Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-04-28
2002-06-25
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
Reexamination Certificate
active
06410421
ABSTRACT:
FIELD OF THE INVENTION
The present invention is, in general, directed to a semiconductor device having an anti-reflective structure. In particular, the present invention relates to a semiconductor device with an anti-reflective structure which contains indium tin oxide and is especially useful for patterning metal layers with light having a wavelength between about 190 to about 300 nm.
BACKGROUND OF THE INVENTION
Over the last few decades, the electronics industry has undergone a revolution through the use of semiconductor technology to fabricate small, highly integrated electronic devices. As these devices become smaller, there is a need for forming increasingly narrow conductive lines and interconnects in these devices. Many of these conductive lines and interconnects are formed using metals, including, for example, aluminum or copper. A layer of the metal is often formed over the substrate and previously formed layers of the device and then the metal layer is patterned to form the conductive lines and interconnects. A standard patterning technique is photolithography, in which a photoresist is deposited over the layer of metal and a mask is used to expose the photoresist with light which is passed through the mask. The machines used today are referred to as steppers or scanners and the pattern created by the mask can be the same size as the mask or reduced by a factor of, for example, five or ten. After exposure to light, the photoresist is developed, for example, by rinsing in a developing solution. The metal layer can then be etched to remove the unwanted material according to the desired pattern.
The wavelength of light used to expose the photoresist will typically determine the minimum size of a feature that can be patterned. Current 0.25 &mgr;m generation design rules call for patterning 0.4 &mgr;m lines and spaces in the metal interconnect layers. The exposure wavelength for patterning the photoresist for 0.4 &mgr;m design rules is typically 365 nm. For more aggressive gate layer design rules, requiring 0.25 &mgr;m lines and spaces, the exposure wavelength is 248 nm.
Future CMOS devices are expected to have gatewidths of about 0.18 &mgr;m and metal line widths and spaces of about 0.3 &mgr;m. This will require light with shorter wavelengths. One convenient wavelength is 248 nm, available from a KrF laser. Furthermore, CMOS devices may be designed with 0.13 &mgr;m or smaller gatewidths. These devices will require photoresist patterning with even shorter wavelengths, including, for example, the 193 nm line of an ArF laser.
One particular difficulty with patterning metal layers is the inherent reflectivity of the metal. High reflectivity can distort the mask image in the photoresist In general, there are three phenomena which degrade the resist image on reflective surfaces, such as metal or silicon. First, standing waves can be generated within the resist in the vertical direction due to the constructive and destructive interference of the incident and reflected light. Standing waves in the resist profile produce vertical waves in the resist which can lead to etching problems. A second effect, referred to as “swing”, occurs when there is a change in the resist thickness due to a topographical change in the underlying layers (e.g., a change in thickness of the underlying layers). The horizontal width of the line is affected due to the path length difference of light reflected from either side of the topographical feature. The third effect is called “reflective notching” and occurs when the topography of the underlying surface (e.g., a slope in the topography) causes the reflection of light at angles which are not perpendicular to the surface of the photoresist. The reflected light then exposes portions of the photoresist which results in the removal of inappropriate portions of the desired lines (i.e., notches in the lines). Thus, to properly expose the resist, the reflectivity of the substrate below the resist must be very low. Ideally, this reflectivity should be 3% or less.
Aluminum and copper are commonly used metals for conductive lines and interconnects in semiconductor devices. These metals have reflectivities of about 80-90%. Therefore, an anti-reflective structure is applied over the metal layer prior to applying the photoresist. One commonly used anti-reflective structure is titanium nitride (TiN), which has a low reflectivity at 365 nm. However, at 248 nm, the reflectivity of titanium nitride is much greater than 3% and the reflectivity of titanium nitride is even larger for 193 nm light.
SUMMARY OF THE INVENTION
Generally, the present invention relates to a method of manufacturing a semiconductor device with an anti-reflective structure for use in patterning metal layers. One embodiment is a method of making a semiconductor device which includes forming a metal layer over a substrate of the semiconductor device. An anti-reflective coating is then formed over the metal layer. The anti-reflective coating is made with indium tin oxide. A photoresist layer is formed over the anti-reflective coating. In the presence of the photoresist layer, the anti-reflective coating reflects no greater than about 3% of light having a wavelength within the range of 190-300 nm.
In another embodiment, the anti-reflective coating includes two sublayers. The first sublayer is formed over the metal layer and contains titanium nitride. The second sublayer is formed over the first sublayer and contains indium tin oxide.
A further embodiment is a method of making a semiconductor device by forming a metal layer over a substrate of the semiconductor device. An anti-reflective coating is formed over the metal layer. The anti-reflective coating is made with indium tin oxide. A photoresist layer is then formed over the anti-reflective coating. The photoresist layer is irradiated with light having a wavelength from about 190 to about 300 nm to generate a pattern in the resist layer. In the presence of the photoresist layer, the anti-reflective coating reflects less than about 3% of the light. Following the illumination, a portion of the metal layer is removed according to the pattern.
Another embodiment is a semiconductor device having a substrate and a metal layer formed over the substrate. An anti-reflective coating is formed over the metal layer. The anti-reflective coating includes indium tin oxide. A photoresist layer is formed over the anti-reflective layer. In the presence of the photoresist layer, the anti-reflective coating reflects less than about 3% of light having one or more wavelengths within the range of 190-300 nm.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.
REFERENCES:
patent: 5126220 (1992-06-01), Tokitomo et al.
patent: 5591566 (1997-01-01), Ogawa
patent: 6162586 (2000-12-01), Sengupta et al.
Ghandehari Kouros
Sengupta Samit
Hoang Quoc
Koninklijke Philips Electronics , N.V.
Nelms David
Zawilski Peter
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