process impacts of chemistry preparation on dhf process · pdf filef 1043 - version 01 ....

F 1043 - Version 01 . AP&S International GmbH

Process impacts of chemistry preparation on DHF process

Thomas Kopp

Levitronix User Conference

Zürich, April 11th 2013

AP&S International GmbH


Agenda

Company

Products & Applications

Products - Impressions

Motivation

Initial situation

Root cause analysis

New solution

Test results

Summary


Worldwide Locations in

Europe & Asia


Obere Wiesen 9

D-78166 Donaueschingen

Germany

www.ap-s.de | www.ap-s.cn | www.ap-s.sg | www.semi-parts.com

Company


Products & Applications

Clean

• SC1

• TMAH/H2O2

• DSP

• EKC / ACT a.o.

• SOM, DIO3

• SPM

• Scrubber

• Post CMP

• Megasonic

• Etc.

Etch

• DHF

• BOE

• HF 49%

• DHF/HCI

• KOH

• H3PO4

• P-Etch

• Etc.

Metal etch

• Poly-Si

• Alu

• Ti, TiN

• Ni, NiCr

• BiSb

• Co

• CoSi

• Cu

• Etc.

PR Strip

• SPM

• SOM

• Etc.

Eless Plating

• Nickel-Gold

• Nickel-Palladium-Gold

Lift-off

• Metal • Etc.

Drying

• Marangoni • Spin • Hot air

Coating and Developing

• Positive resist • Negative resist • SU8

Wet bench

Single wafer

Parts cleaning

Facility

Refurbishment

Lotus systems products

Customized solutions


Products - Impressions


DHF process in semiconductor industry

DHF ≡ Diluted Hydro-Fluoric Acid

DHF is used in various applications in semiconductor industry. Most important applications are:

• Removal of natural Si-Oxide from wafer surface (natural etch

stop when Si-Oxide is removed)

• Etching of a defined layer-size of Si-Oxide (controlled by time)

• Saturation of wafer surface with hydrogen

Motivation


Motivation

Process parameters

∆ 𝐸𝑡𝑐ℎ 𝑟𝑎𝑡𝑒 ~ 𝑝 ∗ ∆ 𝑇

- Etch rate - Uniformity

tim

e

etchrate vs. DHF concentartion

0

5

10

15

20

25

30

0 20 40 60 80 100 120 140 160 180 200

mixing ratio HF:H2O (1 : X)

etc

h r

ate

[n

m/m

in]

Etch rate vs. DHF concentration

0

20

40

60

80

100

120

0 200 400 600 800 1000

etch rate vs. process time

∆ 𝐸𝑡𝑐ℎ 𝑟𝑎𝑡𝑒 ~ 𝑝 ∗ ∆ 𝑇


Motivation

In standard wet process equipment, mostly the SiO2-layer removal is controlled by the etch time (process time). This requires a very exact etch rate and therefore a stable status for:

• DHF concentration

• DHF mixture homogenity

• Temperature


Initial situation - Problem

Problems, that could be seen in this process:

• Etch rate fluctuation over days; the etch rate differs between different days

• Etch rate fluctuation over lots; the etch rate differs between different lots

• Uniformity of etched wafer surface within a wafer or within one lot of wafers doesn‘t fulfill the requirements


Initial situation - Hardware setup

Preparation

tank

5% HF dilution

DIW

5% HF dilution

0,5%/0,2%

HF dilution

Spiking pump

Static mixer

Static immersion tank

Facility supply


Initial situation – Measurment results

Fluctuation of oxide-removal day to day

Etch rate fluctuation day to day

8

8.5

9

9.5

10

10.5

11

avg. etch rate [A°] vs. different days [date] A°/min

∆ ~ 𝟐𝟎 𝑨°

Avg. Etch [A°] rate vs. Process time [sec] – Linearity curve

Std.dev.: > 0,5


Root cause analysis

Following possible root causes where verified:

• Process time – OK; no fluctuation

• Temperature fluctiation – OK; no fluctuation that could cause the fluctuation of the etch rate

• HF concentration preparation tank (5%) – OK; measured with online analytic measurement device

• HF concentration in bath (0,5%/0,2%) – NOK; fluctation observed

• DIW supply – NOK; significant fluctuation of DIW input pressure & flow observed


Root cause analysis - Measurement results

6.000

7.000

8.000

9.000

10.000

11.000

12.000

16:1

8:5

6

16:1

9:0

4

16:1

9:1

2

16:1

9:1

9

16:1

9:2

7

16:1

9:3

5

16:1

9:4

3

16:1

9:5

0

16:1

9:5

8

16:2

0:0

6

16:2

0:1

3

16:2

0:2

1

16:2

0:2

9

16:2

0:3

6

16:2

0:4

4

16:2

0:5

2

16:2

0:5

9

16:2

1:0

7

Series1

Fluctuation of DIW input flow was caused by very high fluctuation of DIW input pressure at process module between approx.

1 bar and 3,5 bar.

