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[ EN ]

Automated Acoustic Micro Imaging System and Method

The present invention is directed to a system and method for automating the inspection of semiconductor wafers and other parts through the use of an acoustic micro imaging system or "AMI" system. An AMI system operated at the high resolutions needed to inspect semiconductor wafers and other parts having microscopic detail requires that the scanning ultrasonic (or "acoustic") beam be coupled to and from the inspected part through water, alcohol or other coupling fluid. The acoustic coupling between the acoustic beam generator, often called a "transducer", and the part is typically accomplished by submerging the beam generator and part in a bath or by creating a gravity or pressure jet or flow between the beam generator and the part through which the acoustic beam travels. The necessitated presence of this coupling fluid creates a very wet scanning environment.
It is common to store wafers in cassettes before and after they are inspected. However, it is important that the wafers after inspection in the wet-environment of the AMI be returned to their storage cassettes in a dry condition - that is, not laden with significant surface moisture. Robots employed to handle wafers commonly employ a vacuum end effector. The wet-environment of an AMI system could be hostile to such commonly available wafer handling robots. Thus the presence of the coupling fluid creates a wet scanning environment that is inimical to automated AMI inspection processes.
Semiconductor wafers typically are circular in shape and are manufactured in a variety of diameters, including 100 mm, 125 mm, 150 mm, and recently 300 mm. During various manufacturing operations, semiconductor wafers are commonly retained by the use of a vacuum chuck having perforated vacuum plate upon which the wafers are situated. Such a vacuum chuck would be rendered inoperative in the wet AMI operating environment.
The processing of different size wafers requires different-sized vacuum chucks which presents yet another obstacle to a fully automated AMI inspection system.

It is an object of the present invention to provide an AMI system and method for automated inspection of semiconductor wafers and other parts which overcomes the innate incompatibility of commonly employed robotic devices and the hostile wet-environment of an AMI system, and satisfies the need to satisfactorily dry inspected parts before being returned to storage or passed on to another manufacturing process.
It is another object to provide an AMI system which makes possible the automated interchange of part-retention chucks capable of handling parts of different sizes and configurations.
It is a further object to provide for use in an AMI system a part-retention stage in which a vacuum chuck is so constructed as to be capable of quick-change, position-repeatable kinematic mounting without loss of vacuum integrity.

Many other objects will become evident from the following description and claims.
Figure 1 is a schematic perspective view of a portion of the system of the invention for automated inspection of semiconductor wafers and other parts in an AMI inspection system.
Figure 2 is a sectional side elevation view of a part of a scanning station shown in Figure 1.
Figures 3-5 schematically illustrate different system layout configurations according to the invention to reduce the moisture content of AMI-inspected wafers before return to storage. In the layout of Figure 3, a part-handling robot is located in a combined transport-storage station separated from a scanning station by a moisture barrier. In the layout of Figure 4, a part-handling robot is located in a discrete transport station and moisture barriers are provided on each side of the transport station. In the Figure 5 layout a parts-handling robot is wet-adapted and is located in the wet-environment AMI part scanning station.
Figure 6 is a schematic perspective view of an alternative preliminary dryer that may be employed instead of the dryer illustrated in Figures 1 and 2.
Figures 7, 7A, and 7B are perspective, side elevation, and exploded views of a part-retention stage illustrated in Figures 1-2 and constructed according to the principles of the present invention.
Figures 8, 8A, 9, 9A, 9B, 10, 10A, 11, 11A and 1 IB are orthographic projection views of the part-retention stage shown in Figures 7 A and 7B.

Figure 12 is a schematic view of another portion of the system of the invention for automated inspection of semiconductor wafers in an AMI inspection system, illustrating robotic means for automatically interchanging vacuum chucks of the type detailed in Figures 7-1 IB.
Figure 13 illustrates a buffer tank for softening the gas blast to the air knives depicted in Figures 1 and 6, for example.
Figure 14 shows an alternative vacuum chuck main plate having provision for expediting drainage of coupling fluid.
Figures 15 and 16 are schematic illustrations of AMI system arrangements for automated inspection of parts which improve the robot duty cycle and throughput of the system.

