JPS63166241A - Equipment for annealing semiconductor substrate - Google Patents

Abstract

PURPOSE:To enable monitoring of the activation quantity of implanted impurity ions in a real time by measuring the transmittivity of a semiconductor substrate by keeping the temperature of the substrate constant. CONSTITUTION:Infrared light for measurement is directed onto a semiconductor substrate 102 from irradiation means 103. The quantity of the infrared light is measured from the semiconductor substrate 102 by measurement means 104, annealing the semiconductor substrate 102. The activation state of impurity ions implanted in the semiconductor substrate 102 is detected by measuring the quantity of the infrared light transmitted through the semiconductor substrate 102 by detection means 105. This can appropriately control annealing time to facilitate the activation which minimizes crystal defects without elongating heating time unnecessarily.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an annealing apparatus for detecting the activation amount of implanted impurities during annealing of a semiconductor substrate into which ions have been implanted.

B. Conventional Technology In the semiconductor manufacturing process, it is essential to electrically activate impurity ions implanted into a semiconductor substrate by annealing. The amount of activation of impurity ions depends on the 2-hour annealing temperature, but conventionally, the effectiveness of annealing was evaluated by estimating this activation amount by measuring the resistance of the semiconductor substrate itself after the annealing was completed. There is. In order to achieve sufficient activation, it is sufficient to perform annealing at a high temperature and for a long time, but in this case, diffusion of impurities becomes a problem. In recent years, in order to suppress this impurity diffusion, optical heating devices that can perform heat treatment at high temperatures in a short time have been developed, but they have the following problems.

Problems to be solved by the C0 invention: If the heating temperature and heating time using the optical heating device are below the predetermined values, activation will not be sufficient. On the other hand, if the temperature and time are too high for activation, problems such as impurity diffusion will occur. ,
Since the temperature of the chamber in which the semiconductor substrates are placed rises excessively, the time required to exchange wafers in single wafer processing increases, resulting in a problem of reduced throughput.

Furthermore, there is a close relationship between activation rate and crystal defects in semiconductors, and heating conditions also affect device characteristics. Therefore, there is an optimal value for the heating conditions determined by the amount of activation of impurities, but conventionally, since the amount of activation cannot be monitored in real time during annealing, the annealing temperature is set for 2 hours for each semiconductor substrate during annealing. Conditions needed to be set.

An object of the present invention is to provide an annealing apparatus that can monitor the activation state of impurity ions in real time during annealing and easily control heating.

Means for Solving the D0 Problem Fundamental absorption and free carrier absorption are known as infrared light absorption by semiconductors. Fundamental absorption is due to the band gap of the crystal, and in the case of silicon, as shown in Figure 7,
Its wavelength range is approximately 1.1 μm or less, and its absorption coefficient does not depend on the carrier concentration P in silicon. On the other hand, free carrier absorption mainly occurs in a wavelength range of 1 μm or more, and its absorption coefficient increases with carrier concentration P and wavelength. That is, when impurity ions are implanted into a semiconductor substrate, only basic absorption exists in that state, but when this is annealed, free carriers are generated due to activation, and free carrier absorption appears. Therefore, it can be seen that there is a close relationship between the activation amount of impurity ions and free carrier absorption.

On the other hand, in FIG. 8, the activation state of the implanted impurity ions is used as a parameter, and the horizontal axis represents the wavelength and the vertical axis represents the spectral transmittance of the semiconductor substrate.

The solid line A shows the spectral transmittance of the semiconductor substrate before activation, the dashed line B shows the case where the semiconductor substrate is activated by annealing to a certain extent, and the broken line C shows the case where the semiconductor substrate is activated by further annealing.

■This figure shows that as the free carrier concentration increases with the activation of impurity ions, the infrared absorption coefficient increases and the transmittance decreases.

The present inventors paid attention to the above facts (1) and (2) and found that the activation state of impurity ions could be detected in real time by measuring the transmittance of the semiconductor substrate to infrared light while annealing the semiconductor substrate.

