Abstract:
Microwave radiation, perhaps with microwave absorbing materials, is utilized to provide heating of partially formed integrated circuits in a variety of circumstances.

Description:
TECHNICAL FIELD 
     This invention relates to methods for fabricating integrated circuits. 
     BACKGROUND OF THE INVENTION 
     Typical integrated circuit manufacturing processes utilize many steps in which a wafer is heated. Wafer heating may be performed to: activate dopants, initiate silicidation reactions, flow dielectrics, etc. 
     In the past, wafer heating was accomplished by placing the wafer in a furnace for a predetermined period of time or else by subjecting the wafer to a rapid thermal anneal (RTA) process. Conventional processes presents a variety of disadvantages. Furnace heating must be carefully controlled because of thermal budget considerations. RTA processing requires careful control of gas flows and cleaning of the backside of the wafer for pyrometry purposes. Those concerned with the development of integrated circuit manufacturing processes, have consistently sought improved methods of thermal processing. 
     SUMMARY OF THE INVENTION 
     These concerns are addressed by the present invention which includes subjecting a substrate having partially fabricated integrated circuits thereon to microwave radiation without generation of a plasma. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view; and 
     FIGS. 2-4 are cross-sectional views useful in understanding various embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Microwave radiation may be desirably utilized to perform a variety of thermal processes upon partially fabricated wafers. In FIG. 1, reference numeral 11 denotes a microwave oven. Reference numeral 13 denotes a source of microwave power, which may be typically a klystron, magnetron, etc. 
     In FIG. 2, reference numeral 15 denotes a silicon wafer which may have partially fabricated integrated circuits upon its upper surface 19 (the integrated circuits are not shown for reasons of clarity). A microwave- absorbing substance 17 is coated on the underside of wafer 15. By way of example, some suitable microwave absorbers are carbon and silicon nitride. (A carbon coating can be made, illustratively by coating the surface with photoresist and then charring the photoresist.) Wafer 15 together with underside coating 17 is placed within microwave chamber 11 and subjected to microwave radiation. Microwave heating of substance 17 causes a uniform heating of wafer 15 suitable for dopant activation, flowing of dielectrics etc. In general, microwave radiation is radiation with frequencies between 3 and 300 GHz. No plasma is generated. 
     In FIG. 3, reference numeral 25 represents a portion of a silicon semiconductor wafer. Region 23 of wafer 25 is n+ doped. Region 21 of wafer 25 is p+ doped. Typically, the n+ and p+ dopants have been introduced into silicon wafer 25 by ion implantation. If it is desired to active the p+ dopants, a patterned layer of microwave absorbing material 17 may be positioned adjacent the p+ material. Then the structure of FIG. 3 is placed within cavity 11 and subjected to microwave radiation. The radiation is preferentially absorbed by patterned absorber 17, thereby causing activation of the p+ dopants without a similar effect upon the n+ dopants. 
     In FIG. 4, reference numeral 31 denotes a silicon substrate 31 with a gate structures 33 formed thereon. Dielectric 35 covers gate structures 33 and silicon substrate 31. (Source and drain regions are not shown.) Reference numeral 37 denotes a metal layer, such as aluminum or tungsten. Layer 37 is covered by flowable dielectric 39 which may be typically a doped glass or silicon dioxide, such as glass formed from TEOS, commonly denoted BPTEOS. The structure of FIG. 4 may be subjected to microwave radiation, thereby causing flow of dielectric 39. (If necessary, dielectric 39 may be coated with a microwave absorbing substance such as that denoted by reference numeral 17 in FIGS. 2 and 3 before flowing.) 
     Microwave radiation may be also utilized to dry or remove unwanted moisture from wafers. Conventional wafer drying techniques rely upon the drying of wafers using centrifugal properties of a dryer together with a heat sink to remove water from the wafers. Wafers may be dried by placing them in a microwave oven with or without the present of microwave absorbing coatings. 
     Depending upon the particular embodiment, microwave power and heating time, together with the frequency of microwave radiation may be adjusted. The frequency of the microwave radiation may be adjusted or tuned to match resonances in the microwave absorbing material 17. Appropriate tuning and filtering may be accomplished by those of skill in the art. Dopants may be introduced into various semiconductor substrates by introducing appropriate dopant containing gases through pipe 51 into cavity 11 during microwave heating.