Patent Application
20050284570
1. Field of the Invention
This invention relates generally to the field of plasma processing, and more particularly to devices for in-situ measurement of plasma properties within a plasma processing system.
2. Brief Description of the Prior Art
With recent developments in the technology of in-situ plasma metrology, it has become possible to obtain virtually noninvasive measurements of actual physical and electrical properties of a plasma within an operational plasma processing environment. For example, a wireless diagnostic plasma probe may comprise sensor devices disposed upon a substrate body that is comparable in physical structure and dimensions to a standard process workpiece, as for example a semiconductor wafer. An onboard power source may be provided, as well as electronic components for collecting, processing and storing data received from the sensors. A wireless communication interface receives and transmits the sensor data outside of the plasma processing environment for further processing and analysis. Further description of the operation and utility of exemplary plasma wafer probe devices is presented in U.S. Patent Application No. 10/194,526, assigned to the assignee of the present application.
Diagnostic plasma sensors may also be disposed at fixed locations within a plasma processing system itself. For example, plasma sensor devices may be disposed along a portion of the chamber liner of a vacuum processing system, about the dielectric isolation ring or gas injection ring of the chamber, or upon a portion of a substrate holder or “chuck.” In-situ sensor arrays may obtain diagnostic data, such as ion current flux and effective electron temperature, from multiple locations about the boundary of the plasma body for use in deducing the global or spatial properties of the plasma. Further description of the operation and utility of exemplary in-situ plasma sensor arrays is presented in U.S. patent application Ser. No. 10/640,892, owned by the assignee of the present application.
Sensors disposed upon a diagnostic plasma probe may include devices that measure thermal, optical, and electromagnetic properties of the process environment, and ideally include sensors such as dual floating Langmuir probes that can measure physical and electrical properties of the plasma itself without disturbing the properties being measured. In a typical diagnostic probe, sensors may be modular sub-components mounted onto a discrete circuit substrate such as a ceramic or high temperature thermal plastic. Sensor modules are then bonded to the surface of the wafer probe using, for example, a stress relieving adhesive. Alternatively, sensors may be fashioned as diced chips and bonded to the base wafer using flip-chip bonding techniques. U.S. Pat. No. 5,444,637 describes a programmable semiconductor wafer having sensors formed lithographically upon the wafer substrate.
Output leads of sensors may be connected by wirebond or similar technique to conductive interconnection paths between the sensors and the onboard processing electronics and power source of the wafer probe. Electrical interconnection paths may be formed using silver paint or a silk-screened conductive paste, for example, or alternatively by patterning techniques used in the manufacture of integrated circuits. Materials used in the construction of sensors and sensor modules, as well as those used for adhering and electrically bonding sensors to the probe surface, must all be compatible with and tolerant of the processing environment such that the use of the plasma probe does not result in either physical or chemical contamination of the processing chamber, or of material subsequently processed in the processing chamber.
For diagnostic plasma measurement probes to be cost effective for high-volume commercial applications, such as in the manufacture of semiconductor devices, it should be possible to mass produce probes for use in large quantities as consumable articles. To this end, a diagnostic probe having a simplified and standardized design with minimal part count would be advantageous. It would be further desireable to utilize manufacturing techniques having reduced risks of product contamination. It would be further desirable to provide enhanced flexibility in customizing or modifying the elements and interconnections of a diagnostic probe for differing applications.
This invention provides a diagnostic plasma measurement device having sensors and features disposed using pattern transfer fabrication techniques. A measurement device of the invention generally comprises a primary substrate with sensors for measuring plasma or surface properties disposed by stepped pattern transfer about the surface of the probe. Electrical interconnections are provided between the sensors and power, communications, and processing and control elements of the measurement device.
In one embodiment of the invention, a diagnostic plasma probe comprises a plurality of sensor fields patterned upon a silicon wafer substrate using step-and-repeat photolithography. Sensor fields include sensors that measure physical and electrical properties of a plasma, as well as sensors that measure properties of the wafer surface. In a preferred embodiment, multiple sensor types are combined into a single field that is patterned repeatedly across the wafer surface. The wafer-based probe is introduced into a plasma processing environment and the sensors and processing electronics of the probe are activated to collect data relating to surface or plasma properties. The probe is fitted with an on-board wireless transceiver system for communication of data and instructions with a base station transceiver outside the plasma processing system.
