JP2009123850A - Method of measuring surface temperature of substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure an uppermost surface temperature of a substrate supplied to an oxidation process system using an oxidation treatment gas and light irradiation. <P>SOLUTION: The uppermost surface temperature of the substrate is measured based on a measured result of a film thickness of an oxide film formed on the substrate supplied to the oxidation process system using the oxidation treatment gas and the light irradiation. The oxidation treatment gas is an oxidative gas such as oxygen gas. The film thickness of the oxide film is instantiated by an elliptic polarization analytical method or an X-ray photoelectron spectroscopy. This method is applicable for measuring a surface temperature of a substrate surface not irradiated directly with the light, when the substrate is arranged in midair in the oxidation process system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor polysilicon TFT, a technique for producing a gate oxide film in an FET element, and a semiconductor manufacturing process technique using ozone oxidation.

In the semiconductor field in recent years, there has been a demand for lowering the semiconductor manufacturing process temperature from the viewpoint of mass productivity and cost reduction. Ozone is known to have strong oxidizing power, and attention is being focused on ozone technology to lower the temperature of semiconductor manufacturing processes. As an example, in the production of a gate oxide film (Si oxidation technology) in a TFT (thin film transistor) element, the film forming temperature, which conventionally required 1000 ° C. or more, can be reduced to 400 ° C. by using ozone ( Patent Document 1). Here, it is known that the strong oxidizing power by ozone is actually borne by atomic oxygen (O ^* ) generated during ozonolysis.

  The decomposition reaction of ozone can be given by equation (1).

O ₃ → O ^* + O ₂ (1)
The lower the Si oxidation temperature, the higher the probability that the thermal decomposition of ozone is 400 ° C. or higher. It is known that ozonolysis is induced not only by heat but also by light. Ozone molecules have a large absorption edge (Hartley band) in the wavelength band of 200 to 300 nm, and a decomposition reaction occurs due to light in this wavelength band. By using this photolysis, the Si oxidation temperature can be reduced to near room temperature (see Patent Document 2). The ability to reduce the temperature to near room temperature is expected to not only contribute to the mass production and cost reduction of semiconductor devices in the future, but also contribute to the manufacturing process of next-generation devices such as flexible displays. Is done.

The ozone technique can be applied not only to the process film forming technique as described above but also to etching, surface modification, cleaning, and the like, and is expected to be widely used.
JP 2003-209108 A (paragraphs 0117 to 0123) JP 2006-080474 A (paragraphs 0011 to 0034)

  In the case of ozonolysis using ultraviolet light, excited oxygen atoms generated by photolysis from ozone are known to be extremely reactive but immediately deactivated to become oxygen (patent publication 2004-085407). No. publication). For this reason, the ozone photo-oxidation treatment is generally performed in such an arrangement that the ultraviolet light strikes the surface of the treatment substrate. This is because excited oxygen atoms are generated very close to the surface of the target sample. On the other hand, with such a light source arrangement, ultraviolet light reaches the surface of the substrate. At this time, it is presumed that the temperature of the substrate surface has risen due to light absorption. While such a surface heating effect is an important factor in determining the oxidation rate, there is a concern that this heat affects the underlying substrate from the viewpoint of low temperature fabrication. Therefore, knowing the surface temperature of the substrate is essential for process control. However, since heating occurs in the vicinity of the substrate surface, there is a large thermal gradient with respect to the thickness direction in the substrate, and the temperature of the outermost surface of the substrate cannot be examined by a method in which a conventional thermometer is placed nearby. .

  Therefore, a substrate surface temperature measurement method for solving the above problems is based on the measurement result of the thickness of the oxide film formed on the substrate provided in the oxidation process system using the oxidation treatment gas and light irradiation. Measure the surface temperature. Since the film thickness of the oxide film formed on the substrate used in the oxidation process system using the oxidation treatment gas and light irradiation has a correlation with the outermost surface temperature of the substrate, the surface temperature of the substrate Can be measured. The evaluable temperature range is as wide as room temperature to 1000 ° C. Further, since the temperature distribution in the surface direction of the substrate can be grasped from the distribution of the measured film thickness, the spatial resolution in the substrate surface direction can be obtained.

