Patent Application
20120060353
This disclosure relates to a method and mechanism for ensuring the alignment of a workpiece to a mask, such as a shadow mask for use in an ion implantation process.
An electronic device may be created from a workpieces that has undergone various processes. One of these processes may include introducing impurities or dopants to alter the electrical properties of the original workpiece. For example, charged ions, as impurities or dopants, may be introduced to a workpiece, such as a silicon wafer, to alter electrical properties of the workpiece. One of the processes that introduces impurities to the workpiece may be an ion implantation process.
An ion implanter is used to perform ion implantation or other modifications of a workpiece. A block diagram of a conventional ion implanter is shown in
In operation, a workpiece handling robot (not shown) disposes the workpiece 114 on the workpiece support 116 that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source 102 and extracted by the extraction electrodes 104. The extracted ions 10 travel in a beam-like state along the beam-line components and implanted on the workpiece 114. After implanting ions is completed, the workpiece handling robot may remove the workpiece 114 from the workpiece support 116 and from the ion implanter 100.
Referring to
In some embodiments, it is desirable to use a mask that has a fixed position relative to the platen. In some embodiments, the mask is fixed to the platen. In such instances, the mask is clamped to the platen, such as by mechanical means, such as a clamp. Any electrical connections can easily be made between the mask and the platen, since the mask is not moveable. In other embodiments, the mask is movable with respect to the platen. For example, a platen may be adapted to hold one of a plurality of masks. One of the masks may be selected, such as by a robotic arm, for placement on the platen. The mask may be aligned to the platen using techniques known to those of skill in the art. After the mask is placed on the platen, it may be secured, such as by a mechanical clamping mechanism. In addition, the alignment of the mask to the platen may also serve to provide a connection between electrical signals in the platen and in the mask. For example, one of more pins in the platen may be movable such that they are retracted while the mask is being placed on the surface of the platen. These pins may then be extended through the surface of the platen and contact the mask after the mask is properly clamped to the platen. In either embodiment, these pins may be used to supply power connections, such as voltage and ground to circuitry on the mask. In addition, one of more pins may be used to transmit data between the platen and the mask.
Two or more projections may be positioned on the mask which serve as alignment features. The workpiece is then placed on the platen, as described above.
Alignment features 191, 192 are positioned on the underside of the shadow mask 195 to allow alignment with the workpiece 114 along one axis. These alignment features 191, 192 may serve to attach the shadow mask 195 to the platen 175. In other embodiments, the shadow mask 195 is held on the platen 175 using other means, such as using a clamping mechanism. In some embodiments, alignment features 193, 194 are also positioned on the underside of the shadow mask 195 to help align the workpiece 114 along an orthogonal axis. In this embodiment, the shadow mask 195 is assumed to be stationary, while the workpiece 114 can be moved relative to the shadow mask 195 and the alignment features 191-194. However, in other embodiments, the workpiece 114 may be kept in a fixed position and the shadow mask 195 may be moved relative to the workpiece 114.
In practice, the workpiece 114 is placed on the platen 175. The platen (with the shadow mask clamped thereto) is then typically tilted such that it is not horizontal, such that the platen 175 tilts allowing alignment features 191, 192 to be lower than the rest of the platen 175. This allows the workpiece 114 to slide relative to the platen 175 and the shadow mask 195 toward alignment features 191, 192. In some embodiments, a second tilting operation may be performed to align with alignment features 193, 194. In most embodiments, it is assumed that, by sufficiently tilting the platen 175 and holding it in the tilted position for an adequate amount of time, the workpiece 114 will move so that it abuts the alignment features 191-194 and is therefore properly aligned. However, in some cases, the workpiece 114 may not slide as expected, and is left misaligned after the tiling process is completed. Typically, this error is not detected until the workpiece 114 has been completely processed, thereby wasting process time and materials.
Therefore, it would be beneficial if there were a mechanism and method to ensure that the workpiece is indeed properly aligned with the shadow mask. This would reduce processing time, and improve yield, as the alignment process could be repeated if there was a mechanism to determine that the previous alignment was unsuccessful prior to workpiece processing.
The problems of the prior art are overcome by the mechanism and method of this disclosure. A workpiece support having alignment features to allow the proper alignment of the shadow mask to the workpiece is provided. The alignment features include tactile sensors, so as to measure the pressure being applied to each alignment feature. Based on these pressure readings, a determination can be made as to whether the workpiece is properly aligned with the shadow mask. In some embodiments, corrective actions may be initiated if a determination is made that the workpiece is not properly aligned.
In order to facilitate a fuller understanding of the present disclosure, reference is now made to the accompanying drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present disclosure, but are intended to be exemplary only.
In the present disclosure, several embodiments of an apparatus and a method for aligning a workpiece and a shadow mask are introduced. For purpose of clarity and simplicity, the present disclosure will focus on an apparatus and a method for aligning a workpiece that is processed by a beam-line ion implanter. Those skilled in the art, however, may recognize that the present disclosure is equally applicable to other types of processing systems including, for example, a plasma immersion ion implantation (“PIII”) system, a plasma doping (“PLAD”) system, an etching system, an optical based processing system, and a chemical vapor deposition (CVD) system. As such, the present disclosure is not to be limited in scope by the specific embodiments described herein.
Returning to
However, the tilting process described above does not always result in the proper alignment.
