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

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.

(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.

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.

(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.

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.

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.

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.

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 110/120/130/140/150/160/180 ºC , 5 h in DI water 110/120/130/140 ºC : no hydrolysis (patterned OTS SAMs remain upto 140 ºC) 150 ºC : slightly hydrolysis 160/180 ºC : fully hydrolysis Substrate : slide glass Cleaning : ammonium persulfate (NH4S2O8) in 1M sulfuric acid (ultra sonicate for 10 min) 28% ammonia water (2-3 min) Inorganic Chemistry, SungKyunKwan Univ.

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.

( 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.

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.