CN1381897A - Ferroelectronics/semiconductor memory structure based on AIxGa1-xN/GaN heterojunction and its making method - Google Patents

Abstract

Based on Al _x Ga _1-x N/GaN heterojunction ferroelectric/semiconductor memory structure and its manufacturing method, Al _x Ga _1-x N/GaN modulation doping was first grown on sapphire substrate by MOCVD technology Then the PZT ferroelectric film was grown on the Al _x Ga _1-x N layer by PLD technology, and finally the Ti/Al ohmic contact electrode was deposited on the Al _x Ga _1-x N layer by electron beam evaporation technology and the Al electrodes are deposited on the PZT layer. This structure utilizes the high-temperature stability of the PZT/Al _x Ga _1-x N interface, avoiding the interface interdiffusion and interface reaction problems of the common ferroelectric/SiMFS structure. At the same time, this structure uses the high-concentration and high-mobility two-dimensional electron gas at the _{AlxGa1 -xN} /GaN heterointerface as channel carriers, which is beneficial to improve the response speed of the memory structure and other properties.

Description

A kind of based on Al xGa 1-xFerroelectric/the semiconductor memory structure of N/GaN heterojunction and method for making thereof

One, technical field

The present invention relates to a kind of based on Al _xGa _1-xFerroelectric/the semiconductor memory structure of N/GaN heterojunction comprises iron electric polarization effect and Al in the ferroelectric _xGa _1-xPiezoelectric polarization effect in the N layer is to Al _xGa _1-xThe modulation scheme of N/GaN heterogeneous interface two-dimensional electron gas density, and the preparation method of this memory structure.

Two, technical background

Since the seventies in last century, just make various effort in the world, want to utilize extremely strong polarity effect of ferroelectric material and very high relative dielectric constant, in the microelectric technique of ferroelectric introducing based on semi-conducting material, wherein most promising a kind of device architecture is metal-ferroelectric-semiconductor field effect transistor (MFS-FET), and this device can be used for making the read-only memory of non-volatile type.

Angle from semiconductor device, MFS-FET still belongs to the category of metal-insulator-semiconductor field effect transistor (MIS-FET), but in the MFS-FET structure, make insulator, replaced the SiO in common metal-oxide-semiconductor (MOS) fieldtron with ferroelectric ₂Since a very long time, people use the Si material as the semiconductor channel material among the MFS-FET always, main advantage be in the device preparation with conventional semiconductor MOS device technology compatibility.But the subject matter that this structure runs into technically is Si, and last deposit ferroelectric thin film must at high temperature carry out, and ferroelectric thin film need carry out thermal anneal process again after the deposit, the atom counterdiffusion at ferroelectric in these processes/Si interface is very serious, and the interface solid phase reaction takes place, thereby ferroelectric/Si interfacial property is difficult to control.Simultaneously, the high interface state density heavy damage that exists of ferroelectric/Si interface the characteristic of MFS-FET memory structure.These problems have seriously restricted the development of the ferroelectric memory of Si base for many years.

III group-III nitride wide bandgap semiconductor materials (containing GaN, AlN, InN and ternary alloy three-partalloy thereof) is the third generation novel semiconductor material of paying much attention in the world in recent years, have high temperature resistant, corrosion-resistant, high saturated electron drift velocity, high disruptive field intensity, the physicochemical properties that direct band gap etc. are excellent.Al _xGa _1-xThe N/GaN heterostructure is considered to develop the preferred material system of high temperature, high power, high-frequency semiconductor device, Al _xGa _1-xN/GaN hetero-structure field effect transistor (HFET) claims the development level of High Electron Mobility Transistor (HEMT) to improve rapidly again, and technology is mature on the whole, and device performance is near practicability.Simultaneously, with SiO ₂Al for grid material _xGa _1-xThe research of N/GaN MIS-HFET also has been subjected to great attention.Therefore, if use III group nitride material, particularly Al _xGa _1-xThe N/GaN heterogeneous structure material replaces the Si material to be used to develop the MFS-HFET memory structure, both can solve the high temperature instability problem at ferroelectric/Si interface, also can make full use of Al _xGa _1-xN/GaN heterogeneous interface two-dimensional electron gas (2DEG) is transport property well, improves the response speed of this type of memory structure.

Three, summary of the invention

The objective of the invention is to develop with Al _xGa _1-xThe N/GaN heterostructure is the MFS structure of semiconductor channel, realizes its storage performance, improves the response speed of this type of memory structure.

The object of the present invention is achieved like this:

With the sapphire is substrate, is provided with high-quality Al _xGa _1-xThe N/GaN modulation-doped heterostructure, the X value is between 0.15-0.30; Again at Al _xGa _1-xGrowth PZT ferroelectric thin film on the N layer is at last respectively at Al _xGa _1-xPreparation hearth electrode and top electrode on N layer and the PZT layer.

GaN thickness 1-2um, Al _xGa _1-xN layer thickness 10-100nm, PZT layer thickness 100-500nm.

