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WO2016112596A1 - 金刚石层的分离方法 - Google Patents

金刚石层的分离方法 Download PDF

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Publication number
WO2016112596A1
WO2016112596A1 PCT/CN2015/077120 CN2015077120W WO2016112596A1 WO 2016112596 A1 WO2016112596 A1 WO 2016112596A1 CN 2015077120 W CN2015077120 W CN 2015077120W WO 2016112596 A1 WO2016112596 A1 WO 2016112596A1
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Prior art keywords
diamond
diamond layer
layer
laser
separating
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PCT/CN2015/077120
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English (en)
French (fr)
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王宏兴
颜建平
王菲
陈烽
符娇
张景文
卜忍安
侯洵
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西安交通大学
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Publication of WO2016112596A1 publication Critical patent/WO2016112596A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/04—Diamond
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
    • C30B33/04—After-treatment of single crystals or homogeneous polycrystalline material with defined structure using electric or magnetic fields or particle radiation

Definitions

  • the invention belongs to the technical field of semiconductors, and in particular relates to a method for separating diamond layers.
  • diamond is a substrate for electronic devices and is widely used in industry. In all applications, it is desirable to use large size diamond as a raw material.
  • polycrystalline diamond polycrystalline substrates larger than 2 inches have been able to be synthesized and used as fields for optical windows, superhard tools, and the like.
  • a single crystal diamond substrate is formed by cutting a natural or synthetic diamond into a sheet by laser cutting, cleavage or the like. Polish the corresponding surface as needed.
  • natural diamonds are very rare, and large-size natural diamonds are very expensive.
  • high-temperature and high-pressure synthetic diamond is widely used in various industrial fields, there are certain limitations in this method, such as a slow synthesis rate, and the yield will drop sharply as the size increases. Therefore, a single crystal of 1 ⁇ 1 cm 2 has almost become the limit.
  • commercially available high temperature and high pressure synthetic diamonds the common size is generally 5 x 5 mm 2 .
  • a large-area single crystal diamond substrate can be further obtained by a large-area growth technique on a high-temperature and high-pressure diamond crystal.
  • a large-area single crystal diamond substrate is used as a seed crystal, and the epitaxially grown single crystal diamond layer is separated from the seed crystal by a lift-off method, thereby obtaining a commercial substrate for industrial and research use.
  • the diamond substrate we need is cut, and the usual methods are laser cutting, diamond saw cutting, and the like.
  • the damage thickness of the cutting region is about several tens to several hundreds of micrometers, and such thickness has been equivalent to the thickness of the semiconductor substrate, which greatly reduces the utilization efficiency of the seed crystal. It is therefore necessary to find new cutting methods to minimize the damage caused during the cutting process.
  • the technical problem to be solved by the present invention is to provide a method for separating a diamond layer according to the above-mentioned deficiencies of the prior art, which does not damage the diamond surface, and reduces the loss in diamond cutting compared with the laser cutting technique; Compared with the ion implantation separation technology, the cost is saved and the processing time is shortened.
  • the technical solution adopted by the present invention is a method for separating a diamond layer, the method comprising the following steps:
  • the inside of the diamond to be processed by the laser is subjected to two-dimensional scanning to destroy the diamond structure at the scanning, and a non-diamond layer is formed at a certain depth below the surface of the diamond to be processed; the non-diamond layer is removed to achieve upper and lower separation of the diamond.
  • non-diamond layer is etched away by electrochemical etching.
  • the diamond to be treated is annealed in a vacuum of ⁇ 800 ° C before the removal of the non-diamond layer, so that the non-diamond layer is graphitized.
  • the energy density of the laser used is: the breakdown threshold of the diamond to be treated - 1.2 J/cm 2 .
  • the formed non-diamond layer has a depth of 1 ⁇ m to 10 ⁇ m under the surface layer and a thickness of 100 nm to 10 ⁇ m.
  • the surface area of the non-diamond layer is less than or equal to the surface area of the diamond.
  • the diamond is a polycrystalline structure or a single crystal structure, and may be an insulated natural diamond or an insulated synthetic diamond.
