Cleaning and liquid contact with solids – Apparatus – Electrically controlled
Reexamination Certificate
2000-06-23
2002-09-24
Coe, Philip R. (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
Electrically controlled
C134S113000, C134S144000, C134S153000, C134S172000, C134S902000
Reexamination Certificate
active
06453916
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to semiconductor processing, and in particular to a system and method for applying an edge bead removal material to the edge of a photoresist material layer disposed on a semiconductor wafer.
BACKGROUND OF THE INVENTION
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 device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic 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 structure is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist material, thickness uniformity of the photoresist material is a significant factor in achieving desired critical dimensions. The photoresist material should be applied such that a uniform thickness is maintained in order to ensure uniformity and quality of the photoresist material layer. The photoresist material layer thickness typically is in the range of 0.1 to 3.0 microns. Good resist thickness control is highly desired, and typically variances in thickness should be less than ±10-20 Å across the wafer. Very slight variations in the photoresist material thickness may greatly affect the end result after the photoresist material is exposed by radiation and the exposed portions removed.
Application of the resist onto the wafer is typically accomplished by using a spin coater. The spin coater is essentially a vacuum chuck rotated by a motor. The wafer is vacuum held onto the spin chuck. Typically, a nozzle supplies a predetermined amount of resist to a center area of the wafer. The wafer is then accelerated to and rotated at a certain speed, and centrifugal forces exerted on the resist cause the resist to disperse over the whole surface of the wafer. The resist thickness obtained from a spin coating process is dependent on the viscosity of the resist material, spin speed, the temperature of the resist and temperature of the wafer.
After the photoresist is spin coated onto the wafer, a rim or bead of photoresist remains on the edge of the wafer. This rim or bead is removed by applying an edge bead removal solvent by using an edge bead removal (EBR) nozzle, so that loose particles from the rim or bead do not become a source of contamination that can cause wafer defects. Typically, the solvent is either applied at the bottom edge of the wafer, while the wafer is spun causing the solvent to wick around the edge and wash off the photoresist bead or the solvent is applied on the top outside edge of the wafer. However, applying the solvent to the top edge of the wafer has its own inherent problems. One of the problems is that when the solvent spray or jet is shut off, a drop of solvent can remain in a nozzle tip of the nozzle, and may free fall onto the wafer undesirably dissolving useful portions of the photoresist material layer, thus destroying the uniformity of the wafer ultimately causing wafer defects.
Another problem is that when the solvent stream is dispensed onto the surface of wafer edge at a relative high angle (>30 degree relative to horizontal wafer plane), splashes are produced that became airbone particles. The airbone solvent particles inside the coater cup will eventually fall back onto wafer surface after resist coating causing pinholes in the resist film or localized resist film thickness variation. Consequently, following exposure with a mask and development, the resist pattern will be deformed then transferred to final etch pattern, resulting in yield loss.
FIG. 1
illustrates a typical conventional edge bead removal system
10
. A wafer
34
is vacuum held onto a rotating chuck
32
. The wafer
34
is spin rotated by a shaft
30
driven by a motor (not shown). A stand
12
supports a rotatable handle
14
for rotating a edge bead removal nozzle assembly
20
above the edge of the wafer
34
. An L-bracket
16
is coupled to a support bracket
18
, which holds a nozzle bracket
22
. The nozzle bracket
22
holds the tip of an edge bead removal nozzle
26
at a fixed angle
24
. Fixed angle
24
is typically above 45° and results in splashing of edge bead removal solvent splashes.
Another system for removing an edge bead on a wafer that alleviates the problem of solvent use is known as an optical edge bead removal system or track system such as the family of CLEAN TRACK® systems manufactured by Tokyo Electron Limited, Inc. in Tokyo, Japan. Such track systems are used in the various modes of photoresist processing. However, for thick resist film applications (greater than 1.5 micron), optical EBR alone is not adequate due to low power output of exposure source on the track systems and throughput constraint. The current solvent nozzle designs employed on most track equipment are not effective in reducing solvent splashes on wafer surface during edge bead removal. Solvent splashes will dissolve resist material or cause partial thickness loss leading to distorted pattern upon exposure. This type of bad pattern transfer will eventually result in IC device failure and/or yield loss. If the edge bead removal process employs back-side solvent dispense and/or optical methods only, the resist edge bead removal process will be less than optimal and residual resist will be left around wafer edges. These residual resist particles can flake off during an etch or ion implantation process causing defects on the wafer.
In view of the above, an edge bead removal nozzle is needed that ensures that droplets formed at a nozzle tip of the nozzle do not fall onto a photoresist material layer that is being worked upon.
SUMMARY OF THE INVENTION
The present invention relates to an edge bead removal system and method that employs a nozzle for applying edge bead removal solvent to an edge bead of a photoresist material layer disposed on a wafer. The edge bead removal solvent can be a developer, a rinse or a cleanser. A fine stream of solvent is dispensed from a fine, needle-like nozzle. The nozzle of the present invention eliminates solvent splash by lowering the angle of dispense to less than 20° as well as providing more degrees of freedom to the nozzle arm adjustments. The present invention employs adjustment screws and a built-in protractor to precisely set the application angle. The nozzle of the present invention includes a clamp design having a nozzle body clamp which holds the nozzle and a main shaft with a protractor assembly for up and down angle adjustments. A support bracket is coupled to the protractor assembly and allows for pivoting and side to side movement of the protractor assembly and the support bracket with respect to one another. A clamp connects a main arm
Phan Khoi
Tran Quang
Advanced Micro Devices , Inc.
Amin & Turocy LLP
Coe Philip R.
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