JPH05315271A - Method and apparatus for diffusing impurity - Google Patents

Abstract

PURPOSE:To accurately control a depth of a diffused layer in a real time by heating a sample in a vacuum chamber, introducing doping gas, irradiating a side face of the sample with an electron beam, and detecting a generated secondary electron signal and an electron beam induced current. CONSTITUTION:A sample 7 is held in a heating holder 11 in a vacuum chamber 1, and gas containing a diffusion source is introduced from a doping gas inlet 2. In this case, an electron beam generated from an electron gun 3 is converged to obtain an electron probe. A voltage is applied to a scanning coil 5 to scan the probe on a side face of the sample. Generated secondary electron signal and an electron beam induced current are intensity modulated, and projected on a CRT 10. Thus, a p-n junction surface due to diffusion can be controlled with high intensity in a real time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and device for diffusing impurities into a semiconductor substrate layer using an electron beam induced current method or a photoluminescence method.

[0002]

2. Description of the Related Art Conventionally, in a process of diffusing impurities into a semiconductor substrate, a closed tube type and an open tube type diffusing device have been used. The former is a quartz tube with a semiconductor substrate and a diffusion source (for example,
By encapsulating ZnAs or the like at the time of Zn diffusion and raising the temperature, and by the latter, the semiconductor substrate is placed in a high-temperature quartz tube through which a gas composed of a diffused substance (phosphine or the like at p diffusion) flows. By inserting, the impurities are diffused into the semiconductor layer.

[0003]

When the impurity diffusion is applied to the device fabrication, the controllability of the depth of the diffusion layer is an important point. However, the diffusion rate largely depends on the surface state of the target semiconductor layer, the crystal quality, the temperature distribution of the diffusion device, and the like. In particular, in the diffusion of compound semiconductors, the reproducibility is poor, and the accuracy of the diffusion depth is about several hundreds nm at present.

An object of the present invention is to solve the above problems and provide an impurity diffusion method and diffusion device capable of monitoring the depth of a diffusion layer in real time and controlling it with an accuracy of several tens nm. It is in.

[0005]

The impurity diffusing apparatus of the first invention comprises a vacuum chamber, a holder provided in the vacuum chamber for holding a sample, and a heating means for heating the sample. A gas inlet for introducing a doping gas into the vacuum chamber, an electron gun for irradiating the side surface of the sample with an electron beam, and a secondary electron signal and electron beam induced current generated by the electron beam irradiation. And means for detecting.

According to a second aspect of the present invention, a method for diffusing impurities diffuses impurities into a sample by fixing the sample to a sample heating holder in a vacuum chamber and introducing a doping gas from a gas inlet provided at one end of the vacuum chamber. At the time of irradiation, the side surface of the sample is irradiated with an electron beam from an electron gun provided in the vacuum chamber,
The depth of the pn junction surface formed in the sample is controlled in real time while detecting the secondary electron signal and the electron beam induced current from the sample.

An impurity diffusion device according to a third aspect of the present invention comprises an open tube type reaction tube provided with a high frequency coil on the surface thereof, into which a doping gas can be introduced, and a susceptor provided in the reaction tube for holding a sample. A laser for irradiating the sample surface with a laser beam and a means for detecting photoluminescence light generated from the sample surface by the laser beam irradiation are included.

In the method for diffusing impurities according to the fourth aspect of the invention, the sample is held in a susceptor in an open tube type reaction tube having a high frequency coil provided on the surface, and a doping gas is introduced from one side of the reaction tube into the sample. When diffusing impurities, the surface of the sample is irradiated with laser light emitted from a laser, and the photoluminescence from the sample is detected by a photodetector through a spectroscope while the depth of the pn junction surface formed in the sample is measured in real time. It is controlled by.

