Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-01-31
2001-09-18
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C438S717000, C438S715000, C438S906000, C438S949000, C438S944000
Reexamination Certificate
active
06291135
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to improving lithography by reducing defects on a mask. In particular, the present invention relates to reducing defects on a next generation lithography mask using ionization.
BACKGROUND ART
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required. Since numerous conductive features are typically present on a semiconductor wafer, the trend toward higher device densities is a notable concern.
The requirement of small features (and close spacing between adjacent features) requires high resolution lithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the photoresist. The photoresist coated substrate is baked to evaporate any solvent in the photoresist composition and to fix the photoresist coating onto the substrate. The baked coated surface of the substrate is next subjected to selective radiation using a mask; that is, a mask is employed to effect an image-wise exposure to radiation. The mask permits radiation to contact certain areas of the photoresist and prevents radiation from contacting other areas of the photoresist. This selective radiation exposure causes a chemical transformation in the exposed areas of the photoresist coated surface. Types of radiation commonly used in microlithographic processes include visible light, ultraviolet (UV) light and electron beam radiant energy. After selective exposure, the photoresist coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist (depending upon whether a positive photoresist or a negative photoresist is utilized) resulting in a patterned or developed photoresist.
The mask is a critical element in lithography. Defects in the mask lead to imprecise exposure and consequent decreases in resolution, precise pattern formation and/or the quality of subsequent processing steps. For example, a contaminant particle on a mask may prevent radiation from contacting an area of a photoresist that should receive radiation, resulting in an incompletely exposed photoresist, which would lead to an undesirable pattern formation in the subsequently developed photoresist. Mal-formed structures inhibit the proper function of semiconductor devices.
Contaminant particles that adhere to a mask surface and are capable of at least partially blocking light that should pass through the mask constitute mask defects. Moreover, airborne contaminant particles that are capable of at least partially blocking light that should pass through the mask constitute defects as well. The concern or potential damage attributable to contaminant particles increases as the wavelength of light used to selectively expose photoresists decreases. That is, it is more likely for a contaminant particle to block light having a small wavelength compared to light having a large wavelength. This is especially true for small wavelengths below about 160 nm. Small wavelengths below about 160 nm involves next generation lithography (NGL). The concern over contaminant particles is great because one defect or particle on a mask may constitute a fatal defect requiring expensive and burdensome mask replacement. Moreover, as geometries shrink, small defects have an increasingly detrimental impact on NGL processing.
A pellicle is a transparent, thin membrane (often 99% or more light transmission) that seals off the mask surface from airborne particles and is not damaged by repeated illumination over time. Pellicles are therefore useful for preventing contaminant particles to cause defects in photolithography. However, at small wavelengths below about 160 nm, suitable pellicles with such properties (good light transmission, no damage due to illumination exposure over time) are unavailable.
When a photoresist clad semiconductor substrate is charged into a processing chamber, such as a reticle chamber, it is desirable for the lithography mask to be free of contaminant particles. However, it is difficult to remove contaminant particles from a mask, as it is often required to remove the contaminated mask from the processing chamber. It is also difficult to remove contaminant particles from a mask without damaging the mask or other hardware within the processing chamber. Since NGL masks are expensive, since suitable NGL pellicles are unavailable, and since NGL masks are particularly difficult to repair, it is highly desirable to avoid any damage to NGL masks.
SUMMARY OF THE INVENTION
The present invention provides an improved lithography process wherein ionization is employed to reduce mask defects. The present invention particularly provides methods for reducing mask defects using an inert plasma, wherein the ionized ions remove mask defects. The methods of the present invention also provide for the removal of airborne particles from processing chambers, thereby preventing contamination of lithography masks, and particularly NGL masks. As a result of the present invention, a subsequently patterned resist of increased quality (fewer pattern defects, improved resolution, improved critical dimension control, etc.) comparable to a patterned resist where the present invention is not employed is obtainable.
In one embodiment, the present invention relates to a method of processing a semiconductor structure including a resist thereon, involving contacting the semiconductor structure including the resist with a plasma comprising at least one inert gas selected from the group consisting of nitrogen, helium, neon, argon, krypton and xenon; exposing the semiconductor structure including the resist to actinic radiation having a wavelength of about 160 nm or less through a lithography mask; and developing the resist with a developer.
In another embodiment, the present invention relates to a method of reducing defects on a lithography mask, involving the steps of providing a semiconductor structure and the lithography mask in a processing chamber, the lithography mask having defects thereon; charging the processing chamber with a plasma comprising at least one inert gas selected from the group consisting of nitrogen, helium, neon, argon, krypton and xenon to provide the lithography mask having a reduced number of defects thereon; and exposing the semiconductor structure in the processing chamber to actinic radiation having a wavelength of about 160 nm or less through the lithography mask.
In yet another embodiment, the present invention relates to a method of processing a lithography mask and a semiconductor structure containing a photoresist, involving the steps of contacting the lithography mask and the semiconductor structure including the photoresist with a plasma comprising at least one inert gas selected from the group consisting of nitrogen, helium, neon, argon, krypton and xenon under a pressure from about 0.0001 Torr to about 0.1 Torr; exposing the semiconductor structure including the photoresist to actinic radiation having a wavelength of about 160 nm or less through the lithography mask; and developing the photoresist with an aqueous alkaline developer.
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patent: 02-183531-a (199
Phan Khoi A.
Rangarajan Bharath
Singh Bhanwar
Advanced Micro Devices , Inc.
Amin & Turocy LLP
Hamilton Cynthia
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