JP2003515914A - Detection of wafer fragments in wafer processing equipment - Google Patents

Abstract

(57) Summary During the rapid thermal process, fragments are broken from the wafer and fall on the temperature sensors in the processing chamber. Wafer fragments may compromise the accuracy of the temperature signal generated by the sensor probe. In particular, the fragments may attenuate or otherwise interfere with the radiation received from the wafer. This interference can gradually compromise the accuracy of the temperature measurement signal generated by the probe. If the temperature control function is compromised, excessive temperature gradients will damage the wafer, reducing device yield and degrading device quality. To mitigate the effects of wafer fragments, the presence of wafer fragments is detected. The image acquisition device acquires an image of the wafer. The processor analyzes the acquired images to determine if a wafer fragment is present. A processor analyzes the acquired image for changes in optical density contrast indicative of the presence of a wafer fragment. Detection of wafer fragments aborts the rapid thermal process so that fragments are wiped out before the next wafer is inserted into the deposition chamber.

Description

Detailed Description of the Invention

FIELD OF THE INVENTION The present invention relates generally to wafer processing, and more specifically to systems and methods for quality control in wafer processing.

(Prior Art) When manufacturing a semiconductor device, various techniques can be used for processing a wafer. Rapid thermal processing (RTP), for example, is widely used in semiconductor fabrication, where rapid temperature ramp cycles are required or desirable. Examples of general RTP include annealing, oxidation, nitriding and the like. RTP chambers typically include a pedestal for a wafer to be processed, one or more heat sources such as a lamp that produces radiant heat to heat the wafer, and a reflector that forms a reflective cavity for effective heating. Is provided.

Regarding the quality of RTP, temperature uniformity is an important factor. The wafer may have different energy absorption or emission characteristics depending on the location. In addition, the spatial heating profile of the heat source may also be somewhat non-uniform. As a result, RTP can create a significant temperature gradient across the surface of the wafer.
Excessive temperature gradients can also result in structural damage to the wafer, which can directly affect device yield and quality. When using flood lamp heat sources, it is often difficult to control the temperature across the substrate. However, zoned heat sources can be used to spatially control temperature and effectively minimize temperature gradients across the wafer.

With respect to spatial control of temperature across the wafer, especially for zoned heat sources, the RTP chamber is typically equipped with a temperature sensing device. The temperature sensing device may include, for example, an array of temperature sensor probes such as a pyrometer. Temperature sensing devices sense the temperature of the wafer, often at several points during the heating cycle. The temperature signal generated by the temperature sensing device is processed to generate a control signal for the heat source. Therefore, the accuracy of the temperature signal produced by the temperature sensing device is important for effective control of the heat source, and thus it is an important factor for device fabrication quality and yield. Poor temperature measurement accuracy can impede the effectiveness of temperature control functions, such as opening the door for temperature gradients that could damage the wafer being processed.

SUMMARY OF THE INVENTION The present invention is directed to systems and methods for detecting wafer fragments in a wafer processing apparatus. The system and method are useful for maintaining the accuracy of temperature control functions in the wafer deposition process. In particular, the system and method facilitates easy detection of wafer fragments in the deposition processing chamber. Such wafer fragments can adversely affect the accuracy of temperature measurements within the chamber.

The present system and method is particularly useful for RTP, especially when the temperature requirements of the process are stringent.
Useful for controlling the quality of. However, the system and method are not limited to RTP as they are effective in any of the various wafer processes where the presence of fragments is a concern. However, for ease of explanation, in the representative embodiment of the present invention, the characteristics of RTP will be taken up and described. During the RTP, fragments can break from the wafer and fall onto the temperature sensing device or onto a surface such as a reflector between the device and the wafer. Wafer fragments can reduce the accuracy of the temperature signal generated by the temperature sensing device. For example, when using a pyrometer probe, a wafer fragment may fall on the reflector at about the same location as the probe. Wafer fragments can attenuate or interfere with infrared radiation received from the wafer.

This interference reduces the accuracy of the temperature measurement signal generated by the probe and ultimately reduces the ability to control the temperature across the surface of the wafer. Failure of the temperature control function can result in wafer damage due to excessive temperature gradients, resulting in poor device yield and poor device quality. Also, the effect of a wafer fragment will continue to the next wafer processed in the RTP chamber unless the fragment is removed from the reflector, for example.

According to one embodiment of the present invention, the potential for wafer fragments to be present on a temperature sensing device, such as an array of probes, is detected in order to mitigate the effects of the wafer fragments.
The presence of wafer fragments can be detected using, for example, machine vision techniques. An image acquisition device acquires an image of at least a portion of the wafer being processed in the RTP chamber. The image can also be acquired as the wafer is removed from the RTP chamber and transferred to the observation chamber. The observation chamber may form part of a process station that follows, such as a cooling chamber. The acquired image is analyzed to see if any part of the wafer is missing. If missing, wafer fragments are RTP
It may be in the chamber.

In one example, the analysis of the wafer can be done with the optical contrast between the wafer surface and the missing parts of the wafer. In particular, the wafer may be set against an illuminated background that creates backside illumination on the wafer during imaging. The optical contrast between the wafer surface and the illuminated background indicates the lack of a portion of the wafer, so that the wafer fragment is on the temperature measuring device or somewhere between the wafer mount and the temperature measuring device. There is a possibility that it exists in terms of.

Optical density contrast can be detected by analyzing the optical density of pixels in the wafer image and comparing the density to a target density range. Once the number of pixels in the vicinity that exhibits the required density range is detected, the size of the area defined by the pixels can be analyzed. For example, the size of the pixel area can be compared to another threshold that corresponds to the size of the fragments that could interfere with the temperature measurement function.

When a wafer fragment is detected, the RTP can be turned off and the fragment removed from the RTP chamber. For example, when a wafer fragment is detected, a warning can be issued.
The alert may serve as a basis for the automatic removal of fragments or as a warning for manual intervention by a human operator. The removal of fragments can eliminate the source of error in temperature measurements made by the temperature sensing device before the next wafer is processed. In this way, the accuracy of the temperature measurement can be maintained, thereby avoiding processing problems associated with the next wafer in the process. As a result, it is possible to reduce the possibility of excessive temperature gradients that can lead to poor device yield and quality.

