Method of stabilizing anti-reflection coating layer

Details Method of stabilizing anti-reflection coating layer Method of stabilizing anti-reflection coating layer

1999-12-20

2001-05-01

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S029000, C438S048000, C438S199000, C438S584000, C438S671000, C438S636000, C438S072000, C438S952000, C257S021000, C257S069000, C257S204000

Reexamination Certificate

active

06225219

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of fabricating an anti-reflection coating (ARC) layer. More particularly, the present invention relates to a method of stabilizing the ARC layer.
2. Description of Related Art
During a photolithography module of an integrated circuit (IC) fabrication, masks are often made to allow several patterns to be transferred onto a wafer. Each of the masks is usually formed by irradiating a layer of photoresist with light, while unwanted areas of photoresist are removed in a development step to leave behind the desired mask. However, those masks have known to be formed over many reflective materials such as aluminum or polycrystalline silicon which often reflect light into regions of photoresist that are not intended to be irradiated. The unintentional irradiation causes the resulting mask to be inaccurate by causing reflective notching in the mask or inaccurate line width.
Reflective notching on highly reflective substrates and linewidth (or critical dimension, CD) variations due to topography and film thickness non-uniformity have been a difficult problem for semiconductor manufacturers. A useful method such as an anti-reflective coating (ARC) has been developed to suppress reflectivity, which method involves applying an ARC layer over the reflective material before the application of the photoresist. Conventionally, different types of ARC layers, including organic and inorganic ones have been developed. Since problems, such as reacting with the underlying layers have occurred when the organic ARC layers are used, most of the process preferentially adopts the inorganic ARC layer instead.
Typically, an inorganic ARC layer, such as silicon oxy-nitride (SiON) layer is used to prevent the above-mentioned problem.
FIGS. 1A and 1B
are cross-sectional, schematic diagrams illustrating the fabrication of ARC layer during a conventional photolithography module, in which a substrate
100
is provided with a gate oxide layer
102
, a polysilicon layer
104
, and a SiON layer
106
formed in sequence thereon. A photoresist layer
108
is then formed over the SiON layer
106
. Next, an exposure step is performed where a selected light source that passes through a photomask
110
irradiates the photoresist layer
108
to initiate a photochemical transformation, which replicates a desired mask pattern in the photoresist layer
108
a
. A development step is then performed to transfer the mask pattern onto the wafer.
It has recently been known that reflectance of the SiON layer
106
fluctuates over time, while the reflectance fluctuation of the SiON layer
106
makes it difficult to control the exposure conditions during the photolithographic process. This leads to reflective notching in the photomask
110
, where the desired pattern is distorted. Subsequently, a part of the photoresist layer
108
b
is removed, leading to formation of IC device with non-uniform CD. A quality control step, such as after develop inspection (ADI) is executed to check whether the specification of the photolithography process is met, while the photolithography module is stripped and reworked to compensate any abnormalities that causes permanent damage to the wafer in the subsequent process. However, measurements of CD taken during ADI indicate that the reflectance of the SiON layer
106
still fluctuates under the same exposure conditions even after reworks. Therefore, it is necessary to develop a method for stabilizing the specificity of the SiON layer.
SUMMARY OF THE INVENTION
The invention provides a method of stabilizing an anti-reflection coating (ARC) layer, which method provides a substrate with a dielectric layer, a conductive layer, and the ARC layer. The ARC layer is treated in an alloy treatment step prior to forming a photoresist layer over the ARC layer. A photomask with a desired pattern is provided over the photoresist layer and a photolithographic process is performed, so that the pattern is transferred onto the wafer.
As embodied and broadly described herein, the invention provides an alloy treatment which mix the ARC layer with a gas source, such as a mixture of H
2
and N
2
gases, followed by heating the ARC layer with the gas source in a furnace. The treatment is performed in this case to stabilize the specificity of the ARC layer, which has been known to suppress the undesired reflection.
Accordingly, the alloy treatment is performed to stabilize the specificity of the ARC layer, so that the reflectance of the ARC layer is maintained as a stable value even the photolithographic module is reworked to ensure that critical dimensions (CD) are within the specified tolerances. Therefore, the exposure conditions are stabilized in the photolithographic process, while it is possible to control the critical dimension (CD) of the IC device. The problems related to CD inaccuracy are thus solved according to the method developed in the present invention, so that the fabrication is verified as correctly carried out.
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.


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