DIW Flow [l/min]


New solution - requirements

1. Suitable for wide input pressure range 0,8 to 3,7 bar

2. Variable mixing rates (500:1; 200:1)

3. Repeatability of Mixing Ratio ±1%

4. Absolute Accuracy of Mixing Ratio ±2%

5. Compact design

6. Extremely low particle generation

7. Homogeneous mixture of DIW and 5% DHF dilution

8. Smooth, continuous flow without pressure pulsation


New solution (1) – Pre-preparation tanks

Advantages: • Accuracy an Repeatability • Independend of DIW input pressure

Disadvantages: • No compact design • No mixing function/inhomogeneous mixture of HF and DIW • For variable mixing rates a) different pre-mixing tanks or b) waste of chemistry

Pre mixing of Chemistry in additional tanks

5%HF DIW

0,5

% H

F d

ilu

tio

n

Prep- tank 0.5% HF

5%HF DIW

0,2

% H

F d

ilu

tio

n

Prep- tank 0.2% HF

Static immersion tank


New solution (2) – Pressure regulator

Advantages: • Compact design • Very stable output pressure

Disadvantages: • Only stable output pressure within a small range

of input pressure variation • No linearity over complete area of operation • No mixing function

Pressure regulator for DIW


New solution (3) – Blending system

Single Pump system for DIW

Control loop

Advantages: • Compact design • Very stable flow

Disadvantages: • Only stable output flow for

one fluid • No mixing function


New solution (4) – Blending system

Disadvantages: • Costs

Double Pump system for DIW&HF5%

Advantages: • Compact design • Very stable flow • Two flows

controlled • Mixing function

to static immersion tank


New solution – Overview

Solution DIW input pressure 0,8 – 3,7 bar

Variable mixing rates

Repeatability / Accuracy

Compact design

Mixing function

Pre-preparation tank OK Premixing not

depending on DIW pressure

a) different tanks for pre mixture

b) Waste of chemistry in case of using one tank

NOK NOK NOK

Precision pressure regulator

For stable output pressure 2,5 – 4,5

bar required

OK (spiking pump)

OK OK NOK

Blending system with one pump

OK OK NOK Only one chemistry

flow controlled.

OK NOK

Blending system with two pumps

OK OK OK OK OK


New solution – Decision

Based on:

• system requirements

• specifications of blending systems with one and two control loops

Decision:

Solution 4 (Blending System with two pumps/control loops) will be used for further tests.

Hardware:

LeviFlowsensors (Levitronix): LFS-50-Z;LFS-04-Z; 2x LFC-1C

Pumps (Levitronix): BPS-600.2; BPS-200.2; LPC-600; LPC-200


Test results – Etch rate stability

7

7.5

8

8.5

9

9.5

10

13.03.2010 18.03.2010 23.03.2010 28.03.2010 02.04.2010 07.04.2010 12.04.2010 17.04.2010 22.04.2010

Avg. Etch [A°] rate vs. different days [date] with Blending System A°/min

Standard deviation: 0,18

8

8.5

9

9.5

10

10.5

11

Avg. etch [A°] rate vs. different days [date]- original A°/min

Etch rate stability over different days can be improved significantly

Std.dev.: < 0,18

Std.dev.: > 0,5


Test results – Etch rate linearity

0

20

40

60

80

100

120

140

160

0 100 200 300 400 500 600 700 800 900 1000

Oxid

e l

os

s (

A°)

Process time (sec)

Avg. Etch [A°] rate vs. Process time [sec] with Blending System ( Linearity curve)

Week 14

Week 18

Stability of oxide-removal can be improved significantly

Avg. Etch [A°] rate vs. Process time [sec] – Original (Linearity curve)

∆ ~ 20 𝐴°

∆ < 1 𝐴°


Summary

Etching a defined oxide layer in a DHF process, only controlled by time, requires an absolute stable process environment.

The blending system in this test showed

• Repeatability of Mixing Ratio better than ±1%

• Absolute Accuracy of Mixing Ratio better than ±2%

• Homogeneous mixture of DIW and 5% DHF dilution guaranteed

• Variable mixing rates (requires fluid calibration)

Thanks to Levitronix for providing hardware and technical support for these tests !


Thank you…

Please, contact us for

more information!

Europe


Obere Wiesen 9 . Aasen

78166 Donaueschingen . Germany

Phone +49-771-8983-0

Fax +49-771-8983-100

[email protected]

www.ap-s.de

China

AP&S Semiconductor Equipment

(Shanghai) Co., Ltd.

Phone +86-21-5042-9053 ext. 107

Fax +86-21-5042-9053 ext. 105

[email protected]

www.ap-s.cn

Europe

SemiParts

An AP&S Business Unit

Obere Wiesen 9 . Aasen

78166 Donaueschingen . Germany

Phone +49-771-8983-200

Fax +49-771-8983-100

[email protected]

www.semi-parts.com

Singapore/Malaysia

AP&S Asia Pte. Ltd.

Phone +60-403-9007

Fax +60-408-0031

[email protected]

www.ap-s.sg

process impacts of chemistry preparation on dhf process · pdf filef 1043 - version 01 ....

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