Embodiments of the invention include integrated diode temperature sensors disposed by pattern transfer upon a substrate of a diagnostic plasma probe device. Embodiments of the invention also include plasma property sensors such as dual floating Langmuir probes disposed by pattern transfer for measurement of ion current flux and apparent electron temperature of the plasma. Additional plasma or substrate sensors disposed by pattern transfer in accordance with the invention include electrostatic charge sensors, optical emission and photo sensors, surface acoustic wave sensors for measuring pressure, film thickness and deposition rates, and the like. In certain embodiments of the invention, sensor pads are protected from the corrosive plasma environment with plugs of corrosion resistant conductive materials applied using for example a damascene process.
The invention also features electrical interconnections disposed by pattern transfer techniques. In one embodiment of the invention, electrical interconnection fields in addition to sensor fields are disposed by pattern transfer upon the substrate of a wafer-based plasma probe. Electrical interconnection fields comprise conductive pathways for electrical connection of sensor fields to probe electronics and power source. By employing field stitching techniques in the lithographic processes used to create the sensor and interconnection fields, the conductive pathways overlap and electrically connect to interconnection leads of the sensor fields, or to the conductive pathways of other interconnection fields. By creating electrical interconnections as well as sensors of a plasma probe device by pattern transfer techniques, manufacture of the probe device may largely be performed on any modern integrated circuit (IC) production line, and may be modified to suit the requirements of particular applications or users.
In another embodiment, electrical interconnections on a diagnostic probe device are provided by an overlayed wafer-level interconnection field. In one example, the interconnection field is disposed using wafer-level pattern transfer operations upon a wafer having sensor fields previously disposed by step-and-repeat photolithography. The interconnection field comprises conductive pathways for electrical connection of interconnection leads of the sensor fields to electronics and power source of the probe. In a preferred embodiment, the wafer-level lithographic operations also provide elements of additional plasma or surface sensors. In this approach, the advantages of mass production of die in a traditional IC manufacturing environment are combined with the simplicity and selectivity of wafer-scale pattern transfer techniques.
Further embodiments of the invention comprise photovoltaic power elements disposed by pattern transfer techniques. The photovoltaic power elements collect and convert radiant energy to electrical energy for use by sensors and electronics of a diagnostic probe device. Photovoltaic elements may be optimized for conversion of ambient light for recharging an onboard energy reservoir of the probe, or of plasma radiance for supplementing the power demands of the sensors and electronics of the probe during their operation. Use of photovoltaic power fields can lessen reliance upon a modular power source such as a battery adhered onto the substrate surface. As a result, the height, weight, and center of mass of an in-situ plasma probe can be better optimized for compatibility with multiple plasma processing platforms.
In accordance with further embodiments of the invention, logic, processing, communications, and other electronic components and circuitry of a plasma probe device are disposed by pattern transfer techniques. By patterning electronics of the probe in proximity to sensor fields, noise and power loss in the circuits may be substantially reduced. Disposition of these additional features by pattern transfer operations also improves flexibility and reliability of the design while further reducing part counts, size and cost.
The invention includes wafer-based probe devices in which integrated sensing, processing, and wireless communication fields operate as parts of a wafer-based local area network (LAN). In other embodiments, sensor system fields disposed upon a wafer substrate are diced into sensor chips for fixed placement within a plasma processing system. In this way, for example, sensor and circuit designs may be used for both wafer-based as well as fixed, in-situ diagnostic probes while reducing die cost through economies of scale.
By utilizing semiconductor fabrications techniques, the invention generally provides reduced risk of contamination by residues of manufacturing steps not maintained at cleanliness level dictated by the IC industry. Use of stepped pattern transfer techniques serves also to reduce part count, simplify fabrication and increase function and reliability of the completed sensor device. A sensor probe design may thus be optimized for cost effective production techniques while ensuring mechanical, chemical, and thermal compatibility with the wafer or other carrying substrate and the environment to which it is exposed.
