Study On The Damaged Surface Layer Of Sliced Silicon And Germanium Wafer

Semiconductor materials are the basic material for the manufacture of IC chips and semiconductor devices. The size of single crystalline wafers becomes lager as the development of IC process. With the IC technology stepping into the nanometer electronic times , higher surface quality of wafers is demanded. Wafer slicing is one of the most significant sections during the wafer process, and the surface damage induced by the slicing process determine not only the machining time of subsequent technology,but also the machining quality of wafers and the performance of final device. Research on the damaged surface layer of sliced wafers can provide evidence for the selection of grinding time, which can not only reduce cost, but also improve the yield of slices. Consequently, how to measure the damaged layer of wafer surface and how to estimate the degree of damage and surface roughness are the key questions to be solved, and the key points to be studied in this work. Although the inner diameter (ID) sawing technology has grown matured during the seventies of the twentieth century, and the wire-saw slicing has been used intensively for large diameter wafers, many studies on the mechanism of slicing damage, the structure and severity of damaged layer, surface topography and roughness are the far from perfection. Few researches were reported on the WEDM using for silicon and germanium wafers slicing.By the study of machining mechanism and the principle of constant etching rate and step etching, a set of characterization methods, such as excess minority carrier lifetime test, field emission scanning electron microscope, x ray diffraction, optical microscope, AFM and surface profiler have been used to discuss the damaged surface layer and the wafer surface topography and roughness of different cutting methods. The results showed that the above methods are proposed to meet the different requirements on detecting the damaged surface layer of silicon and germanium wafer. The wafers sliced by ID sawing method have two damaged layers, one includes polycrystalline and micro crack, and the other includes elastic distortion zone. Wafers sliced by WEDM has one damage layer, named"coagulation zone", and wafers machined by the multi-wire slicing have a thinner damaged layer called"parquetry layer", and the depth decreased in turn. This research will supply important evidence for the optimization of parameter during slicing process and the determination of polishing time.Alkaline etching had taken the place of acid etching for the removal the damaged layer on the sliced surface gradually, because the etch rate of alkaline etching can be controlled. In this work, a systematic was performed on the removal of the damaged surface layer of Si (100) crystal wafer etched by NaOH solution. The effect of temperature and weight concentration of NaOH solution on the surface roughness was studied in details. In addition, a new method combining the common NaOH etching with ultrasonication was applied to the etching of single-crystalline wafers in order to get smaller surface roughness and reduce the waste during the etching. The results show that it is much easier to get flat surface in the NaOH solution at the concentration of 20%~30%, and temperature has a more important effect on the wafer roughness than the concentration of solution. The surface roughness of silicon wafers was reduced and the volume of silicon removed by means of ultrasonication declined, which will optimize the etching process and save cost for the manufacturer. Furthermore, on the basis of experiments and analysis, the etching process using ultrasonication was discussed. The collapse of the cavitations, which is beneficial to the etching of bumps on the surface of silicon wafers as long as inhibited the contact of the etch pit with the etching solution, is the main cause of the reduction of the amount of erosion and the surface roughness of silicon wafers.