Brief analysis of diamond wire cutting technology

Key words: diamond wire, abrasive, polysilicon

According to the production process, diamond wire can be divided into electroplated diamond wire and resin diamond wire.Diamond cutting line is through a certain method, the diamond plating on the steel wire made, through the diamond cutting machine, diamond cutting line and the object can form a relative grinding...

Technology introduction:

According to the production process, diamond wire can be divided into electroplated diamond wire and resin diamond wire.Diamond cutting line is made by plating diamond on steel wire through certain methods. Through diamond cutting machine, the diamond cutting line can form relative grinding movement with the object, so as to achieve the purpose of cutting.

Diamond wire is a composite electroplating method to consolidate the high hardness, high abrasion resistance of diamond powder on the steel wire matrix, and make consolidated abrasive diamond saw wire.90% of the tensile strength in the cutting process comes from steel wire, so steel wire is essential to diamond wire.

In the process of free abrasive wire saw cutting, the grinding fluid is directly sprayed on the steel wire and silicon crystal by the nozzle, and the steel wire of wire mesh drives the free abrasive to cut the silicon crystal.Unlike free abrasive, the diamond wire binds the diamond to the wire, and the wire moves back and forth to cut the silicon crystal.

Figure: section diagram of diamond wire forming axis

Technical advantages:

The traditional mortar USES the rapid movement of steel wire to bring the liquid containing abrasive into the workpiece cutting seam, producing cutting effect.In the cutting process, silicon carbide is washed down, only continuous rolling grinding, and reduce the cutting efficiency.Silicon carbide has a hardness of 9.5, while diamond has a hardness of 10.The linear speed of steel wire cutting is basically 15m/s, and that of normal cutting mortar is basically 9-11.5m/s.If the gold and steel wire to make a breakthrough, it should be harder, but also better self-sharpening (polycrystalline diamond), more stable consolidation way, faster linear speed.

Diamond cutting line has three advantages over traditional technology:

1) diamond wire-cutting has less leakage, long life, fast cutting speed, high cutting efficiency and improved productivity;

2) the quality is controlled and the cost of a single piece is low. The damage layer caused by diamond wire cutting is less than that caused by mortar wire cutting, which is conducive to cutting thinner silicon chips;

3) environmental protection, the diamond wire USES water-based grinding fluid (mainly water), which is conducive to improving the operating environment and simplifying the cleaning and other processing procedures.

Additive principle

With the development of diamond wire-cutting technology and the increasingly fierce competition of single polycrystalline, polycrystalline silicon chips will all be converted from mortar wire-cutting to diamond wire-cutting.However, due to the problems of shallow damage layer and obvious line mark of diamond wire cutting polysilicon sheet, it is difficult to etch effective anti-reflection lint on the surface of conventional mortar line made by acid.

At present, in view of the diamond wire polycrystalline silicon slice of the problem of pile, the main solutions include: diamond wire direct additive method, dry black silicon (RIE) and wet black silicon (MCCE) and so on, because RIE and MCCE cost and process, at present most enterprises to diamond line of diamond wire cutting polycrystalline silicon slice prepared by direct additive minus reflection of suede, of course, due to the additive of battery prepared by the low conversion efficiency factors, determine its just diamond wire cutting polycrystalline silicon slice of comprehensive promotion of a transitional phase.

-- principle of making wool with diamond wire additive

Diamond wire cutting polycrystalline silicon slice with two-dimensional cutting method, the diamond particles by using the method of plating or resin fixed inlaid on the stainless steel wire, direct use of the high speed grinding was carried out on the silicon wafer cutting, cutting with high efficiency, environmental protection, suitable for high silicon wafer cutting and material utilization, but shallow surface damage layer and have more thick line mark;Mortar wire cutting polycrystalline silicon slice using three-dimensional cutting method, using stainless steel wire to SiC micro powder and polyethylene glycol into the cutting area for grinding cutting method, has a deep surface damage layer and basic wireless mark advantage, but low production, silicon material loss, environmental pollution, etc..As the damage layer of diamond wire polysilicon sheet is quite different from that of mortar wire silicon sheet, the reflectance of diamond wire polysilicon sheet is about 28% when making wool with mortar wire acid, and the average Eta is about 0.2% lower than that of conventional mortar wire. The main reason is that the reflectance of diamond wire polysilicon sheet is too high after making wool, which leads to the decrease of Isc.

