JPH07159246A - Temperature measuring method for semiconductor wafer - Google Patents

Abstract

PURPOSE:To provide a noncontact temperature measuring method for measuring the temperature of a semiconductor wafer under surface treatment with emissivity varying every moment accurately regardless of the variation of the emissivity. CONSTITUTION:Infrared radiation from a semiconductor wafer under surface treatment process is divided into a p-polarization component and an s- polarization component. The temperature is measures by means of a radiation thermometer starting from an angle where the predetermined emissivity of p-component(epsilonp) is constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for accurately measuring the temperature of a semiconductor wafer in a non-contact state during a heating process in which a surface treatment such as sputtering, etching or oxide film formation is performed.

[0002]

2. Description of the Related Art Among semiconductor device manufacturing processes, for example, S
At the processing step of forming an oxide film on the surface of the i-wafer, it is necessary to accurately control the temperature of the wafer in order to obtain an appropriate film formation state. For this reason, conventionally, the temperature of the wafer being heated is measured by a method of measuring the temperature by bringing a thermocouple into contact with the back surface of the wafer or a method of measuring the temperature by using a radiation thermometer.

Of these, the latter method using a radiation thermometer has a high practical use rate as compared with the thermocouple method because it has the advantage of being able to measure the temperature in a state of non-contact with the semiconductor wafer, but the red color from the measured object is high. It is necessary to set the emissivity of the wafer in order to convert the external radiation into temperature. However, since the emissivity of the semiconductor wafer during processing is not constant, an emissivity measuring system is provided in addition to the temperature measuring system, and the data measured here is fed back to obtain the temperature (Japanese Patent Laid-Open No. Hei 3).
-165514, Japanese Patent Laid-Open No. 4-297054), and a method of measuring the temperature of a susceptor in close contact with a semiconductor wafer by a radiation thermometer without directly measuring the semiconductor wafer (Japanese Patent Laid-Open No. 4-226047). Has been.

[0004]

However, in the above-described conventional temperature measuring method using the radiation thermometer, even if the emissivity measuring system is installed separately from the temperature measuring system, the simultaneous progress during the processing such as film formation. Since the emissivity cannot be measured, there is a problem that the temperature cannot be continuously monitored in real time.

The present invention has been made in order to solve such a problem, and accurately measures the temperature of a semiconductor wafer during surface treatment in which the emissivity changes every moment without being affected by the change in the emissivity. The purpose is to provide a method of measuring temperature.

[0006]

A method for measuring the temperature of a semiconductor wafer according to the present invention to achieve the above object is to convert infrared radiation emitted from a semiconductor wafer undergoing a surface treatment into a p component and a s component of polarized light. Divided and p obtained in advance
A structural feature is that the temperature is measured using an emission thermometer from an angle at which the emissivity (εp) of the component is constant.

Generally, in the process of forming a film on a semiconductor wafer, the reflectance of the surface changes periodically due to the interference effect of light with the change of the surface state due to the film thickness and the like. The emissivity ε depends on the reflectance R and the transmittance T.
Is expressed as ε = 1- (R + T), but since the Si wafer is opaque (T = 0) in the wavelength range of 1 μm or less, the change in reflectance R should be regarded as the same as the change in emissivity ε. You can However, when the SiO ₂ film is formed on the surface of the Si wafer, the change in the emissivity due to the change in the film thickness is extremely large as shown in FIG. 1, and it is difficult to measure the temperature with an ordinary radiation thermometer.

The reflected light from the semiconductor wafer whose film thickness changes in this way can be divided into an s component and a p component by using a polarizing filter, a polarizing prism or the like. First, l of refractive index n _j and thickness d _j (j = 1,2, ..., l)
It is known that the Snell's law of the following equation (1) holds when considering a non-absorbing multilayer film of layers ["Optical Engineering Handbook", published 1986, February 20, 20 (Asakura Shoten), p160-169] . n ₀ sin φ ₀ = n _j sin φ _j (j = 1,2,… l + 1) …… (1)

In the equation (1), the incident angle φ ₀ is an angle formed by the incident light and the normal line of the wafer. On the other hand, the effective refractive index η _j for the s component and p component of polarized light is η _j = -n _j · cos φ
_{When j} (s component), η _j = n _j / cos φ _j (p component), and δ _j = 2π n _j · d _j cos φ _j / λ are set, a characteristic matrix Μ showing the properties of a homogeneous single layer film _j is expressed as in equation (2).

[0010]

[Equation 1]

Therefore, the matrix Μ representing the multilayer film is given by the equation (3) as the product of the characteristic matrices corresponding to each layer.

[0012]

[Equation 2]

The amplitude reflection coefficient of the multilayer film when viewed from the first medium side is expressed by the equation (4).

[0014]

[Equation 3]

However, according to Snell's law of equation (1), η
_{Since 1 + 1} = η _o holds, Eq. (4) becomes Eq. (5).

[0016]

[Equation 4]

Since the value of the equation (5) includes a complex number, the reflectance R ₀ of the multilayer film is obtained by the equation (6) as its effective value.

