Patent Application
20110074341
Sensor wafers are used to obtain non-invasive, in-situ measurements of actual physical and electrical properties of plasma within an operational plasma processing environment. These sensor wafers are configured to collect, process, and store data received during measurement of the plasma. These sensor wafers may include devices to measure thermal, optical, and electromagnetic properties of the process environment. During the measurement process, these sensor wafers may be exposed to harsh conditions such as excessive heat, corrosive chemicals, and bombardment by high energy ions, and high levels of electromagnetic and other radiative noise. It is important for the sensor wafer to remain resilient in the harsh environment associated with in-situ measurement of plasma.
Sensor wafers are currently housed and stored in a front operating universal pod (FOUP) during the in-situ process survey. A FOUP is a specialized plastic enclosure designed to hold wafers securely and safely in a controlled environment, and configured to allow the wafers to be removed for processing or measurement by tools equipped with appropriate load ports and robotic handling systems. A FOUP may be used to communicate with a sensing wafer and recharge the sensing wafer's batteries during the process survey. Existing communication between a FOUP and sensor wafer is based on operation with a pair of coupled inductors. These coupled inductors are equivalent to an air-core transformer. The physical implementation of these inductors is accomplished by having one coil, the secondary, embedded in the sensor wafer and a second coil, the primary, on a substrate in close proximity. The coupling coefficient, k, is heavily reduced as the distance between the primary and secondary coils grows. Hence, the induced current in the secondary coil and the back reflected impedance of the secondary coil rapidly decrease as a function of distance. In order to obtain an optimal transfer of power and data between the primary and secondary coils, the primary coil must be in close proximity with the secondary coil in the sensor wafer.
The forward power transfer between the primary coil and the secondary coil provides power for the re-charging of the sensor wafer batteries. On-Off-Key (OOK) modulation is used to encode the carrier frequency (RF) from the primary coil to the secondary coil with a data stream that can be detected by the sensor wafer as a command. Communication from the wafer/secondary coil to the FOUP/primary coil may be accomplished by altering the load (e.g., impedance) of the secondary coil such that reflection from the secondary coil to the primary coil may be detected by the FOUP as an AM modulated bit stream.
The current trend amongst wafer sensors and FOUPs is to scale down the size of primary and secondary coils, thus reducing the resistance associated with the size of the coil. However, the close proximity between the primary coil and the sensor wafer necessitated by reduced coil diameter, as well as the moving parts and exposed electronics within the enclosed FOUP all contribute to particle generation. Particle generation affects the accuracy of the survey process and creates a barrier for entry into particle sensitive applications.
It is within this context that embodiments of the present invention arise.
The teachings of embodiments of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
Embodiments of the present invention overcome the disadvantages associated with the prior art by increasing the diameters of the primary and secondary coils used to charge and/or communicate with a sensor wafer. As a result of the increased coil size, a large inter-coil spacing may be used.
The energy storage device 103 preferably supplies electrical energy at an operating voltage, current handling and has an energy storage capacity that is sufficient to power the electronics 105 on the sensor wafer 100 over a period of time for which the sensor wafer is expected to operate. Furthermore, it is often desirable for the energy storage device 103 thin enough to fit within a recess in the substrate 101 and have a sufficiently small footprint to allow room for the measurement electronics, memory, transceiver and sensors. It is further desirable for the energy storage device 103 to be made of materials suitable for use in the environment of a semiconductor wafer processing tool in which the sensor wafer 100 is to be used. By way of example, and not by way of limitation, the energy storage device 103 may be a rechargeable battery, such as a lithium ion battery. Other suppliers of suitable batteries include Front Edge Technology, Inc. of Baldwin Park, Calif., Infinite Power Solutions of Littleton, Colorado and Cymbet Corporation of Elk River, Minn. One example of a Lithium ion battery is a 4.2 LiPON solid state lithium ion battery from Infinite Power Solutions of Littleton, Colo. The energy storage device 103 may be supplemented with an energy harvesting device, again by way of example, and not by way of limitation, a thermopile generator or photovoltaic cell.
The processor module 107 may be configured to execute instructions stored in the main memory 109 in order for the sensor wafer 100 to properly measure process parameters. The main memory 109 may be in the form of an integrated circuit, e.g., RAM, DRAM, ROM and the like. The transceiver 111 allows the sensor wafer 100 to communicate data stored in the memory 109 to an external processing system or to receive data from an external system for storage in the memory 109 or processing by the processor module 107. The energy storage device 103 provides power for operating the measurement electronics 105 and sensors 113, 115, 117. The sensors may include an electromagnetic sensor 113 to measure electromagnetic properties of a given plasma, a thermal sensor 115 to measure thermal properties of a given plasma, and an optical sensor 117 to measure optical properties of a given plasma.
As seen in
Existing sensor wafers have been configured such that the wafer coil 121 is scaled down in size to reduce the resistance associated with the coil. In such a configuration, obtaining optimal signal strength to facilitate communication between the FOUP coil and the wafer coil 121 often results in the FOUP coil coming into contact with the sensor wafer 100. This can introduce particle contamination into the measurement process, which may result in inaccuracies in the result. The wafer coil 121 generally includes one or more conductive (e.g., copper) windings in the form of a flat spiral coil having an inner diameter D1 and an outer diameter D. In order to overcome particle contamination, the wafer coil 121 according to an embodiment of the present invention may be configured to have a much larger outer diameter D (e.g., at least 50 mm) in order to allow for a greater distance between the FOUP coil and the wafer coil 121 during communication and power transfer. This greatly reduces the particle contamination involved with the measurement process and allows for the sensor wafer to be more widely used with particle sensitive applications. In order to assist with the non-contact transfer of information, the wafer coil 121 may include a transformer core so that the wafer coil 121 may be kept at a larger distance from the FOUP coil during power transfer and communication. In
The FOUP coil may transfer power to the wafer coil 121 through induction, and may also transmit data to the wafer coil 121 through modulation of a carrier frequency. The wafer coil 121 is coupled to both the energy storage device 103 and the measurement electronics 105. The power transferred from the FOUP coil to the wafer coil 121 is further transferred to the energy storage device 103 so that the sensor wafer 100 as a whole may be charged.
