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Publication numberUS20050164608 A2
Publication typeApplication
Application numberUS 10/860,019
Publication dateJul 28, 2005
Filing dateJun 4, 2004
Priority dateMay 23, 1995
Also published asUS7169015, US20050009450
Publication number10860019, 860019, US 2005/0164608 A2, US 2005/164608 A2, US 20050164608 A2, US 20050164608A2, US 2005164608 A2, US 2005164608A2, US-A2-20050164608, US-A2-2005164608, US2005/0164608A2, US2005/164608A2, US20050164608 A2, US20050164608A2, US2005164608 A2, US2005164608A2
InventorsMoshe Finarov
Original AssigneeNova Measuring Instruments Ltd.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus for optical inspection of wafers during processing
US 20050164608 A2
Abstract
Abstract of the Disclosure
An optical system is disclosed for the inspection of wafers during polishing which also includes a measurement system for measuring the thickness of the wafers top layer. The optical system views the wafer through a window and includes a gripping system, which places the wafer in a predetermined viewing location while maintaining the patterned surface completely under water. The optical system also includes a pull-down unit for pulling the measurement system slightly below the horizontal prior to the measurement and returns the measuring system to the horizontal afterwards
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Claims(114)
1. A measurement station for use with a processing machine, which includes a processing station for processing an article and an exit station including an article transfer assembly and at least one articles’ cassette, the measurement station being so dimensioned as to be installable in association with the exit station of the processing machine and comprising an optical system and a holding unit for receiving and holding the article in a measuring position during measurements, said optical system comprising: a spectrophotometer; an imaging system operable to locate measurements; a beam directing assembly for directing illuminating light towards the article and directing collected light from the article towards a beam splitting assembly for separating a first portion of the collected light to propagate towards the spectrophotometer and a second portion to propagate to said imaging system.
2. The measurement station according to Claim 1, wherein said beam splitting assembly comprising an inclined mirror surface.
3. The measurement station according to Claim 1, wherein said beam splitting assembly comprising a pin hole mirror.
4. The processing machine according to Claim 1, wherein said imaging system comprises a charge coupled device (CCD).
5. The measurement station according to Claim 1, wherein said optical system is configured and operable to enable measuring a thickness of at least a top layer of the article.
6. The measurement station according to Claim 1, wherein said optical system is configured and operable to carry out optical inspection of the processed article.
7. The measurement station according to Claim 1, comprising a support assembly for supporting the article.
8. The measurement station according to Claim 7, wherein said support assembly is configured for supporting the article that is to be received from the holding unit.
9. The measurement station according to Claim 7, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
10. The measurement station according to Claim 8, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
11. The measurement station according to Claim 1, wherein the optical system and the holding unit are separated by a window through which at least a part of the article being held is viewable to enable optical measurements.
12. The measurement station according to Claim 1, wherein said holding unit comprises an assembly movable along an axis perpendicular to the article’s surface, thereby enabling said holding of the article in the measuring position.
13. The measurement station according to Claim 1, having a footprint in at least one dimension of about a size of the article’s diameter.
14. The measurement station according to Claim 1, wherein said processing machine is a polisher.
15. The measurement station according to Claim 1, configured for receiving the processed article from the processing machine via said article transfer assembly of the exit station.
16. The measurement station according to Claim 1, wherein said optical system includes a focusing optics for focusing the illuminated light onto the article and collecting the light from the illuminated article.
17. The measurement station according to Claim 7, wherein the support assembly is configured to receive the article from the article transfer assembly of the exit station and to enable the article transfer into the measuring position.
18. The measurement station according to Claim 7, wherein the support assembly includes two support elements displaceable with respect to each other.
19. The measurement station according to Claim 7, wherein the support assembly is configured for supporting the article at its periphery region.
20. The measurement station according to Claim 1, wherein the imaging system is operable to perform pattern recognition.
21. The measurement station according to Claim 16, wherein the optical system comprises a fiber optics for directing light from a light source towards the focusing optics.
22. The measurement station according to Claim 16, wherein the focusing optics comprises an objective lens arrangement.
23. The measurement station according to Claim 1, wherein the imaging system includes a lens arrangement accommodated between an imaging detector and the beam splitting assembly.
24. The measurement station according to Claim 1, wherein the optical system comprises a lens arrangement accommodated between the beam splitting assembly and the spectrophotometer.
