James D. Oliver

Whisker Growth from Tin Coatings

Conditions favouring spontaneous growth of whiskers from tin coatings are discussed. Observations are reported concerning orientations and geometry of whiskers. The driving force for growth arises from elastic stress in the coating and can be expressed as a Gibbs free energy in terms of the decrease in pressure. An analysis of diffusion-controlled growth based on grain boundary diffusion seems to be capable of accounting for the fast growth kinetics that are observed in practice at room temperature.

Trends in commercially available SiC substrates

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.

A Designed Experiment Approach to Improvement and Understanding of the SiC Epitaxial Growth Process

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.

In Situ Mass Spectrometry for Chemical Identification in SiC Epitaxial Deposition

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.

Comparison between measurement techniques used for determination of the micropipe density in SiC substrates

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.

Temperature Effects in SiC Epitaxial Growth

This work discusses the results from a series of experiments designed to determ ine he effects of SiC epitaxial process parameters on the layer thickness and c arrier concentration. A secondary goal was to improve the overall process understanding of Si C epitaxy and enable easy determination of growth parameters for epitaxial device structures ra nging from thin, high doped MESFET’s to very thick, low doped layers for power switching diod es. The factors were separated into various designed experiments conducted over the last y ar. This paper discusses the effect of temperature on epitaxial layer parameters.

High Workfunction, Compound Gate Metal Engineering for Low DIBL, High Gain, High Density Advanced RF Power Static Induction Transistor (SIT) and HV Schottky Diode in 4H Silicon Carbide

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].

Low Temperature Epitaxy of 3C SiC Using Hexamethyldisilane Precursor on Si Substrates

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.

Uniformity Improvement of Planetary Epitaxial Growth Processes through Analysis of Intentionally Stalled SiC Wafers

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.