Annealing treatment in N₂ ambient (before RIE and acid treatment)

A problem in the beginning of study

A study of pretreatment process on selective area growth of GaN

using SiN masks S. Man1, R. Kayanuma1, Y. Takei1, T. Takahashi3, T. Ide3, M. Shimizu3,

K. Tsutsui1,K. Kakushima1, H. Wakabayashi1, Y. Kataoka2 and H. Iwai2

Tokyo Tech. 1, Tokyo Tech. FRC2, AIST Advanced Power Electronics Research Center3

Email: man.s.aa@m.titech.ac.jp

Backgroud・ Purpose of this work

Improving quality of epitaxial layers（ELO technology）

Fabrication technique of nano devices

Promising for forming a three dimensional structure with

a high quality

a variety of

applications

mask

GaN GaN

MOCVD

Reasons for using SiN mask・Subject

Selective area growth of GaN

It was reported that GaN is not grown on SiN.

Oxygen contamination to GaN by SiO2 mask will be suppressed.

Acid treatment

Experimental Procedures:

SiN GaN

2µm

・Growth of GaN was not

observed.

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Some pretreatment processes are required to solve the problem

that GaN was not grown.

・GaN was grown with island

shapes

5µm

GaN SiN

Acid treament to clean GaN surface had some effects for GaN

growth. However, GaN was not grown appropriately.

RIE(reactive ion etching) treatment

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

depth：20nm

GaN SiN

5µm

・GaN was grown as a continuous

film.

・The surface of grown GaN was

rough.

RIE treatment was effective for growth of GaN. However, surface

roughness and inhibition of growth near SiN mask were problems.

Annealing treatment in MOCVD reactor (between RIE and acid treatment)

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

Sapphire

GaN

SiN

We expect to establish the process of the

selective area growth of GaN using SiN mask

so that GaN is grown appropriately as in the

right figure.

Purpose of this work

GaN

SiN mask

SiN GaN

5µm

SiN GaN

5µm

Annealing treatment in MOCVD reacto rwas remarkable to solve the

problem that GaN was not grown near the SiN mask edges.

However, surface roughness of grown GaN was remained.

(something on the GaN

surface inhibited GaN

growth ?)

SiN GaN

5µm

SiN GaN

5µm

Process of selective area growth of GaN using SiN mask has not been

established yet.

Conclusion

・For growth of GaN, RIE treatment is more effective than acid treatment.

SiN

GaN

Sapphire

1. Deposition of

SiN films on

GaN epi-layer

(by sputtering method)

Resist SiN

GaN

Sapphire

3. SiN etching by BHF

for 5min.

Resist

SiN

GaN

Sapphire

2. Resists patterning

to form

stripe windows

(by photolithography)

4. Resists were removed

5. GaN was grown

by MOCVD with

conditions for 300nm

growth at 1040℃

Grown GaN

Sapphire

GaN

SiN

Results（by SEM）:

(a) plane veiew (b) cross section

Fig 1. SEM micrographs after GaN selective growths

Experimental Procedures (partially omitted):

Treated by

H2SO4/H3PO4(3:1) 200℃ 30min

Resists were removed The growth of GaN

Results（by SEM）:

Fig 2. SEM micrographs after GaN selective growths with acid treatment

(a) plane view (b) cross section

(Some of inhibitors were

removed？)

Experimental Procedures (partially omitted):

Treated by

RIE with BCl3 and Cl2 gas Results（by SEM）:

Fig 3. SEM micrographs after GaN selective growths with RIE treatment

(a) surface (b) cross section

・GaN was not grown near the SiN

mask edge.

Experimental Procedures (partially omitted):

Treated by RIE

with BCl3 and Cl2 gas

Treated by annealing with

NH₃+H₂, 1040℃, 10min

（in MOCVD reactor）

Treated by

H2SO4/H3PO4(3:1)

150℃ 1h

Resists were removed The growth of GaN

The growth of GaN

Results（by SEM）:

Fig 3. SEM images after GaN growths without and with annealing treatment in MOCVD reactor. (a) without annealing (b) with annealing

・GaN was grown as a continuous

film.

・The surface of grown GaN was

rough.

・GaN was grown appropriately

near SiN mask edges.

Experimental Procedures (partially omitted):

Treated by annealing in

N₂, 1040℃, 10min

（by RTA: rapid thermal process）

Treated by

H2SO4/H3PO4(3:1)

150℃ 1h

The growth of GaN Treated by RIE

with BCl3 and Cl2 gas

Results（by SEM）:

Fig 3. SEM micrographs after GaN growths with annealing treatment by RTA in N2 ambient. (a) ) plane view (b) cross section

・GaN was grown appropriately

near SiN mask edges.

・The surface of grown GaN was

flattened.

Annealing treatment in N2 before RIE and acid treatment is

remarkable to solve the problem of surface roughness of grown GaN.

・By annealing treatment, GaN was grown appropriately near SiN edges.

・Surface roughness of grown GaN was suppressed by changing the order

and conditions of annealing treatment. Further optimization is expected.