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  System and method for low temperature plasma enhanced bondingUSPTO Application #: 20070272349Title: System and method for low temperature plasma enhanced bonding Abstract: A method for bonding a plurality of substrates includes performing a gas plasma treatment on the plurality of substrates, and performing a water plasma treatment on the plurality of substrates. Additionally, a system for performing low temperature plasma enhanced bonding includes a substrate housing structure having a substrate receiving volume, a gas source fluidly coupled to the substrate housing structure, a water vapor source fluidly coupled to the substrate housing structure, and a radio-frequency (RF) generator coupled to the substrate housing structure, wherein the system is configured to perform both a gas plasma treatment and a water plasma treatment on a substrate. (end of abstract) Agent: Hewlett Packard Company - Fort Collins, CO, US Inventors: Chien-Hua Chen, Paul F. Reboa, Tracy B. Forrest USPTO Applicaton #: 20070272349 - Class: 156272200 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070272349. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] A number of bonding techniques are known for joining semiconductor substrates including intermediate-layer bonding (such as adhesive, glass frit, or solder), anodic bonding, thermal compression bonding, fusion bonding, etc. The selection of a bonding technique to be used for specific substrates may vary depending on thermal budget, hermeticity requirements, properties of the bond interface, and so on. [0002] Fusion bonding can join two substrates without an intermediate layer; however, fusion bonding includes using high annealing temperatures that approach 900 degrees Celsius to achieve good bond strength. Due to the high temperature requirement, fusion bonding is limited to a few niche applications such as silicon-on-insulator (SOI) substrate fabrication, limited MEMS assembly, etc. The high temperatures used in fusion bonding is not compatible with complementary metal oxide semiconductor (CMOS) devices. [0003] In contrast to fusion bonding, plasma-activation of semiconductor bonding surfaces enables direct covalent bonding at significant lower temperatures and has found applications from silicon-on-insulator (SOI) substrate fabrication to 3-dimensional substrate stacking. The traditional plasma surface activation process involves polished bond interfaces receiving a brief O.sub.2 or N.sub.2 plasma treatment followed by a wet-dip process in a standard clean one (SC1) or de-ionized water bath. The post-plasma wet dip process step increases the bond strength of the plasma enhanced bonding. Unfortunately, the post-plasma wet-dip process is not compatible with most MEMS devices or substrates that include desiccants which cannot generally be exposed to water. More specifically, the traditional post-plasma wet-dip process increases the likelihood of problems in the MEMS due to stiction. [0004] One alternative to the traditional post-plasma wet-dip process is to hydrate the plasma treated interface by exposing it to ambient for an extended period of time. However, this approach in general is difficult to control and the bond interface can react with contaminants in air which degrade the bonding surface energy. SUMMARY [0005] A method for bonding a plurality of substrates includes performing a gas plasma treatment on the plurality of substrates, and performing a water plasma treatment on the plurality of substrates. [0006] Similarly, a system for performing low temperature plasma enhanced bonding includes a substrate housing structure having a substrate receiving volume, a gas source fluidly coupled to the substrate housing structure, a water vapor source fluidly coupled to the substrate housing structure, and a radio-frequency (RF) generator coupled to the substrate housing structure, wherein the system is configured to perform both a gas plasma treatment and a water plasma treatment on a substrate. BRIEF DESCRIPTION OF THE DRAWINGS [0007] The accompanying drawings illustrate various embodiments of the present system and method and are a part of the specification. The illustrated embodiments are merely examples of the present system and method and do not limit the scope thereof. The summary as well as other features and aspects of the present system and method will become apparent upon reading the following detailed description and upon reference to the drawings in which: [0008] FIGS. 1A and 1B are side views of simple block diagrams illustrating the components of exemplary MEMS configurations, according to a number of exemplary embodiments. [0009] FIG. 2 is a block schematic illustrating a plasma processing system, according to one exemplary embodiment. [0010] FIG. 3 is a simple block diagram illustrating a method for bonding substrates using low temperature plasma activation and hydration, according to one exemplary embodiment. [0011] FIG. 4 is a side view of a plurality of substrates being joined in a bond tool, according to one exemplary embodiment. [0012] FIGS. 5A through 5C are chemical structures illustrating a reaction that occurs at a bonding interface, according to one exemplary embodiment. [0013] Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. DETAILED DESCRIPTION [0014] The present specification describes a system and a method for low temperature plasma-enhanced bonding of substrates. More specifically, the present system and method provide for plasma treating and bonding two or more substrates in ambient without a wet treatment. In addition to performing an O.sub.2 or N.sub.2 plasma treatment on the substrates to be bonded, a few mono-layers of water are also deposited by a low-power water plasma treatment, thereby eliminating the need for a post plasma wet dip process. The following specification and claims disclose exemplary embodiments for performing the above-mentioned system and method. [0015] As used in this specification and the appended claims, the term "Micro-Electro Mechanical System" or "MEMS" is meant to be understood broadly as describing any very small (micro) mechanical device that may be constructed on one or more semiconductor chips and which may be fabricated using integrated circuit (IC) batch-processing techniques. MEMS may be broadly classified as sensors, actuators, a combination of sensors and actuators, or added circuitry for processing or control. For the purposes of present specification and appended claims, the term MEMS is meant to refer to any of the above-mentioned classes. [0016] Additionally, as used in the present specification and in the appended claims, the term "desiccant" is meant to be understood as referring to any substance that promotes drying, including, but in no way limited to, calcium oxide. A desiccant is often included in MEMS to prevent the accumulation of moisture which may result in stiction of the individual MEMS components. [0017] "Stiction" is one of the key causes of low yield in the fabrication of MEMS devices and is believed to result from a number of sources, some of the most significant being capillary forces, surface contaminants, van der Waals forces, and electrostatic attraction. Factors which may contribute to stiction include, but are in no way limited to, high surface tension liquids like water that induce collapse of nearby surfaces through large capillary forces. [0018] In the following specification, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present system and method for performing low temperature plasma-enhanced bonding of substrates. It will be apparent, however, to one skilled in the art, that the present method may be practiced without these specific details. Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearance of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment. Exemplary Structure [0019] FIGS. 1A and 1B illustrate a number of exemplary MEMS structures that include one or more bonded interfaces. As illustrated in FIG. 1A, an optical MEMS structure (100) may include a base substrate (145) supporting a number of elements, such as contact pads (125), an electrode (140), a pixel plate (135) disposed adjacent to the electrode, and a tetraethylorthosilicate silicon-oxide (TEOS) member (120) formed on the base substrate. A bond material (115) and a glass lid (110) are bonded to the TEOS member (120). Additionally, an anti-reflective coating (105) may be formed on the glass lid (110) to enhance the optical properties of the MEMS device (100). FIG. 1A also illustrates a dielectric plug (130) disposed in the TEOS member (120) to prevent moisture from contacting and affecting the internal components of the MEMS structure (100) such as the pixel plate (135). As illustrated in FIG. 1A, a number of the MEMS structure (100) components are bonded together, and consequently, will benefit from the present system and method. Continue reading... Full patent description for System and method for low temperature plasma enhanced bonding Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this System and method for low temperature plasma enhanced bonding patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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