JP2007165655A - Direction sensor of wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensing device of the edge of an almost disk-shaped work piece. <P>SOLUTION: A device which determines the edge of an almost disk-shaped work piece such as a semiconductor wafer includes a light source which is arranged so that the optical beam may be turned to the surface of the work piece near the edge of the work piece, in order that a first portion of an optical beam may pass the work piece and a second portion of the optical beam may be intercepted by the work piece. An angle formed by the optical beam and normal line to the surface is equal to the degree of critical angle made by the total inner reflection of the optical beam within the work piece, or larger than the critical angle. Furthermore, the device has a mechanism whereby the work piece is rotated, and is arranged so that the first portion of the optical beam may be detected. The device contains an optical sensor which generates an edge signal showing the edge of the work piece when the work piece is rotated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direction sensor for a disk-shaped workpiece such as a semiconductor wafer, and more particularly to a wafer direction sensor capable of detecting the direction of various types of wafers, including quartz wafers.

  Ion implantation has become a standard technique for introducing conductivity modifying impurities into semiconductor wafers. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam having a predetermined energy, and the ion beam is directed to the surface of the wafer. Ions with the energy of the beam penetrate into the bulk of the semiconductor material and are embedded in the crystal lattice of the semiconductor material to form the desired conductive region.

  An ion implantation system typically includes an ion source for converting a gas or stationary material into a well-defined beam. The ion beam is analyzed to remove unwanted ion species, accelerated to the desired energy, and directed to the target surface. The beam is distributed over the target area by beam scanning, by target movement, or by a combination of beam scanning and target movement. In one previous approach, the semiconductor wafer is placed near the periphery of the disk. The disk rotates about its central axis and is moved with respect to the ion beam to distribute the ion beam across the semiconductor wafer. An ion implanter typically includes an end station having an automated wafer handling device for introducing wear into the ion implanter and removing the wafer after implantation.

  Wafer handling systems typically move the wear from the cassette holder to a processing station such as a wafer mounting site on disk. One condition is that the wafer or flat or notch is oriented as desired and the wafer is accurately placed at the processing station. The slot of the cassette holder is slightly larger than the wafer, so accurate wafer placement is not possible. Furthermore, the flat or notch direction of the wafer cannot be controlled within the cassette holder. However, accurate placement at the processing station is necessary to ensure reliable wear retention and avoid wafer damage. Also, ion implantation systems typically require a special wafer flat or notch direction, which indicates the crystal orientation of the wafer to control channeling by the implanted ions.

A wafer transfer system that incorporates a wafer orienter is disclosed in US Pat. No. 6,037,009 issued on June 6, 1989, by Hertel et al. The wafer is placed on the directional chuck and rotated. A direction sensor includes a light source positioned below the edge of the wafer and a solar cell positioned above the edge of the wafer aligned with the light source. The light beam from the light source is directed perpendicular to the wafer surface. The wafer prevents a part of the light source from reaching the solar cell. The signal output from the solar cell represents an index such as wafer eccentricity and flat or notch. Based on the signal from the direction sensor, the eccentricity and rotation direction can be corrected. Wafer aligners are also described by Niewmierzycki, US patent specification issued on September 26, 1995 (Patent Document 2), and Volovich issued on August 24, 1993 (Patent Document). 3) and US patent specification (Patent Document 4) issued on Aug. 24, 1982 by Phillips.
U.S. Pat.No. 4,836,733 U.S. Pat.No. 5,452,521 U.S. Pat.No. 5,238,354 U.S. Pat.No. 4,345,836

  Prior art wafer orientation sensors generally provide satisfactory results for conventional silicon wafers. However, in some cases, ion implanters are also required to work with wafers of a variety of materials, including but not limited to quartz, sapphire, and glass with notches or flats as indicators. ing. For example, quartz wafers are used to test non-uniformities and impurity levels in ion implanters. Conventional optical direction sensors cannot detect the edge of a quartz wafer. The reason is that the light beam from the light source is not blocked due to the transparent quartz wafer, and the wafer is almost invisible to the sensor.

