Patent Publication Number: US-4095344-A

Title: Scribe tool and mount therefor

Description:
This invention relates to improvements in scribing machines and, more particularly to an improved diamond headed scribe tool and tool mount for use with such a machine. 
     BACKGROUND OF THE INVENTION 
     The scribe tool of a conventional scribing machine for scribing semiconductor wafers is comprised of a relatively long shank provided with a diamond head at the normally lowermost end thereof. The diamond head, during manufacture of the tool, is lapped and polished to provide the necessary facets therefor so that the side margins of certain facets will present scribe edges that can be used to scribe an article when the tool is secured to a floating arm of the scribing machine. 
     It is extremely important that the facets of the diamond head be properly oriented with respect to the direction of movement of the floating arm relative to the wafer to be scribed to prevent creation of lateral stresses in the wafer which cause fractures in the structure thereof transverse to the desired scribe line. These fractures propagate through the wafer and destroy its structural integrity. As a result, some of the semiconductor chips which are obtained when the scribed wafer is broken will be imperfect and not usable. Thus, the yield from a particular wafer is minimized. 
     To avoid this problem, attempts have been made to provide some type of correlation between the locations of the scribe edges of the diamond head and the way in which the shank of the tool is mounted on or secured to the floating arm. For instance, flats on the shank have been used as the reference surfaces for aligning the facets of the head. However, this technique lacks the latent precision needed for radial orientation resulting in improper alignment of the scribe edges relative to the direction of tool movement relative to the article to be scribed. 
     A need has, therefore, arisen for improvements in either or both the scribe tool and the tool mount of a scribing machine to avoid the errors in alignment of the scribe edges of the tool relative to a desired scribe direction to thereby avoid structural damage to the article to be scribed and, in the case of semiconductor wafers, to increase the yield from a particular wafer. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the foregoing need by providing an improved scribe tool and a mount for the tool itself wherein the tool can be properly positioned accurately and easily by the most unskilled worker, yet the scribe edges of the tool will be properly aligned relative to the direction of scribing to thereby substantially eliminate all errors arising from misalignment of the scribe edges of the tool. This is accomplished by permitting the shank of the tool to be mounted on the floating arm of a scribing machine in precisely the same orientation of the shank when connected to a predetermined reference mount, the latter being used during formation of the scribe edges by lapping and polishing techniques. This assures repeatability of tool mounting and provides for precision in the placement of the scribe edges of the diamond head relative to the desired direction of movement of the floating arm relative to the article to be scribed when the tool is mounted thereon. The result, in the case of scribing of semiconductor wafers, will be an increase in the yield of the given wafer over that obtainable with the use of conventional tools and mounting devices therefor. 
     The tool itself is provided with a bar on the normally upper end of the shank, the diamond head being on the lower end of the shank. The bar is perpendicular to the shank and is transversely circular. The shank is radial to the bar intermediate the ends of the latter. In manufacturing the tool, the bar is oriented so that it is parallel to the common plane of a first pair of aligned scribe edges of the diamond head and perpendicular to the common plane of the second pair of scribe edges. 
     The tool mount includes a tool holder on the floating arm with the tool holder including a tube for receiving the tool shank. The tube is carried by a beam secured at one end to the floating arm and adjustable in position at its opposite end by an additional screw carried by the arm. The tube is inclined relative to the beam and extends through the latter and through a slot in the floating arm. The bar on the tool shank is engageable with surface means secured to the tube itself. The surface means includes surfaces on first and second pairs of projections secured to respective radial arms on a plate rigid to the upper end of the tube, with the surfaces of each pair of diametrically opposed projections being coplanar to each other. and the plane of one pair of surfaces being perpendicular to the plane of the other pair of surfaces. 
     The bar on the tool shank is adapted to engage simultaneously the inclined surfaces of one pair of projections so that a corresponding scribe edge of the diamond head will be properly aligned relative to the desired scribe direction. By changing the location of the tool so that the bar engages the surfaces of the second pair of projections, another scribe edge of the diamond head will be in alignment with the scribe direction. For four scribe edges of the diamond head, the tool can be oriented in four different rotative positions on the tool holder. 
