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Development of Free Wet Etching Chemical for Interconnect

TOK (Tokyo Ohka Kogyo Co., Ltd.), Japan *Takuya Ohashi, Yukihisa Wada, Mai Sugawara, Tomoya Kumagai

IMEC, Belgium Quoc Toan Le, Els Kesters, Yusuke Oniki, Jens Rip, Frank Holsteyns

*[email protected]

© 2019 TOKYO OHKA KOGYO CO., LTD. 2 OUTLINE

1. Introduction

2. Design of Ru wet etch chemical

3. CVD-Ru Bulk properties

4. Summary

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 3 OUTLINE

1. Introduction

2. Design of Ru wet etch chemical

3. CVD-Ru Bulk properties

4. Summary

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 4 ALTERNATIVE METAL FOR INTERCONNECT

Ruthenium has been recently considered as a promising candidate to replace and as MOL and BEOL interconnect material.

✔ Low resistivity in the scaled dimensions ✔ Better EM

[Marleen H. van der Veen et al, IITC2018, IMEC]

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 5 TARGET RUTHENIUM WET-ETCH APPLICATIONS

Ru Bevel and Backside clean Liner/Metal deposition BV/BS clean CMP

Ru recess for FULLY SELF-ALIGNED VIAS

After M1 CMP M2V1 Etching M2 Fill

Metal recess

[Efrain Altamirano Sanchez, IITC2018 Short course, IMEC]

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 6 RUTHENIUM IN THE

The periodic table

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

H He

Li Be B C N O F Ne - Metal Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg TI Pb Bi Po At Rn

Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Hn FI Mc Lv Ts Og

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 7 CHEMICAL RESISTANCE OF RUTHENIUM

Commodity Pourbaix diagram of Ru- system CVD-Ru* E.R. @R.T. chemistry

HCl 0.0nm/min CAN

H2SO4 0.0nm/min

HNO3 0.0nm/min HF 0.0nm/min NaOCl

H2O2 0.0nm/min SC2 SC1 0.0nm/min H2O2 SC2 0.0nm/min SC1 NH3 0.0nm/min KOH 0.0nm/min TMAH 0.0nm/min

** CAN+HNO3 1.1nm/min NaOCl 5% 11.9nm/min [M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions * As depo CVD-Ru p. 346, National Association of Engineers, 1974-644]

** 50mM CAN (Ceric Nitrate) + HNO3 1M Strong oxidizers (CAN, NaOCl, ...) can etch ruthenium.

+ - 0 Ru(s) + 4H2O ⇔ RuO4 + 8H + 8e E = 1.032V © 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 8 OUTLINE

1. Introduction

2. Design of Ru wet etch chemical

3. CVD-Ru Bulk CVD-Ru Bulk properties

4. Summary

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 9 DESIGN OF RUTHENIUM WET ETCH CHEMICAL

TOK Ruthenium Wet Etch chemical is targeting the following requirements.

 Metal free solution

 Metal impurities should be avoided for advanced semiconductor processing.

 Currently, most of the strong oxidizers include metal elements. (CAN, NaOCl etc.)

 High selectivity to low-k, SiOx, SiNx, and TaN

 Prevent (RuO4) generation

 Volatile and toxic RuO4 should be avoided for EHS reasons.

 Preservation of surface roughness to be targeted after controlled Ru recess

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 10 DESIGN OF RUTHENIUM WET ETCH CHEMICAL

 Metal free solution

 Metal impurities should be avoided for advanced semiconductor processing.

 Currently, most of the strong oxidizers include metal elements. (CAN, NaOCl etc.)

 High selectivity to low-k, SiOx, SiNx, TiN and TaN

 Prevent ruthenium tetroxide (RuO4) generation

 Volatile and toxic RuO4 should be avoided for EHS reasons.

 Preservation of surface roughness to be targeted after controlled Ru recess

Chemical Metal Ru etching Low-k (2.55) SiN TiN TaN NaOCl Yes Good - - - - CAN Yes Good - - - - Chemical A No Good <0.1nm/min <0.1nm/min <0.1nm/min <0.1nm/min Chemical B No Good <0.1nm/min <0.1nm/min <0.1nm/min <0.1nm/min Chemical C No Good <0.1nm/min <0.1nm/min <0.1nm/min <0.1nm/min

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 11 DESIGN OF RUTHENIUM WET ETCH CHEMICAL

 Metal free solution

 Metal impurities should be avoided for advanced semiconductor processing.

 Currently, most of the strong oxidizers include metal elements. (CAN, NaOCl etc.)

 High selectivity to low-k, SiOx, SiNx, TiN and TaN

 Prevent ruthenium tetroxide (RuO4) generation

 Volatile and toxic RuO4 should be avoided for EHS reasons.

 Preservation of surface roughness to be targeted after controlled Ru recess

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 12 RUTHENIUM TETROXIDE

Mechanism of RuO4 toxic gas generation

Ru(s) + *CAN(Ⅳ) ⇒ RuO4↑ + Ce(Ⅲ)↓

*CAN (Ceric Ammonium Nitrate)

Ruthenium tetroxide is volatile and toxic.