  • the laser is a femtosecond laser or a wide pulse laser.
  • the invention also provides for the use of a separation method for a diamond layer for stripping a surface layer of a diamond substrate.
  • the invention also provides another application of the separation method of the diamond layer for stripping the epitaxially grown diamond layer on the diamond substrate, in particular: performing two-dimensional scanning on the inside of the diamond substrate to be processed by the laser, destroying the scanning portion a diamond structure, forming a non-diamond layer at a depth below the surface of the diamond substrate to be processed; epitaxially growing a diamond layer of a certain thickness on the surface of the diamond substrate; removing the non-diamond layer to achieve upper and lower separation of the diamond to obtain a non-diamond A diamond substrate above the layer and an epitaxially grown diamond layer, and a diamond substrate below the non-diamond layer.
  • the invention provides a method for stripping diamond, which has the following advantages: 1.
  • the diamond thin layer ie, the surface layer of the diamond substrate
  • the epitaxial diamond on the diamond substrate can be peeled off on the diamond over 3 mm ⁇ 3 mm in a short time.
  • the layer forms the ability to mass produce large-area single crystal diamond. 2. Not affected by the crystal structure of the diamond. 3.
  • the preferred femtosecond laser utilizes nonlinear effects such as avalanche ionization or multiphoton ionization, which does not undergo a melting process and can be microfabricated or even nanoscale.
  • FIG. 1 is a schematic view of a laser system for forming a non-diamond selected in a diamond in the present invention
  • Figure 2 is an electrochemical corrosion system of the present invention
  • Figure 3 is a metallographic view of a non-diamond layer inside a diamond obtained in an embodiment of the present invention.
  • the method for separating a diamond layer of the present invention comprises the steps of: performing a two-dimensional scanning on the inside of the diamond to be processed by the laser, destroying the diamond structure at the scanning portion, forming a non-diamond layer at a certain depth below the surface of the diamond to be processed; removing the non-diamond layer A diamond layer to achieve upper and lower separation of the above diamond.
  • the non-diamond layer can be etched by electrochemical etching. Prior to removal of the non-diamond layer, the diamond to be treated is annealed in a vacuum of > 800 ° C to graphitize the non-diamond layer.
  • the invention also provides for the use of a separation method for a diamond layer for stripping a surface layer of a diamond substrate. It can also be used to peel off the epitaxially grown diamond layer on the diamond substrate. Specifically, the inside of the diamond substrate to be processed by the laser is scanned two-dimensionally, and the diamond structure at the scanning portion is destroyed, and formed at a certain depth below the surface of the diamond substrate to be processed. Non-diamond layer; using chemical vapor deposition, etc.
  • Method epitaxially growing a diamond layer of a certain thickness on a surface of a diamond substrate; removing the non-diamond layer to achieve upper and lower separation of the diamond, obtaining a diamond substrate and an epitaxially grown diamond layer other than the non-diamond layer, and a non-diamond layer or less Diamond substrate.
  • the above two applications only increase the step of epitaxially producing the diamond layer, and the remaining steps are the same.
  • the invention is equally applicable to applications in other industries where the diamond layer needs to be stripped.
  • the diamond may be an insulated natural diamond or an insulated synthetic diamond, which may be a single crystal diamond or a polycrystalline diamond.
  • the single crystal diamond there are different crystal faces (100) (111), and there may be a tilt angle at the crystal faces, and the present invention is applicable.
  • the laser is used to scan the diamond two-dimensionally, and a large number of free electrons are formed by the multiphoton absorption process. Under the condition of strong light field, light breakdown occurs, and the sp 3 bond in the diamond is transformed into the sp 2 bond.
