Technical-Report

Device Isolation Processing ofGaN on Si Power Devices
Process Development Department 1, Samco, Inc.

▪ Introduction
Gallium nitride (GaN)-based semiconductors are expected to supersede
Silicon (Si) as the material for next-generation power devices and have beenstudied and developed together with Silicon Carbide (SiC) due to their excellent
physical properties1. GaN-based semiconductors are already in practical use
in the high-frequency device and power device fields, and the market is likely toexpand further2. In particular, electronic devices such as GaN-HEMTs, whichrequire low ON-resistance and high channel mobility, have been fabricated on
Si substrates3, and production using ø6˝ and ø8˝ substrates is underway.
We provide ICP-RIE and CVD systems and process technologies for GaNbased light-emitting devices, and have a proven track record in R&D andmass production. In this report, we introduce the device isolation process ofGaN-based power devices formed on ø6-inch Si substrates using the RIE800iPC ICP-RIE system for mass production.

Figure 1. ICP-RIE system RIE-800iPC

Figure 2 displays the actual processed sample structure where a photoresist (PR)is applied to a GaN and AlGaN layer (5.5 µm) formed on a ø6-inch Si substrate,
which is exposed and developed. The aperture area of the PR pattern is about
10%. Since the element isolation process is an etching process to reach theSi substrate, a degree of over-etching is required. However, excessive overetching must be avoided, necessitating etching uniformity within the wafer.

PR mask
GaN + AlGaN(5.5 μm)

Etching▪ Sample Structure and Processing Requirements
PR mask
GaN + AlGaN(5.5 μm)

Si substrate▪ Etching Endpoint Detection and Observation Results
Figure 2. Sample structure

In order to strictly monitor the progress of over-etching, an optical emission
spectroscopic endpoint monitor, which can accurately detect the endpoint
using differences in material composition, was used in this report.
The measurement results from the endpoint monitor are shown in Figure 3.
The green and red line waveforms represent the emission intensities of N2 andSi, respectively. After etching the GaN + AlGaN layer to reach the Si substrate,changes in emission intensities are evident as Si etching commences. In thisinstance, Si was over-etched for about one minute. Following over-etching, Si
luminescence intensity (red line waveform) was detected consistently.
Lot ID[RLotID] Wafer[1]
ϭϬϬ

ϭϬϬϬ

ϵϬ

ϴϬϬ

Signal (a.u.)ϲϬϬGreen waveform ofemission intensities of N2ϳϬ
ϲϬ

ϰϬϬ
ϮϬϬ

ϱϬ

Ϭ

ϰϬ

ͲϮϬϬ

Red waveform of emission
intensities of Si(Al and Ga also superimposed)

ϯϬ
ϮϬ

ͲϰϬϬ
ͲϲϬϬ

ϭϬ

Figure 3. Endpoint detection
by optical emission
spectrometer (OES)

vol.122 / 2023. JUL.

Ϭ

Derivative Signal1 (a.u.)ϴϬͲϴϬϬ
Ϭ

Cursor time (1249.0s)

ϳϴϬEmission changes witharrival of Si substrateͲϭϬϬϬElapsed Time (1249.0s)

1Technical-Report
The SEM cross-sectional observation results of the etched ø6-inch full wafer
are shown in Figure 4: after GaN + AlGaN (5.5 μm) penetration, the Si substrate
was over-etched by about 1.3 μm as targeted, consistent with the emission
spectroscopy observation results. A processing shape with a forward taperof about 40° was obtained. This is because the initial shape of the PR mask
is about 60°, which is the target shape. To obtain a vertical shape, a vertical
PR mask or a hard mask such as SiO2 can be used.

GaN + AlGaN (5.5 µm)

Si substrate

Figure 4. Cross-sectional SEM imageϭϬϬϬϭϬ͘ϬϬϵϬϬϵ͘ϬϬϴϬϬϴ͘ϬϬϳϬϬϳ͘ϬϬϲϬϬϲ͘ϬϬϱϬϬϱ͘ϬϬϰϬϬϰ͘ϬϬϯϬϬϯ͘ϬϬϮϬϬϮ͘ϬϬϭϬϬϭ͘ϬϬϬϭ Ϯ ϯ ϰ ϱ ϲ ϳ ϴ ϵ ϭϬ ϭϭ ϭϮ ϭϯ ϭϰ ϭϱ ϭϲtĂĨĞƌEŽ͘hŶŝĨŽƌŵŝƚǇ΀㼳й΁PR mask
PRmask'ĂEнů'ĂEƚĐŚŝŶŐZĂƚĞ΀ŶŵͬŵŝŶ΁

Figure 5 shows the results of continuous processing of 16 ø6-inch fullwafers. The etching rate was stable at 600 nm/min or higher, and all showed
excellent in-plane uniformity of ±3% or less. The repeatability among the 16wafers was ±2.46%, representing an impressive outcome. The etching rate
was derived from the time the Si substrate was reached, as measured by
an optical emission spectroscopic endpoint monitor. For in-plane uniformity,
etching depths at five points (center and four peripheral points (5 mm fromthe edge)) were measured with a step-measuring device.

Ϭ͘ϬϬFigure 5. Results of repeatability of 16 wafers continuous process▪ Conclusion
The mass production ICP-RIE system, RIE-800iPC, demonstrated its
proficiency in the separation and processing of GaN-based power devices.
The RIE-800iPC, a production system with excellent process reproducibility,
can not only etch GaN-based semiconductors, but also process compound
semiconductors such as GaAs and InP, Si-based semiconductors such as
SiO2 and SiN, ferroelectric materials such as PZT and Pt, metal materials,
and resin materials such as polyimide. GaN-based power devices are key
devices for realizing a low-carbon society. Our commitment to developing
process technologies for GaN-based power devices contributes to thisimportant societal goal.

▪ References
1 Jun Suda, Masahiro Horita, Kazutaka
Kanegae. “Evaluation of point defects forrealization of GaN vertical power devices.”
JSAP 90.10 (2021): 628-631.
2 Kumazaki, Yusuke, et al. “Over 80% poweradded-efficiency GaN high-electron-mobility
transistors on free-standing GaN substrates.”
Physics Express 14.1 (2020): 016502.
3 Egawa, Takashi. “Growth of GaN single
crystals on Si substrates and their device
applications.” JSAP 81.6 (2012): 485-488.

Samco Inc.
For more information please email: info@samco.co.jp
vol.122 / 2023. JUL.

URL: https://www.samco.co.jp/en/2