Chemistry Reference
In-Depth Information
RF plasma etching of a polyimide film with oxygen
mixed with nitrogen trifluoride
∗
,1,
†
1
SATORU IWAMORI,
NORIYUKI YANAGAWA,
1
2
3
MITSURU SADAMOTO,
RYOUSUKE NARA
and SHIGEKI NAKAHARA
1
Material Science Laboratory, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura-City,
Chiba 299-0265, Japan
2
Functional Materials Laboratory, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura-City,
Chiba 299-0265, Japan
3
Mitsui Chemical Analysis and Consulting Service, Inc., 580-32 Nagaura, Sodegaura-City,
Chiba 299-0265, Japan
Abstract—Oxygen mixed with nitrogen trifluoride (NF
3
) was used as the gas source for the plasma
etching to increase the etching rate of the polyimide (PI) film.
In order to investigate the effects of NF
3
addition, surfaces of the etched PI films were analyzed
with various methods. From the results of x-ray photoelectron spectroscopy (XPS), the chemical
bonding state of the etched PI surface with 30% NF
3
/ 70% O
2
plasma was similar to that of the sur-
face prepared using 100% O
2
plasma. The results of FT-IR analyses showed that a part of materials
deposited on the etched PI film was soluble in chloroform and it contained carbonyl and ether com-
pounds.
Furthermore, the etching products were analyzed using quadrupole mass spectrometry (QMS)
and gas chromatography. The main products were found to be H
2
O, HF, CO and CO
2
. In addition,
CO/CO
2
ratio was found to be related to the etching rate which depended on the NF
3
concentration.
Keywords
: Polyimide; etching; nitrogen trifluoride; oxygen; RF plasma.
1. INTRODUCTION
Polyimides (PI) have excellent thermal stability, chemical stability and electrical
properties [1, 2]. PI films have been used as an insulating layer in print circuit
boards (PCBs) [3]. Oxygen plasma has been used for the surface modification and
etching of polymer films [4-10]. Oxygen mixed with carbon tetrafluoride (CF
4
) or
sulfur hexafluoride (SF
6
) has been used as the gas source for the plasma etching to
increase the etching rate of the polyimide (PI) film [11-20]. However, there are
only a few reports on the PI etching with nitrogen trifluoride (NF
3
) [21, 22]. We
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