Patent Application
20080087116
Semiconductor processing systems are characterized by extremely clean environments and extremely precise semiconductor wafer movement. Industries place extensive reliance upon high-precision robotic systems to move substrates, such as semiconductor wafers, about the various processing stations within a semiconductor processing system with the requisite precision.
Reliable and efficient operation of such robotic systems depends on precise positioning, alignment, and/or parallelism of the components. Accurate wafer location minimizes the chance that a wafer may accidentally scrape against the walls of a wafer processing system. Accurate wafer location on a process pedestal in a process chamber may be required to optimize the yield of that process. Precise parallelism between surfaces within the semiconductor processing system is important to ensure that minimal substrate sliding or movement occurs during transfer from a robotic end effector to wafer carrier shelves, pre-aligner vacuum chucks, load lock elevator shelves, process chamber transfer pins and/or pedestals. When a wafer slides against a support, particles may be scraped off that cause yield loss. Misplaced or misaligned components, even on the scale of fractions of a millimeter, can impact the cooperation of the various components within the semiconductor processing system, causing reduced product yield and/or quality.
This precise positioning must be achieved in initial manufacture, and must be maintained during system use. Component positioning can be altered because of normal wear, or as a result of procedures for maintenance, repair, alteration, or replacement. Accordingly, it becomes very important to automatically measure and compensate for relatively minute positional variations in the various components of a semiconductor processing system.
In the past, attempts have been made to provide substrate-like sensors in the form of a substrate, such as a wafer, which can be moved through the semiconductor processing system to wirelessly convey information such as substrate inclination and acceleration within the semiconductor system. One particular example of such a system is shown in U.S. Pat. No. 6,266,121 to Reginald Hunter. That system includes an inclinometer that has a cavity that is partially filled with a conductive fluid, such as mercury, and an array of probes disposed vertically in the cavity into the conductive fluid. Additionally, the system of the '121 patent provides an accelerometer that mounts to the support platform and senses the acceleration of the sensor device.
High accuracy accelerometers used for level sensing tend to be relatively expensive and large, most notably in the z-axis, because they contain large moving parts. The utilization of bulky accelerometers, such as bulky electrolytic accelerometers, or large microelectromechanical system (MEMS) accelerometers can provide a high signal-to-noise (S/N) ratio, but demand large vertical z-axis space. Additionally, these accelerometers are generally relatively costly and increase the overall cost of the substrate-like sensor.
Given that a substrate-like sensor must, by virtue of its design, be able to move through a semiconductor processing system in the same way that a substrate does, it is imperative that the substrate-like sensor not exceed the physical envelope allowed for the substrate. Common wafer dimensions and characteristics may be found in the following specification: SEMI M1-0302, “Specification for Polished Monochrystoline Silicon Wafers”, Semiconductor Equipment and Materials International, www.semi.org. The selection of the accelerometer for use with the substrate-like sensor is constrained by the issue of cost as well as the height of the overall accelerometer. Providing an accelerometer system that is low-cost, and extremely low-profile would provide significant advantages to the art of wireless substrate-like sensing.
An acceleration measurement system is provided. The system includes at least first and second accelerometers. The first accelerometer has an electrical characteristic that varies with acceleration in a first axis. The second accelerometer also has an electrical characteristic that varies with acceleration in the same first axis. A controller is operably coupled to the first and second accelerometers and provides an acceleration output that is based on the electrical characteristics of the first and second accelerometers. In one aspect, the acceleration system is in the form of a substrate-like sensor.
Embodiments of the present invention generally provide a plurality of relatively low-cost, low-height accelerometers arranged such that at least two accelerometers are responsive to acceleration in the same axis. This arrangement allows multiple low-cost accelerometers to provide a more accurate signal, with a higher signal-to-noise ratio than would be available from each sensor individually. Moreover, the overall cost of the plurality of low-cost sensors, as well as the height required to house such sensors is believed to be beneficial for wireless substrate-like sensors.
While acceleration sensors 220 are illustrated in
As illustrated in
Controller 208 is coupled via a suitable port, such as a serial port, to radio frequency communication module 212 in order to communicate with external devices. In one embodiment, radio-frequency module 212 operates in accordance with the well-known Bluetooth standard, Bluetooth core specification version 1.1 (Feb. 22, 2001), available from the Bluetooth SIG (www.bluethooth.com). One example of module 212 is available form Mitsumi under the trade designation WMLC40. Additionally, other forms of wireless communication can be used in addition to, or instead of, module 212. Suitable examples of such wireless communication include any other form of radio frequency communication, acoustic communication, infrared communication or even communication employing magnetic induction.
Controller 208 is coupled to acceleration sensors 220 and senses acceleration experienced by the wireless substrate-like sensor. Such acceleration may include that caused by physical movements of the wireless substrate-like sensor, the force and orientation of gravity, or a combination thereof.
Acceleration sensor module 220 includes a plurality of individual accelerometers where at least two acceleration sensors are arranged to be responsive to acceleration in the same direction. In this manner, the at least two accelerometers are considered redundant. Preferably, each of these individual accelerometers is a relatively low-cost, low-profile accelerometer. By utilizing a plurality of such sensors, in parallel, the result is a higher accuracy accelerometer that does not require a large-z-axis space. Preferably, each such accelerometer is a MEMS accelerometer. In theory, is believed that the internal noise of a low-cost MEMS accelerometer is approximately a Gaussian function distribution, and that by paralleling N such devices, the overall signal-to-noise ratio of the resulting sensor is improved by the square root of N. For example, an array of 16 redundant accelerometers arranged in parallel would show a signal-to-noise ratio improvement of 4. Further, if the noise distribution is not Gaussian, but is more limited in amplitude, then the improvement could be even greater.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/848,773, filed Oct. 2, 2006, the content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60848773 | Oct 2006 | US |
