Overview of Advanced Technology Research Laboratories

Nippon Steel had sales of over ¥2 trillion in 1996 worldwide. In 1987, the corporation launched an effort in new materials, electronics, information, and communication technology, which is supported in part by its Advanced Technology Research Laboratories. This laboratory is one of 3 laboratories of the Technical Development Bureau of Nippon Steel. The electronic products associated with the Advanced Technology Research Laboratories include the following:

• electronics materials
  • 300-mm (12-inch) Si wafers
  • 200-mm and 150-mm SIMOX wafers
  • 25-mm (1-inch) SiC wafers (with 2-inch wafers under development)
• circuit design products
  • 60-micron fine-pitch bonding with 22-micron gold bonding wire
  • 40-micron micro ball bumps for high density LSI packaging

The laboratory employs 130 researchers. The research directions also include advanced materials design using computations, development of new glass/plastic materials (flexible glass), and new materials characterization techniques based on positron annihilation and X-ray characterization methods.

SiC program at Advanced Technology Research Laboratories

Nippon Steel produces SiC substrates grown by modified Lely method. (Several other Japanese companies might be developing SiC bulk and epitaxial growth capabilities.) Nippon Steel has shown interest in expanding its SiC program to include epitaxial growth of SiC and, possibly, of GaN-based materials. Plans are underway to develop 2-inch SiC bulk technology and (in a more distant future) 3-inch bulk SiC technology.

Most SiC work has been funded internally. However, Nippon Steel is one of the participants in the NEDO-funded National Project on Combustion Control Systems for Conservation.

The SiC substrates are doped n or p type by N and B, respectively. The doping range is from 1x10¹⁷ cm^-3 to 3x10¹⁸ cm^-3. The wafer resistivity varies from less than 10^-2 ohm cm (for n-type wafers) to more than 1000 ohm cm for p-type wafers. Breakdown voltages over 1,000 V have been demonstrated for 2x10¹⁶ cm^-2 material.

Typical surface roughness is 1.3 nm to 1.8 nm. Dislocation density is on the order of 10⁴ - 10⁵ cm^-2. The price is ¥125,000 for a 1-inch SiC wafer.

The biggest market seen in the short term is in substrates for blue GaN LEDs and laser diodes. In year 2000 and beyond, a larger market is expected in substrates for high temperature, high power electronics components.

These are some of the examples of the Nippon Steel SiC research. Ohtani et al. (1998a) have studied impurity incorporation kinetics during modified-Lely growth of SiC as a function of several growth parameters. Results show that dynamic equilibrium is established between the vapor phase and the adsorbed nitrogen. The polytype of the grown crystal and the seed orientation and face polarity affect the impurity incorporation (Takahashi et al. 1995). The AFM studies reveal a noticeable difference in the growth morphology between 6H-SiC and 4H-SiC .

Ohtani et al. has reported on the stepped structure on the {0001} facet plane of 6H-SiC. The height steps are equal to 1.5 nm (Ohtani 1998b).

This group has also reported on a dramatic reduction of the micropipe density (as revealed by KOH etch) from 1,000 to 10 cm^-2 (Ohtani et al. 1998c).

By optimizing growth conditions, the Nippon Steel group has obtained 6H-SiC and 4H-SiC samples with resistivities as low as 7x10^-3 cm and 5.37x10^-3 cm, respectively (Onoue et al. 1996).

SiC crystals have been also grown in and directions (Takahashi et al. 1997).

All in all, Nippon Steel has one of the strongest SiC programs in Japan.

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