In one embodiment, the present invention provides a system for analysis of a wafer for wafer fragment defects, the system comprising an observation chamber, a wafer support member disposed within the chamber, and an observation chamber. A background surface located in the chamber adjacent to the wafer support member, an illumination source that directs illuminating radiation to a wafer located on the wafer support member, and from the side of the wafer support member opposite the background surface. An image acquisition device directed to acquire an image representing at least a portion of the wafer.

In another embodiment, the invention provides a system for detecting the presence of wafer fragments in a deposition processing chamber, the system comprising: An illumination source that provides a pattern of illuminating radiation to the substrate and an image acquisition device that is oriented to acquire an image representing at least a portion of the surface of the wafer, the illumination source providing backside illumination to the edge of the wafer. In addition, a processor is provided that analyzes the collected images to detect wafer defects and issues a warning if a wafer defect is detected.

In yet another embodiment, the present invention provides a method for detecting the presence of wafer fragments in a deposition process chamber, the method comprising: an edge of a wafer being processed in the chamber. Illuminating an area adjacent to the substrate with a pattern of radiation and acquiring an image representing at least a portion of the wafer set against a background surface, the pattern of radiation being the edges of the wafer. Is back-illuminated, and further includes analyzing the acquired images to detect a wafer defect and issuing a warning if a wafer defect is detected.

In yet another embodiment, the present invention provides a system for analysis of a wafer for defects of wafer fragments, the system comprising an observation chamber and a wafer support member disposed within the chamber. An illumination source disposed adjacent to the first side of the wafer, an illumination source that provides illumination radiation around an edge portion of the wafer, and an illumination source that provides an image representing at least a portion of the wafer disposed on the wafer support member. And an image acquisition device oriented for acquisition from the opposite side of the wafer support member.

In yet another embodiment, the present invention provides a system for analysis of a wafer for wafer fragment defects, the system including an observation chamber and a wafer support member disposed within the chamber. An image of at least a portion of the wafer disposed on the wafer support member and a background surface disposed adjacent to the wafer support member in the observation chamber, the side of the wafer support member opposite the background surface. An image acquisition device that is oriented for acquisition from an illumination chamber, an illumination source that projects illumination radiation within the observation chamber, and an illumination shield disposed within the observation chamber, the illumination shield comprising an inner region and an outer region. Defining an area, the illumination shield limiting the illumination radiation to a substantially outer area and limiting the field of view of the image acquisition device to a substantially inner area. The outer region is oriented so that the illuminating radiation illuminates a portion of the background surface adjacent the edge of the wafer, thereby providing backside illumination of the edge of the wafer.

In each of the above embodiments, the change in the contrast of the optical density is identified, and whether or not a part of the wafer is defective is determined based on the identification of the change in the contrast of the optical density. The image can be analyzed. Especially for analysis
Identifying a contrast region having an optical density that contrasts with a target range of optical densities, inferring the size of the contrast region, comparing the inferred size to a threshold,
Displaying the detection of a partial defect in the wafer is included if the estimated size exceeds a threshold.

If the image was taken with the wafer set against the background surface,
The target range of optical density will correspond to the range associated with the background surface. In addition, the background surface can be illuminated. In some embodiments, the background surface may be illuminated adjacent the edge portion of the wafer, thereby providing backside illumination for the wafer. The illumination shield serves to substantially prevent the incidence of illumination radiation on the top surface of the wafer, thereby maintaining good optical contrast for any analysis. In yet another embodiment, the illumination source can be located on the side of the wafer adjacent the background surface.

The edge portion of the wafer is most likely to cause wafer fragments. Therefore, if necessary, the analysis can be limited to the edge portion. In that case, the missing portion of the wafer edge will exhibit a sharp optical contrast with the wafer due to the presence of the illuminated background surface visible through the damaged area. at the same time,
Image processing overhead can also be minimized.

In addition to optical density contrast analysis, the size of the contrast region can also be estimated to estimate the size of the possible wafer fragments. The estimated size can be compared to a threshold size that represents the size of a wafer fragment that can affect temperature measurement and control functions. As an example, the size of the contrast region can also be approximated by the number of image pixels that present the required contrast. The pixel count can then be compared to the threshold pixel count. A warning can be raised if the size exceeds the threshold. In response to the warning, the operation of the RTP chamber can be stopped automatically or by human intervention.

Other advantages, features, and embodiments of the invention will be apparent with reference to the following detailed description and claims.

DETAILED DESCRIPTION Like reference symbols in the various drawings indicate like elements. FIG. 1 is a side view of a rapid thermal processing chamber 10. As shown in FIG. 1, the chamber 10 includes a bottom wall 12, opposing side walls 14, 16, a top wall 18 and front and rear walls (not shown in FIG. 1). The walls 12, 14, 16 and 18 surround the heat source 20, the wafer support 22 and the reflector 24. FIG. 1 also shows a wafer support 22.
The wafer 26 mounted on the wafer is shown. Although only one wafer 26 is shown as an example, the rapid thermal processing chamber 10 can be designed to process more than one wafer. Chamber 10 may include other conventional equipment commonly used in rapid thermal processing applications. As such equipment, for example, the chamber 1
There are various fixtures for supporting the pump equipment for exhausting 0, the pipeline for processing / gas supply to the chamber, the heat source 20 and the reflection plate 24.

The heat source 20 may be in the form of a floodlighted lamp source, or in the form of a row 28 of lamp sources, as shown in FIG. The lamp sources 28 can be arranged in a two-dimensional array and individually controlled to provide zoned heating of the surface of the wafer 26. An example of a rapid thermal processing system incorporating a spatially zoned lamp source is disclosed in US Pat. No. 5,155,336 to Gronet et al., Which is incorporated herein by reference. Each lamp source 28 may be fixed in a reflective zone to concentrate heat onto the wafer 26. The heat generated by the heat source 20 is absorbed by the wafer 26 during processing. The reflection plate 24 forms a reflection cavity so as to reflect heat onto the wafer 26 and perform more effective heating.