Because Al _xGa _1-xLattice mismatch between N and the GaN, and Al _xGa _1-xThe piezoelectric modulus that N is very high, the last Al of GaN _xGa _1-xThere is very strong piezoelectric polarization effect in the N layer, causes Al _xGa _1-xThe N/GaN heterogeneous interface forms concentration and reaches～and 10 ¹³Cm ^-2Two-dimensional electron gas (2DEG), the 2DEG mobility reaches 1000cm ²More than/the V.s, form Al with this _xGa _1-xComparatively desirable raceway groove in the N/GaN base MFS structure.

With pulsed laser deposition (PLD) technology at Al _xGa _1-xDeposit Pb (Zr on the N layer _0.53Ti _0.47) O ₃(lead zirconate titanate is called for short PZT) film.PZT is a kind of typical ferroelectric material, and residual polarization charge can reach 10 μ C/cm under its zero electric field ², its relative dielectric constant can be up to more than 1000.Very thin PZT film (hundreds of nanometer) just can produce very strong polarized electric field and modulate Al _xGa _1-x2DEG concentration in the N/GaN heterogeneous interface raceway groove.

Adopt electron beam evaporation method on the PZT film, to make Al electrode (top electrode) at last, at Al _xGa _1-xMake Ti/Al Ohm contact electrode (hearth electrode) on the N/GaN, formation can be carried out the Al that electrical properties is measured _xGa _1-xN/GaN base MFS structure.

The present invention adopts Al in the world first _xGa _1-xThe N/GaN heterostructure is as the semiconductor channel of MFS memory structure, and main innovate point comprises: (1) because the high-temperature stability of III group nitride material, can solve problems such as the unstable and interface solid phase reaction of the high temperature at ferroelectric/Si interface; (2) utilized Al _xGa _1-xThe polarity effect that the N layer is very strong makes Al on the one hand _xGa _1-xThe N/GaN heterogeneous interface produces the two-dimensional electron gas of high concentration, high mobility, has formed comparatively ideal device channel; On the other hand, Al _xGa _1-xPolarization field that the N layer forms and polarization field (both directions are opposite under the back bias voltage) acting in conjunction that the PZT layer forms make capacitance-voltage (C-V) the storage window of MFS structure realize under back bias voltage fully.This means is not needing the PZT ferroelectric thin film to carry out just can producing under the situation of polarization reversal C-V storage window, thereby has reduced greatly in the Si base MFS structure because the variety of issue that ferroelectric counter-rotating fatigue effect is brought.It is this that to need not the characteristic that iron electric polarization counter-rotating just can realize C-V storage window be that Si base MFS structure can not realization.

Four, description of drawings

Fig. 1: PZT/Al _0.22Ga _0.78N/GaN MFS structural representation

Fig. 2: Al _0.22Ga _0.78The high-resolution X-ray diffraction ω of N/GaN modulation-doped heterostructure/2 θ swing curves.A plurality of satellites have illustrated the precipitous of the high-quality of heterostructure and heterogeneous interface.This is at Al _0.22Ga _0.78The N/GaN heterogeneous interface forms the basis of high concentration, high mobility 2DEG.

Fig. 3: (a) PZT/Al _0.22Ga _0.78N/GaN MFS structure diagram, (b) the CHARGE DISTRIBUTION schematic diagram of this structure under back bias voltage, (c) conduction band structure schematic diagram, solid line represents to exist the situation of PZT iron electric polarization, and dotted line represents not have the situation of PZT iron electric polarization, P _fIron electric polarization vector (under the back bias voltage) in the expression PZT layer, P _pExpression Al _0.22Ga _0.78Piezoelectric polarization vector in the N layer, P _fWith P _pDirection is opposite.P _fChange with applying bias, it is raised under back bias voltage at the bottom of the GaN layer conduction band, makes Al _0.22Ga _0.78N/GaN heterogeneous interface triangle quantum well shoals, and causes the 2DEG lowering of concentration.P _pDo not change with applying bias, its effect just in time with P _fOn the contrary, make Al _0.22Ga _0.78N/GaN interface quantum well deepens, and causes 2DEG concentration to rise.

Fig. 4: Al _0.22Ga _0.78High Frequency C-V curve during N/GaN base MFS structure 1MHz, full figure is the curve of whole voltage scan range, interior figure is the curve under the back bias voltage.When bias voltage during greater than 0.7V (positively biased), capacitor C depends on the PZT film, because its very big relative dielectric constant, C is very big; When bias voltage became negative bias, voltage was added in Al _0.22Ga _0.78On the N layer, C sharply descends.The variation of C is exhausting owing to 2DEG near the-9V bias voltage.

Fig. 5: Al _0.22Ga _0.78The C-V scanning lag loop of N/GaN base MFS structure is counter-clockwise direction.The ferroelectric storage window of C-V near-9V, width 0.2V, it be since voltage just sweeping with anti-inswept journey in different iron electric polarization states cause, whole C-V storage window shows that the iron electric polarization of PZT film reverses in the back bias voltage scope.