The present invention is directed to an automated acoustic micro imaging ("AMI") inspection system and method that enables the automated inspection of various part sizes and configurations in the hostile wet-environment of an AMI system. As used herein "robot" means any programmable computer-controlled mechanical for performing prescribed motion functions. "Kinematic" or "kinematic mount" means any arrangement wherein two structures are separably coupled in such a way that relative movement therebetween is uniquely constrained, with the assistance of gravity or other force, in all six degrees of freedom, namely X-axis, Y-axis, Z-axis, roll, pitch and yaw.
A preferred apparatus and method of execution of the invention is illustrated in the Figures, in which like reference numerals in different figures indicate like structure and function. The elements of the depicted execution will be first listed and identified with brief descriptive annotations where necessary to enlighten one skilled in the art, followed by a concise description of the operation of the system. Finally, structure and method equivalents of the preferred execution will be described.

Structure of the Preferred Execution
Reference Numeral Description
20 scanning station
22 part-storage station
23 ultrasonic beam
24 ultrasonic beam generator Sometimes termed a transducer.
25 coupling fluid
26 X-Y motion stage
28 support for X-Y motion stage
30 electrical cabling and coupling fluid hose for ultrasonic beam generator

32 part to be inspected Here shown as a semiconductor wafer.
34 vacuum chuck Accords with an aspect of the present invention

36 scanning station legs
38 tank For retaining coupling fluid drainage.
42 preliminary dryer nozzle Directs a jet of air or other gas at robot-engaged lower surface of part 32 to be inspected when nozzle is elevated into its operative position. See Figure 2, dotted-line position 90.

44 preliminary dryer nozzle Directs a jet of air or other gas at surface opposite to robot-engaged lower surface of part 32 when nozzle is elevated into its operative position. See Figure 2, dotted-line position 90.
46 gas hose for nozzle 42
48 gas hose for nozzle 44
50 arm Supports nozzles 4 and 44.
52 moisture barrier
54 air knife
56 air knife Air knives 54, 56 create a moisture barrier which minimizes the migration of the wet-environment created in the scanning station during part inspection into the storage station 22 containing part-holding cassettes 76J8 and robot 62. Air knives 54 and 56 are preferably canted toward the scanning station 20 to improve the effectiveness of the moisture barrier 105.
58 air hose for air knife 54
60 air hose for air knife 56
62 robot For retrieving a part 32 from cassette 78, placing it on the vacuum chuck 34 in the scanning station 20, and returning same to the cassette 78 or the cassette

76 after it has been inspected. Robot 62 may, for example be of a type manufactured by

Genmark, PRI Automation, and other suppliers.
63. controller For controlling the operation of the robot 62.
64 column 72 head
73 presence detector Used to determine whether a part is in a particular cassette storage slot.
74 end effector
75 vacuum recess For gripping a part when end effector 74 is activated with a vacuum.
76 cassette For storing parts, here shown by way of example as wafers 32.

78 cassette For storing parts; may be used to store rejected parts which failed inspection.
80 support base
82 support base
84 pneumatic piston See Figure 2. For pivoting nozzles 42,44 between an inoperative position (shown in unbroken lines in Figure 2) and an operative position

(shown in broken lines 90 in Figure 2). In its operative position, nozzle 44 is directed to the undersurface of part 32 in the region where it is to be engaged by the end effector 74 of robot head 72. In its operative position nozzle 42 is directed at the opposed surface of part 32.
86 pivot bolt for arm 50
88 nozzle support bracket Attached to arm 50 and supports nozzles 42,44.

90 operative position of nozzles 42,44
91 stage base Kinematically supports vacuum chuck 34, as will be described.