To facilitate control of heat source 20, chamber 10 further includes a temperature sensing device. For example, chamber 10 may include one or more temperature sensor probes 30 that sense temperature at different locations across wafer 26. Two sensor probes 30 are shown in FIG. 1 for ease of explanation. The sensor probe 30 may take the form of a pyrometer that converts the infrared radiation emitted by the wafer 26 into a temperature signal. An example of such a temperature measurement system is Peuse
U.S. Pat. No. 5,660,472, which is hereby incorporated by reference. Alternatively, chamber 10 may incorporate an infrared camera, lone thermocouple, thin film thermocouple, or other temperature sensing device suitable for measuring temperature across the surface of wafer 26. The use of the pyrometer-based sensor probe 30 is described below.

The temperature signal generated by the sensor probe 30 is fed back to a controller (not shown), which adjusts the intensity of the individual lamp sources 28 to provide the desired spatial heating distribution, and thereby the wafer. Minimize the thermal gradient across the surface of 26. Each sensor / probe 30 may be mounted adjacent to the lower surface 31 of the reflector 24 or may be integral with the reflector, as shown in FIG. In any case, the sensor / probe 30 detects infrared rays emitted from the wafer 26 mounted on the wafer supporting member 22. Each sensor probe 30 has a wafer 26
Are positioned to monitor the temperature within a particular area of the. The array of sensor probes 30 may be provided over the entire surface area of the wafer 26. However, in many applications, locating the sensor probe 30 within certain subsections of the reflector 24 or in an irregular pattern will provide sufficient information for the temperature control function, especially , Sufficient information can be obtained about the zoned lamp source that provides a given spatial heating distribution for a given application.

During the rapid thermal processing, fragments can flake off the wafer 26 and drop onto a region located between the wafer processing location and the temperature sensor probe 30, for example, the top surface of the reflector 24. Wafer fragments typically result from thermal gradients at the outer edge of wafer 26. Unfortunately, wafer fragments can reduce the accuracy of the temperature signal generated by the sensor probe 30, especially when it falls onto the reflector 24 at a location that is substantially coincident with the probe. In particular, the fragments include the sensor probe 30 and the wafer 2.
It may land at a position between 6 and and interfere with the temperature signal received by the probe.
This fragment-induced interference can attenuate or degrade the temperature measurement signal and adversely affect the temperature regulation function across the surface of the wafer 26. Excessive temperature gradients occur in the absence of effective temperature control. Such a gradient is
The wafer 26 is damaged, the device yield is reduced, and the device quality is deteriorated. Also,
The effect of the wafer fragment is that the chamber 10 will be affected unless it is scraped off the reflector 24.
It may extend to the next wafer processed in. In other words, wafer fragments flaking off a single wafer could damage the entire process with many subsequent wafers. According to embodiments of the present invention, a wafer fragment detection system is provided to reduce the potential effects of wafer fragments.

FIG. 2 is a functional block diagram of a system 32 for detecting wafer fragments in the rapid process chamber 10. As shown in FIG. 2, the system 32 includes a charge coupled device (CCD).
) An image capture device such as a camera 34, an illumination source 36, a processor 38 and a memory 40. System 32 may also include controller 42. The controller deactivates the rapid thermal processing chamber 10 in response to the alarm generated by the processor 38. The camera 34 controls the wafer 2 processed in the chamber 10.
It is designed to capture 6 images. The camera 34 is positioned to capture images while the wafer 26 is in the rapid thermal processing chamber 10. However,
In one embodiment, the camera 34 is adapted to capture an image of the wafer 26 after the wafer exits the chamber 10.

For example, a camera 34 may be mounted on the viewing chamber that receives the wafer 26 emerging from the chamber 10. The observation chamber may also be formed as a wafer cooling chamber. In this way, the observation chamber forms both an area for analysis of the wafer 26 and an area for cooling the wafer before further processing. As a result, the analysis can proceed without affecting the throughput of the rapid thermal processing. The camera 34
It may be attached to the observation port of the cooling chamber to capture a significant portion of the wafer 26 within its field of view. The image may take the form of a top view of wafer 26. Therefore, the camera 34 may be located above the wafer 26 or may be coupled via an optical element to receive the top surface of the wafer.

Processor 38 detects the absence of a portion of the wafer by analyzing the image captured by camera 34 to identify light density contrast changes. Then, it is determined whether or not a part of the wafer is absent based on the identification of the light density contrast change. Contrast regions on the surface of the wafer 26 can be identified by comparing the light density in that region to a target range of light densities. The data representing the target range may be stored in the memory 40 as density range data. Alternatively, processor 38 may be configured to compare successive pixels in the image for a given density difference.

When processing pixel by pixel, for example, areas on the wafer 26 where no wafer fragment loss is found will produce a given range of light densities. However,
In the area where the wafer fragment is missing, the pixels will show different ranges of light densities. Therefore, by analyzing contrast changes along one or several pixel rows, the potential presence of wafer fragments can be detected. This analysis can proceed by recording subsequent pixels that follow the contrast change until another contrast change is detected. In this way, the length or width of the potential fragment can be determined. Here again, contrast changes can be recorded within pixel rows or columns and between adjacent rows or columns to quantify the size, eg length, width or surface area of individual wafer fragments. If the size of the regions exhibiting different light densities is quite large and exceeds a predetermined threshold, it indicates the presence of wafer fragments on the wafer 26.

