Semiconductor device manufacturing: process – With measuring or testing – Optical characteristic sensed
Reexamination Certificate
1999-03-03
2003-04-01
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
Optical characteristic sensed
Reexamination Certificate
active
06541287
ABSTRACT:
BACKGROUND OF THE INVENTION
When the film is formed on the semiconductor wafer in CVD the temperature of a semiconductor wafer is measured by a radiation thermometer chamber, generally.
The radiation thermometer measures the wafer's temperature with a constant emissivity.
However, if the emissivity of the object is unknown or changeable, it is impossible to measure the temperature of the object accurately. When the film is formed on the surface of the object within the CVD chamber, the emissivity of the object is changed like a sine wave by affect of the thin film interference. As a result, intensity of the radiated light form the object changes like a sine wave as shown in
FIG. 35
, if the temperature of it doesn't change. This leas errors in measuring of the temperature with a radiation thermometer as shown in FIG.
36
.
To measure the surface temperature of a wafer in the process of forming a thin film on the surface of the wafer (substrate), the surface temperature is measured by a contact method in which a sensor such as a thermocouple is disposed inside the wafer stage. Alternatively, a radiation thermometer is located above the wafer surface to detect the intensity of the radiated light for a single wavelength or two wavelengths, thereby to measure the temperature. The intensity of the radiated light changes with temperature change.
On the other hand, to measure the formation amount of a thin film, a wafer is illuminated with light emitted from a light source having a continuous spectral distribution. Then, the interference intensity of the reflected light, which is changed with increase in the film thickness, is detected so as to measure the film thickness.
Also, an ideal waveform is obtained based on an ideal model of the film construction such as the number of films, the kinds of films and the order of formation these films. In this case, the film thickness is determined based on the matching of the waveform with the ideal waveform.
However, the conventional surface temperature measuring methods described above give rise to serious problems. Specifically, in the contact method, a film is unlikely to be formed in the vicinity of the thermocouple, leading to a ununiform film formation. In the method of measuring the temperature by detecting the spectral intensity of the radiated light, it is impossible to measure accurately the surface temperature of the film. To be more specific, if the films laminated on the substrate such as a wafer differ from each other in, for example, kind, construction and thickness, the radiated light will be repeatedly reflected on the upper and lower surfaces of the films so as to bring about interference. This makes it impossible to obtain a sufficient detecting sensitivity over a measuring wavelength. It follows that it is impossible to measure accurately the surface temperature.
On the other hand, the conventional film thickness measuring method described above gives rise to an additional problem. Specifically, in this method, the film thickness is calculated by detecting how the wavelength characteristics of the reflected light are changed compared with the illuminated light. Therefore, under such a high temperature as hundreds of degrees centigrade as in a film formation process, the influence given by the radiated light is not negligible. Consequently, the film thickness cannot be measured accurately.
Further, in a film formation apparatus in which a wafer is rotated at a high speed, the film formation is affected by eccentricity and planar vibration of the wafer rotation. Therefore, it is impossible to measure the reflected light stably with a high reproducibility, making it impossible to measure accurately the film thickness.
Still further, an ideal waveform is calculated in the conventional method by using as an ideal model the construction of a film consisting of plural layers. Thus, it is impossible to measure accurately the film thickness unless the film construction is known in advance.
FIG. 37
schematically shows the principle of a wafer temperature monitoring apparatus
1
used in, for example, a conventional semiconductor processing apparatus. The wafer temperature monitoring apparatus
1
comprises a He—Ne laser device
3
for irradiating a semiconductor wafer &ohgr; housed in a chamber
2
with a laser beam
6
, which is shown in
FIG. 38
, and a pair of CCD cameras
4
and
5
for detecting the diffracted light reflected from the semiconductor wafer co. If the semiconductor wafer &ohgr; housed in the chamber
2
is heated to a high temperature, the wafer &ohgr; is expanded so as to change a reflection angle &thgr; of the diffracted light. As a result, the position at which the diffracted light
7
is detected by the CCD cameras
4
and
5
is moved in accordance with the change in temperature. In the wafer temperature monitoring apparatus
1
, the temperature is measured by detecting the amount of the movement of the position noted above.
However, the conventional wafer temperature monitoring apparatus
1
gives rise to a problem. Specifically, as shown in
FIG. 38
, films n
1
and n
2
are formed on the semiconductor wafer &ohgr; in accordance with progress of the treatment. Also, if the temperature of the gas within the film formation chamber
2
is changed to form gaseous layers n
3
and n
4
differing from each other in temperature, the diffracted light
7
is refracted to form a diffracted light
8
. As a result, the positions at which the diffracted light beams
7
and
8
reach the CCD camera
4
or
5
are made different from each other by an amount of &Dgr;d. Hence, it is impossible to distinguish the temperature change of the semiconductor wafer &ohgr; from the change in the film thickness or from the change in the temperature of the ambient gas. It is therefore impossible to monitor accurately the temperature.
It is very important to control the temperature of the wafer surface in the various steps such as the film formation step and the etching step employed in the manufacture of a semiconductor device. In general, a thermocouple is used as a highly reliable temperature measuring means. During the manufacturing process of the semiconductor device, a thermocouple is brought into contact with the back surface of the wafer or with a tool for supporting the wafer so as to perform the temperature control. However, use of a thermocouple gives rise to problems in terms of contamination and life of use. In addition, it is impossible to use a thermocouple for measuring the most important temperature, i.e., temperature on the wafer surface at which chemical reactions are carried out.
On the other hand, a radiation thermometer is a typical example of the known non-contact type thermometer. However, if the film quality or the film thickness is changed during the process, the radiation thermometer is rendered incapable of measuring the temperature by a change in emissivity and the film interference. It should also be noted that the radiation thermometer is for measuring high temperatures exceeding, in general, 500° C. In other words, the radiation thermometer cannot be used for measuring intermediate and low temperatures lower than 500° C. The thermometer cannot be used in the intermediate and low temperature processes such as the etching process, P-CVD process, and sputtering process.
Recently, a new method for measuring temperature is proposed, in which a pattern of holes formed in a wafer such as contact holes and trenches is illuminated with a laser beam. In this method, a change in the diffraction angle of the diffracted light is detected and the temperature is calculated from the relationship between the diffraction angle and the temperature. In the temperature measuring method of this type, however, it is difficult to form in advance a predetermined pattern of holes in the wafer.
In a film thickness measuring apparatus used in a process apparatus such as a CVD apparatus for formation a thin film on a semiconductor wafer, the waveform before the film formation is taken in for every wafer to be measured. A
Akama Yoshiaki
Ino Tomomi
Soga Akira
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Niebling John F.
Stevenson André C
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