Effects Of Nanochannel Morphology On Electrical Characteristics In GaN-based FinFET Devices

In the development of the semiconductor industry,as the gate length of devices continues to shrink,the gate control capabilities of traditional planar devices will deteriorate,and devices will begin to exhibit short channel effects.Three-dimensional FinFET devices have better gate control capabilities than planar devices due to the good encapsulation of the gate metal to the conductive channel.Compared with Si and GaAs materials,GaN exhibits more obvious advantages in terms of material properties and device performance.Therefore,GaN-based FinFET devices have very important scientific value and broad application prospects.In this paper,the GaN-based FinFET devices are studied in detail from two aspects of structural simulation and device fabrication.The research idea of this paper is as follows:Firstly,the research status of GaN-based FinFET devices is introduced.Then,various models of GaN-based FinFET devices are established through Silvaco software,and simulations are performed one by one.Then the conclusions obtained through simulation are used to guide the experiment.In the simulation part of the paper,the DC characteristics of GaN-based FinFET devices are studied in terms of the geometry of the nanochannels,the Al composition of the barrier layer,the presence or absence of an oxide layer under the gate,and the thickness of the barrier layer.According to the difference between the angle ? of the side wall of the nanochannel and the horizontal direction,six kinds of device models with different channel shapes have been established in the third chapter.With the decrease of the included angle ?,the wrap around of the gate metal to the conductive channel is enhanced,the depletion region generated by the metal-semiconductor contact also increases,and the control capability of gate is enhanced,resulting in the drift in the positive direction of the threshold voltage.In the simulation of the Al composition,it is found that when the Al composition is reduced,the concentration of the two-dimensional electron gas will decrease,and the threshold voltage of the device will move in the positive direction.After adding an oxide layer between the gate and the channel,the linearity of the device is improved,but the transconductance and subthreshold characteristics are degraded at the same time.After reducing the thickness of the barrier layer in the simulation,it was found that the concentration of two-dimensional electron gas in the channel decreased,the threshold voltage of the device drifted in the positive direction,and the peak value of the transconductance increased gradually.In the fourth chapter,the technological process and inductively coupled plasma etching technology of GaN-based FinFET devices are introduced,and the influence of chamber pressure on the etching morphology of SiN and GaN materials is studied.It was found in the study that when the pressure in the chamber was increased,the plasma density increased and the reaction rate increased.If the chamber pressure continues to increase,the density of the plasma will saturate gradually,the free path of the ions will decrease.As a result,the etching tends to be isotropic,and the lateral chemical corrosion will be strengthened.Based on the above conclusions,two types of GaN-FinFET devices were fabricated in this paper.The chamber pressure of one type is 5mT while the other is 25mT.Each type of device is provided with four different widths of nanochannels,100 nm,200 nm,300 nm,and 500 nm,respectively.It is found that for the same type of device,the threshold voltage moves in the positive direction as the channel width decreases.Both the sub-threshold swing and the reverse leakage with the gate of the two types of devices are larger than the conventional HEMT device,which is mainly caused by the etching damage introduced in the thin line process.After the small signal test,it was found that the cutoff frequency and maximum oscillation frequency of the two types of FinFET devices are lower than those of conventional HEMT devices.This is mainly due to the formation of new nanochannel capacitances in the channel sidewalls,resulting in the increase of the equivalent capacitance of the gate.Finally,the wet etching effect of TMAH solution on GaN materials is studied.After the AFM test,it was found that the roughness of the GaN material soaked in the TMAH solution decreased significantly,which can be used to repair the etching damage introduced during the device manufacturing process.