Devices and Methods for Improved Detection of Anomalous Substrates in Automated Material-Handling Systems

Abstract

The present invention provides a method for detecting Anomalous Substrates in Automated Material-Handling Systems comprising the following steps. A substrate cassette having at least one substrate is provided. The substrate cassette is positioned within the material handling system. Each substrate has a top surface and a bottom surface. A first beam is emitted from a first emitter wherein the first beam is in optical communication with the top surface of the substrate. A second beam is emitted from a second emitter wherein the second beam is in optical communication with the bottom surface of the substrate. The first beam and the second beam are detected using at least one detector.

Claims

1. An apparatus for detecting Anomalous Substrates in Automated Material-Handling Systems comprising: a substrate cassette having at least one substrate, the substrate cassette is positioned within the material handling system, the substrate having a top surface and a bottom surface; a first beam positioned within the material handling system, the first beam is in optical communication with the top surface of the substrate; a second beam positioned within the material handling system, the second beam is in optical communication with the bottom surface of the substrate; and a first detector positioned within the material handling system, the first detector is in optical communication with the first beam and the second beam.

2. The apparatus according to claim 1 wherein the first beam further comprising a first optical path and a first angle between the first optical path and the substrate, wherein the first optical path does not intersect more than one substrate at a time in the substrate cassette.

3. The apparatus according to claim 2 wherein the second beam further comprising a second optical path and a second angle between the second optical path and the substrate, wherein the second optical path does not intersect more than one substrate at a time in the substrate cassette.

4. The apparatus according to claim 3 wherein the first optical path intersects the top surface of at least one substrate in the substrate cassette and the second optical path intersects the bottom surface of at least one substrate in the substrate cassette.

5. The apparatus according to claim 1 wherein the first beam is a laser beam.

6. The apparatus according to claim 5 wherein the second beam is a laser beam.

7. An apparatus for detecting Anomalous Substrates in Automated Material-Handling Systems comprising: a substrate cassette having at least one substrate, the substrate cassette is positioned within the material handling system, the substrate having a top surface and a bottom surface; a first beam positioned within the material handling system, the first beam is in optical communication with the top surface of the substrate; a second beam positioned within the material handling system, the second beam is in optical communication with the bottom surface of the substrate; a first detector positioned within the material handling system, the first detector is in optical communication with the first beam; and a second detector positioned within the material handling system, the second detector is in optical communication with the second beam.

8. The apparatus according to claim 7 wherein the first beam further comprising a first optical path and a first angle between the first optical path and the substrate, wherein the first optical path does not intersect more than one substrate at a time in the substrate cassette.

9. The apparatus according to claim 8 wherein the second beam further comprising a second optical path and a second angle between the second optical path and the substrate, wherein the second optical path does not intersect more than one substrate at a time in the substrate cassette.

10. The apparatus according to claim 9 wherein the first optical path intersects the top surface of at least one substrate in the substrate cassette and the second optical path intersects the bottom surface of at least one substrate in the substrate cassette.

11. The apparatus according to claim 7 wherein the first beam is a laser beam.

12. The apparatus according to claim 11 wherein the second beam is a laser beam.

13. A method for detecting Anomalous Substrates in Automated Material-Handling Systems comprising: providing a substrate cassette having at least one substrate, the substrate cassette is positioned within the material handling system, the substrate having a top surface and a bottom surface; emitting a first beam from a first emitter, the first beam being in optical communication with the top surface of the substrate; emitting a second beam from a second emitter, the second beam being in optical communication with the bottom surface of the substrate; and detecting the first beam and the second beam using a first detector.

14. The method according to claim 13 further comprising a second detector positioned within the material handling system, the second detector is in optical communication with the first beam or the second beam and wherein the first detector is in optical communication with the first beam or the second beam.

15. The method according to claim 14 further comprising comparing a first signal detected by the first detector to a second signal detected by the second detector.

16. The method according to claim 13 wherein the first beam further comprising a first optical path and a first angle between the first optical path and the substrate, wherein the first optical path does not intersect more than one substrate at a time in the substrate cassette.

17. The method according to claim 16 wherein the second beam further comprising a second optical path and a second angle between the second optical path and the substrate, wherein the second optical path does not intersect more than one substrate at a time in the substrate cassette.

18. The method according to claim 17 wherein the second optical path intersects the bottom surface of at least one substrate in the substrate cassette.

19. The method according to claim 13 further comprising moving the first emitter or the second emitter relative to the substrate cassette.