As shown in the diagram corresponding to the claims in FIG. In order to measure the amount of light, impurity ions implanted into the semiconductor substrate 102 are measured using a measurement means 104 provided on the opposite side of the semiconductor substrate 102 from the irradiation means 103 and the amount of infrared light transmitted through the semiconductor substrate 102. and detection means 105 for detecting the activation state of.

80 action irradiation means 103 irradiates the semiconductor substrate 102 with infrared light for measurement. While the semiconductor substrate 102 is being annealed, the amount of infrared light from the semiconductor substrate '102 is measured by the measuring means 104. Then, the detection means 105 detects the activation state of the impurity ions implanted into the semiconductor substrate 102 by measuring the amount of infrared light transmitted through the semiconductor substrate 102.

F. Embodiment An embodiment in which the present invention is applied to an optical heating device will be described based on FIGS. 2 to 6.

In FIG. 2(a), a semiconductor substrate 3 is placed on a base 2 in a chamber 1 made of quartz. As shown in FIG. 2(b), on the upper wall 1a and lower wall 1b of the chamber 1, three heating infrared lamps 4a, 4b+4c and 5'a, each having a different radius and arranged concentrically, are provided. '5b and 5c are installed to heat the semiconductor substrate 3. Upper wall Fa, lower wall 1
Opposed through holes 1c and 1d are formed in the center of b, and above these holes is an infrared lamp 6 for a IIl standard use, and the emitted light is converted into parallel light by a lens 7. A choker 8 that opens and closes the optical path of the parallel light is rotatably supported around a shaft 9, and the optical path is opened and closed by a drive device (not shown). Further, an infrared detector 10 is provided at a position facing the measurement infrared lamp 6 with the chamber 1 in between, and in front of the infrared detector 10 is a wavelength filter that matches the emissivity measurement wavelength of the substrate and the radiation measurement wavelength from the substrate. 11, and a lens 12 for condensing parallel light.

FIG. 3 shows the control section of this device. An infrared detector 10 is connected to a microcomputer 22. The microcomputer 22 includes a drive circuit 23 for the chopper 8, a lighting control circuit 24 for the measurement infrared lamp 6, and heating infrared lamps 4a to 4c.

A lighting control circuit 25 of 5a to 5c, a temperature display meter 26, and an activation amount display meter 27 follow.

In the above configuration, the measurement infrared lamp 6 is used as the irradiation means 1.
03, the infrared detector 10 constitutes the measuring means 104, and the microcomputer 22 constitutes the detecting means 105, respectively.

Next, the operation of this apparatus will be explained according to the processing procedure shown in FIG. 4 and the graphs shown in FIGS. 5 and 6.

Before explaining the processing procedure, the principle of temperature measurement of the semiconductor substrate 3 using the infrared detector 10 will be explained.

The spectral radiance N(
λ, T) is N(λ, T)=tλ(T)・Wλ(T)
...(1) However, it can be expressed as Eλ(T): emissivity of the substrate Wλ(T): spectral radiance of a black body. Further, the spectral radiance Wλ(T) of a black body can be expressed as C1, C,: constant λ: wavelength of emitted light T: black body temperature. Therefore, if the emissivity ελ(T) of the substrate 3 is given, N(λ, T
), and from equation (1), the spectral radiance Wλ(T) of the black body
is determined, and then the black body temperature T is determined from equation (2), and this value indicates the temperature of the substrate 3.

On the other hand, the emissivity Eλ(T) of the substrate 3 is ελ(T)=1−(τλ(T)+ρλ(T))
(3) However, Eλ(T) is the emissivity of two substrates, ρλ(T), and the reflectance of two substrates, τλ(T): can be expressed as the transmittance of the substrates. ρλ(T) is a unique value related to the refractive index of the substrate 3 and is a substantially constant value. therefore.

If τλ(T) is measured for the substrate 3 to be measured.

Eλ(T) can be easily calculated from equation (3), and the substrate temperature can be determined as described above.

Next, a procedure for measuring temperature and detecting the activation state of impurity ions will be explained.

First, the measurement infrared lamp 6 is turned on, and the output data NO. of the amount of infrared light from the infrared lamp 6 is input to the infrared detector 10 without the substrate 3 being placed on the base 2. is measured and its data number is stored in the microcomputer 22. The amount of light supplied from the measuring infrared lamp 6 is controlled by a control circuit 24 so as to be constant at least during measurement, and by a microcomputer 22.

