Reactive Ion Etching of Piezoelectric Films for Acoustic Wave Devices

Abstract

Iowa S t a t e U n i v e r s i t v Ames, Iowa A b s t r a c t R e a c t i v e I o n E t c h i n g ( R I E ) which combines some advantages o f b o t h plasma e t c h i n g and s p u t t e r e t c hi n g has been used i n p r o c e s s i n g ZnO/Si and A l N / S i s t r u c t u r e f o r a c o u s t i c wave d e v i c e s . In t h i s s t u d y , t h e e t c h i n g gases used a r e CF4, HC1 and HI w i t h v a r y i n g amounts o f 02 and A r . The s u b s t r a t e s o f i n t e r e s t , which a r e p l a c e d on t h e cathode e l e ct r o d e o f a p a r a l l e l p l a t e r f r e a c t i o n chamber, a r e ZnO, A l N , A l , S i and SiO2. E t c h i n g was t y p i c a l l y c a r r i e d o u t a t 50 m i l l i t o r r s p r e s s u r e and 75 w a t t s r f power. When u s i n g CF4 and 4% 02 gas, S i e t c h r a t e was measured as h i g h as 2500 Ao/min. t h e ZnO and A1N e t c h r a t e s were v e r y l o w i n r e a ct i v e i o n e t c h i n g o r were found u n a t t a c k e d i n CF4 plasma e t c h i n g . By u s i n g t h i s h i g h e t c h s e l e ct i v i t y , edqe-only s u p p o r t e d ZnO and A1N p l a t e s were c o n s t r u c t e d f r o m ZnO/Si o r A l N / S i composite s t r u c t u r e . When HI gas was used, t h e e t c h r a t e o f ZnO was determined t o be 2000 Ao/min. The e t c h s e l e c t i v e r a t i o s found here were 4 0 : l o v e r S i 0 2 and mo e t h a n 1OO:l o v e r S i and A l . The l o w A1 mask e r o s i o n and h i g h s t o p p i n g r a t i o f o r ZnO o v e r S i on Al/ZnO/Si s t r u c t u r e i s o f p r a c t i c a l importance o r b o t h BAW and SAW d e v i c e s . However, I n t r o d u c t i o n Due t o new demand o f microwave d e v i c e s i n a s m a l l dimension and h i g h e r p a c k i n g d e n s i t i e s f o r i n t e q r a t e d c i r c u i t f a b r i c a t i o n , a s e l e c t i v e and a n i s o t r o p i c e t c h p r o c e s s i n g t e c h n i q u e t u r n s o u t t o be tremendously i m p o r t a n t . In t h i s work, r ea c t i v e i o n e t c h i n q which removes m a t e r i a l s by a c o m b i n a t i o n o f chemical r e a c t i o n and i o n bombardment was s t u d i e d i n p r o c e s s i n g Al/ZnO/Si and A l / A l N / S i s t r u c t u r e s f o r a c o u s t i c wave d e v i c e s . S p u t t e r e t c h i n g , d e s c r i b e d elsewhere,l i s t h e process o f u s i n g A r i o n beams i m p i n g i n g on a s u rf a c e t o s p u t t e r o f f m a t e r i a l b y momentum t r a n s f e r . The e t c h i s u s u a l l y h i g h l y a n i s o t r o p i c b u t n o t s e l e c t i v e f o r one m a t e r i a l o v e r a n o t h e r . Plasma e t c h i n g . 2~3 i n w h i c h t h e r e a c t a n t s p e c i e s c o l l i d e and r e a c t w i t h t h e s u r f a c e t o be etched, produces v o l a t i l e compounds w h i c h a r e t h e n pumped o u t by t h e vacuum system. T h i s r e s u l t s i n s e l e c t i v e e t c h i n g w i t h an a n i s o t r o p i c e t c h p r o f i l e . r e a c t i v e i o n e t c h i n q 4 ...

Anisotropic Plasma Etching of Sputtered Zinc Oxide

“…The experiment described here was developed considering discrepancies in past research (6) and the availability of ion implantation equipment (used in the experiment) to industry (7). Research conducted in the mid-1960s (8,9) has indicated that certain dopants could be ionimplanted into diamond, but the relative amounts of radiation damage and the apparently small amount of boron that was electrically active redirected most diamond research efforts toward other, more promising techniques (10,11).…”

“…However, few successful attempts in dry etching of ZnO have been reported. Wang et al (6) used HBr and H1 to plasma etch ZnO, but the corrosive nature of HBr and H1 in most vacuum systems places practical limitations on delineation approaches using these gas mixtures (7).…”