Diagnostic probes of the invention are ideally suited for measuring in-situ plasma properties in semiconductor fabrication processes. Devices and technology of the invention are also suitable for use in other plasma applications and process environments. For example, embodiments may be employed in the production of flat panel displays, architectural glass, storage media, and the like. Substrates comprising technology of the invention may include but are not limited to all semiconductor substrates (silicon, gallium arsenide, germanium or others), as well as micro machine substrates, quartz, Pyrex and polymeric substrates.
a and 6b illustrate a wafer-based plasma probe comprising sensors, interconnections, and other features disposed in accordance with another embodiment of the invention.
Plasma 34 is ignited to perform an etching, stripping, or deposition process on the surface of the wafer, at which time the apparatus sensors and microprocessor are activated or triggered to collect data relating to surface or plasma properties in close proximity to the apparatus surface in real time. An on-board wireless transceiver system 36 is used to communicate data and instructions with a base station transceiver 38 outside the plasma processing system. The base station transceiver 38 allows for communication of data and instructions between the software of the external computer 40 and the probe 100 in real time. Alternatively, it is possible to have the probe collect information inside the process and then download data once it is removed from the process chamber.
In accordance with the present invention, sensors 110 are disposed by stepped pattern transfer upon substrate 102. In one approach, images corresponding to the features of sensor fields are contained within sets of photolithographic masks. A photomask is mounted upon an imaging reticle, and the image of the mask is exposed onto a photoresist layer sequentially across the wafer surface using for example a step-and-repeat or step-and-scan projection printing technique. The photoresist is developed, leaving resist patterns that define and limit areas affected by subsequent etching, implantation, or other operations performed upon the wafer. The image of a succeeding photomask of the mask set is exposed upon a subsequently applied photoresist layer so as to overlay the preceding image, followed by additional feature-building operations upon the wafer. This sequential layering process continues until the fabrication of all features of the sensor fields is complete. While use of a photolithographic technique is described in connection with the present embodiment, other techniques such as soft lithography, ink jet lithography, or other forms of “direct write” lithography may be employed for pattern transfer of sensors and features of the invention.
To obtain a temperature measurement, two unique scaled currents I1 and I2 from the probe controller sequentially bias the temperature diode. The two resulting forward diode voltages are measured and subtracted by the controller to create a difference voltage ΔVf. The difference voltage represents an accurate, process independent relationship to absolute wafer temperature T according to the relationship:
T=ΔVf* q/[k*ln(I2/I1)]
where q is electron charge and k is the Boltzmann constant. Calibration of the bias current ratio at the controller is required to insure the accuracy of the overall temperature sense function. In a preferred embodiment of the invention, a diode current ratio of 10:1 (for example, I1=5 μA and I2=50 μA) results in a difference voltage of 59.6 mV when the diode is at 27° C. Other diode current ratios can be selected in order to increase the measured difference voltage at the temperature diode such as might be necessary to optimize the resolution of a measured wafer temperature, as well as to reduce signal-to-noise in the related A/D measurement circuitry.
In alternative embodiments of the invention, recesses created in an outer passivation layer, such as those depicted in the foregoing embodiment, are filled with plugs of corrosion resistant conductive materials. For some processing applications, the aluminum conductive pads of a sensor are quickly eroded by the application chemistries, as for example in metal or polysilicon etch operations using chlorine, bromine boron tri-chloride, or other corrosive gases. A variety of metals, including tungsten, palladium, platinum, molybdenum, and nickel, have significantly greater resistance to these corrosive chemistries. After forming a recess to expose a sensor pad, such as the recesses 230 shown in
In a preferred embodiment of the invention, an integrated sensor field combines a diode temperature sensor, a DFP sensor, and an electrostatic charge sensor within the field. The integrated sensor field is replicated across the surface of a wafer diagnostic probe using a step-and-repeat pattern transfer technique. Electrical interconnections are provided between some or all of the sensors of the repeated integrated sensor fields and the electronics and power source of the probe.