25. The measurement station according to claim 1, wherein the optical system is configured for providing substantially normal incidence of the illuminating light.
26. The measurement station according to Claim 3, wherein the pin hole mirror is accommodated so as to be an aperture stop in an optical path of the collected light, the pin hole mirror thereby appearing as a dark area in an image of a measurement spot on the article and allowing for locating the measurement spot.
27. The measurement station according to Claim 1, wherein the holding unit comprises a vacuum assembly for holding the article by vacuum.
28. The measurement station according to Claim 17, wherein the support assembly includes two support elements displaceable with respect to each other.
29. The measurement station according to Claim 1, configured to be installable within the exit station of the processing machine.
30. The measurement station according to Claim 1, wherein said optical system is configured and operable to measure in the patterned article.
31. The measurement station according to Claim 2, wherein said inclined mirror surface is a surface of a pin hole mirror.
32. The processing machine according to Claim 2, wherein said imaging system comprises a charge coupled device (CCD).
33. The measurement station according to Claim 2, wherein said optical system is operable to measure a thickness of at least a top layer of the article.
34. The measurement station according to Claim 2, wherein said optical system is operable to carry out optical inspection of the processed article.
35. The measurement station according to Claim 2, comprising a support assembly for supporting the article.
36. The measurement station according to Claim 35, wherein said support assembly is configured for supporting the article that is to be received from the holding unit.
37. The measurement station according to Claim 35, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
38. The measurement station according to Claim 36, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
39. The measurement station according to Claim 2, wherein the optical system and the holding unit are separated by a window through which at least a part of the article being held is viewable to enable optical measurements.
40. The measurement station according to Claim 2, wherein said holding unit comprises an assembly movable along an axis perpendicular to the article’s surface, thereby enabling said holding of the article in the measuring position.
41. The measurement station according to Claim 2, having a footprint in at least one dimension of about a size of the article’s diameter.
42. The measurement station according to Claim 2, wherein said processing machine is a polisher.
43. The measurement station according to Claim 2, configured for receiving the processed article from the processing machine via said article transfer assembly of the exit station.
44. The measurement station according to Claim 2, wherein said optical system includes a focusing optics for focusing the illuminated light onto the article and collecting the light from the illuminated article.
45. The measurement station according to Claim 35, wherein the support assembly is configured to receive the article from the article transfer assembly of the exit station and to enable the article transfer into the measuring position.
46. The measurement station according to Claim 35, wherein the support assembly includes two support elements displaceable with respect to each other.
47. The measurement station according to Claim 35, wherein the support assembly is configured for supporting the article at its periphery region.
48. The measurement station according to Claim 2, wherein the imaging system is operable to perform pattern recognition.
49. The measurement station according to Claim 44, wherein the optical system comprises a fiber optics for directing light from a light source towards the focusing optics.
50. The measurement station according to Claim 44, wherein the focusing optics comprises an objective lens arrangement.
51. The measurement station according to Claim 2, wherein the imaging system includes a lens arrangement accommodated between an imaging detector and the beam splitting assembly.
52. The measurement station according to Claim 2, wherein the optical system comprises a lens arrangement accommodated between the beam splitting assembly and the spectrophotometer.
53. The measurement station according to Claim 2, wherein the optical system is configured for providing substantially normal incidence of the illuminating light.
54. The measurement station according to Claim 31, wherein the pin hole mirror is accommodated so as to be an aperture stop in an optical path of the collected light, the pin hole mirror thereby appearing as a dark area in an image of a measurement spot on the article and allowing for locating the measurement spot.
55. The measurement station according to Claim 2, wherein the holding unit comprises a vacuum assembly for holding the article by vacuum.
56. The measurement station according to Claim 35, wherein the support assembly includes two support elements displaceable with respect to each other.
57. The measurement station according to Claim 2, configured to be installable within the exit station of the processing machine.
58. The measurement station according to Claim 2, wherein said optical system is configured and operable for measuring in the patterned article.
59. The measurement station according to Claim 5, comprising a support assembly for supporting the article.
60. The measurement station according to Claim 59, wherein said support assembly is configured for supporting the article that is to be received from the holding unit.
61. The measurement station according to Claim 59, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
