JP2001085489A - Temperature measurement method - Google Patents

Abstract

(57) [Problem] To provide a novel method for measuring temperature by capturing Raman scattered light. SOLUTION: As in the prior art, a substrate to be measured is irradiated with laser light, and Raman scattered light generated is measured, and Stokes lines having an intensity higher than that of the anti-Stokes lines are separated to obtain a peak wave number. The temperature is obtained by collating the relationship between the temperature (° C.) and the peak wave number (peak intensity) of the Stokes line with the peak wave number. Since the peak wave number shifts in a direction in which the wave number decreases almost linearly as the temperature rises, such a temperature measurement becomes possible. For more accuracy, it can be fitted almost completely with a quadratic function. This measuring method utilizes the phenomenon that the wave number of Raman scattered light shifts with temperature.
The measurement is completed in a short time because the anti-Stokes line is not used unlike the related art.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring temperature, and more particularly to a method for measuring the temperature of a semiconductor wafer using Raman scattered light.

[0002]

2. Description of the Related Art In general, a semiconductor device has a design process of designing a semiconductor device, a process of growing a semiconductor single crystal such as silicon in an ingot and slicing the same into a wafer, a process of forming a thin film on the wafer, A product is obtained through a wafer processing process of forming a plurality of chips having semiconductor elements formed on the wafer by performing oxidation treatment, doping, and the like, an assembling process of separating and packaging the chips from the wafer, and an inspection process. In the wafer processing step, chips are formed along a chip forming area defined by a dicing line on the main surface of the wafer obtained in the wafer forming step, and then the wafer is diced along the dicing line to separate each chip. .
The semiconductor device is assembled based on the chip, inspected, and shipped.

In a semiconductor device manufacturing process, there are many thermal processes in a wafer processing process. In the thermal process, a process is caused by thermal energy, whether an oxidation process or a diffusion process, and the temperature is the most important process parameter. And, as the process becomes more precise, the temperature measurement and its precise control are required. In the manufacture of semiconductors, non-contact temperature measurement is necessary because impurities are extremely disliked. There is a radiation thermometer as a method for measuring temperature in a non-contact manner. It measures the radiant energy emitted by a substance, and is used for temperature measurement because it is proportional to the fourth power of temperature. The difficulty with this method is that the emissivity varies with material and with temperature.
In the semiconductor manufacturing process, for example, a thin film such as SiO ₂ or SiN is formed, but since such semiconductor substrates have different emissivities, if the temperature is measured with the same radiation thermometer, a large error may occur. Become. As a method of avoiding such material dependence, a method of measuring Raman scattered light is known. When a solid having a Raman-active vibration mode is irradiated with laser light, Raman scattered light is emitted. That is, when light enters a substance, scattered light having a frequency component lower or higher by the frequency corresponding to the molecular motion of the substance or the lattice vibration energy in the solid is emitted in the scattered light.

[0004] There are two types of Raman scattered light: a Stokes line whose energy is smaller than that of incident light by the frequency inherent to the substance, and an anti-Stokes line which is the opposite of the Stokes line. Since the intensity ratio between the Stokes line and the anti-Stokes line changes exponentially with respect to temperature, it has been proposed to utilize this phenomenon for temperature measurement (see Japanese Patent Application Laid-Open No. 7-218355). For example, a case in which Ar ion laser light is irradiated will be described. The wavelength of the oscillation line of the Ar ion laser is 48
If 8 nm is selected, since SiO ₂ and SiN hardly absorb this wavelength, the laser beam reaches the silicon substrate and further penetrates to a depth of about 0.5 to 1 μm. Since the Raman scattered light is generated from this region, the temperature measured using the Raman scattered light is not the surface temperature but the internal substrate temperature. Therefore, even if any thin film is formed on the substrate surface, the temperature can be measured without being affected by the thin films, and the problem of the radiation thermometer can be solved.