Sensor probes of the invention may comprise sensors of any type and number as may be desired to provide spatial and temporal characterization of various plasma or substrate properties, as described for example in U.S. application Ser. Nos. 10/194,526 and 10/640,892. Additional plasma or substrate sensors that may be disposed by pattern transfer in accordance with the invention include electrostatic charge sensors, optical emission and photo sensors, surface acoustic wave sensors for measuring pressure, film thickness and deposition rates, and the like. A diagnostic sensor probe in accordance with the invention may include additional sensors disposed by any means.
Referring again to
By creating electrical interconnections as well as sensors of a plasma probe device by pattern transfer techniques, manufacture of the probe device may largely be performed on any modem integrated circuit (IC) production line. Manufacturing the probe device in an IC fabrication facility can result in significant production efficiencies and cost savings, as well as reduced risks of contamination from equipment or processes not maintained at the cleanliness level dictated by the IC industry. The approach also provides flexibility in that individual pattern modules may be modified or added without the need to remake the entire mask set for the product. The patterning of routing and interconnect fields may also be modified to suit the requirements of particular applications or users, improving utility and reducing the costs of customization. “Open” fields, or those having electrical attachment points, provide further flexibility for add-on components, such as remote power modules, third-party sensors, or other electronics.
a and 6b illustrate an alternative embodiment of the invention having sensors and interconnections disposed by hybrid pattern transfer techniques. Diagnostic probe 100 comprises temperature diode sensor fields 111 disposed across substantially the entire surface of probe substrate 102 by step-and-repeat photolithography. Each sensor field 111 comprises an integrated temperature diode sensor such as that described in connection with the embodiment illustrated in
Electrical interconnections are disposed upon probe substrate 102 by overlayed interconnection field 140. In a preferred embodiment, interconnection field 140 is disposed using wafer-level photolithographic pattern transfer operations upon a wafer having temperature diode sensor fields 111, or other sensor fields, previously disposed thereupon. Interconnection field 140 comprises conductive pathways 142 for electrical connection of electrical interconnection leads of sensor fields 111 to electronics and power source of probe 100. Alignment marks are provided in interconnection field 140 for alignment of the wafer-level interconnection field mask to the underlying sensor circuits and interconnection leads. Additional alignment marks are also provided in sensor fields 111 to define module-to-module locations and layer-to-layer placement during stepper exposure operations.
Interconnection field 140 further comprises elements of additional sensors for measurement of plasma or substrate properties. Interconnection field 140 further comprises a plurality of DFP sensor pads 144 and a plurality of differential voltage probe pads 148. Circular DFP sensor pads 144 are metallic disks approximately 1.5 mm in diameter. Common DFP pad 146 serves as a collection pad for each of DFP pads 144, such that each of DFP pads 144 and common pad 146 operates as a DPF sensor that senses electrical properties of the plasma as between each of DFP pads 144 and common pad 146. Metallic DFP pads 144 are disposed so as to shield underlying temperature sensor diodes from ultraviolet radiation emitted from the plasma that would otherwise degrade performance of the diodes. Charge sensors 148 for measurement of electrostatic field patterns across the wafer surface are disposed as metallic pads adjacent to DFP pads 144. A sensor ground reference is provided as a ground bus (not shown) routed about the edge of interconnection field 140.
While retaining the advantages of manufacturing the probe device on modern IC production lines, use of hybrid pattern transfer techniques results in additional advantages. A variety of sensor technologies may be incorporated into a sensor field that is patterned economically in large numbers across substantially the entire surface of a probe substrate. With the sensor fields already thus disposed, an interconnection field may be designed and disposed in a separate lithographic process that selectively interconnects any or virtually all of the sensors to the electronics and power source of the probe device. In certain embodiments of the invention, the overlayed interconnection field comprises common power, ground bus, and control lines to which any or all of the previously patterned sensors may be interconnected. The wafer probe architecture and functionality may thus be tailored to different processes, tools, and user preferences, providing adaptibility and flexibility. To add or remove sensors, the interconnection pattern of the probe may be updated without having to modify the entire sensor mask set. Alternatively, sensor fields may be improved or updated while retaining the same wafer-level interconnection pattern.