62. The measurement station according to Claim 60, wherein said support assembly is configured for supporting the article that is to be received by the holding unit.
63. The measurement station according to Claim 5, wherein the optical system and the holding unit are separated by a window through which at least a part of the article being held is viewable to enable optical measurements.
64. The measurement station according to Claim 5, wherein said holding unit comprises an assembly movable along an axis perpendicular to the article’s surface, thereby enabling said holding of the article in the measuring position.
65. The measurement station according to Claim 5, having a footprint in at least one dimension of about a size of the article’s diameter.
66. The measurement station according to Claim 5, wherein said processing station is a polisher.
67. The measurement station according to Claim 5, configured for receiving the processed article from the processing machine via said article transfer assembly of the exit station.
68. The measurement station according to Claim 5, wherein said optical system includes a focusing optics for focusing the illuminated light onto the article and collecting the light from the illuminated article.
69. The measurement station according to Claim 59, wherein the support assembly is configured to receive the article from the article transfer assembly of the exit station and to enable the article transfer into the measuring position.
70. The measurement station according to Claim 59, wherein the support assembly includes two support elements displaceable with respect to each other.
71. The measurement station according to Claim 59, wherein the support assembly is configured for supporting the article at its periphery region.
72. The measurement station according to Claim 5, wherein the imaging system is operable to perform pattern recognition.
73. The measurement station according to Claim 68, wherein the optical system comprises a fiber optics for directing light from a light source towards the focusing optics.
74. The measurement station according to Claim 68, wherein the focusing optics comprises an objective lens arrangement.
75. The measurement station according to Claim 5, wherein the imaging system includes a lens arrangement accommodated between an imaging detector and the beam splitting assembly.
76. The measurement station according to Claim 5, wherein the optical system comprises a lens arrangement accommodated between the beam splitting assembly and the spectrophotometer.
77. The measurement station according to Claim 5, wherein the optical system is configured for providing substantially normal incidence of the illuminating light.
78. The measurement station according to Claim 5, wherein the beam splitting means comprises a pin hole mirror that is accommodated so as to be an aperture stop in an optical path of the collected light, the pin hole mirror thereby appearing as a dark area in an image of a measurement spot on the article and allowing for locating the measurement spot.
79. The measurement station according to Claim 5, wherein the holding unit comprises a vacuum assembly for holding the article by vacuum.
80. The measurement station according to Claim 59, wherein the support assembly includes two support elements displaceable with respect to each other.
81. The measurement station according to Claim 5, configured to be installable within the exit station of the processing machine.
82. The measurement station according to Claim 5, wherein said optical system is configured and operable for measuring in the patterned article.
83. The measurement station according to Claim 7, wherein the optical system and the holding unit are separated by a window through which at least a part of the article being held is viewable to enable optical measurements.
84. The measurement station according to Claim 7, wherein said holding unit comprises an assembly movable along an axis perpendicular to the article’s surface, thereby enabling said holding of the article in the measuring position.
85. The measurement station according to Claim 7, having a footprint in at least one dimension of about a size of the article’s diameter.
86. The measurement station according to Claim 7, wherein said processing station is a polisher.
87. The measurement station according to Claim 7, configured for receiving the processed article from the processing machine via said article transfer assembly of the exit station.
88. The measurement station according to Claim 7, wherein said optical system includes a focusing optics for focusing the illuminated light onto the article and collecting the light from the illuminated article.
89. The measurement station according to Claim 7, wherein the imaging system is operable to perform pattern recognition.
90. The measurement station according to Claim 88, wherein the optical system comprises a fiber optics for directing light from a light source towards the focusing optics.
91. The measurement station according to Claim 88, wherein the focusing optics comprises an objective lens arrangement.
92. The measurement station according to Claim 7, wherein the imaging system includes a lens arrangement accommodated between an imaging detector and the beam splitting assembly.
93. The measurement station according to Claim 7, wherein the optical system comprises a lens arrangement accommodated between the beam splitting assembly and the spectrophotometer.
94. The measurement station according to Claim 7, wherein the optical system is configured for providing substantially normal incidence of the illuminating light.
95. The measurement station according to Claim 7, wherein the beam splitting means comprises a pin hole mirror that is accommodated so as to be an aperture stop in an optical path of the collected light, the pin hole mirror thereby appearing as a dark area in an image of a measurement spot on the article and allowing for locating the measurement spot.