     The primary object of this invention is to provide an improved tool and tool mount wherein the tool can be used on a scribing machine to scribe articles, such as semiconductor wafers or the like, in a manner to assure proper alignment of a scribe edge of the tool relative to the desired direction of scribing and to eliminate damage to the scribed article due to misalignment of the scribe edge. 
     Another object of this invention is to provide a tool and tool mount of the type described wherein the tool and tool mount have cooperating surface means which is prealigned to assure immediate and precise orientation of a scribe edge of the tool relative to the desired scribe direction when the tool is coupled to the mount in preparation for a scribing operation. 
     Other objects of this invention will become apparent as the following specification progresses, reference being had to the accompanying drawings for an illustration of an embodiment of the tool and tool mount. 
    
    
     IN THE DRAWINGS: 
     FIG. 1 is a top plan view of a floating arm of a scribing machine for mounting a scribe tool in accordance with the present invention; 
     FIG. 2 is a side elevational view, partly in section, of the arm, showing the improved tool and tool mount of this invention; 
     FIG. 3 is a side elevational view of the tool; 
     FIG. 4 is a view of the tool mount looling in the direction of line 3--3 of FIG. 2; 
     FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 2; and 
     FIGS. 6 and 7 are schematic views of the floating arm, showing the unflexed and flexed positions thereof. 
    
    
     The tool mount of the present invention is broadly denoted by the numeral 10 and is adapted for use in mounting an improved scribe tool 12 on a scribing machine, such as a machine for scribing semiconductor wafers. Tool 12 includes a cylindrical shank 14 having a diamond head 16 at one end thereof, head 16 having a number of facets (not shown) defining four scribing edges 18, only three of which are shown in FIG. 3. Tool 12 has a bar 20 of transversely circular cross section secured to the opposite end of shank 12, such as by welding, brazing, soldering or the like. Shank 14 is located substantially midway between the ends of bar 20 and projects radially therefrom. Typically, the length of shank 14 and head 16 is about 0.75 inch, the diameter of the shank is about 0.118 inch, and the length and diameter of bar 20 are about 0.875 inch and 0.0625 inch, respectively. 
     A floating arm 22 adapted to be mounted on the scribing machine has a first segment 24 and a second segment 26 connected to segment 24 by a spring or flexure member 28 which, for purposes of illustration, is of generally rectangular shape (FIG. 1). A gap 32 separate segments 24 and 26. Arm 22, when mounted on the scribing machine, reciprocates in the direction of arrows 30 (FIG. 1) along the longitudinal axis of the arm relative to an article to be scribed, such as a semiconductor wafer. In the alternative, arm 22 can be stationary and the article to be scribed and its mounting means can reciprocate relative to the arm. Flexure member 28 allows lateral flexing of segment 24 relative to segment 26, such as back and forth along a circular arc in the direction indicated by curved arrows 32 (FIG. 1). The reason for this flexure is to compensate for slight misalignment of a scribe edge 18 on tool 12 to avoid a &#34;tiller effect&#34; as described. 
     Segment 24 of arm 22 has an elongated slot 34 therethrough and a tool holder 36 is disposed within slot 34 for holding tool 12 in an operative position. Tool holder 36 includes a rigid tube 38 having an inner, cylindrical surface substantially complemental to the outer cylindrical surface of shank 14 with the diameter of tube 38 being sufficient to permit longitudinal movement of shank 14 therethrough. The length of tube 38 is less than that of shank 14. 
     Tube 38 is rigidly secured in an inclined position to a beam 40, the latter being secured at one end thereof to segment 24 of arm 22 by screws 42 near one end of slot 34. Beam 40 is initially provided with a hole 44 therethrough of elliptical shape as shown in FIG. 1 to accommodate tube 38 so that the tube can extend through beam 40 at an acute angle as shown in FIG. 2. The tube is welded, brazed or soldered to beam 40 and the lower end of tube 38 is near the normally forwardmost end 46 of arm 22 slightly below the lower surface of beam 40 as shown in FIG. 2. 