  • Figure 1 shows a laser system for forming a non-diamond in diamond, comprising a laser 8, a regenerative amplifier 9, an attenuator 1 and a focusing lens 4, said laser 8 for emitting laser light, said laser optical path A regenerative amplifier 9, a mirror 10 and an attenuator 1 are disposed in sequence, and the exiting light side of the attenuator 1 is provided with a beam splitter 2, and the emitted light is irradiated on the spectroscope 2 into two paths, one of which is transmitted through the laser
  • the electric drive 6 is connected; the laser 8 is also connected to the control unit 7. It should be noted that, in the present invention, it is not limited to a certain laser system, and other laser
  • the laser generated by the titanium-doped sapphire (Ti:sapphire, hereinafter referred to as titanium gemstone) laser has a single pulse energy of 3.7 mJ and a pulse width of 50 fs under the amplification of the regenerative amplifier, and the laser energy is achieved by selecting the attenuation sheet.
  • Wear threshold or above naturally diamond light breakdown threshold: 0.4J/cm 2 , CVD diamond light breakdown threshold: 0.3J/cm 2 ), and then focus the laser onto the diamond surface through the focusing lens 4 and the high-precision three-dimensional displacement platform 5 Within a certain depth below, and perform a two-dimensional scan.
  • 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.
  • the laser energy density is typically selected from a threshold to a range of 1.2 J/cm 2 .
  • the depth of laser focus is determined by the focusing lens 4 and the displacement stage 5. In order to achieve repeated use of the diamond in the industry, the depth of focus is selected in the range of 1 ⁇ m to 10 ⁇ m below the surface of the diamond.
  • the thickness of the non-diamond layer is determined by 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 ⁇ m/s to 100 ⁇ m/s depending on the experiment. The thinner the thickness of the non-diamond layer, the smaller the loss of the diamond to be treated, but due to the limitation of the process conditions, the thickness of the non-diamond layer can be controlled in the range of 100 nm to 10 ⁇ m.
  • the diamond structure at the focal plane in the diamond is destroyed by light breakdown to form a non-diamond structure, so that the non-diamond layer in the diamond can be removed by electrochemical etching or the like.
  • the whole diamond to be treated is annealed in a vacuum of ⁇ 800 ° C to graphitize the non-diamond layer, thereby accelerating the electrochemical corrosion rate.
  • a single crystal diamond film is epitaxially grown on the diamond by microwave plasma chemical vapor deposition (MPCVD).
  • MPCVD microwave plasma chemical vapor deposition
  • the microwave plasma epitaxial growth technique is mentioned here, it is not limited to this technique, such as hot filament CVD, direct current CVD, or the like.
  • a high-quality high-purity diamond single crystal thin film can be epitaxially grown by microwave plasma CVD for epitaxial growth under specific growth conditions.
  • the growth gas a mixed gas of, for example, hydrogen and methane can be used. Furthermore, adding an appropriate amount of nitrogen can greatly increase the growth rate, and it is also possible to formulate abnormal nucleation and abnormal growth, especially in the case of single crystal diamond, which can achieve single crystal growth in a short time.
  • the proportion of the gas is generally: CH 4 /H 2 is from 1% to 20%; and N 2 /CH 4 is from 0 to 3%.
  • the frequency of the microwave plasma CVD used is generally 2.45 GHz or 915 MHz, etc., and the power is not particularly limited herein, and is generally 0.5 KW to 30 KW.
  • the power is adjusted according to the structure of the CVD so that the temperature reaches 900 ° C to 1250 ° C. Maintaining diamond at this temperature promotes graphitization of the laser processed non-diamond layer.
  • the diamond substrate will form a non-diamond layer at a certain depth below the surface.
  • the substrate was placed in a vessel containing an electrolyte for electrochemical etching. The specific process is as follows:
  • the electrochemical corrosion system includes an alternating current or direct current power source 14, a graphite or platinum electrode 12, a container 11 and an electrolyte.
  • the diamond sample 13 is vertically placed in the middle of the electrode, and the added electrolyte is high resistance ( ⁇ 18 ⁇ ⁇ cm) solution, the amount of addition to flood the diamond sample 13 .
  • the voltage applied to the electrode 12 is controlled by the power source 14, and the electric field between the electrodes is generally brought to a certain value. The larger the electric field, the faster the corrosion rate. However, the voltage is too high, which may cause discharge between the electrodes, which may cause damage to the diamond surface.
