JPH0425729A - Temperature measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate the need to set emissivity and to accurately measure the temperature of a body to be measured without contacting by finding the difference between the quantities of radiation from the body to be measured corresponding to plural absorption peak wavelengths and the quantity of radiation from a reference body. CONSTITUTION:A reference plate 18 is rotated by a specific speed by driving the rotary solenoid 17 of a 1st opening/closing mechanism 19 at a specific speed to chop infrared rays at the entrance part of an optical system 12 and an opening/closing plate 22 is rotated by the motor 21 of a 2nd opening/closing mechanism 20 in synchronism with the 1st opening/closing mechanism 19 to chop infrared rays at the exit part of the optical system 12. Then the influence of an optical noise component is removed by calculating the difference between the signals in the opening and closing states of the 1st opening/closing mecha nism 19 and pulse signals obtained by the opening and closing of the 2nd opening/closing mechanism 20 are averaged to obtain measurement signals of two kinds of the quantity of infrared rays from the body to be measured (semiconductor wafer 2 and photoresist 2a) while electric noises are reduced, thereby measuring the temperature according to the signal.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a temperature measuring device.

(Prior Art) In general, temperature measuring devices that measure the temperature of a measured object have conventionally been divided into temperature measuring devices that measure the temperature of a measured object by bringing a temperature sensor such as a thermocouple into contact with the measured object, and There is a temperature measurement device that measures emitted infrared rays and calculates the temperature of a measured object from the amount of radiation.

Of these devices, the latter device utilizes the Stefan-Boltzmann law, and is expressed by the following equation, T-(E/(70ε
)” is used to calculate the temperature of the object to be measured, but in actual measurements, these estimated values E′ε′ are used because there is no way to accurately know the emissivity E and the radiation rate ε. hand,
The temperature T- is estimated by the following equation.

T=-(E-/σ0ε-, l/4 In these equations, σ0 is the Stefan Boltzmann constant [4,88X10-' (Kcal/ 12hK
')] is shown.

According to this temperature measuring device, the temperature can be measured without contacting the object to be measured.

(Problem to be Solved by the Invention) However, among the conventional temperature measuring devices described above,
Temperature measuring devices that measure temperature by bringing a temperature sensor such as a thermocouple into contact with a measured object have a problem in that it is not possible to measure the temperature of a portion that cannot be brought into contact with the temperature sensor.

For example, in a baking device that places a semiconductor wafer on a heating plate and bakes a photoresist coated on the surface of the semiconductor wafer, it is preferable to control the heating temperature by detecting the temperature of the photoresist.

However, since it is not possible to bring a temperature sensor into contact with the photoresist coated on the surface of a semiconductor wafer (this would damage the photoresist film), for example, a temperature sensor such as a thermocouple is buried inside the heating plate. The temperature of the photoresist is estimated from the temperature. However, this method has a problem in that it is not possible to accurately detect the temperature of the photoresist.

In addition, conventional temperature measurement devices that measure infrared rays etc. emitted from a measured object and calculate the temperature of the measured object using the Stefan-Boltzmann law from the amount of radiation do not make contact with the measured object. Since the temperature can be measured, the temperature of the photoresist can be directly measured even in the case of the above-mentioned baking device.

However, in this case, for example, silicon wafers and photoresists have high transmittance to infrared rays, so the infrared rays from the heating plate are mainly measured and the temperature of this heating plate is measured. The problem is that temperature cannot be measured. Another problem with this device is that it is necessary to set the emissivity, which cannot be accurately known.

The present invention has been made in response to such conventional circumstances, and aims to provide a temperature measuring device that does not require emissivity settings and can more accurately measure the temperature of a measured object without contact. That is.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a means for measuring the amount of radiation at a plurality of absorption peak wavelengths determined from the absorption characteristics of an object to be measured, and a method for measuring radiation incident on the means. radiation from the object to be measured;
means for switching to radiation from a reference whose emissivity is known; and calculating the temperature of the object to be measured from the difference between the amount of radiation from the object to be measured and the amount of radiation from the reference at the plurality of absorption peak wavelengths. It is characterized by comprising means.