  In the substrate surface temperature measuring method, the method for measuring the film thickness of the oxide film includes elliptical ellipsometry or X-ray photoelectron spectroscopy. The oxidation treatment gas is an oxidizing gas exemplified by oxygen gas.

  In the substrate surface temperature measurement method, when a device used for the film thickness measurement is provided in the chamber, the surface temperature can be measured in situ during the oxidation process.

  In the substrate surface temperature measuring method, the process light irradiation amount can be fed back by measuring the surface temperature.

  Assuming that the frequency of light associated with the light irradiation is in the range from ultraviolet light to visible light, the substrate surface temperature can be measured without causing damage to the substrate surface.

  If the substrate is disposed in the oxidation process system, the substrate can be applied to the surface temperature measurement of the substrate surface that is not directly exposed to light.

  Therefore, according to the above invention, the outermost surface temperature of the substrate used in the oxidation process system using the oxidation treatment gas and light irradiation can be measured.

  The substrate surface temperature measuring method according to the invention is calculated based on the relationship between the oxidation rate of the oxide film and the temperature when measuring the outermost surface temperature of the sample irradiated with light. FIG. 1 is a flowchart showing a procedure for measuring a substrate surface temperature according to the invention.

  First, an oxidized sample is prepared (S1). Here, it is limited to those that can be oxidized (for example, aluminum, Si, etc.). Cleaning is performed in advance to remove the natural oxide film. Next, an oxidation process using light irradiation is performed in the oxidation chamber (S2). The frequency of light related to the light irradiation is preferably in the range from ultraviolet light to visible light. Light having a wavelength of 200 nm or less is not desirable. Light having a wavelength of 200 nm or less damages the underlying sample (substrate (Si)). Utilizing the oxidation temperature dependence of the oxide film thickness, the surface temperature of the oxidized sample is known from the film thickness. That is, the place irradiated with light utilizes the fact that oxidation proceeds at a rate corresponding to the surface temperature. When the oxidation process is finished, the film thickness is evaluated (S3). Examples of the film thickness measurement include an optical measurement method using an ellipsometer (elliptical ellipsometry) and an X-ray measurement method such as XPS (X-ray photoelectron spectroscopy). The obtained film thickness is compared with basic data (reference) (S4). Then, the surface temperature of the oxidized sample is estimated. The reference is an oxide film thickness obtained by oxidation (thermal oxidation) in a state heated by a hot plate or the like without using light. The reason why the oxide film thickness by thermal oxidation is used as a reference is that the sample heated by the hot plate has a uniform temperature in the sample, and the surface temperature of the sample is regarded as the same. An embodiment of the present invention will be described with reference to an example in which the surface temperature of a Si (100) substrate to which irradiation of ultraviolet light (wavelength 248 nm) is applied is estimated. In-situ measurement can be performed by providing a film thickness measurement probe in the chamber. In-situ analysis enables feedback of the amount of light irradiation.

(First embodiment)
In the present embodiment, the surface temperature of silicon (100) by KrF excimer laser (wavelength: 248 nm) irradiation is also obtained. Si (100) was prepared as an oxidation substrate used for estimation of the substrate surface temperature in FIG. Si is suitable for surface temperature measurement because it has excellent surface flatness and can measure even a very thin film (<1 nm) precisely. The light source KrF excimer laser is a light source having an optimum wavelength for photoexciting ozone. Therefore, it is assumed that the surface temperature for low-temperature oxidation of ozone is known, and the following examples were able to observe the effect of surface heating by light.

[1] Photo-oxidation treatment FIG. 2 is a schematic configuration diagram of an oxidation treatment apparatus 1 according to an embodiment of the invention. The oxidation treatment apparatus 1 includes an oxidation treatment gas supply device 11, a chamber 12, and an exhaust pump 13. The arrows shown represent gas flow. The piping system that connects the oxidizing gas supply device 11 and the chamber 12 and the piping system that connects the chamber 12 and the exhaust pump 13 preferably have room temperature.

  The oxidation treatment gas supply device 11 is an oxidation treatment gas cylinder or a generator. An oxidizing gas such as an oxygen mixed gas is used as the oxidizing gas. In the examples, oxygen gas having a purity of 100% was used. This is because even in the reference, 100% oxygen gas is used for thermal oxidation, and the thermal oxidation rate is calculated. Since the oxygen concentration affects the oxidation rate, it must be aligned.

