Chapter 25
Advanced Chemically Amplified Resist Process Using Non-Ammonia Generating Adhesion Promoter M . Endo and A . Katsuyama ULSI Process Technology Development Center, Matsushita Electronics Corporation, 19 Nishikujo-Kasugacho, Minami-ku, Kyoto 601, Japan
We have developed a new non-ammonia generating adhesion promoter, 4-trimethylsiloxy-3-pentene-2-one. Its adhesion capability for a substrate is superior to a conventional adhesion promoter, hexamethyldisilazane, owing to its high reactivity. We obtained high aspect ratio and precise chemically amplified resist patterns on Si and TiN substrates using this new adhesion promoter.
Chemically amplified resist system is a promising technology to attain high resolution and high sensitivity for sub-quarter micron device fabrication. However, air-borne contamination (1-3), such as ammonia mainly generated from conventional adhesion promoter, hexamethyldisilazane ( H M D S ) , severely affects this kind o f resist. It causes surface insoluble layer o f resist patterns, which results in failure of the pattern fabrication. We developed a non-ammonia generating adhesion promoter, isopropenoxytrimethylsilane ( I P T M S ) , in place o f H M D S and its application to chemically amplified resist process was successful (4). However, the adhesion capability o f the promoter has been an issue. The short treatment time o f adhesion promoter in a gas phase is strongly necessary for actual device production in terms of throughput. We have evaluated several adhesion promoters and finally have developed a new adhesion promoter, 4-trimethylsiloxy-3-pentene-2-one ( T M S P ) . It effectively prevented air-borne contamination and substrate dependency (5). In this paper, we describe its adhesion capability.
© 1 9 9 8 American Chemical Society
337
338
Experimental O n a hydrophilic Si substrate (contact angle: 3° ), an adhesion promoter is treated in a gas phase by N bubbling of the promoter. 2
We measured the contact angles at
several treatment times and substrate temperatures for evaluation o f adhesion capability. Semi-empirical molecular orbital calculation P M 3 was performed to clarify the reactivity o f an adhesion promoter. We also evaluated contact angles on various device substrates (Si02, A l , poly Si, T i N ) and measured minimum dot i-line resist pattern size fabricated on each substrate using each adhesion promoter. For the pattern profile evaluation, K r F resist was coated to a thickness o f 0.7 / i m on a Si or T i N substrate treated with an each adhesion promoter.
After
exposure, P E B and the alkaline development, we observed S E M o f line-and-space pattern profiles.
A 0.7 pt m thick K r F excimer laser positive chemically amplified
resist with acid-labile protecting group was used. Adhesion promoters evaluated are the newly developed T M S P , the formerly developed I P T M S and conventional H M D S ( F i g l ) . For exposure, a K r F excimer laser stepper o f a numerical aperture ( N A ) 0.50 was used. The alkaline development was done with 2.38wt% tetramethylammonium hydroxide solution, N M D - 3 (Tokyo Ohka) for 60 sec. Results and Discussion Comparison of Contact Angles. in Fig. 2.
The contact angles using H M D S are shown
The contact angle becomes higher as increasing treatment time and
substrate temperature.
The maximum contact angle is below 75° in the range o f
allowed throughput (within 30 sec. treatment). The contact angles using I P T M S are below 60° ( F i g 3). contact angle is obtained at 140°C.
The maximum
Although the g^s concentration o f this
promoter is high owing to its low boiling point (94.5°C), the low reactivity resulted in this phenomenon. B y using T M S P , the adhesion capability becomes better.
The contact angle
o f greater than 75° is attained by treatment at 140°C for 30 sec. ( F i g 4).
This
value is best in using any adhesion promoter. For T M S P , the Lowest-UnoccupiedMolecular-Orbital ( L U M O ) energy level is relatively small (0.77 eV) as compared with that o f I P T M S (1.03 eV). A s a smaller L U M O energy level represents a more electrophilic state o f the molecule, this suggests the higher reactivity o f ( C H ) S i o f 3
3
T M S P to O H sites on a substrate, which leads to a higher contact angle. For the use o f T M S P , as the boiling point is relatively high (198.0°C), the preferred substrate temperature is over 100°C.
Over 160°C, the contact angle
339
(CH ) Si-0-C=CH-C=0 -C=CH-C=0 3
(CH (CH )) Si-OC-CH Si-OC-C
3
CH^ '3
3 3 33
CH^ ^ 3
3
3
3
CH2 ^ 2
n
n
(a)
Figure 1.
(CH ) Si-NH-Si(CH )
3
(b)
(c)
Chemical structures o f (a) T M S P , (b) I P T M S and (c) H M D S .
80
w 70 O < hO