(Function) In the temperature measuring device of the present invention having the above configuration, the amount of radiation is measured at a plurality of absorption peak wavelengths determined from the absorption characteristics of the object to be measured. That is, since the emissivity and absorption rate of the object to be measured are equal, the amount of radiation is measured at a wavelength with high absorption rate (absorption peak wavelength), that is, a wavelength with high emissivity.

Further, the radiation amount from the object to be measured and the amount of radiation from a reference whose emissivity is known are switched and measured, and the temperature of the object to be measured is calculated from the difference between these amounts of radiation.

Therefore, the temperature of the object to be measured can be accurately measured without contact, and there is no need to set the emissivity.

(Example) Hereinafter, an example in which the temperature measuring device of the present invention is applied to temperature measurement in a baking process after applying a resist solution to the surface of a semiconductor wafer will be described with reference to the drawings.

The baking apparatus 1 is provided with a heat generating plate 3 on which a semiconductor wafer 2 can be placed. This heating plate 3 is provided with a resistance heater 4 as a heating means, for example, and this resistance heater 4 is equipped with a temperature controller 5.
A power source 6 configured to be able to control the electric power supplied to the resistance heater 4 is connected thereto.

The heat generating plate 3 is housed in a casing 8 having a heat insulating material 7. In addition, in order to measure radiation from the semiconductor wafer 2 with a temperature measuring device 10 to be described later, for example, the ceiling of the housing 8 is provided with a transmittance of electromagnetic waves (for example, infrared rays) in the wavelength range to be measured by the temperature measuring device 10. A window 9 made of a high quality material is provided.

Note that the surface of the heat generating plate 3 on which the semiconductor wafer 2 is placed is given a mirror finish by, for example, forming a metal thin film by sputtering or the like. This is to reduce the influence of infrared rays from the heat generating plate 3 on temperature measurement, which will be described later. Even if the infrared rays emitted from the surface of the heat generating plate 3 are reduced in this way, the semiconductor wafer 2 has a high transmittance of infrared rays, and since heating is primarily performed by thermal conduction rather than by radiation, the semiconductor wafer 2 The reduction in heating efficiency is slight.

A temperature measuring device 10 is provided above the window 9 of the baking device 1. This temperature measuring device 10 includes a photoresist 2a attached to the surface of a semiconductor wafer 2 placed on a heat generating plate 3 or a semiconductor wafer 2 placed on a heat generating plate 3.
As the infrared detector 11 configured to be able to detect electromagnetic waves emitted from itself, such as infrared rays, for example, a thermomobile type light receiving element without wavelength dependence is provided.

Moreover, between this infrared detector 11 and the window 9,
An optical system 12 is provided to converge the infrared rays and make them enter the infrared detector 11. This optical system 12 includes, for example, a convex mirror 14 provided facing downward on the ceiling in a lens barrel 13, a concave mirror 15 having an opening in the center and provided opposite to this convex mirror 14, and this concave mirror 15.
It is composed of an annular light shielding plate 16 provided at the lower part of the screen.

The light shielding plates 16 are arranged in multiple stages and have a labyrinth structure to form a still air layer to prevent dust from adhering to the light and temperature fluctuations due to air convection.

As shown by the arrow in the figure, stray light components are removed from the infrared rays that enter the lens barrel 13 through the window 9 by the light shielding plate 16, and after passing through the opening of the concave mirror 15, the infrared rays are reflected by the convex mirror 14 to the concave mirror 15. Then, the concave mirror 15 focuses the infrared light onto the infrared detector 11 .

A reference plate 1 rotated by a rotary solenoid 17, for example, is provided between the optical system 12 and the window 9.
8, a first opening/closing mechanism 19 is provided which intermittently cuts off (chops) infrared rays incident on the optical system 12 (therefore, the infrared detector 11) from the window 9.

