Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Utility Patent
1999-05-03
2001-01-02
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S636000, C438S669000, C430S318000
Utility Patent
active
06169029
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for providing an improved anti-reflective coating (ARC) layer during the fabrication of sub-micron or deep-sub-micron semiconductor devices utilizing the deep UV technology. More specifically, the present invention relates to an improved method which solves the often-encountered low production yield problem when an inorganic ARC, such as TiN, and an organic ARC are both used to form a combined anti-reflective coating above a metal layer during the fabrication of sub-micron and/or deep-sub-micron semiconductor devices. The method disclosed in the present invention allows a more precise image transfer of the photoresist onto the metal layer so as to allow a further reduction of the critical dimension of the metal pattern, without incurring the penalty of reduction in production yield.
BACKGROUND OF THE INVENTION
During the fabrication of semiconductor devices, an inorganic anti-reflective coating (ARC) such as TiN is often deposited on top of a metal layer. By providing an anti-reflective coating, less light is reflected back through the photoresist and toward the photomask. As a result, the photoresist can be more precisely patterned on the metal layer with the additional step of providing the TiN anti-reflective layer.
The need for precise patterning of photoresists becomes even more critical for the fabrication of sub-micron and/or deep-sub-micron semiconductor devices, especially in the formations of shallow trench isolations (STI), poly gates, etc. which involve the deep UV technology to satisfy the ever-decreasing critical dimension of semiconductor devices. More recently, the deep UV technology is also commonly used in forming metal layers, allowing the metal conducting lines to assume an even smaller critical dimension. When the deep sub-micron technology now moves from 0.25 &mgr;m, 0.20 &mgr;m, to 0.18 &mgr;m and even smaller geometry, the need for a more precise patterning technology, and, thus, an improved anti-reflective coating technology, cannot be overstated.
In the fabrication of the metal layer, typically a combined Ti and TiN layer is sputtered to serve as a barrier layer. Then an aluminum layer is sputtered on the barrier layer. Finally, a TiN layer is sputtered on the metal layer to form the top anti-reflective coating. It has been observed that NH
3
is often generated during the deposition of the TiN layer. The NH
3
gas, which is basic in nature (i.e., pH>7), can react with the acidic material which may be released during the deep UV exposure of the photoresist layer. As a result, the so-called “bottom foot” can be formed at the bottom face of the photoresist, causing the formation of an irregular critical dimension profile.
To ameliorate this problem, an organic anti-reflective coating can be coated on top of the TiN layer so as to prevent the direct contact of the NH
3
gas with the photoresist. The provision of the additional layer of organic anti-reflective coating can also prevent the generation of standing waves and enlarge the process window of the underlying lithography process.
However, the addition of the organic anti-reflective coating on top of the TiN coating appears to cause another type of problem, in that the occurrence of the incidents of metal line shorting is observed to have increased, thus causing the wafer yield to be reduced. The use of inorganic and/or organic anti-reflective coatings is well-known in the art. The following most recent U.S. patents are cited to provide useful background information.
U.S. Pat. No. 5,760,483 discloses methods to enhance the contrast between alignment targets and adjacent materials on a semiconductor. In one embodiment, the TiN layer that is deposited during earlier processing step is tripped away to enhance the reflectivity of the metal layer. The contrast between the alignment target and the adjacent material that is more consistent over variations in oxide thickness. The more uniform contrast makes it easier for the stepper system to identify the edges of the alignment target, resulting in a more exact placement of the mask.
U.S. Pat. No. 5,670,298 discloses a method to form a metal pattern on a substrate. It mentions the use of an anti-reflective coating to restrain the notching phenomenon which may occur when carrying out a photolithography process for forming a metal pattern. While there is widely used an inorganic anti-reflective coating process which reduces the light reflection of metal film formed under the photoresist pattern, an organic anti-reflective coating which uses a polymer as a coating material may also be used.
U.S. Pat. No. 5,767,013 discloses a method for forming an interconnection pattern in a semiconductor device for reducing metallic reflection without requiring an anti-reflective coating. The method includes the steps of forming a conductive layer on a substrate, polishing the conductive layer to form a rugged surface on the conductive layer, and selectively removing the polished conductive layer to form the interconnection. The '013 patent mentioned that for an anti-reflective coating, the inorganic process uses TiN, SiN
4
, and TiW as inorganic film, whereas the organic process uses polymer as organic film. The '013 patent also mentioned the difficulty in controlling etch selectivity for the ARC film and the metal film, and overetching of the metal film can often occur, causing formation of unnecessary gaps in a planarizing film formed thereon.
At the present time, it is not known why a combination of the organic and inorganic anti-reflective coatings would cause the production yield to suffer. In light of the several advantages of using the combined organic and inorganic anti-reflective coatings, it is highly desirable to develop a method that will overcome the prior art problem and allow a more precise patterning of the photoresist to be achieved for the sub-micron and deep submicron processes which utilize the deep UV technology.
SUMMARY OF THE INVENTION
The primary object of the present invention is to develop a method that will allow precise patterning of photoresist to be achieved in conjunction with the use of the deep UV technology without suffering reductions in the production yield. More specifically, the primary object of the present invention is to develop a method which will allow an anti-reflective coating layer to contain both an organic anti-reflective film and an inorganic anti-reflective film, more particularly a TiN film, so as to enjoy the advantages of the combined anti-reflective coating while eliminating the production yield problems that may be associated therewith, during the fabrication of sub-micron or deep sub-micron semiconductor devices.
After careful examination of the combined organic and inorganic anti-reflective coatings that have been provided on a metal layer, it was discovered by the inventor of the present invention, that an oxidized composition can be formed between the organic anti-reflective film and the inorganic anti-reflective film when the two different types of films were formed adjacent to each other. It was also found that the oxidized composition so formed cannot be easily etched away by the conventional oxide etcher or a metal etcher. As a result, a metal stringer can be formed from the metal line, causing the metal line to short and the production yield to drop, sometimes precipitously.
In the process disclosed in the present invention, a partitioning layer is formed on top of the inorganic anti-reflective film prior to the deposition of the organic anti-reflective film. The partitioning layer, which can be easily removed by an oxide etcher or metal etcher, serves to isolate the organic anti-reflective film from being in direct contact with the inorganic anti-reflective film. Unexpected results were observed in that production yield can be substantially improved by the implementation of the process disclosed in the present invention. The formation of such a partitioning layer between the two types of anti-reflective films effectively prevents the
Liauh W. Wayne
Nguyen Ha Tran
Niebling John F.
Winband Electronics Corp.
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