1. Field of the Invention
The present invention relates to a novel semiconductor processing system. The invention also relates to a method for controlling the moisture level in a semiconductor process chamber. The system and method allow for accurate control of the moisture level in a semiconductor processing tool. The invention has particular applicability to the manufacture of semiconductor devices in processes employing water vapor as a process gas.
2. Description of the Related Art
Recently, several dry (i.e., vapor phase) processes employed in the semiconductor manufacturing industry have made use of water vapor as a process gas. The moisture, in the form of water vapor in the process chamber, is typically present in combination with other process gases. Such process include, for example, wet oxidation, copper chemical vapor deposition (Cu-CVD), and photoresist and post-etch residue removal processes.
In such processes, the semiconductor wafers to be treated are introduced into the process chamber of the semiconductor processing tool. The moisture can be introduced into the process chamber in liquid form, where it is subsequently vaporized, or in vapor form, for example, in a carrier gas. Alternatively, the water vapor can be formed in-situ, for example, by reaction of hydrogen (H2) and oxygen (O2) in the process chamber at elevated temperature. In all cases, however, the moisture level in the process chamber is difficult to control as a result of the large influence of adsorption-desorption phenomena taking place in the gas conduits leading up to the process chamber and/or within the process chamber itself.
In light of the foregoing, it has been found that in-situ measurement of moisture levels inside the process chamber can be a very useful tool for process development as well as in mass production to assess run-to-run process reproducibility to help ensure uniformity in semiconductor processing.
Among the analysis tools which can be used in the measurement of water vapor is a type of mass spectrometer, commonly referred to as a residual gas analyzer (RGA). See, e.g., D. Lichtman, Residual Gas Analysis: Past, Present and Future, J. Vac. Sci. Technol., A 8(3) (1990). Mass spectrometers generally require pressures in the range of about 10xe2x88x925torr for operation, whereas the operating pressures of semiconductor processing tools are often higher, for example, in the range of from about 0.1 to 760 torr. Consequently, mass spectrometers require sampling systems and dedicated vacuum pumps, and hence are generally both expensive and not compact in construction. Moreover, the differentially pumped chamber in which the mass spectrometer is housed typically contributes a high level of residual water vapor which is difficult to remove and which severely limits the sensitivity of the mass spectrometer for water vapor measurement.
Optical emission spectroscopy has been widely used for monitoring plasma processes. In principle, optical emission spectroscopy should be useful to monitor the presence of water vapor in the processing tool. However, the optical emission spectrum is very complicated and, furthermore, this method cannot be used in non-plasma processes.
Other spectroscopic techniques have been widely employed in research situations to study process chemistry. See, e.g., Dreyfus et al., Optical Diagnostics of Low Pressure Plasmas, Pure and Applied Chemistry, 57(9), pp. 1265-1276 (1985). However, such techniques generally require specially modified process chambers. For example, the possibility of in-situ moisture monitoring by intracavity laser spectroscopy has been mentioned generally in a review of that technique. See, e.g., G. W. Atkinson, High Sensitivity Detection of Water via Intracavity Laser Spectroscopy, Microcontamination, 94 Proceedings Canon Communications (1994).
Finally, conventional gas analyzers have been applied to in-situ moisture measurement, usually for processes running at or close to atmospheric pressure. See, e.g., Smoak et al., Gas Control Improves Epi Yield, Semiconductor International, pp. 87-92 (June 1990). According to such techniques, a portion of the process gas is extracted into a probe which then delivers the sample to the analyzer. However, use of a probe is undesirable in the measurement of moisture since moisture tends to adsorb on the surfaces of the probe. Moreover, this approach is often impractical as it requires considerable space to accommodate the conventional gas analyzers, which space is typically at a minimum in a semiconductor fabrication cleanroom.
A method for measuring the instantaneous moisture concentration and drydown characteristics of a processing environment is disclosed in U.S. Pat. No. 5,241,851, to Tapp et al. According to this method, a moisture analyzer alternately samples the effluent from a process chamber and the gas generated by a standard gas generator. The output of the standard gas generator is adjusted until the analyzer indicates no difference between the effluent and standard gas streams. Because the moisture content in the output of the standard gas generator is known, the level in the effluent stream can be determined. This system, however, is inconvenient and complicated as it requires a standard gas generator and complicated piping to effect switching between the effluent and standard gas streams. Moreover, there is a risk of backflow from the standard gas generator to the process chamber, resulting in contamination thereof which would be deleterious to the product being formed.
To meet the requirements of the semiconductor processing industry and to overcome the disadvantages of the related art, it is an object of the present invention to provide a semiconductor processing system which allows for monitoring and control of the level of water vapor present as a process gas in an accurate and fast manner.
It is a further object of the invention to provide a method for controlling the moisture level in a semiconductor process chamber which can be practiced on the inventive system.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended hereto.
According to a first aspect of the invention, novel semiconductor processing systems are provided. The systems comprise a process chamber for treating a semiconductor substrate with one or more process gases comprising water vapor, means for delivering the water vapor or one or more precursors thereof to the process chamber, an exhaust conduit connected to the process chamber, an absorption spectroscopy system for sensing water vapor in a sample region, and a control system which controls water vapor content in the process chamber. The control system comprises a controller responsive to a signal from the absorption spectroscopy measurement system, the controller sending a control signal to the means for delivering the water vapor or precursors thereof.
According to a further aspect of the invention, methods for controlling the moisture level in a semiconductor process chamber are provided. Water vapor or one or more precursors for forming water vapor is introduced to the process chamber. The water vapor is to be employed as a process gas. The water vapor level in a sample region is measured by absorption spectroscopy. The water vapor content in the process chamber is controlled based on the absorption spectroscopy measurement.