Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
1998-12-15
2001-04-17
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C134S001100, C134S001200
Reexamination Certificate
active
06218084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for removing a photoresist layer and polymers layer in the fabrication of a semiconductor device. More particularly, the present invention relates to a high-density plasma method using mixing gases as source for removing a photoresist layer and polymers layer generated during plasma etching process.
2. Description of the Related Art
In the fabrication procedure of a metal oxide semiconductor (MOS), photoresist layers are widely used in patterning processes. However, after an etching step is performed, the photoresist layer and the sidewall polymers generated during plasma etching step needs to be removed for subsequent processes. When the photoresist/polymers layer is not removed completely, the residue affects subsequent processes and debases the quality of the device. Accordingly, it is important to avoid leaving any photoresist/polymers layer residue when the photoresist/polymers layer is removed.
In the conventional photolithography method, integrated circuit patterns transferred on wafers comprises steps of coating a photoresist layer over the wafer. The photoresist layer is sensitive to light and resistant to etching. The image of the master mask is replicated on the photoresist layer by an exposure system to form a photoresist layer. An etching step is performed to form the predetermined pattern on the wafer by using the patterned photoresist layer as an etching mask layer. At present, high-density plasma (HDP) is usually used to perform an anisotropic etching step, and during the etching step, heavy sidewall polymers are deposited to meet etching requirements (e.g. etching selectivity to substrate and profile control etc.). Following the oxide plasma etching, the patterned photoresist layer and sidewall polymer layers are stripped away in-situ. However, during high-density plasma etching, some undesirable residues are generated and accumulated on the surface of the photoresist layer and/or the sidewall of the opening formed by etching. The residues cannot be removed easily by oxygen plasma and leave on the wafer to affect the subsequent processes. The main residues include the following:
1. Cross-linking polymer generated by ultraviolet irradiation is generated on the top surface of the photoresist layer;
2. Silicon-containing polymer is generated while performing the etching step; and
3. The polymers on the sidewall of the opening are generated during etching from the gasses such as C
4
H
8
, CH
2
F
2
, and C
3
H
2
F
6
.
The residues often cannot be cleaned by solvents and result in contamination and defects in the following subsequent process. Recently, in order to avoid photoresist residues as mentioned above left on the wafer, a bias is applied to the wafer to enhance the ion bombardment when the oxygen (O
2
) plasma is performed to remove the photoresist layer.
FIG. 1A
is schematic, cross-sectional view of the conventional HDP oxide etcher for removing a photoresist/polymers layer by plasma.
FIGS. 1B through 1C
are schematic, cross-sectional views of the conventional plasma method for removing a photoresist layer.
As shown in
FIG. 1A
, a bias is applied on a wafer
114
to enhance the ion bombardment of plasma for removing a photoresist layer
104
(as shown in FIG.
1
B).
As shown in
FIG. 1B
, after an opening
108
is formed, an in-situ oxygen plasma etching step is used to remove the photoresist layer
104
and polymer layer
106
. As the residual polymers
106
are generated on the top surface of the photoresist layer
104
, it is difficult to strip away the photoresist layer
104
completely.
As shown in
FIG. 1C
, since the ion bombardment of the oxygen plasma is enhanced, the substrate
100
and an oxide layer
102
underneath the photoresist layer
104
are attacked by the plasma. Accordingly, it is desirable to develop a new method to solve the problems such as the loss of substrate and oxide and an inability to control the critical dimension of the opening during in-situ oxygen plasma etching step.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a method for removing a photoresist layer and polymers on the wafer surface without any photoresist residues left.
It is an another objective of the present invention to provide a method for removing a photoresist layer as well as controlling the critical dimension of the openings formed during etching.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, this invention provides a method for removing photoresist and polymer layer without any residues by using an additional gas mixed with oxygen as a source for in-situ plasma etching. The present method comprises the steps of providing a wafer having an oxide layer, a photoresist layer, an opening penetrating through the photoresist layer and the oxide layer. An in-situ plasma-etching step is performed by using a mixing gases containing oxygen as a source of plasma to remove the photoresist layer.
In a preferred embodiment of the present invention, the gases for mixing with oxygen as a source for plasma etching is selected from the group consisting of nitrogen, hydrogen-containing gas, the combinations thereof and the likes.
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.
REFERENCES:
patent: 5908319 (1999-06-01), Xu
patent: 5908735 (1999-06-01), Kim
patent: 6040110 (2000-03-01), Shirai
Chen Tong-Yu
Huang Michael W C
Yang Chan-Lon
Barreca Nicole
Huff Mark F.
Oppenheimer Wolff & Donnellv, LLP
United Microelectronics Corp.
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