Description of the Prior Art Lithography techniques are used in the manufacturing of microdevices, such as integrated circuits (ICs), flat panel displays, microelectromechanical systems (MEMS), the formation of bump IC interconnects for"flip chip"interconnection technology, and the like.

The lithographic process involves the use of photosensitive workpieces ("wafers") and the selective exposure of such workpieces with radiation (e. g. , UV light). Workpiece photosensitivity is typically achieved by coating or otherwise applying a layer of photosensitive material called photoresist to the workpiece surface. Photoresist can either be"positive-tone", in which the exposed resist is removed upon developing, or"negative- tone", in which the unexposed resist is removed upon developing. Generally, the lithography process includes the steps of coating the workpiece with photoresist, exposing the photoresist with the image of a mask to form a latent pattern in the photoresist, developing the photoresist to form a three dimensional image, etching the photoresist to form a corresponding three dimensional pattern in the workpiece, and then removing the excess photoresist. These steps are repeated a requisite number of times to form the particular device structure in the workpiece.

In certain lithography applications involving positive photoresist, it is preferred that select regions of the workpiece outside of the individual exposure fields be removed upon developing. One example application is bump interconnect lithography, which involves the formation of conductive (e. g. , gold or aluminum) bumps on a workpiece (wafer) that are used to contact circuit lines on a circuit board. Bump lithography includes an electrochemical plating step to form the conductive bumps that requires contacting most of the edge portion of the wafer with an electrode. For this purpose, substantially all of the edge of the wafer must be free of photoresist to ensure uniform electrical contact.

When one-to-one contact or near-contact photolithography is used, the entire wafer is exposed at once with the exclusion of exposure at the edge that is achieved by incorporating the desired exclusion into the mask pattern. However, in step and repeat photolithography it is not possible to define the exclusion area in the mask pattern since the stepping pattern depends on the pattern size and the step sizes.

There are several techniques presently used to remove photoresist from select regions of a workpiece. Ushio, Inc. of Japan makes an optical edge-bead removal system (Model PE-250 R2) that performs an exposure of a photoresist-coated wafer near the wafer's edge so that an edge-bead of photoresist is removed upon development.

Unfortunately, the Ushio tool is a relatively large stand-alone device (about the size of a home laundry washing machine) and is dedicated to removing photoresist at the wafer periphery only.

SUMMARY OF THE INVENTION The present invention relates to the lithographic exposure and patterning of workpieces, and in particular relates to methods and apparatus for optically defining select exposure exclusion regions on a photosensitive workpiece prior to or after performing lithographic exposure of the workpiece.

A first aspect of the present invention is an apparatus for exposing select regions of a photosensitive workpiece. The apparatus includes a workpiece pre-aligner that has an arm that movably supports and aligns the workpiece and that delivers the workpiece to a workpiece stage of a lithography tool. An optical head is in optical communication with the workpiece when the workpiece is supported by the workpiece pre-aligner. The optical head is movable with respect to the workpiece using, for example, a movable stage to which the optical head is attached. An optical system is optically coupled to the optical head for delivering radiation to the optical head. A radiation source is optically coupled to the optical system to provide the radiation, which is of a wavelength capable of activating the photosensitive workpiece.

A second aspect of the present invention is a method of removing photoresist from select regions of a photosensitive workpiece prior to or after lithographic exposure of the workpiece in a lithography tool. The method includes supporting the photosensitive workpiece on a pre-aligner for supporting and aligning a workpiece for delivery to a workpiece stage of the lithography tool. Radiation from a radiation source is then generated and coupled into an optical system. The radiation is provided to an optical head that is optically coupled to the optical system and that is in optical communication with the photosensitive workpiece. The radiation is delivered through the optical head to the select regions of the photosensitive workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of a lithography tool showing the workpiece stage, workpiece pre-aligner and main controller and housing, and a workpiece exposure system of the present invention integrated with the pre-aligner ; FIG. 2 is a side view of the workpiece pre-aligner with a workpiece supported on the fork of the aligner and the optical head of the workpiece exposure system arranged in

proximity to the workpiece near the workpiece edge; FIG. 3A is a close-up cross-sectional view of a first example embodiment of the optical head of the workpiece exposure system of the present invention, wherein the optical head includes a prism and a focusing lens; FIG. 3B is a close-up cross-sectional view of a second example embodiment of the optical head of the workpiece exposure system of the present invention, wherein the optical head includes just a focusing lens; and FIG. 4 is a close-up plan view of a portion of the pre-aligner and workpiece exposure system of FIG. 2 illustrating exposure of an annular region adjacent the edge of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the lithographic exposure and patterning of workpieces, and in particular relates to methods and apparatus for optically defining select exposure exclusion regions on a photosensitive workpiece prior to or after performing lithographic exposure of the workpiece.