In other words, the size of the contrast area can be estimated, for example, by counting the number of pixels occupying the contrast area. The approximate size can then be compared to a temperature measurement and a threshold that represents a fragment size large enough to affect the control functions of the rapid thermal processing chamber 10. If the estimated size exceeds the threshold, it indicates that a portion of the wafer (i.e., wafer fragment) has been detected to be absent. The threshold may be determined empirically to eliminate false and definitive detection results, especially considering perspective distortion, different reflectivity due to different fragment shapes, and illumination variations in the chamber. In many cases, it may be desirable for the user to be able to set the threshold according to a desired level of sensitivity and intervention. It may be desirable to recalibrate the thresholds used in the fragment detection process for changing conditions within the processing chamber 10. If desired, the threshold can be set not only for a single contrast region, but also for the cumulative contrast region. In this case, the threshold is
It would represent the total number of contrast pixels across the surface of the wafer, which together could potentially present a fragment or fragments that could impair the temperature control function. Indicates. For example, a single fragment may not be large enough to alter the temperature measurement function, but the cumulative effect of multiple fragments is undesirable. Therefore, the processor 38 may compare the size of the individual fragments to a threshold, or simply sum the contrast pixels across the analyzed wafer surface portion and compare the sum to a cumulative threshold. .

When indicating a wafer fragment, the processor 38 generates an alarm that warrants automatic or manual intervention and deactivates the rapid thermal processing. This alert may be notified to the operator in the case of human intervention or, optionally, sent to the controller 42. The controller 42 automatically intervenes in the rapid thermal processing workflow. For example, controller 42 may stop the rapid thermal process and perform manual or automatic cleaning of reflector 24 before inserting the next wafer into chamber 10. If desired, alerts may be provided for operator review, or
Information may be included indicating the approximate size, number of any wafers for recording in a file for later analysis. This information may move the position of the wafer fragment along at least one side of the wafer 26. All of the above information can be sent to the user in graphic and / or text format. If desired, a monitor may be provided so that the operator can view the acquired image.

The wafer 26 is preferably set against an illuminated background surface to facilitate the identification of contrast areas in the acquired image. In this case, the range of light densities covered corresponds to the range of light densities exhibited by the illuminated background surface. To improve the contrast analysis, the background surface can be illuminated with an annular pattern of illuminating radiation with respect to the edge portion of the wafer 26, thereby providing backside illumination for the wafer. When the wafer fragments are gone, the backside illumination is visible through the lost area of the wafer for ease of identification by the processor 38.

An illumination shield may be used to project an annular pattern of illuminating radiation onto the upper surface of the wafer 26 and to substantially prevent the incidence of radiation on said surface. The illumination shield defines an inner region and an outer region, and so that the illumination radiation projected by the light source is substantially confined to the outer region and the view of the image acquisition device is substantially confined to the inner region. Is placed. The outer regions are also arranged such that the illuminating radiation illuminates a portion of the background surface adjacent the edge portion of the wafer 26, thereby providing backside illumination while preventing illumination of the top surface of the wafer. It

To minimize image processing, the portion of the acquired image corresponding to the edge of the wafer 26 can be analyzed, while discarding the rest of the image. Wafer fragments are most commonly at the edge of the wafer. Therefore, analysis of the edges of the wafer 26 will usually be sufficient to identify potential wafer fragments. In this way, the necessary image processing is performed in a more economical way and it is known that the focus on said part of the wafer 26 is very susceptible to fragmentation. With the analysis mainly confined to the edge portion, the backside illumination of only the edge portion is sufficient for effective contrast analysis. To that end, the annular pattern of light provides effective illumination.

FIG. 3 is a cross-sectional side view of the observation chamber 46 for analyzing the wafer 26.
FIG. 4 is an exploded view of the observation chamber 46. As shown in FIGS. 3 and 4, the observation chamber 46 includes a base 48 and a main housing 50. Figure 3
The observation chamber 46 also includes an observation assembly 52, as described in FIG. The base 48 is
Side ports for receiving the wafer 26 in the support region 56.
port) 54 may be included. Wafer 26 may be moved to side port 54 using conventional wafer transfer mechanisms such as transfer blades. Observation chamber 4
6 can be integrated with the cooling chamber. Thus, the base 48 may take the form of a cooling block and may include appropriate accessories for coolant flow and internal conduits. The wafer 26 is supported in the support area 56 above the background surface 58 by a wafer mounting structure (not shown). The wafer mounting structure may include, for example, a conical quartz having points that contact the wafer. The rod may be mounted in a machined hole in the base 48. The base 48 further includes an opening 59 with a mounting lip 60 for receiving the bottom mounting flange 62 of the main housing 50. The mounting flange 62 is, for example, a bolt 64, and is used to mount the mounting lip 6
It can be connected to 0. The main housing 50 typically has a cylindrical sidewall 66 and houses a conical lighting shield 68. The illumination shield 68 can be hung above the wafer 26 and into the opening 59 by a machining bracket (not shown). The bracket may be attached to the base 48 at points along the perimeter of the opening 59.

With further reference to FIGS. 3, 4, 5 and 6, the viewing assembly 52 includes an image acquisition device in the form of a camera 72 and a light source that may take the form of a light ring 74. Including. The light ring 74 defines a central opening 76. The lens portion 77 of the camera 72 extends through the central opening 76 and has a collar (col).
lar) 78, which is split by a light ring 74. 4, the main housing 50 defines an upper opening 80 and an upper mounting lip 82.
The mounting ring 84 is mounted on the mounting lip 82 with bolts 85 and defines a recess 86 for receiving a transparent viewing plate 87. The viewing plate separates the camera 72 and light ring 72 from the vapor within the main housing 50. The camera mount 88 is bolted to the upper surface 90 of the main housing 50.
Fixed to. The camera 72 is secured to the camera mount 88 with screws 94 and is positioned through the bracket 95 and into the main housing 50, looking downward. To simplify installation and removal of the observation assembly 52,
The handles 96, 98 are also mounted on the upper surface 90 of the main housing 50 with, for example, bolts 100.