96. The measurement station according to Claim 7, wherein the holding unit comprises a vacuum assembly for holding the article by vacuum.
97. The measurement station according to Claim 7, configured to be installable within the exit station of the processing machine.
98. The measurement station according to Claim 7, wherein said optical system is configured and operable to measure in the patterned article.
99. The measurement station according to Claim 13, wherein said processing station is a polisher.
100. The measurement station according to Claim 13, configured for receiving the processed article from the processing machine via said article transfer assembly of the exit station.
101. The measurement station according to Claim 13, wherein said optical system includes a focusing optics for focusing the illuminated light onto the article and collecting the light from the illuminated article.
102. The measurement station according to Claim 13, wherein the imaging system is operable to perform pattern recognition.
103. The measurement station according to Claim 101, wherein the optical system comprises a fiber optics for directing light from a light source towards the focusing optics.
104. The measurement station according to Claim 101, wherein the focusing optics comprises an objective lens arrangement.
105. The measurement station according to Claim 13, wherein the imaging system includes a lens arrangement accommodated between an imaging detector and the beam splitting assembly.
106. The measurement station according to Claim 13, wherein the optical system comprises a lens arrangement accommodated between the beam splitting assembly and the spectrophotometer.
107. The measurement station according to claim 13, wherein the optical system is configured for providing substantially normal incidence of the illuminating light.
108. The measurement station according to Claim 13, wherein the beam splitting means comprises a pin hole mirror that is accommodated so as to be an aperture stop in an optical path of the collected light, the pin hole mirror thereby appearing as a dark area in an image of a measurement spot on the article and allowing for locating the measurement spot.
109. The measurement station according to Claim 13, wherein the holding unit comprises a vacuum assembly for holding the article by vacuum.
110. The measurement station according to Claim 13, configured to be installable within the exit station of the processing machine.
111. The measurement station according to Claim 13, wherein said optical system is configured and operable to measure in the patterned article.
112. A measurement station for use with a processing machine, which includes a polisher for polishing an article and an exit station including an article transfer assembly and at least one articles’ cassette, the measurement station being so dimensioned as to be installable in association with the exit station of the processing machine and comprising an optical system and a holding unit for receiving and holding the article in a measuring position during measurements, said optical system comprising a spectrophotometer; an imaging system operable to locate measurements; a beam directing assembly for directing illuminating light towards the article and directing collected light from the article towards a beam splitting assembly including a pin hole mirror for separating a first portion of the collected light to propagate towards the spectrophotometer and a second portion to propagate to said imaging system.
113. A measurement station for use with a processing machine, which includes a processing station for processing an article and an exit station including an article transfer assembly and at least one articles’ cassette, the measurement station being so dimensioned as to be installable in association with the exit station of the processing machine and comprising an optical system, a holding unit for receiving and holding the article in a measuring position during measurements, and a support assembly for supporting the article while transporting it in between said transfer assembly of the exit station and said holding unit, said optical system being configured and operable to enable measurement of a thickness of at least a top layer of the article, said optical system including a spectrophotometer; an imaging system operable to locate measurements; a beam directing assembly for directing illuminating light towards the article and directing collected light from the article towards a beam splitting assembly for separating a first portion of the collected light to propagate towards the spectrophotometer and a second portion to propagate to said imaging system.
114. A measurement station for use with a processing machine, which includes a processing station for processing an article and an exit station including an article transfer assembly and at least one articles’ cassette, the measurement station being so dimensioned as to be installable in association with the exit station of the processing machine and comprising an optical system, and a holding unit for receiving and holding the article in a measuring position during measurements, said optical system being configured and operable to enable measurement of a thickness of at least a top layer of the article, said optical system including a spectrophotometer; an imaging system operable to locate measurements; a beam directing assembly for directing illuminating light towards the article and directing collected light from the article towards a beam splitting assembly including a pin hole mirror for separating a first portion of the collected light to propagate towards the spectrophotometer and a second portion to propagate to said imaging system.
Description
Detailed Description of the Invention CROSS-REFERENCE OT RELATED APPLICATION