An exemplary photovoltaic cell comprises a shallow p-n junction formed using standard IC manufacturing techniques upon the surface of wafer probe 100, and which converts incident photons to photoelectric power. A basic discussion of the physics and operation of photovoltaic devices appears in Sze, Physics of Semiconductor Devices, pp. 790-838 (1981). A photo-transparent protective overcoat (not shown), such as SiO2 or a polyimide resist material, is disposed to protect the photovoltaic cells from the plasma environment. A DC-DC regulator with associated current switching electronics is provided adjacent to each photoelectric cell for filtering and regulation of power generated by photocells to voltage and current levels required by probe sensors and electronics. Photoelectric cells are optimized for power conversion of either ambient lighting or photo emission from the plasma. By way of example, energy conversion efficiency of a photoelectric cell may be optimized for a given spectral irradiance by engineering the device band-gap characteristics of the device or by incorporating a multi-layer, thin-film anti-reflection coating which improves transmission of various spectra to the active junction of the photoelectric cell(s). Referring to
As illustrated in
In other embodiments of the invention, photovoltaic cells distributed about a wafer probe provide power locally to sensors, or groups or clusters of sensors that have been spatially patterned across the wafer.
A further embodiment of the invention comprising both sensors and probe electronic elements disposed by pattern transfer techniques is illustrated in
As illustrated in
Integrated system fields 170 function as Application Specific Integrated Circuit (ASIC) devices that perform high level sensing, computing, data storage, logic, and power management functions, reducing or eliminating need for these electronics in a centralized electronics module or elsewhere on the wafer. In the embodiment illustrated in
In yet other embodiments, sensor system fields are compartmentalized into separate sensor, power, logic, and communication fields that are interconnected to form complete system fields. Referring to
The invention includes wafer-based probe devices in which sensor system fields, such as those of the aforementioned embodiment, are interconnected into a wafer-level probe architecture. Alternatively, the sensing and wireless communication functions of system fields operate independently as part of a wafer-based local area network (LAN). In this embodiment, rather than transmitting measurement data through a central communication module, each system field or “die” has the ability to broadcast and receive communications independently. Each die on the wafer is assigned a unique address or other identifier during initialization of the probe device. A base station, either internal or external to the plasma environment, polls each die and receives transmissions of sensor data measured locally to the die, using for example a standard IEEE 802.11 protocol. The individual system fields of the wafer probe thus operate as a sensor network to provide spatially resolved measurements of surface and plasma properties across the wafer surface and throughout the plasma environment.
In another application of the invention, sensor system fields disposed upon a wafer subsrate are diced into sensor chips for fixed placement within a plasma processing system.
The outputs 238 and 240 of the sensor arrays are connected to an external electronic subsystem 242 that houses the stimulating electronics, multiplexer, data acquisition and microprocessor controls for the apparatus. The output 244 of the electronic subsystem 242 is then communicated to a central processor or computer 246. Since the sensor apparatus can be operated during an actual process, the central processor or computer 246 can use the data from the apparatus to monitoring the process conditions and to provide real-time feedback and control signals to various inputs to the plasma processing system. The electronic subsystem 242 may be a separate box, a special micro-electronics add-in card associated with another piece of electronic hardware or computer 248.
Referring to
Diagnostic sensor arrays 212 further comprises an electronics module 213 having communications, power, and processing and control circuitry interconnected to sensor elements 211. Electronics module 213 also comprises a wireless communication interface and processing electronics disposed to operate as a base station for polling and receiving sensor data from a wafer-based diagnostic probe. Undiced wafer-based diagnostic probe 236, configured as a wireless sensor LAN, is introduced into the plasma processing environment as illustrated in
Although there is illustrated and described herein specific structure and details of operation, it is to be understood that these descriptions are exemplary and that alternative embodiments and equivalents may be readily made by those skilled in the art without departing from the spirit and the scope of this invention. Accordingly, the invention is intended to embrace all such alternatives and equivalents that fall within the spirit and scope of the appended claims.