With particular reference to FIG. 3, the lighting shield 68 includes an interior region 102 and an exterior region 1.
Define 04. The light shield 68 has a substantially conical shape, the first substantially circular opening 106 has a first diameter, and the second substantially circular opening 1
08 has a second diameter. The second opening 108 is defined by the cylindrical portion 110 of the light shield 68. FIG. 7 shows the illumination shield 68 mounted within the opening 59 in the base 48. The second opening 108 of the illumination shield 68 is slightly larger than the wafer 26. In particular, the diameter of the second opening 108 is slightly larger than the diameter of the wafer 26 and is coaxial with the diameter. Illumination shield 68 and viewing assembly 52 are arranged such that the annular pattern of illuminating radiation produced by light ring 74 is not directly incident on the top surface of wafer 26. Instead, as described in FIG. 3, the illuminating radiation is typically confined to the outer region 104 and impinges on the background surface 58 adjacent the edge portion 112 of the wafer 26. In this way, illuminating radiation is incident on the background surface 58, but not on the top surface of the wafer, to provide backside illumination to the wafer 26. At the same time, the field of view of the camera 72 is typically confined to the interior region 102 and therefore does not receive the illumination radiation projected by the light ring 74.

To avoid the incidence of illuminating radiation on the top surface of the wafer 26, the illumination shield 68 is made of a substantially opaque material that blocks radiation to the interior region 102. at the same time,
The outer surface of the illumination shield 68 and the inner surface of the main housing 50 may be made substantially reflective to allow less attenuated propagation of the illuminating radiation, such as a light pipe. The diameter of the second opening 108 is also sized such that the annular pattern of radiation projects slightly outside the diameter of the wafer 26, down to the background surface 58. The radiation incident on the background surface 58 is
Reflected upward, but substantially improving the optical contrast between the unaffected portion of the wafer 26 and the portion through which the backside illumination is visible.

To provide a uniform pattern of backside illumination, the light ring 74 preferably provides a light scattering pattern. Also, the background surface 58 can be configured to be more diffuse and reflective of the illuminating radiation, if desired. The lens portion 77 of the camera 72 is arranged coaxially with the first opening 106 and only looks at the top surface of the wafer 26. Specifically, the field of view of camera 72 is substantially invisible to the stray illuminating radiation projected by light ring 74. In this way, the lighting shield 68
The contrast analysis performed by the processor 38 to identify potential wafer fragments can be significantly enhanced. The contrast is chamber 46
This can be further enhanced by adjusting the height of the wafer 26 in and relative to the base 48, for example with a wafer lift pin mechanism provided in the chamber. Also, a dark ring may be formed on the inner surface of the cylindrical portion 110 to eliminate back reflection. Such a dark ring can be formed by a hard, black anodized, aluminum ring that is riveted in place.

FIG. 8 is a top view of a wafer 26 having a fragmented edge. As shown in FIG. 8, the wafer 26 has a background surface 58 for contrast analysis.
Is set for. Operationally, the processor 38 analyzes the image of the wafer 26, as captured by the camera 72, pixel by pixel to identify contrast changes. In the example depicted in FIG. 8, processor 38 monitors edge portion 112, one portion of which has a contrast region corresponding to fragment portion 114 of wafer 26. In particular, the processor 38 identifies the contrast regions by comparing the light densities of the regions to a range of light densities of interest associated with the background surface 58. For example, the surface of the wafer 26 typically exhibits a uniform light intensity, or at least a light intensity with a range of fragment portions 114 exhibits a light intensity equal to the illuminating radiation reflected by the background surface 58. . In most cases, the illuminating radiation will be of sufficient intensity to provide a clear contrast between the wafer 26 and the background surface 58. In particular, the difference in light density is sufficient to cancel out the optical inconsistencies that could lead to inconsistencies in the images obtained.

As further described in FIG. 8, the image obtained by the camera 72 may be processed by the processor 38 to discard a substantial portion and retain only the edge portion 112. Specifically, the processor 38 can effectively remove the central portion 116 from consideration in the contrast analysis. The central portion 116 may be discarded, recognizing that wafer fragments are most commonly found at the edge portion 112. Therefore, in order to avoid excessive processing overhead, the processor 38
Can be configured to focus on the areas where wafer fragments are most common.
From experience, the user may adjust the size of the edge portion 112 under analysis, or optically, perform an analysis of the entire surface of the wafer 26. However, in most cases, analysis of the edge portion 112 will be sufficient to identify wafer fragments that can adversely affect temperature measurement and control functions. As an example, analysis of an edge band having a width of approximately 2 millimeters will usually be sufficient to identify potentially problematic wafer fragments.

Also, in some applications it may be sufficient to analyze only a portion of the edge portion 112. Referring to FIG. 1, for example, a sensor probe (sens)
The or probe 30 may be located within a sub-section of the reflector plate 24, rather than the entire surface area of the plate 24 consistent with the spatial temperature profile of the heat source 20. As a result, analysis of only that portion of the wafer 26 that corresponds to the position of the sensor probe 30 on the reflector plate 24 identifies wafer fragments that tend to significantly affect the accuracy of the temperature signal produced by the probe. Is enough to do. In this case, other wafer fragments may be removed from consideration as less harmful to the temperature control function. However, in many cases it may be desirable to identify wafer fragments without having to consider their impact on temperature control functions to detect imperfect wafers. However, if the location of the sensor probe 30 extends to a larger area of the reflector plate 24, the processor 38 may account for the larger area. It will also be appreciated that wafer fragments may sprinkle onto different areas of the reflector plate once the wafer 26 is removed from the chamber 10.

FIG. 9 is a flow chart illustrating a technique for detecting wafer fragments in a rapid process chamber. As shown in FIG. 9, the processor 38 includes a camera 72 and an illumination source 7.
Drive 4 to obtain an image of wafer 26 in observation chamber 46, as indicated by block 118. If desired, the camera 72 may obtain an actual image from the rapid thermal process chamber 10 before removing the wafer 26, for example by providing the proper optical path to the camera 72 for viewing the wafer. it can. However, the observation of the wafer in the rapid thermal process chamber 10 is often ambiguous. Therefore, after ejection, it is usually necessary to capture a wafer image, for example in a cooling chamber. In this embodiment, following image capture of the wafer, processor 38 discards the central portion and retains the portion corresponding to the edge of the wafer, as indicated by block 120. Processor 38 analyzes the acquired image to determine changes in optical density contrast, as indicated by block 122. Processor 38 then defines either the overall size of the contrast regions or the size of the individual regions, as indicated by block 124. Thereafter, processor 38 determines if the magnitude exceeds a predetermined threshold, as indicated by block 126.
If so, processor 38 issues an alert, as indicated by blocks 128 and 130, optionally stopping the rapid thermal process of the next wafer until the wafer debris is removed. If the magnitude is not above the threshold, processor 38 does not issue a warning and the rapid thermal process continues, as indicated by block 132.

