CN1265210C - Microstrip particle detector and preparation method thereof - Google Patents

Abstract

The invention relates to a microstrip particle detector made of directional growth [100] crystal plane diamond film on a silicon chip as a base material and a preparation method thereof. The microstrip particle detector of the present invention comprises a substrate and its surface coating, as well as a top electrode and a back electrode, and the substrate adopts a [100] silicon wafer; the upper surface of the substrate is a [100] oriented diamond film coating ; On the surface of the diamond film coating is the top electrode, the top electrode is made of chrome-gold composite, and processed by photolithography to form a micro-strip electrode with a width and spacing of 25 μm, and each micro-strip electrode has a magnesium-aluminum wire lead. ; The lower surface of the substrate is a back electrode, which is also a chrome-gold composite electrode. The preparation method of the detector of the present invention comprises the following steps: hydrogen plasma in-situ etching, silicon surface carburization, nucleation process, diamond surface growth process and chromium-gold compound electrode deposited on the surface. The invention prepares particle detectors by oriented growth of [100] diamond films on silicon wafers, which solves the problem of poor comprehensive performance of polycrystalline diamond films with arbitrary orientations, and at the same time solves the problem of high price caused by the use of detector-level natural diamonds. The production cost is reduced, which is beneficial to industrialized production. Therefore, it has broad application prospects.

Description

A microstrip particle detector and its preparation method

technical field

The invention relates to a microstrip particle detector made of directional growth (100) crystal plane diamond film on a silicon chip as a base material and a preparation method thereof.

Background technique

Semiconductor detector is a new type of nuclear radiation detection element that has been developed rapidly since the 1960s. Its characteristics are: high energy resolution, good linear response, short pulse rise time, simple structure, high detection efficiency, and low operating voltage. , easy to operate. Since the first use of germanium semiconductors to detect particles in Bell Telecom and Telephone Laboratories in the United States in 1949, this detector immediately attracted the attention of countries all over the world. Since the 1970s, with the continuous improvement of the preparation process of silicon materials and semiconductor plane technology, silicon detectors have been developed rapidly. Silicon detector is the only detector suitable for simultaneous analysis of wide energy spectrum, so it has been widely used in the detection technology of particle physics. However, in a strong radiation environment, the silicon lattice is easily damaged by radiation, which increases the leakage current of the detector and degrades its performance. In addition, the intrinsic conductivity generated by thermal excitation increases exponentially with temperature. Since the forbidden band width of silicon is small, devices made of silicon materials are not suitable for working in an environment higher than 150°C.

Due to many excellent properties of diamond, such as: large band gap (about 5.5eV), high radiation intensity, good chemical and temperature stability, etc., it can replace silicon to work under extreme conditions. However, detector-grade natural diamond is expensive and has poor reproducibility, which limits its application as a radiation detector. In recent years, due to the development of chemical vapor deposition (CVD), the quality and application of synthetic diamond films have been greatly improved. At present, almost any shape of diamond film with high purity and low defect level can be prepared, and its properties are even better than natural diamond in many aspects. Recent advances in the growth of "detector-grade" diamond films by chemical vapor deposition (CVD) have aroused great interest among researchers in the fields of high-energy physics, heavy-ion physics, the nuclear industry, and radiation dosimetry.

According to the detection principle of the detector, it can be seen that the strength of the transport ability of electrons and holes in the material determines its performance. "Detector grade" diamond films require extremely strong charge transport capabilities. However, since the diamond film prepared by the general method is polycrystalline with any orientation, the properties exhibited are the average result of the combined effects of grain properties in different directions, impurities, defects, etc. Moreover, due to the inconsistency of orientation, the existence of a large number of defects such as grain boundaries hinders the transport of charges, so it cannot have the excellent performance of natural single crystal diamond. For example, the thermal conductivity of natural single crystal diamond is as high as (20W/cm K), while the polycrystalline diamond film with arbitrary orientation has low thermal conductivity even if its purity is very high, so that the performance of polycrystalline thin film detectors is not as good as that based on single crystal materials. of detectors. In addition, the surface flatness of the randomly oriented diamond film is not high, which is not conducive to surface photolithography electrodes and signal extraction.

