The semiconductor or integrated circuit (IC) industry aims to manufacture ICs with higher and higher densities of devices on a smaller chip area to achieve greater functionality and to reduce manufacturing costs. This desire for large scale integration requires continued shrinking of circuit dimensions and device features. The ability to reduce the size of structures, such as, trenches, contact holes, vias, gate lengths, doped regions, and conductive lines, is driven by lithographic performance.
IC fabrication often utilizes a mask or reticle to form an image or pattern on one or more layers comprising a semiconductor wafer. Electromnagnetic energy such as radiation is provided or reflected off the mask or reticle to form the image on the semiconductor wafer. The wafer is correspondingly positioned to receive the radiation transmitted through or reflected off the mask or reticle. The radiation can be light at a wavelength in the ultraviolet (UV), vacuum ultraviolet (UV), deep ultraviolet (DUV), or extreme ultraviolet (EUV) range. The radiation can also be a particle beam such as an x-ray beam, an electron beam, etc.
Typically, the image on the mask or reticle is projected and patterned onto a layer of photoresist material disposed over the wafer. The areas of the photoresist material upon which radiation is incident undergo a photochemical change to become suitably soluble or insoluble in a subsequent development process. In turn, the patterned photoresist layer is used to define doping regions, deposition regions, etching regions, and/or other structures comprising the IC.
As integrated circuit device dimensions continue to shrink to increase the speed and density of devices, it becomes necessary to print contact hole and via features as well as gate and trench features with dimensions that are smaller than the resolution limit of conventional lithographic techniques. Sub-lithographic patterning of gate conductors is extremely difficult because of mask error enhancement factor (MEEF). MEEF increases as the exposure wavelength decreases. In general, lithographic resolution (w) is governed by three parameters: wavelength of light used in the exposure system (λ), numerical aperture of exposure system (NA), and a k1 factor which is a measure of the level of difficulty of the process. Lithographic resolution can be defined by the following equation:   w  =            k      1        ⁢          λ      NA      
Resolution can be improved by an improvement in any of these factors or a combination of these factors (i.e., reducing the exposure wavelength, increasing the NA, and decreasing the k1 factor). However, reducing the exposure wavelength and increasing the NA are expensive and complex operations.
Sub-lithographic resolution has been achieved using photoresist modification processes. Conventional photoresist modification processes typically pattern the photoresist in a conventional lithographic process and use chemical or heat procedures after development of the photoresist to reduce the size of the patterned features. One such process is the chemical amplification of resist lines (CARL) process developed by Siemens Corporation. In the CARL process, a liquid chemical is applied over the line features, resulting in a chemical reaction between corresponding chemical moities in the resist lines and the liquid chemical. This leads to swelling of the lines and a decrease in the width of the spaces between the line. During plasma etching, the width of the space transferred down into the underlying substrate is thus effectively reduced. Another such process is a heat reflow process, in which photoresist is partially liquified to reduce the distance between photoresist line spaces. Yet another such process reduces feature sizes by chemical etching.
Processes which manipulate the photoresist pattern after it is formed can be susceptible to unpredictable mechanical deformation as well as poor mechanical stability. For example, mechanical deformations can be caused by capillary forces, inadequate inherent mechanical stability, and/or the impact of etch and species. Accordingly, there is still a need to increase the resolution available through lithography.
Thus, there is a need to improve the resolution of lithography by decreasing the k1 factor. Further, there is a need to achieve sub-lithographic patterning of gates and conductive lines. Further still, there is a need to reduce feature sizes without the use of heat flow and/or processes. Further still, there is a need for an inexpensive process for improving (reducing) the size of gate features which can be lithographically patterned. Yet further, there is a need to lithographically pattern photoresist using lower doses of radiation.