Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-04-19
2002-02-26
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S117000, C700S116000, C700S108000, C438S008000, C438S009000, C438S017000, C438S010000, C156S345420, C156S346000, C156S348000, C324S622000, C324S623000, C324S647000
Reexamination Certificate
active
06351683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to systems and processes which use electrically generated gas plasma. The invention is particularly applicable to systems and processes which utilize a plasma in manufacturing solid state and/or semiconductor devices.
2. Discussion of the Background
Many semiconductor or solid state manufacturing processes utilize a gas plasma to perform a fabrication step. This step can be, for example, a chemical modification or an etching of a thin film, and may use chlorine gas or oxygen, among others. Often, particularly in the semiconductor industry, extremely precise control of the reaction conditions and the timing of the reaction is required. It is therefore important to accurately monitor the plasma conditions, the condition of the equipment, and the progress of the reaction.
Conventional plasma reaction systems have used optical spectrometry of the optical light emissions from the plasma in order to detect various chemical species produced by the reaction between the substrate and the plasma. Concentrations of these species can be used as an indication of the plasma conditions, or as an indication of the progress of the process being performed with the plasma (e.g., to determine the end point of the process). However, this technique is not sufficiently precise for certain processes. In particular, the optical detection method does not always provide a sufficiently reliable and timely indication of when a processing step (such as the etching of a photoresist or a metal layer) is complete.
Conventional plasma processes systems have also used timing to determine the end of a step. Several test runs are performed under the conditions to be utilized in an actual manufacturing run, in order to determine the reaction rate. During the actual manufacturing run, the plasma processing step is performed for a predetermined amount of time, and then terminated. However, slight variations in, e.g., the ambient environment, the manufacturing equipment, the plasma, and the workpiece can vary the reaction rates/times, thus making this method less than optimal.
Particularly where the processing step requires only a short amount of time, accurate determination of the end point can be crucial. For example, during etching of an extremely thin layer, a delay in the termination of the step can result in the plasma etching into the layer beneath the layer for which etching is intended. As semiconductor processes require increasingly thinner films, and as high density plasma systems allow for shorter etching and reaction times, it has become increasingly important to accurately determine the time at which a processing step is complete.
In addition, integration densities of semiconductor devices have continued to increase, demanding new levels of precision in controlling the reactive processes used for producing the devices. During a processing step, it is increasingly important to carefully control/monitor the conditions of the plasma (e.g., ion density and gas mixture), which directly impact not only rates of reaction, but also thin film material properties. System conditions, such as the cleanliness of the system, proper assembly/configuration of electrical/RF connections, RF matching, age of components, etc., can also affect the plasma conditions. Accordingly, a system and method are needed for accurately monitoring and controlling plasma and system conditions during a given process step, and for detecting the completion of the process step in order to shut down the plasma process at an appropriate time.
Known references have discussed using the harmonic content of an electrical signal to determine the condition of the plasma by exploiting the inherent non-linearity of the plasma. See Miller & Kamon (U.S. Pat. No.5,325,019 (hereinafter “the '019 patent”)), Gesche & Vey (U.S. Pat. No. 5,025,135 (hereinafter “the '135 patent”)), Patrick et at. (U.S. Pat. No. 5,474,648 (hereinafter “the '648 patent”)), Turner et al. (U.S. Pat. No. 5,576,629 (hereinafter “the '629 patent”)), and Williams & Spain (U.S. Pat. No. 5,472,561 (hereinafter “the '561 patent”)).
The '135 patent discloses a high-pass filter of a sampled electrical signal wherein the presence of high frequency content determines the existence of a plasma. The '019 patent uses the fundamental and harmonic frequency components of voltage and current measurements (measured at an electrode within the plasma electrical system) to select operating conditions. However, it does not teach correlating harmonic content with plasma process input parameters, such as pressure, RF input, etc. Furthermore, it does not teach control functions based upon the linear and/or non-linear combination of harmonic amplitude ratios (ratio to the amplitude of the fundamental frequency). Likewise, none of the '019, '629, and '561 patents recognize that information regarding a plasma process can be obtained by modulating the RF power.
Several patents address some aspects of intelligent control of plasma processes. In particular, some patents attempt to characterize the plasma system performance, generate a database, monitor electrical components during run conditions, and compare to the database to determine the plasma conditions. For example, Kochel (U.S. Pat. No. 4,043,889) addresses this issue. It discloses a method of using a pre-determined bias voltage versus pressure characteristic to tune a process to ‘optimal’ conditions (in a chamber performing RF sputtering of a thin film). Moreover, Tretola (U.S. Pat. No. 4,207,137), describes controlling a plasma process.
Additionally, several patents teach monitoring the electrical properties of a plasma system and correlating their variation with plasma conditions. For example, Patrick et al. (U.S. Pat. No. 5,474,648) discloses (a) a control method to improve repeatability and uniformity of process and (b) monitoring the power, voltage, current, phase, impedance, harmonic content and direct current bias of the RF energy transferred to the plasma. Additional references describing electrical property characterization for plasma processing devices include Logan, Mazza & Davidse, “Electrical characterization of radio-frequency sputtering gas discharge,” J. Vac. Sci Technol., 6, p. 120 (1968); Godyak, “Electrical characteristics of parrallel-plate RF discharges in Argon,” IEEE Transactions on Plasma Sci., 19(4), p. 660(1991); and Sobolewski, “Electrical characterization of radio-frequency discharges in the Gaseous . . . ”, J. Vac. Sci. Technol., 10(6) (1992). For real-time control of etching processes using multi-variate statistical analysis, see Fox & Kappuswamy (U.S. Pat. No. 5,479,340).
Some patents also discuss monitoring the optical properties of a plasma. Using an optical emission spectrometer, information about the species present within the plasma (and their approximate concentration) can be ascertained from monitoring the emission spectrum of the light present. In fact, several spectrometers (or those which comprise a rotary grating) may monitor the presence of several species and, hence, provide a plurality of inputs to a plasma process control system. See Cheng (U.S. Pat. No. 5,160,402) and Khoury, Real-time etch plasma monitor system, IBM Technical Disclosure Bull., 25(11A) (1983).
Turner (U.S. Pat. No. 4,166,783) proposes a computer control system for use with deposition rate regulation in a sputtering chamber. The system records the use of the sputtering device and compiles a history of its performance. During future use of the device, the past performance, age, etc., are incorporated into adjustments made during a run condition.
Automatic impedance matching systems are also known which employ a (quasi-)intelligent controller to monitor an electrical property of the plasma chamber. In fact, some systems attempt to obtain some correlation between settings for variable reactances (i.e., capacitors and inductors) and plasma conditions such as the load impedance or plasma chamber input parameters (i.e., RF
Johnson Wayne
Parsons Richard
Grant William
Patel Ramesh
Tokyo Electron Limited
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