Contents of the invention

One of the objectives of the present invention is to provide a microstrip particle detector made of directional growth of diamond film on a silicon wafer as a base material, through appropriate processing technology, the diamond film on the detector can form an ohmic contact with the electrode , so as to finally improve the comprehensive performance of the diamond film/silicon composite substrate as a microstrip particle detector.

The second object of the present invention is to provide a method for preparing the above-mentioned particle detector.

To achieve the above object, the present invention adopts the following technical solutions:

A kind of microstrip particle detector of the present invention, comprises substrate and surface coating thereof and top electrode and back electrode, is characterized in that, substrate adopts [100] silicon chip; On the upper surface of this substrate is [100] The diamond film coating on the crystal surface; on the surface of the diamond film coating is the top electrode, which is made of chrome-gold composite, and processed by photolithography into micro-strip electrodes with a width and spacing of 10-50 μm. Each microstrip electrode is led out by a magnesium-aluminum wire, and the one close to the diamond film coating is a chromium electrode, and the one above the network electrode is a gold electrode; the lower surface of the substrate is a back electrode, which is also a chromium-gold composite electrode. Electrodes, wherein the electrode close to the substrate is a chromium electrode, and the electrode below the chromium electrode is a gold electrode.

The thickness of the substrate is 0.5mm, and the area is 2×2cm ² ; the thickness of the diamond film coating is 50-400μm; the thickness of the chromium electrode in the top electrode and the back electrode is 50-100m, and the thickness of the gold electrode is 200- 800nm.

The preparation method of the microstrip particle detector of the present invention is characterized in that the method comprises the following steps:

a. Hydrogen plasma in-situ etching: the substrate material, i.e. [100] silicon wafer, is firstly cleaned by ultrasonic cleaning, and then placed in a microwave plasma chemical vapor deposition device (MPCVD) with a frequency of 2.45 GHz and a power of 300 kW. In the deposition chamber; hydrogen is used as the reaction gas to carry out hydrogen plasma in-situ etching; the hydrogen flow rate is 100 standard milliliters per minute, and the air pressure in the deposition chamber is at 2.7kPa at this time, and the temperature of the substrate in the deposition chamber is adjusted by controlling the microwave power 800-900°C, etching time is 15-45 minutes;

b. Silicon surface carburization: change the reaction gas into hydrogen and methane mixed gas, wherein the flow rates of hydrogen and methane are 100 standard ml/min and 480 standard ml/min respectively, hydrogen and methane enter the deposition chamber after mixing, at this time The air pressure in the deposition chamber is 3.2kPa, the substrate temperature is constant, and the carburizing time is 30 minutes;

c. Nucleation process: In this process, the reaction gas is still a mixture of hydrogen and methane, wherein the flow rates of hydrogen and methane are 100 standard ml/min and 480 standard ml/min respectively, and hydrogen and methane enter the deposition chamber after being mixed. The air pressure in the deposition chamber is 3.2kPa; the substrate temperature is lowered to 800°C, and at the same time, a -100~-200V DC negative bias is applied to the substrate to make the substrate material have a negative surface potential; the optimal nucleation time is 30 minutes;

d. Diamond film growth process: first, the reaction gas is still a mixture of hydrogen and methane, the methane flow rate is adjusted to 100 standard ml/min, the hydrogen flow rate remains unchanged, the substrate temperature is controlled at 810°C, and no bias is applied to realize the diamond film Then turn off the methane gas switch, only feed hydrogen, and use hydrogen plasma to etch the crystal grains; repeat this for 8 times, wherein the duration of each cycle is 8 hours, and the film growth period is the same as the hydrogen plasma etching The time ratio of the eclipse period is 6:2;

