon carbide particles can be uniformly dispersed on the surface of the steel wire and do not precipitate in the mortar. During the cutting process, due to the friction between the silicon carbide particles and the silicon block will produce more heat, cutting fluid cooling performance can reduce the mortar temperature, to prevent high temperature caused by silicon burns.

The cleaning performance of the cutting fluid will have a direct effect on the appearance quality of the silicon wafer. The formation of the stained flakes on the wafer surface is important. Therefore, the cutting fluid must meet the following parameters: the viscosity of the cutting fluid must ensure that the silicon carbide particles Of the suspension effect, but also to ensure that the mortar on the wire saw the appropriate adhesion to enhance the heat transfer efficiency of mortar, cutting fluid viscosity range of 45-60pas; cutting fluid acidity, not only directly affect the cleanliness of the silicon surface, but also Affect the service life of the equipment, so the acidity of the cutting fluid is not too strong, usually 5-7.

(2) the effect of fine powder content in mortar. Mortar in the silicon carbide particles less than 2μm does not have the ability to cut, in addition, during the cutting process will produce a lot of silica powder and iron powder and other powder mixed into the mortar to form a layer of film, with the cutting of the mortar in the powder Content will be higher and higher, when the amount of powder is large enough, it will adhere to the surface of the silicon, it is difficult to clean. Therefore, in the silicon block cutting to ensure that the amount of mortar and mortar to improve the quality of mortar to reduce the powder content.

(3) the effect of mortar viscosity. The viscosity of the mortar will affect the attraction of the mortar on the surface of the silicon, the greater the viscosity of the mortar, the more the amount of mortar on the surface of the wafer, the more difficult to clean. The viscosity of the mortar is mainly determined by the viscosity of the cutting fluid, but it is influenced by the temperature. It is proved that the viscosity increases with the decrease of the temperature in the range of 0-25 ℃. When the temperature is higher than 25 ℃, Viscosity changes slowly with increasing temperature. At the same time, the process of heating and cooling of the mortar is irreversible for viscosity. Wafer cutting process, the mortar temperature control in the 21 ± 2 ℃ range of the best.

(4) pre-cleaning spray properly. Pre-cleaning spray bath water pressure, water quality, nozzle flow and angle and spray time, etc., will have a great impact on the cleaning effect. Many enterprises to reduce costs, pre-cleaning process using water spray, due to the acidity of the water and mortar chemical reaction, will lead to difficult to clean the surface of the silicon, so the water before use to test its ph value Meet the requirements. The nozzle of the water pressure is generally 2.5MPa, nozzle flow and angle and spray time to be adjusted according to the actual cleaning to ensure that the surface of the silicon no dirt, and then degumming.

(5) degreasing tank temperature is too high lead. Dehydration tank temperature is too high, will make the silicon surface of the water surface does not flow from the silicon surface when the evaporation, leaving the surface of the silicon with mortar or silica powder imprint. If the use of lactic acid degumming, the requirements of the degassing tank temperature shall not exceed 80 ℃.

(6) silicon surface mortar, silicon powder residue too much. If the silicon wafer in the degumming before falling off from the tray, due to the adhesion of the mortar between the Silicon Part will be stuck together, spray the spray can not spray between the two pieces of silicon mortar, resulting in silicon Sheet surface mortar, silica powder residue too much to produce dirty tablets. The general silicon wafer drop is mainly caused by bonding: glass and silicon block adhesive surface is not wiped clean, the surface of debris, bonding is not strong; glue mixed uneven; scraping gum uneven, the thickness of the adhesive layer is inconsistent Layer; bonding silicon block when the bubble did not row out; bonding is completed, the curing time is not enough to cut. For the resulting loss of dirty film, the general can be adjusted by pre-cleaning machine technology and cleaning machine process to solve. Pre-cleaning machine process adjustment: to extend the spray and ultrasonic soak, to reduce the residual mortar after degreasing, to reduce the burden of cleaning; also without affecting the degumming effect under the premise of repeated replacement of ultrasonic cleaning tank water, Add the right amount of lactic acid or washing machine, so that after the degumming of the wafer will be relatively clean, reduce the possibility of dirty stains. Washing machine process adjustment: increase the overflow rate of pure water rinse tank, or extend the rinse time; while cleaning a certain amount of silicon, the alkali tank to add a certain amount of cleaning agent to reduce the production of dirty stains.

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