Development of Atomic Layer Etching (ALEt) for GaN-based materials

(1)

HAL Id: hal-02008012

https://hal.archives-ouvertes.fr/hal-02008012

Submitted on 5 Feb 2019

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Development of Atomic Layer Etching (ALEt) for GaN-based materials

Congying You, C. Mannequin, G. Jacopin, T. Chevolleau, C. Durand, C. Vallee, H. Mariette, M. Sasaki, E. Gheeraert

To cite this version:

Congying You, C. Mannequin, G. Jacopin, T. Chevolleau, C. Durand, et al.. Development of Atomic Layer Etching (ALEt) for GaN-based materials. International Workshop on Nitride Semiconductors, Nov 2018, Kanazawa, Japan. �hal-02008012�

(2)

Development of Atomic Layer Etching (ALEt) for GaN-based materials

Congying You

1,2*

, C. Mannequin

1 , G. Jacopin

2 , T. Chevolleau

3 , C. Durand

4 , C. Vallée

1,3

, H. Mariette

1,2

,

M. Sasaki

1 , E. Gheeraert

1,2

_{*E-mail: congying.you@neel.cnrs.fr}

1

_{University of Tsukuba, Tsukuba 305-8573, Japan,}

2

_{Univ. Grenoble-Alpes, Institut Néel, 25 Avenue des Martyrs, Grenoble 38000, France,}

3

_{Univ. Grenoble-Alpes, LTM, Grenoble 38000, France,}

4

_{Univ. Grenoble-Alpes, INAC/PHELIQS, 18 Avenue des Martyrs, Grenoble 38000, France}

1. What is Atomic Layer Etching (ALEt)?

1

Advantages:

• Fast and deep etching

• Separate controlled of Plasma density (neutrals, radicals, ions), Ionic Fluxes and Ions Energies

Advantages:

- Separation:

Chemistry (precursor)/ionic bombardment (co-reactant)

- Etch rate controlled by Numb. of cycles

- Different plasma (or gases): for chemistry and ionic bombardment

Challenges:

- Keep the “self-limiting” feature - Slow:

Etch profile defined by Numb. of cycles (< 1nm/cycle) - Monitoring of etched thickness

Limitations:

• Simultaneous effect of chemistry and ionic bombardment • Difficult to control Surface States (morphology and

composition)

Atomic Layer Etching

2. Experimental procedures

sapphire GaN (3 μm) SiO₂(450nm) sapphire GaN (3 μm) SiO₂ coating SQW sample SiO₂ patterning SiO₂ sapphire GaN (3 μm) ALEt 200 cycles SiO2 sapphire GaN (3 μm) SiO₂ sapphire GaN After-etch Characterization sapphire GaN (3 μm) sapphire GaN (3 μm) Photoresist (1400nm) sapphire GaN (3 μm) PR PR ALEt 200 cycles sapphire GaN (3 μm) PR PR sapphire GaN After-etch Characterization Photoresist (PR) coating PR patterning

Capping layer: GaN (5 nm ) Single quantum well: InGaN

with 18% In (2.75 nm; 750°C ) GaN (20 nm; 850°C) Underlayer: InGaN with 3-5% In (50 nm; 750°C) sapphire GaN (3 μm)

Thomas Swan (AIXTRON) MOCVD

Development of ALEt on SAMCO ICP-RIE 200 iP

Deposition:

GaN layers with embedded

InGaN Single Quantum

Well (SQW)

Holes fabrication process and Experimental procedures:

1- Planar GaN layer

2- Planar InGaN SQW layer

PR removed sapphire

GaN

SAMCO ICP-RIE 200iP

+

ICP-Coil

RF-Source

(Wsource)

Polarization

RF-Bias

(Wbias)

Plasma Neutrals,Radicals Ions

Ions

Energies:

V

_plasma

– V

_DC

(Wbias)

Plasma density:

Neutrals, Radicals

Ions

(Wsource)

+

Other

Parameters:

Gas comp.

Pressure

Exposition

time

Our ALE process (to be patented):

Total repetition: 200 ALEt cycles

pur

ge

Cl

₂

time

1st _cycle 2nd _cycle ₃rd _cycle

Adsorption

pur

ge

Activation

Cl₂-based gas mixture (M_ad) Exposure time t_ad Wsource No Wbias Gas mixture (M_ac) Exposure time t_ac Wsource Wbias

4. Comparison of in- and out-of ALEt window etched samples

3. ALEt Etch rate as a function of Activation Bias

etched SQW samples with gas X: ICP/Bias 100/25W (Vdc=19V) (top) and ICP/Bias 100/45W (Vdc=32V) (down) and death layer on the etch edge

Cathodo-Luminescence of SQW samples : Estimation of deadlayer thickness

SEM SQW CL signal_T=300K SQW CL signal T=300K SEM 400nm 1um

Effect of Wbias on ALE etching rate

and

( Self-bias voltage and ion energy)

0 0,5 1 1,5 2 2,5 3 0 5 10 15 20 25 30 35 40 e tc h r ate/cycl e (nm) Vdc(V) 1 monolayer/cycle 2 monolayers/cycle

Etch rate in function of the self-bias voltage

0 0,5 1 1,5 2 2,5 0 5 10 15 20 25 30 35 40 Et ch r ate/cycl e (nm) Vdc (V)

Etch Rate in function of the self-bias voltage

1 monolayer/cycle 2 monolayers/cycle

Argon _{Gas X}

Atomic Layer Etching window

Optimization of the Activation step:

The best Etch rate: near 2 monolayers/ cycle

Gas X have a better control of ALEt

RMS=68pm

RMS=177pm RMS=428pm

For undoped-GaN

and GaN + embedded SQW GaN

200 ALE cycles

Etching rate = etched thickness (SEM)/200

Contrast SEM: 370nm (tilted edge) Dead layer(CL 425nm slope): 900nm

pur

ge

Cl

₂

time

1st _cycle

Adsorption

pur

ge

Activation

Cl₂-based gas mixture (M_ad) Exposure time t_ad Wsource No Wbias Gas mixture (M_ac) Exposure time t_ac Wsource Wbias

M

_ac

= Ar

M

_ac

= X

SiO₂-masked samples _{In-window quasi-ALEt} _{Out-of-window cyclic etching}

Contrast SEM: 175nm (sharp edge) Dead layer(CL 425nm slope): 400nm In-window quasi-ALEt

Out-of-window cyclic etching

6. Conclusions and perspectives

tad - tp - tac+15 - tp

ER about 0.74

t

ad

+1 - t

p

- t

ac

- t

p

ER 0.59nm/cycle

Activation step

Not fully self-limiting Need to improve

Adsorption step self-limiting verified

longer adsorption time

longer activation time

tad+2 - tp - tac – tp

ER 0.57nm/cycle

Optimizations  real ALEt +limiting the dead layer

Improve the Activation step (take a Bias on the ALEt windowchange the ICP power);

change pressure in different steps, etc

verify other advanced properties Apply to Electronic/optoelectronic device

5.Demonstration of the self-limiting

1. Gas X has a better etch control on the ALEt process

2. Quasi ALEt has a better etch quality: sharp border; thinner dead layer

t

ad

- t

purge

(t

p

)- t

ac

- t

p

ER 0.58nm/cycle

tad - tp - tac+5 - tp

ER 0.59nm/cycle Base point (gas X in-window sample)