Key Engineering Materials Vols. 389-390

Abstract: This paper reports the effect of nanogrinding conditions on the formation of subsurface structures of monocrystalline silicon (100) substrates. It was found that the amorphization and the transformation of high pressure phases were related to the grit depth of cut employed in nanogrinding. The formation mechanisms were found to be different from those previously reported from the nanoindentation studies.

Abstract: Ultraprecision diamond-cut silicon wafers were irradiated by a nanosecond pulsed Nd:YAG laser, and the resulting specimens were characterized using transmission electron microscopy and micro-Raman spectroscopy. The results indicate that at specific laser energy density levels, machining-induced amorphous layers and dislocated layers were both reconstructed to a complete single-crystal structure identical to the bulk region. Similar effects were confirmed for diamond-ground silicon wafers. Effects of overlapping irradiation were investigated and perfect crystallographic uniformity was achieved in the boundary region. The recovery process involved rapid melting of the near-surface amorphous layer, followed by epitaxial regrowth from the damage-free crystalline bulk.

Abstract: In the process of CMP SiO2 ILD, the nano-particle with high surface energy in slurry has an essential impact on the efficiency and quality of CMP. In this paper the mode of nano-particle on the surface of SiO2 ILD is analysed and adhesion removal model corresponding to that is established. Through cycle polishing experiments, the change of nano-particle size and the state of particle surface before and after polishing is observed with TEM and Zeta potential analyzer, based on which the adhesion removal model is verified.

Abstract: The primary consumables in chemical mechanical polishing (CMP) are the polishing pad and the slurry. The polishing pad significantly influences the stability of the polishing process and the cost of consumables (CoC). During the polishing process, a diamond dresser must be frequently employed to remove the debris to prevent accumulation, a process known as pad conditioning. In this paper, we investigated the physical properties of the CMP pad such as compressibility, thickness, and surface roughness. The difference between new and used pads has been studied. Conclusively, conditioning via a diamond dresser will extend pad life and reduce CoC.

Abstract: A mechanical polishing process was used to reduce surface roughness through mechanical fracturing and removal of the substrate’s roughened regions. It was thus necessary to understand the effect of grain size and morphology on the material removal mechanisms of silicon wafers by stepwise polishing using a fixed abrasive pad. A hybrid process combining the optimized silicon polishing recipe for rapid roughness reduction with a micro-sized diamond, and then polishing using a nano-sized diamond to produce a final finished surface, may be the optimum approach. The best result using the hybrid polishing process was the surface roughness (Ra) value of 3.32 nm.

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: The calculating model of surface non-uniformity of polishing pad and the kinematical model between polishing pad and conditioner are initially established. Then the effects of several conditioning parameters were investigated by using the two models. The results of simulation and calculation show that the width ratio of diamond band of conditoner and the rotation speed at the same speed ratio between pad and conditioner have little effect on the surface non-uniformity of polishing pad, while at high non-integer rotation speed ratio, the surface non-uniformity of polishing pad is better than that at low integer speed ratio. The research results are available to select appropriate conditioning parameters especially for the stringent requirement of within-wafer non-uniformity in next generation IC.

Abstract: This paper experimentally investigates the micro-structural changes in mono-crystalline silicon induced by abrasive polishing with abrasive grain size and applied pressure. It was found that while the large abrasives of about 15 μm and 300 nm in diameter induce both residual amorphous phase and various residual crystalline structures and dislocations, the finer abrasives of about 50 nm in diameter only produce residual amorphous phase in the top subsurface of polished silicon. With the fine abrasives, reducing applied pressure reduces the amorphous layer thickness, and a damage-free polishing can be achieved at the pressure of 20 kPa.

Abstract: This paper experimentally investigates the effect of time and pressure on the condition of polishing pads and the material removal rate (MRR) of single crystal silicon. It was found that as the pad deteriorates with time, MRR decreases. Surfaces with a required quality can only be achieved before the texture deterioration reaches a critical limit. At a higher pressure, 25 kPa, deterioration is slower, and the effective life of pads and MRR is enhanced.

Abstract: A series of polishing experiments have been carried out using Mn2O3 as abrasive grains to examine the polishing characteristics of CMP for oxygen-free copper. It has been found that the polishing rate increases as the polishing speed and/or polishing pressure increases, also the role of polishing speed on the polishing rate is more significant than that of the polishing pressure. The effects of the polishing conditions are however small, when polishing a finished surface roughness of about Ra 5 nm. A long polishing time, with an approximately constant polishing rate, can be achieved, without dressing, with a polishing pressure P = 9.4 kPa. It was found that higher polishing pressures could achieve a higher polishing rate, however the polishing pressure would decrease as the polishing time increased.