By way of example, and not by way of limitation, the wafer coil 121 may have an outside diameter between about 50 mm and the diameter of the substrate 101. By way of example, the outside diameter may be about 50 mm when the wafer coil 121 is operated at a distance of about 11 mm from the FOUP coil. The wafer coil 121 may be formed as a thin film circuit directly on the substrate 101. Alternatively, the wafer coil 121 may be a sub-assembly attached within a cavity or depression in the surface of the substrate 101 to maintain a low profile. The wafer coil 121 may have the same number of turns as the FOUP coil. By way of example, the wafer coil 121 may have about 5 to 20 turns.
By way of example, the FOUP coil 215 includes one or more turns of electrically conductive (e.g., copper) wire that wind around a hat shaped ferrite core 213. In the example depicted in
The FOUP coil 215 may be coupled to an electronics module 216, referred to herein as FOUP electronics. The FOUP electronics 216 may provide power to the FOUP coil 215 for charging the energy storage device 103 on the sensor wafer 100. In addition, the FOUP electronics 216 may include processor logic and/or a memory and transceiver to facilitate exchange of data between the FOUP electronics 216 and the electronics module 105 on the sensor wafer 100.
The FOUP coil 215 is preferably situated and oriented in the FOUP such that it is concentric with the wafer coil 121 when the sensor wafer 100 is positioned in a slot 203 on the FOUP 201. To determine the distance d between the wafer coil 121 and the FOUP coil 215 necessary to facilitate optimal data and power transmission, a ratio between the wafer coil diameter and the distance d may be determined experimentally. In the example shown, by increasing the diameter of the wafer coil 121 to a diameter greater than 50 mm, the distance d between the wafer coil 121 and the FOUP coil 215 may be increased to 20 mm or greater. Preferably, however, wafer coil 121 is at least 8 mm, e.g., between 8 mm and 12 mm, from the FOUP coil 215 when the sensor wafer 100 is in its slot 203 in the FOUP 201. Generally, the frequency of the voltage signal applied to the FOUP coil 215 is in the range of 1 to 3 Megahertz and the amplitude of the signal is sufficient to supply an RMS current of about 100 to 200 milliamps to the FOUP coil.
It was initially believed, even by the inventors themselves, that such a spacing was simply too large and the coil resistance too great to allow for effective inductive coupling between the FOUP coil 215 and the wafer coil 121. However, a system having a wafer coil and FOUP coil with the following dimensions was found to work effectively.
As proof of concept, a FOUP coil and wafer coil were built. Each coil had an outside diameter of 50 mm and included 10 turns. The coils were separated from each other by a distance of about 11 mm. The FOUP coil was operated as a series LC (tuned trap) circuit at a frequency of about 2 MHz.
In an alternative embodiment illustrated in
This interface system may optionally have an optical detector 223 and a network interface 225. The network interface 225 is configured to allow for bi-directional communication between the FOUP electronics 216 and any computers within a network. In the example shown, the optical detector 223 is configured to detect the presence of a sensor wafer 100 through the side of the FOUP 201. An optical beam 219 initially passes from a source 217 through the transparent sidewall of the FOUP 201. The optical light guides 221, 221′ may be index matched with the wall of the FOUP 201 such that no reflection or refraction of the optical beam 219 occurs at the interface between the light guides 221, 221′ and the side wall of the FOUP 201. Optical coupling through the wall of the FOUP 201 avoids having to drill a hole through the wall. The optical beam 219 then travels via a first transparent light guide 221 and is reflected at a beveled end of the light guide 221 through a short gap to a second light guide 221′, which is oriented in a mirror image configuration with respect to the first light guide 221. The second light guide 221′ guides the optical beam 219 back towards the wall of the FOUP 201 and into a detector 223, which may be coupled to the FOUP electronics 216. When a sensor wafer 100 is situated in the beam path, the wafer interrupts the optical beam 219 and a signal produced by the detector 223 changes as a result. The signal from the detector 223 may be coupled to the FOUP electronics 216 so that the FOUP electronics 216 are notified of the presence of the wafer. It is important to note that the optical source 217, optical detector 223, light guides 221, 221′ and optical beam 219 may be configured to detect the presence of a sensor wafer through the transparent back wall 227 of a FOUP 201 rather than the transparent sidewall.
By way of example, the FOUP coil 215 may be formed on a printed circuit board (PCB) in a single layer of spiral turns with an outer diameter of about 50 mm. The wafer coil may have a dual layer of spiral turns with an outer diameter of about 50 mm formed on a backside of the substrate 101. One or more of the light guides 221 for the wafer presence detector may also be implemented in the PCB. In some embodiments a tertiary coil may be formed on the support 211 on a side opposite the secondary coil and used in conjunction with the primary coil. This forms a multiple tuned transformer coupling.
While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A”, or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”
