process guidelines for using e-beam resist ma-n...

Sangeeth.K, Nagaraj.K.SCeNSE, IIScBangalore, India

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Centre for Nano Science and Engineering (CeNSE)

Indian Institute of Science

Process guidelines for using

E-beam resist ma-N 2401

Nagaraj K.S, Sangeeth.K

National Nanofabrication Centre

CeNSE, IISc

Bangalore,India

12.7.2013


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Photoresist – ma-N 2401From Microresist technology

Negative Tone Photoresist suited for Electron Beam Lithography

Properties• High wet and dry etch resistance • Good thermal stability • Excellent pattern resolution - down to 40 nm• Aqueous alkaline development (TMAH)• Easy to remove (soluble in Acetone)

Applications• Mask for etching, e.g.Si, SiO2, Si3N4 or metals• Mask for ion implantation • Stamp fabrication for NIL

http://www.microresist.de/products/negative_photoresists/overview_neg_en.htm

http://www.microresist.de/products/negative_photoresists/overview_neg_en.htm


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Processing

Sample preparation:• Si Substrate is cleaned in Piranha solution• Cleaned Si is dipped in dil. HF • Dehydration bake done at 150°C for about 5 minutes

EHT 20k V

Aperture 30 µm

Working distance 9.5 mm

Write field 50 µm

Spin coating parametersSpin Speed (rpm) Measured thickness

(nm)

Soft bake (°C)

2000 240 115 – 2 minutes

3000 150 115 – 2 minutes

4000 120 115 – 2 minutes

Patterning parameters

Tool parameters

Figure 1 exposure dose Vs feature size

Lines (nm) Exposure window

(µC/cm²)

Development

100 90 - 207 TMAH (90 sec) +

Water (45 sec)

200 90 - 207 TMAH (90 sec) +

Water (45 sec)

300 90 - 207 TMAH (90 sec) +

Water (45 sec)


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Figure 2 - SEM images of ma-N 2401 spin coated at 2000 rpm.


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Overdose testing

The test is conducted to check if the critical dimension saturates at a certain point regardless of increasing the dose.

Spin Speed

(rpm)

Thickness

(nm) Soft bake (°C) Exposure

window

(µC/cm²)

Development

2000 240 115 – 2

minutes

213 – 1959.6 TMAH (90

sec) + Water

(45 sec)

Figure – 3 SEM image of 100nm line being Overdosed.

Figure – 4 50nm lines being overdosed.

Observation • The thickness of the resist

drastically reduces to about 110nm from 240nm.

• The thickness measurements were done using both Dektakand X-SEM.

• The edges of the lines are morestraighter and stiff.


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Overdose testing

Figure – 5 Graph representing the curve for 100 and 50 nm lines being overdosed.

Proximity testing

Figure – 6 SEM image for a pitch of 100/300 nm Figure – 7 SEM image for a pitch of 100/500 nm

Observations:• 100nm lines are exposed to almost 10 times

the critical dose (~200µC/cm²). Lines are tapered in vertical direction with 210nm at the bottom and 110nm at the top

• The dependence of dose on CD is relatively less as compared to HSQ

• When the pitch is ~100nm, 100nm lines get

merged


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Figure – 8 Graph predicting the critical dimension for varied dose andpitch.

Figure – 9 Pitch measurement for varied doses

process guidelines for using e-beam resist ma-n...

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