PUBLIC

COBALT PRE-METALLIZATION CLEAN AND FUNCTIONAL WATER

RINSE IN BEOL INTERCONNECTE. KESTERS*1, Q.T. LE1, M. VAN DER VEEN1, Y. AKANISHI2, H. IINO3, A. MIZUTANI4,

AND F. HOLSTEYNS1

1* Imec, Kapeldreef 75, 3001 Heverlee, Belgium – kesterse@imec.be – +32 16 288609

2 SCREEN Semiconductor Solutions Co

3 Kurita Ltd.

4 Fujifilm Electronic Materials (Europe) N.V.

SPCC 2019, Portland, April 1-3rd, 2019

OUTLINE

▪ BEOL pre-metallization cleaning

▪ Introduction

▪ Galvanic corrosion study

▪ Background

▪ Different combinations of metals

▪ Effect of HF pre-treatment: role of dissolved oxygen and oxygen ambient atmosphere

▪ Co pre-metallization clean and functional water rinse

▪ Co corrosion prevention

▪ 22 nm HP using Co fill at M1in BEOL: electrical, TEM (EDS)

▪ Alternative contact Co metal in MOL: FIB-SEM

▪ Summary and outlook

2

BEOL PRE-METALLIZATION CLEAN: INTRODUCTION

3

and on wafer discharge

MATERIAL LOSS PREVENTION DURING WET CLEAN:

EFFECT OF HF PRE-TREATMENT ON GALVANIC CORROSION

BACKGROUND

5

Pre-metallization clean

▪ Need for cleaning with minimum etching of exposed metals

▪ Exposed metal interface (e.g. metal fill and liner/barrier metals)

➔ concern of galvanic corrosion during wet cleaning when

bimetal is exposed → causes unwanted metal loss

▪ Introduction of new interconnect material with barrier/liner

Objectives

▪ Investigation & prevention of galvanic corrosion occurrence during wet clean

▪ Study corrosion characteristics between different metal types

▪ Impact of oxygen atmosphere and dissolved oxygen (DO) is investigated in dHF cleaning for different

combinations of metals

Plasma-modified low-k layerPost-etch residues

Metal

(Cu, Co, W)

Low-k dielectric

Bottom Hardmask

Top Hardmask (TiN)

BACKGROUND

6

Galvanic corrosion:

▪ Large difference of electrode potentials of the metals in contact can cause

galvanic corrosion

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Li K Ca Na Mg Al Ti Mn Ta Zn Cr Fe Cd Co Ni Sn Pb H Cu Ru Hg Ag Pt Au

Sta

nd

ard

Ele

ctr

od

e P

ote

nti

al [V

]

Electronegative

Electropositive

electron supplied by the “Metal A dissolution reaction”, is consumed for the O2 reduction at

the Metal B interface

→ By eliminating dissolved O2 (DO) from cleaning solution, these reaction is estimated to

be suppressed

Cu

Co

ΔVCu-Co=0.62

GALVANIC CORROSION STUDY: DIFFERENT METAL COMBINATIONS

7

▪ Test structure

▪ Damascene test vehicle: 45nm HP metal hanging trenches with different barrier/liner

▪ Test Flow

0.05% HF 60-180s RT

DO : 30~3000ppb

Coupon on

Dummy

DryRinse

X-SEM

TEM

Objectives and experiments

▪ Study the impact of dissolved oxygen (DO) on

galvanic corrosion at Co/Cu interface

▪ HF (1:1000, RT) on Screen Single Wafer Cleaning

Tool (SU-3200)

▪ Variables: dissolved oxygen concentration

(30-3000 ppb) and cleaning time (60-180s)

Ref: Y. Akanishi et al., Solid State Phenomena,

1012-0394, Vol. 282,p.256-262

EFFECT OF DISSOLVED OXYGEN (DO) ON Co/Cu CORROSION

8

Incoming sample

(post CMP)30 ppb DO/ 180 s 3000 ppb DO/ 60 s 3000 ppb DO/ 180 s

500 ppb DO/ 180 s

30 and 500 ppb of DO: no visible galvanic corrosion observed

3000 ppb of DO: clear corrosion occurred at the Cu/Co interface

Co/TaN

(liner/barrier)

Cu

OSG2.55

9

EFFECT OF DO CONCENTRATION ON Co/Cu CORROSION: TEM RESULTS

▪ Galvanic corrosion of Co was observed with higher DO condition, even in very small trenches (~5nm)

▪ Chemical etching and galvanic corrosion (both enhanced by dissolved oxygen)

▪ By controlling DO in HF, galvanic corrosion of Co can be suppressed

▪ Cu is also slightly recessed with higher DO condition

▪ Chemical etching continuous after Co is lost by galvanic corrosion

30 ppb DO 30 ppb DO

CORROSION BEHAVIOR OF TaN/Co/Cu

10

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Li K

Ca

Na

Mg

Al

Ti

Mn

Ta

Zn

Cr

Fe

Cd

Co Ni

Sn Pb H

Cu

Ru

Hg

Ag Pt

Au

Sta

nd

ard

Ele

ctr

od

e P

ote

nti

al

[V]

ΔVCu-Co = 0.62

Co loss by galvanic corrosion

@Co : Co ➔ Co2+ + 2e-

@Cu : O2 + 4H+ + 4e-➔ 2H2O

Cu chemical etching after Co

is etched

Cu

Co TaN

Reference

No data for TaN potential

Electropositive

Electronegative

EFFECT OF DISSOLVED OXYGEN (DO) ON TiN/Co CORROSION

11

Ref0.05% HF 180sec RT

30 ppb 1200 ppb 3000 ppb

▪ Incoming surface has already some roughness induced by CMP

▪ Co recess amount increases as DO increases, Co is completely removed at 3000 ppb

▪ Mainly due to chemical etching of HF solution

▪ Not clear from x-sem if TiN is removed or not

Whole Co lost

Co

TiN

Reference

TiN: ??