At present, many additive manufacturers have developed additives for diamond wire cutting polysilicon sheet, which can be directly used in acid linting machine of mortar line polysilicon sheet. After linting, the reflectivity is about 2% higher than mortar line, the conversion efficiency is about 0.05% lower than mortar line, and the cost is low and 100% compatible with production line.Generally speaking, according to the HF/HNO3/DI initial match recommended by the diamond wire additive manufacturer, when no additives are added, the weight loss is higher, the reaction is more intense, the bubble is larger and less, the reflectivity is high, and the suede surface will be larger and shallow.After the addition of additives, the weight loss will be significantly reduced and the reaction will be slower, but the bubbles will be smaller and more, the reflectivity will be lower, the surface will be dark as a whole, and the suede surface will be generally smaller and deeper, because:Diamond wire additives can reduce the surface tension of liquid, is advantageous to the bubbles, reaction of complex compound containing silicon to form "mask" from silicon wafer surfaces, especially for the bottom of the wafer has a significant effect, therefore the diamond wire under the action of additives to promote suede fore-and-aft development, this system when the pile vertical response speed and the transverse response speed difference much smaller than when no diamond wire additive, which is advantageous to the silicon wafer suede smaller darker, achieve the goal of reducing reflectivity.It shows that the diamond wire additive first inhibits the reaction of cashmere production, making the overall reaction speed slow, and reduces the reflectivity by controlling the width and depth of the cashmere to achieve the effect of light trapping.The following figure is the 3D nap photo with or without diamond wire additive. By comparison, it can be found that the nap is significantly smaller with diamond wire additive and the nap rate is more, which is the result of the additive's relative promotion of the longitudinal reaction of silicon wafer.

-- realization of the ideal ratio of HF/HNO3 required by diamond wire direct additive method --

At present, the primary proportion of direct wool production of diamond wire additives varies greatly among different manufacturers.On the other hand is because most additives and battery manufacturers are only at the beginning of the line of conventional slurry polysilicon piece on the basis of appropriate adjustments, and not at the beginning of a very good debugging the match ratio, this will cause system after the velvet reflectivity is difficult to achieve additive can achieve the lowest, is not conducive to improve the conversion efficiency of batteries, the waste at the same time can cause a lot of HF and HNO3.

According to the characteristics and principles of diamond wire additive, I think that any diamond wire additive only reduces the reflectivity of wool making, so it has the lowest reflectivity.If the amount of diamond wire additive is too small and the amount of HF/HNO3 is too much, it will not only cause a waste of chemicals, but also make it difficult to achieve the purpose of reducing the wool reflectivity of diamond wire polysilicon sheet.In particular, HNO3 is sensitive to reflectivity. A little more HNO3 will lead to white surface, rapid increase of reflectivity, and excessive HF will lead to acceleration of black velvet and overall reaction.If the amount of additive is too large, it will not only lead to waste, but also hinder the improvement of battery conversion efficiency (diamond wire additive contains organic matter, etc.). Meanwhile, it is difficult to determine whether the amount of HF/HNO3 reaches the appropriate ratio, which is not conducive to the acquisition of lower wool reflectivity.Therefore, I believe that in the initial matching of diamond wire additives, the appropriate amount of diamond wire additives should be considered first, and then the optimal HF/HNO3/DI ratio should be obtained through process adjustment, so as to obtain the lowest reflectivity and improve the Isc and Eta of diamond wire polycrystalline batteries.

Then, how to get the best process ratio through debugging?Through the diamond wire additive experiment, it is found that under the appropriate initial proportion, the ideal drug solution ratio (including dosage, HF, HNO3 and DI dosage, even band velocity, temperature, circulation flow, etc.) can be obtained through gradual process adjustment.Process follow the principle of single variable, in the process of debugging and monitored suede, reflectance (surface sensitivity), parameters such as weight loss and the status of the appearance of black silk, with each process after adjusting the monitoring parameters analysis of the changes in the amount of chemicals in liquid state (or small) excessive, especially pay attention to some changes of paroxysmal, it helps to quickly help us grasp the suitability of the amount of certain chemicals.With the understanding of the principle of diamond wire additive and the role of various chemicals, a model of the velvet reaction of diamond wire polysilicon sheet can be established. Through logical reasoning on the changes of monitoring parameters during the process of process debugging, the ideal drug solution ratio of diamond wire additive can be obtained.Different appropriate HF/HNO3/DI ratios can be adjusted according to different amounts of diamond wire additives. Meanwhile, the optimal HF/HNO3 automatic supplement ratio can also be adjusted by this method.

