CN1159772C - Methods of making photodetectors - Google Patents

Abstract

A method of making a photodetector. It adopts special layout design, wide lead aluminum covering part of the field area, chloride ion treatment furnace tube, annealing in a low temperature furnace with hydrogen atmosphere, slow cooling and phosphorus gettering process. The photodetector prepared by this method has high reverse breakdown, small dark current, small junction capacitance, fast response speed, wide spectral response range, and excellent and stable parameters. The method can be widely used in the preparation field of photodetectors.

Description

Methods of making photodetectors

Technical field: The present invention relates to a method for preparing a silicon material semiconductor device, especially a method for preparing a photodetector.

Technical background: The photodetector is a silicon material semiconductor device, which is composed of the P region and the N region of the PN junction and the i intrinsic layer between the two regions. The photodetector is a high-purity single wafer. In the process, a certain amount of boron impurities is injected into the silicon wafer, and the P region of the boron shallow junction is formed after annealing. Phosphorus is injected on the back of the silicon wafer to form N-region and ohmic contact. The high-purity silicon material between the P and N regions is the i intrinsic layer. Because of this structure, it is also called a PIN photodiode.

Due to the different manufacturing process of the existing photodetectors, the device parameters vary greatly. Even if it is a process, it will cause a large difference in the performance of the prepared devices. Therefore, it is difficult to meet the needs of the application.

Summary of the invention: The purpose of the present invention is to provide a stable photodetector preparation method, so that the photodetector prepared by this method has a high reverse breakdown voltage, a small dark current, a small junction capacitance, a fast response speed, and a wide spectral response range. Wide, excellent and stable parameters.

The method for preparing photodetector of the present invention, its step comprises:

1. Prepare the layout of the photodetector unit,

The unit layout can adopt the following designs: the four corners of the aluminum ring, aluminum lead, and boron expansion area are designed as arcs, and the radius of the arc is greater than 100 microns; the width of the aluminum lead is 50-100 microns, the width of the lead hole is 10-20 microns, and the distance from the thick oxygen area is greater than 20 microns, covering thick oxygen 5-10 microns; aluminum ring width 50-100 microns; thick oxygen layer thickness in the field area greater than 500 nanometers; boron expansion in the P area, junction depth 100-500 nanometers.

2. Pretreatment of furnace tube before growing silicon oxide:

Purify the furnace tube; raise the furnace temperature to 1100°C; pass trichlorohexene to treat the furnace tube for 2 hours; lower the furnace temperature to 800°C; then put the cleaned silicon wafer into the furnace tube;

3. Growth of silicon oxide:

Raise the temperature of the furnace to more than 1000°C, and pass oxygen for 2-10 minutes; simultaneously pass oxygen and nitrogen for more than or equal to 10 minutes to grow silicon oxide; oxidize water vapor in the furnace tube for 2-3 hours; then grow with dry oxygen for 20-30 minutes, Then nitrogen and oxygen are switched off to grow silicon oxide with a thickness greater than or equal to 800 nanometers; the furnace tube is cooled slowly; finally, the silicon wafer is taken out;

The slow cooling process is to slowly cool the furnace tube to less than 800°C, and then cut off the power to let it cool down naturally.

After taking out the silicon wafer, all the oxide layer can be rinsed off, and the oxidation process can be repeated to regenerate the oxide layer with a thickness greater than or equal to 800 nanometers.

4. Phosphorus expansion on the back side: protect the front side of the silicon wafer with glue, etch off the oxide layer on the back side, and then expand phosphorus on the back side:

5. Photolithographic active area;

6. Boron is injected into the shallow junction, the condition can be 35keV (kiloelectron volts), BF ₂ (boron fluoride) concentration 5E14/cm ² ;

7. Annealing: high-temperature rapid annealing under nitrogen protection at 1000°C for 1 minute; then low-temperature furnace annealing under nitrogen and hydrogen protection for 2-4 hours;

8. Photolithography lead hole;

9. Sputter aluminum leads to obtain a photodetector chip.

The invention has a new design for the layout, widens the width of the aluminum lead, covers thick oxygen in the field area, and the four corners are designed as circular arcs, which can avoid low-voltage leakage and breakdown, and also increase the reliability of the device. Otherwise, the device will have a reverse voltage breakdown within 100 volts during use.

Before growing the oxide layer, the furnace tube should be treated with trichlorethylene to prevent metal ion contamination in the growing oxide layer. Otherwise, the positive charge of metal ions in the oxide layer will form a leakage channel in the interface layer.

Anneal in a low-temperature furnace with a hydrogen atmosphere to reduce the unsaturated dangling bonds and other interface states in the oxide layer, and cut off the interface state leakage mechanism.