At least the surface 18a of the reference plate 18 of the first opening/closing mechanism 19 facing the optical system 12 is made of a material with a known emissivity. In other words, when the first opening/closing mechanism 19 is closed, the reference plate 1 is connected to the infrared detector 11.
Infrared rays from the surface 18a (material with known emissivity) of 8 and various parts of the optical system 12, such as the convex mirror 14, the concave mirror 15,
When infrared rays from the light shielding plate 16 and the like are incident, and on the other hand, the first opening/closing mechanism 19 is open, infrared rays from the object to be measured (semiconductor wafer 12 and photoresist 2a) that have passed through the window 9 are detected by the infrared detector 11. The optical system 12 is configured such that infrared rays from each part of the optical system 12, such as the convex mirror 14, the concave mirror 15, and the light shielding plate 16, are incident.

Therefore, when calculating the temperature described later, by subtracting the infrared measurement signal when the first opening/closing mechanism 19 is closed from the infrared measurement signal when the first opening/closing mechanism 19 is open, noise components from, for example, the optical system 12 are removed. However, it is configured to be able to measure temperature with high accuracy.

Note that the material for which the surface 18a of the □reference plate 18 is made has a known emissivity, and the emissivity does not change over time.
, and one that emits as little infrared rays as possible is preferable. Therefore, the surface 18a of the reference plate 18 is
For example, it is preferable to have a mirror finish by gold plating, but it is also possible to use an aluminum surface, for example.

Furthermore, as described above, if a mirror finish is applied, for example, by gold plating, the radiation from the surface 18g of the reference plate 18 can be reduced to a negligible level in normal measurements. Therefore, the temperature of the object to be measured can also be calculated using a signal obtained by subtracting the infrared measurement signal when the first opening/closing mechanism 19 is closed from the infrared measurement signal when the first opening/closing mechanism 19 is open. Further, a contact type temperature detector such as a thermocouple is provided on this reference plate 18, and the amount of radiation from the surface 18a of the reference plate 18 is calculated from the temperature measured by this temperature detector and the known emissivity. By adding to the signal difference and correcting it, the measurement accuracy can be further improved.

Further, between the optical system 12 and the infrared detector 11, there is a second opening/closing mechanism 20 that intermittently blocks (chops) infrared rays incident on the infrared detector 11 from the optical system 12.
is provided. This second opening/closing mechanism 20 is provided with, for example, a motor 21, a disk-shaped opening/closing plate 22 rotated by the motor 21, and a symmetrical position of the opening/closing plate 22. It is composed of a plurality of, for example, two narrowband bandpass filters 23 and 24 that selectively transmit infrared rays of λ2).

That is, by rotating the opening/closing plate 22 of the second opening/closing mechanism 20, the infrared detector 11 receives chopped infrared rays with a wavelength of λ1 and chopped infrared rays with a wavelength of λ2.
The structure is such that infrared rays of wavelengths of 1 and 2 are incident alternately. Therefore, the output signal of the infrared detector 11 is a pulse-like signal, and when calculating the temperature described later, for example, these pulse-like signals are averaged to reduce electrical noise.

Then, the output of the infrared detector 11 is amplified by the amplifier 25, and based on this amplified signal, the temperature calculator 26
The device is configured to calculate the temperature of the object to be measured (semiconductor wafer 2 and photoresist 2 a, ).

The temperature signal calculated by the temperature calculator 26 is configured to be fed back to the temperature controller 5, and the temperature controller 5 controls the power supply 6 based on the temperature measurement result, and the semiconductor wafer 2 Alternatively, the power supplied to the resistance heater 4 is adjusted so that the photoresist 2a reaches a predetermined temperature.

The temperature measuring device 10 having the above configuration measures the temperature of the photoresist 2a or the semiconductor wafer 2 in the following manner.

That is, by first driving the rotary solenoid 17 of the first opening/closing mechanism 19 at a predetermined speed and rotating the reference plate 18 at a predetermined speed, the infrared rays are chopped at the entrance of the optical system 12, and the second The opening/closing plate 22 is rotated by the motor 21 of the opening/closing mechanism 20 in synchronization with the first opening/closing mechanism 19, and the infrared rays are chopped at the exit portion of the optical system 12.

