Be applicable to the aluminium/titanium/aluminium/titanium of gallium nitride device/golden ohmic contact system
Technical field
The present invention relates to the ohmic contact technical field of AlGaN/GaN HEMT device, particularly a kind of alloy system that is applicable to the novel ohmic contact Al/Ti/Al/Ti/Au of AlGaN/GaN HEMT device.
Background technology
Current, the development of GaN device has become the research focus of compound devices circuit field, ohmic contact is the key technology of AlGa/GaN device, its principle is that the ternary or the quaternary alloy of the nitride of the Ga, the Ti that produce at semiconductor material surface and metal interface place and Al may be the contact material of low potential barrier, and the solid-state reaction between metal and AlGaN has also caused the heavy doping at metal/AlGaN interface in addition; The diffusion of overflowing of N increases the N room of playing alms giver's effect at the interface among the GaN simultaneously, has more increased the weight of this regional electron concentration, therefore can form good Ohmic contact.
The ohmic contact technology is one of AlGaN/GaN HEMT (the HEMT full name is " High Electron Mobility Transistor " (high electronic migrate transistor)) structural key technology, and it directly influences DC characteristic, the high frequency characteristics of device and circuit.The evaporation of metal of ohmic contact obtains ohmic contact by high temperature alloy on AlGaN.For the n-AlGaN ohmic contact, broad research be Ti/Al or Ti/Al improvement (as Al, Ti/Al, Ti/Au, Ti/Al/Ni/Au and Pd/Al) for the basis.
The development process of ohmic contact is as follows at present:
1.Ti/Al:(Ti/Al=0.3 900 ℃ of 15S 10 of alloy temperature
-4Ω cm
2) reaction of Ti and N, Al diffuses into gold/half interface, because Ti/Al is easy to oxidation, and impracticable, and pattern is bad, needs to improve.
2.Ti/Al/Au (600/1000/500 ) outer Au that covers stops the oxidation of Ti, Al.
3.Ti/Al/Ni/Au (150/2200/400/500 ) adds Ni (or Pt) owing to react between the Al/Au after the temperature rising, plays the barrier layer.(900 ℃ of 30S, resistivity 10
-8Ω cm
2)
4.Ti/Al/Ti/Au because unnecessary Al may be excessive, make Ni into Ti, the Al reaction with unnecessary forms the Ti-Al alloy.
Art methods often adopts different metal components and alloy condition for the HEMT material of different structure, and very harsh to the requirement of alloy condition.Mix and non-doped structure for the AlGaN layer, difference is very big.The alloy overlong time is too short, extremes of temperature all will influence the performance of ohmic contact greatly.
Bibliographical information all is systems such as Ti/Al/Ti/Au Ti/Al/Ni/Au basically, and temperature causes technology difficulty to increase up to 800 ℃-950 ℃ even higher, and from existing result, pattern is often unsatisfactory behind the alloy, haves much room for improvement, and this also is a ubiquitous problem in the development of GaN device.Existing document is thought, for the Ti/Al/Ti/Au structure, N among ground floor Ti and the AlGaN reacts when high temperature, thereby extraction N forms the N room like this on the surface of AlGaN, be equivalent to heavy doping, and TiN is a conductor simultaneously, Al plays the barrier layer, and the 3rd layer of Ti stops the reaction between Al, the Au, to guarantee pattern.But we find that by test this theory remains to be discussed.
Summary of the invention
The object of the present invention is to provide the ohmic contact system of a kind of novel ohmic contact Al/Ti/Al/Ti/Au of the AlGaN/GaN of being applicable to HEMT device.
The invention relates to a kind of ohmic contact technology-five layer metal ohmic contact technology of new construction, be a key technology in the GaN element manufacturing, the present invention is the new technical method that forms in finishing the Chinese Academy of Sciences's great innovation item Microwave Devices ﹠ Circuits process.Specifically the invention belongs to the ohmic contact technology of AlGaN/GaN HEMT device, is a kind of ohmic contact of novel multi-layer metal structure.
A kind of ohmic contact alloy of new construction provided by the present invention, can the 680-760 degree between obtain desirable consistent ohmic contact.And the pattern of metal is more smooth behind the alloy, and bigger process choice scope has been arranged, and has reduced the requirement to process equipment.
For achieving the above object, constituting of this ohmic contact, metal by Al/Ti/Al/Ti/Au (300/200/900/400/2000 ) adopt thermal evaporation, electron beam evaporation can, be Al/Ti/Al/Ti/Au successively in the part that contacts with AlGaN, be five-layer structure, be different from traditional four-layer structure.
Technical scheme
A kind of ohmic contact alloy system adopts five-layer structure during the metal ohmic contact evaporation
The AlTiAlTiAu structure is different from Al/Pt/Au, also is different from Ti/Al/Ti/Au.Al/Ti/Al/Ti/Au
The thickness of each layer has certain excursion.
The metal the first metal layer that contacts with AlGaN is Al, is Al/Ti/Al/Ti/Au in turn then, adopts
Use this structure, the alloy pattern obviously improves.
The scope of alloy temperature is 660 ℃-760 ℃, and the alloy time is in the scope of 20---60S.