With reference now to FIG. 1, there is shown a lithography tool 10 that includes a workpiece stage 16 and a workpiece pre-aligner 26 in operable communication with the workpiece stage. Workpiece stage 16 and pre-aligner 26 are enclosed in a housing 34 that provides for control of the environment within tool 10. Other elements of lithography tool, <BR> <BR> such as the projection lens, mask stage, illuminator, etc. , that reside above the wafer stage are not shown in FIG. 1 for clarity.

Workpiece stage 16 is designed to movably support a workpiece (wafer) 40.

Workpiece 40 includes a reference feature 42, such as a notch or a flat that facilitates alignment of the workpiece to another reference. Workpiece 40 also includes an upper surface 44 that is photosensitive (e. g. , a layer of photoresist) and an edge 46 (Fig. 2).

Workpiece 40 is moved beneath the projection lens by workpiece stage 16 so that multiple exposure fields 50 can be formed (exposed) on the workpiece.

Pre-aligner 26 is for receiving a workpiece from a workpiece handler or other workpiece source (not shown) and precisely aligning and centering the workpiece to a known reference position on the pre-aligner. This allows for the workpiece to be transferred to workpiece stage 16 in a known alignment state. Consequently, the workpiece can be quickly finely aligned on workpiece stage 16 and exposed.

Lithography tool 10 also includes a main controller 54 that controls the operation of the lithography tool, and is operatively connected to workpiece stage 16 and pre-aligner 26 to control the pre-alignment and delivery of workpieces to workpiece stage 16. Main controller 54 also optionally controls the overall operation of pre-aligner 26 in carrying out the exclusion-region exposure method described below, which is performed either prior to

or after lithographic exposure.

With reference now also to FIG. 2, in an example embodiment, pre-aligner 26 includes a base 60 with an upper surface 62. A motor unit 70 is attached to upper surface 62 towards one end of base 60. An arm 80 with first and second ends 82 and 84 is connected to a motor unit 70 located at first end 82, allowing the motor to rotate the arm about an axis Al passing through the first end 82. Second end 84 of arm 80 includes a fork 86 capable of supporting workpiece 40. Motor unit 70 is also adapted to raise and lower arm 80 at first end 82 so that fork 86 can be raised and lowered when moving. This allows for adjusting the position of workpiece 40, or for receiving and engaging workpiece 40 from a workpiece handler (not shown).

Pre-aligner 26 also includes a workpiece rotation member 90 arranged beneath fork 86 on surface 62. Member 90 is capable of measuring the position of the workpiece on fork 86 (e. g. , the location of reference mark 42) and engaging the workpiece to rotate it about axis A2 to properly orient the workpiece. Such rotation is generally necessary for pre- aligning (e. g. , centering and orienting) workpiece 40 prior to it being transferred to workpiece stage 16 via the movement of arm 80. Generally, pre-aligner 26 serves in the present invention as a convenient device for providing the necessary support and rotation of a workpiece to perform an exposure. It is advantageous to use pre-aligner 26 to optically form the exposure exclusion regions on the workpiece, since it is already integral with lithography tool 10 and is designed for quickly moving and positioning a workpiece onto workpiece stage 16 in anticipation of lithographically exposing the workpiece.

With continuing reference to FIGS. 1 and 2, a workpiece exposure system 110 with an optical head 112 is arranged near fork 86 so that, when workpiece 40 is supported by the fork, optical head 112 is in optical communication with workpiece upper surface 44.

Optical head 112 is preferably movable over workpiece upper surface 44 (as indicated by arrows 116) so that it can expose regions anywhere on the workpiece upper surface. In an example embodiment of the present invention, system 110 need only move along a radial line extending from axis A2 as workpiece 40 is rotated on rotation member 90 underneath the optical head. Further, optical head 112 is preferably movable vertically (as indicated by arrows 118) so that the exposure field size and focus can be adjusted. Movement of optical head 112 is performed in a preferred embodiment by attaching the optical head to a movable stage 120.

In an example embodiment of the present invention, optical head 112 is optically coupled to a radiation source 122 via an optical system 124. In a preferred embodiment, optical system 124 is an optical fiber, and radiation source 122 includes a lamp (e. g. , a<BR> mercury lamp) or laser capable of emitting radiation at a wavelength (e. g. , ultraviolet or deep ultraviolet) that exposes or otherwise activates photosensitive upper surface 44.