[0009]

FIG. 1 is a block diagram of a diffusion device using the electron beam induced current method of the present invention. The sample 7 is held by the sample heating holder 11 in the vacuum chamber 1, and a gas containing a diffusion source is introduced from the doping gas inlet 2 to diffuse impurities into the sample. At that time, this vacuum chamber 1
An electron beam generated from an electron gun 3 provided on the upper part of the condenser is converged through a condenser lens 4 and an objective lens 6 to obtain an electron probe. A voltage is applied to the scanning scan coil 5 by a signal from the scanning signal generator 9 to scan the side surface of the sample with this electron probe. The secondary electron signal and electron beam induced current (EBIC) generated by the interaction between the electron probe scanned on the side surface of the sample and the sample are brightness-modulated, and the amplifier 8
Through CRT10.

Here, EBIC means that among electron-hole pairs generated in the crystal by irradiation with a high-speed electron beam, minority carriers diffuse and some reach the pn junction, and as a result, they occur at both ends of the pn junction. It refers to the current that flows in an external circuit by generating electric power.

Therefore, when the side surface of the sample is irradiated with the electron probe and scanned, the EBIC becomes maximum at the pn junction surface. Secondary electron image on CRT and EBI in depth direction of sample
By projecting the C profile, pn due to diffusion
The joint surface can be controlled in real time with good brightness.

FIG. 2 shows the photoluminescence (P
It is a block diagram of the diffusion apparatus which uses the L) method. By placing the sample 7 on the susceptor 14 in the open tube type reaction tube 12, heating the inside of the reaction tube by heating with the high frequency coil 13 provided around the reaction tube, and flowing a gas containing a diffusion source therethrough. Impurities are diffused into the sample. At that time, the laser light emitted from the laser 15 is irradiated onto the surface of the sample, the luminescence light from this sample is converged by the converging lens 16, the photodetector 18 receives the light through the spectroscope 17, and the signal is detected by the phase detection amplifier 20. And the photoluminescence light intensity is monitored by the waveform monitor scope 21 or the recorder 22 to perform real-time control of the pn junction surface.

For example, when the sample structure is an InP / InGaAs / InP DH structure and Zn diffuses only to the InP layer of the surface layer, if the luminescence light intensity from the InGaAs layer is monitored, the pn junction surface becomes the surface. As soon as it enters the InGaAs layer from the InP layer, the photoluminescence light is attenuated. Therefore,
At this time, by ending the diffusion, the pn junction surface can be formed at the hetero interface.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a diffusion device for explaining a first embodiment of the present invention.

In FIG. 1, the diffusion apparatus comprises a vacuum chamber 1, a heating holder 11 provided in the vacuum chamber 1 for holding and heating a sample 7, and a gas for introducing a doping gas into the vacuum chamber 1. Inlet 2
And an electron gun 3 for irradiating the side surface of the sample 7 with an electron beam.
And an amplifier 8 for amplifying a secondary electron signal and an electron beam induced current (EBIC) signal generated by electron beam irradiation,
It is mainly composed of a CRT 10 which projects these signals. The EBIC signal is detected by the holder 11, and the secondary electron signal is detected by, for example, a photomultiplier tube and sent to the amplifier. The impurity diffusion method using this device will be described below.

First, the sample 7 was fixed to the sample heating holder 11, and the doping gas was introduced from the gas inlet 2. Diffusion was performed by using dimethyl zinc (DMZ) as a doping gas at 10 ^-5 T in a chamber having an ultimate vacuum of 10 ^-9 Torr.
orr (measured with a beam flux monitor at the position of the sample holder) was introduced. The applied voltage of the electron beam is 20 kV and the diffusion temperature is 450 ° C. Resistance heating is used as the sample heating method, and the sample holder is electrically insulated from its heating coil and chamber.
It is configured to detect the current.

FIG. 3 shows the planar type made in the first embodiment.
It is a sectional view of an InGaAs photodiode (PD). n ⁺
-Metal organic chemical vapor deposition (MO) on the InP (100) substrate 23.
VPE) method, n-InP buffer layer 24, n ^-- InGaAs
And growing a layer 25 and n-InP layer 26, it is deposited SiO ₂ / SiN _x layer 27 in the subsequent vapor deposition. p ⁺ region 28
Were formed using the diffusion method according to the first embodiment.

