CN104630899A - Separation method of diamond layer - Google Patents

Abstract

The invention discloses a method for separating a diamond layer. The method comprises the following steps: using a laser to perform two-dimensional scanning inside the diamond to be processed, forming a non-diamond layer at a certain depth below the surface of the diamond to be processed; removing the non-diamond layer, In order to realize the upper and lower separation of the above-mentioned diamonds. The diamond substrate surface will not be damaged by the method, and compared with the laser cutting technology, the loss in diamond cutting is reduced; compared with the ion implantation separation technology, the cost is saved and the processing time is shortened.

Description

Separation method of diamond layer

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a method for separating a diamond layer.

Background technique

As a superhard tool and the substrate of electronic devices, diamond is widely used in industry. In all applications it is desirable to use large size diamond as the starting material. For polycrystalline diamond, polycrystalline substrates larger than 2 inches have been able to be synthesized and used as optical windows, superhard tools and other fields. On the other hand, single crystal diamond substrates are formed by cutting natural or synthetic diamond into pieces by laser cutting, cleavage, and the like. If necessary, polish the corresponding surface. However, we know that natural diamonds are very rare and large-sized natural diamonds are very expensive. Furthermore, although high-temperature and high-pressure synthetic diamond is widely used in various industrial fields, this method has certain limitations, such as slow synthesis rate, and the output will drop sharply as the size increases. Therefore, ^a single crystal of 1 × 1 cm has almost become the limit. The common size of high temperature and high pressure synthetic diamond used commercially is generally 5×5mm ² .

The high-speed synthesis of single crystal diamond by chemical vapor deposition (CVD) has been reported. Adding a small amount of nitrogen during the growth and adjusting the growth process can make the growth rate of diamond exceed 150 μm/h[1]. Using this approach, the thickness of the synthesized crystals can exceed 1 cm [2]. In addition, the technology of synthesizing single crystal diamond by CVD method can increase the area of synthetic diamond more easily when the structure of CVD cavity is enlarged. By controlling the process and adjusting the introduction of a small amount of impurity gas, epitaxial growth can be performed on a large area and at a high speed. Microwave plasma chemical vapor deposition (MPCVD) is currently the most common technology for large-area single-crystal diamond growth. Combined with the three-dimensional growth and splicing technology of diamond on a high-temperature and high-pressure substrate, the size of single-crystal diamond obtained by the current large-area growth technology is has reached 2 inches [3].

Therefore, large-area single-crystal diamond substrates can be further obtained through large-area growth techniques on high-temperature, high-pressure diamond crystals. In this way, the large-area single-crystal diamond substrate is used as the seed crystal, and the epitaxially grown single-crystal diamond layer is separated from the seed crystal by the method of exfoliation, thereby obtaining a commercial substrate used in industry and research.

As mentioned above, on the single crystal diamond crystal synthesized by chemical vapor deposition technology, the diamond substrate we need is cut, and the commonly used methods are laser cutting, diamond saw cutting and so on. When these methods are used for cutting, the thickness of the damage in the cutting area is about tens to hundreds of microns, which is equivalent to the thickness of the semiconductor substrate, which greatly reduces the utilization efficiency of the seed crystal. Therefore it is necessary to find a new cutting method to minimize the loss caused in the cutting process.

Teams such as Fairchild and Mokuno have reported that high-energy carbon ions or helium ions are implanted into diamond substrates to form a non-diamond layer at a certain depth below the surface of the substrate, and then annealed at high temperature, and then corroded by electrochemical corrosion. The non-diamond layer separates the diamond surface from the original diamond substrate [4,5]. However, a high-energy ion implanter with a required energy of about 3 MeV is very expensive, and the ion implantation time is also very long, so the use of ion implantation to separate diamonds is limited in industrial applications and scientific research.

references

[1] "High optical quality multicarat single crystal diamond produced by chemical vapor deposition" Yu-fei Meng*, Chih-shiue Yan, Szczesny KrasnickiPhys.Status Solidi A 209, No.1, 101–104 (2012)