e. Evaporation of chromium-gold composite electrodes on the surface: The upper and lower surfaces of the above-mentioned samples are evaporated in the LDG-2A ion beam sputtering instrument, wherein the thickness of the chromium electrode is 50-100nm, and the thickness of the gold electrode is 50-100nm. 200-800nm; then use the MJB6 photolithography machine to photo-etch the chrome-gold composite electrode on the diamond film edge, that is, the top electrode, to form a micro-strip electrode with a strip width and spacing of 10-50μm, and use MgAl wire as the lead wire; finally In an annealing furnace, under a nitrogen atmosphere, anneal at 350-450° C. for 10-30 minutes to prepare a diamond film microstrip particle detector.

Since the etching effect of hydrogen plasma on non-[100]-oriented grains is much greater than that on [100]-oriented grains, in the method of the present invention, a cyclic growth process is adopted, that is, in the grain growth process Controlled methane and hydrogen are introduced as reaction gases to realize the growth of the diamond film, and then the methane gas switch is turned off, only hydrogen is introduced, and the hydrogen plasma is used to etch the crystal grains, and this is repeated many times. With this approach, the number of non-[100]-oriented grains in the film can be minimized, while the [100]-oriented grains are preferentially deposited due to weaker etching action. That is, under the etching effect of hydrogen ions, the [100] oriented grains grow preferentially, and the non-[100] oriented grains gradually decrease due to the selection rule. When the film grows to a certain thickness, the [100] orientation of the diamond film is finally realized. Directed growth.

In the process of induced nucleation, DC bias treatment is adopted, that is, the circular molybdenum sheet is used as the positive electrode, and the copper wire of the quartz boat is used as the negative electrode, and a DC negative bias is applied to the substrate silicon wafer to make the substrate material have a negative Surface potential, which can reduce the surface potential of the substrate silicon wafer, accelerate electron bombardment, and facilitate the directional nucleation of the texture and increase the nucleation density.

Considering that the adhesion between diamond and gold electrodes is not ideal, it is necessary to evaporate a layer of chromium with a thickness of about 50-100nm before evaporating gold electrodes. The samples were annealed in a nitrogen atmosphere.

Compared with the prior art, the present invention has the following significant advantages:

1. Since the present invention adopts the [100] oriented diamond film on a silicon wafer as the matrix material for preparing particle detectors, it solves the problem of high price caused by the use of detector-level natural diamonds, reduces production costs, and is conducive to industrial production .

2. Because the (100) crystal plane of diamond has better surface flatness and lower defect density, the highly oriented diamond film (HOD) almost shows the property of single crystal in the growth direction. Therefore, the problem of poor charge transport ability, low thermal conductivity and low surface flatness of diamond with any orientation is overcome, which is not conducive to the derivation of surface photolithographic charge signals.

3. Since the signal collection in the m-d-m detector is coaxial, the performance of the highly oriented diamond film in the direction of charge collection also shows the performance similar to that of a single crystal, which is beneficial to the transport of charges.

To sum up, the various performances of the particle detector of the present invention are completely comparable to those of detector-grade natural diamond. Therefore, it has broad application prospects.

Description of drawings

Fig. 1 is the structural representation of a kind of particle detector of the present invention

Figure 2 is a top view of the example in Figure 1

Detailed ways

Embodiment 1: first referring to Fig. 1 and Fig. 2, the specific process steps for the preparation of this product are as follows:

a. Hydrogen plasma in-situ etching: A [100] silicon wafer with an area of 2×2 cm ² and a thickness of 0.5 mm was subjected to acetone, HF acid (25%), deionized water and acetone suspension containing diamond powder three times After ultrasonic cleaning, put it into the deposition chamber of a microwave plasma chemical vapor deposition device (MPCVD) with a frequency of 2.45 GHz and a power of 3000 kW; use hydrogen as the reaction gas for hydrogen plasma in-situ etching; the hydrogen flow rate is 100 standard ml/min. At this time, the air pressure in the deposition chamber is 2.7kPa, and the annealing temperature of the substrate in the deposition chamber is adjusted to 815°C by controlling the microwave power, and the optimal etching time is 30 minutes;

