CN101478007A - Infrared detector in PbTe semi-conductor photoconduction and manufacturing process thereof - Google Patents

Abstract

An IR detector based on PbTe semiconductor epitaxial material in a photoconductor comprises a substrate, a semiconductor photosensitive resistance film deposited on the substrate, a protection layer on the surface of the photosensitive resistance film, and an electrode, wherein a non-doped PbTe semiconductor film grows on the CdZnTe substrate by Molecular Beam Epitaxial Equipment (MBE); a Ti-Au film is coated on the PbTe film by RF magnetron sputtering technique by using ZnS as an insulation layer to protect the main body part of the photoconductor to serve as the electrode; and the ZnS insulation protection layer has excellent transmittance in the IR wavebands of 2 to 10 mum. The PbTe IR detector in the photoconductor has higher photosensitivity and responsivity in the IR wavebands of 2 to 10 mum.

Description

PbTe semiconductor photoconductive mid-infrared detector and preparation method

technical field

The patent of the present invention relates to a narrow-bandgap semiconductor detector with mid-infrared band response and its preparation method.

Background technique

In recent years, with the traction of system applications, infrared detectors, as the core components of infrared complete machine systems, have attracted more and more attention in their research, development and even production. The infrared detector is a device that converts the incident infrared radiation signal into an electrical signal output. The photoconductive detector is a kind of infrared detector, also known as photoresistor. After the semiconductor absorbs photons with sufficient energy, some carriers in the body change from the bound state to the free state, thereby increasing the conductivity of the semiconductor. The detector made by using this photoconductive effect is a photoconductive detector.

PbTe is an important narrow-bandgap semiconductor mid-infrared optoelectronic material. The mid-infrared photoconductive detector made of this material has the advantages of high quantum efficiency, high sensitivity, and low device noise. As early as the early 1930s, PbS, which belongs to the same group of IV-VI semiconductors, was an infrared photoconductive detector first developed by the Germans. It was used in infrared communication devices in World War II. This kind of detector is also used for the fuze and detection target on the "Sidewinder" infrared guided missile, and it is still used until now. Due to the simple manufacturing process, low cost and high performance of IV-VI semiconductor photoconductive infrared detectors, they have been widely used until now.

Chinese patent 200810060092.7 discloses a method of preparing IV-VI semiconductor single crystal thin film by molecular beam epitaxy on CdTe substrate. PbTe is a kind of IV-VI semiconductor. The band gap of PbTe is narrower than that of PbS, and it can detect mid-infrared The undoped PbTe single crystal semiconductor thin film has a longer wavelength band, but this patent does not apply this undoped PbTe single crystal semiconductor thin film to a device for effectively detecting light in the mid-infrared band.

Contents of the invention

The purpose of the present invention is based on the non-doped PbTe semiconductor single crystal thin film prepared in Chinese patent 200810060092.7, to provide a device for effective detection of light in the mid-infrared band, and to improve the detection rate and response rate of mid-infrared light.

The photoconductive mid-infrared detector based on PbTe narrow-bandgap semiconductor epitaxial material provided by the present invention comprises a substrate, a narrow-bandgap semiconductor photoresistor film deposited on the substrate, a protective layer and an electrode on the surface of the photoresistor film, and the substrate is deposited on a CdZnTe semiconductor The narrow bandgap semiconductor on the surface is undoped PbTe single crystal thin film, ZnS is used as the insulating protective layer, the electrode is Ti-Au thin film, and the electrode lead is obtained by bonding the electrode with gold wire. It has high sensitivity and responsiveness.

The preparation method of the photoconductive detector based on PbTe narrow-bandgap semiconductor epitaxial material provided by the present invention is: according to the method of Chinese patent 200810060092.7 semiconductor single crystal thin film, using molecular beam epitaxy equipment (MBE) to grow undoped on the CdZnTe substrate PbTe semiconductor thin film; then on the PbTe thin film, vacuum evaporation method is used to evaporate the insulating protective layer ZnS, and radio frequency magnetron sputtering method is used to evaporate Ti-Au electrodes, and gold wires are bonded to the electrodes to obtain electrode leads to make PbTe Photoconductive mid-infrared detectors. Proceed as follows:

1. In the molecular beam epitaxy device, the molecular beam epitaxy growth method is adopted. The Pb atoms and Te atoms evaporated from the beam source furnace meet the surface of the single crystal substrate CdZnTe, and the atoms and molecules reaching the substrate surface pass through the substrate surface. Adsorption, migration and crystallization form a single crystal film of undoped PbTe;

2. The steps of preparing a PbTe photoconductive mid-infrared detector on a PbTe epitaxial semiconductor film include: (1) vapor deposition of ZnS; (2) photolithography; (3) corrosion of ZnS; (4) radio frequency magnetron sputtering and titanium gold plating; (5) Stripping; (6) Overlaying; (7) Corrosion of titanium gold; (8) Corrosion of ZnS isolation area; (9) Corrosion of PbTe isolation area; (10) Bonding of gold wires and electrodes.