[0005]

However, the intensity of Raman scattered light is usually very low. In particular, the anti-Stokes line is orders of magnitude weaker than the Stokes line (see FIG. 6). Therefore, it takes a certain amount of time to measure the strength more accurately than to measure the strength. On the contrary, there is a problem that the accuracy is deteriorated in the short-time measurement. Further, the intensity ratio between the Stokes and anti-Stokes lines varies exponentially with temperature. That is, the intensity ratio changes sensitively to a temperature change in a low temperature region, but hardly changes in a high temperature region. That is, there is a problem that the accuracy of the temperature measurement in the high temperature region is extremely reduced. Also,
In an actual semiconductor process, measurement is performed through a window provided in a heat treatment apparatus. However, when a thin film or the like adheres to the window, the Raman scattering light is naturally absorbed or reflected there, and the Raman scattering reaching the spectroscope is naturally observed. The amount of light decreases. Therefore, the accuracy is further reduced.

In the semiconductor process, various thin films such as a silicon oxide film and a silicon nitride film are formed on a silicon substrate, and these have different thermal expansion coefficients. It will be deformed. This shifts the focus of Raman spectroscopy. One of the problems in the method of measuring the intensity, that is, the amount of light, is that it is greatly affected by the focus. For the above reasons, at present, the method of obtaining the temperature from the intensity ratio of the Stokes line and the anti-Stokes line is not a method that can be practically used in a semiconductor process. The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a novel method of capturing Raman scattered light and measuring the temperature using the captured light.

[0007]

Means for Solving the Problems As a result of the development, the inventors have found that the peak wave number of the Stokes line shifts with the temperature in a direction in which the wave number decreases. That is,
The present invention measures the Raman scattered light generated by irradiating the substrate to be measured with laser light in the same manner as in the prior art, disperses the Stokes line having an intensity higher than that of the anti-Stokes line, determines the peak wave number, and determines the peak wave number in advance. It is characterized in that the temperature is obtained by collating the relationship between the set temperature and the peak wave number of the Stokes line with the peak wave number. Since the peak wave number shifts in a direction in which the wave number decreases almost linearly as the temperature rises, such a temperature measurement becomes possible. For more accuracy, it can be fitted almost completely with a quadratic function. The above measuring method utilizes a phenomenon in which the wave number of Raman scattered light shifts with temperature. The measurement is completed in a short time because the anti-Stokes line is not used unlike the related art. Further, since the temperature dependence of the peak wave number is used and the light quantity is not measured, there is no influence from the contamination of the window of the heat treatment apparatus. Further, there is no influence of a decrease in the amount of light due to the defocus.

In other words, the temperature measuring method of the present invention is a method for measuring the peak value of the Stokes line of Raman scattered light emitted by irradiating a crystalline sample with laser light and the temperature of the sample at that time. Calculating the relationship between the peak wave number and the temperature by calculating in advance, irradiating the sample to be measured with laser light to measure the wave number of the Stokes line of Raman scattered light, and this value is referred to as the peak wave number. Measuring the temperature of the sample to be measured by collating with a relationship with the temperature. The sample to be measured may be monocrystalline silicon or polycrystalline silicon. The laser light may be applied to the single crystal silicon or the polycrystalline silicon via an insulating film coated thereon. The intensity of the laser beam applied to the sample to be measured may be 10 ⁴ W / cm ² or less.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. First, referring to FIG. 1 to FIG.
Example (temperature measurement method) will be described. 1 is a schematic cross-sectional view of a heat treatment apparatus, FIG. 2 is a spectrum diagram showing Stokes lines of Raman scattered light generated by irradiating a silicon substrate with laser light, and FIG. 3 is a laser light on a silicon substrate at a predetermined temperature. FIG. 4 is a spectrum diagram showing Stokes lines of Raman scattered light generated by irradiating light, FIG. 4 is a characteristic diagram showing a relationship between peak intensity of a spectrum representing Stokes lines and temperature, and FIG.
FIG. 4 is a correlation diagram showing a relationship between a laser light irradiation time and a temperature rise of an irradiated portion. In FIG. 1, an argon (Ar) ion laser 1 having a power supply, a Raman spectroscope 2, a microscope 3, a heated sample table 4, and a control computer 5 are installed in the apparatus. A thermocouple 6 is installed on the heated sample stage 4, and the temperature is displayed on a thermometer 7. A sample to be measured 8 such as a silicon substrate is placed on the heated sample table 4. An Ar laser beam having a wavelength of 488 nm is irradiated to focus on the silicon substrate 8.