  • the electrolyte absorbs CO 2 in the air, causing the electrolyte resistance to decrease, the current through the electrolyte rises, the bubbles in the solution increase, and the bubbles will wrap the sample, thereby failing to achieve corrosion.
  • the role At the same time, the increased current generates a large amount of heat, so that the electrolyte is heated to boiling. Therefore, the electrolyte should be replaced in time during the corrosion process so that the current is maintained in the range of 0 to 1A.
  • a commercial single-sided polished single crystal diamond substrate having a size of 3 ⁇ 3 ⁇ 0.3 mm 3 is specifically selected, and firstly subjected to acid boiling treatment to clean the polished surface.
  • the diamond substrate was then ultrasonically cleaned with alcohol, acetone, deionized water.
  • the femtosecond laser processing system is then used to focus the laser at a depth below the diamond surface and perform a two-dimensional scan.
  • the laser spot diameter at the focal point is about 8 ⁇ m
  • the focal point is 10 ⁇ m below the surface
  • the average laser power at the surface of the sample is about 9 mW
  • the scanning speed is 40 ⁇ m/s
  • the scanning pitch is 7 ⁇ m.
  • the color of the diamond changed from light yellow to black.
  • the cross section was observed by an electron scanning microscope.
  • a clear interface layer was found at the focal plane, as shown in Fig. 3. This shows that light breakdown occurred in the diamond 16 and formed.
  • a non-diamond layer 15 is provided.
  • the diamond processed by the femtosecond laser is placed in a microwave plasma CVD chamber for epitaxial growth.
  • the surface temperature of the substrate was adjusted to 1000 ° C for five minutes in a hydrogen plasma atmosphere to clean the surface of the diamond substrate on the one hand, and to promote graphitization of the non-diamond layer on the other hand, and then perform epitaxial growth.
  • the microwave power is about 5kW
