Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
2000-06-21
2002-04-16
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S309000, C430S326000, C430S327000, C430S331000, C430S958000
Reexamination Certificate
active
06372408
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to semiconductor fabrication lithography, lithographic resist, and the development of same, and to a method for reducing the incidence of undesired post-development defects, denoted as “Blob Defects”, which may remain on a surface of a semiconductor wafer being processed after the development of the resist.
BACKGROUND OF THE INVENTION
As the minimum feature size of semiconductor devices has become smaller and smaller, new techniques, equipment and materials have been developed to meet the needs and requirements of those practicing the art of semiconductor fabrication. This has been especially true in the area of lithography, or more specifically, photolithography. As the size of the features of the semiconductor device have decreased from the thousandths of an inch (25000 nm) employed in initial semiconductor devices, to features with sizes of 130 nm, or less, the wavelength of the light employed to expose the photoresist has decreased from around 500 nm to 248 nm or less. This decrease in optical wavelength has required the development of new light sources, new equipment to project the image of a mask onto the surface of a semiconductor wafer (body), and new photoresist materials and photoresist developer materials. Present efforts are concentrated on the use of 248 nm deep ultraviolet (DUV) light. Several DUV sensitive photoresist materials have been developed and are in use in the industry. The characteristics important in a photoresist material include, among others, cost, sensitivity, adherence to the films in use, purity, reproducibility of characteristics, and most important, the ability to achieve a low density of photolithographic related defects.
DUV photoresist materials have been identified, and are in use around the world, which demonstrate most, but not all of these important characteristics. One of the required characteristics which has not been adequately demonstrated is the ability to achieve a low density of photolithographic related defects. Typically, most of the DUV photoresist materials which are in common use exhibit a class of post-development defects which are defined as “Blob Defects”, in which fragments, pieces, or particles of the original components of the photoresist material, which should have been removed, remain in and around small openings in the photoresist after the photoresist has been exposed and developed, potentially blocking or partially blocking such openings. Such fragments of photoresist interfere with etching of the material under the photoresist, or with ion implantation or deposition through these openings in the photoresist. Such Blob Defects have been observed on semiconductor wafers being processed with all available DUV photoresists, regardless of the resist chemistry. The observation has been that the better the resist contrast and surface inhibition, the higher the Blob Defect density.
Modem photoresist materials are typically developed using a technique known as Puddle Development. The use of this technique is well known in the field of semiconductor lithography. This prior art method comprises the following steps. A semiconductor wafer which has been prepared with photoresist material and which has been exposed to the desired pattern of light is first given a post exposure bake and then cooled to near ambient room temperature. The photoresist is then developed as follows. The semiconductor wafer is placed on a spinner head and rotated at a high speed while a small amount of liquid, either developer solution or deionized water, is dispensed onto the surface of the semiconductor wafer to pre-wet the surface of the photoresist. The high speed of rotation generates sufficient centrifugal force to cause the liquid to be thrown off of the periphery of the semiconductor wafer as it is dispensed onto the central portion of the wafer. No liquid remains on the surface of the semiconductor wafer. The speed of rotation of the semiconductor wafer is then reduced to a lower value and a quantity of developer solution is dispensed onto the surface of the semiconductor wafer. The lower speed of rotation is such that centrifugal force spreads the developer solution out to the periphery of the semiconductor wafer, but the centrifugal force is insufficient to overcome the surface tension of the developer solution, and the developer solution is not thrown from the surface of the semiconductor wafer but remains as a pool, or puddle, on the surface. The puddle of developer solution is allowed to remain on the surface of the semiconductor wafer for a time sufficient to allow complete development of the exposed photoresist material. The speed of rotation is then increased to a higher value at which centrifugal force will cause the developer solution to be thrown from the surface of the semiconductor wafer. The semiconductor wafer is then rinsed and dried, completing the development of the photoresist.
It is known in the art to use multiple development steps in the development of photoresist material.
The selection of photoresist for contact hole lithography has become a compromise between defect density and lithographic performance. Blob defects have become a limiting factor in resist selection and yield enhancement.
It is desired to reduce the density of Blob Defects in the lithographic processing of semiconductor devices.
SUMMARY OF THE INVENTION
We have found that the fabrication of semiconductor devices can be improved and the density of a particular type of processing defect can be reduced by making changes to the method by which the photoresist is developed. The present inventive method of developing photoresist employs the use of at least one Puddle Development cycle and at least one Puddle Rinse cycle.
We denote the sequence of steps, as described in the Background of the Invention, from the dispensing of the puddle of developer through the time the developer is thrown from the surface of the semiconductor wafer as a “Puddle Development” cycle. We denote the same sequence of process steps, but in which deionized water is substituted for developer solution, as a “Puddle Rinse” cycle. When we wish to refer to either of these sequences we use the notation “Puddle” cycle.
When certain types of photoresist material are exposed to light and the photoresist is subsequently developed, it is found that particles of the components of the photoresist, denoted as “Blob Defects”, can remain in and around the openings created in the photoresist. The photoresist material is composed of a mixture of various components, including a base polymer and photosensitive elements. The Blob Defects appear to be an aggregation of hydrophobic materials having low solubility in the photoresist developer solution. The mechanisms and dynamics by which these Blob Defects are formed and adhere to the structures being processed are not completely understood.
We have observed that by developing the photoresist using at least one Puddle Development cycle and at least one Puddle Rinse cycle, the density of such defects is reduced. In one particular experiment a reduction of defects by 98%, from 127 defects per wafer to 2 defects per wafer, was observed.
Viewed from a first aspect, the present invention is directed to a method of developing an exposed layer of photoresist material on a semiconductor wafer to reduce the incidence of Blob Defects. The method comprises the steps of developing the layer of photoresist first using a Puddle Development cycle, and upon completion of the Puddle Development cycle, subjecting the semiconductor wafer to a Puddle Rinse cycle. The semiconductor wafer may be subjected to multiple additional Puddle Rinse cycles.
Viewed from a second aspect, the present invention is directed to a method of developing an exposed layer of photoresist material on a semiconductor wafer to reduce the incidence of Blob Defects. The method comprises the steps of subjecting the semiconductor wafer to a sequence of Puddle cycles which are chosen from a group consisting of a Puddle Development cycle and a Puddle Rinse cycl
Chen Kuang Jung
Gutmann Alois
Lawson Margaret C.
Lu Zhijian
Thomas Alan
Infineon - Technologies AG
Schilling Richard L.
LandOfFree
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