Five, specific implementation method

Is substrate with the surface for the sapphire of (0001) face, with the MOCVD Al that grows _0.22Ga _0.78The N/GaN modulation-doped heterostructure.During growth, be 488 ℃ of resilient coating (thickness 30nm) growth temperatures with GaN; Then, epitaxial growth GaN layer (thickness 2 μ m) growth temperature is 1030 ℃; And then the unadulterated Al that grows _0.22Ga _0.78The N layer, thickness 3nm, 1080 ℃ of growth temperatures; The Si Doped n-type of growing at last Al _0.22Ga _0.78The N layer, thickness 75nm, 1080 ℃ of growth temperatures.MOCVD is grown under the normal pressure and carries out, and growth source is respectively trimethyl gallium (TMG), trimethyl aluminium (TMA) and high-purity ammonia (NH ₃), carrier gas and diluent gas are hydrogen (H ₂).Al _0.22Ga _0.78N layer component is than the flow-rate ratio decision by TMG and TMA.

At Al _0.22Ga _0.78With pulsed laser deposition (PLD) growth pzt thin film, thickness 400nm, laser are KrF excimer laser (wavelength 248nm), form 2.5J/cm on the target surface during deposit on the N/GaN heterostructure ²Energy density, 750 ℃ of growth temperatures.

Adopt electron beam evaporation method on the PZT film, to make Al electrode (top electrode) at last, at Al _xGa _1-xMake Ti/Al Ohm contact electrode (hearth electrode) on the N/GaN, form Al _0.22Ga _0.78N/GaN base MFS structure.

High-quality Al _xGa _1-xThe preparation of N/GaN modulation-doped heterostructure is Al _xGa _1-xThe core technology of N/GaN base MFS storage structure preparation, following process is typical A l _0.22Ga _0.78N/GaN modulation-doped heterostructure MOCVD growth technique:

The growth of GaN resilient coating and annealing:

TMG flow: 15 μ mol/min, NH ₃Flow: 3.5SLM/min, H ₂Flow: 3.0SLM/min

Growth temperature: 488 ℃

Growth time: 140 seconds, thickness 30nm

Growth pressure: 760 Torr

Growth after annealing: H ₂Flow: 1.0SLM/min, NH ₃Flow: 0.5SLM/min; 1030 ℃; 5min

Non-Doped GaN (i-GaN) outer layer growth:

TMG flow: 60 μ mol/min, NH ₃Flow: 4.0SLM/min, H ₂Flow: 0.5SLM/min

Growth temperature: 1030 ℃

Growth time: 60min, thickness 2 μ m

Growth pressure: 760 Torr

Non-doped with Al _0.22Ga _0.78N (i-AlGaN) outer layer growth:

TMG flow: 10 μ mol/min, TMA flow: 12 μ mol/min, NH ₃Flow: 4.0SLM/min,

H ₂Flow: 0.5SLM/min

Growth temperature: 1080 ℃

Growth time: 39 seconds, thickness 3nm

Growth pressure: 760 Torr

Si Doped n-type Al _0.22Ga _0.78N (n-AlGaN) outer layer growth:

TMG flow: 10 μ mol/min, TMA flow: 12 μ mol/min, NH ₃Flow: 4.0SLM/min,

H ₂Flow: 0.5SLM/min, SiH ₄Flow: 1.0sccm/min

Growth temperature: 1080 ℃

Growth time: 675 seconds, thickness 75nm

Growth pressure: 760 Torr

Claims (3)

1. A metal/ferroelectric/semiconductor (MFS) memory structure based on _{AlxGa1 -xN} /GaN heterojunction, which is characterized by growing _{AlxGa1 -xN} /GaN heterojunction on a sapphire substrate texture structure, and the value of X is between 0.15-0.30; then grow PZT ferroelectric film on the Al _x Ga _1-x N layer, and finally prepare the bottom electrode and the top electrode on the Al _x Ga _1-x N layer and the PZT layer respectively. electrode. 2. by the MFS memory structure based on _{AlxGa1 -xN} /GaN heterojunction described in claim 1, it is characterized in that GaN thickness 1-2um, _{AlxGa1 -xN} layer thickness 10-100nm , PZT layer thickness 100-500nm. 3. by the preparation method of the MFS memory structure based on Al _x Ga _1-x N/GaN heterojunction described in claim 1 is to be substrate with the sapphire of (0001) plane, after conventional cleaning, adopt MOCVD Growth techniques, after pretreatment, GaN buffer layer growth and annealing, undoped GaN epitaxial layer growth, undoped Al _x Ga _1-x N epitaxial layer growth and Si-doped n-type Al _x Ga _1-x N epitaxial layer The preparation of Al _x Ga _1-x N/GaN modulation doped heterostructure was completed in several stages of growth, and the growth sources were trimethylgallium (TMG), trimethylaluminum (TMA) and high-purity ammonia (NH ₃ ), the carrier gas and dilution gas are hydrogen (H ₂ ); the PZT ferroelectric thin film is prepared by pulsed laser deposition (PLD) technology; the Ti/Al ohmic layer is deposited on the Al _x Ga _1-x N layer by electron beam evaporation. A contact electrode (bottom electrode) and an Al electrode (top electrode) is deposited on the PZT layer.

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