92 base plate of stage base 93 See detail in Figures 7A, 7B, 11 , 11 A, and 11B.
93 part-retention stage Retains part 32 during AMI inspection and comprises stage base 91 and vacuum chuck 34.
94 vacuum line
96 kinematic plate Tilt-adjustably connected to base plate 92 by means of adjustment screws 146 working against the bias of springs 144. See Figures 7A and 7B. 98 vacuum chuck cover plate Has provisions for making a position-repeatable kinematic mating engagement with kinematic plate 96, as will be explained below. See Figures 7B, 9, 9A, and 9B.
100 vacuum chuck main plate Completes a vacuum conduit from an external vacuum source (not shown) through vacuum line 94, vacuum coupling 142 on base plate 92, channel 164 in base plate 92, coupling member 150, a vacuum recess 154 in main plate 100 to hollow cores 101 vacuum posts 102, 103, 104. See Figures 7A, 8, and 8 A, for example. Details below. The vacuum chuck main plate 100 tends to collect a heavy accumulation of coupling fluid during the acoustic inspection operation which can aggravate the effort to dry the inspected part before return to storage. In accordance with an aspect of the invention, the plate 100 may be slightly domed or grooved or coated with a hydrophobic material to expedite drainage of coupling fluid collected on the chuck. Figure 14 illustrates a vacuum chuck main plate which is slightly domed and provided with radial grooves.
101 hollow cores in vacuum posts 102, 103, and 104.
102 vacuum post 103 vacuum post
104 vacuum post The vacuum posts 102, 103, 104 have a height sufficient to: 1 ) elevate a supported part above coupling fluid drainage, 2) provide access for the end effector 74 of robot 62, and 3) provide a passageway for gas from gas nozzle 42 to clear moisture from the undersurface of a part to be gripped by the robot and puddling from the top surface of vacuum chuck main plate 100.
105 moisture barrier Function is to minimize moisture migration from the wet-environment scanning station 20 to the dry-environment part-storage station 22.
106 wall section Moisture impervious.
107 wall section Moisture impervious
109 transport station Contains robot 62 in the Figure 4 layout. May also include auxiliary dryers to further reduce the moisture content on parts being returned to part-storage station 110. Examples here shown as including radiant energy dryer 111, and spin dryer 112 accessible to robot 62.
110 part-storage station
111 radiant energy dryer
112 spin dryer Shown as holding a part 113.
113 part
114 wall section Moisture impervious.
116 wall section Moisture impervious.
117 moisture barrier A tertiary moisture barrier to further insure that part returned to the part-storage station are adequately surface dry.
118 air knife 120 air knife
128 combined scanning-transport station In the Figure 5 layout, the robot 129 is wet-adapted and resides in the wet-environment scanning station with the AMI system.

129 robot Wet-adapted. May be of a type manufactured by PRI Automation and other suppliers.
132 dryer nozzle
134 dryer nozzle
136 dryer nozzle Figure 6 is an alternative to the preliminary dryer illustrated in Figures 1-2, comprising three permanently mounted nozzles 132, 134, 136 oriented such that at least a directional component of the gas stream is aimed away from the adjacent station to minimize the migration of moisture from the wet-environment AMI scanning station toward the part-storage station.
142 vacuum coupling
144 springs
146 adjustment screws
148a, 148b, 148c balls For use in effecting position-repeatable kinematic coupling of vacuum chuck 34 (through provisions on vacuum chuck cover plate 98) and stage base 91 (through provisions on kinematic plate 96). Balls 148a, 148b, 148c are preferably adhered to kinematic plate 96. See Figures 7A, 7B, 9, 9A, 10 and 10A.
150 vacuum coupling member Anchored in opening 190 (Figure 11 A) in base plate 92 at the terminus of channel 164, passing through loose fit opening 184 in plate 96 (Figure 10) to complete a vacuum conduit section between base plate 92 and cover plate 98. See Figure 7 A.

