本文選題：太陽能硅片 + 電解磨削��； 參考：《南京航空航天大學》2016年博士論文

【摘要】：多線切割是當前太陽能硅片的主要加工方法,該方法是通過線網的高速運動把磨料帶入硅錠加工區(qū)域進行研磨,最終將硅錠切割成薄片。根據磨料的附著形式多線切割又分為游離磨料和固結磨料兩種。當前單晶硅片基本采用固結磨料切割,切割后的硅片通過各向異性腐蝕在表面形成隨機分布的金字塔絨面,該技術路線成熟,硅片制造效率高成本低。多晶硅由于晶粒取向的隨機性,固結磨料切割后的多晶硅片無法沿用現有的酸制絨工藝,暫時只能采用成本較高的黑硅技術來獲得較好的絨面結構。多晶硅片的加工目前主要還是采用游離磨料切割。但是游離磨料切割多晶效率較低,尤其是多晶硅錠中含有硬質點時,切割難度更大風險較高。針對目前多晶硅片加工所存在的困難和障礙,本文在現有的多線切割系統基礎上,提出了一種電磨削多線切割復合加工方法,該方法在硅錠與切割線間加上連續(xù)或脈沖電源,利用切削液的弱導電性產生微區(qū)氧化或腐蝕,在機械磨削的同時復合電化學氧化(或腐蝕)實現材料去除。本文針對該加工方法的作用機理、關鍵技術等進行了深入研究和試驗,主要完成了以下幾個方面的研究內容。(1)對硅電極進行循環(huán)伏安測試發(fā)現,在含0.5mol/L KCl的乙二醇溶液中,正向掃描電壓為5V時,P型多晶硅片的循環(huán)伏安曲線上出現了一個電流峰,峰電流密度約為0.07A/dm2。硅電極在含0.5mol/L KCl的水溶液中循環(huán)伏安掃描時,測得了與HF溶液中較為類似的循環(huán)伏安曲線,正向掃描電壓為1.5V和4V時分別出現了電流峰,峰電流密度分別為0.03、0.08 A/dm2。結果表明,在陽極電場的作用下,硅電極會產生陽極氧化,在水溶液中還會伴隨有微弱的陽極腐蝕。隨著反應時間的增加,氧化層不斷累積,陽極反應逐漸停止,若能及時去除氧化層,電化學反應可持續(xù)不斷進行。20V直流電壓下反應100s氧化層厚度大約為100nm,其表面存在孔洞,孔洞的直徑大約為2-3μm,整個氧化層表面致密性差,并檢測到氧元素的存在,進一步證明了硅片表面發(fā)生了陽極氧化反應。(2)采用分子動力學方法對硅以及硅氧化物進行納米壓痕仿真,結果表明在同樣的載荷下疏松狀硅氧化物的壓痕深度更深,載荷卸載后的殘余深度也更大。隨后對原始硅片和陽極氧化后的硅片開展納米壓痕實驗,結果表明:在4mN的載荷下,原始硅片的最大壓入深度約300nm,卸載后的壓痕深度約100nm;而陽極氧化后的硅片其最大壓入深度約550nm,卸載后的壓痕深度約200nm,實驗結果與仿真結果基本一致。同時硬度檢測結果也表明,陽極氧化后的硅片硬度要小,壓頭更容易壓入其表面,電化學反應產生的氧化層有利于切割時磨�！扒度搿边@一瞬間過程。(3)針對該方法在工程應用中所存在的難題,對其中的關鍵技術展開研究。陽極進電設計了端部進電法,陰極進電設計了碳刷進電、滾筒進電、石墨塊進電和雙工位進電等多種線網進電方案。研制了電磨削專用電源,該電源可以設置單極性和雙極性兩種輸出模式,輸出的頻率(0-500Hz)、脈寬可調,能量可控。并以該電源為載體,設計了一種分布式太陽能硅片電磨削多線切割遠程監(jiān)控系統,便于對加工過程中的電參數和設備狀態(tài)的監(jiān)測以及對電參數的遠程控制。(4)在NTC 442DW多線切割設備上開展了游離磨料電磨削多線切割及其對比試驗。結果表明,電磨削切割后硅片的TTV和BOW的均值分別為11.37μm和7.38μm,對比試驗的TTV和BOW的均值分別為12.06μm和10.12μm,兩項統計指標的均值和分布區(qū)間均優(yōu)于對比試驗。而且,電磨削能減少硅片表面線痕的出現以及顆粒脫落的發(fā)生,減小硅片亞表面損傷層,提高切片合格率。同時,該方法因為切割負載的降低能減小切割過程中對切割線的損傷,減少切割線上周向切痕出現,降低斷線幾率。基于HCT B5多線切割系統,將該方法分別應用于點雜多晶硅和結構線切割,均取得了較好的試驗效果,綜合良率分別提高了2.54%和2.08%。(5)通過單絲線鋸金剛線電磨削對比切割試驗,發(fā)現對比試驗片表面光亮,而電磨削試驗片表面顏色偏暗并存在腐蝕跡象。采用酸制絨后,電磨削硅片表面能形成均勻致密的絨面結構,制絨后的硅片反射率低于對比試驗硅片,尤其在短波范圍內(波長300-600nm)其反射率明顯低于對比試驗片。然而,電磨削金剛線多線切割后的硅片與普通金剛線切割無明顯差異,表面仍然十分光亮,制絨后絨面結構較差。這是因為電磨削多線切割時電流密度由單絲切割時的3.4A/dm2急劇減小到0.18A/dm2,導致電化學腐蝕產生的缺陷中心大大減少,不利于制絨。后續(xù)可進一步研究和試驗,攻克相關工程難題,提高多線切割時單根鋼線的電流密度,促進多線切割過程中電化學缺陷中心的形成,該方法將有望為未來的金剛線切割多晶提供一條可能的技術路徑。
[Abstract]:Multi wire cutting is the main processing method of solar silicon wafer at present. This method is to lapping the abrasive into the processing area of the silicon ingot through the high-speed motion of the wire mesh. Finally, the silicon ingot is cut into thin slices. According to the attachment form of the abrasive, the multi wire cutting is divided into two kinds of free abrasive and consolidation abrasive. The current single crystal silicon chip is basically used as a consolidation abrasive. The silicon wafer after cutting, after cutting, forms a random distribution of Pyramid suede on the surface through anisotropic corrosion. The technology is mature and the efficiency of silicon wafer manufacturing is high and low. Polysilicon, due to the randomness of grain orientation, can not follow the existing acid cashmere process by the consolidated abrasive cutting. Silicon technology is used to obtain better suede structure. The processing of polysilicon chips is currently mainly used by free abrasive cutting. However, when free abrasive cutting has low polycrystalline efficiency, especially in polysilicon ingot, it is more difficult