FIG. 2 is a spectrum showing a Stokes line when a silicon substrate is irradiated with a laser beam for one minute and measured. The vertical axis represents the peak intensity of the Raman scattered light,
The horizontal axis represents the wave number (cm ^-1 ). In the case of silicon, at room temperature, a Stokes line is observed around a wave number of 520 cm ^-1 . FIG. 3 is a diagram showing a temperature change of the Stokes line.
The vertical axis represents the peak intensity of Raman scattered light, and the horizontal axis represents
Indicates the wave number (cm ^-1 ). Silicon substrate from 25 ° C to 1
The spectrum up to 00 ° C is shown. According to this figure, when the temperature rises, the half width of the peak increases, and the peak intensity also decreases. The spread of the half width is caused by the fact that the degeneracy of the rotating state is released when the temperature rises. FIG. 4 shows the peak intensity detected by fitting the curve and plotted against the temperature measured with a thermocouple. A quadratic function gives the best match, but can be approximated as a straight line. By using this as a calibration curve, the temperature of the silicon substrate during the process can be obtained. When the temperature is obtained by irradiating a laser beam, the temperature rise due to the laser beam must be considered. FIG.
Is a simulation result of a temperature rise in an irradiation area when the silicon substrate is irradiated with an Ar ion laser. It can be seen that the temperature rises in about 0.1 second from the start of laser irradiation and the tendency to saturate immediately. The temperature of saturation naturally depends on the incident power density, and is 10 ³ W / c.
The temperature is about 0.1 ° C. for m ² and about 1 ° C. for 10 ⁴ W / cm ² .

[0011] The allowable temperature rise can be adjusted to the required accuracy.
Dependent. If the accuracy is good at 10 ° C,
A 1 ° C. increase with laser would be no problem. However
Therefore, in the ordinary temperature measurement, an accuracy of about 1 ° C. is required.
Considering that, the temperature rise by the laser is
Preferably, it should be kept below 0.1 ° C. Accordingly
And the laser incident power density is 10^FourW / cm^TwoBelow, good
Preferably 10^ThreeW / cm ^TwoIt is appropriate to suppress
is there. This is a limitation on the power density of the laser,
Larger total power can be input by expanding the irradiation area
As a result, a sufficient Raman signal can be obtained.
As described above, the embodiments have been described using the single crystal silicon substrate.
However, the present invention can be applied to any crystalline material.
For example, used for polycrystalline silicon film, ferroelectric memory
PZT film, which is also used for ferroelectric memory
SRO (SrRuO) of capacitor electrode_Three), Compound semiconductor
GaAs, InP or the like can be applied.

Next, a description will be given of a second embodiment in which the temperature measuring method of the present invention is applied to a method of manufacturing a semiconductor device. A ferroelectric capacitor constituting a ferroelectric memory (FRAM) has, for example, a PZT film formed on a silicon substrate. For a PZT film to have ferroelectric properties, it must be crystalline. Therefore, crystallizing the PZT film from an amorphous state is an important step. FIG.
FIG. 2 is a cross-sectional view of a semiconductor substrate for explaining a step of crystallizing a PZT film. A P-type silicon (100) substrate (wafer) 10 is heat-treated at 950 ° C. in an oxygen atmosphere to form a thermal oxide film 11. A Ti film 12 is formed thereon by sputtering. In sputtering, a Ti target is sputtered with Ar, and the wafer 10 during sputtering is maintained at room temperature. The thickness of the Ti film (bonding layer) 12 is 30 nm. A Pt film (underlying electrode) 13 having a thickness of 200 nm is formed thereon. Pt
The film 13 is also formed by sputtering using Ar gas. On this Pt film 13, a PZT film 14 is formed by sputtering. The sputtering of the PZT film 14
The treatment is performed at room temperature using Ar gas, and the film thickness is 200 nm. Since the sputtering was performed at room temperature, it is in an amorphous state.