  The chamber 12 stores a substrate 20 to be subjected to an oxidation process as shown in FIG. Connected to the chamber 12 are a pipe 21 through which the oxidizing gas is supplied from the oxidizing gas supply device 11 and a pipe 22 through which the gas sucked by the exhaust pump 13 is discharged. The form of the pipes 21 and 22 may be in accordance with the pipe system of the oxide film forming apparatus related to photoexcited ozone oxidation disclosed in JP-A-2006-080474. The substrate 20 in the chamber 12 is placed on the susceptor 23. The susceptor 23 can be moved in the chamber 12 by a moving mechanism 24. The moving mechanism 24 may be a substrate moving means employed in semiconductor manufacturing technology.

  The chamber 12 is provided with a pressure gauge 25. The pressure gauge 25 has a pressure range of 0.1 Pa-100,000 Pa.

  Further, an irradiation window 27 for introducing ultraviolet light emitted from an ultraviolet light source 26 is provided on the ceiling of the chamber 12. The irradiation window 27 is made of a material that transmits light from the light source 24. In the embodiment, since a KrF excimer laser is applied as the light source 24, a material (for example, synthetic quartz) made of a material that transmits light in a wavelength band of 200 nm to 300 nm is used. The light source 26 is not limited to the laser type and may be a lamp type as long as the light from the light source 26 is set so as to be irradiated on the surface of the substrate 20.

  In order to cope with the exhaust treatment, the material of the chamber 12 is limited to a vacuum-compatible material made of aluminum metal, SUS metal, or quartz glass. Further, during decompression, the surface in the chamber 12 is subjected to processing such as electropolishing so as not to discharge contaminants from the material of the chamber 12.

  FIG. 4 is a perspective view showing the positional relationship between the gas flow of an oxidation treatment gas (oxygen) used for the oxidation treatment of the substrate surface and the ultraviolet light irradiation region. The arrows shown indicate the direction of the oxidation process gas flow. The light wavelength of the light source is 200 nm or more. This is because the Si substrate is not damaged. The irradiation method is not limited to either the continuous light method or the pulsed light method. In the embodiment, for example, a KrF excimer laser (wavelength: 248 nm) is used as the light source 26. The ultraviolet light from the light source 26 is irradiated in a rectangular shape like an irradiation region 28 having an irradiation area of 1 cm × 20 cm, for example. The gas flow of the oxidation treatment gas is controlled so as to be perpendicular to the long side of the irradiation region 28. As the substrate 20 and the susceptor 23, those that can accommodate an 8-inch wafer are used.

[2] Measurement of oxide film thickness The method of measuring the film thickness of the oxide film formed on the substrate 20 by the oxidation treatment gas is not particularly limited as long as it can be matched with the reference. For example, in the case of a SiO ₂ film of a Si (100) substrate, elliptical ellipsometry using a spectroscopic ellipsometer is used when the film thickness is 2 nm, and X-ray photoelectron spectroscopy (XPS) is used when the film thickness is 2 nm or less.

FIG. 5 is a characteristic diagram showing the XPS measurement result of a sample obtained by oxidizing Si (100). Measurements are made for two film thicknesses. For the film thicknesses of 3.1 nm and 4.9 nm measured with a spectroscopic ellipsometer (GESP5 made by SOPRA), the measurement data of each XPS measurement device (ESC model 5800 made by PHI) The curve shape is different. Specifically, the ratio of the peak intensity in the vicinity of 99 eV indicated as Si and the peak intensity indicated as Si ⁴⁺ (SiO ₂ ) is different. In general, the peak intensity of Si ⁴⁺ (SiO ₂ ) increases as the film becomes thicker. Thus, the film thickness can be obtained from the intensity ratio. In this example, since the surface temperature was in the range of 500 ° C. or less, the evaluation oxide film was thin (<1 nm), and the film thickness was obtained from the XPS measurement result.

