Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2001-02-21
2002-09-17
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S325000, C430S326000, C430S330000, C430S331000
Reexamination Certificate
active
06451510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the fabrication of electronic components such as integrated circuit semiconductors and, in particular, to a method for avoiding resist pattern collapse in the microlithography steps of integrated circuit fabrication wherein a resist pattern is formed on the wafer surface for subsequent etch removal or material addition steps.
2. Description of Related Art
The fabrication of electrical circuits on electronic component substrates such as thin film integrated circuits and semiconductor devices such as wafers requires circuit pattern definition using a microlithographic process. Lithographic processes define substrate regions for subsequent etching removal or material addition and the trend for integration is to continue decreasing feature size which includes the line width of the electrical circuit.
Photolithography is the production of a three-dimensional relief image based on the patterned exposure to light and subsequent development of a light-sensitive photoresist on the wafer surface. Microlithography is used to print ultra small patterns in the semiconductor industry but the basic steps to form a resist image is essentially the same as in conventional optical lithography.
Broadly stated, a radiation-sensitive photoresist is applied to a substrate such as a wafer and then an image exposure is transmitted to the photoresist, usually through a mask. Depending on the type of photoresist used, exposure will either increase or decrease the solubility of the exposed areas with a suitable solvent called a developer. A positive photoresist material will become more soluble in exposed regions whereas a negative photoresist will become less soluble in exposed regions. After exposure, regions of the substrate are dissolved by the developer and no longer covered by the patterned photoresist film and the circuit pattern may now be formed either by etching or by depositing a material in the open patterned areas.
Basic steps involved in photoresist processing for microlithography comprise first cleaning the substrate and priming the substrate for adhesion of the photoresist. The wafer substrate is then coated with a photoresist typically by spin coating the resist over the wafer surface. The spin coating procedure typically has three stages wherein the photoresist is dispensed onto the wafer surface, the wafer is accelerated to a final rotational speed and then the wafer is spun at a constant speed to spread and dry the resist film. After the spinning stage, the coating acquires a relatively uniform symmetrical flow profile typically about 0.1 to 10 micrometers thick. Spin coating is typically performed at a speed from 3,000 to 7,000 rpm for twenty to sixty seconds producing coatings with uniformities to ±100 Å over a wafer with a 150 mm diameter. After spin coating, the wafers are typically soft baked to remove solvents from the resist.
The photoresist is then exposed to form the desired pattern in the resist. A post-exposure bake is then typically used and then the resist developed with a developer to remove unwanted parts of the resist and forming the desired resist pattern. The development may be done by immersing the wafer into the developer or spraying a developer solution onto the resist surface. A puddle technique may also be used in which the developer solution is puddled or dripped onto the surface of the wafer and then the wafer is spun (similarly to apply the resist material) to simultaneously spread the developer over the wafer surface. The above development techniques are described in U.S. Pat. No. 6,159,662 to Chen et al., which patent is hereby incorporated by reference.
To stop the development process, the developer then is rinsed from the substrate surface with a rinse solution and this is also typically performed by immersion, spraying or puddling as described above.
A post-development baking step is typically performed to remove residual solvents, improve adhesion and increase the etch resistance of the resist. The wafer can then be treated by etching or the addition of materials depending on the results desired.
Unfortunately, as the demands of industry require smaller feature sizes, the line width defined by the resist is likewise smaller. However, the resist pattern height cannot be significantly reduced because the pattern must have a certain height or thickness in order to remain functional. The ratio of the height of the resist to the width of the standing line defined by the resist is called the aspect ratio and when lined patterns with a high aspect ratio are formed, a serious problem occurs since the resist pattern has a tendency to fall down or collapse.
An article by Tanaka et al. in Japan J. Appl. Phys. vol. 32 (1993) pps. 6059-6064 entitled “Mechanism of Resist Pattern Collapse During Development Process” discusses the problem of fine resist pattern collapse. In one form of collapse, the tips of the pattern come in contact with each other and the pattern collapse results in a bending, breaking, tearing or peeling of the resist pattern which results in the patterned wafer being unsuitable for further processing.
Image collapse is a serious problem especially as the features on the wafer become smaller, for example, for aspect ratios greater than about 3 and lines less than 150 nm in width. As a person skilled in the art would appreciate, as the aspect ratio is increased and the line width decreases, the problem becomes more pronounced and in lines having an aspect ratio of 6 and 100 nm line width the collapse problem is very severe.
Industry has tried a number of solutions to solve the collapse problem. In the Tanaka article, supra, it was concluded that the source of resist pattern collapse was the surface tension of the rinse liquid and a low-surface-tension rinse liquid was proposed such as a mixture of tert-butylalcohol and water in a mixture ratio of 50:50 volume percent. Use of a supercritical resist dryer to prevent pattern collapse is proposed in an article by Namatsu et al. entitled “Supercritical Resist Dryer” reported in the J. Vac. Sci. Technol. B 18(2), March/April 2000. U.S. Pat. No. 4,784,937 to Tanaka et al. shows the use of an aqueous developing solution for a positive-working photoresist composition containing an organic base such as tetramethyl ammonium hydroxide and an anionic or non-ionic fluorine-containing surface active agent to improve the dissolving selectivity between the exposed areas and unexposed areas of the photoresist layer. U.S. Pat. No. 5,474,877 to Suzuki shows a method for developing a photoresist pattern using a rinsing liquid close to its boiling point to decrease the surface tension of the rinsing liquid so that the collapse of the photoresist pattern is avoided. The above articles and patents are hereby incorporated by reference.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for developing a photoresist pattern on an electronic component substrate such as a semiconductor wafer to avoid pattern collapse of the developed photoresist.
In another object of the present invention an apparatus is provided for developing photoresist patterns on electronic component substrates such as semiconductor wafers to avoid pattern collapse of the developed photoresist.
It is further object of the invention to provide electronic component substrates including semiconductor wafers which have been developed using the method and apparatus of the invention.
It is yet another object of the present invention to provide electronic components such as semiconductor wafers made using electronic component substrates developed using the method and apparatus of the invention.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention wh
Messick Scott A.
Moreau Wayne M.
Robinson Christopher F.
Cioffi James J.
Delio & Peterson LLC
International Business Machines - Corporation
Schilling Richard L.
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