The wafer 10 is mounted on a heat treatment apparatus. Thereafter, the temperature was increased at a rate of 30 ° C. for 1 second while flowing oxygen, and the temperature was maintained at 650 ° C. for 30 seconds. Wafer 10
Is then cooled to room temperature to complete the crystallization. It is necessary to keep the temperature constant during this crystallization process in order to maintain uniform film formation on the wafer, and it is necessary to detect the substrate temperature quickly and adjust the temperature promptly. Therefore, the temperature measurement method of the present invention is applied to this crystallization treatment. That is, the peak value of the Stokes line of the Raman scattered light emitted by irradiating the crystalline PZT film with the laser beam and the temperature of the PZT film at that time are calculated in advance, and the relationship between the two is determined. At a desired point in time, the PZT film is irradiated with laser light, the wave number of the Stokes line of the Raman scattered light is measured, and this value is compared with the relationship between the peak wave number and the temperature to determine the PZ at that time.
That is, the temperature of the T film is measured.

According to this method, the measurement is completed in a short time because no anti-Stokes line is used unlike the conventional method.
After the crystallization, a so-called metal mask having a hole in a portion to be measured in the capacitor pattern is placed on the PZT film-like surface, and a Pt film (thickness: 20 nm) 15 serving as an upper electrode is formed by sputtering. When the metal mask is removed, the Pt film 15 is formed in a capacitor pattern over the entire surface of the wafer.
Are formed, and this completes the fabrication of the ferroelectric capacitor. The ferroelectric capacitor thus formed constitutes an FRAM together with a transistor formed on a silicon substrate. In the present invention, the Ar ion laser is used as the laser light for generating the Raman scattered light, but a dye laser or the like may be used in addition to this.

[0015]

According to the present invention, the above configuration utilizes the phenomenon that the wave number of Raman scattered light shifts with temperature, so that the measurement can be completed in a short time without using an anti-Stokes line as in the prior art. I do. In addition, since the temperature dependency of the peak wave number is used, and the light quantity is not measured, there is no influence from the contamination of the window of the heat treatment apparatus. Further, there is no influence of a decrease in the amount of light due to the defocus.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a heat treatment apparatus for performing temperature measurement using Raman spectroscopy of the present invention.

FIG. 2 is a spectrum diagram of Raman scattered light for explaining the present invention.

FIG. 3 is a diagram of Raman scattering spectra at various temperatures for explaining the present invention.

FIG. 4 is a characteristic diagram showing a change in Raman shift with temperature for explaining the present invention.

FIG. 5 is a correlation diagram showing a relationship between a laser light irradiation time and a temperature rise of an irradiated portion.

FIG. 6 is a characteristic diagram illustrating the intensity of Raman scattered light.

FIG. 7 is a cross-sectional view of a semiconductor substrate on which a PZT film to which the present invention is applied is formed.

[Explanation of symbols]

1 ... Ar ion laser, 2 ... Raman spectrometer,
3 ... microscope, 4 ... heated sample stage, 5 ... computer, 6 ... thermocouple, 7 ... thermocouple thermometer, 8, 10 ... silicon substrate, 11 ... heat Oxide film, 12 ... Ti film (junction layer), 13 ... Pt film (base electrode), 14 ... PZT film, 15 ... Pt
Membrane (top electrode).

Continuation of the front page (72) Inventor Atsushi Yagishita 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Katsuya Okumura 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Yokohama Co., Ltd. In-house F-term (reference) 2F056 VF01 VF11 VF17 4M106 AA01 BA05 DH02 DH11 DH15 DH32 DH44 DH46 DH60 DJ11

Claims (4)

[Claims] 1. A peak wave numerical value of a Stokes line of Raman scattered light emitted by irradiating a laser light to a crystalline sample to be measured and a temperature of the sample to be measured at that time are calculated in advance. And the step of obtaining a relationship between the temperature, and irradiating the sample to be measured with laser light to measure the wave number of the Stokes line of the Raman scattered light, and comparing this value with the relationship between the peak wave number and the temperature Measuring the temperature of the sample to be measured. 2. The temperature measuring method according to claim 1, wherein the sample to be measured is single crystal silicon or polycrystalline silicon. 3. The temperature measuring method according to claim 2, wherein the laser light is applied to the single crystal silicon or the polycrystalline silicon via an insulating film coated thereon. 4. The temperature measuring method according to claim 1, wherein the intensity of the laser beam applied to the sample to be measured is 10 ⁴ W / cm ² or less.