  Thus, there is a need for an improved wafer orientation sensor that can detect the edges of wafers of various materials, including transparent materials.

  In accordance with a first aspect of the present invention, an apparatus for detecting the edge of a generally disc-shaped workpiece is provided. The apparatus is arranged to direct the light beam near the edge of the surface of the workpiece so that the first part of the light beam passes through the workpiece and the second part of the light beam is blocked by the workpiece. Includes light source. The angle between the light beam and the normal to the surface is equal to or greater than the critical angle for total internal reflection within the workpiece. The apparatus further includes a mechanism arranged to detect a first part of the light beam, a mechanism for rotating the workpiece, and to generate an edge signal indicating the edge of the workpiece when the workpiece is rotating. Includes sensors. The apparatus can be used to detect the orientation and position of semiconductor wafers of various materials, including those that are transparent to the light beam.

  The workpiece may be a semiconductor wafer of a material selected from the group including, but not limited to, quartz, silicon, sapphire, and glass. The light source and the optical sensor are arranged to detect an index such as a notch or a flat on the wafer. The angle between the light beam and the normal to the surface can be equal to or greater than 65 degrees to accommodate the wear and manufacturing range of various materials.

  The light sensor may comprise a linear sensor. The length direction of the linear sensor is preferably oriented radially with respect to the center of rotation. The light source may also include an optical system for directing the collimated light beam toward the surface of the workpiece. The optical system can generate a rectangular beam directed to the surface of the workpiece, the length of the rectangular beam being in the radial direction with respect to the center of rotation.

  In accordance with another embodiment of the present invention, a method for detecting the edge of a generally disk-shaped workpiece is provided. The method includes directing the light beam near the surface of the workpiece such that the first portion of the light beam passes through the workpiece and the second portion of the light beam is shielded by the workpiece. The angle between the light beam and its normal to the surface is equal to or greater than the critical angle that forms total internal reflection of the light beam in the workpiece. The method further includes rotating the workpiece, detecting a first portion of the light beam, and generating an edge signal that indicates the edge of the workpiece as the workpiece rotates.

  An example of a wafer transfer apparatus suitable for incorporating the present invention is shown in FIG. The wafer transfer device may be an end station for the ion implanter and can be used to transfer the wafer to the processing station for any type of processing or treatment system. That is, the device operates as follows. Cassette holders 10 (each holding a plurality of wafers 12) are placed on cassette locks 14, 16, and 18. The cassette locks 14, 16, 18 are evacuated and the cassette holder 10 is lowered into the evacuated elevator chamber. Wafers are removed from the cassette holder 10 one at a time by the connected wafer transfer arm 22 and moved to the wafer direction station 26 in the transfer vacuum chamber 24. The position and direction of the wafer are detected at station 26 by wafer direction sensor 34. The angular orientation of the wafer can be changed as needed at station 26. The arm 22 extends along the X axis and the wafer is transferred to the processing station 28 of the processing system. When placing the wafer at station 28, the position error detected at station 26 can be eliminated by compensating for the displacement. At station 28, lift pins 30 are provided to transfer the wafer from transfer arm 22.

  After processing, the transfer arm 22 returns the wafer to the cassette holder 10 without using the direction station 26. When the wafer is transferred from one of the outer cassette locks 14 and 18, the transfer arm 22 is moved by the drive assembly 40 to each cassette lock along the Y axis. The wafer is removed from the cassette, the transfer arm returns to the center position, and the arm extends to station 28. In the embodiment of FIG. 1, the processing station 28 is located on the disk 47 for placing a plurality of wafers in a batch type ion implanter. Wafers are placed one by one near the periphery of the disk by a wafer transfer device. During wafer loading and unloading, the disk begins to rotate and each wafer placement site on the disk is presented to the wafer transfer device.

