AlGaAs/1nGaAs HEM[Ts Passivttedwith Atomrc Layer Deposited SiO2
using Aminosilane Precursors
Takayuki Suzuki,Yosulce Takigawa,Naotaka lwata,Dongyan Zhang,and Yoshio Ohshia
Toyota Technological lnstitute
2‑12… 1,Hisakata,Tempaku,Nagoya,Aichi 468‑8511,Japansd15420(DtoyOta¨ ti.acjp

Abstract-Atomic layer deposited SiO2 has been applied toTABLE I

AlGaAs/InGaAs high electron mobitity transistors fimMTs)

GROWl■ RATE PER CYCLE AND ETCHING RATE OF

ALD― SI02FLMSUSING BEMAS m 3DNIAS

for surface passivation employrng bis(ethylmethylamino)silane(BEMAS) and tris(dimethylamino)silane (3DMAS). TheBEMAS SiO2 HEMT has achieved a lower on-resistance, ascompared to the 3DMAS. This suggests excellent terminationof surface dangling bonds by BEMAS.

Keywords-AlGaAs/InGaAs;(.iro*1h ratc pcr e1,cie[:tching ratclnrrr rlclcl

fnm slBEヽ AS SiC)ュ

O11162

3DMAS Si0101)ヽ

315

high electron mobility

toransistor (HEMT); surface passivation; SiO2; atomic layet
deposition (ALD) ; bis(ethylmahylamino)silane (BEMAS).
SourceI.

Ilr-rnonucrloN

AlGaAs/InGaAs high eleckon mobility transistors(IIEMTs) which show excellent performances including alow on-resistance and a high current gain cut offfrequency

are used for low noise amplifiers of direct broadcast
satellite TV services. For obtaining the performances, SiOz
is deposited on a device surface commonly by thechemical vapor deposition (CVD) method [1]. However,termination of dangling bonds by CVD is restricted due toits deposition mechanism of gas phase reaction. Dangling
bonds on the semiconductor surface near the gate electrodeact as trapping defects. Electrons trapped at the defects
enhance the surface potential of the I{EMT, thus
decreasing an electron concentration in the channel. As aresult, a channel current decreases. In this study, wecharacteized the effects of SiO2 passivation films on
HEMTs by the atomic layer deposition (ALD) method

which shows excellent capability for termination ofdangling bonds using aminosilane precursors l2l,l3l.

II.

EXPERnIENTALPRocEDURES

SiOz films were formed at a substrate temperature of150 oC by the plasma enhanced ALD, wherebis(ethyknettrylamino)silane @EMAS: H2Si[N(CrH5XCH3)]r)and tris(dimethylamino)silane (3DMAS: HSi[N(CI{3)rh)[3] were employed as precursors. The plasma enhanced
ALD-SiO2 can be deposited using an alternate supply ofprecursor and oxygen plasma. A procedure of the film
formation is as follows; the Ar flowed constantly at 100
sccm during the entire cycle as diluted and purge gas. The

precursor was firstly introduced to the reactor to beabsorbed on a semiconductor surface during 0.4 s with avapor pressure at a room temperature. Five seconds lateq
remote oxygen plasma generated by a 13.56 MIIZ RFpower of 300 W was exposed to react with precursor absubed978‑1‑4799‑8615‑6115'S3100@2015 1EEEFigure 1. Schematic cross section of the AlGaAs,{InGaAs HEMT.

on the surface for 20 s. These two steps were repeated toform the SiO2 film.

The ALD-SiO2 using BEMAS and 3DMAS wereevaluated by a growth rate per cycle (GPC) and an etchingrate in buffered hydrofluoric acid (HF : NII+F : 1 : 5). Theresults of the GPC and the etching rate are shown inTable 1. The GPC of BEMAS SiOz film was about 2 times
higher than that of 3DMAS. This is due to the larger
number of Si-H bonding of BEMAS. In addition, theetching rate of BEMAS is half of 3DMAS Sio2. These
results impty that BEMAS is more reactive than 3DMAS,
thus resulting in tightly bounded SiOz.
The structure of a fabricated AlGaAs/InGaAs HEMT isschematically illustrated in Fig. 1. Epitaxial layers weregrown on a semi-insulating GaAs substrate by themolecular beam epitaxy method. For fabricating HEMTs,
mesa isolation was firstly achieved with the wafer. Then,
AuGeNi was deposited on the patterned wafer for sourceand drain electrodes by the vacuum evaporation method,oC for 60 s. Next, aand the wafer was annealed at 430
recessed gate structure was formed utilizing InGaP as anetching stoppff layerby a self-aligned technique [4]. Then,
Al was deposited by tlre evaporation method, and gate
elecEodes were formed employing the lift-off technique.
Continuously, SiO2 with 3 nm thick was deposited on the‑26‑

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