This is a continuation of U.S. Application No. 09/898,467, filed on July 5, 2001, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to wafer polishing apparatus in general and to measuring systems incorporated into such apparatus in particular.

BACKGROUND OF THE INVENTION

Wafer polishing systems are known in the art. They polish the top layer of semi-conductor wafers to a desired thickness. To do so, the wafer being polished is immersed in a slurry of water and chemicals during the polishing process. Once the wafer has been polished and washed down, it is placed into an exit station known by some companies as a "water track", after which the wafer is placed into a cassette of wafers. The cassette is maintained within a water bath until full, after which the entire cassette is brought to a cleaning station to remove any chemicals and slurry particles still remaining on the wafers in the cassette and to dry the wafers. After cleaning, the wafers are brought to a measurement station to determine if the polisher produced the desired thickness of their top layers.

Fig. 1, to which reference is now briefly made, illustrates a prior art water track, such as the water track of the #372 Polisher manufactured by IPEC Westech Inc. of Phoenix, Arizona, USA. The water track, labeled 10, comprises a frame 12 and a base 14. Frame 12 has jet holes 16 connected to jets (not shown) which emit streams 18 of water through holes 16. Base 14 has holes 20 connected to bubblers (not shown) which bubble small amounts of water 22 through holes 20. When a wafer 25 is dropped into water track 10, pattern-side down, the jets and bubblers are activated. Streams 18, from the water jets, serve to force the wafer 25 in the direction indicated by arrow 24. Small streams 22 push the wafer 25 slightly away from the base 14 and ensure that, while the wafer 25 moves through the track, it never rubs against base 14 and thus, the pattern on the wafer is not scratched.

Other companies produce polishers whose exit stations are formed just of the cassettes. Such a polisher is in the 6DS-SP polisher of R. Howard Strasbaugh Inc. San Luis Obispo, California, USA.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a measurement system installable within a polishing machine and, more specifically, within the exit station of a polishing machine.

In accordance with a preferred embodiment of the present invention, the present invention includes an optical system, which views the wafer through a window in the exit station, and a gripping system, which places the wafer in a predetermined viewing location within the exit station while maintaining the patterned surface completely under water. The present invention also includes a pull-down unit for pulling the measurement system slightly below the horizontal prior to the measurement and returns the measuring system to horizontal afterwards.

In accordance with a first preferred embodiment of the present invention, the gripping system includes a raisable gate which collects the wafer in a predetermined location, and a gripper which grips the wafer, carries it to the viewing location and immerses the wafer, along a small angle to the horizontal, in the water. The gripper also holds the wafer in place during the measurement operation, after which, it releases the wafer and the raisable gate is raised

The present invention incorporates the method of immersing an object into water such that very few bubbles are produced on the wafer surface. The method of the present invention preferably includes the step of immersing the object while it is held such that its surface plane is at a small angle to the horizontal.