  • the cavity pressure is set to 150torr
  • the hydrogen flow rate is 500sccm
  • the methane is 50sccm.
  • a certain amount of nitrogen is artificially added during the growth, where the addition amount is 1.0sccm, and the growth temperature is controlled at Around 1200 °C. After 12 hours of growth, the epitaxial growth thickness reached 0.58 mm.
  • the epitaxially grown diamond sample is then placed in an electrochemical corrosion system. Platinum was used as the electrode, and the sample was perpendicular to the platinum electrode, and the pitch of the electrodes was about 1 cm. Deionized water was used as the electrolyte, and the amount added was to submerge the diamond sample. Connect 1000V AC power to the electrode for corrosion. Periodically replace the deionized water during corrosion. After 5 hours of corrosion, the black color of the sample receded. The epitaxial diamond layer is separated from the diamond substrate.

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Abstract

本发明公开了一种金刚石层的分离方法，该方法包括以下步骤：采用激光对待处理的金刚石内部进行二维扫描，在待处理的金刚石表面以下一定深度形成非金刚石层；去除该非金刚石层，以实现对上述金刚石的上下分离。采用该方法不会破坏金刚石衬底表面，与激光切割技术相比，降低了金刚石切割中的损耗；与离子注入分离技术相比，节约了成本、缩短了加工时间。

Description

金刚石层的分离方法 技术领域
本发明属于半导体技术领域，具体涉及金刚石层的分离方法。
背景技术
金刚石作为超硬工具，电子器件的衬底，在工业中的应用十分广泛。在所有的应用中，都希望使用大尺寸金刚石作为原材料。对于多晶金刚石而言，大于2英寸的多晶衬底已经能够合成，并用作光学窗口，超硬工具等领域。另一方面，单晶金刚石衬底是通过对天然或者合成金刚石利用激光切割、解理等方法切割成片而形成的。根据需要，对相应的表面进行抛光处理。然而，我们知道，天然金刚石非常稀有，大尺寸天然金刚石价格又非常昂贵。进一步讲，高温高压合成金刚石虽然被广泛应用在各个工业领域，但是这种方法又存在着一定的限制，如合成速率慢，随着尺寸增大，产量会急剧下降。因此，1×1cm2的单晶几乎已经成为极限。商业上使用的高温高压合成金刚石，常见的尺寸一般是5×5mm2。
使用化学气相沉积(CVD)的方法高速合成单晶金刚石目前已有报道，在生长中加入少量氮气，调整生长工艺，可以使得金刚石的生长速度超过150μm/h[1]。采用这种办法，可以使得合成的晶体厚度超过1cm[2]。另外利用CVD方法合成单晶金刚石的技术能够在CVD腔体构造扩大的情况下更容易增大合成金刚石的面积。通过控制工艺，调整导入的少量杂质气体，可以大面积高速度地进行外延生长。微波等离子体化学气相沉积(MPCVD) 是目前大面积单晶金刚石生长中最常见的技术，结合在高温高压衬底上进行金刚石的三维生长和拼接技术，目前大面积生长技术得到的单晶金刚石尺寸已经到达了2英寸[3]。
因此，在高温高压金刚石晶体上通过大面积生长技术可以进一步得到大面积单晶金刚石衬底。这样，再将大面积单晶金刚石衬底作为种晶，通过剥离的方法将外延生长的单晶金刚石层从种晶上分离，从而得到工业和研究上使用的商业化衬底。