The beneficial effect of the invention is that: in a low temperature environment (≤200K), the detector is sensitive to light in the mid-infrared band and has a large responsivity.

The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

Description of drawings

Figure 1 is the overall production process.

Figure 2 is a picture of the surface of PbTe after evaporating ZnS taken by a 50X optical microscope.

Fig. 3 is a photoetched PbTe surface image of No. 1 photolithographic plate taken by a 50 times optical microscope.

Figure 4 is a picture of the surface of PbTe after ZnS corrosion taken by a 50X optical microscope.

Fig. 5 is a 50 times optical microscope photographed PbTe surface of titanium-coated gold.

Fig. 6 is a picture of the surface of PbTe after stripping the titanium gold on the photoresist taken by a 50 times optical microscope.

Fig. 7 is a lithographic image of the No. 2 overlay photoresist plate taken by a 50X optical microscope.

Fig. 8 is a picture of the surface of PbTe after corrosion of titanium gold taken by a 50X optical microscope.

Fig. 9 is a picture of the PbTe surface after etching the ZnS isolation region taken by a 50X optical microscope.

FIG. 10 is a surface view of the etched PbTe isolation region taken by a 50X optical microscope.

FIG. 11 is a surface view taken by a 50X optical microscope after removing the photoresist.

Figure 12 is the photocurrent gain under different bias voltages.

Detailed ways

Example 1

The overall process steps of the detector are shown in Figure 1.

A. Epitaxial wafer cleaning

According to the method of Chinese patent 200810060092.7 semiconductor single crystal thin film, utilize molecular beam epitaxy equipment (MBE) to grow undoped PbTe semiconductor thin film on the single crystal substrate CdZnTe substrate; soak the epitaxial wafer with carbon tetrachloride successively for 5 minutes 2 times, soak in acetone for 5 minutes and 3 times, soak in alcohol 3 times for 5 minutes, rinse with deionized water 10 times, blow dry with nitrogen, and finally put it in an oven at 100 degrees Celsius for 10 minutes to dry.

B. Evaporation of ZnS

Prepare a piece of ZnS material, a ZnS evaporation boat, and install it in a thermal evaporation vacuum chamber. Take the epitaxial wafer and a silicon wafer and fix them on the thermal evaporation tray. The two pieces need to be close together and put the tray into the cavity. Close the bell jar of the vacuum chamber, the evaporation baffle, and the air leakage valve, plug in the power supply of the mechanical pump, open the valve of the lower pipeline and the valve of the upper pipeline successively, turn on the power supply of the diffusion pump to heat the diffusion pump, and turn on the cooling water and the vacuum of the resistance gauge. count. When the vacuum reaches 5Pa, close the upper pipeline valve and open the main pipeline valve. Turn on the ionization gauge, and when the vacuum degree drops to 3×10 ^-2 Pa, turn on the power supply of the vacuum cavity baking belt, bake the cavity for 30 minutes, and then disconnect the baking power supply. Heat the temperature of the tray to 100 degrees Celsius, and when the vacuum degree drops to 2×10 ^-3 Pa, the evaporation vacuum condition is reached. Turn on the evaporation power supply, increase the current until the ZnS starts to evaporate, open the evaporation baffle, evaporate for 45 seconds, close the evaporation baffle, reduce the evaporation current to zero, and disconnect the evaporation power supply. After 20 minutes, turn off the cooling water and the valve of the lower pipeline, and disconnect the power supply of the mechanical pump. Open the inflation valve, and after 7 minutes, open the bell jar of the vacuum chamber, and take the wafer for use (approximately 200nm ZnS is vapor-deposited on the epitaxial wafer). The surface of PbTe after evaporating ZnS is shown in Figure 2.