In a second embodiment, the measurement system includes a water bath and a gripping system thereabove. The gripping system includes wafer holding elements, which receive the wafer, and a gripper whose initial location is above the expected reception location of the wafer. The gripper is flexibly connected at an angle to a piston such that the wafer is immersed in the water at an angle to the horizontal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

Fig. 1 is a schematic illustration of a prior art water track;

Fig. 2 is a schematic illustration of a measurement system installable within a polishing machine, the measurement system being constructed and operative in accordance with a preferred embodiment of the present invention;

Figs. 3, 4, 5, 6, 7 and 8 are schematic, side view illustrations of a gripping system forming part of the measurement system of Fig. 2 in various stages of operation;

Fig. 9 is a schematic illustration of an example optical system forming part of the measurement system of the present invention;

Fig. 10 is a top view of a second embodiment of the measurement system of the present invention; and

Figs. 11, 12 and 13 are side views of the measurement system during receipt, transfer and measurement of the wafer, respectively.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to Fig. 2, which illustrates a measurement unit installable within a polishing machine, such as the IPEC Westech machine, the measurement system being constructed and operative in accordance with a preferred embodiment of the present invention and to Figs. 3, 4, 5, 6, 7 and 8 which illustrate the operation of a gripping system forming part of the measurement system of Fig. 2. Similar reference numerals are utilized to refer to elements of the water track previously discussed.

The measurement system, labeled 30, comprises an optical system 32 and a gripping system 34 operative in conjunction with a water track 36. The optical system 32 can be any optical system which measures the thickness of the top layer of the wafer through water. Fig. 9 provides one example of such a optical system; other optical systems are also incorporated into the present invention.

The gripping system 34 comprises a raisable gate 40, a translatable gripper 42, a vacuum pad 44 and a vacuum system 46. Gate 40 is controlled by a lifting mechanism 48 which raises and lowers gate 40 as necessary. Gate 40 has an upper surface 50 with a curved outer edge 52 and a plurality of protrusions 54 extending downward into the water from the upper surface 50. Protrusions 54 provide a lower surface onto which the gate 40 is lowered while enabling the water to pass through the gate 40. Curved edge 52 is shaped to match the curved edge of the wafer 25 so that, when gate 40 is in its lowered position, gate 40 will both keep the wafer 25 from passing out of the water track and to hold the wafer 25 in a repeatable location.

Gripper 42 translates between the wafer collecting position defined by the curved edge 52 and a wafer measuring location indicated in Fig. 2 by the wafer 25. Although not visible in Fig. 2, the base of the water track at the wafer measuring location has been replaced by a window 60 (Figs. 3-9) to enable the optical system 32 to view the patterned surface 62 of the wafer 25. For the purposes of the explanation, the patterned surface 62 is shown exaggeratedly in the Figures.

Gripper 42 can be translated by any translation system; an example of one such system is provided in Fig. 2 and labeled 64.

The vacuum pad 44 is typically a bellows-shaped pad and is mounted at the end of the gripper 42 and is connected to the vacuum system 46. The vacuum pad 44 creates a suction so that gripper 42 can raise the wafer 25 and move it from the wafer collecting position to the wafer measuring location. In addition, the vacuum is maintained during the measurement and only released once the measurement is complete.

Figs. 3-8 illustrate the operation of the gripping system 34. Initially, and as shown in Fig. 3, the jets, labeled 70, and the bubblers, labeled 72, of the water track are operated and the gate 40 is lowered. The polisher (not shown) places the wafer 25 within the water track and the streams 18 from the jets 70 push the wafer 25 towards the gate 40. The gripper 42 is at the wafer collecting position, shown to the left in Figs. 3-8.