  2 and 3, a schematic side view and a plan view of the direction station 26 and the direction sensor 34 are shown, respectively. At the direction station 26, the wafer 12 is placed on a support pedestal 50 connected to a motor 54 by a shaft 52. When the motor 54 is activated, the pedestal 50 and the wafer 12 rotate about the axis 56. As shown in FIG. 3, the axis of rotation 56 is offset from the center 58 of the wafer 12 when the wafer 12 is preferably not centered on the support pedestal 50. The pedestal 50 extends upward through the opening 60 (FIG. 1) of the transfer arm 22 for orientation and retracts through the opening 60 when orientation is complete.

  Wafer direction sensor 34 includes a light source 100 and an optical sensor 102. The light source 100 generates a light beam 110 that is collimated within 5 °. The light beam 110 is directed to the edge of the wafer 12 at an angle θ relative to the normal 114 to the surface of the wafer 12. As will be described below, the angle θ is equal to or greater than the critical angle at which the total internal reflection of the light beam occurs at the wafer 12. However, a part of the light beam 110 blocked by the wafer 12 is blocked although the wafer is transparent in the wavelength range of the light beam 110.

  In the example of FIGS. 2 and 3, the light source 100 is positioned below the wafer 12 and radially outward, and the light beam 110 is directed to the lower surface of the wafer 12 at an angle θ. Furthermore, the light source 100 is arranged such that the first part of the light beam passes over the edge of the wafer 12 and the second part of the light beam is blocked by the wafer 12. Since the position of the edge 112 changes due to the index on the wafer and due to the deviation of the wafer center 58 with respect to the rotation axis 56, the light beam 110 goes beyond the range of the assumed position of the edge 112 to the edge. Should be wide enough so that 112 is partially blocked. The direction sensor cannot determine the position of the edge of the wafer when the light beam 110 is totally blocked by the wafer 12, as an extreme example, or, as another extreme example, is not incident on the wafer 12. .

  The optical sensor 102 is disposed above the wafer 12 so as to be aligned with the light beam 110. The light beam 110 passing through the wafer 12 enters the sensor 102, but the second portion of the light beam 110 blocked by the wafer 12 does not enter the sensor 102. As shown in FIG. 3, the sensor 102 has a rectangular detection area, and the longitudinal dimension of the rectangular detection area is directed in the radial direction with respect to the rotation axis 56. The optical sensor 102 generates an increasing edge signal when the detection area portion that receives the light beam 110 increases. As shown in FIG. 3, the first portion 110 a of the light beam 110 is incident on the sensor 102 and the second portion 110 b of the light beam 110 is blocked by the wafer 12. The position of the edge 112 relative to the light beam 110 and the sensor 102 changes during rotation of the wafer 12 about the axis of rotation 56 as a result of an index such as the notch 120 and wafer eccentricity. As a result, the portion of the light beam 112 blocked by the wafer 12 changes. That is, the relative proportion of the first portion 110a and the second portion 110b changes, and an edge signal change (indicating the position and direction of the wafer) occurs. In FIG. 2, the light source 100 and the sensor 102 are variously arranged within the scope of the present invention. For example, the light source 100 may be disposed above the wafer 12 and radially outward, and the sensor 102 may be disposed below the wafer 12. In such a case, the light beam 110 is directed at the surface of the wafer 12 at an angle θ relative to the normal 114 that is equal to or greater than the critical angle. Further, the light beam 110 is positioned such that the first portion of the light beam passes through the workpiece and is blocked by the sensor, and the second portion of the light beam is blocked by the wafer.

