In various fabrication processes used in semiconductor industry, a substrate such as a semiconductor wafer may be exposed to various types of the energetic treatments (plasma, energetic particles, light irradiation etc.). An example of such a process is known as electron beam (e-beam) lithography. Electron beam lithography has been used, e.g., for writing patterns, such as electrical circuit patterns, on substrates used as masks for more conventional photolithography. In such a process, a suitably prepared surface of the substrate is supported on a horizontal moveable stage (sometimes called a stepper) and exposed to a focused e-beam, in particular a writing spot or probe of the beam.
While e-beam lithography can be used in industry for direct writing of integrated circuit features on a semiconductor wafer, the process is used mainly to generate exposure masks to be used with conventional photolithography. E-beam direct writing may also be used in applications for which it is more cost-effective to avoid the use of masks, e.g., low volume production or prototyping. In conventional direct electron beam (e-beam) writing, an intense beam of electrons from a fixed source is focused onto a point on a resist on the surface of the wafer. A stepper translates the wafer relative to the electron beam as the beam is turned on and off to produce a pattern of exposure of the resist. Due to limitations on the steppers used to translate the wafer, e-beam lithography processes in their existing configurations are too slow for economical direct writing of integrated circuit patterns on a wafer. Consequently, e-beam lithography has not been used for large volume semiconductor processing. Chip production using conventional photolithography can typically produce about 1 wafer per minute. Manufacturing the same wafer using e-beam lithography processes is expected to take 5-10 hours per wafer using conventional steppers. Thus, the production rate for e-beam lithography would have to improve by factor of about 500 in order to be competitive with conventional photolithography.
Ways to improve the speed of writing patterns on the wafer are normally associated with switching from single point writing to a parallel, multi-beam or wide beam, writing strategy. In such cases, the direct writing is associated with fast movement of the wafer relative to the position of the writing e-beam. The requirement of fast mechanical translation combined with extremely tough positioning precision requirements (e.g., 5 nm or better for the advanced states of technology) does not allow for significant physical contacts between the moving wafer stage and external objects. This imposes significant limitations in providing thermal flow management and wafer temperature stabilization.
To provide the required throughput the e-beam has to bring to the wafer about 1 Watt of energy that may cause the local wafer temperature to increase by up to 10° C. This temperature increase is usually distributed non-uniformly across the surface of the wafer. This non-uniform variation in wafer temperature distorts the wafer, introducing errors in the position of the electron beam relative to the actual wafer coordinates. For small design rules (e.g., 65 nanometers or less), such thermally induced errors can critically affect the applicability of the e-beam direct write technique. It is estimated that a wafer temperature change of about 0.001° C. can correspond an uncertainty of roughly 1 nanometer (nm) in the position of the electron beam with respect to the actual wafer surface coordinates. Consequently, a good thermal management system is required to keep the wafer at a given temperature or within a safe temperature interval. However, conventional approaches to thermal management (e.g., backside gas conduction, liquid or gas convection, liquid evaporation, etc.) are not compatible with the direct e-beam writing process conditions, e.g. high vacuum, fast, vibration-less motion, no physical contacts with the external objects for heat transfer to or from the wafer during processing.
For example, US Patent Application Publication Number 2001/0001248A1 teaches a temperature adjusting mechanism collecting heat from a driving mechanism, wherein the amount of cooling implemented by a temperature adjusting mechanism is controlled on the basis of a signal applied from a drive controlling device to the driving mechanism. However, the design of the temperature adjusting mechanism in this prior art is complicated, and particularly unsuitable for a fast moving system due to vibrations generated by the electrical wiring.
US Patent Application Publication Number 2005/0092013 A1 teaches a cooling mechanism based on vaporization of a liquid. However, this cooling mechanism requires a complicated exhausted unit, which is not suitable for performing e-beam lithography under ultra-high vacuum conditions and on a rapidly moving wafer.
Thus, there is a need in the art, for thermal management and temperature stabilization concept and a method for stabilizing the temperature of fast moving objects under ultra-high vacuum conditions that overcomes the above drawbacks.