Slow cooling after the high temperature process can make the crystal lattice recover better, thereby increasing the minority carrier lifetime. Because the dark current is inversely proportional to the minority carrier lifetime. (Theoretical relational formula I=qnXA/2τ of dark current/minority carrier lifetime, I is electric current, q is electricity, n is charge quantity, XA is volume, τ is minority carrier lifetime).

Phosphorus gettering process

There are many kinds of gettering processes, such as polysilicon gettering, intrinsic gettering, etc. The application of phosphorus gettering process is relatively simple and compatible. Gettering can absorb defects and heavy metal ions in the crystal to the highly doped region of phosphorus. Reduce recombination center current. Because the defects in the space charge region and the recombination centers are the origins of the dark current.

The photodetector of the invention can be applied to the calorimeter of a high-energy particle collider to receive the violet light spectrum generated when the particles collide. Through detection, calculation, and comparison, it can be judged whether new substances are produced in the collision of particles. The photodetector of the present invention with a photosensitive effective area of 16.1* ^17.1mm2 is suitable for coupling large-area lead tungstate crystals to detect weak fluorescent light with a peak wavelength of 450 nanometers. It has characteristics different from ordinary photoelectric devices. At 25°C, the dark current is extremely small under the condition of full depletion voltage, about 3nA (nanoampere). When the spectral wavelength is 400-500nm, the quantum efficiency is 70-80%, and the fully depleted capacitance is less than 120pF.

The photodetector of the invention has extremely small dark current and small capacitance, so the noise of the device is low and the frequency response is high. Its most prominent feature is its high sensitivity to ultraviolet light and near ultraviolet light (300nm), which is the highest level of similar devices at home and abroad.

The test data of the spectral responsivity of the photodetector of the present invention is in the test certificate of the China Institute of Metrology (see the annex to the description). According to the data according to the quantum efficiency/responsivity relationship

        η＝1.24R(λ)/λ

(η means quantum efficiency, R(λ) spectral responsivity, λ means wavelength)

The quantum efficiency at the 300nm place of near ultraviolet light can be calculated, the quantum efficiency of the AME type detector produced in Norway is 4%, and the quantum efficiency of the photodetector of the present invention is 20%, which is five times of them.

Fig. 3 is the spectral response curve of the photodetector of the present invention. Fig. 4 is the quantum efficiency curve of the photodetector of the present invention. Figure 5 is the relationship curve between photoelectric detection dark current and reverse voltage. The test environment is 25°C. It can be seen from the figure that at -10 volts, the dark current per square centimeter of photosensitive area is about 0.4 nanoampere. Figure 6 shows that the greater the reverse voltage applied to the two poles of the detector, the smaller the junction capacitance. When it reaches -30 volts, the junction is completely depleted, and the junction capacitance is a stable value. The photosensitive area per square centimeter is 45pF.

Comparison of main parameters between the photoelectric detector of the present invention and the AME type detector produced in Norway

Invention (China) AME (Norway)

Effective photosensitive area (mm 16.1*17.1 16.1*17.1

Spectral Responsivity (A/W)(400nm) 0.262 (450nm) 0.302(450nm)0.29

Quantum Efficiency (%) (300nm) 20 (400nm) 70(300nm)4(400nm)41

Breakdown voltage (V) 150--700 120--500

Dark current (nA) 3 5

Fully Depleted Capacitance (pF) 120 150

Description of drawings:

Fig. 1 schematic diagram of planar structure of photodetector of the present invention

1---Aluminum ring arc angle 2---Aluminum lead arc angle 3---Aluminum lead wire 4---Aluminum ring

5---pressure point 6---field area 7---effective photosensitive area

Fig. 2 schematic diagram of photodetector sectional structure of the present invention

8----ceramic shell 10---P area boron expansion 11---silicon oxide 12----silicon nitride film layer

13----electrode leads 14---silicon-based high-resistance i intrinsic region 15---N area, that is, the electrode ohmic contact area

The spectral response curve of Fig. 3 photodetector of the present invention

Fig. 4 is the quantum efficiency curve of photodetector of the present invention

Figure 5 is the relationship curve between photodetection dark current and reverse voltage

Fig. 6 photodetector capacitance-voltage relationship curve of the present invention

Detailed ways:

1. Layout preparation.

Considering the breakdown voltage and surface leakage current, the graphics should be designed as circular as possible to avoid sharp corners and prevent electric field concentration and tip leakage. The active area of the device and the aluminum leads are designed with rounded corners. In addition, wide aluminum strips are designed on the outside of the surface to equalize the electrostatic field of charged particles.

2. Manufacturing process

1. Before SiO Growth

First of all, the furnace tube should be cleaned. The method is: raise the furnace temperature to 1100°C and pass the trichlorohexene treatment furnace tube for 2 hours, then lower the furnace temperature to 800°C. Then slowly put the cleaned silicon wafer into the furnace tube. In order to avoid sudden temperature changes, causing the silicon wafer to deform too much. Nitrogen protection was maintained for 40 minutes.