Radiation source 122 may also be the same radiation source as used in lithography tool 10 for conducting lithographic exposures. Connected to radiation source 122 is a control unit 126 that controls the emission of radiation from the radiation source. Control unit 126 is also connected to main controller 54 that communicates with pre-aligner 26 so that information about the position and rotation of the workpiece, etc. (i. e. , generally, the workpiece state) can be provided to control unit 126. Further, movable stage 120 is connected to control unit 126 so that the motion of optical head 112 can be coordinated with the state of the workpiece. Thus, workpiece exposure system 110 includes optical head 112, movable stage 120, optical system 124, radiation source 122 and control unit 126.

Control unit 126 can be programmed with exposure instructions so that workpiece exposure system 110 selectively exposes upper surface 44 of workpiece 40. In the present invention, the radiation used is that which exposes or otherwise activates photosensitive upper surface 44. In an example embodiment, the amount of radiation provided by system 110 is that sufficient to remove photoresist upon development, and is readily determined empirically or by knowing the type of photoresist used.

With reference now to FIGS. 3A, in an example embodiment optical head 112 includes a prism 132 and a focusing lens 134. Prism 132 is used to fold the optical path so that light received by the prism from optical system 124 is directed at an angle (e. g. , 90 degrees) and received by focusing lens 134. Focusing lens 134 is arranged to relay radiation onto surface 44 over a predetermined exposure area 140. For example, exposure area 140 might be a few millimeters in diameter to ten millimeters in diameter for the purpose of exposing surface 44 at the edge of workpiece 40. Further, the exposure area may be circular or rectangular. In another example embodiment shown in FIG. 3B, the optical system 124 has an axis A3 that is normal to surface 44 of workpiece 40, obviating the need for prism 132 in optical head 112. By moving optical head 112 vertically (arrows 118), the size of exposure field 140 can be changed. In an example embodiment, focusing lens 134 (which may comprise one or more lens elements) is designed and arranged so that the imaging of radiation onto surface 44 is telecentric. This allows for the size of exposure field 140 to be changed without shifting the position of the exposure field relative to the workpiece.

Workpiece exposure system 110 (Fig. 1) is capable of patterning surface 44. The patterns capable of being formed include alphanumeric characters, bar codes, various small- and large-scale line patterns, including an annulus of a few millimeters in width formed along the very edge of the workpiece. Though some exposure patterns may be more useful than others, any feature capable of being formed with a conventional optical system can be formed with workpiece exposure system 110. For example, by programming control unit 126 and coordinating the movements of workpiece 40 via main controller 54 and workpiece rotation member 90, a desired feature can be scanned into photosensitive surface 44. Such

patterning may include making exposure area 140 very small (e. g. , fractions of a millimeter up to several millimeters) so that optical head 112 serves as an optical stylus.

In one method of operation, workpiece 40 to be processed using lithography tool 10 is first provided to and arranged on and supported by pre-aligner 26. Because pre-aligner 26 has the capability to rotate workpiece 40 via rotation member 90, the rotation of the workpiece can be coordinated with the operation of workpiece exposure system 110 via control unit 126, and optionally main controller 54, to expose select regions on photosensitive surface 44, including forming a desired exposure pattern (e. g. , indicia). For example, to remove photoresist from the edge of workpiece 40, the workpiece edge can be rotated beneath optical head 112, which illuminates a narrow (e. g. , several millimeters) wide swath 180 (FIG. 4). In another example, workpiece 40 is held stationary while optical head 112 scans across a region of the workpiece surface 44 to write indicia 190, which includes a symbol, barcode and/or alphanumeric code (FIG. 4). In a further example, indicia 190 is imaged directly onto photosensitive surface 44 over exposure area 140 in a single exposure.

There are a number of key advantages of using a workpiece exposure system of the present invention to remove photoresist from select regions of a workpiece. A first advantage is that one or more selectively exposed exclusion regions can be defined with very high accuracy. A second advantage is that the particular mask pattern can be tailored to suit the array of exposure fields printed on the workpiece using the lithography tool. A third advantage is that the size of the masked regions can be changed by programming controller unit 126 rather than by having to make mechanical adjustments of the system. A fourth advantage is that the workpiece exposure system does not involve physical contact with the workpiece. Thus, non-flat workpiece surfaces can be accommodated. A fifth advantage is that the system is integrated with the pre-aligner, so that there is no need for a stand-alone tool and the cost associated therewith (e. g. , footprint, workpiece transfer time and apparatus, etc). The in-situ exposure operation prior to or after lithographic exposure allows for another workpiece to be exposed on the workpiece stage, so that there is minimal impact on the overall lithography process and thus minimal or no impact on throughput.

The many features and advantages of the present invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the described apparatus that follow the true spirit and scope of the invention. Furthermore, since numerous modifications and changes will readily occur to those of skill in the art, it is not desired to limit the invention to the exact construction and operation described herein. Accordingly, other embodiments are within the scope of the appended claims.