and more difficult to cut. In view of the difficulties and obstacles existing in the processing of polysilicon chips, this paper is in the present. On the basis of multi wire cutting system, a multi wire cutting compound machining method is proposed. This method is combined with continuous or pulse power supply between the silicon ingot and the cutting line, using the weak conductivity of the cutting fluid to produce micro zone oxidation or corrosion, and the compound electrochemical oxidation (or corrosion) is used to remove the material at the same time in the mechanical grinding. The mechanism and key technology of the method have been studied and tested in depth. (1) the cyclic voltammetry test of silicon electrode has found a current peak in the cyclic voltammetry curve of the P polycrystalline silicon wafer when the positive scanning voltage is 5V in the glycol solution containing 0.5mol/L KCl. When the current density is about 0.07A/dm2. silicon electrode in the water solution containing 0.5mol/L KCl, the cyclic voltammetry curve is similar to that in the HF solution. The current peak of the positive scanning voltage is 1.5V and 4V respectively. The peak current density is 0.03,0.08 A/dm2., respectively, and the silicon electrode under the action of the anode electric field. There will be anodic oxidation and weak anodic corrosion in aqueous solution. As the reaction time increases, the oxide layer accumulates continuously and the anode reaction gradually stops. If the oxidation layer can be removed in time, the electrochemical reaction continues to react to the.20V DC voltage and the thickness of the 100s oxide layer is about 100nm, and the surface has holes and holes. The diameter of the hole is about 2-3 mu m, the surface of the whole oxidation layer is not dense, and the presence of oxygen is detected. It is further proved that the surface of the silicon surface has been anodized. (2) the molecular dynamics method is used to simulate the nano indentation of silicon and silicon oxide. The results show that the indentation depth of the loose silicon oxide under the same load. Further, the residual depth after loading is also greater. Then the nano indentation test of the original silicon wafers and anodized silicon wafers is carried out. The results show that the maximum penetration depth of the original silicon wafer is about 300nm under the load of 4mN, and the indentation depth after unloading is about 100nm; and the maximum pressure of the silicon wafer after the anodic oxidation is about 550nm, the pressure after unloading. The depth of the trace is about 200nm, and the experimental results are basically consistent with the simulation results. At the same time, the hardness test results also show that the hardness of the silicon wafer after anodic oxidation is smaller and the pressure head is more easily pressed into its surface. The oxidation layer produced by the electrochemical reaction is beneficial to the "embedding" of the abrasive particles in the cutting process. (3) the difficulty of the method in engineering application is difficult. The key technology is studied. The anode incoming power is designed by the end feed method. The cathode intake is designed for a variety