- Email: [email protected]
Sputtering at low ion velocities
VACUUM Classified A b s t r a c t s
III
--
Vacuum
Processing
Techniques
--
III
Abstract No. and References
Contd.
deformation at the s u b s t r a t e t e m p e r a t u r e during deposition and again at 25°C. At 75°C deposition t e m p e r a t u r e (a) was 0.4 × 10 * dyn/cm-% The intrinsic stress w a s determined as a function of b o t h s u b s t r a t e deposition t e m p e r a t u r e and annealing t e m p e r a t u r e . The results for four nickel-mica specimens, produced at different s u b s t r a t e t e m p e r a t u r e s , are s h o w n in a g r a p h d e m o n s t r a t i n g t h a t annealing reduces intrinsic stress, reaching a m i n i m u m value at 25°C and rising again thereafter. If the concept of M u r b a c h and W i l m a n applied, the film should be stable during annealing at lower t e m p e r a t u r e s . I t is concluded t h a t the intrinsic stress in a t h i n m e t a l film can be related to the imperfections formed during deposition which undergo changes s h o r t l y after being t r a p p e d b y succeeding layers of deposited metal. The density of the initial imperfections a p p e a r s to d e p e n d on the surface mobility of the e v a p o r a t e d metal. Copper shows low intrinsic stress. I t s surface m o b i l i t y is k n o w n to be higher t h a n t h a t of nickel. A table, p a r t l y reproduced below, gives c o m p a r a t i v e d a t a for nickel and copper. Metal
Xi
Total stress (I(P dyn. era. -*)
6.80
Diff, exp. stress (10* dyn. era. -2
O
Xi 125
Substrate deposit temp (°C)
Intrinsic stress (10 * dyn. era.-*)
0.94 6.40
C~t
ZVgo7-
Cu
75
0- 3!
3.76
Sommaire: Les causes de tension d a n s les films de mdtal 6vapor6s o u t 6t6 6tudids, et on a trouv6 que, mis k p a r t les effets thermiques, les imperfections dans le film agissent sur la tension totale.
The Electron Microscopy of Photographic Grains.
Letter by R. W. ttoffman
R. D. Daniels &
Specimen Preparation Techniques and Applications
E.C.Crittenden,Jr. Prec. Phys. See. 67B , June 1954 497-500
120/I XI
See A b s t r a c t No. : l l l / I I 121/III
An Improved Replica Technique for Electron Microscopy of Paint Films See A b s t r a c t No. : 186/I
A Simple Method of Preparing Silica Replicas. See A b s t r a c t No. : 113/II
31 - -
Advantages Offered by the Cathodic Etching of Specimens
CATHODIC
SPUTTERING
-- 3: 123/Ili
Sputtering at Low Ion Velocities
O
United States. Arising out of the p r o b l e m of determining the threshold voltage for s p u t t e r i n g the a u t h o r s developed a sensitive m e t h o d for m e a s u r i n g s p u t t e r i n g at ion velocities in the region of 100V. The principle of t h e m e t h o d is to measure, d u r i n g deposition a n d b y m e a n s of a probe, the change in collection of electrons furnished b y a plasma. The a p p a r a t u s consists of a bell-jar housing a t u n g s t e n helical cathode, a s p u t t e r i n g electrode (negative w i t h respect to the p l a s m a d u r i n g operation), a cylindrical m o l y b d e n u m anode, coaxial w i t h the cathode, and a t u n g s t e n probe. The latter is m o v a b l e and can be placed 5-10 m m . a w a y from the s p u t t e r i n g electrode. The difference in the w o r k function of the p r o b e before and after s p u t t e r i n g is a m e a s u r e of the thickness of the s p u t t e r e d deposit. The a u t h o r s discuss several possible sources ot error, such as general c o n t a m i n a tion of the p r o b e from the s y s t e m resulting in a creep of the value of the w o r k function of the probe. This h a s to be overcome b y a strict and t h o r o u g h b a k i n g schedule. A n o t h e r source of c o n t a m i n a t i o n of the p r o b e is the h o t cathode. A l t h o u g h the cathode is m a d e from t u n g s t e n this c o n t a m i n a t i o n m a y become appreciable as the t e m p e r a t u r e of the cathode is 2,400°K and e x p e r i m e n t a l r u n s take u p to 6 hours. F u r t h e r , care m u s t be t a k e n t h a t the p r o b e does n o t a s s u m e t e m p e r a t u r e s above a critical level which m a y induce surface m i g r a t i o n of the deposit and in the w o r s t case re-evaporation. The o p t i m u m operational pressure for such m e a s u r e m e n t s is governed b y a n u m b e r of factors e n u m e r a t e d in the article, b u t in e x p e r i m e n t s s p u t t e r i n g p l a t i n u m in a x e n o n a t m o s p h e r e this pressure w a s determined practically to be b e t w e e n 20 and 30 micron Hg. This is the region where ion c u r r e n t t e n d s to d e p a r t f r o m a c o n s t a n t value. A typical cycle of m e a s u r e m e n t is: (1) Characteristics of the clean probe, (2) period of sputtering, (3) characteristics of the covered p r o b e and (4) characteristics of the freshly cleaned probe. S p u t t e r i n g at 200 V for 5 seconds p r o d u c e d a change in the w o r k function of 9.1V. At 150 V t h e s a m e increase in w o r k f u n c t i o n was obtained after l0 seconds, at 100 V after 34 seconds and at 40 V after 5,400 seconds. Sommaire : Des t a u x rninimes de projection cathodique s e n t mesurds, au m o y e n d ' u n e sonde pla~de d a n s la d~charge.