FIG. 10 is a side view of another observation chamber 134. The observation chamber 134 is
Substantially the same as the observation chamber 46 of FIG. Therefore, the same reference numbers are used throughout FIGS. 3 and 10 to indicate the same structures. However, the observation chamber 46
In contrast, the viewing chamber 134 incorporates another backside illuminator for the wafer 26. In particular, viewing chamber 46 uses light ring 74 and illumination shield 68 mounted on top of the chamber, but viewing chamber 134
Incorporates a light ring 136 mounted in a recessed area 138 in the base 48. Therefore, as shown in FIG. 10, a light ring 136 is provided below the wafer 26, thereby providing backside illumination directly from the opposite side of the image capture device. In particular, the light ring 136 emits illumination upwards with respect to the backside 140 of the wafer 26. The light ring 136 may be covered by a quartz window 142 received in the recessed area 138. Also, suitable electrical feedthroughs are formed in the base 48 to provide power to the optical ring 136.

FIG. 11 is a top view of the wafer 26 with the light ring 136. As shown in FIG. 11, the optical ring 136 is enlarged and arranged so that the edge portions of the wafer 26 overlap. The wafer 26 substantially blocks some of the illuminating radiation to the camera 72. However, some of the illumination from outside the edge portion 144 of the wafer 26 is visible by the camera, thereby increasing the optical density contrast at the edge. In this way, the unaffected areas of the wafer 26 appear relatively dark to the fragmented areas outside the edge portion 144 and the backside illumination provided by the light ring 136 is transmitted to the camera 72. To enable. When the fragment leaves the edge portion of the wafer 26, as indicated by reference numeral 146, the optical contrast provided by the light ring 136 facilitates identification of the fragment using machine vision techniques, as described above. To do.

As described herein, contrast analysis is accomplished using well-known machine vision techniques and devices that are commercially available to implement them. For example, a machine vision technique that can embody a contrast analysis technique is available from the Cognex Corporation of Natick in Massachusetts.
An example of a suitable machine vision technology device is the Cognex MVS 8000 series, which includes a set of PC-based machine vision hardware and software tools. With such a device, the image is analyzed pixel by pixel to evaluate the differences in optical density. If the optical densities differ by more than a threshold value, the pixel is recorded as a contrasting pixel.

In view of the commercial availability of devices generally dedicated to machine vision applications, in the feasibility of contrast analysis, the processor 38 is conventionally a general purpose single or multi-chip microprocessor, eg, Pentium® processor, P
An entium Pro (registered trademark) processor, 8051 processor, MIPS processor, Power processor, Alpha (registered trademark) processor, or the like can be used. Alternatively, the processor 38 may take the form of a special purpose microprocessor incorporated within a specialized machine vision system. Example Cognex above
In the MVS 8000 series of devices, the processor 38 is a Pentium® processor with MMX instructions set. In any case,
The processor 38 executes a program provided for performing conventional image processing for comparative analysis of the optical contrast of the actual and reference images. In addition, other processors 38 may use customer logic provided to perform the wafer fragment detection process described herein.

The camera 72 may take the form of a two-dimensional CCD pixel array with lateral and vertical fields of view spanning multiple pixels. In this method, the acquired image provides a large number of rows and columns of pixels for quantification of both the width and the length of the fragments for comparison with thresholds such as the number of pixels. Therefore, an overall shift threshold can be established by reference to the total number of control images in the image. Instead, the control images can be classified by proximity in nearby columns and rows, thereby quantifying the overall cross-sectional size of individual wafer fragments. In this case, the offset threshold is established with respect to the maximum size tolerance of the wafer fragments. Light ring 74 or 136 is Aubu in New York City
It may take the form of a fiber optic based ring light, especially configured for mechanical field of view and microscopy applications, such as those commercially available from Fostec of Rn. The above detailed description is provided for purposes of illustration only, in order to provide a better understanding of the present invention. It will be apparent to those skilled in the art that modifications can be made without departing from the spirit and scope of the appended claims.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a rapid thermal processing chamber.

FIG. 2 is a functional block diagram of a system for detecting wafer fragments in a rapid thermal processing chamber.

FIG. 3 is a side cross-sectional view of an observation chamber for analyzing a wafer with a backside illumination system for the wafer.

FIG. 4 is a development view of the observation chamber shown in FIG.

5 is a perspective view of an observation assembly forming part of the observation chamber shown in FIG.

6 is a perspective view of an observation assembly forming part of the observation chamber shown in FIG.

FIG. 7 is a perspective view of an illumination shield forming part of the observation chamber shown in FIG.

FIG. 8 is a top view of a wafer having fragment edges.

FIG. 9 is a flow diagram illustrating a technique for detecting wafer fragments in a rapid thermal processing chamber.

FIG. 10 is a side view of an observation chamber incorporating another backside illumination system.

