Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-04-26
2002-09-03
Trinh, Michael (Department: 2822)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S735000, C438S757000
Reexamination Certificate
active
06444588
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the fabrication of integrated circuits. More particularly, the present invention relates to anti-reflective layers used in such fabrication.
BACKGROUND OF THE INVENTION
One important process in fabrication of integrated circuits (ICs) is photolithography. Generally, photolithography involves reproducing an image from a mask in a layer of photoresist that is supported by underlying layers of a semiconductor substrate assembly. Photolithography is a very complicated and critical process in the fabrication of ICs. The ability to reproduce precise images in a photoresist layer is crucial to meeting demands for increasing device density.
In the photolithographic process, first an optical mask is positioned between the radiation source and the photoresist layer on the underlying layers of a semiconductor substrate assembly. A radiation source can be, for example, visible light or ultraviolet radiation. Then, the image is reproduced by exposing the photoresist to radiation through the optical mask. Portions of the mask contain an opaque layer, such as, for example, chromium, that prevents exposure of the underlying photoresist. The remaining portions of the mask are transparent, allowing exposure of the underlying photoresist.
The layers underlying the photoresist layer generally include one or more individual layers that are to be patterned. That is, when a layer is patterned, material from the layer is selectively removed. The ability to pattern layers and material enables ICs to be fabricated. In other words, the patterned layers are used as building blocks in individual devices of the ICs. Depending on the type of photoresist used (e.g., positive type or negative type photoresist), exposed photoresist is either removed when the substrate is contacted with a developer solution, or the exposed photoresist becomes more resistant to dissolution in the developer solution. Thus, a patterned photoresist layer is able to be formed on the underlying layers.
One of the problems experienced with conventional optical photolithography is the difficulty of obtaining uniform exposure of the photoresist underlying transparent portions of the mask. It is desired that the light intensity exposing the photoresist be uniform to obtain optimum results.
When sufficiently thick layers of photoresist are used, the photoresist must be or become partially transparent so that photoresist at the surface of underlying layers is exposed to a substantially similar extent as the photoresist at the outer surface. Often, however, light that penetrates the photoresist is reflected back toward the radiation source from the surface of the underlying layers of the substrate assembly. The angle at which the light is reflected is at least in part dependent upon the topography of the surface of the underlying layers and the type of material of the underlying layers. The reflective light density can vary in the photoresist throughout its depth or partially through its depth, leading to non-uniform exposure and undesirable exposure of the photoresist. Such exposure of the photoresist can lead to poorly controlled features (e.g., gates, metal lines, etc.) of the ICs.
In an attempt to suppress reflectivity, or in other words to minimize the variable reflection of light in a photoresist layer, anti-reflective coatings, i.e., anti-reflective layers, have been used between the underlying layers of a substrate assembly and the photoresist layer or between the photoresist layer and the radiation source. Such anti-reflective coatings suppress reflectivity from the underlying substrate assembly allowing exposure across a photoresist layer to be controlled more easily from the radiation incident on the photoresist from the radiation source.
Anti-reflective coatings can be formed of organic materials. Organic layers can, however, lead to particle contamination in the integrated circuit (IC) due to the incomplete removal of organic material from the underlying layers after the photolithography step is performed. Such particle contamination can potentially be detrimental to the electrical performance of the IC. Further, the underlying layers upon which the organic materials are formed may be uneven, resulting in different thicknesses of the organic material used as the anti-reflective coating, e.g., thicker regions of organic material may be present at various locations of the underlying layers. As such, when attempting to remove such organic material, if the etch is stopped when the underlying layers are reached, then some organic material may be left. If the etch is allowed to progress to etch the additional thickness in such regions or locations, the underlying layers may be undesirably etched.
Further, inorganic anti-reflective layers have also been introduced for suppressing reflectivity in the photolithography process. For example, silicon-rich silicon dioxide, silicon-rich nitride, and silicon-rich oxynitride have been used as inorganic anti-reflective layers, such as in the patterning of metal lines and gates.
After a patterned photoresist layer is formed on a substrate assembly, many other processes are typically performed in the fabrication of ICs. For example, the photoresist can act as an implantation barrier during an implant step, the photoresist can be used to define the outer perimeter of an area (e.g., a contact hole) that is etched in one or more underlying layers of the substrate assembly, or the photoresist may be used in any other typically used fabrication process. In many of such cases, the photoresist acts as a barrier during the etching process, such that only selective material of the one or more underlying substrate assembly layers is removed.
After the processes involving photolithographic techniques are carried out (e.g., implantation, etching, etc.), in many circumstances not only must the photoresist material used in the photolithographic process be removed, but the anti-reflective coating may also be removed. For example, in many cases, the photoresist and the anti-reflective coating used to define the contact opening needs to be removed prior to subsequent processing of the structure. However, in many other circumstances, after the photoresist material used in the photolithographic process is removed, the anti-reflective coating is still required in later processing steps. Therefore, the anti-reflective coating is not removed. For example, the anti-reflective coating may be used to level the topography to increase dimensional stability of later deposited lines. Further, anti-reflective coatings in subsequent processing steps may also include use of the anti-reflective coating as an etch stop layer, such as for self-aligned contact etch processes or for other etch hardmask techniques.
Generally, anti-reflective coatings used for photolithographic processing are easily removed using wet etchants. Such removal of the anti-reflective coatings may even be removed during the etching of layers underlying the anti-reflective coating and patterned photoresist during photolithographic processing. Such ease of removal of the anti-reflective coatings is not always desirable.
SUMMARY OF THE INVENTION
There is a need for inorganic anti-reflective coating material layers used in photolithographic processing which are not easily removed such that the layers can be used in later processing steps. Anti-reflective coating material layers according to the present invention have decreased wet etch rates relative to conventionally used inorganic anti-reflective coatings. As described herein, the etch rate of an inorganic anti-reflective coating material layer is decreased to desired levels as a function of thermally treating, e.g., annealing, the inorganic anti-reflective coating material layer.
A method of forming an anti-reflective coating material layer in the fabrication of integrated circuits according to the present invention includes providing a substrate assembly having a surface and providing an inorganic anti-reflective coating material layer on the substrat
Holscher Richard
Yin Zhiping
Micro)n Technology, Inc.
Mueting Raasch & Gebhardt, P.A.
Trinh Michael
Vockrodt Jeff
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