Gate‐recessed normally‐off GaN‐on‐ Si HEMT using a new O₂‐BCl₃ digital etching technique

Abstract

A new, semi‐self‐limiting, digital etch process using separate oxygen (O2) and boron trichloride (BCl3) plasmas to sequentially remove layers of material from AlGaN/GaN high electron mobility transistors (HEMTs) on the order of a few angstroms per cycle is presented. This novel digital or atomic layer etching (ALE) technique was used for the conversion of AlGaN/GaN HEMT devices from depletion mode (normally‐on operation) to enhancement mode (normally‐off operation). For a fixed BCl3 time of 60 sec per cycle, the etch rate per cycle was increased from 1.4 nm/cycle to 2.5 nm/cycle by increasing the O2 time per cycle from zero to 15 seconds, and remained fairly constant with higher O2 time per cycle for a self‐limiting etch process. Two GaN‐on‐Si wafers from the same CVD growth were processed side‐by‐side using the device layout and process steps, except for the depletion‐to‐enhancement conversion step, to compare ALE and fluorine treatment. The ALE‐processed had a peak gm of 250 mS/mm, 67% higher than the fluorine‐treatment process. The ALE process resulted in a threshold voltage variation of +/‐ 150 mV across the 3 inch wafer (σ = 63 mV), which was less than half of that of the fluorine‐treatment wafer. The three‐terminal breakdown voltage of the ALE‐processed wafer exceeded 1100 V, which is the first demonstration of such a high voltage device using GaN‐on‐Si and a gate recess technique, and the drain leakage current was in the μA/mm range at 1100 V. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A 16 GS/s 3‐Bit DAC Core in GaN HEMT Technology

“…The incorprated SiO 2 interlayer not only can reduce the parasitic capacitance (owing to its lower dielectric constant of 3.9 as compared to 7.5 for SiN), but also help to maintain the gate length due to its superior anisotrope when compared with SiN. After complete removal of the dielectric in the gate foot area of the E‐mode device, a semi‐self‐limiting two‐step etching technique using O 2 and BCl 3 plasma step was applied to achieve a uniform recess depth . Subsequently, the D‐mode gate foot area was opened and the gate metal of Ni/Au was evaporated.…”

Enhancement‐mode AlGaN/GaN HEMT and MIS‐HEMT technology

“…Continuous efforts focused on developing a low‐damage etching process with good uniformity and reproducibility. One approach explored the digital controlled dry etching technique using O 2 /BCl 3 4. Another method employed an in situ ‐grown‐SiN/ thin‐AlGaN barrier in which the SiN layer can be selectively etched 5.…”

High Performance Enhancement-Mode AlGaN/GaN MIS-HEMT with Selective Fluorine Treatment

“…However, most AlGaN/GaN HEMTs show normally on operation for the high-density two-dimensional electron gas (2DEG). Normally off operation on AlGaN/GaN heterostructures has been obtained with several approaches, such as recessed gate structures [3], PN junction gate structures [4], thinned AlGaN barrier [5], InGaN cap layer [6], and F − treatment [7]. F − treatment in the AlGaN layer is used to realize normally off HEMT [8] but the gate leakage during on-state operation strongly limits the device performance, especially when high threshold voltage ( TH ) and high current densities are required.…”