[2] "Synthesizing single-crystal diamond by repetition of high rate Homoepitaxial growth by microwave plasma CVD" Y.Mokuno*, A.Chayahara, Y.Soda, Y.Horino, N.Fujimori.Diamond&Related Materials 14(2005)1743–1746

[3] "A 2-in.mosaic wafer made of a single-crystal diamond" H.Yamada, A.Chayahara, Y.Mokuno, Y.Kato, and S.Shikata.Applied Physics Letters 104, 102110(2014)

[4] "Fabrication of Ultrathin Single-Crystal Diamond Membranes**" Barbara A. Fairchild, *Paolo Olivero, Sergey Rubanov. Adv. Mater. 2008, 20, 4793–4798.

[5] "Synthesis of large single crystal diamond plate by high ratehomoepitaxial growth using microwave plasma CVD and lift-off process" Y.Mokuno,A.Chayahara,H.Yamada.Diamond&Related Materials 17(2008)415–418.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for separating the diamond layer for the above-mentioned deficiencies in the prior art, the method will not damage the diamond surface, and compared with the laser cutting technology, the loss in the diamond cutting is reduced; Compared with ion implantation separation technology, it saves cost and shortens processing time.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is a method for separating the diamond layer, the method comprising the following steps:

Use laser to scan two-dimensionally inside the diamond to be treated, destroy the diamond structure at the scanning place, and form a non-diamond layer at a certain depth below the surface of the diamond to be treated; remove the non-diamond layer to realize the upper and lower separation of the above diamond.

Further, the non-diamond layer is removed by electrochemical corrosion.

Further, before removing the non-diamond layer, the diamond to be treated is annealed in vacuum at ≥800° C., so that the non-diamond layer is graphitized.

Further, the energy density of the laser used is: the breakdown threshold of the diamond to be processed -1.2J/cm ² .

Further, the depth of the formed non-diamond layer is 1 μm-10 μm below the surface layer, and the thickness is 100 nm-10 μm.

Further, the surface area of the non-diamond layer is smaller than or equal to that of diamond.

Further, the diamond has a polycrystalline structure or a single crystal structure, and can be insulated natural diamond or insulated artificial diamond.

Further, the laser is a femtosecond laser or a wide pulse laser.

The invention also provides the application of the method for separating the diamond layer, which is used for peeling off the surface layer of the diamond substrate.

The present invention also provides another application of the separation method of the diamond layer, which is used to peel off the epitaxially grown diamond layer on the diamond substrate, specifically: using a laser to perform two-dimensional scanning inside the diamond substrate to be processed, destroying the Diamond structure, a non-diamond layer is formed at a certain depth below the surface of the diamond substrate to be processed; a diamond layer of a certain thickness is epitaxially grown on the surface of the diamond substrate; the non-diamond layer is removed to achieve the above-mentioned diamond. The diamond substrate above the layer and the epitaxial growth diamond layer, and the diamond substrate below the non-diamond layer.

A method for stripping diamond of the present invention has the following advantages: 1. In a short period of time, the diamond thin layer (i.e. the surface layer of the diamond substrate) or the epitaxial growth diamond on the diamond substrate can be stripped on a diamond exceeding 3mm × 3mm layer, thereby forming the ability to mass-produce large-area single crystal diamond. 2. Not affected by the diamond crystal structure. 3. Compared with the existing laser cutting technology, the loss in diamond cutting is greatly reduced. Compared with the ion implantation separation technology, the cost is saved and the processing time is shortened. 4. Since the diamond layer can be easily peeled off, the diamond or epitaxial layer can be reused many times in industry without causing waste. 5. The preferred femtosecond laser utilizes non-linear effects such as avalanche ionization or multi-photon ionization, and there is no melting process in the processing process, and micron or even nanoscale fine processing can be performed.

Description of drawings

Fig. 1 is the schematic diagram of the selected laser system of forming non-diamond in diamond in the present invention;

Fig. 2 is electrochemical corrosion system among the present invention;

Fig. 3 is a metallographic diagram of the non-diamond layer inside the diamond obtained in the embodiment of the present invention.