     A rigid, flat plate 48 (FIGS. 2 and 4) is rigidly secured to the upper end of tube 38 and has a central opening 50 aligned and communicating with the central bore of tube 38 so that shank 14 of tool 12 can be inserted through plate 48 and extend into and through tube 38. The plane of plate 48 is perpendicular to the central axis of tube 38. Plate 48 has four radial arms 52, 54, 56 and 58 (FIG. 4) which are integral with the plate and are substantially coplanar therewith. 
     Each of the radial arms of plate 48 has a blocklike projection 60 at the outer end thereof with each projection having an upper surface 62 as shown in FIG. 2, each surface being inclined relative to the plane of plate 48. Surfaces 62 of arms 52 and 56 are in a common plane inclined with respect to the central axis of tube 38. Similarly, surfaces 62 of arms 54 and 58 are in a common plane perpendicular to the plane of the surfaces 62 of arms 52 and 56. Surfaces 62 of diametrically opposed pairs of arms are adapted to be engaged by bar 20 of tool 12 in the manner shown in FIGS. 2 and 4 when the tool shank 14 extends through tube 38. Thus, surfaces 62 serve as stops for the tool and locate the latter relative to the lower end of tube 38 for scribing purposes. Surfaces 62 also determine the orientation of shank 14 and thereby scribe edges 18 relative to the scribe direction represented by arrows 30 (FIG. 1). To hold the tool coupled in the manner shown in FIGS. 2 and 4, a retainer 64 is pivotally mounted by a screw 66 on a post 68 secured to and extending outwardly from plate 48 as shown in FIG. 2. Retainer 64 is pivotal into and out of its operative position shown in FIGS. 2 and 4 in which it overlies and engages bar 20 to hold the same on respective pairs of surfaces 62. 
     Inclination of tube 38 can be adjusted by changing the initial position of beam 40 relative to arm 22. To this end, a screw 70 is threadedly mounted in a sleeve 72 rigidly secured to and generally perpendicular with one end of arm 22. The lower end of screw 70 bears against the upper surface of beam 40 so that, by moving screw 70 downwardly, beam 40 can be caused to flex downwardly and thereby decrease the angle of tube 38 with respect to the vertical. Movement of screw 70 in the opposite direction will have the opposite effect on the inclination of tube 38. 
     In use, tool 12 is inserted into tube 38 until bar 20 engages a respective pair of surfaces 62 as shown in FIGS. 2 and 4. Then, retainer 64 is moved into overlying relationship to bar 20 to retain the tool in place. When so arranged, a scribe edge 18 will be properly aligned with respect to the scribe direction (arrows 30 of FIG. 1). Then, movement of the arm 22 relative to the article to be scribed can commence and can continue until it is deemed necessary to change to a new scribe edge 18. When this is required, retainer 64 is pivoted away from bar 20, the tool is then lifted slightly and turned 90° so that bar 20 can become aligned with and be lowered into engagement with the second pair of surfaces 62, then retainer 64 is moved back into the position shown in FIGS. 2 and 4, overlying the bar to retain the tool in place. Then, scribing can be started again and continued until it is required to change the third scribe edge and so on. 
     In the event that a scribe edge 18 is slightly askew to the orientation of bar 20 on shank 14, such as might result during manufacture of the tool, the movement of scribe edge 18 during a scribe operation will result in a &#34;tiller effect&#34;, causing flexure member 28 to flex to one side or the other until segment 24 is pivoted sufficiently to cause the scribe edge to move parallel to the desired scribe direction. This, is shown schematically in FIGS. 6 and 7, wherein FIG. 6 shows the unflexed condition of segment 24 with a scribe edge 18 at an acute angle relative to the scribe direction 30 (FIG. 1) and FIG. 7 shows the flexed condition of segment 24 with the scribe edge parallel to the scribe direction 30 (FIG. 1). The distance X (FIG. 7) indicating displacement of segment 24 and can be as much as 0.0004 inch without undesirable effects. At the end of the scribing of each line, segment 24 returns to its position shown in FIG. 1 relative to segment 26. 
     During use of the tool, its inclination can be changed by changing the initial position of beam 40 relative to arm 22. This is accomplished by adjusting screw 70.