Furthermore, RuO4 is a strong oxidizer.

[H. Aoki et. al Extended Abstracts of the 2001 International Conference on State Device and Materials. 2001]

Staining reaction by OsO Plastic coloration by RuO4 reaction 4 O O O O RuO and OsO are used as agent for 4 4 Os TEM observation of polymeric materials. Os O O O O

 OsO4 : Oxidize unsaturated type polymer C C C C

 RuO4 : Oxidize saturated and unsaturated type polymer H H H H

Staining reaction can be used to detect the generation of RuO4 © 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 13 RUTHENIUM TETROXIDE GENERATION TEST PLASTIC COLORATION BY RUTHENIUM TETROXIDE GAS Bottle A : Reference Plastic

2days

Chemical

Bottle B : Ru wafer dipping (Bottle C : Ru Powder dipping)

RuO4 RuO4

RuO 2days CVD-Ru/40ml RuO 4 RuO4 4 (2×2cm, 30nm) Check discoloration of the RuO RuO or 4 4 plastic on top of the bottle Ru powder 0.01g/10ml

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 14 RESULT OF PLASTIC COLORATION TEST PLASTIC COLORATION BY RUTHENIUM TETROXIDE GAS w/Ru WF w/Ru powder Chemical Bottle A w/o Ru Bottle B w/Ru WF Bottle C w/Ru powder NaOCl NaOCl NaOCl No change Change to black Change to black CAN No change Change to black Change to black Chemical A No change Change to black Change to black CAN Chemical B No change No change No change CAN Chemical C No change No change No change

SEM-EDX of plastic C Ru Chemical A Chemical A O

Chemical B Chemical B

Chemical C Chemical C

Chemical B and C can prevent RuO4 gas

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 15 OUTLINE

1. Introduction

2. Design of Ru wet etch chemical

3. CVD-Ru Bulk properties

4. Summary

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 16 CVD RUTHENIUM BULK PROPERTIES

IMPACT OF THERMAL BUDGET OF POST DEPOSITION ANNEAL IN N2/H2 (FGA)

© 2019 TOKYO OHKA KOGYO CO., LTD. 17 IMPACT ON ETCHING BEHAVIOR

IMPACT OF THERMAL BUDGET OF POST DEPOSITION ANNEAL IN N2/H2 (FGA) By NaOCl 5% wet etching @R.T. (See SPCC2019 Q.T. Le for more detail)

Etching rate decrease and delay for higher anneal temp.

Passivation by surface ?

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 18 RUTHENIUM OXIDE GROWTH

IMPACT OF THERMAL BUDGET OF POST DEPOSITION ANNEAL IN N2/H2 (FGA)

© 2019 TOKYO OHKA KOGYO CO., LTD. 19 RUTHENIUM WET ETCHING BEHAVIOR

NaOCl 5% @R.T. CAN50mM+HNO3 @R.T.

Chemical C @R.T. Chemical C @35°C

Chemical C @35°C can break through

the passivation layer in© a201 short9 TOKYO OHKAtime KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 20 DESIGN OF RUTHENIUM WET ETCH CHEMICAL

 Metal free solution

 Metal impurities should be avoided for advanced semiconductor processing.

 Currently, most of the strong oxidizers include metal elements. (CAN, NaOCl etc.)

 High selectivity to low-k, SiOx, SiNx, TiN and TaN

 Prevent ruthenium tetroxide (RuO4) generation

 Volatile and toxic RuO4 should be avoided for EHS reasons.

 Preservation of surface roughness to be targeted after controlled Ru recess

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 21 SURFACE ROUGHNESS

30nm CVD-Ru (FGA 420°C 20min) AFM 5×5um2 NaOCl CAN+HNO Chemical C Chemical C@35°C Reference 3 4.8nm etch 9.9nm etch 6.8nm etch 8.8nm etch

2.5

2 : Pit corrosion 1.5 Rq Ra 1 : Particle

0.5 Surface roughness

0 Ref. NaOCl CAN+HNO3 Chemical C Chemical C @35C No significant surface roughness change observed with Chemical C

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 22 OUTLINE

1. Introduction

2. Design of Ru wet etch chemical

3. CVD-Ru Bulk properties

4. Summary

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 23 Summary

 New chemical is developed for Ru BV/BS clean and controlled recess.

 TOK Ru etching chemical targets the following requirements a. Metal free process (no need for an additional clean step)

b. Eco and tool friendly process (no RuO4 by product) c. Preservation of surface roughness after controlled Ru recess d. High selectivity to dielectrics and barrier

Chemical Metal RuO4 by product Ru etching Roughness Selectivity* NaOCl Yes Yes Good Non uniform - CAN Yes Yes Good Non uniform - Chemical B No Undetected Good Good Good Chemical C No Undetected Good Good Good

*low-k, SiN, TiN and TaN

© 2019 TOKYO OHKA KOGYO CO., LTD. ©2019 Tokyo Ohka Kogyo Co., Ltd 24

Thank you for your kind attention.

© 2019 TOKYO OHKA KOGYO CO., LTD.