As described above, by taking the difference between the signals when the first opening/closing mechanism 19 opens and closes, the influence of optical noise components can be removed, and the pulse shape obtained by opening and closing the second opening/closing mechanism 20 can be removed. By taking the average of the signals, the infrared measurement signal from the object to be measured (semiconductor wafer 2 and photoresist 2a) with reduced electrical noise is converted to wavelength λ1,
λ2, and based on this signal, the temperature is calculated as follows.

As is well known, according to Blank's law, the monochromatic emission power E of electromagnetic waves (mainly infrared rays) from a black body is bλ Ebλ"C1"λ-5/ [exp (C2/λT)
-1] However, λ: Wavelength (m) T Kelvin temperature (K) C1: Constant -3,2179X 10-" (Kcal
・m2/h)C2: Constant -1,4388XIO
-Xl0-2 (can be expressed as

Therefore, if we express the estimated monochromatic output power E - and λ1 E22' at wavelengths λ1 and λ2 using Blank's law, then η1 and η2 are the efficiency of the infrared detector 11 at wavelengths λ1 and λ2, K1, K2 As the gain for wavelengths λ1 and λ2, E'
ε λ1 λ1 1 °η1 ・C, -λ1-5
/ [exp (C2/λ+T) −1−]−ελ1
・K1 ・f(λ1.T) Eλ2゛−ελ2 and 2φη2・cl・λ2−5/ [
exp (C2/λ2T)-11-ελ2・K2・f
(λ2.T). Here, ε λ 1 8 K 1 ・η 1 − ε
Calibrate K2 to the gain of the amplifier 25 so that it becomes K2- η 2λ 2 , and take the ratio of both equations: E −/E “−f(λ1.T) λ1 λ
2/f (λ2.T).

The temperature calculator 26 is, for example, NEWTON-RAPHS.
The temperature T is calculated from the above equation by numerical analysis such as the ON method.

Calibration of the above gains, K2, can be easily accomplished as follows.

For example, first, in the wavelength range of the radiation to be measured in practice, η1*η2, that is, the infrared detector 11
For example, a thermomobile type light receiving element is selected whose efficiency has no wavelength dependence and whose efficiencies η1 and η2 are equal with sufficient accuracy.

Next, monochromatic emissivities ελ1 and ελ2 at wavelengths λ1 and λ2 are determined from the previously measured absorption spectrum of the object to be measured. Using these ελ1 λ2, set the gain to 1 and 2 so that the ratio of 1 to 2 becomes K + / K 2 "Fε /ε λ2 λ1. In this case, 1 and 2 are set for the gain. There is a great advantage that the ratio is determined only from the optical properties of the object to be measured, regardless of the type of infrared detector 11.

Furthermore, if both the efficiencies η1 and η2 are known, K +
K1 and K1 may be set to 2, as shown in the following formula: /K2 εη2/ελ1η1λ2.

On the other hand, according to Kirchhoff's law, the ratio of emission power and absorption rate of all objects is equal, and its value is equal to the emission power of a black body. That is, the ejection powers of various objects are expressed as E, , K2.
...El, absorption rate φ1゜φ2.・・・・・・
φ. If the blackbody emission power and E1 absorption rate are φ, then the following equation holds true.

E, /φ+-E2/φ2-・・・・・・・・・-E/φ
-E If you transform this, E1/E-φ,, E2/E-φ2゜..., E, /E-φ.

However, EIl/E-ε, (emissivity) Because it is, ε1−φ1. ε2−φ2. ......, ε, -φ.

Therefore, it is derived that the emissivity of every object is equal to the absorption rate of the same object. Therefore, when making temperature measurements,
The wavelength at which the measured object has a high emissivity, that is, a high absorption rate (
By measuring infrared rays at the absorption peak wavelength), it is possible to realize highly accurate temperature measurement with less influence of infrared radiation from the background of the object to be measured.