OXYGEN AMBIENT ATMOSPHERE IMPACT ON GALVANIC CORROSION

12

Test flow

Cross section

45nm HP

Cu/TaNCo pattern DHF 180s

(1:1000 RT, 30 ppb DO)

In Air

In N2

X-SEM

(Center, Middle, Edge)

N2

Atmosphere Center (R=0) Edge (R=110mm)

Air

N2

TEM

Galvanic

corrosion?▪ Co liner (5 nm) dissolved at wafer edge

after HF clean in Air atmosphere

Dissolved oxygen concentration & oxygen

ambient atmosphere control is needed for

galvanic corrosion control

OXYGEN AMBIENT ATMOSPHERE IMPACT (TEM/EDS MAP)

13

▪ Void at bottom corner (& partially

on sidewall)

▪ Co signal negligible

▪ Ta layer diffusion

▪ Oxide on Cu surface (native oxide)

▪ No void or gap between Cu and

barrier/liner

▪ Co liner remains uniformly

▪ Oxide on Cu surface (native oxide)

AIR

N2

Co PRE-METALLIZATION CLEAN AND FUNCTIONAL WATER RINSE

Co CORROSION PREVENTION

15

Pourbaix diagram of Co▪ For the post-etch residue removal (PERR)

▪ FFEM formulated chemistry required to suppress any metal corrosion

▪ Approach for Co Loss reduction in rinsing water

▪ Conventional rinse water (CO2W / DIW) causes Co corrosion

▪ Two approaches assessed to reduce the Co loss during rinse

Co loss can be suppressed by pH adjust functional water rinse:

NH4OH water (pH control)

Further Co loss reduction is achieved by H2O2 addition which forms passivation

layer on Co surface:

NH4OH + H2O2 water (Oxidation Reduction Potential - ORP control)

H. Iino et al., Solid State Phenomena 282, 268-272 (2018)

H. Iino et al., SPCC 2019

Co PRE-METALLIZATION CLEAN

▪ Test Structure: 22 nm HP structures

▪ M2 Cu & V1 Cu on M1 Co

▪ Via resistance (Kelvin via, 25 dies) measured

after via clean split performed with different

rinse conditions

▪ Test flow

16

Purpose M2 Via clean

Cu-on-Cu POR for Cu

Co clean test #1 FFEM PERR chem. + 180s CO2W rinse (reference)

Co clean test #2 FFEM PERR chem. + 180s dNH4OH rinse

Co clean test #3 FFEM PERR chem. + 180s dNH4OH/H2O2 rinse

Co clean test #4 20s 0.05%HF (30ppb DO) + PERR chem. + 180s CO2W rinse

V1/M2

metallizationClean split

Via resistance measurements

and TEM/EDS analysis

Co PRE-METALLIZATION CLEAN

17

▪ Via resistance variation reduction confirmed by introducing functional water rinse

▪ Variation: (dNH4OH/H2O2) < (dNH4OH) < (CO2W)

▪ Low resistance: caused by shorts (not related to cleaning)

CO2W dNH4OH dNH4OH

/H2O2

dHF/

CO2W

Cu

Cu

POR clean

for Cu

TEM-EDS COMPARISON

18

D15 D17 D18

▪ CO2W rinse: during via wet clean, the Co trench of M1 is being partially attacked

▪ dHF +CO2W rinse: during via wet clean, the entire Co of M1 under the via is removed ▪ lateral etch along the Co line is observed and, the etched Co is replaced by Cu during metallization process

▪ dNH4OH/H2O2 rinse: Minor Co etch was observed, confirmation of electrical data

CO2W dNH4OH/H2O2

dHF + CO2W

CO2W dHF + CO2W dNH4OH/H2O2

ADDITIONAL RESULT ON Co CLEAN FOR MOL

19

D11 D12 D13 D14

Co is removed by clean Co is partially eroded Co is partially erodedNo Co attack observed

Co clean

D11 10s 0.05%HF + 2 min FFEM PERR chem. + 30s CO2W

D12 10s 0.05%HF + 2 min FFEM PERR chem. + 30s dNH4OH/H2O2 rinse

D13 2 min FFEM PERR chem. + 30s dNH4OH/H2O2 rinse

D14 20s 0.05%HF + 2 min FFEM PERR chem. + 30s dNH4OH/H2O2 rinse

SUMMARY

▪ Galvanic corrosion behavior of metal in contact with different materials▪ Oxygen reduction in dHF and reduced oxygen ambient atmosphere are mandatory for a good control of

galvanic corrosion

▪ Co Pre-metallization clean and functional water rinse▪ FFEM PERR chem in combination with functional water rinse: Co clean achieved together with TiN HM

removal and without removing ALD TiN liner

▪ Less Co wet etching and reduction of via resistance variation by using functional water rinse (Kurita unit)

20

Co/Cu:

Galvanic corrosion of

Co with high DO

concentration in HF

TiN/Co:

Chemical etching of

Co with high DO

concentration in HF

PUBLIC