As described above, the light beam 110 is directed to the wafer 12 at an angle θ relative to the normal 114 of the surface of the wafer 12 that is equal to or greater than the critical angle that causes total internal reflection of the light beam within the wafer. . As is known in the art, the critical angle is defined as:
I _c = arc sin (N ₁ / N ₂ ) (1)
I _c is the critical angle relative to the surface normal, N ₁ is the refractive index of the material with the lower refractive index, and N ₂ is the refractive index of the material with the higher refractive index. The critical angle to the air-glass surface has a value of about 42 degrees when the refractive index of the glass is 1.5. In the preferred embodiment, the angle θ is equal to or greater than about 65 degrees for quartz, silicon, sapphire, and glass wafers so that total reflection occurs. It will be appreciated that various angles can be used depending on the material of the wafer. The angle θ is selected to be equal to or greater than the critical angle defined by equation (1) above. Thus, the wear 12 is transparent or partially transparent in the wavelength range of the light beam 110, but a part of the light beam 110 incident on the wafer 12 is reliably blocked.

  The critical angle is the angle at which the transmitted light contacts the boundary between the higher refractive index medium and the lower refractive index medium (light enters the boundary from the higher refractive index side). At the critical angle or higher, no transmitted light passes from the higher refractive index medium. This is opaque because there is no light on the opposite side of the wafer from the sensor.

  All semiconductor wafers and substrates have a higher concentration (higher refractive index) than the air or vacuum that the wafer faces. The refractive index of substrates and wafers, including quartz and sapphire, is typically higher than 1.5. In order to ensure total internal reflection, light travels to the wafer at approximately 65 degrees with respect to the normal 114. This light passes through the wafer at about 48 degrees with respect to the normal 114. When the light reaches the other side of the wafer, it becomes parallel to the wafer surface or returns into the wafer so that the light does not pass through the wafer.

  An example of introduction of the wafer direction sensor 34 is shown in FIGS. The light source 100 includes a light emission diode (LED) 140, a polarizer 142, a lens 144 and a mirror 146. The lens 144 may be a plano-convex cylindrical lens, and the mirror 146 may be a 60 degree offset parabolic mirror with a gold or silver reflecting surface 148. The LED 140 may be a single high intensity light emission diode with a wavelength of 880 nanometers and a 30 degree light pattern, which can be driven from a controlled current source (FIG. 5). The optical system is anamorphic, which recreates the light into a beam with a rectangular cross section and makes it parallel. The collimated light beam is directed to the wafer 12 at an angle θ with respect to the normal 114 of 65 degrees. The output of the LED 140 passes through the polarizer 142 and then the cylindrical lens 144. As a result, the polarized light becomes a fan-shaped beam. The fan-shaped beam is then reflected by a parabolic mirror 146 and parallelized to a beam having a rectangular cross section. The optical system collimates light with high optical efficiency.

  For example, the LED 140 may be a metal-based TO-18 package. The LED mount may be a machined aluminum block that holds the LED in place and functions as a heat sink. A mounting base (not shown) is attached to the printed circuit board 150. The lens may be 5mm x 10mm with a focal length of 8mm. The lens 144 is focused on the LED 140. A strip of polarizer 142 is located on the flat portion of lens 144. The line of polarization is perpendicular to the plane of the wafer. This reduces the effect of shallow reflection angles from the wafer surface. The mirror 146 is attached below the lens 144 and the LED 140. The mirror 146 is focused on the LED 140.

  The optical sensor 102 may be a dual photodiode having a detection area of 1 mm × 37 mm. The sensor is hermetically sealed and has a built-in infrared filter. The filter may be a controlled layer of silicon monoxide that optically transmits infrared radiation. The filter allows infrared light from the LED 140 to pass through, but blocks visible light. Sensor 102 may be attached to printed circuit board 150. The output of sensor 102 is applied to sensing circuit 154 (FIG. 5), which may include amplification and processing circuitry known to those skilled in the art.