Why is it more efficient

The cutting efficiency of diamond wire can be improved compared with free silicon carbide cutting in the following aspects:

The consolidation method, that is, brings more cutting of diamond to participate in grinding, and also reduces the mutual abrasion phenomenon between abrasives.

The hardness of diamond is high and the wear resistance of diamond is strong.

With high cutting line speed, the contact area between diamond and silicon wafer will increase, and the diamond line will be able to withstand other disadvantages brought by high cutting speed, thus giving play to the advantages of high cutting speed.

The traditional mortar USES the rapid movement of steel wire to bring the liquid containing abrasive into the workpiece cutting seam, producing cutting effect.In the cutting process, silicon carbide is washed down, only continuous rolling grinding, and reduce the cutting efficiency.Silicon carbide has a hardness of 9.5, while diamond has a hardness of 10.Diamond line cutting line speed is basically 15m/s, our normal cutting mortar line speed is basically 9-11.5m/s.However, if the diamond wire is to make a breakthrough, it should be harder, with better self-sharpness (polycrystalline diamond), more stable consolidation mode and faster linear speed.

A place of efficiency

High cutting efficiency: first of all, the first high cutting efficiency reduces the equipment plant and all depreciation, the cost of single piece of manual processing.

Single chip cost is low: diamond line to replace the traditional mortar cutting of silicon carbide, suspension, steel wire, compare the three,, according to the use of mortar structure line and line recycle slurry system of single chip control in 0.65 yuan more frontier, but not every one can reach this level, diamond wire electroplating line flat, resin diamond line 1 cent can descend.

 

Quality control:

1. In terms of quality control, sand line fluid must be divided into three suppliers. If two or three suppliers are added, the number of three auxiliary materials should reach 6-12.

2, the cutting process of broken wire, is a major killer affecting the yield.The purchase unit price of the bus of diamond wire is several times higher than that of the ordinary straight-drawn wire. The quality requirements of the straight-drawn wire are also higher, and it needs to go through the sanding, cleaning and grinding process for many times.

3, the manufacturing process of diamond line, need to pass the test of multichannel diamond wire tensile machine, quality inspection, and to set up three respectively from bus bar detection, a, secondary product testing, product testing needs for each roll line will have a corresponding traceability inspection report, the surface coating on the sand particle number, breaking force, outstanding amount and a series of testing data.

4. In addition, the quality performance of diamond wire needs to be based on a large number of actual cutting data. Before providing it to customers for application, the existing diamond wire manufacturers will add 1 or more diamond wire multi-wire cutting.It is suggested that a production and test department with demonstrable and reproducible promotion and application of cutting-edge technologies should conduct cutting and exploration of cutting-edge technologies for each batch of rigid lines, and pass the two-way test of quality inspection and actual production.

5. The production of diamond wire is to completely establish a data tracking system, which can be used to trace the data of each coil, which also improves the quality control.

Environmental protection:

The cost of environmental protection treatment is still too low in modern China. The cod of mortar reaches hundreds of thousands, while the cod of diamond wire cutting liquid after pure water dilution and cutting liquid is 200-1000, which will greatly improve the treatment of sewage.

Reduction of silicon consumption:

The potential of silicon powder for recycling and recycling is still being explored.

The problem to be solved

As the domestic mainstream solar silicon chip market is polysilicon chip (about 80% of the silicon chip, the polysilicon chip is mainly cut with mortar), the main problem of diamond wire cutting polysilicon chip is the production of wool.

The defects of diamond wire-cut polysilicon sheet in lint making and the corrosion and heat release of the traditional groove lint making process lead to the surface reflectivity far greater than that of the mortar cutting silicon sheet. How to control the heat is the key to the lint making of diamond wire-cut silicon sheet. Currently, there are two main solutions:

First the chain is used to make lint and the solution is adjusted to control the reaction speed.

Secondly, polycrystalline additives were introduced to improve the surface morphology of silicon wafers after corrosion of polysilicon, so as to reduce the amount of corrosion and achieve uniform and dense corrosion structure on the surface of silicon wafers.
 

-All diamond tools can be ordered and fabricated!
-Henry Wang | Quote Manager
-WhatsApp:+86-13459035657
-Email: ceo@zdiamondtools.com
-Web www.zdiamondtools.com

Company Profile

Certifications

Company Team

Exhibition

Logistics

FAQ