Here, the graphs in Figure 2 and Figure 3, where the vertical axis is the transmittance and the horizontal axis is the wavelength, show the infrared rays when a silicon wafer and a photoresist film with a thickness of approximately 5 μm are formed on the silicon wafer, respectively. It shows the absorption characteristics for As shown in the graph of FIG. 2, the silicon wafer has absorption peaks at wavelengths of 9 μm and 16 μm, and as shown in the graph of FIG. has several absorption peaks at wavelengths of 3 μm and about 7 μm, for example.

Therefore, in this embodiment, when measuring the temperature of the semiconductor wafer (silicon wafer) 2, temperature measurement is performed with wavelengths λ1 and λ2 of 9 μm and 16 μm. Further, when measuring the temperature of the photoresist 2a, temperature measurement is performed with λ1 and λ2 set to 3 μm and 7 μm.

Note that the aforementioned gain of the amplifier 25, K2, needs to be calibrated separately in advance for measuring the temperature of the semiconductor wafer 2 and for measuring the temperature of the photoresist 2a.

That is, in this embodiment, the object to be measured (semiconductor wafer 2
Alternatively, the amount of infrared radiation at two wavelengths λ1 and λ2 corresponding to the infrared absorption peak wavelength of photoresist 2a) is measured, and the temperature is calculated from these measured values, so the amount of radiation at wavelengths with high emissivity can be calculated. By measuring, the measurement accuracy can be improved and the first
The opening/closing mechanism 19 and the second opening/closing mechanism 20 make it possible to obtain highly accurate measurement signals with reduced optical noise and electrical noise, so the temperature of the object to be measured can be accurately measured without contact. be able to.

Further, there is no need to set the emissivity as in the conventional case.

Furthermore, since the heating plate 3 has a mirror finish, the amount of infrared rays incident on the infrared detector 11 from the heating plate 3 can be reduced, allowing more accurate temperature measurement of the semiconductor wafer 2 and photoresist 2a. be able to.

Therefore, based on the accurate temperature of the photoresist 2a or the semiconductor wafer 2, the resistance heater 4 is connected to the power source 6.
The temperature of the photoresist 2a can be maintained at a desired temperature and a good baking process can be performed.

In the above embodiment, an example was explained in which the temperature side of the silicon wafer and photoresist in the baking process of semiconductor wafer \2 is kept constant, but the temperature measuring device of the present invention It can also be applied to temperature measurements, such as polyimide and silicone insulation films, insulation boards, ion-sensitized polyvinyl chloride films, and epoxy, acrylic, and polyurethane resins, as long as they have an absorption peak wavelength. Applicable.

[Effects of the Invention] As described above, according to the temperature measuring device of the present invention, it is not necessary to set the emissivity, and the temperature of the object to be measured can be accurately measured without contact.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a temperature measuring device according to an embodiment of the present invention, Fig. 2 is a graph showing the infrared absorption characteristics of a silicon wafer, and Fig. 3 is a graph showing the infrared absorption characteristics of a silicon wafer.
3 is a graph showing absorption characteristics for infrared rays when a photoresist film of m is formed. 1...Baking treatment, 2...Semiconductor wafer, 2a...Photoresist, 3...
...Heating plate, 4...Resistance heater, 5...
...Temperature controller, 6...Power supply, 7...
・Insulating material, 8... Housing, 9... Window, 10... Temperature measuring device, 11...
Infrared detector, 112...Optical system, 13...
... Lens tube, 14 ... Convex mirror, 15 ...
・Concave mirror, 16... Light shielding plate, 17...
Rotary solenoid, 18... Reference plate, 19... First opening/closing mechanism, 20...
・Second opening/closing mechanism, 21...Motor, 22...
...Opening/closing plate, 23.24...Filter
25...Amplifier, 26...Temperature calculator. Figure 1

Claims (1)

[Claims] (1) A means for measuring the amount of radiation at a plurality of absorption peak wavelengths determined from the absorption characteristics of the object to be measured, and a means for measuring the amount of radiation at a plurality of absorption peak wavelengths determined from the absorption characteristics of the object to be measured; radiation, and means for calculating the temperature of the object to be measured from the difference between the amount of radiation from the object to be measured and the amount of radiation from the reference at the plurality of absorption peak wavelengths. Characteristic temperature measuring device.