July, 1954
122/III
Vacuum Vol. I V No. 3
Article by G. Wehner & G. Medieus J. Appl. Phys. 25, June 1954 698-702
382
III
--
Vacuum
Processing
Techniques
--
III
Abstract No. and References
Contd.
deformation at the s u b s t r a t e t e m p e r a t u r e during deposition and again at 25°C. At 75°C deposition t e m p e r a t u r e (a) was 0.4 × 10 * dyn/cm-% The intrinsic stress w a s determined as a function of b o t h s u b s t r a t e deposition t e m p e r a t u r e and annealing t e m p e r a t u r e . The results for four nickel-mica specimens, produced at different s u b s t r a t e t e m p e r a t u r e s , are s h o w n in a g r a p h d e m o n s t r a t i n g t h a t annealing reduces intrinsic stress, reaching a m i n i m u m value at 25°C and rising again thereafter. If the concept of M u r b a c h and W i l m a n applied, the film should be stable during annealing at lower t e m p e r a t u r e s . I t is concluded t h a t the intrinsic stress in a t h i n m e t a l film can be related to the imperfections formed during deposition which undergo changes s h o r t l y after being t r a p p e d b y succeeding layers of deposited metal. The density of the initial imperfections a p p e a r s to d e p e n d on the surface mobility of the e v a p o r a t e d metal. Copper shows low intrinsic stress. I t s surface m o b i l i t y is k n o w n to be higher t h a n t h a t of nickel. A table, p a r t l y reproduced below, gives c o m p a r a t i v e d a t a for nickel and copper. Metal
Xi
Total stress (I(P dyn. era. -*)
6.80
Diff, exp. stress (10* dyn. era. -2
O
Xi 125
Substrate deposit temp (°C)
Intrinsic stress (10 * dyn. era.-*)
0.94 6.40
C~t
ZVgo7-
Cu
75
0- 3!
3.76
Sommaire: Les causes de tension d a n s les films de mdtal 6vapor6s o u t 6t6 6tudids, et on a trouv6 que, mis k p a r t les effets thermiques, les imperfections dans le film agissent sur la tension totale.
The Electron Microscopy of Photographic Grains.
Letter by R. W. ttoffman
R. D. Daniels &
Specimen Preparation Techniques and Applications
E.C.Crittenden,Jr. Prec. Phys. See. 67B , June 1954 497-500
120/I XI
See A b s t r a c t No. : l l l / I I 121/III
An Improved Replica Technique for Electron Microscopy of Paint Films See A b s t r a c t No. : 186/I
A Simple Method of Preparing Silica Replicas. See A b s t r a c t No. : 113/II
31 - -
Advantages Offered by the Cathodic Etching of Specimens
CATHODIC
SPUTTERING
-- 3: 123/Ili
Sputtering at Low Ion Velocities
O
United States. Arising out of the p r o b l e m of determining the threshold voltage for s p u t t e r i n g the a u t h o r s developed a sensitive m e t h o d for m e a s u r i n g s p u t t e r i n g at ion velocities in the region of 100V. The principle of t h e m e t h o d is to measure, d u r i n g deposition a n d b y m e a n s of a probe, the change in collection of electrons furnished b y a plasma. The a p p a r a t u s consists of a bell-jar housing a t u n g s t e n helical cathode, a s p u t t e r i n g electrode (negative w i t h respect to the p l a s m a d u r i n g operation), a cylindrical m o l y b d e n u m anode, coaxial w i t h the cathode, and a t u n g s t e n probe. The latter is m o v a b l e and can be placed 5-10 m m . a w a y from the s p u t t e r i n g electrode. The difference in the w o r k function of the p r o b e before and after s p u t t e r i n g is a m e a s u r e of the thickness of the s p u t t e r e d deposit. The a u t h o r s discuss several possible sources ot error, such as general c o n t a m i n a tion of the p r o b e from the s y s t e m resulting in a creep of the value of the w o r k function of the probe. This h a s to be overcome b y a strict and t h o r o u g h b a k i n g schedule. A n o t h e r source of c o n t a m i n a t i o n of the p r o b e is the h o t cathode. A l t h o u g h the cathode is m a d e from t u n g s t e n this c o n t a m i n a t i o n m a y become appreciable as the t e m p e r a t u r e of the cathode is 2,400°K and e x p e r i m e n t a l r u n s take u p to 6 hours. F u r t h e r , care m u s t be t a k e n t h a t the p r o b e does n o t a s s u m e t e m p e r a t u r e s above a critical level which m a y induce surface m i g r a t i o n of the deposit and in the w o r s t case re-evaporation. The o p t i m u m operational pressure for such m e a s u r e m e n t s is governed b y a n u m b e r of factors e n u m e r a t e d in the article, b u t in e x p e r i m e n t s s p u t t e r i n g p l a t i n u m in a x e n o n a t m o s p h e r e this pressure w a s determined practically to be b e t w e e n 20 and 30 micron Hg. This is the region where ion c u r r e n t t e n d s to d e p a r t f r o m a c o n s t a n t value. A typical cycle of m e a s u r e m e n t is: (1) Characteristics of the clean probe, (2) period of sputtering, (3) characteristics of the covered p r o b e and (4) characteristics of the freshly cleaned probe. S p u t t e r i n g at 200 V for 5 seconds p r o d u c e d a change in the w o r k function of 9.1V. At 150 V t h e s a m e increase in w o r k f u n c t i o n was obtained after l0 seconds, at 100 V after 34 seconds and at 40 V after 5,400 seconds. Sommaire : Des t a u x rninimes de projection cathodique s e n t mesurds, au m o y e n d ' u n e sonde pla~de d a n s la d~charge.
July, 1954
122/III
Vacuum Vol. I V No. 3
Article by G. Wehner & G. Medieus J. Appl. Phys. 25, June 1954 698-702
382