Papers by Keyword: Chemical Mechanical Polishing (CMP)

Abstract: The modified SiC slurry for CMP process was proposed in order to obtain high-quality surface of 150 mm SiC wafer and then tried to explain the mechanism of the effect of added transition metal ion to improve polishing characteristics of SiC crystal substrate. SiC substrate with using modified slurry exhibited slightly higher MRR value and lower platen temperature than those with using commercial slurries. The addition of transition metal ion into the slurry enhanced oxidation efficiency of SiC crystal surface and improved MRR and the quality of SiC surface.

Abstract: Transition metal ion was added to CMP (chemical-mechanical polishing) slurry without abrasive particle to solve the problem of CMP. MRR (material removal rate) value of SiC substrate processed using non-abrasive slurry was comparable to MRR values of SiC substrates using abrasive slurries. The scratch formation was successfully suppressed in SiC substrate polished with using non-abrasive slurry and no residual particle resulting from agglomeration of abrasive particles could suppress scratches and forms a good quality of SiC substrate surface. Uniform and high-quality SiC substrates could be prepared through the non-abrasive CMP process.

Abstract: The need of removing the mechanical damage and the stress introduced during the thinning step of device process flow is challenging for manufacturing of high quality SiC-based devices. In this respect we have identified two different back finishing approaches, based on material removal and material rearrangement. The first one includes dry polishing (DP) and chemical mechanical polishing (CMP); the second one includes bulk and laser annealing. Systematical investigation on wafer warpage, sample morphology and die mechanical reliability have been conducted and comparison between the two approaches has been done. The CMP and DP processes can remove the damage produced by back grinding, recovering wafer warpage and resulting in a smoother surface. Bulk thermal annealing has provided better roughness levels and has been successful in stress relief, although the wafer permanence at high temperature is not compliant with the device process flow. Under laser annealing process, the surface features keep almost unchanged as well as warpage level. Despite being not effective in stress relief, from a mechanical point of view, the laser annealing process, does not impact die reliability, representing a suitable back finishing process especially in the optic of its use in backside ohmic contact formation.

Abstract: Developing an observation method for distributing sub-surface damage (SSD) on large-diameter 4H-SiC bulk wafers formed by mechanical processing can significantly improve the epitaxial and bulk growth processes. This study used a novel laser light scattering (LLS) technique to observe SSD distribution on a 6-inch 4H-SiC (0001) wafer. As a result, scattering intensity distributions similar to the grinding and lap-polishing traces and the shape of the jig used to hold the wafer during polishing were observed on the CMP-finished SiC wafer surface. Since the surface topography of the area was flat by a laser microscopy observation, it is assumed that this is the SSD. This result suggests that LLS can be a wafer inspection method that can observe SSD distribution. In addition, wafer inspection using LLS has demonstrated that it is possible to observe scratches, particles, and macrostep bunching. This method is anticipated to allow further optimization of the mechanical processing and thermal etching process prior to CVD epitaxial growth.

Abstract: Improving the visibility of defects in nitrogen-doped 4H-SiC (0001) bare wafers by photoluminescence imaging (PLI) is essential for improving the epitaxial growth process and device yields. This study proposes sub-surface damage (SSD) introduced during the mechanical process of SiC wafers as a new factor in reducing defect visibility in PL images. To verify the effect of SSD, we observed the surface of a SiC wafer, which was thermally etched at about 3 μm. As a result, dramatic defect visibility improvement was observed when the surface roughness was sufficiently flat (Ra < 0.3 nm) after thermal etching. Thus, the results suggest that defect visibility in PL images can be improved by controlling SSD and surface roughness. Using the background noise reduction effect of the SSD removal, not only PLI but also many other wafer surface inspections are expected to be improved.

Abstract: Lithium tantalate (LiTaO₃) has piezoelectric, electro-optical and nonlinear optical characteristics, and a wide transparency range going from ultraviolet to infrared. It is desirable that LiTaO₃ wafer was a smooth surface in order to function with good quality. Chemical mechanical polishing (CMP) has been used to planarize integrated circuits (ICs) or obtain a high surface quality of the substrates. This paper investigates the effect of citric acid as an additive in the slurry for LiTaO₃ CMP. The roughness of the wafers was measured by an atomic force microscopy (AFM, XE-100) after polishing. The slurry, which contains citric acid as an additive, has a higher material removal rate and friction force than a slurry without an additive. After polishing, the surface roughness of the LiTaO₃ wafer can be reduced down to 1.7Å of R_a.

Abstract: In this paper, lapped C-face of single crystal SiC wafer was irradiated by femtosecond laser. Chemical mechanical polishing (CMP) was then carried out to polish the irradiated SiC C-face. The authors compared the results of femtosecond laser-assisted CMP process. A white-light interferometer was used to investigate the surface morphology of the processed SiC substrate before and after laser irradiation. It was found that the material removal rate (MRR) of the irradiated substrate is about 3 times higher than that of the substrate not treated by femtosecond laser. In addition, lower surface roughness was realized after femtosecond laser assisted CMP process.

Abstract: With the developing of integrated circuit(IC) technique, improving of integration level, reducing of feature size and increasing the wafer size, the stringent requirements for global planarization during IC fabrication are raised. During chemical mechanical polishing(CMP) of multilevel interconnect for IC, there are obvious influence of the polishing quality on performances of the device．CMP slurry is one of the important factors of influencing the polishing quality. In this work, the stability of tungsten plug CMP slurry for IC multilevel interconnect was studied. Through experiment, interaction between the components in the CMP slurry was analyzed, and stable slurry with optimized polishing parameters to achieve higher removal rate were defined．

Abstract: The design ideas of intelligent control and the influence mechanism of process parameters on chemical mechanical polishing (CMP) are combined to develop the CMP intelligent monitoring system, which has the function of learning, inference and memory. The system can be used in many kinds of CMP facilities, the process parameter from the system can be used to control each unit of the CMP facility. And compared with the past way of processing by virtue of experience, the system has friendly operating interface and is easy to operate. The volume production of silicon wafers can be achieved by the total CMP intelligent monitoring. The efficiency of production can be improved highly on condition that the quality can be ensured.

Abstract: The light emitting diode (LED) development technology is an important topic for green industry. This study focused on the efficient cleaning for LAO hydrolysis material, which is a potential LED substrate. The 99.5% ethanol or an alternative solution is used to clean the LAO substrate and dry with the help of anhydrous gas. To improve the cleaning performance, the Taguchi-based orthogonal array of experimental planning and the Grey Relation Analysis are employed to optimize the cleaning parameters. Four control factors are cleaning time, soaking time, PVA sponge type, drying method. The multiple performance characteristics of responses include the residual traces of impurities and water mark after the cleaning process for LAO substrate. With the proposed cleaning process, the surface foreign matter removal rate of target 80% and the residual water marks of declining to 20% are achieved.