[0018]

[Equation 5]

As described above, the reflectance of the multilayer film in which d changes can be calculated for both the s and p components of polarized light. When this calculation is performed on a Si wafer,
It was verified that the emissivity was constant at a certain incident angle.

In the present invention, the above principle is applied to a semiconductor wafer in the process of surface treatment, in which the field of view of the radiation thermometer is set at an angle at which the emissivity (εp) of the p component obtained in advance is constant. The temperature of is measured continuously.

[0021]

According to the present invention, the incident angle at which the emissivity is constant is taken as the measurement angle, and the radiation corresponding to the temperature from the semiconductor wafer as the temperature-measuring object is divided into polarization components and detected, so that the film thickness It is possible to measure the temperature of the semiconductor wafer without being affected by the change in the emissivity due to the change in the temperature. Therefore, it is possible to perform accurate temperature monitoring in real time in a non-contact state at all times for a semiconductor wafer undergoing surface treatment whose emissivity changes from moment to moment, and improve the reliability of quality.

[0022]

EXAMPLES Hereinafter, the temperature measuring method of the present invention will be described with reference to an example in which it is applied to temperature measurement in a surface treatment process for forming SiO ₂ and Si ₃ N ₄ films on the surface of a Si wafer.

A radiation thermometer using a silicon solar cell as an infrared detector was used, and the measurement wavelength was 0.9 μm at which the Si wafer was opaque. Si at the same wavelength,
The refractive indices of SiO ₂ and Si ₃ N ₄ are 3.65,
They are 1.45 and 2.00. This is a model of j = 1, 2 in the process of calculating the reflectance of each polarization component described above.

2 to 9 show the reflectance of a Si wafer at various incident angles φ ₀ when the thickness of the SiO ₂ film changes from ₀ to 5000 angstroms at a measurement wavelength of 0.9 μm. 2 is a graph showing calculation results for each polarization component (s component and p component) of FIG.
Similarly, FIGS. 0 to 17 are graphs of the Si ₃ N ₄ film. SiO ₂ film (FIGS. 2-9) and Si ₃ N ₄ film (FIG. 1)
0 to 17), when the incident angle is about 10 ° to 30 °,
Both of the s component and the p component show a remarkable change in the reflectance R due to the change in the film thickness, but when the incident angle is 50 to 60 °, the reflectance R of the p component does not change regardless of the change in the film thickness. . Therefore, the range of this incident angle of 50 to 60 ° is
The emissivity (εp) of the p component becomes constant, and Si under the above conditions
This is the optimum measurement angle for the wafer.

In the above-mentioned incident angle range of 50 to 60 °,
The radiation thermometer was placed so that the Si wafer during the surface treatment forming the SiO ₂ and Si ₃ N ₄ coatings was in view. On the front surface of the radiation thermometer, a polarization filter (50φ × 2.0t) for detecting the infrared radiation from the Si wafer by dividing it into polarization components (s component, p component) was attached. In this way, the temperature of the Si wafer was monitored during the surface treatment process in which the film thickness varied from 0 to 5000 angstroms. When the treatment temperature was set to 900 and 1050 ° C., and the results of the thermocouple measured at the same time were used as the true temperature and the measurement results were compared, the measurement error was within ± 1 ° C. From this result, it was confirmed that the temperature measuring method according to the present invention can accurately measure the temperature of the semiconductor wafer without being affected by the change in the emissivity due to the increase in the film thickness.

[0026]

As described above, according to the present invention, it is possible to accurately and in real time measure the temperature of a semiconductor wafer in a surface treatment process, which has been impossible to measure temperature in the prior art, in a non-contact state. Become. Therefore, it is extremely useful for a temperature control operation for continuously monitoring the temperature of a semiconductor wafer in a surface treatment process such as sputtering, etching, and oxide film formation.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between film thickness and emissivity when a SiO ₂ film is formed on the surface of a Si wafer.

FIG. 2 shows S observed from an incident angle of 10 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 3 shows S observed from an incident angle of 20 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 4 shows S observed from an incident angle of 30 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 5 shows S observed from an incident angle of 40 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 6 shows S observed at an incident angle of 50 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 7 shows S observed from an incident angle of 60 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 8 shows S observed from an incident angle of 70 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 9 shows S observed from an incident angle of 80 ° in the example.
5 is a graph showing the relationship between the SiO ₂ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 10 shows S observed from an incident angle of 10 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 11 shows S observed at an incident angle of 20 ° in the example.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 12 shows S observed at an incident angle of 30 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 13 shows S observed at an incident angle of 40 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

[FIG. 14] S observed from an incident angle of 50 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 15 is an S image observed at an incident angle of 60 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 16 is an S image observed at an incident angle of 70 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

FIG. 17 shows S observed from an incident angle of 80 ° in Examples.
6 is a graph showing the relationship between the Si ₃ N ₄ film thickness on the i-wafer surface and the reflectance for each polarization component.

Claims (1)

[Claims] 1. Infrared radiation emitted from a semiconductor wafer undergoing surface treatment is divided into a p component and a s component of polarized light.
A method for measuring a temperature of a semiconductor wafer, which comprises measuring a temperature from an angle at which a predetermined p-component emissivity (εp) is constant, using a radiation thermometer.