Abstract:
A laser-assisted direct imprint process enables direct transfer of patterns on a contact mold to molten semiconductor material. During the pattern transfer, sonic energy may be applied to improve the efficacy of the pattern transfer.

Description:
BACKGROUND 
     This invention relates generally to the manufacture of semiconductor integrated circuits. 
     It is generally desirable to transfer a pattern repeatedly to a semiconductor wafer in the course of semiconductor manufacturing. Conventionally, this is done using processes involving lithography and etching. However, lithography and etching may tend to be relatively expensive and are limited in their resolution or throughput. Thus, there has been a demand for better ways to transfer patterns repeatedly to semiconductor wafers. 
     One such technique is called laser-assisted direct imprint (LADI). In this process, a pattern is formed on a quartz mold and the quartz mold with the pattern is pressed against a silicon substrate. An excimer laser irradiates the quartz mold. Due to the irradiation of the quartz mold, the upper surface of the silicon substrate is melted. As a result, the pattern on the mold is transferred to the molten silicon over a relatively short time period, generally less than 250 nanoseconds. After the silicon has solidified, the mold and substrate are separated. 
     LADI has been used to transfer patterns to structures with resolutions better than 10 nanometers. See Chou, Stephen Y., Keimel, Chris, and Gu, Jian, “Ultrafast and direct imprint of nanostructures in silicon,” Nature, 835-837 (2002). 
     While the techniques of laser-assisted direct imprint show considerable promise, there is still a need for better ways to transfer the pattern to the molten silicon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of one embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of the embodiment shown in FIG. 1 at a subsequent stage in accordance with one embodiment of the present invention; 
     FIG. 3 is a cross-sectional view of the embodiment shown in FIG. 2 at a subsequent stage in accordance with one embodiment of the present invention; and 
     FIG. 4 is a cross-sectional view of the embodiment shown in FIG. 3 at a subsequent stage in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Using laser-assisted direct imprint, a pattern may be transferred from a quartz contact mold  12  to a silicon wafer  10 . The quartz contact mold  12  may have a pattern  14  formed thereon which is to be transferred directly to the silicon wafer  10 . 
     A laser pulse, such as a single XeCl excimer laser pulse, may be used to heat a quartz contact mold  12  by exposure to laser irradiation, indicated as L, in FIG.  1 . In one embodiment, the laser pulse may be a 308 nanometer wavelength twenty nanosecond pulse that passes through the quartz contact mold  12 . The quartz contact mold  12  does not absorb the laser energy because it has a band gap larger than the photon energy. 
     As shown in FIG. 2, a molten layer  16  may be formed as a result of the irradiation. The molten silicon layer  16  may be about 300 nanometers deep and may remain molten for hundreds of nanoseconds in one embodiment of the present invention. Generally, the exposure to radiation occurs for a time between 0 and 250 nanoseconds in some embodiments of the present invention. 
     During this period of irradiation, the wafer  10  may be subjected to sonic energy through a sonic energy generator  20 . The sonic energy generator  20  may be a source of ultrasonic or megasonic energy. The ultrasonic source may use frequencies from 300 to 1000 kilohertz, dissipating about 5 to 10 watts per square centimeter in one embodiment of the present invention. 
     The application of sonic energy assists in providing good contact between the quartz contact mold  12  and the molten silicon  16 . For example, sonic pulses may be applied to break up surface tension forces between the mold  12  and the molten silicon  16 . In some embodiments, this may improve the uniformity during fill in of the quartz contact mold  12  with the molten silicon  16 . This may result in the ability to transfer patterns having dimensions smaller than  100  nanometers with relatively high aspect ratios, for example, greater than four to one, to the silicon wafer  10 . 
     Referring to FIG. 3 with the application of pressure, after the cessation of laser irradiation, the quartz contact mold  12  may emboss the pattern  14  into the molten silicon  16 . During this process, sonic energy is applied continuously or in a series of pulses. 
     As shown in FIG. 4, after solidification of the molten silicon  16 , the quartz contact mold  12  may be separated from the wafer  10  leaving the pattern  18  formed in the wafer  10 . 
     The same process may be applied to other materials, such as polysilicon. Thus, the same techniques may be utilized to directly pattern gates for field effect transistors. The same technique may be utilized for non-silicon based materials, such as germanium, and group III/V and II/VI compound semiconductors and dielectrics using appropriate laser wavelengths.