Advanced ELID Process Development for Grinding Silicon Wafers
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Advanced ELID Process Development for Grinding Silicon Wafers M. M. Islam1, A. Senthil Kumar1, S. Balakumar2, H. S. Lim1 and M. Rahman1 1 National University of Singapore, Singapore 119260 2 Institute of Microelectronics, 11, Science Park Road, Science Park-II, Singapore 117685 ABSTRACT A completely new and novel electrolytic system, Injection Electrode (IE) assisted electrolysis, has been tried here to improve the quality of the silicon wafer surfaces generated by Electrolytic In-process Dressing (ELID) grinding process. The Experiments were conducted by varying the injection flow rate in order to perform extensive analysis on the effect of injection flow rate on the generated wheel surface condition and the consequent grinding performance. Experimental results showed that lower injection flow rate greatly improved the wheel surface condition resulting in superior ground surface qualities. INTRODUCTION The achievement of the Silicon on Insulator (SOI) substrate has opened up the likelihood of co-integration of photonics and electronics. To stop unwanted leaky currents towards the substrate in standard CMOS electronics, this substrate has been primarily developed. However, downsizing devices has brought challenges to the manufacturing processes for surface nanotopography of the silicon materials. Achievement of thin silicon in SOI with good uniformity is one of the challenges, and it would be more difficult for 300 mm wafers. Currently the grinding and final finishing of the wafer is done by conventional grinding and Chemical Mechanical Polishing (CMP) processes. These processes have, however, some disadvantages such as poor machinability, waste water problem and high manufacturing cost [1]. Efficient machining is, therefore, essential for grinding silicon wafer more cost effectively with nano-scale surface accuracy. The Electrolytic In-process Dressing (ELID) grinding technique has great potential as an easy, efficient and effective grinding process especially for machining hard material with fine super-abrasive wheel. Most importantly, this grinding technique realizes mirror quality surface of silicon wafer, and the process has started to take the place of substrate thinning for Silicon on Insulator and also potentials for polishing processes [2]. Although the ELID is an effective process for machining silicon wafer, but the non linear electrolytic dressing shows unstable grinding performance-breakage of bonding material [3] and generation of wear flat [4]-during ELID grinding process, which draws limitation to use this process for wafer machining. A completely new and novel electrolytic system, Injection Electrode (IE) assisted electrolysis, has been, therefore, tried here to improve the phenomena occurring in electrolysis and hence to improve the process performance. The machining performance of this modified ELID grinding process has been compared with that of CMP process as well.
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