Among them: 1. Attenuator; 2. Beam splitter; 3. Power meter; 4. Focusing lens; 5. Displacement platform; 6. Electric drive; 7. Control device; 8. Laser; 9. Regenerative amplifier; , 11. container, 12. electrode; 13 diamond sample after scanning; 14 power supply; 15. non-diamond layer, 16 diamond.

Detailed ways

The separation method of the diamond layer of the present invention comprises the following steps: using a laser to perform two-dimensional scanning inside the diamond to be processed, destroying the diamond structure at the scanning place, and forming a non-diamond layer at a certain depth below the surface of the diamond to be processed; removing the non-diamond The diamond layer is used to realize the upper and lower separation of the above-mentioned diamonds. Wherein, the non-diamond layer may be etched and removed by means of electrochemical etching. Before removing the non-diamond layer, the diamond to be treated is annealed in vacuum at ≥ 800° C., so that the non-diamond layer is graphitized.

The invention also provides the application of the method for separating the diamond layer, which is used for peeling off the surface layer of the diamond substrate. It can also be used to peel off the epitaxial growth diamond layer on the diamond substrate, specifically: use laser to scan the inside of the diamond substrate to be processed two-dimensionally, destroy the diamond structure at the scanning place, and form a certain depth below the surface of the diamond substrate to be processed. Non-diamond layer; using methods such as chemical vapor deposition to epitaxially grow a diamond layer with a certain thickness on the surface of the diamond substrate; remove the non-diamond layer to realize the upper and lower separation of the above-mentioned diamond, and obtain a diamond substrate above the non-diamond layer and epitaxy A diamond layer, and a diamond substrate below the non-diamond layer are grown. The above two applications only increase the step of epitaxially producing the diamond layer, and the rest of the steps are the same. At the same time, the present invention is also applicable to applications when the diamond layer needs to be peeled off in other industries.

In the separation method of the Fang Ming diamond layer:

1. Diamond selection

Diamond can be insulated natural diamond, insulated synthetic diamond, single crystal diamond or polycrystalline diamond. In single crystal diamond, there are different crystal planes (100)(111), and there may also be tilt angles at the crystal planes, and the present invention is applicable to all of them.

2. Formation of non-diamond layer

Using a laser to scan diamond two-dimensionally, a large number of free electrons are formed through the process of multi-photon absorption. Under the condition of strong light field, light breakdown occurs, which makes the sp ³ bond in the diamond transform into sp ² bond.

As shown in Figure 1, it is a kind of laser system selected for forming non-diamond in diamond, including laser device 8, regenerative amplifier 9, attenuator 1 and focusing lens 4, and described laser device 8 is used for emitting laser light, and described laser light path A regenerative amplifier 9, a reflector 10 and an attenuator 1 are arranged in sequence, and a beam splitter 2 is arranged on the exit light side of the attenuator 1, and the exit light is irradiated on the beam splitter 2 and divided into two paths, wherein one path of laser light is transmitted into the Power meter 3, another laser beam is reflected into the focusing lens 4, and the light output side of the focusing lens 4 is provided with a displacement platform 5 for placing the diamond to be processed. The electric drive 6 is connected; the laser 8 is also connected with the control device 7 . It should be noted that the present invention is not limited to a certain laser system, and other laser systems that meet the conditions can also be selected.

The details are as follows: the laser generated by the titanium-doped sapphire (Ti:sapphire, hereinafter referred to as Ti:sapphire) laser is amplified by the regenerative amplifier, the single pulse energy reaches 3.7mJ, and the pulse width is 50fs. Transition threshold or above (natural diamond optical breakdown threshold: 0.4J/cm ² , CVD diamond optical breakdown threshold: 0.3J/cm ² ), and then focus the laser on the diamond surface through the focusing lens 4 and the high-precision three-dimensional displacement platform 5 Below a certain depth, and perform two-dimensional scanning.

In this process, choosing the appropriate laser pulse energy to scan the diamond is the key. If the energy is lower than the threshold, the laser is not enough to cause light breakdown. If the energy is too high, the diamond surface will be damaged. Generally, the laser energy density is selected within the range from the threshold value to 1.2J/cm ² .