11 is a top view of the wafer with the backside illumination system shown in FIG.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor White Anthony F             United States California             95014 Coupatino Forrestor             Venue 20061 (72) Inventor Pose Bruce W             United States California             94070 San Carlos Cobblestow             Lane 27 (72) Inventor Hogan Finver Jay             United States California             95054 Santa Clara Riverside               Court 400 Apartment 302 (72) Inventor Ahmad Waits Are             United States California             95035 Milpitas Stratford             Drive 2213 F term (reference) 2F067 AA51 AA65 BB01 CC17 HH09                       JJ08 KK08 LL16 RR24 SS15                 2G051 AA51 AB03 BB17 CA04 CB01                       DA13 EA11 EA12 EA14                 4M106 AA01 BA10 CA38 DB04 DB07                       DJ20

Claims (49)

[Claims] 1. A system for analyzing a wafer for the absence of a wafer portion, comprising: an observation chamber, a wafer support member disposed in the chamber, and a wafer disposed on the wafer support member. And an image acquisition device oriented to collect an image representative of at least one end of the wafer. 2. The apparatus further comprises a background surface and an illumination shield disposed within the observation chamber, the illumination source disposed on one side of the wafer facing the background surface, the illumination shield including an interior region. An outer region is defined and the illumination shield is such that the illuminating radiation produced by the illumination source is substantially confined to the outer region, and the field of view of the image acquisition device is substantially confined to the inner region. Oriented and said outer region is arranged such that illumination radiation illuminates a portion of the background surface adjacent the edge of the wafer to provide backside illumination radiation to the edge of the wafer. The system described. 3. The light shield has a substantially conical shape with a first substantially circular opening having a first diameter and a second substantially circular opening having a second diameter. A second opening such that the illuminating radiation produced by the light source of the illumination source is projected onto the background surface adjacent to the edge of the wafer, rather than directly onto the upper surface of the wafer. 3. The system of claim 2, wherein is larger than the size of the wafer supported in the wafer support area. 4. The system of claim 3, wherein the illumination source emits illuminating radiation in a substantially annular pattern. 5. The system of claim 4, wherein the illumination source has a substantially annular shape defining a central opening and the image acquisition device has a field of view extending through the central opening. 6. The image acquisition device and the illumination source are disposed adjacent to each other, the image acquisition device having a lens extending through at least a portion of a central opening, the illumination source comprising a lens. The system of claim 5 extending circumferentially. 7. The system of claim 1, wherein the illumination source is located on a side of the wafer adjacent the background surface and facing the image acquisition device. 8. The system of claim 7, wherein the illumination source emits a substantially annular pattern of illuminating radiation toward a side of the wafer adjacent the background surface. 9. The system of claim 8, wherein the substantially annular pattern of illuminating radiation covers the edge of the wafer. 10. The processor of claim 1, further comprising a processor that analyzes the collected images to detect the absence of a portion of the wafer and alerts if the absence of the portion of the wafer is detected. System. 11. The processor analyzes the collected image by identifying light density contrast changes to determine if a portion of the wafer is absent based on the identification of the light density contrast changes. 11. The system of claim 10 for determining. 12. A method of identifying a contrast area having a light density that is in contrast with a target range of light density, estimating the size of the contrast area, comparing the estimated size with a threshold value, 13. The system of claim 11, wherein the processor is configured to analyze the acquired image by indicating detection of the absence of a portion of the wafer if the estimated magnitude exceeds a threshold. 13. The system of claim 10, further comprising a controller that shuts down the rapid thermal processing chamber in response to the processor issuing an alarm. 14. The system according to claim 10, wherein the observation chamber forms part of a cooling chamber. 15. Identifying contrast regions along the edge of the wafer that have a light density that contrasts with the range of light densities exhibited by the backside illumination radiation,
Gathering by estimating the size of the contrast area, comparing the estimated size to a threshold, and showing detection of the absence of a portion of the wafer if the defined surface area exceeds the threshold. The system of claim 10, wherein the processor is configured to analyze a captured image. 16. A system for detecting the presence of a portion of a wafer in a deposition processing chamber, the illumination source providing backside illumination radiation near one end of the processed wafer in the chamber, and at least an edge of the wafer. An image acquisition device that is oriented to collect an image of the area, and the collected images are analyzed to detect the absence of a portion of the wafer, and if the absence of a portion of the wafer is detected. And a processor for issuing an alarm. 17. A method for identifying light density contrast changes and determining whether a portion of the wafer is absent based on the identification of the light density contrast changes.
The system according to item 6. 18. A contrast area having a light density that makes a contrast with a target range of light density is identified, the size of the contrast area is roughly estimated, and the estimated size is compared with a threshold value to perform the rough estimation. 17. The system of claim 16, wherein the processor is configured to analyze the acquired image by indicating detection of the absence of a portion of the wafer if the magnitude exceeds a threshold. 19. The system of claim 18, wherein the processor identifies contrast regions by identifying a plurality of adjacent pixels having light densities within a common range of light densities different from a target range of light densities. . 20. The processor determines the size of the contrast region by counting the number of adjacent pixels in the contrast region, the counted number of adjacent pixels being a threshold number of pixels. 20. The system of claim 19, wherein detection of absence of a portion of the wafer when exceeded. 21. The illumination source provides backside illumination radiation to an edge portion of a wafer relative to the image acquisition device, and a target range of light densities coincides with a range of light densities indicated by the backside illumination radiation. Item 19. The system according to Item 18. 22. The system of claim 16, further comprising a controller that deactivates the rapid thermal process chamber in response to the generation of an alert by the processor. 23. The system of claim 16, wherein the image acquisition device is oriented to acquire an image after the wafer is removed from the rapid thermal process chamber. 24. The system of claim 23, wherein the image acquisition device is oriented to acquire an image after the wafer is received in the cooling chamber. 25. The wafer further includes an observation port located above the position where the wafer is received in the cooling chamber, and the image acquisition device collects an image as a top view of the wafer through the observation port. 25. The system of claim 24, which is oriented as follows. 26. Further comprising an illumination shield defining an interior region and an exterior region, the illumination shield being substantially confined to the exterior region by the illumination radiation projected by the illumination source and the field of view of the image acquisition device. Are oriented so as to be substantially confined to the inner region, the outer region illuminating a portion of the background adjacent to the edge portion of the wafer by the illuminating radiation, thereby to the edge portion of the wafer. 24. The system of claim 23, wherein the system is arranged to provide backside illumination radiation. 27. The processor further comprises an image collected by identifying contrast regions along an edge portion of the wafer having a light density that contrasts with the range of light density exhibited by the background surface during illumination. And estimating the size of the contrast region and comparing the estimated size to a threshold,
