Research On Diamond Lift-off Process And Electronic Devices

As one of the representatives of the emerging ultra-wide bandgap semiconductor materials,diamond has a series of advantages such as high carrier mobility and high thermal conductivity.Nowadays diamond substrates are primarily produced by homogenous epitaxy using Microwave Plasma Chemical Vapor Deposition technique.However,the epitaxial wafer need to be separated from the substrate by laser cutting,and this method causes a great loss of the diamond material.In addition,homogeneous epitaxy of large size single crystal diamond is mainly realized by mosaic growth technique.The technique demands very strictly on the repeatability of the shape and size of the diamond plates as mosaic blocks,and the repeatability is almost impossible to be achieved by laser cutting.Another problem for diamond applications in electronic devices is that boron and phosphorus dopants are difficult to be activated at room temperature.Therefore,the fabrication of high performance electronic devices such as diodes and field effect transistors based on the p-type surface conduction of hydrogen-terminated diamond(H-diamond)is still a research hotspot.Based on the above background,the diamond lift-off process and H-diamond electronic devices were studied.The main work and conclusions are as follows:1.The lift-off process rather than traditional laser cutting was researched to separate diamond epilayer from the substrate using the self-constructed high-voltage electrolytic system.The available process steps and the process conditions were determined after many experiments:C⁺was used as the implantation source,the implantation energy was 400 ke V,and the dose was 2.5×10¹⁶cm^-2.The electrolytic etching voltage was 4?5 k V and the current was 2?30 m A.Using this method,a single crystal wafer with a thickness of 90?m and a size of 1×1 mm² was successfully lifted off.It solved the problem of large diamond loss caused by laser cutting,and would realize the preparation of ultra-thin single crystals and replication of seed crystal.2.The surface of the CVD diamond film produced by lift-off method was characterized by AFM and Raman spectroscopy.It was found that the single crystal surface exposed by lift-off was smooth and the roughness was only 1.8nm.It is proved by Raman spectra that the single crystal prepared by lift-off method is of high quality and can be used directly in the fabrication of electronic devices without polishing.3.Planar schottky barrier diodes were fabricated on single crystal H-diamond substrate.Current-voltage characteristics of the devices show good rectification properties.The current density is 5 A/cm² at the forward voltage of-4 V,and is?10^-7A/cm² at reverse bias.The conduction mechanism of the device was analyzed,and the schottky barrier height was extracted to be 1.01 e V.The direct current characteristics of the devices with different schottky-ohmic interspaces or schottky contact areas are compared.In addition,a high reverse breakdown voltage of 1200 V has been achieved on the device with the interspace of 10?m,which suggests that the average breakdown field reaches 1.2 MV/cm,which is similar to the current international high level.4.The H-diamond MOSFETs with Zr O₂ gate dielectric was fabricated.The output characteristics,transfer transconductance characteristics of the FETs and the C-V characteristics and gate leakage characteristics of the source-gate diode were analyzed.For devices with a gate length of 2?m,the drain current I_D of-143.6 m A·mm^-1 and the on-resistance of 78.49?·mm were achieved at the gate bias voltage of-6 V.The gate leakage mechanism was found to be F-N tunneling when gate voltage in range of-2.5?-4 V,and the Ohmic mechanisms in range of-5?-10 V.The effective mobility of the channel is56.9 cm²·V^-1·s^-1 for-6 V<V_GS<-1 V.In summary,this thesis covers both diamond material and device researches.In terms of materials,the diamond lift-off process conditions were determined,and the diamond epitaxial wafer with a thickness of 90?m was successfully separated with smooth surface and good crystal quality.On the device research,H-diamond high-voltage diodes and zirconia gate MOSFETs were fabricated.Quite good device performance was analyzed.