如上所述，在由化学气相沉积技术合成的单晶金刚石晶体上，切割我们所需要的金刚石衬底，通常使用的方法是激光切割，金刚石锯切割等。使用这些办法切割时，切割区域的损伤厚度在数十到数百微米左右，这样的厚度已经与半导体衬底厚度相当，大大降低了种晶的利用效率。因此有必要寻找新的切割办法，尽量降低切割过程中造成的损失。
Fairchild和Mokuno等团队已经报道了使用高能碳离子或者氦离子注入到金刚石衬底中，在衬底表层以下一定深度形成非金刚石层，再在高温中退火后，然后使用电化学腐蚀的方法腐蚀掉非金刚石层，使得金刚石表层从原有金刚石衬底上分离[4，5]。但是，所需能量约为3MeV级的高能离子注入机非常昂贵，离子注入时间也很长，这样使用离子注入的方法分离金刚石在工业应用和科学研究上受到了限制。
参考文献
[1]“High optical quality multicarat single crystal diamond produced by chemical vapor deposition”Yu-fei Meng*,Chih-shiue Yan,Szczesny Krasnicki Phys.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 rate homoepitaxial growth using microwave plasma CVD and lift-off process"Y.Mokuno,A.Chayahara,H.Yamada.Diamond&Related Materials 17(2008)415–418.
发明内容
本发明所要解决的技术问题在于针对上述现有技术的不足，提供一种金刚石层的分离方法，采用该方法不会破坏金刚石表面，与激光切割技术相比，降低了金刚石切割中的损耗；与离子注入分离技术相比，节约了成本、缩短了加工时间。
为解决上述技术问题，本发明采用的技术方案是，金刚石层的分离方法，该方法包括以下步骤：
采用激光对待处理的金刚石内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石表面以下一定深度形成非金刚石层；去除该非金刚石层，以实现对上述金刚石的上下分离。
进一步地，采用电化学腐蚀的方法腐蚀去除该非金刚石层。
进一步地，在去除该非金刚石层之前，对待处理金刚石在≥800℃真空中退火，使得非金刚石层石墨化。
进一步地，所使用激光的能量密度为：待处理金刚石的击穿阈值-1.2J/cm2。
进一步地，所述形成的非金刚石层的深度为表层下1μm-10μm，厚度为100nm-10μm。
进一步地，所述非金刚石层的表面积小于或等于金刚石的表面积。
进一步地，所述金刚石为多晶结构或者单晶结构，同时可以为绝缘的天然金刚石或者绝缘的人造金刚石。
进一步地，所述激光为飞秒激光或者宽脉冲激光。
本发明还提供了金刚石层的分离方法的应用，用于剥离金刚石衬底表层。
本发明还提供了金刚石层的分离方法的另一种应用，用于剥离金刚石衬底上的外延生长金刚石层，具体是：采用激光对待处理的金刚石衬底内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石衬底表面以下一定深度形成非金刚石层；在金刚石衬底表面外延生长一定厚度的金刚石层；去除该非金刚石层，以实现对上述金刚石的上下分离，得到非金刚石层以上的金刚石衬底和外延生长金刚石层、以及非金刚石层以下的金刚石衬底。
本发明一种用于剥离金刚石的方法，具有如下优点：1.短时间内可以在超过3mm×3mm以上的金刚石上剥离金刚石薄层(即金刚石衬底表层)或者金刚石衬底上的外延生长金刚石层，进而形成大面积单晶金刚石批量生产的能力。2.不受金刚石晶体结构的影响。3.与现有激光切割技术相比，大大降 低金刚石切割中的损耗。与离子注入分离技术相比，节约了成本，缩短了加工时间。4.由于能够方便的剥离金刚石层，工业上实现了可以多次重复使用金刚石或外延层，不会造成浪费。5.所优选的飞秒激光利用的是雪崩电离或者多光子电离等非线性效应，其加工过程不会出现熔化过程，可以进行微米甚至是纳米尺度精细加工。
附图说明
图1是本发明中在金刚石内形成非金刚石所选用的激光系统的示意图；
图2是本发明中电化学腐蚀系统；
图3是本发明实施例所得的金刚石内部的非金刚石层的金相图。
其中：1.衰减器；2.分光镜；3.功率计；4.聚焦透镜；5.位移平台；6.电动驱动器；7.控制装置；8.激光器；9.再生放大器；10.反射镜，11.容器，12.电极；13扫描后金刚石样品；14电源；15.非金刚石层，16金刚石。
具体实施方式