of wire mesh intake schemes, such as carbon brush intake, roller power intake, graphite block intake and double station power intake. The electric grinding special power supply is developed. The power supply can set two output modes, single polarity and bipolar, and the output frequency (0-500). Hz), the pulse width is adjustable and the energy is controllable. And with the power as the carrier, a distributed multi wire cutting remote monitoring system for solar silicon wafer grinding is designed to facilitate the monitoring of electrical parameters and equipment state and the remote control of electrical parameters in the process of machining. (4) free abrasive cutting is carried out on the NTC 442DW multi wire cutting equipment. The results show that the mean values of TTV and BOW of the silicon wafers after cutting are 11.37 m and 7.38 m respectively. The mean values of TTV and BOW in the comparison test are 12.06 m and 10.12 u m respectively. The mean and distribution range of the two statistical indexes are all superior to those of the contrast test. The occurrence of particle shedding reduces the subsurface damage layer of silicon wafer and improves the slice qualification rate. At the same time, the method can reduce the damage to cutting line in cutting process, reduce the cutting line cut mark and reduce the broken line probability because of the reduction of the cutting load. Based on the HCT B5 multi wire cutting system, this method is applied to the point miscellaneous polysilicon and the junction respectively. Good experimental results were obtained. The comprehensive good rate increased by 2.54% and 2.08%. (5) through the single wire wire saw diamond wire electric grinding contrast cutting test. It was found that the surface of the test piece was bright, while the surface of the electric grinding test sheet was dark and there was a sign of corrosion. The surface of the silicon wafer was formed by the acid cashmere. With dense suede structure, the reflectivity of the silicon wafer after cashmere is lower than that of the contrast test silicon, especially in the range of short wave (wavelength 300-600nm), its reflectivity is obviously lower than that of the contrast test piece. However, there is no obvious difference between the silicon chip and the common diamond wire cutting after the electric grinding of the diamond wire multi wire cutting, and the surface is still very bright, and the structure of the wool after the cashmere production is poor. It is because the current density in the multi wire cutting is reduced sharply to 0.18A/dm2 when the 3.4A/dm2 is cut from the single wire. The defect center of the electrochemical corrosion is greatly reduced and it is not conducive to the cashmere making. Further further research and testing can be done to overcome the related engineering problems, improve the current density of the single steel wire in multi wire cutting and promote multi wire cutting. The formation of the electrochemical defect center will hopefully provide a possible technical path for future polycrystalline diamond wire cutting.

【學位授予單位】：南京航空航天大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TN305.1

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