The program shown in FIG. 4 starts, and in step S1, the chopper drive circuit 23 is driven to close the optical path of the measurement infrared light by the chopper 8. The light emitted from the infrared lamp 6 is converted into parallel light by a lens 7, but is blocked by a chopper 8 and does not reach the substrate 3. At this time, heating infrared lamps 4a to 4c, 5
The substrate 3 is heated by a to 5c, and infrared light that depends on the surface temperature of the substrate 3 and the like is emitted. The emitted infrared light is filtered by a wavelength filter 11, then condensed by a condensing lens 12, and then incident on an infrared detector 10.

And an infrared detector 10 corresponding to the spectral radiance of the substrate 3
The output Ni is stored (step S2).

Next, the chopper drive circuit 23 is driven to open the optical path of the measuring infrared light using the chopper 8 (step S3). As a result, the substrate 3 is irradiated with infrared light from the measurement infrared lamp 6. This infrared light activates the ions implanted into the substrate 3.
It passes through the substrate 3 at a rate that depends on the state of sexualization and the temperature. Therefore, the transmitted light and the emitted light from the substrate 3 described above are incident on the infrared detector 10, and a combined output Ni' of both is outputted. The microcomputer 22 stores this data Ni' (step S4).

Next, in step S5, the output data N0 of the infrared detector 10 when the infrared light from the measurement infrared lamp 6 directly enters without going through the substrate 3, which has been measured in advance, and the above-mentioned data N i , N x', (Ni' - Ni) /No=τi
...(4) is calculated, and i is determined from the transmittance at measurement time ti.

However, some of the infrared light for measurement that has passed through the substrate due to diffraction due to the pattern provided in the substrate may be transmitted to the infrared detector 10.
If it deviates from the range, Ni2 needs to be corrected. Next, the process proceeds to step S6, and from this transmittance i and the preset reflectance ρC, the emissivity εi is determined based on equation (3). Then, in step S7, this emissivity t
i and the output data Ni of the infrared detector 10 when the eyelid brim 8 is closed, the temperature Ti of the substrate 3 is determined by equations (1) and (2), and this temperature Ti is determined in step S8. is output to the temperature display meter 26. Also, although not shown,
The substrate heating set temperature Ts is set in advance by the microcomputer 22.
and compare it with the measured temperature Ti to determine the set temperature Ts.
A control signal is supplied to the lamp drive control circuit 25 until the heating infrared lamps 4a to 4c and 5a to 5c are turned on.

Next, in step S9, whether or not the substrate temperature is constant (Ti
=Ts). If the substrate temperature is constant, the contribution due to temperature to the concentration of free carriers that determines the transmittance τi determined in step S5 will be constant, and only the contribution of the activation amount of impurity ions will remain, so step S10 , the transmittance τi is converted into a value representing the amount of activation of impurity ions and output. If a negative determination is made, step S9
Skip.

The above procedure (steps 81 to 5IO) is carried out at time t1o+t2°lt in FIG. 5 while the substrate temperature is rising. ...
and when the substrate temperature is constant, the time t5°t ts in FIG. + tto * teo... By repeating this sequentially at predetermined time intervals, the annealing temperature of the substrate can be accurately measured in real time, and based on the results, the heating infrared lamps 4a to 4c, 5a to
5c, accurate temperature control is possible. In addition, the activation amount of impurity ions can be accurately determined based on the transmittance τi detected when the substrate temperature is constant.
Heating infrared lamps 4a to 4c, 5 in a desired activated state
Efficient annealing becomes possible by reducing or extinguishing lights a to 5c. In fact, the annealing may be completed when the activation amount calculated from the transmittance reaches a desired value, or when the amount of change thereof reaches a desired value.