本发明金刚石层的分离方法，该方法包括以下步骤：采用激光对待处理的金刚石内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石表面以下一定深度形成非金刚石层；去除该非金刚石层，以实现对上述金刚石的上下分离。其中，可以采用电化学腐蚀的方法腐蚀去除该非金刚石层。在去除该非金刚石层之前，对待处理金刚石在≥800℃真空中退火，使得非金刚石层石墨化。
本发明还提供了金刚石层的分离方法的应用，用于剥离金刚石衬底表层。还可用于剥离金刚石衬底上的外延生长金刚石层，具体是：采用激光对待处理的金刚石衬底内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石衬底表面以下一定深度形成非金刚石层；采用化学气相沉积法等 方法在金刚石衬底表面外延生长一定厚度的金刚石层；去除该非金刚石层，以实现对上述金刚石的上下分离，得到非金刚石层以上的金刚石衬底和外延生长金刚石层、以及非金刚石层以下的金刚石衬底。上述两种应用只是增加了外延生产金刚石层的步骤，其余步骤均相同，同时，本发明同样适用其他工业中需要剥离金刚石层时的应用。
本方明金刚石层的分离方法中：
1.金刚石的选择
金刚石可以是绝缘的天然金刚石，也可以是绝缘的人造金刚石，可以是单晶金刚石也可以是多晶金刚石。在单晶金刚石中，有不同的晶面(100)(111)，在晶面处还可以存在倾斜角，本发明都可以适用。
2.非金刚石层的形成
利用激光二维扫描金刚石，通过多光子吸收过程形成大量自由电子，在强光场的条件下，发生光击穿，使得金刚石中sp3键向sp2键转变。
如图1所示为一种在金刚石内形成非金刚石所选用的激光系统，包括激光器8、再生放大器9、衰减器1和聚焦透镜4，所述激光器8用于发射激光，所述激光光路上依次设置有再生放大器9、反射镜10和衰减器1，所述衰减器1的出射光侧设置有分光镜2，所述出射光照射在分光镜2上分为两路，其中一路激光透射进入功率计3，另一路激光反射进入聚焦透镜4，聚焦透镜4的出光侧设置有用于放置待处理金刚石的位移平台5，该路激光经聚焦透镜4聚焦于待处理金刚石内部，位移平台5还与电动驱动器6相连接；激光器8还与控制装置7相连接。需要说明的是，本发明中并不局限于某一种激光系统，也可以选用其他满足条件的激光系统。
具体如下：掺钛蓝宝石(Ti:sapphire，以下简称钛宝石)激光器产生的 激光在再生放大器放大作用下，单脉冲能量达3.7mJ，脉冲宽度50fs，通过选择衰减片，使激光能量达到金刚石的击穿阈值或者以上(天然金刚石光击穿阈值：0.4J/cm2，CVD金刚石光击穿阈值：0.3J/cm2)，再通过聚焦透镜4和高精度三维位移平台5将激光聚焦到金刚石表面以下一定深度内，并进行二维扫描。
在此过程中，选择合适的激光脉冲能量扫描金刚石是关键，能量低于阈值，激光不足以导致光击穿，能量太高，则会损伤金刚石表面。一般选择激光能量密度从阈值到1.2J/cm2范围内。
激光聚焦深度由聚焦透镜4和位移平台5决定，为了实现工业中金刚石多次的重复使用，聚焦深度选取在金刚石表层以下1μm-10μm范围。非金刚石层的厚度由能量密度和扫描速度共同决定，非金刚石层的厚度在扫描速度一定时与能量密度成正比；在能量密度一定时与扫描速度成反比。扫描速度根据实验需要，可以选择在10μm/s-100μm/s。非金刚石层的厚度越薄，对待处理的金刚石的损耗越小，但是由于工艺条件的限制，非金刚石层的厚度可以控制在100nm-10μm范围。
在对金刚石聚焦并进行二维扫描后，金刚石中的焦平面处金刚石结构由于光击穿而被破坏，形成非金刚石结构，这样可以利用电化学腐蚀等方法去除金刚石中的非金刚石层。
在激光加工金刚石形成非金刚石层后，将待处理金刚石整体在≥800℃真空中退火后，使得非金刚石层石墨化，从而加快电化学腐蚀速率。
3.外延生长
当金刚石被激光扫描加工后，在该金刚石上用微波等离子体化学气相沉积技术(MPCVD)外延生长单晶金刚石膜。这里虽然提到微波等离子体外 延生长技术，但是这里并不局限于该技术，比如利用热丝CVD、直流CVD等。作为特例，利用微波等离子体CVD来外延生长，在特定的生长条件下，可以外延生长高质量高纯度金刚石单晶薄膜。作为生长气体，可以使用例如氢气和甲烷的混合气体。更进一步来讲，加入适量的氮气，可以大幅度提高生长速率，而且也可以拟制异常成核和异常生长，特别是在单晶金刚石的情况下，可以在短时间内使得单晶生长达到所需的厚度。气体的比例一般为：CH4/H2为1％-20％；N2/CH4为0-3％。
这里说明上面提到的特定生长条件，使用的微波等离子体CVD的频率，一般情况下为2.45GHz或者915MHz等，对于功率，这里不作特殊的限定，一般情况下为0.5KW-30KW。在此情况下，根据CVD的结构调整功率，使得温度达到900℃-1250℃。维持金刚石在此温度下，可以促进激光加工的非金刚石层石墨化。
4.电化学腐蚀非金刚石层
