The need for high voltage and high current devices for multiple applications, particularly electric and hybrid vehicles, trains, in electricity transport and distribution and smart grid, is pushing changes that suit a new semiconductor material: SiC.
In 2014, the SiC chip business was worth more than $133M. As diode penetration keeps increasing and transistors start to be implemented in different applications, SiC market value is expected to grow steadily at a 14.3% CAGR from 2015–2020.
Later on, learn more about this outlook in Yole Développement’s analysis of the GaN and SiC for Power Electronics Applications. But right now, read this interview with SiC wafer supplier Norstel, which plays an important role in the wide band gap market. Per Zellman, the company’s CEO, shares his views on the industry and the challenges SiC faces.
Yole Développement: As one of the leading SiC material manufacturers, can you explain how Norstel is positioned in this sector?
Per Zellman: As a pioneer in SiC material production since the mid-1990’s and with two in-house bulk growth technologies Norstel has a unique position in the industry. The company has gone from a mainly R&D-oriented company to now being a preferred supplier of excellent SiC material to electronic device applications. We are happy to share our views on the industry and explain where we see our role in the future.
YD: There are different technologies for growing SiC material. What are the competitive advantages of the technology used by Norstel for crystal growth?
PZ: Norstel masters both sublimation and high temperature chemical vapor deposition (HTCVD) crystal growth techniques and operates both in commercial production. Norstel is unique as the only manufacturer commercially growing SiC bulk crystals from gases by HTCVD. On the other hand sublimation is the best established technology in the industry and Norstel considers the two methods as clearly complementary through their different benefits. Therefore Norstel presently produces conducting material and seed crystals by sublimation and semi-insulating material by HTCVD. The main benefits provided by HTCVD are material purity and its potential for continuous and high-speed growth. The only serious challenger to HTCVD and sublimation is solution growth or liquid phase growth technology which is promising but has not yet entered a commercial stage.
YD: Could you describe the product portfolio and services that Norstel has developed to leverage HTCVD and sublimation technologies?
PZ: Our products include conducting SiC substrates and epi-wafers for power applications and semi-insulating SiC wafers for RF applications. Key features of our products include high purity and few defects. One example is our semi-insulating wafers, for which customers express appreciation that we provide non-doped material, where others have to use vanadium doping.
Presently we offer wafers up to 100 mm diameter, with 150 mm being developed and coming later.
What is perhaps not so well known to the industry is that Norstel also offers pure epitaxy services performed on substrates provided to us. It is often about supporting device manufacturers facing capacity shortages in their own epi-lines.
YD: Which applications are mainly driving SiC market growth? How does this compare to the segments where Norstel is positioned today?
PZ: We rarely get any information about targeted system applications but intended types of devices are of course reflected by the wafer specifications we receive from customers. Apart from the established and still growing Schottky Barrier Diodes used in various power conversion applications we see an increasing interest for substrates related to power MOSFETs and semi-insulating wafers for HEMT devices in RF applications. As a provider of high quality material we also get increasingly involved in early development of new high voltage and high current devices, like PiN-diodes and IGBTs.
Norstel provides wafer solutions for all SiC device variants and application areas. Whereas higher performance and higher voltage applications will be targeted with differentiated higher quality wafers. These high performance applications are primarily large-area or high-voltage SiC devices and GaN-on-SiC HEMT devices.
YD: With the SiC market expecting to finally take off, concerns have been presented that there might be a shortage of good SiC material in the future. What is Norstel’s view on this?
PZ: There might at least be a shortage of supplier alternatives, since the SiC wafer industry presents high entry barriers for new players and there are rather few already established. It is a fact that high quality SiC material has to be grown from high quality seed wafers which are not generally available in the market. That means all high quality SiC wafers produced worldwide today originate from high quality seeds being produced by only a handful of established companies, including Norstel. These companies have over many years and through large efforts developed sophisticated techniques to produce such high quality seeds and wafers. Companies wanting to enter SiC wafer production for electronic applications will therefore be forced to both establish the right expertise and spend many years of development and heavy investments before they can provide similar high quality SiC material as today’s top suppliers. This will clearly limit the number of new suppliers in the market.
YD: What are the main SiC crystal growth technical challenges and how is Norstel addressing them?
PZ: Cost still is a main issue for SiC devices. Norstel perceives that material quality, together with general process efficiency improvements, is of key importance to reduce device cost. We and many of our customers consider quality as more important than wafer size and as we see it 150 mm and 200 mm can only take off when remaining quality and processing issues have been solved. This is especially true for new demanding devices for high currents or high voltages. Even though Norstel wafers were confirmed to perform well in line with other state-of-the-art wafers a long time ago, we have in recent years further improved our 100 mm material within our “SiC Perfection” program and are now introducing our latest low defect production grade of conducting wafers for power device applications.
