Abstract:
An edge bead removal system and method is provided that employs a nozzle for applying edge bead removal solvent to an edge bead of a photoresist material layer disposed on a wafer. The nozzle 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. Adjustment screws and a built-in protractor provide precision in setting the application angle. The nozzle 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 structure that moves the entire edge bead removal nozzle assembly over the wafer.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/210,718, filed Jun. 9, 2000, entitled LOW ANGLE SOLVENT DISPENSE NOZZLE DESIGN FOR FRONT-SIDE EDGE BEAD REMOVAL IN PHOTOLITHOGRAPHY RESIST PROCESS. 
    
    
     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 (&gt;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 structure that moves the entire edge bead removal nozzle assembly over the wafer. The nozzle assembly of the present invention is particularly useful for removing edge beads formed on photoresist material layers having a thickness equal to or greater than 1.5 microns thick. 
     One particular aspect of the invention relates to an edge bead removal system that includes an edge bead removal nozzle having a processor for controlling the application angle. The processor is coupled to a user interface that allows a user to set the application angle. Defect analysis can then be used to determine an optimal application angle for a given production run. The processor is also coupled to a stepper motor that rotates the nozzle to the desired application angle. A protractor component provides verification of the programmed application angle. An alternate edge bead removal system utilizes a measurement system adapted to measure defects on the wafer after edge bead removal. The measurement system is coupled to the processor and provides for automatic adjustment of the application angle. 
     Another aspect of the present invention relates to an edge bead removal system for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The system comprises an edge bead removal nozzle assembly having an adjustable application angle and an arm coupled to the edge bead removal assembly. The arm is adapted to move the nozzle assembly between a rest position and an application position. 
     Another aspect of the present invention relates to an edge bead removal nozzle assembly for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The nozzle assembly comprises an edge bead removal nozzle disposed in a nozzle bracket and a protractor component coupled to the nozzle bracket. The nozzle bracket is rotatable about a fixed point on the protractor component. The protractor component provides incremental application angle setting information based on the setting of an application angle of the nozzle with respect to a top surface of the wafer. 
     In yet another aspect of the invention, an edge bead removal system is provided for removing an edge bead formed on a wafer by a photoresist material application system. The system comprises means for applying an edge bead solvent on the edge bead and means for adjusting an application angle of the means for applying an edge bead solvent on the edge bead. 
     Another aspect of the invention relates to a method for minimizing defects in an edge bead removal process. The method comprises the steps of providing an edge bead removal nozzle assembly having an adjustable application angle and setting the edge bead removal nozzle assembly to a first application angle. The edge bead removal developer is then applied to an edge bead formed on a photoresist spin coated onto a wafer and the defects formed on the photoresist due to the edge bead removal process is determined. Based on the defect level the application angle is adjusted and the steps of applying edge bead removal developer and the step of determining the defects formed until and acceptable defect level is achieved is repeated. 
     Yet another aspect of the present invention relates to an edge bead removal nozzle assembly for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The nozzle assembly comprises an edge bead removal nozzle disposed in a nozzle bracket and a protractor component coupled to the nozzle bracket. The nozzle bracket is rotatable about a fixed point on the protractor component. The nozzle assembly also includes a support bracket coupled to the protractor component wherein the protractor component is pivotable with respect to the support bracket. Additionally, the protractor component provides incremental application angle setting information based on the setting of an application angle of the nozzle with respect to a top surface of the wafer. The application angle is adjustable between 0° and 20°. 
     To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a front view of an edge bead removal system in accordance with the prior art; 
     FIG. 2 illustrates a front view of an edge bead removal system in accordance with the present invention; 
     FIG. 3 a  illustrates a front detailed view of a nozzle assembly in accordance with the present invention; 
     FIG. 3 b  illustrates a rear detailed view of the nozzle assembly of FIG. 3 a  in accordance with the present invention; 
     FIG. 3 c  illustrates a top detailed view of the nozzle assembly of FIG. 3 a  in accordance with the present invention; 
     FIG. 3 d  illustrates a partial top view of an alternate support bracket in accordance with the present invention; 
     FIG. 4 a  is a graph illustrating wafer defects group according to defect size using an edge bead removal system in accordance with the prior art; 
     FIG. 4 b  is a graph illustrating wafer defects group according to defect size using an edge bead removal system on a photoresist having a thickness of 1.81 microns in accordance with the present invention; 
     FIG. 4 c  is a graph illustrating wafer defects group according to defect size prior to using an edge bead removal system on a photoresist having a thickness of 1.56 microns in accordance with the present invention; 
     FIG. 4 d  is a graph illustrating wafer defects group according to defect size after using an edge bead removal system on a photoresist having a thickness of 1.56 microns in accordance with the present invention; 
     FIG. 4 e  is a graph illustrating wafer defects group according to defect size prior to using an edge bead removal system on a photoresist having a thickness of 1.81 microns in accordance with the present invention; 
     FIG. 4 f  is a graph illustrating wafer defects group according to defect size after using an edge bead removal system on a photoresist having a thickness of 1.81 microns in accordance with the present invention; 
     FIG. 5 is a representative schematic block diagram of an automated edge bead removal system in accordance with the present invention; 
     FIG. 6 is a representative schematic block diagram of a closed automated edge bead removal system in accordance with the present invention; and 
     FIG. 7 is a flow diagram illustrating one specific methodology for carrying out the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. The present invention is described with reference to an edge bead removal nozzle that is rotatably adjustable for changing the angle of application of the edge bead removal solvent. It should be understood that the description of these embodiments are merely illustrative and that they should not be taken in a limiting sense. 