按照上述方法，金刚石衬底在激光作用后，将在表面以下一定深度下形成非金刚石层。将该衬底放入盛有电解液的容器中进行电化学腐蚀。具体过程如下：
如图2所示，电化学腐蚀系统中包括交流或直流电源14，石墨或者铂金电极12、容器11及电解液，扫描后金刚石样品13竖直放置于电极中间，加入的电解液为高电阻(～18Ω·cm)溶液，加入量要淹没金刚石样13。电极12上所加电压由电源14控制，一般要使得两电极间的电场达到一定值。电场越大，腐蚀速率越快。但是电压太高，可能会导致电极间放电，容易对金刚石表面造成损伤。在电化学腐蚀的过程中，随着时间的推移，电解液吸收空气中的CO2，使得电解液电阻下降，通过电解液的电流上升，溶液中气泡 增多，气泡会包裹样品，从而无法达到腐蚀的作用。与此同时增大的电流会产生很大热量，使得电解液被加热至沸腾。所以在腐蚀过程中要及时更换电解液，使得电流维持在0～1A范围内。
实验举例：
本实施例中，具体选用一尺寸为3×3×0.3mm3商业化单面抛光单晶金刚石衬底，首先将其进行酸煮处理，清理抛光面。然后对金刚石衬底用酒精、丙酮、去离子水超声清洗。然后，使用飞秒激光加工系统将激光聚焦在金刚石表面下一定深度内，并进行二维扫描。焦点处激光光斑直径约8μm，焦点在表面下10μm处，样品表面处激光平均功率约9mW,扫描速度40μm/s，扫描间距为7μm。扫描后金刚石的颜色由浅黄变成黑色，用电子扫描显微镜对其截面进行观察，在焦平面处发现了明显的界面层，如图3，这说明了在金刚石16中发生了光击穿，形成了非金刚石层15。
经过飞秒激光加工后的金刚石放入微波等离子体CVD腔中进行外延生长。生长前，在氢等离子体氛围中，将衬底表面温度调整到1000℃进行五分钟退火，一方面清洁金刚石衬底表面，另一方面促使非金刚石层的石墨化，然后进行外延生长。微波功率在5kW左右，腔体压强设定为150torr，氢气流量为500sccm,甲烷为50sccm，为了加快生长速度，在生长中人为的加入一定量的氮气，这里加入量为1.0sccm，生长温度控制在1200℃左右。生长12h后，外延生长厚度达到0.58mm。
然后，将外延生长后的金刚石样品放入电化学腐蚀系统中。使用铂金作为电极，样品与铂金电极垂直，电极的间距在1cm左右。用去离子水作为电解液，加入的量要淹没金刚石样品。在电极上接上1000V的交流电源，进行腐蚀。在腐蚀中要定时更换去离子水。在腐蚀5h后，样品中黑色退去， 外延金刚石层与金刚石衬底分离。

Claims (10)

  1. 金刚石层的分离方法，其特征在于，该方法包括以下步骤：
    采用激光对待处理的金刚石内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石表面以下一定深度形成非金刚石层；
    去除该非金刚石层，以实现对上述金刚石的上下分离。
  2. 按照权利要求1所述的金刚石层的分离方法，其特征在于，采用电化学腐蚀的方法腐蚀去除该非金刚石层。
  3. 按照权利要求2所述的金刚石层的分离方法，其特征在于，在去除该非金刚石层之前，对待处理金刚石在≥800℃真空中退火，使得非金刚石层石墨化。
  4. 按照权利要求1或2或3所述的金刚石层的分离方法，其特征在于，所使用激光的能量密度为：待处理金刚石的击穿阈值～1.2J/cm2。
  5. 按照权利要求1或2或3所述的金刚石层的分离方法，其特征在于，所述形成的非金刚石层的深度为表层下1μm-10μm，厚度为100nm-10μm。
  6. 按照权利要求1或2或3所述的金刚石层的分离方法，其特征在于，所述非金刚石层的表面积小于或等于金刚石的表面积。
  7. 按照权利要求1或2或3所述的金刚石层的分离方法，其特征在于，所述金刚石为多晶结构或者单晶结构，同时可以为绝缘的天然金刚石或者绝缘的人造金刚石。
  8. 按照权利要求1或2或3所述的金刚石层的分离方法，其特征在于，所述激光为飞秒激光或者宽脉冲激光。
  9. 如权利要求1至8任一所述的金刚石层的分离方法的应用，其特征在于，用于剥离金刚石衬底表层。
  10. 如权利要求1至8任一所述的金刚石层的分离方法的应用，其特征在于，用于剥离金刚石衬底上的外延生长金刚石层，具体是：
    采用激光对待处理的金刚石衬底内部进行二维扫描，破坏扫描处的金刚石结构，在待处理的金刚石衬底表面以下一定深度形成非金刚石层；
    在金刚石衬底表面外延生长一定厚度的金刚石层；
    去除该非金刚石层，以实现对上述金刚石的上下分离，得到非金刚石层以上的金刚石衬底和外延生长金刚石层、以及非金刚石层以下的金刚石衬底。
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