  A monitor photodiode 170 may be placed outside the measurement area and adjacent to the sensor 102. The photodiode 170 can also include a built-in infrared filter. The output of the photodiode 170 is used to detect the light intensity from the light source and adjust the current applied to the LED 140. As shown in FIG. 5, a monitor photodiode 170 and an intensity reference digital-to-analog converter 172 are coupled to the input of the intensity regulator circuit 174. Intensity regulator circuit 174 provides a controlled current to LED 140.

  A graph of edge signals from the wafer direction sensor as a function of time is shown in FIG. The edge signal changes with time as the wafer rotates about axis 56 (FIG. 2). Waveform 200 represents an edge signal from a notched quartz wafer with a finished edge. The coarse sine shape of the waveform 200 indicates the wafer eccentricity with respect to the rotational axis 56. By analyzing the amplitude of the waveform 200 as a function of the angle with respect to the rotation axis 56, the X and Y components of the offset with respect to the rotation axis 56 can be determined. The index notch 120 (FIG. 3) is clearly seen in the waveform as a spike 210, which indicates the angular orientation of the wafer 12. The waveform 200 can be correlated to the rotation of the wafer 12 about the axis of rotation 56 by using a shaft encoder attached to the output shaft of the motor 54.

  A graph of the edge signal of the wafer direction sensor as a function of time is shown in FIG. Waveform 300 shows the signal for a notched glass wafer with an unfinished edge. The noise superimposed on the approximately sinusoidal waveform 300 indicates a rough edge of the wafer, and the notch is indicated by a spike 310.

  As described above, the angular direction and eccentricity of the wafer are determined from the edge signal generated by the wafer direction sensor. The determined value is then used to correct the angular orientation and position of the wafer. In particular, the angular orientation can be corrected by rotating the wafer 12 about the axis of rotation 56 on the support pedestal 50 as it is transferred from the direction station 26 to the process station 28 (FIG. 1). Position errors can be eliminated by compensating for the displacement.

  The wafer orientation sensor of the present invention detects index and position errors of semiconductor wafers of various materials including, but not limited to, quartz, silicon, sapphire and glass. The direction sensor detects an index such as a notch or a flat of the semiconductor wafer. The edge signal will be the same for all wafer types. Thus, different types of wafers, such as quartz test wafers and product silicon wafers, can be mixed in the same process cycle.

  Thus, while preferred embodiments of the invention have been described and illustrated, those skilled in the art will recognize that various changes and modifications may be made without departing from the scope of the invention as defined by the claims. It is obvious that you can get none.

FIG. 1 is a schematic plan view of an embodiment of a wafer transfer apparatus incorporating a wafer direction sensor according to the present invention. FIG. 2 is a schematic side view of the wafer direction sensor. FIG. 3 is a schematic plan view of the wafer direction sensor of FIG. FIG. 4 is a schematic side view of an embodiment of the wafer direction sensor of the present invention. FIG. 5 is a schematic block diagram of a circuit used in the wafer direction sensor of FIG. FIG. 6 is a graph showing the edge signal as a function of time for a notched wafer including a finished edge. FIG. 7 is a graph showing the edge signal of a glass wafer with a notch including an unfinished edge as a function of time.

Explanation of symbols

12 wafers
26 stations
34 Wafer direction sensor
50 Support base
52 shaft
54 Motor
56 axis
100 light sources
102 Light sensor
112 edge
114 normal

Claims (20)