b. Silicon surface carburization: change the reaction gas into hydrogen and methane mixed gas, wherein the flow rates of hydrogen and methane are 100 standard ml/min and 480 standard ml/min respectively, hydrogen and methane enter the deposition chamber after mixing, at this time The air pressure in the deposition chamber is 3.2kPa, the substrate temperature is constant, and the optimal carburizing time is 30 minutes;

c. Nucleation process: In this process, the reaction gas is still a mixture of hydrogen and methane, wherein the flow rates of hydrogen and methane are 100 standard ml/min and 480 standard ml/min respectively, and hydrogen and methane enter the deposition chamber after being mixed. The air pressure in the deposition chamber is 3.2kPa; the substrate temperature is lowered to 800°C, and at the same time, a -150V DC negative bias is applied to the substrate to make the substrate material have a negative surface potential; the optimal nucleation time is 30 minutes;

d. Diamond film growth process: first, the reaction gas is still a mixture of hydrogen and methane, the methane flow rate is adjusted to 100 standard ml/min, the hydrogen flow rate remains unchanged, the substrate temperature is controlled at 810°C, and no bias is applied to realize the diamond film Then turn off the methane gas switch, only feed hydrogen, and use hydrogen plasma to etch the crystal grains; repeat this for 8 times, wherein the duration of each cycle is 8 hours, and the film growth period is the same as the hydrogen plasma etching The time ratio of the eclipse period is 6:2; at this time, the thickness of the diamond film is 100 μm;

e. Evaporation of chromium-gold composite electrodes on the surface: the upper and lower surfaces of the above-mentioned samples were deposited in an LDG-2A ion beam sputtering instrument, wherein the thickness of the chromium electrode was 50nm, and the thickness of the gold electrode was 800nm ; Then use the MJB6 photolithography machine to photoetch the chrome-gold composite electrode on the diamond film edge, that is, the top electrode, to form a micro-strip electrode with a width and spacing of 25 μm, and use MgAl wire as the lead; finally, in the annealing furnace, nitrogen atmosphere The diamond film microstrip particle detector was prepared by annealing at 400°C for 10 minutes.

The diamond thin film microstrip particle detector prepared above was tested for its α particle energy spectral response characteristics (applied voltage 200V) under the irradiation of a ²⁴¹ Am source (characteristic energy 5.5MeV) by a microcomputer multi-channel spectrometer. The test results show that after collecting for 180s, the spectral peak at the energy of 289.6eV is narrow, the full width at half maximum is 0.294eV, and the energy resolution is 0.1%. Signal peaks are clearly separated from bottom noise with excellent signal-to-noise ratio. The time response characteristics of the detector were tested under X-ray irradiation with an energy of 40keV. The test results showed that the detector had a fast response speed and a rise time of 3ns.

Embodiment two: present embodiment is carried out by the same steps of embodiment one preparation process, difference is:

In the growth process of the diamond film, the number of cycles between the film growth period and the hydrogen plasma etching period is 32 times, and the duration of each cycle is 8 hours, and the time ratio between the film growth period and the hydrogen plasma etching period is 6 : 2, now the thickness of the diamond film is 400 μm;

In the process of evaporating the chromium-gold composite electrode on the surface, the thickness of the chromium electrode is 100nm, and the thickness of the gold electrode is 200nm; then, the MJB6 photolithography machine is used to photoetch the chromium-gold composite electrode on the diamond film edge, that is, the top electrode, to form the strip width and spacing Both are microstrip electrodes of 50 μm, and MgAl wires are used as leads; finally, in an annealing furnace, under a nitrogen atmosphere, anneal at 400 ° C for 10 minutes to manufacture a diamond film microstrip particle detector.

