Hybrid Polymers for Lithographic

Applications

Supervisor

Dr. Pradeep C. Parameswaran

Presented by

Anjali Varshney

1) What is lithography2) Photo resist materials a) Positive tone photo resist materials b) Negative tone photo resist materials3) Chemical amplification a) Photo acid generators (PAG)4) Non-Chemical amplification5) Pattern Transfer6) Stripping 7) Organic-inorganic hybrid photo resist materials8)Applications

Outline of the presentation…

The word lithography comes from the Greek .

Lithos = stones Graphia = write.

It means quite literally writing on stones.

In the case of semiconductor lithography (also called photolithography) our stones are silicon wafers and our patterns are written with a light sensitive polymer called a photoresist.

Lithography is used to transfer a pattern from a photomask to the surface of the wafer.

What is Lithography…?

Figure.1 General schematic representation of lithographic imaging process.

Silicon substrate

Deposition of photo resists on Silicon substrate

(silicon wafers)

Prebake

UV exposure under mask

Develop

Patterns on silicon wafers

Pattern transfer

Stripping

Diagrammatic Representation of Lithography..

Ref: S. Ghosh, C. P. Pradeep, S.K. Sharma, P. G. Reddy, S. P. Pal and K. E. Gonsalves, RSC Adv., 2016, 6, 74462–74481.

Photoresist material are molecular or polymeric chemical entities which are highly sensitive to the light.

phtoresist materials are classified into two types.

Two typesPhoto resist materials

Negative tone Photo resist materials

positive tone Photo resist materials

Photo Resist Materials

Figure 1. Difference between positive and negative tone photo resists.

Upon irradiation of photoresist coated silicon substrates with suitable wavelength, if the unexposed portion remains the exposed portions soluble in the developer called as positive tone photoresist material.

Ex.

Ref. M. Hatzakis, J. Electrochem. Soc. ,1969, 116 ,1033.

PMMA is the most commonly used positive tone photoresist material for high resolution lithographic applications.

Positive Tone Photoresist Materials

Figure.2 Synthetic route of Poly(methyl methacrylate)

Ref. 1. J. Mater. Chem., 2006, 16, 3701–3707 2. J. vac. Sci. technol. B., 2010, 28, C6S12-C6S18 3. Macromol. Rapid Commun., 2010, 31, 1449–1455 4. J. Polym. Sci. Part A: Polym. Chem., 2012, 50, 4255–4265.

Examples of Positive tone Photoresist Materials

Negative tone materials are opposite to the positive tone materials, i.e. the exposed portion of photoresist material remains the unexposed portion washed out in the developer called as negative tone materials.

OOn

S

CF3SO3

OO

x

S

CF3SO3

yOO

N CO

O

S

CF3SO3

x y

MAPDST Homopolymer Poly (MAPDST-CO-MMA) Poly (NVK-CO-MAPDST)

CO

O

SCF3SO3

x y

OH

Poly (STYOH-CO-MAPDST)

Ex:

Negative tone Photoresist Materials

Ref: V.S.V satyanarayana et al. ACS Appl. Mater. Interfaces., 2014, 6, 4223−4232

CO

O

SCF3SO3

x y

COOH

Poly (STYCOOH-CO-MAPDST)

O

S

O

CH3

n

CF3SO3

MANTMS Homopolymer

O

S

O

CH3

x

CF3SO3

OO

y

Poly (MANTMS-CO-MMA)

OO

OO

S

OO

OO

S

OO

OO

SCF3SO3

OO

OO

SCF3SO3

HfO2

HfO2-methacrylate-MAPDST (HMM)

Ref : 1. J. Mater. Chem. C, 2014, 2, 2118–2122 2. ACS Appl. Mater. Interfaces., 2014, 6, 4223−4232 3. RSC Adv., 2014, 4, 59817-59820 4. Chem. Eur. J., 2015, 21, 2250–2258

The n-CARs stand different from the CARs mainly at the mode of polarity switching upon exposure.

While for CARs the difference in polarity of the exposed area from that of unexposed area is brought out by

exposing the resist films either by radiation or by light in the presence of externally added photoacid generators

(PAGs).

For n-CARs, the PAGs or the photosensitive units are embedded into the resists architecture, and hence external

chemical amplification is not needed.

Chemical and Non-chemical Amplification

Ex: Acid catalysed mechanism

for Chemically amplified resist

Ex: Acid catalysed mechanism

for Non-Chemically amplified resist

Ref: http://henderson.chbe.gatech.edu/Introductions/microlithography%20intro.htm Ref: Soft Matter, 2009, 5, 2738–2745.

After the small patterns have been lithographically printed in photoresist, these patterns must be transferred into the substrate. There are three basic pattern transfer approaches:1)Subtractive transfer (etching) 2) Additive transfer (selective deposition) 3) Impurity doping (ion implantation).Etching is the most common pattern transfer approach.

Lithography is then performed such that the areas to be etched are left unprotected(uncovered) by the photoresist. Etching is performed either using wet chemicals such as acids (HF), or more commonly in a dry plasma environment.

After the imaged wafer has been processed (e.g., etched, ion implanted, etc.) the remaining photoresist must be removed.

There are two classes of resist stripping techniques:

Wet stripping = Organic or Inorganic solutions, Dry stripping = Plasma process.

Pattern Transfer

Stripping

Figure 3. Schematic illustration of Pattern transfer process.

1) Good capability for photon absorption, 2) High etch resistance 3) Lower exposure dose4) Higher resolution 5) Higher contrast6) Higher sensitivity etc

Most of the organic photo resists are facing problems lacking of above characteristics.

Organic-Inorganic Hybrids n-CARs

The Problems are faced in organic n-CARs during photo patterning process are over come by the

incorporation of inorganic components at lower percentages in their polymer matrixes called as Organic-

Inorganic hybrid photoresists

Characteristics of Ideal photoresist in Lithographic Process

OO

OO

S

OO

OO

S

OO

OO

SCF3SO3

OO

OO

SCF3SO3

HfO2

HfO2-methacrylate-MAPDST (HMM)

Examples of Inorganic-Organic Hybrid Photoresists

Ref: 1) Chem. Commun. 2015, 51, 17592–17595; 2) J. Mater. Chem., 2010, 20, 5186–5189; 3) Microelectronic Engineering ., 2014, 127,

44–50; 4) RSC Adv., 2014, 4, 59817-59820; 5) Chem. Eur. J., 2015, 21, 2250–2258

EX: SEM images of hybrid photo resists patterned on the silicon substrates

Figure 3. Line and circular patterns of various hybrid photoresist materials patterned on the silicon substrates at resolution of 200 -16.7 nm.

1) The basic lithographic process is generally more useful for the construction of integrated circuits (Ics) from micron to nano level in the semiconductor industries.

2) Most useful process in micro/nano electronics.

3) lithography process is useful in the various fields like photonic crystals, high density magnetic recording, micro-lens arrays, information storage, tissue engineering and catalysis ect.

The basic principles and types of photoresist materials used in the basic lithography process has been studied.

The advantageous of hybrid materials over by the pure organic materials has also studied to design a novel hybrid photo resist

materials for their nano-patterning applications.

Applications

Conclusion

Thank you!