Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-03-21
2002-07-23
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S314000, C430S330000, C430S950000
Reexamination Certificate
active
06423474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to integrated circuit processing and, more particularly, to a method of using dielectric anti-reflective coating (DARC) in conjunction with bottom anti-reflective coating (BARC) to form an anti-reflective barrier layer that conforms to the topography of the substrate surface and is tuned to function effectively in both annealed and unannealed states.
2. Description of the Related Art
The typical semiconductor process involves implanting or depositing regions or layers of different material either into or on different regions of a semiconductor substrate. To ensure that the material is positioned at the correct location on the semiconductor substrate, a photo imaging process is typically used to define the regions that are to subsequently receive the material. The conventional photo imaging process, known as photolithography, generally involves projecting light waves onto a photoresist surface so that the light can react with the photoresist to create an imaged pattern. The photoresist can then be selectively removed as a result of the exposure such that a region of the semiconductor device is exposed to receive the additional material.
In some cases the light waves are known to propagate through the photoresist, reach the underlying substrate, and reflect from the substrate surface back through the photoresist. The reflected light can interfere with other waves propagating through the photoresist and ultimately reduce the accuracy and precision of the image transferred. In particular, the reflected light can interfere and scatter light waves that are being directed towards a particular region of the photoresist which in turn reduces the effectiveness of exposure intended for the region. As a consequence, the region of the photoresist may not be as uniformly exposed and selective removal of the photoresist during subsequent processing steps may be affected. Furthermore, light reflected from the substrate surface can scatter, especially if the substrate surface is non-planar, such that the scattered light can inadvertently expose the photoresist surrounding the desired region of the photoresist. Hence, the reflected light can expose regions of the photoresist that should otherwise remain unexposed which limits the ability to precisely define regions of the photoresist for selective removal.
To address this particular problem associated with the photo imaging process, anti-reflective coatings are commonly used to attenuate or absorb the light waves reflected from the substrate surface during photo exposure operations. Anti-reflective coatings are materials generally known for their ability to absorb various wavelengths of radiation. They are typically interposed between the substrate surface and the photoresist so as to serve as a barrier that inhibits the reflected waves from traversing back through the photoresist and adversely affecting the imaging process. Dielectric anti-reflective coating (DARC) and bottom anti-reflective coating (BARC) are examples of anti-reflective materials that are commonly used to absorb radiation reflected from the substrate surface during the photo imaging operations of integrated circuit processing.
In particular, BARC is generally available as a low-viscosity liquid that can be applied onto the substrate surface using a well known spin coating process. Disadvantageously, however, BARC cannot be universally applied to all substrate surfaces. The relatively low viscosity of BARC and inherent limitations of the spin coating process render BARC inadequate in covering substrate surfaces with a substantially contoured topography. In particular, BARC is known to accumulate or pool in recessed regions on a non-planar surface while leaving most high profiled areas on the substrate exposed. Furthermore, BARC is known to vaporize under high temperature conditions that are characteristic of most annealing operations and therefore is typically rendered useless following high temperature annealing.
To address this problem associated with BARC, dielectric anti-reflective coating (DARC) is often used in place of BARC for substrates having a contoured topography or for substrates that are subjected to high temperature annealing. DARC is chosen largely for its ability to conform to the contours of the substrate surface and its ability to withstand the typical annealing operation. Furthermore, it is generally known that the composition of DARC can be adjusted or tuned to function effectively in either annealed or unannealed states
Disadvantageously, however, DARC that is adjusted to function effectively in an annealed state tends to be ineffective before being unannealed. Likewise, DARC that is tuned to work effectively before annealing usually loses its anti-reflective properties after high temperature annealing. Consequently, more than one layer of DARC is generally applied to substrates that undergo high temperature annealing between successive photo imaging steps. However, the formation of multiple layers of DARC onto the substrate surface typically involves repeatedly exposing the substrate to high temperature conditions that are characteristic of most DARC deposition methods. It can be appreciated that subjecting substrates to multiple thermal sequences is not only costly and time consuming but also can increase the occurrence of defects in the substrate.
Hence, from the foregoing, it will be appreciated that there is a need for a method of inhibiting light waves from reflecting back through the photoresist during photo exposure operations such that the method can be applied universally to most substrate surfaces and is not affected by thermal cycling. To this end, there is a particular need for an anti-reflective barrier layer that substantially conforms to the topography of the substrate surface and is adapted to function effectively in both annealed and unannealed states.
SUMMARY OF THE INVENTION
The aforementioned needs are satisfied by the method of the present invention which uses dielectric anti-reflective coating (DARC) in conjunction with bottom anti-reflective coating (BARC) to form an anti-reflective barrier layer that substantially conforms to the topography of the substrate surface and is tuned to function effectively in both annealed and unannealed states.
In one aspect, this invention comprises a method of forming an anti-reflective barrier layer on a substrate surface wherein a layer of DARC is first formed on an upper surface of the substrate and a layer of BARC is subsequently formed on an upper surface of the DARC layer. Preferably, the DARC layer substantially conforms to the topography of the substrate surface and provides a surface that is adapted to receive the BARC layer. Preferably, the composition of DARC is adjusted in a manner such that its anti-reflective properties are optimized after undergoing high temperature annealing while the BARC is selected for its ability to absorb light waves before annealing. In one embodiment, the composition of DARC comprises silicon, oxygen, nitrogen and the composition of BARC comprises organic polymers made of carbon, oxygen, and nitrogen. However, it can be appreciated that a variety of other formulations of DARC and BARC can be used without departing from the scope of the present invention.
In another aspect of this invention, the method of using DARC in conjunction with BARC as a barrier layer is adapted to attenuate reflected radiation generated during the photo imaging operations of FLASH memory circuit processing. In particular, the FLASH memory circuit processing typically involves the formation of a gate stack which typically comprises high temperature annealing operations interposed between multiple print and etch steps. As such, it is desirable to form a barrier layer that functions as an effective anti-reflective coating during photo imaging operations both before and after annealing.
In one embodiment, a layer of DARC is formed on an upper surface of a nitride cap layer of a conventional gate stack for FLASH m
Barreca Nicole
Huff Mark F.
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