C. Photolithography (No. 1 photolithography version)

Arrange the darkroom conditions, take out the photoresist from the refrigerator and put it in the uniform fume hood for use, set the oven temperature to 80 degrees Celsius, pass the ZnS-coated epitaxial wafer and silicon wafer through conventional carbon tetrachloride, acetone, alcohol, After rinsing with ionized water, blow dry with nitrogen gas and place in an oven. After about 10 minutes, take out the epitaxial wafer and the silicon wafer for uniform coating. The conditions are 3000 rpm at a constant speed, 40 seconds of coating time, and a photoresist thickness of ~1.5 μm. After homogenizing, put the epitaxial wafer and silicon wafer into an oven at 85 degrees Celsius for pre-baking for photolithography. Time 20 minutes, then put the photoresist back into the refrigerator and clean the homogenizer with alcohol. At the same time, turn on the lithography machine and the mercury lamp power supply for preheating, and install the No. 1 photolithography plate on the lithography machine. After 20 minutes, take out the epitaxial wafer and silicon wafer and set the oven at 120 degrees Celsius. The photolithography condition is an exposure time of 60 seconds, and the exposure intensity is determined by the photolithography machine. After photolithography, the developing operation is carried out, the ratio of developer to water is 1:1, and the developing time is 40 seconds. After blowing dry with nitrogen, put it into an oven at 120 degrees centigrade for photolithography post-baking, and time it for 20 minutes. At this time, disconnect the power supply of the mercury lamp, and disconnect the power supply of the lithography machine after 20 minutes, in order to cool down the temperature of the mercury lamp. After 20 minutes, turn off the power to the oven. Figure 3 shows the photoetching results of No. 1 photolithography plate.

D. Corrosion of ZnS for the first time

Take a piece to etch ZnS, react the epitaxial wafer and silicon wafer with concentrated hydrochloric acid for 3-4 seconds, etch the ZnS film where there is no photoresist, rinse it with deionized water, dry it with nitrogen, and measure the thickness of ZnS on the silicon wafer with a step meter About 200nm, the PbTe surface after etching ZnS is shown in Figure 4.

E. RF magnetron sputtering titanium gold plating

RF magnetron sputtering titanium-plated gold Ti is 10nm, Au is 400nm, the surface of PbTe-plated titanium gold is shown in Figure 5.

F. Stripping the titanium gold on the photoresist

Soak the epitaxial wafer processed by the above steps in acetone under a water bath at 25 degrees for about 3 hours. Then take it out, place it in a petri dish filled with acetone, and wipe the surface of the material with cotton to wipe off the titanium gold film evaporated on the photoresist. Take out the epitaxial wafer, soak it in alcohol 3 times for 5 minutes each, rinse it with deionized water 5-10 times, and dry it with nitrogen gas. The PbTe surface after stripping off the titanium gold on the photoresist is shown in FIG. 6 .

G. Overlay No. 2 photolithography plate

Arrange the darkroom conditions, take out the photoresist from the refrigerator and put it in the uniform fume hood for use, set the oven temperature to 85 degrees Celsius, pass the etched epitaxial wafer and silicon wafer through conventional carbon tetrachloride, acetone, alcohol, After rinsing with deionized water, blow dry with nitrogen gas and place in an oven. After about 30 minutes, take out the epitaxial wafer and the silicon wafer for uniform coating, the condition is that the uniform speed is 6000 rpm, and the coating time is 40 seconds. After homogenizing, put the epitaxial wafer and silicon wafer into an oven at 85 degrees Celsius for pre-baking for photolithography, count for 20 minutes, put the photoresist back into the refrigerator and clean the homogenizer with alcohol. At the same time, turn on the lithography machine and the mercury lamp power supply for preheating, and install the No. 2 photolithography plate on the lithography machine. After 20 minutes, take out the epitaxial wafer and silicon wafer and set the oven at 120 degrees Celsius. This step of photolithography is overlay, and the photolithography plate needs to be aligned and nested with the surface pattern of the epitaxial wafer before exposure. The photolithography condition is an exposure time of 40 seconds, and the exposure intensity is determined by the photolithography machine. After photolithography, the developing operation is carried out, the ratio of developer to water is 1:1, and the developing time is 40 seconds. After blowing dry with nitrogen, put it into an oven at 120 degrees Celsius for post-baking of photolithography, and time it for 20 minutes. At this point, the mercury lamp power supply was disconnected, and the photolithography machine power supply was disconnected after 20 minutes. After 20 minutes, turn off the oven and take out the slices for storage. Overlay No. 2 photolithography plate is shown in Figure 7.

H. Corrosion of titanium gold

React the epitaxial wafer with potassium iodide solution in a _water bath at 25 degrees Celsius for about 30 seconds to etch Au; Ti. The surface of PbTe after corrosion of titanium gold is shown in Figure 8.

