1. Etching of Organo-Siloxane Thin Layer by Thermal and Chemical Methods
Jong-Hyeon Lee and Duk-Young Jung*
Department of Chemistry ,
SungKyunKwan University
South Korea

2. Introduction
Self-Assembled Monolayers (SAMs) have begun to explore applications in microfabrication, including microcontact- printing. For selective deposition, earlier reports show that patterned SAMs of OTS can be utilized as a molecular resist or templates in directing the thin-film. However, in many occasions, the OTS SAMs are found to still remain on the surface.
We observed substrate-effects and stability in microcontact-printed OTS SAMs on oxidized silicon and slide glass by thermal, hydrothermal and photochemical treatments.
Inorganic Chemistry, SungKyunKwan Univ.

3. (OTS : n-octadecyltrichlorosilane) chemical bonding on the surface
SAMs(Self-Assembled Monolayers)
SAMs form spontaneously by chemisorption and self-organization of functionalized, long-chain organic molecules onto the surfaces of appropriate substrates.
Functional group
Alkyl chain
Reaction group
substrate
(OTS : n-octadecyltrichlorosilane)
hydrophobic functional groups
tilted angle : 8-10 º
(22~ 25Å)
cross link
chemical bonding on the surface
oxide layer
(Structure of OTS SAMs)
Inorganic Chemistry, SungKyunKwan Univ.

4. Microcontact Printing
(PDMS : Silicon elastomer)
PDMS
Spin casting of OTS solution
PDMS
Ink
(OTS solution)
Microcontact printing Si
PDMS
Fabrication of patterned OTS SAMs
(OTS SAMs)
hydrophilic area
hydrophobic area
oxide layer Si
Inorganic Chemistry, SungKyunKwan Univ.

5. (Substrate : S i(100) p-type wafer)
Hydrophobicity of OTS SAMs
Optical Microscope Image
OTS SAMs
Moisture
( x 10 )
(Substrate : S i(100) p-type wafer)
OTS SAMs (hydrophobic area)
H2O
oxide layer
H2O
H2O Si
Inorganic Chemistry, SungKyunKwan Univ.

6. Remove OTS SAMs Application of Patterned OTS SAMs
Optical Microscope Image
SEM Image
200m
20m
5m
(selective deposition of CdS)
(selective deposition of zeolite)
Procedure of selective deposition of CdS
OTS SAMs
Patterned OTS SAMs on Si wafer by microcontact printing Si
Solution deposition of CdS Si
Sonication of the sample in acetone Obtain selective deposited CdS. However OTS SAMs remain. Si
Remove OTS SAMs Si
Inorganic Chemistry, SungKyunKwan Univ.

7. Thermal treatment of OTS SAMs Water contact angle critical point
H2O
H2O Si
Water contact angle
Bare Si (100) wafer : 37 degree
critical point
Substrate : Si (100) p-type Complete Decomposition temp  at 15min above 500 ºC  at 30min above 400 ºC
Cleaning : nitric acid (60% , ultra sonicatefor10min) ammonia water (5 M , 2-3min)
Inorganic Chemistry, SungKyunKwan Univ.

8. completely decomposed region
UV treatment
of OTS SAMs
SAMs
H2O Si
Water contact angle
completely decomposed region
Bare Si (100) wafer : 5 degree
Substrate : Si (100) p-type UV lamp(high pressure Hg lamp) : 320 nm / 1000W Complete Decomposition time : over 130 min
Cleaning : piranha solution ( 98% H2SO4 : 28% H2O2 ) = 7 : 3 ( ultra sonicate for 10 min) ammonia water (5 M , 2-3 min)
Inorganic Chemistry, SungKyunKwan Univ.

9. Optical Microscope Image(x10)
Hydrothermal treatment
of OTS SAMs
- slide glass -
Optical Microscope Image(x10)
slide glass
slide glass
plate
plate
(140 ºC)
(150 ºC)
(160 ºC)
(180 ºC)
slide glass
( x 10)
( x 40)
plate
Hydrothermal condition /120/130/140/150/160/180 ºC , 5 h in DI water
110/120/130/140 ºC : no hydrolysis (patterned OTS SAMs remain upto 140 ºC) ºC : slightly hydrolysis /180 ºC : fully hydrolysis
Substrate : slide glass Cleaning : ammonium persulfate (NH4S2O8) in 1M sulfuric acid (ultra sonicate for 10 min) % ammonia water (2-3 min)
Inorganic Chemistry, SungKyunKwan Univ.

10. Optical Microscope Image
Hydrothermal treatment
of OTS SAMs
- Si (100) wafer -
Optical Microscope Image
OTS SAMs
moisture
Si (100) wafer
( x 10)
Hydrothermal condition : 200 ºC, 5 h in DI water
no hydrolysis (patterned OTS SAMs remain up to 200 ºC)
Substrate : Si (100) p-type wafer Cleaning : piranha solution ( 98% H2SO4 : 28% H2O2 ) = 7 : 3 ( ultra sonicate for 10 min) ammonia water (5M , 2-3 min)
Inorganic Chemistry, SungKyunKwan Univ.

11. ( Parikh et al. J. Am. Chem. Soc., Vol. 119, 1997, 3135 )
TGA (Thermal Gravimetric Analysis) of OTS hydrolysis product (PODS)
poly(octadecylsiloxne) (PODS) : OTS hydrolysis product
(white powder)
- 3HCl
OTS +3 H2O
water layer
( Parikh et al. J. Am. Chem. Soc., Vol. 119, 1997, 3135 )
TGA (under Air)
( release of H2O)
TGA(under N2 gas)
(release of H2O)
Inorganic Chemistry, SungKyunKwan Univ.

12. Conclusion
In thermal treatment, OTS SAMs have tendency that the decomposition increases as the temperature rises. They completely decompose above 400 ºC (30 min) and 500 ºC (15 min).
In UV treatment, the decomposition of the OTS SAMs increases as the exposed time increases. In addition, they have clearly decomposed when exposed over 130 min.
In hydrothermal treatment, OTS SAMs show different behaviors on the surface of silicon and slide glass. OTS SAMs on silicon clearly remain up to 200 ºC (5 h). However OTS SAMs on slide glass remain up to 140 ºC (5 h). Particularly they hydrolyze above 150 ºC (5 h).
In thermal treatment, OTS SAMs have tendency that the decomposition increases as the temperature rises. And they have completely decomposed above 400 ºC(at 30mins) and 500 ºC(at 15mins).
In UV treatment, OTS SAMs have tendency that the decomposition increases as the exposed time rises. And they have clearly decomposed above 130 minutes of exposed time.
In hydrothermal treatment, OTS SAMs have different behavior on the surface of silicon and slide glass. OTS SAMs on silicon clearly remain upto 200 ºC(5 hours). but OTS SAMs on slide glass remain upto 140 ºC(5 hours). and they hydrolyze above 150 ºC(5 hours).
Inorganic Chemistry, SungKyunKwan Univ.