The laser focus depth is determined by the focus lens 4 and the displacement platform 5. In order to realize the repeated use of diamonds in the industry, the focus depth is selected in the range of 1 μm-10 μm below the diamond surface. The thickness of the non-diamond layer is determined by both the energy density and the scanning speed. The thickness of the non-diamond layer is proportional to the energy density when the scanning speed is constant, and inversely proportional to the scanning speed when the energy density is constant. The scanning speed can be selected from 10 μm/s to 100 μm/s according to the experimental needs. The thinner the non-diamond layer, the smaller the loss of the diamond to be treated, but due to the limitation of process conditions, the thickness of the non-diamond layer can be controlled within the range of 100nm-10μm.

After the diamond is focused and scanned two-dimensionally, the diamond structure at the focal plane in the diamond is destroyed due to light breakdown, forming a non-diamond structure, so that the non-diamond layer in the diamond can be removed by electrochemical corrosion.

After laser processing diamond to form a non-diamond layer, the whole diamond to be processed is annealed in a vacuum of ≥800°C, so that the non-diamond layer is graphitized, thereby accelerating the electrochemical corrosion rate.

3. Epitaxial growth

After the diamond is processed by laser scanning, a single crystal diamond film is epitaxially grown on the diamond by microwave plasma chemical vapor deposition (MPCVD). Although the microwave plasma epitaxial growth technology is mentioned here, it is not limited to this technology, such as using hot wire CVD, DC CVD, and the like. As a special case, microwave plasma CVD is used for epitaxial growth. Under specific growth conditions, high-quality and high-purity diamond single crystal thin films can be epitaxially grown. As the growth gas, for example, a mixed gas of hydrogen and methane can be used. Furthermore, adding an appropriate amount of nitrogen can greatly increase the growth rate, and can also simulate abnormal nucleation and abnormal growth, especially in the case of single crystal diamond, which can make the single crystal growth reach the desired level in a short time. desired thickness. The gas ratio is generally: CH ₄ /H ₂ is 1%-20%; N ₂ /CH ₄ is 0-3%.

The specific growth conditions mentioned above are described here. The frequency of the microwave plasma CVD used is generally 2.45GHz or 915MHz. There is no special limitation on the power, which is generally 0.5KW-30KW. In this case, the power is adjusted according to the structure of CVD so that the temperature reaches 900°C-1250°C. Maintaining diamond at this temperature promotes graphitization of laser-processed non-diamond layers.

4. Electrochemical corrosion of non-diamond layer

According to the above method, after the laser is applied to the diamond substrate, a non-diamond layer will be formed at a certain depth below the surface. Put the substrate into a container containing electrolyte for electrochemical corrosion. The specific process is as follows:

As shown in Figure 2, the electrochemical corrosion system includes an AC or DC power supply 14, a graphite or platinum electrode 12, a container 11 and an electrolyte. After scanning, the diamond sample 13 is vertically placed in the middle of the electrodes, and the electrolyte added is a high resistance ( ~18Ω·cm) solution, the amount added should submerge the diamond sample 13. The voltage applied to the electrodes 12 is controlled by the power supply 14, generally to make the electric field between the two electrodes reach a certain value. The larger the electric field, the faster the corrosion rate. However, if the voltage is too high, it may cause discharge between electrodes and easily damage the diamond surface. In the process of electrochemical corrosion, as time goes by, the electrolyte absorbs CO ₂ in the air, so that the resistance of the electrolyte decreases, the current through the electrolyte increases, and the bubbles in the solution increase, and the bubbles will wrap the sample, so that the corrosion cannot be achieved. role. At the same time, the increased current will generate a lot of heat, causing the electrolyte to be heated to boiling. Therefore, during the corrosion process, the electrolyte should be replaced in time to keep the current within the range of 0-1A.