     FIG. 2 illustrates an edge bead removal system  40  according to the present invention. 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 arm  14 ′ for rotating an edge bead removal nozzle assembly  41  from a rest position to an application position above the edge of the wafer  34 ′. An L-bracket  16  is coupled to the arm  14 ′ on one end and a support bracket  48  on the other end. The support bracket  48  is also coupled to the nozzle assembly  41 . Referring to FIGS. 2 and 3 a - 3   b,  the nozzle assembly  41  includes a protractor component  42 , which holds a nozzle bracket  46  and an edge bead removal nozzle  50 . The nozzle bracket  46  holds the tip of the edge bead removal nozzle  50  at a solvent application angle  52 . Solvent application angle  52  is preferably at or below 20° with respect to the wafer  34 ′. The nozzle bracket  46  is releasably rotatable about a fixed point on the protractor component  42  by loosening and tightening an adjustment or thumb screw  49 . The adjustment screw  49  can be loosened and the nozzle bracket  46  rotated to any application angle  52  between 0° and 20° by aligning an arrow on the nozzle bracket  46  with an angle measurement on the protractor component  42 . The adjustment screw  49  can then be set and tightened to lock in the desired application angle  52 . 
     It is to be appreciated that it is also advantageous to be able to move the edge bead removal nozzle  50  along different points around the edge of the wafer  34 ′. Referring to FIGS. 3 a - 3   c,  the nozzle  50  is also pivotable about an axis perpendicular to the surface of the wafer  34 ′. An adjustment screw  44  allows for pivotable movement of the nozzle assembly  41  along the surface of the wafer  34 ′. The adjustment screw  44  extends through an aperture at the end of support bracket  44 , through a spacer  51  and through a circular flange  53  that extends perpendicular from a surface of the protractor component  42 . A nut  55  holds the adjustment screw  44  in place. The adjustment screw  44  can be loosened and the nozzle  50  pivoted to any angle between 0° and 180° along the surface of the wafer  34 ′(see FIG. 3 c ). The adjustment screw  44  can then be set and tightened to lock in the desired surface angle. Therefore, by rotating the arm  14 ′ and the nozzle  50  about an axis through the adjustment screw  44 , the nozzle tip can be placed along any edge point on one side of the wafer. Furthermore, by allowing support bracket  48  to be rotatable about L-bracket  16 ′, the nozzle tip can be placed along any edge point of the wafer  34 ′. 
     An alternate support bracket  48 ′ is illustrated in FIG. 3 d  and includes a connecting member  48   b  connecting a first bracket member  48   a  to a second bracket member  48   c . The connecting member  48   b  includes a guide channel  59  that allows for both sideways movement and pivotable movement of the nozzle assembly  41 . The adjustment screw  44  can be loosened and the nozzle  50  rotated to any angle between 0° and 180° along the surface of the wafer (see FIG. 3 c ) and also be moved sideways along wafer edge along the guide channel  59 . The adjustment screw  44  can then be set and tightened to lock in the desired application position. The sideways, pivotable and rotational movement of the nozzle assembly provides for three-dimensional movement of the nozzle. It is to be appreciated that the sideways movement can be implemented by substituting flange  53  of the protractor component  42  with the connecting member  48   b  including the guide channel  59 . Furthermore, first and second bracket members  48   a  and  48   b  can be replaced with a first and second protractor component and support bracket  48  can be coupled to the first and second protractor component at some other location than is shown in the drawings. 
     FIGS. 4 a - 4   f  illustrate defect counts on wafers grouped by defect size using a standard edge bead removal nozzle system and employing the system of the present invention. FIG. 4 a  illustrates the defect counts measured on a wafer using a conventional edge bead removal nozzle system with a resist thickness of 1.01 microns. FIG. 4 b  illustrates the defect counts measured on a wafer using the edge bead removal nozzle system of the present invention with a resist thickness of 1.81 microns. It can be seen from FIGS. 4 a - 4   b  that the edge bead removal system of the present invention provides much lower defect counts for much thicker resist. FIG. 4 c  illustrates the defect counts measured on a wafer prior to applying developer with the edge bead removal system of the present invention on a resist with a thickness of 1.56 microns. FIG. 4 d  illustrates the defect counts measured on a wafer after applying developer with the edge bead removal system of the present invention on a resist with a thickness of 1.56 microns. FIG. 4 e  illustrates the defect counts measured on a wafer prior to applying developer with the edge bead removal system of the present invention on a resist with a thickness of 1.81 microns. FIG. 4 f  illustrates the defect counts measured on a wafer after applying developer with the edge bead removal system of the present invention on a resist with a thickness of 1.81 microns. It can be seen from FIGS. 4 c - 4   f  that the defect count prior to edge bead removal is not much different from the defect count after edge bead removal utilizing the nozzle system of the present invention. 