27. The system of claim 26, configured to direct detection of the absence of a portion of the wafer when the estimated size is greater than a threshold. 28. The system of claim 23, wherein the illumination source is located on one side of the wafer adjacent the background surface and facing the image acquisition device. 29. A method of detecting the presence of a wafer portion in a deposition processing chamber, the method comprising illuminating an area within the chamber adjacent an edge portion of the processed wafer, collecting an image representative of at least a portion of the wafer, and illuminating radiation. Provides backside illumination radiation for an edge portion of the wafer, analyzes the collected image to detect the absence of a portion of the wafer, and issues an alert if the portion of the wafer is detected. 30. Analyzing the collected image by identifying changes in light density contrast and determining if a portion of the wafer is absent based on the changes in light density contrast. The method described. 31. Further identifying a contrast region having a light density contrasting a target range of light densities, estimating the size of the contrast region, comparing the estimated size with a threshold and determining the estimated size. 30. The method of claim 29, comprising analyzing the acquired image by indicating detection of the absence of a portion of the wafer if greater than a threshold. 32. The method of claim 31, further comprising identifying a contrast region by identifying a plurality of adjacent pixels having light densities in a normal range of light densities different from the target range of light densities. 33. The size of the contrast region is further estimated by counting a number of adjacent pixels in the contrast region, and a portion of the wafer is estimated when the count value of the adjacent pixels is greater than the count value of the threshold pixel. 33. The method of claim 32, including directing the detection of the absence. 34. The method of claim 31, wherein the target range of light densities corresponds to the range of light densities exhibited by the backside illumination radiation. 35. The method of claim 29, further comprising deactivating the rapid thermal process chamber in response to the alert. 36. The method of claim 29, further comprising collecting an image after the wafer has been removed from the rapid thermal process chamber. 37. The method of claim 36, further comprising collecting an image after the wafer is received in the cooling chamber. 38. The cooling chamber includes an observation port located above the position where the wafer is received in the cooling chamber, and the image acquisition operation collects a top view of the wafer through the observation port. The method according to 37. 39. further identifying a contrast region along an edge of the wafer having a light density that contrasts with the range of light density exhibited by the background surface during illumination; estimating the size of the contrast region; 39. Analyzing the acquired image by comparing the size of the image to a threshold value and indicating detection of the absence of a portion of the wafer if the estimated surface area is greater than the threshold value. the method of. 40. The image acquisition operation comprises providing an illumination shield defining an inner region and an outer region, the illuminating radiation projected by an illumination source being substantially confined to the outer region, and the field of view of the image acquisition device being the confined region. Orienting the illumination shield to be substantially confined to an interior region, the exterior region illuminating a portion of the background surface adjacent to the edge portion of the wafer by the illuminating radiation, thereby causing the edge portion of the wafer to 30. The method of claim 29, wherein the method is arranged to provide backside illumination radiation. 41. The method of claim 40, further comprising analyzing the acquired image, the analyzing step contrasting with a range of optical densities displayed by a background surface during illumination. Identifying a contrast region along the wafer edge having one optical density that comprises: estimating the size of the contrast region; comparing the estimated size to a threshold; and the estimated surface region. Indicating detection of the absence of a portion of the wafer if exceeds the threshold. 42. The method of claim 37, wherein the illuminating operation illuminates the wafer from the side of the wafer facing the image acquisition device. 43. The method of claim 42, further comprising analyzing the captured image, the analyzing step comprising: measuring a range of optical density and contrast displayed by a background surface during illumination. Identifying a contrast region along a wafer edge having one optical density of: making an estimate of the size of the contrast region; comparing the estimated size to a threshold; Directing the detection of the absence of a portion of the wafer if the threshold is exceeded. 44. A system for analyzing a wafer for the absence of a portion of a wafer, the observation chamber, a wafer support member disposed within the chamber, and generating backside illumination radiation around an edge portion of the wafer. An illumination source and an image acquisition device oriented to capture an image displaying at least an edge portion of the wafer positioned on the wafer support member. 45. The system of claim 44, wherein the illumination source projects a substantially ring-shaped pattern of illuminating radiation. 46. The system of claim 44, further comprising analyzing the acquired image to detect the absence of a portion of the wafer and detecting the absence of a portion of the wafer. A system comprising a processor for generating a warning in. 47. A system for analyzing a wafer for the absence of a portion of a wafer, the observation chamber, a wafer support member disposed within the chamber, and a wafer support member disposed within the chamber adjacent to the wafer support member. An image acquisition device oriented to obtain an image displaying at least an edge portion of the wafer positioned on the background surface and the wafer support member from the side of the wafer support member facing the background surface; An illumination source for projecting illumination radiation into the observation chamber and an illumination shield arranged in the observation chamber are included, and the illumination shield defines an inner region and an outer region, and the illumination shield is , The illuminating radiation is substantially confined to the outer region and the field of view of the image acquisition device is substantially within the inner region. Oriented to be confined to a region, the outer region such that the illuminating radiation illuminates a portion of the background surface adjacent the edge of the wafer to provide backside illuminating radiation for the wafer edge. A system characterized by being placed in. 48. The system of claim 47, wherein the lighting shield is substantially conical in shape, the lighting shield being substantially circular with a substantially circular first diameter first opening. A second aperture of a second diameter, wherein the second aperture is not directly projected onto the upper surface of the wafer by the illuminating radiation produced by the illumination source, but is adjacent the edge of the wafer. A size larger than the size of the wafer supported in the wafer support area as projected onto the system. 49. A system for analyzing a wafer for the absence of a portion of the wafer, the observation chamber, a wafer support member disposed within the chamber, and one side of the wafer positioned on the wafer support member. Means for providing backside illumination, and an image acquisition device oriented to capture an image displaying at least an edge portion of the wafer, wherein the image acquisition device includes a wafer fragment at the edge portion of the wafer. A part of the backside illumination is acquired if not present in the system.