20. The method according to claim 13 further comprising moving the substrate cassette relative to the first emitter or the second emitter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a front view of a substrate cassette on an elevator;

[0019] FIG. 2 is a top view of a substrate cassette;

[0020] FIG. 3 is a side view of a laser light beam in cassette slot at angle from back to front;

[0021] FIG. 4 is a graph of a light sensor electrical signal received by a detector;

[0022] FIG. 5 is a graph of a light sensor electrical signal resulting from a single substrate and multi-stacked substrates;

[0023] FIG. 6 is a perspective view of one embodiment of the present invention showing dual emitters and receivers; and

[0024] FIG. 7 is a graphical representation of the signal differences from a single flat substrate and from a tilted single substrate.

[0025] Similar reference characters refer to similar parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Equipment for manufacturing of complex electronics devices on disks of semiconductor materials (“substrates”) utilizes automated mechanisms to move materials within the equipment. These mechanisms and their methods include material cassettes and cassette elevators.

[0027] A material cassette is a standardized fixture that provides slots that are arranged vertically to hold semiconductor substrates so they are accessible to the automated mechanisms of material-handling systems. Cassette slots are typically arranged with equal vertical spacing (“pitch”) between slots. Each slot is intended to contain no more than one substrate as shown in FIG. 1.

[0028] A cassette elevator is an electrical-mechanical device that moves a cassette vertically to position substrates to be accessed by mechanisms within a material-handling system, see FIG. 1.

[0029] A process that utilizes devices and software within the system to create an accurate representation of substrates (presence and location) within a cassette is known as Substrate Mapping. The typical prior art cassette mapping process utilizes a single emitter (e.g., laser beam) and a receiver/detector (e.g., light sensor). The emitter emits a beam of light that traverses a substrate slot from back to front. The emitter is positioned so the light beam is at an angle to the horizontal plane of the slot. The emitter and sensor are in fixed positions, see FIG. 3.

[0030] A mechanism (“elevator”) moves the cassette vertically at a known rate, so that each cassette slot passes through the light beam. The light beam is received at the sensor when no substrate is present in a slot. When a substrate is present in a slot, the substrate surface blocks the light beam from reaching the sensor. The sensor produces an electrical signal of a first value when the light beam is blocked and a second value when the light beam is not blocked as shown in FIG. 4. The system's software interprets the electrical signal to produce a “map” of the substrates within the cassette.

[0031] In some cases more than one substrate may be located in a single cassette slot (e.g. double-stacked). In the automated material-handling systems described herein, detection of multi-stacked substrates is critical. Failure to detect multi-stacked substrates can result in damage to the equipment and to valuable semiconductor substrates.

[0032] The typical prior art cassette mapping process produces an electrical signal as shown in FIG. 5 in which the duration, or graphed distance, from the first value to the second value is shorter for a single substrate (d) than for double-stacked substrates (d′).

[0033] Another anomalous substrate condition is a “tilted” substrate within a slot. This occurs if a substrate is pushed as far as possible to the back of the slot, which causes the back of the substrate to be higher than the front. The same effect can also be caused by an abnormality in the cassette slot itself. The tilted substrate condition does not necessarily impose a risk of damage. However, with current mapping devices and methods, tilted substrates (OK to proceed) can be incorrectly detected as multi-stacked substrates (not OK to proceed).

[0034] Varying the placement of the emitter and the sensor can result in marginal improvement in the ability of the system to detect tilted substrates. Placement of the laser and the sensor so that the light beam rotates across the substrate during mapping can minimize the effect of tilted substrates being mis-detected as multi-stacked substrates. However, a single laser and single sensor configuration cannot be used to distinguish between tilted and multi-stacked substrates. The optical profile—and therefore the resulting electrical signal from the sensor—is nearly identical for a tilted substrate and multi-stacked substrates.

[0035] In one embodiment of the present invention, there are two emitters (e.g., lasers) and at least one detector (e.g., light sensors), and associated software that analyzes the signals from the sensor to allow the material-handling system to distinguish between tilted and multi-stacked substrates.

[0036] In another embodiment of the present invention, there are two emitters (e.g., lasers) and two detectors (e.g., light sensors), and associated software that analyzes the signals from the sensors to allow the material-handling system to distinguish between tilted and multi-stacked substrates as shown in FIG. 6.

[0037] The emitters and light sensors are positioned so that the light beam from an emitter traverses the substrates in the cassette at opposing angles. A first optical path between a first light beam and a first detector is out of plane with the substrate (e.g., the emitter is positioned above the substrate and the detector is positioned below the substrate). The angle between the first optical path and the substrate must be relatively small—typically less than 5 degrees. The ideal angle is limited by the pitch of the cassette; for a SEMI standard cassette with a slot pitch of 0.1875 inches, for example, the ideal angle was found to be 1 degree. The angle between the first optical path and the substrate must be small enough such that the first optical path does not intersect more than one substrate at a time in the cassette.