     Referring to FIG. 5, a system  70  for automatically adjusting an edge bead removal nozzle application angle is illustrated. A photoresist material nozzle applies a photoresist material to the center of the wafer  34 ′ that is vacuum held onto the rotating chuck  32 ′. The wafer  34 ′ is spin rotated by the shaft  30 ′ driven by a motor (not shown), so that the photoresist material forms a uniform film or layer over the wafer  24 ′. After the photoresist material is applied, the edge bead formed during the process needs to be removed. The edge bead removal nozzle assembly  41  is coupled to a stepper motor  60  adapted to rotate the nozzle  50  at an application angle  52  equal to or less than 20°. A stepper motor driver  78  drives the stepper motor  60  via instruction from a processor  80 . The processor  80  is coupled to a user interface  77  and a display  76  that allows a user to set the application angle  52  for a given production run. 
     The processor  80  is programmed to control and operate the various components within the system  70  in order to carry out the various functions described herein. The processor or CPU  80  may be any of a plurality of processors, such as the AMD K7 and other similar and compatible processors. The manner in which the processor  80  can be programmed to carry out the functions relating to the present invention will be readily apparent to those having ordinary skill in the art based on the description provided herein. 
     A memory  74  which is operatively coupled to the processor  80  is also included in the system  70  and serves to store program code executed by the processor  80  for carrying out operating functions of the system  70  as described herein. The memory  74  includes read only memory (ROM) and random access memory (RAM). The ROM contains among other code the Basic Input-Output System (BIOS) which controls the basic hardware operations of the system  70 . The RAM is the main memory into which the operating system and application programs are loaded. The memory  74  also serves as a storage medium for temporarily storing information such as application angle tables and other data which may be employed in carrying out the present invention. For mass data storage, the memory  74  may include a hard disk drive (e.g., 10 Gigabyte hard drive). Power supply  72  provides operating power to the system  70 . Any suitable power supply (e.g., battery, line power) may be employed to carry out the present invention. 
     FIG. 6 illustrates a closed loop system  70 ′ for controlling the edge bead removal application angle as shown were like parts are denoted by like reference numerals. The system  70 ′ includes a particle defect measurement system  84 . The system  70 ′ includes a light source  93  connected by a fiber optic line  91  to a light driver  82 . The light driver  82  is turned on and off for particle defect measurements on the photoresist material layer  34 ′ by the processor  80 , after the edge bead removal process. The light source  93  sends light at the resist layer  34 ′, which is reflected to a light receiver  99  coupled to the measurement system  84  for making particle defect measurements. The light receiver  99  is connected to the measurement system  84  by a fiber optic line  97 . 
     The processor  80  receives measured particle defect data from the measuring system  84  and determines the overall optimal application angle  52  based on trial and error methods, statistical methods or the like. The memory  74  which is operatively coupled to the processor  80  is also included in the system  70 ′ and serves to store program code executed by the processor  80  for carrying out operating functions of the system  70 ′. Power supply  72  provides operating power to the system  70 ′. Any suitable power supply (e.g., battery, line power) may be employed to carry out the present invention. 
     Any suitable interferometry system and/or spectrometry system may be employed to carry out the present invention and such systems are intended to fall within the scope of the hereto appended claims. In one embodiment, the measurement system  84  is a polychromatic interferometer system or a monochromatic interferometer system to measure the particle defects formed on the photoresist material layer  34 ′. In another embodiment, the measurement system  84  is a spectrometry system. Interferometry systems and spectrometry systems are well known in the art, and therefore further discussion related thereto is omitted for sake of brevity. It is also to be appreciated that any suitable laser scattering or laser doppler anemometry system may be employed to carry out the present invention and such systems are intended to fall within the scope of the hereto appended claims. Laser scattering and laser doppler anemometry systems are well known in the art, and therefore further discussion related thereto is omitted for sake of brevity. 
     FIG. 7 is a flow diagram illustrating one particular methodology for carrying out the present invention. In step  100 , a test wafer is placed on a spin chuck and a photoresist material layer is spin rotated onto the wafer. In step  110 , verification that the edge bead removal nozzle is at or below 20° is performed. In step  120 , the nozzle  50  is moved over the wafer edge and additional adjustments are performed, such as sideways and pivotable adjustments. In step  130 , edge bead removal developer is applied to the edge of the wafer via the nozzle  50 . In step  140 , the amount of defects on the photoresist layer is determined If the amount of defects are acceptable (Yes), the application angle is set for production in step  155 . If the amount of defects are not acceptable (No), the application angle is adjusted in step  160 . 
     What has been described above are preferred embodiments of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.