Experiment example:

In this embodiment, a commercial single-sided polished single-crystal diamond substrate with a size of 3×3×0.3 mm ³ is specifically selected, and it is first subjected to acid boiling treatment to clean the polished surface. Then the diamond substrate was ultrasonically cleaned with alcohol, acetone and deionized water. Then, a femtosecond laser processing system is used to focus the laser within a certain depth under the diamond surface and perform two-dimensional scanning. The diameter of the laser spot at the focus is about 8 μm, the focus is 10 μm below the surface, the average laser power at the sample surface is about 9 mW, the scanning speed is 40 μm/s, and the scanning distance is 7 μm. After scanning, the color of the diamond changed from light yellow to black. The cross-section was observed with a scanning electron microscope, and an obvious interface layer was found at the focal plane, as shown in Figure 3, which indicated that optical breakdown occurred in diamond 16, forming The non-diamond layer 15 was removed.

The diamond processed by the femtosecond laser is placed in a microwave plasma CVD chamber for epitaxial growth. Before growth, adjust the substrate surface temperature to 1000°C for five minutes annealing in a hydrogen plasma atmosphere. On the one hand, the surface of the diamond substrate is cleaned, on the other hand, the graphitization of the non-diamond layer is promoted, and then epitaxial growth is performed. The microwave power is about 5kW, the cavity pressure is set to 150torr, the hydrogen flow rate is 500sccm, and the methane is 50sccm. In order to speed up the growth, a certain amount of nitrogen is artificially added during the growth. The amount added here is 1.0sccm, and the growth temperature is controlled at Around 1200°C. After 12 hours of growth, the epitaxial growth thickness reaches 0.58mm.

Then, put the epitaxially grown diamond sample into the electrochemical corrosion system. Platinum is used as the electrode, the sample is perpendicular to the platinum electrode, and the distance between the electrodes is about 1cm. Deionized water was used as electrolyte in an amount to submerge the diamond sample. Connect a 1000V AC power supply to the electrodes for corrosion. During corrosion, the deionized water should be replaced regularly. After corroding for 5 hours, the black in the sample faded, and the epitaxial diamond layer was separated from the diamond substrate.

Claims (10)

1. the separation method of diamond layer is characterized in that, the method comprises the following steps: Using a laser to scan two-dimensionally inside the diamond to be treated, destroy the diamond structure at the scanning place, and form a non-diamond layer at a certain depth below the surface of the diamond to be treated; This non-diamond layer is removed to achieve the upper and lower separation of the above diamond. 2. The separation method of the diamond layer according to claim 1, characterized in that the non-diamond layer is removed by electrochemical corrosion. 3. The method for separating the diamond layer according to claim 2, characterized in that, before removing the non-diamond layer, the diamond to be treated is annealed in a vacuum of ≥800° C., so that the non-diamond layer is graphitized. 4. The method for separating a diamond layer according to claim 1, 2 or 3, characterized in that the energy density of the laser used is: the breakdown threshold of the diamond to be treated ~ 1.2 J/cm ² . 5. The method for separating a diamond layer according to claim 1, 2 or 3, wherein the depth of the formed non-diamond layer is 1 μm-10 μm below the surface, and the thickness is 100 nm-10 μm. 6. The method for separating diamond layers according to claim 1, 2 or 3, wherein the surface area of the non-diamond layer is less than or equal to the surface area of diamond. 7. The method for separating diamond layers according to claim 1, 2 or 3, wherein the diamond is a polycrystalline structure or a single crystal structure, and can be an insulating natural diamond or an insulating artificial diamond. 8. The method for separating a diamond layer according to claim 1, 2 or 3, wherein the laser is a femtosecond laser or a wide pulse laser. 9. The application of the separation method of the diamond layer according to any one of claims 1 to 8, characterized in that it is used to peel off the surface layer of the diamond substrate. 10. as the application of the separation method of the diamond layer described in any one of claims 1 to 8, it is characterized in that, for peeling off the epitaxial growth diamond layer on the diamond substrate, specifically: Using a laser to scan the inside of the diamond substrate to be processed in two dimensions, destroy the diamond structure at the scanning point, and form a non-diamond layer at a certain depth below the surface of the diamond substrate to be processed; Epitaxially grow a diamond layer with a certain thickness on the surface of the diamond substrate; The non-diamond layer is removed to realize the upper and lower separation of the above-mentioned diamond to obtain a diamond substrate above the non-diamond layer, an epitaxially grown diamond layer, and a diamond substrate below the non-diamond layer.