YD: What are the next steps for Norstel?
PZ: Currently, 6-inch conducting wafers are being developed for ramp-up in 2017 when market demand is expected to rise. In parallel we will continue our route towards defect-free wafers to enable our customers to achieve further device yield, quality and performance gains.
YD: There are many criteria that determine the quality of SiC wafers. What has been Norstel’s strategy to understand how to develop high quality wafers?
PZ: Today the quality of SiC wafers is measured mainly by their specified defect densities. Recently demonstrated SiC wafers from Norstel and a few other leading suppliers show very low defect densities. Defects can be measured and quantified in different ways, so there are sometimes discrepancies between specified and measured values. That means device makers might have difficulties choosing the best or optimal material and comparing suppliers.
This is also why we cannot emphasize enough the importance of close cooperation between us material suppliers and our customers, the device makers, to be able to move from the prevailing focus on defect figures in the industry to optimized wafer performance adapted to device needs. This is the only way forward to real quality. Today we often meet customers who require “same as others” performance without real understanding of what impacts device performance, yield and cost. At Norstel we therefore try to be as open as possible and listen carefully to our customers to understand their needs.
YD: What technical parameters emphasize Norstel’s superior product quality?
PZ: In our “SiC Perfection” program we are concentrating our efforts on the quality parameters most highlighted by our customers in terms of defect densities, like micropipes, basal plane dislocations, threading dislocations, surface damage and epi defects. We are today at a quality level which should not stop any device maker from using Norstel wafers in its processes. Micropipe density, for example, is no longer considered an issue since high quality SiC material like ours is more or less completely free of micropipes. Other defects, like basal plane dislocations and threading dislocations have also reached low density levels never seen before, but customers would still benefit if these can be further reduced. For example threading screw dislocation (TSD) density, which is considered to have negative impact on performance and reliability of some types of SiC devices, is one quality parameter which Norstel has found to give large variations depending on how it is measured and we have spent a lot of effort confirming our results. For our presently best available power wafers we state TSD density figures of as low as 200-300 cm-2, but before such figures could be confirmed, several comparisons between measurement methods were performed. Due to the varying measurement techniques used for TSD we strongly recommend our customers process wafers in their production lines and not rely too much on data provided by their suppliers. At least for n+ substrates we believe that the industry would benefit from a standardized technique for mapping of TSDs.
YD: We have observed that to monitor wafer production quality it is key to master the whole manufacturing line from crystal seed growth to epitaxy. What are Norstel’s production capabilities?
PZ: As you say, we operate a complete production chain from bulk growth to epitaxy and it is a large advantage for us. On the other hand Norstel, even if we are leading technically, is still a relatively small supplier and we are therefore now ramping up the manufacturing capacity substantially to meet expected growth. Presently our semi-insulating wafers for RF applications are attracting a lot of interest due to their purity and lack of vanadium-doping and we are preparing for strong growth over the coming year. In conducting power wafers we expect our latest low defect production grade to generate new opportunities with major device makers and are preparing by installing new furnace, slicing and polishing capacity to meet the growing demand. Even if we rely mainly on expanding our in-house resources we also look for strategic partnerships in manufacturing to create flexibility and readiness for coming peaks in demand.
YD: Some consider that GaN-on-silicon could be an alternative to SiC. What is Norstel’s opinion on this?
PZ: SiC is our speciality and we believe that its benefits in power and RF applications will carry it a long way, even if GaN-on-silicon emerges. The progress in GaN-on-silicon reported in the last year is impressive but we are convinced that the voltage and processing limitations of GaN will make SiC still the only viable alternative to silicon in high power applications. Otherwise it remains to be seen also for us to what extent GaN-on-Si can replace silicon at the low end applications as claimed.
YD: Is there anything else that might be of interest for our readers?
PZ: Anyone who wants to meet with our team’s representatives could see us at upcoming conferences: WUPP in Fukuoka, Japan, from 20-21 August 2015 and TWHN in Takayama, Japan from 23-26 August 2015. Norstel will also exhibit at ICSCRM-2015 in Naxos, Sicily, in October.
Mr. Per Zellman is Norstel’s CEO. He holds an M. Sc. degree in Electrical Engineering from Royal Institute of Technology, Stockholm and an Executive MBA from Lund University School of Economics and Management. He has 27 years’ worth of experience from international automation and power electronic industries and management positions in R&D as well as sales and marketing and general management. Prior to Norstel Mr. Zellman worked for three years within the power engineering group Crompton Greaves. Mr Zellman joined Norstel in May 2014.
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