152 flexible cup Mates with and sealingly engages the periphery of opening

153 in cover plate 98 (Figure 9) when vacuum chuck 34 is placed upon the stage base 91. Coupling member 150 thus functions to automatically complete a vacuum conduit from an external vacuum source to vacuum posts 102, 103, and 104 when vacuum chuck 34 is installed on base 91.
153 opening
154 vacuum recess
160 chamfered hole Part of kinematic mount arrangement, engaging ball 148a.

162 chamfered slot Part of kinematic mount arrangement, engaging ball 148b.

163 recessed flat Part of kinematic mount arrangement, engaging ball 148c. The chamfered hole 160 engages ball 148a, the chamfered slot 162 engages ball 148b, and the recessed flat 163 engages ball 148c to constrain all degrees of freedom of the chuck 34 relative to the base 91, thus defining a position-repeatable kinematic mount of the vacuum chuck 34 upon the base 91.
164 channel or bore
166 chamfered hole For receiving ball 148a (Figure 10).
168 chamfered hole For receiving ball 148b (Figure 10).
170 chamfered hole For receiving ball 148c (Figure 10).
172 vacuum chuck storage rack See Figure 12.
176 vacuum chuck Vacuum chuck 176 may have a different size and/or configuration than vacuum chuck 34, but must have a kinematic mount arrangement which is similar thereto and compatible with that of kinematic plate 96 comprising part of stage base 91.

178 robot For interchanging vacuum chucks 34, 176. May be similar to robot 62 but more robust.
179 controller For controlling the robot 178.
180 magnetic end effector
181 vacuum recesses The function of robot 178 is to automatically retrieve vacuum chuck 34 from the part-retention stage 93 and substitute a predetermined alternate vacuum chuck such as shown at 176. The end effector 180 lifts and vacuum grips the vacuum chucks during the chuck interchange process in a manner similar to operation of robot 62.
190 buffer tank
192 inlet line
194 gas pump
196 outlet line
200 acoustic micro imaging system
202 acoustic micro imaging system
204 X-Y scanning transducer
205 robot
206 dryer
208 dryer
210 storage station
212 storage station
213 scanning transducer
214 part-retention stage 216 part-retention stage.
The preferred system which has been described executes a method for automated AMI inspection of semiconductor wafers or other parts stored in a dry-environment storage station. The various aspects of the present invention for which protection is sought by this patent are described precisely in the appended claims. The preferred method and system illustrated and described above, in broad review, comprises robotically retrieving a dry part from the storage station and placing it on a vacuum chuck in a part-retention stage in an AMI system station. The part is probed with an ultrasonic beam generated by a beam generator in the presence of a coupling fluid such as water. The coupling fluid undesirably creates a wet scanning environment that is hostile to robotic handling and post inspection storage of the part. In accordance with an aspect of the invention, the vacuum chuck elevates the part above the coupling fluid drainage.
To facilitate robotic retrieval of the part from the wet-environment scanning station, the part is subjected to a preliminary drying operation which may, for example, employ gas jets directed on the surface or surfaces to be engaged by the involved robot. The part is then robotically retrieved from the vacuum chuck and returned to the dry-environment storage station.
Because of the high state of wetness of, and space restrictions in, the scanning station, the preliminary drying operation may not sufficiently dry the part before it is returned to storage. To enhance the state of dryness of the part, a moisture barrier is preferably provided between the scanning station and the storage station. The moisture barrier may comprise any of a variety of means such as flexible lips or strands, heat, or forced gas. To further enhance the state of dryness of a part before re-storage, additional dryers may be employed, including a spin station, radiant heat, a vacuum oven or the like.