Based on a large amount of experimental facts, we think
1. have alloy reaction between ground floor Al and the AlGaN, its mechanism remains further research, and Al has also stopped excessive when high temperature alloy of Ga among the AlGaN in addition.Be equivalent to moving down of barrier layer Al, the AlGaN lattice structure when having guaranteed alloy stable.
2. after adding Ti, can form the low potential barrier Ti of higher temperature
xAl
(1-x)Alloy has been avoided at high temperature excessive of Al, and has formed the alloy of low potential barrier, helps the formation of ohmic contact.
3. owing to become the structure of double sandwich between the AlTitiAlTi, Al can fully react with Ti when having guaranteed high temperature alloy, prevents the excessive of upper strata aluminium, obtains even more ideal metal pattern.
4. this structure can both obtain desirable ohmic contact for the AlGaN/GaN HEMT (showing as Fig. 1) of the doping and the two kinds of structures of not mixing.
The ohmic contact system is at 680 ℃--and in 760 ℃ of scopes, the 20-60S scope obtains the ohmic contact of desirable unanimity.There are bigger range of choice alloy temperature, alloy time, have reduced technology difficulty, have improved the repeatability of technology.The advantage of these technical elements is that existing other ohmic contact technology is not available.
Description of drawings
By description, further describe structure of the present invention, advantage and performance below in conjunction with accompanying drawing to specific embodiment, wherein:
Fig. 1 is the AlGaN/GaN schematic diagram of two kinds of different structures.
Fig. 2 is the general structural representation of AlGaN/GaN HEMT.
Fig. 3 is the figure as a result that resist coating develops.
Fig. 4 is the figure as a result after the evaporating drain and source metals.
Fig. 5 is the order and the component figure of the metal of evaporation.
Fig. 6 peels off back institute diagrammatic sketch.
Fig. 7 is the figure as a result behind the alloy.
Fig. 8 is the ohmic contact test result figure under the Ti/Al/Ti/Au different condition.
Fig. 9 is the I-V characteristic test figure as a result between leak in the source between 660 ℃-760 ℃.
Figure 10 is under 730 ℃ of selected situations, can obtain desirable I-V performance plot in the 20-60S scope.
Figure 11 is the pattern comparison diagram behind the Al/Ti/Al/Ti/Au alloy of pattern behind the traditional Ti/Al/Ti/Au alloy and invention.
Figure 12 is the figure as a result of transmission line test.
Embodiment
Among Fig. 1, structure of the present invention can both obtain desirable ohmic contact for the AlGaN/GaN HEMT of the doping and the two kinds of structures of not mixing.
Fig. 2 is the general structural representation of AlGaN/GaN HEMT, and the expression ohmic contact will be made in the AlGaN surface shown in the figure.
Fig. 3 represents the result that resist coating develops.
Fig. 4 represents the result after the evaporating drain and source metals.(evaporation Al/Ti/Al/Ti/Au)
Fig. 5 adopts five layers of Al/Ti/Al/Ti/Au metal structure for the order and the component figure of the metal of evaporation.For traditional Ti/Al/Ti/Au structure, the order of evaporation is Ti, Al, Ti, Au.
The comparison of structure of the present invention and traditional structure.The left side is the alloy structure of traditional ohmic contact, and the right side is the alloy structure of ohmic contact of the present invention.
Result after Fig. 6 represents to peel off.
Fig. 7 represents the result behind the alloy.
Fig. 8 is the ohmic contact test result under the Ti/Al/Ti/Au different condition, 700--800 ℃, still has potential barrier to exist.
The ohmic contact test result of Al/Ti/Al/Ti/Au of the present invention, 730 ℃.
Fig. 9 is the I-V characteristic test result between the leakage of source between 660 ℃-760 ℃.
Under 730 ℃ of situations that Figure 10 selectes, can obtain desirable I-V characteristic in the 2060S scope.
Figure 11 is invention and traditional comparison, and the left side is the pattern behind the traditional Ti/Al/ti/Au alloy, and the right side is the pattern behind the Al/Ti/Al/Ti/Au alloy of the present invention, has clear improvement.
Figure 12 is the result of transmission line test.
Traditional structure, alloy temperature are up to 780 ℃ even 800 ℃, but the ohmic contact I-V characteristic behind its alloy and bad has potential barrier in the small voltage scope.And the pattern of alloy is unsatisfactory.
Five layers of ohmic contact alloy that the present invention adopts, at 680 ℃--the ohmic contact characteristic of comparison unanimity is arranged, at selected 730 ℃ of alloy temperatures, as can be seen in 20---60 scope second in-770 ℃ of scopes, can obtain the I-V characteristic of comparison unanimity, the characteristic test of its ohmic contact is very desirable.Al/ti/Al/Ti/Au structure proposed by the invention has reduced the needed alloy temperature of ohmic contact, has improved performance, has guaranteed the alloy pattern after the ohmic contact.
Test result
Test comprises that I-V characteristic curve test is with, temperature-time response test curve.
1. I-V curve test behind the alloy
2.660 ℃--the I-V change curve between 780 ℃
As can be seen from the figure, between 660 ℃-760 ℃, the I-V curve ratio is consistent,
3. the pattern behind the alloy
Metal pattern behind the alloy has material impact for the performance of device, and alloy pattern of the present invention compares to the conventional alloys pattern very big improvement.