Papers by Keyword: Laser Light Scattering

Abstract: Power devices electronics based on silicon carbide (SiC) are emerging as a breakthrough technology for a wide range of applications [1]. SiC engineered substrates provide a solution that fulfills power devices requirements, namely supplying high quality, ultra low resistivity materials. SmartSiC^TM substrates, based on Smart Cut^TM technology, combine the advantages of high quality single-crystal SiC and innovative pSiC handle material [2]. To achieve high volume manufacturing (HVM) of prime grade SiC engineered substrates, defects monitoring is crucial. This paper explains how a commercially available Deep-Ultraviolet (DUV) laser-based inspection system (KLA Surfscan® SC1) was successfully used for the quality control of SmartSiC^TM and single-crystal 4H-SiC in a production environment. Detection of both surface and grown-in defects was investigated, on 150 mm and 200 mm substrates. Statistical data were collected and utilized for driving quality and yield continuous improvement.

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: By doping three complex dopants in different molar ratio, a series of polypyrroles doped with 9, 10-anthraquinone-2-sulfonic acid sodium, 5-sulfosalicylic acid and toluene-4-sulfonic acid were synthesized by polymerizing the monomer pyrrole in aqueous solution of ferric chloride. The resulting polypyrroles were characterized with the four-probe and laser light scattering, respectively. Our results indicate that optimized value of conductivity reached to 6683 S/m when the molar ratio of anthraquinone-2-sulfonic acid sodium to 5-sulfosalicylic acid to toluene-4-sulfonic acid was 2:1:3. For applications of polymer in optoelectronics, in lithium-ion battery and in electromagnetic shielding, to obtain optimized value of conductivity has great significance for us.

Abstract: By varying the dopant-to-pyrrole ratio in a wide range from 0 to 60% a series of 5-sulfosalicylic acid sodium doped polypyrrole was synthesized in situ in aqueous solution with ferric chloride as the oxidant. The resulting polypyrroles were characterized with the four-probe, laser light scattering and thermo-gravimetry analysis, differential thermal analysis, respectively. Our results indicate that the particle size plays a determinative role to tune the conductivity in the studied range of dopant concentration; and this series of polypyrrole with size-tuned-conductivity exhibits little less thermal-stability although its size and conductivity changes simultaneously and acutely with the dopant concentration. The association of the conductivity with particle size was interpreted in terms of a theoretical model proposed by Baughman and Shacklelette.

Abstract: By varying the dopant-to-monomer ratio in a wide range of 0―110%, a series of polypyrroles doped with 9,10-anthraquinone-2-sulfonic acid sodium were synthesized by polymerizing the monomer pyrrole in aqueous solution of ferric chloride. The resulted polypyrroles were characterized with the four-probe, laser light scattering and differential thermal analysis, respectively. Our results indicated that the average particle size dominates the change in conductivity and thermal stability for the resulted polypyrrole at different dopant concentration.

Abstract: With four-probe technique, we investigated the effects of the mortar-pestle grinding on the conductivity of ferric chloride doped conducting polymer polypyrrole, which had been synthesized by in situ polymerizing the monomer pyrrole in aqueous solutions in the presence of the oxidant iron (III) chloride. As the mortar-pestle grinding duration increased from 0 to 4 hours, the conductivity of the synthesized polypyrrole was found to decrease from about 100 to 10 S/m. In the meantime, the sizes of the grinded polymeric particles were found to decrease from 40.6 to 3.36 m as the grinding duration increased from 0 to 4 hours. Our results demonstrated that the grinding shortened conjugation lengths of the polymeric chains should be responsible for the decrease in the conductivity of the polymer.

Abstract: In the presence of the aqueous solution of ammonia, tetraethyl orthosilicate (TEOS) was hydrolyzed in the mixture of ethyl alcohol and water with the results of silica spacers. The spacer morphology and size distribution of the synthesized silica spacers were characterized with scanning electron microcopy and laser light scattering spectroscopy, respectively. Our results demonstrated that the synthesized silica spacers were monodispersed and were in perfect spherical shape with their sizes of about 0.7 m in diameter. The correlation between the spacer sizes and the amount of ammonia catalyst was examined, and the spacer sizes of the silica spacers strongly depended on the temperature of chemical reaction and the amount of catalyst. The diameter of silica spacers could be well controlled by controlling the amount of ammonia catalyst, and uniformly distributed silica spacers were produced. Behavior of the miscibility of the silica spacers with a nematic liquid crystal was examined.

Abstract: With four-probe and laser light scattering techniques, we have studied the dependencies of the conductivity and the particle sizes of p-toluene sulfonic acid doped polypyrrole on the mechanical grinding time. As the chemically synthesized polypyrrole was mechanically grounded in a mortar from 0 to 8 hours, its conductivity decreased from 607 to 10 S/m while and its particle size decreased from 27 to 4 m. If the mechanical grinding continued, the conductivity of the polymer was found to be up to 1680 S/m. Our results have demonstrated that mechanical grinding is an effective method to control the conductivity of the p-toluene sulfonic acid doped polypyrrole.

Abstract: Micropipes are considered to be a major device killer in SiC wafers. Developing a method to count and map micropipes efficiently and accurately has been a challenging task to date. In this work, a new method based on KOH etching and full wafer, high resolution digital imaging is developed to map and count micropipes in both conductive and semi-insulating SiC wafers. This method is also compared with a non-destructive method based on laser light scattering and a good agreement between the two methods is demonstrated.