I. The second corrosion of ZnS

Etch the ZnS isolation region. React the epitaxial wafer with concentrated hydrochloric acid for 3-4 seconds, and rinse it with deionized water. The surface after etching the ZnS isolation region is shown in FIG. 9 .

J. Etching the PbTe Isolation Area

The epitaxial wafer was reacted with hydrobromic acid solution, etched at room temperature for 20 seconds, rinsed with deionized water, and dried with nitrogen gas. The surface image after etching the PbTe isolation region is shown in Figure 10.

L. Remove photoresist

Soak the epitaxial wafer treated in the above step in acetone, take out the epitaxial wafer, soak in alcohol 3 times for 5 minutes each, rinse with deionized water 5-10 times, and blow dry with nitrogen. The surface after removal of the photoresist is shown in Figure 11. M. Electrode leads are manufactured using a gold wire ball bonder to bond the gold wires to the electrodes, lead out the detector leads, and complete the detector before it can be used for testing.

Test Results

Through the above process, a detector chip with a complete semiconductor photoconductive structure is obtained.

In order to test the performance of the device, the chip was put into the Dewar bottle, and the gold wire on the corresponding electrode was soldered to the pin of the Dewar bottle with indium, and the mechanical pump was evacuated for 2 hours.

Liquid nitrogen was poured into the Dewar bottle, and the test was carried out under low temperature conditions. A total of 9 units were tested this time, and the photoconductive effect with high signal-to-noise ratio was detected. The photocurrent gain under different bias voltages is shown in Figure 12. Figure 12a is the detected photoconductive response at 3V bias, Figure 12b is the detected photoconductive response at 2V bias, and Figure 12c is the detected photoconductive response at 1V bias.

From the comparison in Figure 12, it can be known that the photocurrent gain of 3V bias is larger than that of 2V and 1V bias. Similarly, the photocurrent gain of 4V, 5V, 6V and other bias voltages has been observed, and there is no photocurrent at 3V bias Great gain. Therefore, the PbTe semiconductor photoconductive detector with a thickness of 2.5um produced by the process has the largest photocurrent gain under the bias voltage of 3V.

Claims (5)

1; a kind of based on Infrared Detectors in the photoconduction of PbTe semiconductor epitaxial material; comprise substrate; be deposited on the photosensitive resistance film of suprabasil semiconductor; the protective layer of photo resistance film surface; electrode; it is characterized in that: substrate is the undoped PbTe monocrystal thin films of narrow gap semiconductor that is deposited on the CdZnTe semiconductor; insulating protective layer is ZnS; electrode is Ti-Au film; ZnS has good transmissivity to 2～10 μ m middle-infrared bands, and Infrared Detectors has higher photoconduction sensitivity and responsiveness for the light of 2～5 μ m middle-infrared bands in the PbTe photoconduction.

2, the preparation method of Infrared Detectors in the photoconduction of the described PbTe semiconductor epitaxial of claim 1 material is characterized in that described preparation process is: utilize the molecular beam epitaxial device undoped PbTe semiconductive thin film of growing in the CdZnTe substrate; On the PbTe film, adopt vacuum deposition method evaporation insulating protective layer ZnS then; Adopt radio-frequency magnetron sputter method evaporation Ti-Au electrode; Obtain contact conductor with spun gold and electrode bonding, make Infrared Detectors in the PbTe photoconduction.

3, the preparation method of Infrared Detectors in the photoconduction of PbTe semiconductor epitaxial material according to claim 2 is characterized in that on PbTe epitaxial semiconductor film, and the Infrared Detectors step comprises in the preparation PbTe photoconduction: (1) evaporation ZnS; (2) photoetching; (3) corrosion ZnS; (4) rf magnetron sputtering titanium-gold-plating; (5) peel off; (6) alignment; (7) corrosion titanium; (8) corrosion ZnS isolated area; (9) corrosion PbTe isolated area; (10) spun gold lead-in wire and electrode bonding.

4, the preparation method of Infrared Detectors in the photoconduction of PbTe semiconductor epitaxial material according to claim 3, it is characterized in that utilizing radiofrequency magnetron sputtering technology to prepare Ti-Au membrane electrode, at first on PbTe, plate the metal Ti of 10nm, then the metal A u of plating 400nm on metal Ti.

5, the preparation method of Infrared Detectors in the photoconduction of PbTe semiconductor epitaxial material according to claim 3 is characterized in that corroding titanium and corrodes with liquor kalii iodide; The caustic solution of PbTe material is to corrode with hydrobromic acid solution.

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