[0038] A second optical path of a second light beam and a second detector is also out of plane with the substrate. The angle between the second optical path and the substrate must be relatively small—typically less than 5 degrees. The ideal angle is limited by the pitch of the cassette; for a SEMI standard cassette with a slot pitch of 0.1875 in., for example, the ideal angle was found to be 1 degree. The angle between the second optical path and the substrate must be small enough such that the second optical path does not intersect more than one substrate at a time in the cassette.

[0039] The second optical path intersects the substrate from the opposite side of the substrate that the first optical path intersects the substrate (e.g., if the first emitter is positioned above the substrate then the first optical path intersects the substrate from above, and if the second emitter is positioned below the substrate then the second optical path intersects the substrate from below). In other words, relative to the plane of the substrate—if the angle between the substrate and the first optical path is positive, then the angle between the substrate and the second optical path will be negative. When a substrate is present in a cassette slot, both light sensors produce a similar signal (if the angles between the substrate and optical paths are equal and opposite sign, then the signals will be identical). That is, the light beam from each emitter is blocked for a similar number of elevator motor counts, and the sensors produce the similar electrical signal profile.

[0040] If a substrate is tilted in a cassette slot, the light beam from one emitter is blocked from its sensor for a significantly longer period (during a greater number of elevator motor counts) than the light beam from the second emitter, see FIG. 7.

[0041] When two substrates are present in a single cassette slot, the light beam from each emitter is blocked for a similar period. The resulting electrical signal profile produced by the sensors; however, differs significantly from the signal profile of a single substrate in a cassette slot.

[0042] Two emitters and receivers (e.g., lasers and light sensors), positioned so that the light beams travel across the cassette slots on planes that are angled relative to each other, provide the ability to determine relative thickness (rt) of the material in the cassette slot, without regard to whether the substrate is tilted.

[0043] The ability of the device to accurately detect tilted substrates within a cassette slot increases the ability of the system to distinguish multiple substrates in a slot from a single substrate in a slot. This system allows the software to determine a relative thickness value that is significantly larger than that of a single substrate, whether flat or tilted within the cassette slot.

[0044] Data from testing 100 mm and 200 mm Si wafers proves that the improvement in substrate detection is significant. Testing was performed by mapping cassettes in which a slot contained the following material configurations: [0045] 1. Single substrate [0046] 2. Single substrate tilted by 0.8 mm higher at the front of the cassette slot [0047] 3. Single substrate tilted by 0.8 mm higher at the back of the cassette slot [0048] 4. Stack of two substrates [0049] 5. Stack of two substrates tilted by 0.8 mm higher at the front of the cassette slot [0050] 6. Stack of two substrates tilted by 0.8 mm higher at the back of the cassette slot

[0051] The following are the numeric results from the substrate detection testing using the improved device and methods:

TABLE-US-00001 TABLE 1 Signal data from 100 mm Si substrate. Supporting Data 100 mm diameter standard Si wafer Single/Tilt: Maximum rT = 162 Multi-stack: Minimum rT = 180 Single wafer mapping Single cassette tilt front Single cassette tilt back slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) 21 55 100 156 21 21 129 150 21 93 66 159 22 61 96 157 22 26 121 147 22 97 60 157 23 53 102 155 23 28 133 161 23 84 77 161 24 50 101 151 24 25 133 158 24 84 77 161 25 59 98 157 25 22 129 151 25 85 76 162 Stack wafer mapping Stack cassette tilt front Stack cassette tilt back slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) 21 94 98 192 21 59 123 182 21 129 57 186 22 82 108 190 22 48 133 181 22 122 71 193 23 84 103 187 23 51 129 180 23 122 68 190 24 90 102 192 24 57 127 184 24 127 60 187 25 78 108 186 25 41 139 180 25 113 78 191

TABLE-US-00002 TABLE 2 Signal data from 200 mm Si substrate. 200 mm diameter Si wafer Single/Tilt: Maximum rT = 301 Multi-stack: Minimum rT = 350 Single wafer mapping Single cassette tilt front Single cassette tilt back slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) 21 159 141 300 21 109 182 291 21 170 129 299 22 145 153 298 22 100 190 290 22 167 134 301 23 144 151 295 23 102 188 290 23 166 133 299 24 153 144 297 24 111 180 291 24 178 120 298 25 155 143 298 25 115 176 291 25 182 118 300 Stack wafer mapping Stack cassette tilt front Stack cassette tilt back slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) slot d1 d2 Sum (rT) 21 186 172 358 21 143 209 352 21 213 145 358 22 172 184 356 22 131 221 352 22 214 145 359 23 178 178 356 23 135 215 350 23 209 147 356 24 182 178 360 24 139 211 350 24 217 141 358 25 185 176 361 25 138 213 351 25 220 137 357

[0052] The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.