Papers by Keyword: Si Wafer

Abstract: Experiments on investigation of the radiation defects produced as a result of high energy proton irradiation of single crystal Si wafers are carried out. Parameters of the proton irradiation facility are presented. It is shown that the most efficient radiation defect formation correlates with the position of the Bragg peak of ionization losses. LT spectra were measured just after irradiation and then after keeping Si samples during 3 months of at room T. We did not observe any variation of the number density of the defects, except for the 7th wafer, where most part of protons was stopped. An efficient annealing of the vacancy-type defects starts at temperatures slightly lower than 100 °C (during 10 min). Annealing at about 700 °C leads to recovering of the monoexponrntial shape of the LT spectra.

Abstract: For the backgrinding of semiconductor devices, a rotary grinding process is indispensable for achieving the required wafer thickness. The relative velocity between the grinding wheel and the wafer is maximum at the periphery of the wafer and minimum at the center of wafer. Generally, the grinding performances are discussed in terms of the ratio of the rotational speeds of the grinding wheel and the wafer. However, it is not possible to use this ratio to determine the grinding conditions for different wafer sizes grinding as this ratio does not show the difference in relative velocity. Therefore, a new relative velocity ratio was defined in this study. Then, the Si wafer grinding was performed to investigate the effect of the surface roughness and the power consumption of the grinding wheel spindle on the relative velocity ratio.

Abstract: Chemical mechanical polishing (CMP) is often employed to obtain a super smooth work-surface of a silicon wafer. However, as a conventional CMP is a loose abrasive process, it is hard to achieve the high profile accuracy and lots of slurry must be supplied during CMP operations. As an alternate solution, a fixed abrasive CMP process can offer better geometrical accuracy and discharges less waste disposal. In this paper, in order to enhance the polishing efficiency and improve the work-surface quality, a novel ultrasonic assisted fixed abrasive CMP (UF-CMP) is proposed and the fundamental machining characteristics of the UF-CMP of a silicon wafer is investigated experimentally. The results show that with the ultrasonic assistance, the material removal rate (MRR) is increased, and the surface quality is improved.

Abstract: In recent semiconductor industry, production of ever flatter, thinner and larger Si wafer are required to fulfill the demands in high integration and cost reduction. A severe problem encountered in wafer thinning process is the warp and distortion of wafer induced by the residual stress and subsurface damage. Chemo-mechanical grinding (CMG) process is emerging process which combines the advantages of fixed abrasive machining and chemical mechanical polishing (CMP), offers a potential alternative for stress relief. This paper studies the influence of the wheel manufacturing process on the wheel physical properties. Three-factor two-level full factorial designs of experiment are employed to reveal the main effects and interacted effects of mixing method and filtration of raw materials on the bending strength and elastic modulus of CMG wheel. The difference in wheel properties is discussed by association with CMG performance including wheel wear, grinding force and surface roughness.

Abstract: In this study, basic experiments involving machining using a rotational tool were conducted with the aim of increasing the volume of material removed rate in ductile-mode machining of Si wafers. The machining surface and machining force was compared to experimentally clarify the material removal process for a single cutting edge, the critical cutting thickness tc at which occurs of cracks was set as the machining condition. Then, the three machining modes were experimentally revealed. As the result, the ductile-mode machining surface was obtained that the total depth of cut was under less than 78.5μm on ductile-brittle-mode machining.

Abstract: As the level of Si-wafer surface directly affects device line-width capability, process latitude, yield, and throughput in fabrication of microchips, it needs to have ultra precision surface and flatness. Polishing is one of the important processing having influence on the surface roughness in manufacturing of Si-wafers. The surface roughness in wafer polishing is mainly affected by the many process parameters. For decreasing the surface roughness, the control of polishing parameters is very important. In this paper, the optimum condition selection of ultra precision wafer polishing and the effect of polishing parameters on the surface roughness were evaluated by the statistical analysis of the process parameters.

Abstract: A method to easily and economically manufacture more precise patterns compared with usual MEMS technique has been searched for. Under such circumstances, this research aims to clarify the formation of nano-scale protrusion structure produced by local anodic oxidation on Si wafer surface in expectation of the nano/micro mold production for nanoimprint lithography in future. In this report, the influences of contact width and distance between probe tip and Si wafer surface (distance between terminals) on the size and shape of protrusion patterns were examined in order to clarify the fundamental phenomena in local anodic oxidation. A scanning probe microscope equipped with a current measuring unit was utilized in local anodic oxidation experiments. As a result, it was confirmed that the size of generated protrusion structure became larger with increasing the contact width and became smaller with increasing the distance between probe tip and Si wafer surface. These facts will be useful in producing 3-D nanostructures in future.

Abstract: This study aims to clarify the interaction between Si wafer and individual diamond abrasives in grinding at nanometer level and to estimate the grinding conditions for minimizing the surface defect. This paper reports on the results obtained through nano-scratching experiments in vacuum by an atomic force microscope (AFM) and simulations by using the molecular dynamics method by applying Tersoff potential for Si-Si atomic interaction under room and high temperature, respectively, to examine the influence of the grinding heat on the materials removal process. As a result, it was proven that the scratch groove under high temperature becomes deeper than that under room temperature from the experiments, and it was also observed that the formation of the amorphous phase around the scratch groove under high temperature becomes a little bit larger than that under room temperature from the simulations.

Abstract: In order to reduce and control yield loss in the fabrication process of next generation ULSI devices, nano-defects inspection technique for polished Silicon (Si) wafer surface becomes more essential. This paper discusses a new optical nano-defects detection method, which is applicable to silicon wafer surface inspection for next-generation semiconductors. In our proposed method, the evanescent light is emerged on the wafer surface with total internal reflection (TIR) of infrared (IR) laser at the Si-air interface. By scanning the surface where the evanescent light is emerging with a very shaped fiber probe, it enables to detect nanometer scale defects in the vicinity of Si wafer surface without diffraction limit to resolution. To experimentally verify the feasibility of this method, an evanescent light measurement system was developed and several fundamental experiments were performed. The results show that the proposed Si wafer microdefects detection method can detect the microdefect with 10nm scale on and beneath the surface based on evanescent light distribution.

Abstract: The mechanism of the mechanochemical polishing of Si wafers with BaCO3, CaCO3 and ZnO abrasives was investigated by polishing experiments carried out in air, O2 and Ar gas environments on dry condition and static heat treatment experiments of mixed powder of BaCO3 and Si with various mixture ratios for analyzing the reaction mechanism at the interface in polishing operation. Results obtained were (1) Si wafers were smoothly and effectively polished with these all mechanochemical abrasive whether O2 gas existed in the surrounding environment or not, (2) Heat treatment of the mixed powder suggested that oxidation of Si was more actively promoted even when existence of BaCO3 powder was only a little in the mixture and that formation of Ba-Si oxide increased as the mixture ratio of BaCO3 powder to Si powder increased, (3) As the mechanochemical polishing mechanism, two-step reaction process would be the most reasonable, that is, chemical attack of the mechanochemical abrasive for oxidizing the Si surface as the first step and further chemical reaction to form reaction products between the formed SiO2 and the abrasive as the second step.