Once the wafer 25 is in the wafer collecting position, as shown in Fig. 4, gripper 42 lowers vacuum pad 44 to grab the wafer 25. It will be appreciated that gripper 42 can be formed of any suitable mechanism, such as a piston, which can move vacuum pad 44 up and down on command. Since bubblers 72 are operating, the small streams 22 maintain the wafer 25 away from the base 14 of the water track.

The gripper 42 then pulls the wafer 25 out of the water (Fig. 5) and the jets 70 are deactivated. In accordance with a preferred embodiment of the present invention, the axis 74 of symmetry of the vacuum pad 44 is formed at a small angle α from the vertical axis 76. As a result, a long axis 75 of the wafer 25 is at the same small angle α to the horizontal axis 78. Angle α is typically in the range of 2-5(.

Translation unit 64 then moves gripper 42 to the wafer measuring position, shown to the right in Figs. 4-8. At the same time and as shown in Fig. 6, a pull-down mechanism slightly lowers the entire water track, gripping and optical system unit (at an angle of 1-3(), about a hinge 80 (Figs. 2-8), to force the water toward the wafer measuring position. Other methods of forcing the water towards the measuring position are also incorporated in the present invention.

After the lowering of the water track, gripper 42 lowers the wafer 25 towards the window 60. Since the vacuum pad 44 is angled, the wafer 25 does not enter the water all at once. Instead, wafer 25 enters the water gradually. Initially, only the side labeled 82 is immersed. As the gripper 42 pushes the vacuum pad 44 further down, more and more of the wafer 25 becomes immersed until the entire wafer 25 is within the water. Vacuum pad 44 is flexible enough to accommodate the changed angle of wafer 25.

It will be appreciated that, by gradually immersing the wafer in the water, few, if any, bubbles are created near the patterned surface of the wafer 25.

It is noted that the wafer 25 does not rest against the window 60. Instead, it is held against protruding surfaces 84 such that there is a layer of water 86 between the wafer 25 and window 60. Due to the gradual immersion of wafer 25, layer 86 of water has little, if any, bubbles in it and therefore provides a uniform connecting medium between the optical system 32 and the patterned surface 62 of wafer 25.

Once the optical system 32 has finished measuring the patterned surface 62 of wafer 25, gripper 42 returns vacuum pad 44, with wafer 25 still attached, to its upper position. The pull-down mechanism rotates the water track about hinge 80 to return to its original position, gate 40 is raised, and jets 70 and bubblers 72 are activated. The vacuum system 46 releases the vacuum and the wafer 25 falls into the water track. The flow of water causes the wafer 25 to move toward and under the now raised gate 40. A sensor 90 determines when the wafer 25 successfully passes out of the water track. The process described hereinabove can now begin for the next wafer.

Reference is now made to Fig. 9 which schematically illustrates an example of a suitable optical system 32. Optical system 32 is a microscope-based spectrophotometer and comprises an objective lens 100, a focusing lens 102, a beam splitter 104, a pin hole mirror 106, a relay lens 108 and a spectrophotometer 110. It additionally comprises a light source 112, a condenser 114, a charge coupled device (CCD) camera 116 and a second relay lens 118.

Light from light source 112 is provided, along an optical fiber 113, to condenser 114. In turn, condenser 114 directs the light towards beam splitter 104. Beam splitter 104 directs the light towards the wafer surface via lenses 102 and 100 and via window 60 and water layer 86.

The reflected light from the patterned surface 62 is collected by objective 100 and focused, by lens 102, onto pin hole mirror 106. Relay lens 108 receives the light passed through pin hole mirror 106 and focuses it onto the spectrophotometer 110.

Pin hole mirror 106 passes light through its hole towards spectrophotometer 110 and directs the light hitting the mirror surface towards CCD camera 116. Second relay lens 118 receives the light reflected by pin hole mirror 106 and focuses it onto the CCD camera 116.