[3] Reference In the substrate surface temperature measurement method according to the present invention, reference data is required for temperature estimation. The oxidation rate of Si (100) has been studied for a long time and it is easy to obtain a reference. FIG. 6 is a characteristic diagram showing the film thickness with respect to the thermal oxidation time of the Si substrate. The film thickness varies with temperature even during the same thermal oxidation time. FIG. 7 is a characteristic diagram showing the relationship between the temperature of the substrate and the thickness of the oxide film formed on the substrate when the oxidation time is fixed at 1 hour. As shown in this characteristic diagram, the low temperature data can be predicted by an extension from the high temperature data. In the examples, data in a temperature range of 600 ° C. or lower was used. FIG. 6 discloses the result (broken line) of the Si (111) oxide film thickness in addition to the Si (100) oxide film thickness. Even at the same temperature, the thickness of the oxide film formed differs between the Si (100) substrate and the Si (111) substrate. Therefore, it is important to use a Si wafer having the same crystal orientation plane of the Si substrate (Si (100) in the embodiment).

[4] Application Example in Si Low Temperature Oxidation The surface heating temperature is used from the process of forming the SiO ₂ film on the Si substrate (100).

  As the light source 26 shown in FIG. 3, a KrF excimer laser having the following specifications was used.

Wavelength 248nm
Repetition frequency 15-100Hz
Irradiation pulse time -10ns
Irradiation intensity: 100-5 mJ / cm ²
Irradiation area 1cm x 3-20cm
KrF light is incident from the light source 26 into the chamber 12 (volume up to 5000 cm ³ ). The oxygen gas was controlled to flow in a direction perpendicular to the optical path of the KrF light. The oxygen gas supplied to the chamber 12 passes through the optical path of ultraviolet light and is exhausted. The wall of chamber 12 was kept at room temperature. The substrate 20 and the susceptor 23 were kept at room temperature. The oxygen gas used for the photo-oxidation treatment was used at a concentration of ˜100%. The film thickness was evaluated using an XPS measurement apparatus (ESCA model 5800 manufactured by PHI).

[5] Results (1) Reference FIG. 8 shows an example of thermal oxidation. It is the characteristic view which showed the evaluation result of the film thickness by XPS with respect to Si (100) board | substrate when it oxidizes for 1 hour under the temperature of 20 degreeC, 150 degreeC, and 320 degreeC. As the heating temperature of the sample increases, the thickness of the oxide film formed increases, and it can be considered that the film thickness can be evaluated by XPS.

(2) Light Irradiation Energy Dependency FIG. 9 is a characteristic diagram showing the surface temperature dependence of the Si (100) substrate with respect to incident energy of light irradiation. The underlying substrate is not heated (room temperature), and the oxidation time is 1 hour. As the irradiation energy increases, the surface temperature increases. In addition, the surface temperature was much higher than room temperature, and this proved that a local heating effect on the surface accompanying light absorption occurred.

(3) Irradiation Position Dependence FIG. 10 is a characteristic diagram showing the distribution of surface temperature when a part of the Si (100) substrate B is irradiated with light. The horizontal axis indicates the distance R from one end side of the irradiation region I. A horizontal axis of 0 mm means a place where light irradiation is applied, and as the distance R increases, it means a place farther from the irradiation region I.

  According to the measurement result shown in FIG. 10, it can be confirmed that the surface temperature T of the substrate B is highest in the irradiation region I, and the surface temperature T decreases as the distance from one end of the irradiation region I increases. However, even when the distance R from one end of the irradiation region I is 15 mm, the surface temperature T is much higher than the base room temperature. This is considered because heat is diffusing from the irradiation region I. Thus, it was confirmed that the temperature distribution on the substrate surface can be measured.

  From the examples described above, it is apparent that the resurface temperature of the substrate can be measured by the substrate surface temperature measuring method according to the present embodiment.

(Second embodiment)
The substrate surface temperature measurement method according to the present embodiment measures the surface temperature of the back surface of the region irradiated with light. This measurement method is the same as the measurement method according to the first embodiment of FIG. 1 except for the sample preparation step and the oxidation treatment step.