Currently, there are no techniques for verifying proper alignment of the workpiece to the shadow mask prior to commencement of workpiece processing. Therefore, even in the case of a misaligned workpiece, such as that shown in
To overcome this shortcoming, a tactile sensor may be integrated in the alignment features. The tactile sensor can be of any suitable type, such as a micro stress gauge, or a resistive element whose resistance changes with pressure. The output of the tactile sensor can be of various types. For example, in one embodiment, the tactile sensor may have a binary output, which denotes that either pressure is being applied or no pressure is being applied to the sensor. In another embodiment, the output of the sensor may be a range of values, where the value is an indication of the amount of pressure being applied to the sensor. For example, greater values may indicate greater pressure being applied to the sensor. Furthermore, the output from the sensor may be analog or digital in format. In addition, the output of the sensor can be transmitted in any form, including wirelessly (such as but not limited to BlueTooth, Zigbee, 802.11a, 802.11b, 802.11g, and 802.11n protocols) and wired (including protocols such as USB). In other embodiments, a single wire is used for the output of the sensor, where the voltage of the output is indicative of the pressure applied to the sensor. In one particular embodiment, a tactile sensor having four connections is used. Two of the connections are power and ground connections. Two other connections are used to provide a differential voltage signal, which is indicative of the pressure applied to the sensor. The sensitivity of the tactile sensor may vary, and in some embodiments may be as sensitive as 0.25 mV/g.
A micro stress gauge may have 4 connections; power, ground and two for a differential output voltage. The differential output voltage may be linearly proportional to the pressure applied to the gauge. Although a linear relationship may be used, other relationships between the applied force and output voltage are also possible, including logarithmic and exponential. As long as the relationship between the output voltage and the applied pressure can be defined, any type of relationship may be employed. The micro stress gauge is placed such that it supports the workpiece when it is slide against the alignment features.
In the case of a pressure sensitive resistive element, an external circuit may be used to measure the resistance of the element. For example, a fixed voltage can be applied across the resistive element to determine its resistance by calculating the current passing through the element. In another embodiment, a fixed current is passed through the pressure sensitive resistive element, and the voltage across the element is used to calculate its resistance. This measured resistance is a measure of the pressure being applied to the resistive element.
In another embodiment, the tactile sensors are micro stress gauges. One such sensor 481-484 is positioned near or integral to each alignment feature 491-494. To monitor the force applied to each of the sensors, an external controller or circuit 470 is used to supply power (voltage and ground) to each of the various sensors 481-484. A differential voltage output is available as an output from each tactile sensor 481-484. In some embodiments, four wires are used for each micro stress gauge. The measured differential voltage can then be converted to an applied pressure value. Based on these values, a controller 470 may determine whether the workpiece is properly aligned.
In these embodiments, the controller 470 may comprise a processing unit, adapted to execute instructions and perform arithmetic operations. The controller may also comprise a storage element, which is configured to store the instructions to be executed by the processing unit. In addition, the storage element may store data. The storage element may be non-volatile, such as ROM, or may be volatile, such as RAM. In addition, the controller may include input and output ports to allow interaction with external components, such as the tactile sensors, and the tilt motors of the workpiece support. The processing unit may be any type, such as a general purpose processor, an embedded processor, or a special purpose processor design specifically for this task.
For example,
In some embodiments, a number of different corrective actions may be available. In some embodiments, the controller may attempt a different corrective action after the initial alignment procedure failed. In some embodiments, the controller may perform a predetermined number of corrective actions before it stops. For example, the controller may attempt to correct the alignment three times before notifying the operator. In another embodiment, the controller may instruct the robotic system to unload the workpiece and proceed with the next workpiece. In other embodiments, the controller may not attempt any corrective action, and may simply stop and it determines that the workpiece is misaligned.
Furthermore,
In other embodiments, the platen 175 is tilted at an angle such that the workpiece 114 slides toward all of the alignment features 191-194 in one operation. By performing alignment in two directions simultaneously, other corrective actions may be possible. For example, after tilting the platen 175, the controller 470 may determine that the workpiece 114 is properly aligned with respect to alignment features 191-192, but is not aligned at all with alignment features 193-194. In this case, the controller 470 may cause the platen 175 to alter the tilt angle to allow the workpiece 114 to slide toward the alignment features 193-194, while not affecting the alignment along features 191-192.
In some embodiments, the tactile sensors can be used to insure that the workpiece is not damaged. For example, in some embodiments, the controller can determine the weight of the workpiece based on the measurements received from the tactile sensors. If the workpiece has a predetermined weight, the controller can compare that weight to the measurements received from the tactile sensors. If the readings from the tactile sensors are outside of a predetermined range, the controller may conclude that the workpiece is defective. As an example, a workpiece may be damaged such that a corner or portion of it breaks off before or as it is being transferred to the platen. After the tilting process, the controller may determine that the workpiece is properly aligned (since the weight is evenly distributed between the alignment features). However, a check of the absolute readings may show that the values are lower than expected, indicating that the workpiece is lighter than usual. In another example, two workpieces may be stuck together. When this workpiece is placed on the platen, the controller may determine that the weight is much higher than expected.
In the case of a weight discrepancy, the controller may perform a corrective action. In some embodiments, the controller may stop operation of the equipment and alert the operator. In another embodiment, the controller may instruct the robotic system to unload the workpiece and proceed with the next workpiece.
Although the mask is described as a shadow mask, the disclosure is not limited to solely shadow masks. For example, the present disclosure may also be used to insure that stencil masks are properly to a workpiece.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes.
