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METHOD AND SYSTEM FOR IDENTIFYING
ETCH END POINTS IN SEMICONDUCTOR
CIRCUIT FABRICATION
RELATIONSHIP TO CO-PENDING 5
APPLICATIONS
This application claims priority based on commonly assigned Provisional Patent Application Serial No. 60/090, 086, filed Jun. 20, 1998.
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TECHNICAL FIELD
The present invention is related to semiconductor circuit fabrication, and more particularly to a method of identifying process end points which is particularly well suited for use in real time monitoring and process control. The present invention further comprises a preferred high wavelength resolution spectrometer system for use in developing intensity vs. Wavelength spectra, which are utilized in practice of said method. 2Q
BACKGROUND
It is well known that in the fabrication of semiconductor circuitry, (e.g. integrated circuits), it is necessary to perform etching procedures. For instance, it is common to grow 25 silicon dioxide atop a silicon substrate of a doping type, and then, utilizing photolithography techniques, open windows in said silicon dioxide, so that an opposite type dopant can be diffused into the underlying silicon. Resulting PN junctions are rectifying, and when multiple PN junctions are 30 placed in appropriate relationship to one another, bipolar and mosfet transistors, as well as silicon controlled rectifiers etc., result. Interconnection of various such devices fabricated on a semiconductor substrate, it is noted, results in an integrated circuit. 35
The etching of silicon dioxide, (a very relevant example of an area of application of the present invention), can be accomplished in an etching chamber which contains fluorine or chlorine in the presence of a plasma. A reduced pressure, (e.g. 10~5 Torr), ambient into which is introduced CF4, or 40 more commonly, C2F6 or C4F8, gas is often utilized in industrial settings. While silicon dioxide is being etched in such a setting, certain etch products are formed, and if a beam of electromagnetic radiation is caused to pass through them, said products relatively strongly absorb energy at 45 specific wavelengths, while energy present at other wavelengths is less strongly affected. Alternatively, energy provided by a present plasma serves to excite etch products and emissive electromagnetic radiation therefrom can be monitored. Careful monitoring of such intensity vs. wavelength 50 spectra as a function of time can provide insight as to when silicon dioxide available for etching has been etched away, and when underlying silicon is reached. For instance, upon reaching silicon, the products of etching silicon dioxide are greatly reduced, (some small amount of said silicon dioxide 55 etch products can still be produced as a result of typically undesirable overetching laterally under photoresist defined boundaries, however). And it is possible that new products due to interaction of plasma and etching gas with silicon will appear and affect monitored intensity vs. wavelength spec- 60 tra. This is particularly true where some oxygen is present and the underlying silicon is etched. However, the products of said interaction of plasma and etching gas with silicon, it is to be understood, typically demonstrate very different electromagnetic spectrum absorbance and/or emission char- 65 acteristics. It is to be understood that the procedure comprising detection of products of an etch procedure as an
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indication of etch end point, can be practiced where other than silicon dioxide is etched, (e.g. Al, SiN and W).
A recent paper which describes the use of low pressure high density plasma etching of silicon dioxide is titled "Chemical Challenge of Submicron Oxide Etching", by McNevin et al., J. Vac. Technol. B 15(2) (March/April 1997).
Another paper is titled "An Integrated System of Optical Sensors For Plasma Monitoring And Plasma Control", Anderson & Splichal, SPIE Vol. 2091, (1994). Real-time plasma etching utilizing sensors which measure plasma properties directly related to desired wafer features are discussed.
A paper by Splichal & Anderson titled "Application of Chemometrics to Optical Emission Spectroscopy For Plasma Monitoring", SPIE Vol. 1595, (1992) is also identified as monitoring of real-time plasma etching processes, based upon sensors which measure plasma properties that relate directly to desired etch features, is discussed.
A paper by Benson et al. titled "Sensor Systems For Real-time Feedback Control Of Reactive Ion Etching", J. Vac. Sci. Technol. B 19(1), (January/February 1996), is identified as it describes use of an optical emission spectroscopy system sensor utilized in multivariant feedback control of plasma etching of wafers.
A paper titled "Etching—0.35 m Polysilicon Gates On A High-Density Helicon Etcher", by Kroft et al., J. Vac. Sci. Technol. B 14(1) (January/February 1996), is disclosed as it describes an example of application plasmas in selective polysilicon-to-oxide plasma etching procedures.
A paper by Oh, Stanton, Anderson & Splichal titled "In Situ Diode Laser Absorption Measurements Of Plasma Species In A Gaseous Electronics Conference Reference Cell Reactor", J. Vac. Sci. Technol B 13(3) (May/June 1995). is identified as it discusses monitoring of electromagnetic absorption during etching procedures.
Apaper by Manukonda & Dillon titled "Optical Emission Spectroscopy of H2—CO and H20—CH3OH Plasmas For Diamond Growth", J.Vac. Sci. Technol. A 13(3) (May/June 1995), is identified as it describes monitoring of electromagnetic emissions during a procedure in which diamond was grown.
A paper by Litvak, titled "End Point Control Via Optical Emission Spectroscopy", J. Vac. Sci. Technol. B 14(1) (January/February 1996) describes the use of optical emission spectroscopy in identifying oxide etch end points, utilizing a conventional monochromator/photomultiplier system in conjunction with an end-point detecting algorithm. Many additional papers which describe plasma etching in the semiconductor fabrication area exist.
Known papers which utilize Reflected Electromagnetic Radiation Intensity and Ellipsometry to investigate Etching of semiconductor systems are:
"Optical Etch-Rate Monitoring Using Active Device Areas: Lateral Interference Effects", by Heimann, J. Electrochem. Soc, Vol. 132, No. 8, (1985);
"Ultraviolet-Visible Ellipsometry For Process Control During The Etching Of Submicron Features", by Blayo et al, J. Op. Soc. Am., Vol. 12, No. 3, (1995);
"Multiwavelength Ellipsometry For Real-Time Process Control Of The Plasma Etching Of Patterned Samples", Maynard et al, J. Vac. Sci. Technol. B 15(1) (1997); and
"Optical Etch Rate Monitoring: Computer Simulation Of Reflectance", Heimann et al., J. Electrochem. Soc, Vol 131, No. 4, (1984).