  FIG. 11 is a perspective view showing an arrangement of samples used for substrate surface temperature measurement according to the present embodiment. First, an evaluation sample to be prepared is one in which a material capable of forming an oxide film is deposited on the back side of the surface that is exposed to light (for example, double-side polished Si wafer, Si layer volume glass, etc.). This is because the temperature of the back surface is known by examining the oxidation rate of the surface not exposed to light. Moreover, the evaluation sample is limited to a material made of a material that does not transmit the irradiated light to the back surface. This is because if the irradiated light is transmitted, light absorption occurs in the material that oxidizes on the back surface of the sample.

  Therefore, the form of photooxidation in the present embodiment is such that the evaluation sample 30 is arranged in a hollow state as shown in FIG. That is, the evaluation sample 30 is held in a state of being lifted from the susceptor 23 by the jig 31. The jig 31 is made of a clean material that does not contaminate the system, and is preferably a heat insulating material that does not transmit the heat of the evaluation sample 30 to the susceptor 23. For example, the material can be synthetic quartz. Since the evaluation sample 30 is in a state of floating from the susceptor 23, the oxidation treatment gas bypasses the back surface of the evaluation sample 30 in the light irradiation region indicated by the dotted line. Therefore, not only the oxide film 3a is formed on the surface of the evaluation sample 30, but also the oxide film 30b is formed on the back surface thereof by the oxidation treatment gas. Then, by measuring the thickness of the oxide film 30b, the surface temperature of the back surface can be known.

  As described above, the substrate surface temperature measuring method of the present embodiment can be a useful technique for examining the thermal damage of the substrate base in the low temperature oxidation technique.

The flowchart figure which showed the procedure of the substrate surface temperature measurement which concerns on invention. The schematic block diagram of the oxidation processing apparatus which concerns on embodiment of invention. The schematic block diagram of an oxidation treatment chamber. The perspective view which showed the positional relationship of the gas flow of oxidation process gas, and the irradiation area | region of an ultraviolet light. The characteristic view which showed the measurement result of XPS of the sample which oxidized Si (100). The characteristic view which showed the film thickness with respect to the thermal oxidation time of Si substrate. The characteristic view which showed the relationship between the temperature of a board | substrate in case oxidation time is 1 hour, and the film thickness of the oxide film currently formed in the said board | substrate. The characteristic view which showed the evaluation result of the film thickness by XPS with respect to Si (100) at the time of oxidizing at the temperature of 20 degreeC, 150 degreeC, and 320 degreeC for 1 hour. The characteristic view which showed the surface temperature dependence of Si (100) with respect to the incident energy of light irradiation. The characteristic view which showed distribution of the surface temperature at the time of irradiating light to a part on Si (100) board | substrate. The perspective view which showed the arrangement | positioning form of the sample used for the substrate surface temperature measurement which concerns on 2nd embodiment of invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Oxidation processing apparatus 11 ... Oxidation process gas supply apparatus, 12 ... Chamber, 13 ... Exhaust pump 20 ... Substrate, 21, 22 ... Pipe, 23 ... Susceptor, 24 ... Moving mechanism, 25 ... Pressure gauge, 26 ... Light source, 27 ... Irradiation window 28 ... Irradiation region 30 ... Evaluation sample, 31 ... Jig, 30a, 30b ... Oxide film

Claims (6)

A substrate surface temperature measuring method, comprising: measuring a surface temperature of a substrate based on a measurement result of a film thickness of an oxide film formed on a substrate used in an oxidation process system using an oxidation treatment gas and light irradiation .   2. The substrate surface temperature measuring method according to claim 1, wherein the thickness of the oxide film is measured by ellipsometry or X-ray photoelectron spectroscopy.   3. The substrate surface temperature measuring method according to claim 1, wherein the oxidation treatment gas is oxygen gas.   4. The substrate surface temperature measurement according to claim 1, wherein the substrate surface temperature measurement according to claim 1 can be applied to a surface temperature measurement of a substrate surface that is not directly exposed to light by disposing the substrate in a hollow state in the oxidation process system. 5. Method.   3. The substrate surface temperature measuring method according to claim 1, wherein a surface temperature is measured in-situ during an oxidation process by providing an apparatus used for measuring the film thickness in a chamber.   3. The substrate surface temperature measuring method according to claim 1, wherein the process light irradiation amount can be fed back by measuring the surface temperature.

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