Since the pinhole is placed at the center of the image plane which is the focal plane of lens 102, it acts as an aperture stop, allowing only the collimated portion of the light beam to pass through. Thus, the pinhole drastically reduces any scattered light in the system. Relay lens 108 collects the light from the pinhole and provides it to spectrophotometer 110.

Furthermore, since the pinhole is located at the image plane of the optical imaging system (lenses 100 and 102), only that portion of the light, reflected from the surface of wafer 25, which is the size of the pinhole divided by the magnification will come through the pinhole. Relay lens 118 collects the light and focuses it onto the CCD camera 116.

The pinhole serves to locate the measurement spot in the image of the wafer 25. Since the pinhole allows light to pass through it, rather than being reflected toward the CCD camera 116, the pinhole appears as a sharp dark point in the image produced by the lens 118. Thus, when viewing the CCD image, the location of the measurement spot is immediately known, it being the location of the dark spot.

Reference is now made to Figs. 10-13 which illustrate the thickness measuring of the present invention implemented in a polishing machine similar to that produced by Strasbaugh which has no water track. In this embodiment, the polishing machine or an external robot (not shown) brings the wafers 25 to an exit station of the polisher. When the measurement has finished, the robot brings the wafers 25 to their cassette at another exit station. Fig. 10 is a top view and Figs. 11, 12 and 13 illustrate the measuring station in three states.

The measuring station 130 comprises a gripping unit 132, an optical system 134 and a water bath 136. The optical system 134 is located beneath the water bath 136 and can be any suitable optical system, such as the one described hereinabove. As in the previous embodiment, the water bath 136 has a window in its bottom surface, labeled 140 in Fig. 11, through which the optical system 134 can illuminate the wafer 25.

The gripping unit 132 comprises a wafer support 150, illustrated as being formed of two support elements, a vacuum pad 152, similar to vacuum pad 44, and a piston 160. The polisher places the wafer 25 on the wafer support 150 while the vacuum pad 152 is initially in a position above the support 150, as shown in Fig. 11. Once the wafer support 150 has the wafer in a predefined position, the vacuum pad 152, which is controlled by piston 160, moves toward the wafer and grabs it by applying a vacuum. Now that the vacuum pad 152 is holding the wafer, the wafer supports 150 move away, as indicated.

The piston 160 then pushes the vacuum pad-wafer combination toward the water bath 136. This is shown in Fig. 12 which also illustrates that the vacuum pad 152 holds the wafer 25 at a small angle α to the horizontal. The angle α is provided since, as in the previous embodiment, the axis of symmetry of the vacuum pad 152 is formed at a small angle α from the vertical axis. As in the previous embodiment, by immersing the wafer 25 into the water at the angle α, few, if any, bubbles, remain on the undersurface of the wafer after full immersion.

Fig. 13 illustrates the wafer 25 at its fully immersed, measurement position. Typically, wafer 25 does not directly touch the water surface 163 of the window 140; instead, it sits on a measurement support 168. The result is that there is a water layer 164 between the wafer 25 and the surface 163 of the window.

Once the measurement process has finished, the piston 160 returns the wafer 25 to its original position and the wafer support elements 150 return to their wafer receiving position. The piston 160 places the wafer 25 on the wafer support elements 150 and releases the vacuum. The external robot can now take the wafer to another exit station where there is a cassette of processed and measured wafers.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the claims which follow:

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7190452 *Feb 14, 2005Mar 13, 2007Perceptronix Medical, Inc.Imaging systems for fluorescence and reflectance imaging and spectroscopy and for contemporaneous measurements of electromagnetic radiation with multiple measuring devices
Classifications
U.S. Classification451/6, 356/73
International ClassificationB24B49/12, B24B37/04, H01L21/683, H01L21/00
Cooperative ClassificationH01L21/67253, H01L21/6838, B24B49/12, B24B37/345
European ClassificationB24B37/34F, H01L21/67S8B, H01L21/683V, B24B49/12
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