In this device, the n ^-- InGaAs layer 25 receives light to generate carriers (holes and electrons), and the holes are converted into p ⁺
The structure is such that a signal is obtained by drifting to the region 28. Here, in this device structure, the pn junction surface is n ⁻
-It is important to form the layer directly on the InGaAs layer 25 because the quantum efficiency is improved. That is, as seen in FIG.
The termination of Zn diffusion at the hetero interface between the -InP layer 26 and the InGaAs layer 25 is important for device characteristics. By using the diffusion method of the first embodiment, as shown in FIG.
It became possible to observe and control the joint surface in real time.

FIGS. 4A to 4C show InGaAs shown in FIG.
-In the fabrication of PD, the secondary electron image and the EBIC profile of the side surface of the InP layer when Zn is diffused in the InP semiconductor layer are shown. That is, FIG. 4A shows the secondary electron image and EBIC current profile of the sample before diffusion, and FIG. 4B shows when the p region 28 due to diffusion has reached the middle of the n-InP layer 26. FIG. 4C is a secondary electron image and EBIC current profile of the sample at the end of diffusion.

When a pn junction surface is formed in the semiconductor layer by Zn diffusion, electrons and holes generated by electron beam irradiation move to the pn junction surface by diffusion and generate an electromotive force, which causes a current to flow to an external circuit. Shed. That is, since electrons and holes generated near the pn junction surface are more likely to reach the pn junction surface, the EBIC current takes the maximum value at the pn junction surface as shown in FIG. 4B. .. As the pn junction surface becomes deeper, the position of the maximum value of the EBIC current also follows in real time, so that the pn junction surface can be controlled with high accuracy. Since it is important to diffuse Zn only in the n-InP layer 26 in the fabrication of this element, the diffusion was terminated at the position shown in FIG. 4C, and the pn junction surface could be easily controlled. .. The precision of the diffusion depth was ± 20 nm. The hole concentration is 5 × 10 ¹⁷ cm ⁻³ .

FIG. 2 is a block diagram of a diffusion device for explaining the second embodiment of the present invention. In FIG. 2, the diffusion device includes an open-type reaction tube 12 provided with a high-frequency coil 13 on the surface and capable of introducing a doping gas, a susceptor 14 provided in the reaction tube 12 for holding a sample 7, and a sample Laser 15 for irradiating the surface of 7 with laser light
A focusing lens 16, a spectroscope 17, and a photodetector 18 for detecting photoluminescence light generated from the surface of the sample 7 by irradiation with laser light, a phase detection amplifier 20 for amplifying a light reception signal thereof, and amplification. Waveform monitor scope 21 for monitoring the intensity of the emitted photoluminescence light
Alternatively, it is mainly composed of a recorder 22. In FIG. 2, reference numeral 19 is a light source for the photodetector. The impurity diffusion method using this device will be described below.

First, the sample 7 was fixed to the susceptor 14 and a doping gas was introduced. The diffusion was performed by introducing hydrogen-diluted dimethyl zinc (DMZ) as a doping gas at 5 cc / min. The diffusion temperature is 450 ° C.
The sample heating method uses high frequency heating. An Ar laser is used as the PL light source, and a PbS photodiode (P
Received by D).

Also in the second embodiment, the diffusion process of InGaAs-PD shown in FIG. 3 is performed as in the first embodiment. FIGS. 5A and 5B to FIGS. 7A and 7B are cross-sectional views in which a part of the energy band structure and the element structure drawing of FIG. 3 are extracted. As the diffusion progresses, the energy band structure and the device structure are changed to FIGS.
become that way.

As shown in FIGS. 5A and 5B, since the double hetero structure is formed before the diffusion of the impurities, the carriers are confined in the InGaAs layer 25. When irradiated with, high photoluminescence (PL) intensity can be obtained by recombination of electrons and holes. Even when the diffusion proceeds and the InP layer has a pn junction surface, as shown in the energy band structure diagram of FIG. 6A, the carriers are confined and the PL intensity is about the same as before the diffusion.