In Figure 6, N,, NG, N,, N are the intensity of the emitted light from the substrate 3, and the reason why its magnitude increases even though the temperature of the substrate 3 is constant is This is because the activation amount of impurity ions increases and the emissivity of the substrate increases. Also, ΔN6. ΔN6゜ΔN7. The fact that ΔN decreases over time even though the light intensity of the measurement infrared lamp 6 remains constant indicates that the amount of activated impurity ions in the substrate 3 increases over time. There is.

In addition, it is desirable to use a wavelength of 4 μm or less that can pass through the quartz chamber as the heating infrared light, and in order to improve measurement accuracy, it is necessary to use the wavelength range of the measurement infrared light and the heating infrared light. Moreover, since free carrier absorption increases in proportion to the square of the wavelength at a wavelength of 1 μm or more, it is preferable to use a wavelength of about 5 μm as the infrared light for measurement.

Note that instead of opening and closing the optical path of the measurement infrared light using the chopper 8, an optical modulator, a polarizing element, etc. is provided in the optical path to control the amount of measurement infrared light irradiated onto the semiconductor substrate 3. You can do it like this. In this case, as long as the amount of measurement infrared light transmitted through the semiconductor substrate 3 does not significantly affect the output of the infrared detector, it is not necessary to reduce the amount to completely zero.

In this example, temperature measurement including substrate emissivity correction was performed using the same optical system used to detect the activation state, but this could be done using other temperature detection devices such as a thermal lightning pair. You can go. In other words, for example, a thermocouple may be attached to a dummy saw board placed near the substrate to be processed, and based on this it may be determined whether or not the temperature of the substrate to be processed is constant. Even if you install a thermal lightning pair and find lighting conditions for the heating infrared lamp that will keep the heating temperature of the substrate to be constant, and then heat the substrate under the same lighting conditions. good.

G6 Effects of the Invention According to the present invention, since the transmittance of the semiconductor substrate is measured while keeping the substrate temperature constant, it is possible to measure the transmittance that depends only on the activation state of the implanted impurity ions in the semiconductor.
The activation amount of implanted impurity ions can be monitored in real time. As a result, the annealing time can be appropriately managed without unnecessarily lengthening the heating time, which contributes to shortening the wafer exchange time due to single wafer processing, suppressing the decrease in throughput, and minimizing crystal defects. This makes it easy to suppress activation.

[Brief explanation of the drawing]

FIG. 1 is a diagram corresponding to claims, and FIGS. 2 to 6 are diagrams illustrating embodiments in which the present invention is applied to a light heating device.
FIG. 2(a) is an overall configuration diagram, FIG. 2(b) is a plan view of the heat lamp, FIG. 3 is a block diagram showing the control section, and FIG. 4 is a flowchart showing an example of the processing procedure. FIG. 5 is a graph showing the time change in the output of the infrared detector while the substrate temperature is rising, and FIG. 6 is a graph showing the time change in the output of the infrared detector when the substrate temperature is constant. FIG. 7 is a graph showing the infrared absorption coefficient for each wavelength of irradiation light in silicon, and FIG. 8 is a graph showing changes in the spectral transmittance of a semiconductor substrate due to annealing activation. 1: Chamber 3: Semiconductor substrates 4a to 4c, 5
a to 5c: Infrared lamp for heating 6: Infrared lamp for measurement 8
: Chopper 10: Infrared detector 11: Wavelength filter 101: Heating means 102: Semiconductor board 103: Irradiation means
104: Measuring means 105: Detecting means Patent applicant: Nippon Kogaku Kogyo Co., Ltd. Representative Patent Attorney Fuyuki Nagai JO Netsu Iσ. Fig. 1 Fig. 8 J≧ - to tπttt tstzt taθt3f Fig. 5 Valve surface Fig. 6 Fig. 7

Claims (1)

[Scope of Claims] An apparatus for annealing a semiconductor substrate into which ions have been implanted by controlling its temperature to a constant temperature using a heating means, comprising: an irradiation means for irradiating the semiconductor substrate with infrared light for measurement; a measuring means arranged on the opposite side of the irradiation means with respect to the semiconductor substrate to measure the amount of infrared light; and a measuring means disposed on the opposite side of the semiconductor substrate to the irradiation means; An annealing apparatus for a semiconductor substrate, comprising: a detection means for detecting an activated state of ions.