In order to further automate the process, another aspect of the present invention comprises robotically interchanging vacuum chucks to enable automated handing of parts of different sizes and configurations. In accordance with an aspect of the present invention the novel vacuum chuck is capable of quick-exchange, position-repeat, automatic vacuum restoration, and tilt adjustment.
A part, which may be different from a part inspected employing the first vacuum chuck, is retrieved from storage, and placed upon the exchanged vacuum chuck where it is inspected, dried preliminary to robotic pickup, and robotically returned to storage after subsequent moisture removal, if and as needed.
Thus, by the present invention, for the first time semiconductor wafers and other parts of differing sizes and configurations may be automatically inspected and handled in the hostile wet-environment of an AMI system without the need for manual intervention to change parts or part-retention equipment.

Other Equivalents of the Preferred Embodiment
Structures and methods that may be employed to implement the principles of the invention, other than those identified above, will now be described. Whereas
semiconductor wafers are illustrated as the type of parts handled by the present system, other parts such as flat panels displays, ceramic plates, PC boards and trays of parts may be handled. The storage means is shown as wafer cassettes 76,78, however, other part- storage containers such as flat panel display cassettes, part magazines, etc. may be employed.
A great variety of robotic devices may be employed for transporting parts to and from the scanning station. As noted, if situated in the scanning station the robot 62 is preferably wet-adapted, such as the "WETBOT" manufactured by PRI Automation. If located outside of the wet-environment scanning station, it is not necessary to employ a robot which has been provided with wet-condition resistance.
In the scanning station, an AMI system has been illustrated which is capable of X-Y scanning motion, however, another arrangement is contemplated wherein the beam generator moves in one dimension only and the part is moved in the orthogonal dimension. The part-retention is illustrated as being accomplished by a vacuum chuck, however, aspects of the invention could be implemented with part-retention by other than a vacuum chuck. In the preferred execution of the invention, a vacuum chuck is employed using three vacuum posts to elevate the inspected part above the coupling fluid drainage, however this objective could be accomplished in other ways. Various arrangements other than that shown could be employed for forming a vacuum conduit from an external vacuum source to the part being retained.
The kinematic mount aspect of the invention could be accomplished in a variety of ways other than the illustrated 4-point arrangement employing three balls mating with a countersunk hole, a groove and a flat Various means other than a coupling member as shown at 150 could be employed for completing the described vacuum conduit.
The moisture barrier 52 could be constructed using instrumentalities other than a pair of air knives. The illustrated arrangement of a pair of air knives mounted on a pivoted arm has the advantage of moving the preliminary drying gases in close proximity to the part surface to be engaged by the robot while directing the gas jets away from the part-storage station. These objectives can be accomplished using other means for moving the dryers in and out of such efficacious operating position. And, as noted, dryers other than one or more air knives may be employed.
Commercially available air knives of the type described have a tendency to start with a sharp blast of air which has been found to dislodge the part inspected and dispatch large amounts of moisture where it is not wanted. To overcome this too-sudden volume ramp-up, a buffer tank may be inserted in the line 192 from a gas pump 194, as shown in Figure 13. With this feature, when the air knife pump 194 is activated, the sudden blast of gas it creates first compresses gas in the tank 190 which is then released less suddenly into the outlet gas line 196. The volume of gas discharge from the knife thus builds up more gradually than would be the case without the buffer tank. The discharge volume versus time waveform can be controlled by the capacity of the tank and the diameter and length of the lines 192 and 196.
The present invention contemplates a number of ways to improve the duty cycle of the robot(s) employed. Figure 15 schematically illustrates an arrangement wherein a plurality of wet-environment acoustic micro imaging systems 200, 202, each having a part-retention stage, are serviced by a single X-Y scanning transducer 204 which moves back and forth between the two stages 200, 202. A single robot 205 is active in cycling parts between storage stations 210, 212, micro imaging systems 200, 202, dryers 206, 208 and back to storage stations 210, 212.

An arrangement shown in Figure 16 differs from the Figure 15 arrangement in that the transducer 213 does not move, but has an X-Y span great enough to encompass two part-retention stages 214, 216.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that other changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation on the scope of the invention.