However, the pn junction surface has InP and InGaAs.
When it reaches the hetero interface of No. 3, as shown in FIG. 7A, holes flow out into the InP layer, and the absolute number of holes contributing to recombination with electrons decreases, so that the PL intensity sharply decreases. A graph in which the horizontal axis represents the diffusion time and the vertical axis represents the PL intensity is shown in FIG.
The horizontal axis represents the diffusion time and the vertical axis represents the PL intensity. As described above, the point where the PL intensity drops sharply is that the pn junction surface is InP.
And is the time to reach the InGaAs hetero interface. At this time, by ending the diffusion, the pn junction surface could be easily formed at the hetero interface. Accuracy of diffusion depth is ±
It was 20 nm. The hole concentration is 3 × 10 ¹⁷ cm ⁻³ .

[0026]

As described above, according to the present invention, E
The diffusion bonding surface can be easily controlled in real time by using the BIC method or the PL method. The traditional diffusion process is
Since the reproducibility of the diffusion rate is poor (particularly, in a compound semiconductor, the diffusion depth accuracy is up to several hundreds nm), it was necessary to set a condition every time. However, if the diffusion device of the present invention is used, The process of taking out becomes unnecessary, and the yield becomes almost 100%.

The accuracy of the diffusion depth is about several tens of nm. This can be expected to significantly reduce the time and cost of the diffusion process.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a diffusion device for explaining a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a diffusion device for explaining a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a photodiode made according to an embodiment of the present invention.

FIG. 4 is a partial cross-sectional view of a photodiode for explaining the first embodiment of the present invention.

FIG. 5 is a partial sectional view of an energy band structure and a photodiode for explaining a second embodiment of the present invention.

FIG. 6 is a partial sectional view of an energy band structure and a photodiode for explaining a second embodiment of the present invention.

FIG. 7 is a partial cross-sectional view of a photodiode and an energy band structure for explaining a second embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a diffusion time and a PL intensity for explaining a second embodiment of the present invention.

[Explanation of symbols]

1 Vacuum Chamber 2 Doping Gas Inlet 3 Electron Gun 4 Condenser Lens 5 Scanning Coil 6 Objective Lens 7 Sample 8 Amplifier 9 Scanning Signal Generator 10 CRT 11 Heating Holder 12 Reaction Tube 13 High Frequency Coil 14 Susceptor 15 Laser 16 Focusing Lens 17 Spectrometer 18 Photodetector 19 Photodetector power supply 20 Phase detection amplifier 21 Waveform monitor scope 22 Recorder 23 n ⁺ -InP (100) substrate 24 n-InP buffer layer 25 n ^-- InGaAs layer 26 n-InP layer 27 SiO ₂ / SiN _x layer 28 p ⁺ region

Claims (4)

[Claims] 1. A vacuum chamber, a holder provided in the vacuum chamber for holding a sample, a heating means for heating the sample, and a gas introduction for introducing a doping gas into the vacuum chamber. Impurities characterized by including a mouth, an electron gun for irradiating the side surface of the sample with an electron beam, and means for detecting secondary electron signals and electron beam induced currents generated by the electron beam irradiation. Diffuser. 2. A sample is fixed to a sample heating holder in a vacuum chamber, and a doping gas is introduced from a gas inlet provided at one end of the vacuum chamber to diffuse impurities into the sample. It is characterized in that the depth of the pn junction surface formed in the sample is controlled in real time by irradiating the sample side surface with an electron beam from the electron gun and detecting the secondary electron signal and the electron beam induced current from the sample. How to diffuse impurities. 3. An open-tube type reaction tube having a high-frequency coil on the surface thereof, into which a doping gas can be introduced, a susceptor provided in the reaction tube for holding a sample, and the sample surface is irradiated with laser light. And a means for detecting photoluminescence light generated from the surface of the sample by irradiation of the laser light, and a diffusion device for impurities. 4. A laser is used when a sample is held in a susceptor in an open tube type reaction tube having a high frequency coil on the surface, and a doping gas is introduced from one side of the reaction tube to diffuse impurities in the sample. Impurities characterized by irradiating the surface of a sample with emitted laser light and controlling the depth of a pn junction surface formed in the sample in real time while detecting photoluminescence from the sample with a photodetector through a spectroscope. How to spread.