Optics: measuring and testing – By polarized light examination – Of surface reflection
Reexamination Certificate
1999-12-29
2001-12-18
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
Of surface reflection
C356S630000, C356S364000, C414S255000
Reexamination Certificate
active
06331890
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a film thickness measuring apparatus for measuring the thickness of a thin film formed on a substrate, such as a semiconductor wafer, and also to a substrate processing method and substrate processing apparatus that are provided with a film thickness measuring function.
In general, when a semiconductor device, such as an integrated circuit, is manufactured, desired circuit elements are formed by super fine working technology, with a film forming process, an etching process and other processes being repeated. With the recent development in technology, there is an increased demand for larger storage capacity and higher processing speed of microprocessors in the field of semiconductor devices. It is therefore necessary to provide developing devices having higher integration density and super fine structure.
Under these circumstances, the thickness control of films of various kinds has to be performed with high accuracy. By way of example, reference will be made to the gate oxide film of a transistor used in a microprocessor. When a thermal oxide film, with which to form the gate oxide film, is, for example, 20 nm, there is a thickness allowance of ± about 0.5 nm in the conventional art. In other words, the thickness variation within this range does not result in a change in the characteristics. In the next-generation devices, however, thin films which are 3 nm or less are required. In the case of such very thin films, the allowable thickness variation is less than ±0.05 nm, and highly accurate thickness control is therefore necessary.
One of the problems that has to be solved in connection with the thin films is related to measurement technology. Let us consider the case where a thin film is formed on a semiconductor wafer to have a predetermined thickness and is then measured by the same film thickness measuring apparatus. In this case, the measurement will gradually increase with time, and it is impossible to know the actual thickness of the thin film. For example, when a thermal oxide film having a thickness of 10 nm was formed on a semiconductor wafer and its thickness was measured several times after it was left to stand in a clean room, the results shown in
FIG. 17
were obtained.
FIG. 17
is a characteristic graph wherein the time (minutes) for which the film is left to stand after film formation is plotted against an abscissa, and the measured thickness (nm) is plotted against an ordinate. That is,
FIG. 17
shows how the time is related to the measurement of the film thickness. In
FIG. 17
, the plotted white squares indicate data obtained by film thickness measuring apparatuses (FEIII) based on elliptical polarization method. In other words, they indicate how the measurement of the thickness of the thin film formed on the surface of the semiconductor wafer is dependent on the time. As is apparent from
FIG. 17
, the value measured after a lapse of 3 minutes is about 10 nm, which is a reliable value. However, the measurement value increases to about 10.1 nm when 30 minutes have passed from the film formation, and to about 10.3 nm when 300 minutes have passed.
As described, the next-generation devices, the allowable film thickness measurement variation range of which is ±0.05 nm or so, cannot be measured reliably.
As one of the factors that vary the film thickness measurement, organic matter attaching to the film surface is thought of. That is, the organic matter existing in the atmosphere of the film thickness measurement space attaches to the film surface with time. To prevent this attachment of organic matter, the conventional art, such as that disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-82631, proposes a film thickness measurement space which is provided inside an area separate from the outside air and which is filled with an inert gas, nitrogen gas.
According to this technology, the measurement space must be evacuated of the atmospheric gas and then filled with an inert gas instead. This being so, a large amount of gas is consumed in vain each time a semiconductor wafer is loaded or unloaded, which is uneconomic. In addition, safety measures must be taken, depending upon the kind of gas used.
Technology that employs a vacuum pump to reduce the pressure in a measurement space is known as technology that does not use an inert gas. However, this technology is disadvantageous in that the various driving mechanisms arranged in the measurement space must use a special kind of lubricant, such as vacuum grease, and the use of such lubricant inevitably increases the equipment cost.
Accordingly, the first object of the present invention is to provide a film thickness measuring apparatus which can measure the thickness of a film on a substrate with high accuracy, with no need to introduce an inert gas into a measurement space or to execute evacuation.
Another object of the present invention is to provide a substrate processing apparatus which can measure the thickness of a film on a substrate with high accuracy, ensures substantially stable measurement at all times, and can execute the next processing.
BRIEF SUMMARY OF THE INVENTION
After conducting intensive research on the factors that may vary the film thickness measurement, the present inventors discovered that impurities contained in the atmospheric gas, in particular, moisture and hydrocarbon, attach to the surface of a film on a semiconductor wafer, and thus vary the thickness of that film. Based on this discovery, the inventors have made the present invention.
A film thickness measuring apparatus according to the first aspect of the present invention comprises: a housing which substantially shuts off the internal region thereof from the outside air; an introduction stage on which a cassette is mounted, the cassette containing a plurality of substrates which have thin films formed thereon; a measurement stage which is arranged inside the housing and on which the substrate is placed for measuring the film thickness of the thin film; a conveyance mechanism, arranged inside the housing, for moving the substrates between the inside of the cassette and measurement stage; a film thickness measuring mechanism, arranged inside the housing, for emitting a measurement wave to the thin film on the substrate of the measurement stage, detecting at least one of a reflection wave and an emissive wafer from the thin film, and measuring the thickness of the thin film in a non-contact manner on the basis of detection information; and a filter mechanism, arranged in the housing, for capturing and removing gaseous organic matter from the outside air and supplying the outside air to at least the measurement stage.
In the apparatus described above, pure gas is supplied to the ambient atmosphere of the substrate on the measurement stage. Therefore, even where the thickness of the thin film can be measured after a long time has passed from the formation of that thin film, the variation which the measurement of the film thickness may undergo with time can be suppressed. It is preferable that the substrate be conveyed from the introduction stage to the measurement stage without being exposed to the outside air. The film thickness measuring means described above may include a light source for emitting a measurement wave and a detector for detecting a reflection wave. It is preferable that the film thickness measuring means further include a second exhaust duct which surrounds the light source and the detector and which serves to discharge the gas generated from the light source and the detector. With this structure, the gas generated by the light source and the detector is discharged through the second exhaust duct, the ambient atmosphere of the substrate on the measurement stage is purified further, and the variation which the measurement of the film thickness may undergo with time can be suppressed further.
Preferably, the film thickness measuring means is constructed by elliptical polarization analyzing apparatus that comprises: a light source; a pol
Hayashi Teruyuki
Marumo Yoshinori
Font Frank G.
Nguyen Sang H.
Pillsbury & Winthrop
Tokyo Electron Limited
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