Semiconductor device manufacturing: process – With measuring or testing – Optical characteristic sensed
Reexamination Certificate
1999-09-22
2001-07-31
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
With measuring or testing
Optical characteristic sensed
Reexamination Certificate
active
06268227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to photolithography techniques for patterning semiconductor devices, and, more particularly, to a method for controlling photoresist removal processes.
2. Description of the Related Art
Conventionally, semiconductor devices are patterned using photolithographic processes. A base material, such as a substrate material, a metal, an insulator, etc., is coated with a light sensitive material, referred to as a photoresist material. The photoresist is generally a composition that is sensitive to active rays of light, such as ultraviolet rays, X-rays or electron rays. The photoresist is deposited on the base material to selectively protect non-process portions of the substrate. Light is then selectively directed onto the photoresist film through a photomask to form photoresist patterns on the base material. The photoresist is then developed to remove either the exposed photoresist or the unexposed photoresist.
There are generally two types of photoresist, namely positive type and negative type. The positive photoresist is of such a type that the exposed portion dissolves in the developer, while the unexposed portion does not dissolve therein, and the negative photoresist is of the opposite type. Certain photoresist materials do not complete the transition from being soluble to being insoluble in the developer based solely on the exposure to light. These photoresist materials, referred to as chemically-assisted photoresists, are subjected to a post exposure bake process to complete the chemical reaction to transition from soluble to insoluble (i.e., for a positive resist).
The process of using a chemically-assisted photoresist is described in greater detail in reference to
FIGS. 1A through 1D
.
FIG. 1A
shows a wafer
10
including a base material
12
with a photoresist layer
14
deposited thereon. In
FIG. 1B
, the photoresist layer
14
is exposed to a light source through a photomask (not shown) to define exposed regions
16
. Exposure to the light causes hydrogen free radicals to form in the exposed regions
16
, which are on the surface of the photoresist layer
14
. In
FIG. 1C
, the wafer
10
is subjected to a post exposure bake to complete the solubility transition chemical reaction and form baked regions
18
. During the post exposure bake, the free radicals diffuse downward and react with the photoresist
14
beneath the exposed regions
16
. Typically, for a deep UV photoresist layer
14
, the post exposure bake time is about 60-90 seconds. As shown in
FIG. 1D
, a developer may then be applied to remove the remaining photoresist
14
(i.e., for a negative resist—shown in
FIG. 1D
) or to remove the baked portions
18
(i.e., for a positive resist—not shown).
Accurate control of the developing process, also referred to as the photoresist removal, is important for preventing defects in the wafer. If the photoresist removal time is too short, remnants of the photoresist layer will be present on the wafer, interfering with subsequent processing steps. Typically, a minimum removal time is programmed into the recipe of the developer, however, variations in the photoresist, developer, photoresist layer thickness, etc., may result in different photoresist removal rates for various wafers in the same or different lots. Accordingly, a minimum removal time does not always ensure that all of the photoresist is removed.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
One aspect of the present invention is seen in a method for fabricating wafers. A photoresist layer is formed on a wafer. A first thickness of the photoresist layer is measured, and a portion of the photoresist layer is removed. A second thickness of a remainder portion of the photoresist layer is measured. A photoresist removal rate is determined based on the first and second thicknesses, and a recipe of a developer is modified based on the photoresist removal rate.
Another aspect of the present invention is seen in a wafer processing system including a stepper, a developer, and an automatic process controller. The stepper is adapted to expose a wafer having a photoresist layer deposited thereon. The developer is adapted to remove at least a portion of the photoresist layer based on a recipe. The process controller is adapted to receive a photoresist removal rate and modify the recipe based on the photoresist removal rate.
REFERENCES:
patent: 4661436 (1987-04-01), Lewis et al.
patent: 36206341 (1987-03-01), None
Advanced Micro Devices , Inc.
Bowers Charles
Thompson Craig
Williams Morgan & Amerson P.C.
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