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 the emergence of wireless, wafer-based plasma measurement probes, it has become possible to obtain virtually noninvasive, in-situ measurements of actual physical and electrical properties of a plasma within an operational plasma processing environment. 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 transceiver receives and transmits the sensor data outside of the plasma processing environment for further processing and analysis. Diagnostic sensors 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. Further description of the operation and utility of exemplary plasma wafer probe devices is presented in U.S. patent application Ser. No. 10/194,526, assigned to the assignee of the instant application.
To obtain in-situ measurements within a plasma process, a wafer-based plasma probe must be resilient to the harsh environment of a plasma processing system, which may include conditions such as excessive heat, corrosive chemicals, bombardment by high energy ions, and high levels of electromagnetic and other radiative noise. International Patent Appl. No. WO 02/17030 describes one approach for isolating and shielding electronic components of a wafer-based plasma probe from process conditions. A cavity is provided in the wafer substrate for placement of the information processor, internal communicator, and power source of the device. An electromagnetic shield is placed around the components, and a substrate cover is disposed so as to cover the cavity for protection of the electronic components within. Hermetic sealing of the cover to the substrate is described to prevent the escape of contaminants from the cavity into the process environment.
As an alternative to trenching a protective cavity into the silicon wafer, electronic components of a diagnostic plasma probe may be deployed upon the substrate within a protective package having insulated electrical connections, as described for example in U.S. application Ser. No. 10/194,526. For wafer diagnostic 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. A plasma probe engineered for enhanced manufacturability must nevertheless continue to have acceptable performance and operational life in the harsh process environment, while adhering to structural and dimentional constraints imposed by the workpiece mounting and transfer mechanisms of the process apparatus. Materials used in the construction of a diagnostic probe must also 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.
This invention provides techniques for the configuration, packaging, and encapsulation of components of plasma measurement probe devices. A measurement probe of the invention generally comprises a primary substrate with sensor devices disposed about the surface of the probe. An electronics module contains electronic components or other elements of the diagnostic probe that require isolation and shielding from process conditions. The electronics module is disposed upon the probe substrate and electrically connected to the remote sensor devices through one or more electrical interconnection layers disposed upon the substrate.
In one embodiment of the invention, an electronics module comprises electronic components including one or more of a microprocessor, data storage (RAM), ROM, multiplexer, A/D and D/A converters. An electrostatic shield is incorporated into the electronics module, which is prefabricated and hermetically sealed as a unit. Using a pliable adhesive, the electronics module is mounted to the surface of a wafer-based diagnostic device. Because the electronics module of the embodiment is hermetically sealed, no further sealing or encapsulation of the electronic components is required.
In one embodiment of the invention, the electronics module is electrically connected to the remote sensors and other components of the measurement probe device using flexible wirebond connections. To protect the wirebonds from ionic or chemical attack, an encapsulant is applied over the wires and bond points. In other embodiments, the electrical connections are made by direct bonding of the electronics module to an electrical interconnect layer of the probe device disposed upon the primary substrate. The electronics module may be directly bonded as a hermetically sealed unit, or alternatively may be bonded without a sealed housing and then covered with a high purity encapsulant.
Further integration is accomplished in certain embodiments of the invention by fabricating the electronics module directly on the wafer substrate, or by incorporating functions of discrete electronic components into one or more Application Specific Integrated Circuit (ASIC) devices. An electronics module comprised of one or more ASIC devices is directly bonded to an electrical interconnect layer of a probe device of the invention and encapsulated. Electrostatic shielding is provided by a Faraday cage in the form of a sealed housing, for example, or alternatively by a thin film electrostatic coating applied in addition to the encapsulant layer.
By integrating and modularizing the electronic components of a sensor probe, the invention serves to reduce part count, simplify fabrication and increase function and reliability of the completed sensor device. As a result, the sensor probe design may 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. The use of hermetic housings and/or augmenting encapsulants to protect onboard electronics eliminates the risk of attack from reactive chemicals present in harsh processing environments, and appropriate selection of adhesive and encapsulant materials provides stress relief during thermal cycling. The hermetic housing and/or encapsulant also provide protection to the plasma processing chamber from potential contamination, chemical or otherwise, that may originate from the electronics circuit or components themselves. Incorporation of electrostatic shielding in the electronics module provides noise immunity to the circuit and facilitates package construction. The configuration, packaging, and encapsulation techniques of the invention thus provide for enhanced durability and manufacturability of diagnostic plasma probes for operation in increasingly harsh process environments.
When configured upon a silicon wafer primary substrate, diagnostic probes of the invention are ideally suited for measuring in-situ plasma properties in semiconductor fabrication processes. The device and technology are also suitable for use in other plasma applications and process environments. For example, the described electronics package and accompanying sensors of the invention may be mounted upon typical substrates employed in the production of flat panel displays, architectural glass, storage media, and the like. These substrates 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.
Plasma 120 is ignited to perform an etching or deposition process on the surface of the wafer, at which time the apparatus sensors and microprocessor are activated 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 122 is used to communicate data and instructions with a base station transceiver 124 outside the plasma processing system. The base station transceiver 124 allows for communication of data and instructions between the software of the external computer 126 and the probe 10 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.
Disposed upon the surface of probe 10 is an electronics module 30. In
A hermetically isolated electronics module such as that depicted in
Contained within ceramic substrate 32 is an embedded electrical interconnect 42 for electrical connectivity among electronic components 40. Electrical interconnect 42 is terminated at a point outside the module housing allowing for electrical wirebonding 44 to connect the components of electronics module 30 to the remote sensors or other components of the probe 10 through interconnect layer 16. Compared with a rigid solder joint, for example, wirebond 44 provides a flexible connection that is more tolerant of stresses due to thermal expansion and contraction imposed by the plasma environment. To protect wirebond 44 from ionic or chemical attack, an encapsulant 46 is applied over the wires and bond points. Encapsulant 46 is a material such as Parylene or other high purity polymer or silicone, or any material of sufficient purity that is compatible with the chemical and thermal environment of the plasma and the thermal expansion cycles of the substrate.
Substrate 32 of electronics module 30 has an embedded electrical interconnect with terminals 52 at locations corresponding to attachment points 50. Using for example a ball solder or wave solder technique, terminals 52 are directly bonded to attachment points 50. The direct bonding of terminals 52 to attachment points 50 connects electronics module 30 electrically as well as mechanically to the surface of probe 10. Alternatively, mechanical bonding of the module may be supplemented with a pliable adhesive. To protect the direct bond junctions from chemical attack in the plasma environment, an underfill 54 is provided using a high purity material, such as an epoxy or other polymeric material, for encapsulation of the solder bonds.
In an alternative embodiment of the invention, the hermetic housing and underfill of the embodiment of
Further integration of wafer probe electronics can be accomplished by incorporating functions derived from discrete components into one or more Application Specific Integrated Circuit (ASIC) devices.
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.