Wednesday, May 6, 2015

ALD oxides used in vertical gallium nitride MOSFETs with reduce on-resistance

As reported by Semiconductor Today: Toyoda Gosei Co Ltd in Japan has developed a vertical trench metal-oxide-semiconductor field-effect transistor (MOSFET) on free-standing gallium nitride (GaN) combining 1.2kV blocking voltage with low specific on-resistance [Tohru Oka et al, Appl. Phys. Express, vol8, p054101, 2015]. The researchers comment: "To the best of our knowledge, this is the first report on vertical GaN-based MOSFETs with a specific on-resistance of less than 2mΩ-cm2." 

Interestingly the integration employs a 80 nm ALD SiO2gate dielectric and a100 nm ALD Al2O3 800 nm PECVD SiO2 combo interdielectric. This basically shows two things:

1) Oxides by ALD is not all about high-k
2) ALD is also used for relatively thick layers and not only 10 to 100 Å in microelectronics



Figure 1

Transistor fabrication (Figure 1) involved inductively couple plasma (ICP) etching for mesa isolation, p-body contact recessing, and gate trenching. The gate dielectric was 80nm silicon dioxide, grown using atomic layer deposition (ALD). Interlayer dielectrics of 100nm aluminium oxide and 800nm silicon dioxide were produced by atomic layer deposition and plasma-enhanced chemical vapor deposition (PECVD)(Picture from Semiconductor Today).