High Performance GeOI Transistor And Its Applications In Medical Detection

In recent decades,with the development of microelectronics technology,including microelectronic materials and equipments,Metal-Oxide-Semiconductor Field Effect Transistors(MOSFETs)have been continuously promoted according to Moore’s Law.As transistor feature sizes continue to decrease,there are many new scientific issues that need to be addressed,such as short channel effects and increased power consumption.As a result,many new technologies have been developed to improve the electrical characteristics of transistors,such as strained silicon technology,metal gate/high-k gate oxide technology,silicon-on-insulator(SOI)technology,and fin-type Gate(FinFET)technology,high mobility channel material technology,new mechanism transistor technology,etc.Semiconductor material Ge have much higher mobility than Si indicating it is a promising channel materials.The structure of semiconductor on the ultra-thin insulator can suppress the short channel effect well which is an ideal structure.Combining these two advantages,the ultra-thin Ge on insulator(GeOI)MOSFET is a good choice to improve transistor performance.In addition,the development of the microelectronics industry has brought great convenience to other fields,including medical testing.Ion Sensitive Field Effect Transistor(ISFET)and Polymerase Chain Reaction(PCR)digital chips are two important research directions.In order to realize high performance ultra-thin GeOI MOSFET and cross-combined microelectronics and medical detection,the thesis studies the following aspects:the realization of high quality ultra-thin GeOI substrate;the realization of high performance ultra-thin GeOI MOSFET;back gate voltage modulation of ultra-thin GeOI transistors;implementation and modulation of ultra-thin GeOI ISFETs;implementation and characterization of high-throughput digital PCR chips.The specific research contents are as follows:First,an ultra-thin GeOI substrate with high crystal quality was obtained by direct wafer bonding and polishing techniques.In this study,in order to obtain a flat oxide surface,we grown Al2O3 thin films by Atomic Layer Deposition(ALD).After bonding process,an ultra-thin GeOI substrate was obtained by mechanical polishing,chemical mechanical polishing and etching oxidation thinning.Afterwards,we used a variety of semiconductor characterization techniques to verify the resulting ultra-thin GeOI substrate.In the first step,we verified that the thickness of the Ge film is 9 nm,which is in line with the ultra-thin structure,and there are no obvious defects or dislocations in the Ge film.In the second step,the surface roughness was characterized by a value of about 0.2 nm and uniformity was good.In the third step,the crystal quality of the Ge film was tested by Raman spectroscopy and X-ray diffractometry.The results showed that the crystal quality of the Ge film was maintained.In the fourth step,the carrier mobility of the Ge film is also characterized.When the Ge film is 537 nm,the Hall mobility of the hole reaches 1330 cm2/Vs.Next,we realized the basic characteristics of the GeOI back-gate nMOSFET.This proved that the GeOI substrate obtained by the new method is suitable for the transistor.However,the transistor performance needs to be improved.Therefore,we improved the interface between Al2O3 and Ge through post-oxidation technology,which reduced the interface state density,and optimized the ultra-thin GeOI substrate.Based on this condition,we have realized high-performance GeOI pMOSFETs with different thicknesses,and studied the dependence of transistor characteristics on the thickness of Ge film.It is found that as the thickness of the Ge film decreases,the scattering of the carrier in the inversion channel layer is enhanced,the mobility is lowered,and the transistor drive current is reduced.In addition,we compared the electrical properties of the GeOI obtained by the new method and smart cut GeOI transistors.It was found that the high crystal quality and good interface quality make the performance of the polishing GeOI transistor better than the smart cut MOSFETs.Finally,we studied the carrier characteristics of GeOI transistors at low temperatures.Then,we studied the transport properties of channel carriers in GeOI pMOSFETs by applying back gate voltage(VBG).The study found that VBG can significantly modulate the distribution of channel carriers.When VBG is positive,the carrier distribution is closer to the upper interface,which increases the Coulomb Scattering caused by the interface state and the Surface Scattering caused by the surface roughness.Therefore,a positive VBG reduces the overall carrier effective mobility.When VBG is a negative voltage,the opposite is true,and the carrier distribution moves toward the center of the Ge film,which reduces the scattering probability and improves the mobility.In addition,we also studied the dependence of the mobility of the front gate transistor on the thickness of the Ge film.It was found that as the thickness of the Ge film decreased,the electric field in the Ge film strengthened,and the scattering of the channel carriers was also aggravated.The mobility is also reduced.Finally,this thesis crosses semiconductor technology and medical detection technology,and obtains high sensitivity GeOI ISFET and high-throughput digital PCR chip.Based on the GeOI substrate,we realized the GeOI ISFET for the first time,and studied the ion sensitivity response of VBG to ISFET to improve the sensitivity.In addition,we have obtained a precise etching technique by adjusting the process to achieve a digital PCR micro-reaction chamber with good steepness.Surface passivation of the microreaction chamber is then achieved by oxidation techniques.Finally,through the results of PCR amplification,we can realize that the micro-reaction chamber digital PCR chip can be effectively typed,and the number of effective pores has reached more than 12,000.