Method for high-density plasma etching

A method for high-density plasma etching. A substrate is provided. A material layer is formed on the substrate. A patterned photo-resist layer is formed on the oxide layer. The material layer is patterned by the high-density plasma etching, simultaneously, a formation of a barrier layer over the substrate with the patterning process is suppressed and nitrogen gas generated in the patterned photo-resist layer is reduced.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an etching method. More particularly, the
 present invention relates to a method for high-density plasma etching.
 2. Description of the Related Art
 In the device patterning process, to enhance the photosensitivity contrast,
 amine compounds are often added into a photo-resist layer. While
 performing the conventional etching process using a high density plasma
 (HDP) oxide etcher, a high intensity ultraviolet (UV) radiation is
 generated. It is found that the amine compounds from the photo-resist
 materials would be decomposed under the high-intensity UV radiation and
 produce nitrogen gas. Resist bubblings are thus occurred in the
 photo-resist layer by the diffusion of the nitrogen gas. Being obstructed
 by a barrier layer formed on the photo-resist layer, the bubbles of the
 nitrogen gas are further retained in the photo-resist layer instead of
 sweating out. After accumulated a certain concentration or pressure to
 certain, a pressure burst is easily caused.
 SUMMARY OF THE INVENTION
 Accordingly, the invention provides a method for high-density plasma
 etching. A substrate is provided. A material layer is formed on the
 substrate. A patterned photo-resist layer is formed on the oxide layer.
 The material layer is patterned by the high-density plasma etching,
 simultaneously, a formation of a barrier layer over the substrate Ninth
 the patterning process is suppressed and nitrogen gas generated in the
 patterned photo-resist layer is reduced. Adjustments of high-density
 plasma etching process parameters are made to reduce the intensity of the
 induced UV radiation, the amount of the nitrogen gas, so as to suppress
 the bubbling effect. The parameters includes an operation pressure, a flow
 rate of carbon monoxide, a flow rate of an argon gas, a flow rate of
 octafluorocyclobutane (C.sub.4 F.sub.8), a supplied power, and a process
 temperature.
 Moreover, by adjusting the above parameters, the barrier layer formed on
 the photo-resist layer dog etching process becomes thinner and easier to
 release trapped nitrogen gas. Even nitrogen gas is produced, the bubbles
 can be avoided with less obstruction by the thinner barrier layer.
 It is to be understood that both the foregoing general description and the
 following detailed description are exemplary, and are intended to provide
 further explanation of the invention as claimed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A photolithography process comprises steps of exposure, development of a
 photo-resist layer to transfer a pattern from a photo-mask to the
 photo-resist layer. The photoresist layer is then etched and used as a
 mask to etch and define a layer underlying the photo-resist layer.
 FIG. 1 shows a method of etching an underlayer of a photo-resist layer over
 a substrate A material layer 32 to be patterned is formed on a substrate
 30. The material layer 32 can be made of oxide by chemical vapor
 deposition, for example. A patterned photo-resist layer 34 is formed and
 patterned on the material layer 32.
 During the step of forming the patterned photo-resist layer 34, amine
 compounds are often added into the photo-resist layers to increase the
 photosensitivity contrast. However, it is found that while performing a
 high density plasma dry etching on the material layer 32, a high intensity
 ultra-violet light is induced. Under the high intensity ultra-violet
 light, the amine compounds reacted with the photo-resist layer and are
 decomposed into a nitrogen gas. The nitrogen gas is then diffused through
 the photo-resist layer and cause bubbles therein. In addition, during
 etching, a barrier layer 36, that is, a polymer layer, is produced to
 improve the selectivity and profile control. The formation of the barrier
 layer 36 on the photo-resist layer 34 thus easily blocks the bubbles from
 sweating out. The accumulation of trapped nitrogen gas leads to a pressure
 burst.
 In the invention, parameters of the HDP etching process are adjusted to
 control the intensity of the induced UV radiation With a reduced induced
 UV radiation intensity, the product of the nitrogen gas is suppressed, or
 even eliminated. In another aspect, the parameters of the HDP etching
 process are adjusted to reduce the thickness of the barrier layer which
 obstruct the release of the bubbles trapped within the photoresist layer.
 The parameters comprises a flow rate of argon monoxide (CO), an operation
 pressure in a high-density plasma chamber, a flow rate of argon gas (Ar),
 a flow rate of octafluorocyclobutane (C.sub.4 F.sub.8), a supplied power,
 and a process temperature. The HDP process in the present invention can be
 performed without supplying an argon gas.
 From the experiment, it is found that to achieve the above object, the flow
 rate of CO is preferably ranged about 10 to 25 sccm, or even as high as
 about 50 sccm. The operation pressure is about 3 mTorr to 100 mTorr. The
 flow rate of argon gas is about 100 sccm to 500 sccm. Or alternatively,
 the etching process can be performed without supplying an argon gas. The
 flow rate of C.sub.4 F.sub.8 is preferably about 10 sccm to 20 sccm. The
 supplied bias power is preferably about 500 W to 2000 W. The supplied
 total source power is preferably about 500 W to 2000 W. The process
 temperature preferably is as chill as about -15.degree. C. to 10.degree.
 C. With the parameters described above, the intensity of UV radiation can
 be effectively reduced to prevent generating nitrogen gas. Additionally,
 the formation of the polymer layer is suppressed. With the reduction of
 the polymer layer, the trapped nitrogen gas can be effectively released
 from the polymer layer.
 In summary, the invention includes at least the following advantages:
 1. The invention decreases the amount of the nitrogen gas generated during
 the high-density plasma etching.
 2. In comparison with the conventional method, the thickness of the polymer
 layer formed during high-density plasma etching is specifically decreased.
 Thus, the pressure burst does not occur.
 It will be apparent to those skilled in the art that various modifications
 and variations can be made to the structure and the method of the present
 invention without departing from the scope or spirit of the invention. In
 view of the foregoing, it is intended that the present invention cover
 modifications and variations of this invention provided they fall within
 the scope of the following claims and their equivalents.