Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1999-08-05
2001-06-12
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S312000, C430S313000, C430S314000, C430S320000, C430S324000, C430S329000
Reexamination Certificate
active
06245488
ABSTRACT:
RELATED APPLICATIONS
This application is related to the following co-pending U.S. patent application, Ser. No. 08/715,288, for “Low ‘K’ Factor Hybrid Photoresist” and Ser. No. 08/715,287, for “Frequency Doubling Photoresist,” both filed Sep. 16, 1996.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to the field of semi-conductor manufacturing and, more specifically, to a method, when using a frequency doubling resist material to form sub-lithographic features, of trimming the ends of the printed features.
2. Background Art
Manufacturing of semiconductor devices is dependent upon the accurate replication of computer aided design (CAD) generated patterns onto the surface of a device substrate. The replication process is typically performed using lithographic processes followed by a variety of subtractive (etch) and additive (deposition) processes.
Photolithography, a type of lithographic process, is used in the manufacturing of semiconductor devices, integrated optics, and photomasks. The process basically comprises: applying a layer of a material that will react when exposed to light, known as a photoresist or, simply, a resist; selectively exposing portions of the photoresist to light or other ionizing radiation, i.e., ultraviolet, electron beams, X-rays, etc., thereby changing the solubility of portions of the material; and developing the resist by washing it with a basic developer solution, such as tetramethylammonium hydroxide (TMAH), thereby removing the non-irradiated (in a negative resist) or irradiated (in a positive resist) portions of the layer.
Conventional positive and negative tone photoresists are characterized by a dissolution curve in which there is a single transition from a first dissolution rate to a second dissolution rate as the resist is exposed to varying levels of actinic radiation. In a positive resist, the initially unexposed resist is insoluble in developer, while the exposed resist becomes more soluble as the exposure dose is increased above a threshold value. For a negative resist, similar behavior is observed, except that the initially unexposed resist is soluble in developer, and the exposed area is rendered insoluble. By means of this differential solubility between the exposed and unexposed resist areas, it is possible to form a pattern in the resist film. This pattern can be used to form integrated circuit devices, and is currently a critical component in their manufacture.
In an ideal situation, the exposure tool would only allow the radiation to hit the resist material in the areas of the mask that are clear, thus providing sharp edges for the lines and spaces. However, diffraction patterns are formed at the edges of the clear areas, resulting in partial exposure of the resist in those areas. Certain patents have taken advantage of this phenomenon, such as U.S. Pat. No. 4,568,631 issued to Badami et al. on Feb. 4, 1986 and assigned to the assignee of record for the present invention, which discloses utilizing a positive resist and an additive for image reversal in order to create thin resist lines only in the areas where light intensity has been reduced by diffraction effects. However, this procedure uses a resist with conventional positive and negative tone dissolution responses and requires two separate expose and develop operations to form a resist image from the edge of a reticle image.
It is desirable, therefore, to devise new mechanisms of resist response such that conventional optical lithography can be extended to smaller feature sizes without developing new tools and reticles. Additionally, as these new tools and reticles are eventually developed and implemented, these new resist approaches would remain applicable as a further extension of lithographic capability.
Previously, a new frequency doubling hybrid photoresist was developed to extend photolithography to a smaller feature size. The hybrid resist uses the edges of the mask shapes to define the feature spaces in the resist. However, because the edge of the mask shape continues around the entire perimeter of the shape, these edge defined spaces are all linked together. Thus, features created using hybrid resist are “linked” together. While this linking is acceptable in some situations, such as in the formation of shallow trench isolations, the linking can be unacceptable in other situations where the linking can cause unwanted shorting.
DISCLOSURE OF INVENTION
Accordingly, the present invention provides a photoresist material having, simultaneously, both a positive tone and a negative tone response to exposure. This combination of materials can provide a new type of resist, which we call a hybrid resist.
Additionally, the present invention provides a method for forming unlinked features using hybrid resist. The method uses a trim process in order to trim the linking features from the “loops” formed by the hybrid resist. This allows the method to form a plurality of unlinked features rather than the loops. In order to trim the ends, a relatively larger trim area is formed adjacent the narrow feature line, either by a second exposure step or by utilizing a grey scale reticle.
The present invention can be used in a wide variety of applications to provide a wide variety of features. For example, the present invention can be used to form a Dynamic Random Access Memory (DRAM) cell that requires 4 SQ of spaces rather than the usual 8 SQ by forming portions of the DRAM using hybrid resist and the trim process of the present invention.
Still another feature of the present invention is that isolation trench areas may be accurately printed using the hybrid resist and a grey scale reticle in a single exposure step rather than two exposure steps.
The foregoing and other advantages and features of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.
REFERENCES:
patent: 5776660 (1998-07-01), Hakey et al.
Furukawa Toshiharu
Hakey Mark C.
Holmes Steven J.
Horak David V.
Rabidoux Paul A.
Chadurjian Mark F.
Chea Thorl
International Business Machines - Corporation
Schmeiser Olsen & Watts
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