A device for determining the edge of a substantially disk-shaped workpiece having a surface,
Direct the light beam to the surface of the workpiece near the workpiece edge so that the first part of the light beam passes through the workpiece and the second part of the light beam is blocked by the workpiece. An arranged light source;
A mechanism for rotating the workpiece;
A light sensor arranged to detect a first portion of the light beam and generate an edge signal representative of the edge of the workpiece as the workpiece rotates;
Including
The angle between the light beam and the normal to the surface of the workpiece is equal to or greater than the critical angle within the workpiece at which the light beam is totally reflected,
The light beam has an elongated cross section and is directed to the surface of the workpiece such that the longitudinal dimension of the light beam of the elongated section is along the radial direction with respect to the center of rotation of the workpiece;
But the device. The apparatus of claim 1, wherein the angle is equal to or greater than 65 degrees. The workpiece consists of a semiconductor wafer,
The apparatus according to claim 3, wherein the light source, the rotation mechanism, and the optical sensor are arranged to detect an index on a semiconductor wafer. The apparatus of claim 3, wherein the semiconductor wafer is at least partially transparent to light, and the light source and the light sensor are arranged to detect an indicator on the semiconductor wafer. 4. The apparatus of claim 3, wherein the semiconductor wafer is selected from the group consisting of quartz, silicon, sapphire, and glass, and the light source and the optical sensor are arranged to detect an indicator on the semiconductor wafer. 4. The apparatus of claim 3, wherein the indicator comprises a notch at an edge of the semiconductor wafer, and the light source and the optical sensor are arranged to detect the notch. 4. The apparatus of claim 3, wherein the indicator comprises a flat at an edge of the semiconductor wafer, and the light source and the optical sensor are arranged to detect the flat. The apparatus of claim 1, wherein the optical sensor is an elongated linear sensor, and the longitudinal dimension of the linear sensor is oriented radially with respect to the center of rotation of the workpiece. The apparatus of claim 1, wherein the light source includes an optical system that directs a collimated light beam onto a surface of the workpiece. The apparatus of claim 1, wherein the light source comprises a light emission diode, a polarizer, a lens, and a parabolic mirror for collimating the light output of the light emission diode. The light source includes an optical system that generates an elongated rectangular light beam having a longitudinal dimension, and is elongated such that the longitudinal dimension of the elongated rectangular light beam is along the radial direction with respect to the center of rotation of the workpiece. The apparatus of claim 1, wherein the rectangular light beam is directed to a surface of the workpiece. And a second optical sensor for monitoring the intensity of the light beam and generating a feedback signal representative of the intensity,
The apparatus of claim 1, wherein the light source includes an intensity adjustment circuit to control the intensity of the light beam in response to a feedback signal. The apparatus of claim 1, wherein the angle between the light beam and the normal to the surface of the workpiece is selected to produce total internal reflection at a workpiece having a refractive index of 1.5 or greater. A method for determining the edge of a generally disc-shaped workpiece having a surface, comprising:
Directing the light beam toward the surface of the workpiece near the edge of the workpiece such that the first portion of the light beam passes through the workpiece and the second portion of the light beam is blocked by the workpiece; ,
Rotating the workpiece;
Detecting a first portion of the light beam and generating an edge signal representing the edge of the workpiece as the workpiece rotates;
Including
The angle between the light beam and the normal to the surface of the workpiece is equal to or greater than the critical angle within the workpiece at which the light beam is totally reflected,
The step of directing the light beam includes generating a light beam having an elongated cross section, and directing the light beam to the surface of the workpiece such that a longitudinal dimension of the light beam of the elongated section is along a radial direction with respect to the center of rotation of the workpiece. Including pointing to
The way. The method of claim 14, wherein the angle is equal to or greater than 65 degrees. The method of claim 14, wherein detecting the first portion of the light beam includes detecting an indicator on the semiconductor wafer. 15. The method of claim 14, wherein detecting the first portion of the light beam includes detecting the light beam with an optical sensor having a longitudinal dimension oriented radially with respect to the center of rotation of the workpiece. the method of. The method of claim 14, wherein directing the light beam comprises directing a collimated light beam to a surface of the workpiece. The step of directing the light beam includes generating an elongate rectangular light beam, and causing the elongate rectangular light beam to work along a radial direction with respect to the rotational center of the workpiece. 15. A method according to claim 14, comprising directing to the surface of the piece. 15. The method of claim 14, further comprising monitoring the intensity of the light beam, generating a feedback signal representative of the intensity, and controlling the intensity of the light beam in response to the feedback signal.

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