Claims (3)

1. a Microstrip particle detector comprises substrate (1) and surface coating (2) thereof and top electrode (3) and back electrode (4), it is characterized in that, substrate (1) adopts [100] silicon chip; Upper surface at this substrate (1) is the diamond film coating layer (2) of [100] crystal face; On diamond film coating layer (2) surface is top electrode (3), this top electrode (3) is to be composited by the chromium gold, and be little strip electrode of 10～50 μ m through the wide and spacing of photoetching treatment slivering, every little strip electrode has magnesium aluminum wire to draw, what wherein be close to diamond film coating layer (2) is chromium electrode, and on the network electrode is gold electrode; The lower surface of substrate (1) is back electrode (4), and this back electrode (4) also is a chromium gold combination electrode, and wherein close substrate (1) is chromium electrode, and under chromium electrode is gold electrode.

2. Microstrip particle detector according to claim 1 is characterized in that, the thickness of substrate (1) is 0.5mm, and area is 2 * 2cm ²The thickness of diamond film coating layer (2) is 50～400 μ m; Top electrode (3) is 50～100nm with the thickness of the middle chromium electrode of back electrode (4), and the thickness of gold electrode is 200～800nm.

3. a preparation method who is used for claim 1 or 2 described Microstrip particle detectors is characterized in that this method comprises the steps:

A. hydrogen plasma in situ etching: with backing material, promptly [100] silicon chip carries out surperficial ultrasonic cleaning earlier, and putting into frequency then is that 2.45GHz, power are the settling chamber of the microwave plasma CVD device (MPCVD) of 3000kW; Employing hydrogen is reacting gas, carries out hydrogen gas plasma original position etching; Hydrogen flowing quantity is 100 standard ml/min, and the air pressure of settling chamber is 800～900 ℃ at 2.7kPa by substrate temperature in the controlled microwave power adjustments settling chamber at this moment, and etching time is 15～45 minutes;

B. silicon face carburizing: change reacting gas into hydrogen and methane blended gas, wherein the flow of hydrogen and methane is respectively 100 standard ml/min and 480 standard ml/min, hydrogen and methane enter the settling chamber after mixing, the air pressure of settling chamber is at 3.2kPa at this moment, underlayer temperature is constant, and carburizing time is 30 minutes;

C. nucleation process: in this process, reacting gas still is hydrogen and methane blended gas, and wherein the flow of hydrogen and methane is respectively 100 standard ml/min and 480 standard ml/min, and hydrogen and methane enter the settling chamber after mixing, and the air pressure of settling chamber is at 3.2kPa; Underlayer temperature is reduced to 800 ℃, on substrate, add simultaneously-100～-200V dc negative bias voltage and make backing material have negative surface potential; Nucleation time is 30 minutes;

D. diamond film growth process: at first reacting gas still is hydrogen and methane blended gas, and regulating methane flow is 100 standard ml/min, and hydrogen flowing quantity is constant, and substrate temperature is controlled at 810 ℃, and biasing is realized the growth of diamond thin; Close the methane gas switch then, only feed hydrogen, utilize hydrogen plasma that crystal grain is carried out etching; Carry out so repeatedly 8 times, wherein each cyclic process duration is 8 hours, and the time scale of film growth phase and hydrogen plasma etching phase is 6: 2;

E. surperficial evaporation chromium gold combination electrode: with the upper and lower surface of the above-mentioned sample that makes, carry out evaporation chromium gold combination electrode in LDG-2A ion beam sputtering instrument, wherein the thickness of chromium electrode is 50～100nm, and the thickness of gold electrode is 200～800nm; Adopt the MJB6 litho machine to diamond film limit chromium gold combination electrode then, promptly top electrode carries out photoetching, and the formation bar is wide to be little strip electrode of 10～50 μ m with spacing, and adopts MgAl silk lead-in wire; In annealing furnace, under the nitrogen atmosphere,, make the diamond thin Microstrip particle detector at last through 350～450 ℃ of annealing 10～30 minutes.