Papers by Author: James D. Oliver

Abstract: SEMI Standards charter is to develop standards that benefit the semiconductor industry. The SEMI organization has evolved over the last 40 years into an international organization with covering all aspects of semiconductor and flat panel materials and devices. SEMI Standards provides the framework for the development of consensus based standards documents. At present there are two published standards specific to silicon carbide, the first dealing with dimensions, properties and ordering information for SiC wafers, and the second defining a nomenclature for defects found on SiC: SEMI M55-0817 Specification for Polished Monocrystalline Silicon Carbide Wafers SEMI M81-0611 Guide to Defects Found on Monocrystalline Silicon Carbide Substrates Additional standards applicable to various semiconductor wafers also are available and new SiC related standards are being developed based on industry needs and volunteer participation.

Abstract: Wide bandgap semiconductors, such as 4H SiC, are suitable for power regulating devices, due to compatibility with conventional process integration, high breakdown voltage and thermal conductivity [1]. For RF applications, in order to achieve better switching speed, high cut off frequency, and low series resistance (Rdson), it is essential to choose the right gate metals [2]. Engineering of the gate metals not only improves the critical device parameters by adjustment of the metal workfunction, but also affects how the high aspect ratio trenches are filled for a next generation SIT device configuration [3] - [5].

Abstract: The CVD growth of SiC thin films using hexamethyldisilane (HMDS) as the singular precursor on Si substrates with an AlN nucleation layer was explored in this study. A statistically designed experiment was used to conclude that growth temperature has the largest impact on crystal quality and surface microstructure. In addition to crystal quality, wafer bow was studied. Crystal quality and growth rate are loosely correlated to wafer bow in our study. SEM surface microstructural analysis of the SiC films shows a changing microstructure with growth temperature consistent changes in measured crystal quality. TEM studies reveal that the films are the 3C polytype having a high density of planar faults.

Abstract: A method to improve the uniformity of epitaxial wafers grown in planetary rotation reactors through analysis of intentionally stalled wafer measurements is described. A set of basis functions that are completely uniform when rotated in the reactor environment are described and used to construct a nearest uniformity producing profile (NUPP). The methodology for use of stalled wafer profiles and comparison to the NUUP allows easy identification of the changes in process parameters necessary for more uniform epitaxial growth. Although described here as applied to SiC epitaxial growth, this method is applicable to all planetary rotation reactors which are utilized for SiC and III-V semiconductor epitaxial growth.

Abstract: Device quality SiC wafers are extremely expensive and available from only a limited number of vendors. This has limited the ability of researchers to compare and evaluate quality from various vendors. This paper surveys some properties and characteristics of SiC wafers purchased in the commercial market place and describes the product variability among vendors as a method to highlight the areas where improvements in substrate quality are desirable.

Abstract: A quadrupole mass spectrometer unit was utilized to accurately detect the chemical species present inside a SiC CVD reactor growth chamber before, during, and after epitaxial deposition. The in-situ mass spectrometer has been able to confirm the presence of silane (SiH4) and propane (C3H8) decomposition products (eg. Si and CH4) that were predicted from chemical modelling, and give insight into specific reaction kinetics. Additionally, the mass spectrometer has positively detected trace amounts of oxygen, which has helped to identify process weaknesses and possible sources of vacuum leaks.

Abstract: A series of designed experiments have been conducted over a period of years in a multiwafer, planetary rotation, epitaxial reactor to quantify the effects of various epitaxial growth process parameters on the resulting SiC epitaxial layers. This paper summarizes the results obtained through statistically designed experiments varying process parameters and their resultant effect on the layer thickness, carrier concentration and the variability of these parameters wafer-to-wafer, and within a wafer.

Abstract: Micropipe density (MPD) is a crucial parameter for silicon carbide (SiC) substrates that determines the quality, stability and yield of the semiconductor devices built on these substrates. The importance of MPD is underscored by the fact that all existing specifications for 6H- and 4H-SiC substrates set upper limits for it. Several methods for measuring the MPD are known, however, their reliability and applicability to various types of substrates (e.g. semiinsulating, conducting, etc.) has not been systematically studied. The subject of this paper is a comparative study of various techniques used for the MPD measurement accompanied by statistical analysis of the results. The study was initiated by several organizations working in the immediate field of silicon carbide or in closely related fields and included SiC substrate manufacturers, substrate consumers, equipment manufacturers and universities. The study represented a round robin experiment in which MPD was measured on thirty SiC wafers of various pedigrees. The values of MPD have been determined using both destructive and non-destructive techniques. The repeatability of each technique is analyzed and compared with that of other techniques.