2. Silicon oxide growth

Raise the temperature of the furnace to 1000°C, and pass oxygen for 2-10 minutes. Then, after passing 1 part of oxygen and 2 parts of nitrogen at the same time for more than 10 minutes, turn off the nitrogen, and turn off the oxygen after a few minutes. During this period a dense layer of silicon oxide grows. Then, open the hydrogen-oxygen synthesizer and pass through the furnace tube for 2-3 hours. During this period of time, the water vapor is oxidized, and the texture of the grown silicon oxide is poor, but the silicon oxide grows faster. Next, turn off the hydrogen-oxygen synthesizer to stop the water vapor oxidation, turn on the oxygen and dry oxygen for 20-30 minutes, then turn on the nitrogen and turn off the oxygen. At this time, silicon oxide growth over 8000 Angstroms thick is complete. The following is the slow cooling process. It takes 400 minutes to slowly drop from 1000°C to 800°C. When it reaches 800°C, turn off the power and let the furnace temperature drop naturally. When the furnace temperature is below 200°C, the silicon wafers that have been oxidized can be taken out. After taking it out, rinse off all the oxide layer, repeat the above oxidation process, and regenerate the oxide layer.

3. Protect the front side of the silicon wafer with glue, etch off the oxide layer on the back side, and then expand phosphorus on the back side.

4. Lithographic active area.

5. Shallow junction implanted boron 35keV BF ₂ concentration 5E14/cm ²

6. High temperature rapid annealing nitrogen protection, 950°C for 45 seconds

7. Low temperature furnace annealing (nitrogen, hydrogen protection) N ₂ : H ₂ =60:4, 3.5 hours

8. Photoetched lead holes.

9. Sputtered aluminum leads,

The chip of the photodetector of the present invention is manufactured through the above process. After dicing, testing, and packaging the chip in a ceramic socket, the device is manufactured.

Claims (7)

1. A method for preparing a photodetector, the steps comprising: 1) Prepare the photodetector unit layout; 2) Pretreatment of the furnace tube before growing silicon oxide: Purification furnace tube; Raise the furnace temperature to 1100°C; Pass the trichlorohexene treatment furnace tube for 2 hours; Lower the furnace temperature to 800°C; Then put the cleaned silicon wafer into the furnace tube; 3) Growth of silicon oxide: Raise the temperature of the furnace to more than 1000°C, and pass oxygen for 2-10 minutes; Simultaneously feed oxygen and nitrogen for more than or equal to 10 minutes to grow silicon oxide; Oxidation of water vapor in the furnace tube for 2-3 hours; Then grow with dry oxygen for 20-30 minutes, then pass nitrogen and oxygen off, and grow silicon oxide with a thickness greater than or equal to 800 nanometers; Slowly cool down the furnace tube; Take out the silicon wafer; 4) Phosphorus expansion on the back: Protect the front side of the silicon wafer with glue, etch off the oxide layer on the back side, and then expand phosphorus on the back side: 5) Photolithographic active area; 6) Boron is injected into the shallow junction; 7) annealing; 8) Photolithographic lead holes; 9) Sputtering aluminum leads to obtain a photodetector chip. 2. the method for preparing photodetector as claimed in claim 1, is characterized in that The aluminum ring of the unit layout, the four corners of the aluminum lead, and the boron expansion area are designed as arcs, and the radius of the arc is greater than 100 microns; the width of the aluminum lead is 50-100 microns, the width of the lead hole is 10-20 microns, the distance from the thick oxygen area is greater than 20 microns, and the coverage is thick The oxygen is 5-10 microns; the width of the aluminum ring is 50-100 microns; the thickness of the oxygen layer in the field area is greater than 500 nanometers; the boron is expanded in the P area, and the junction depth is 100-500 nanometers. 3. The method for preparing a photodetector as claimed in claim 1, characterized in that in the process of growing silicon oxide, after taking out the silicon wafer, all the oxide layers are washed away, and the oxidation process is repeated to regenerate the oxide layer with a thickness greater than or equal to 800 nanometers . 4. The method for preparing a photodetector according to claim 1, characterized in that the ratio of oxygen and nitrogen fed simultaneously when growing silicon oxide is 1:2. 5. The method for preparing a photodetector according to claim 1, characterized in that after growing silicon oxide with a thickness greater than or equal to 800 nanometers, the temperature of the furnace tube is slowly cooled to less than 800°C, and then the power is turned off to allow natural cooling. 6. The method for preparing a photodetector as claimed in claim 1, characterized in that the conditions for implanting boron into the shallow junction are 35keV and the BF ₂ concentration is 5E14/cm ² . 7. The method for preparing a photodetector as claimed in claim 1, characterized in that the annealing process is 1000 ° C nitrogen protection high temperature rapid annealing for 1 minute; Then anneal in a low temperature furnace for 2-4 hours under the protection of nitrogen and hydrogen.

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