Method for manufacturing ohmic contacts for semiconductor heterostructure gan/algan

FIELD: ohmic contacts for microelectronic devices such as microwave field-effect transistors.

SUBSTANCE: proposed method includes sequential evaporation of Ti, Al, Ni, Au onto section of AlGsN surface layer and fast thermal annealing of semiconductor heterostructure; fast thermal annealing is conducted using contact method and graphite resistive heater, semiconductor heterostructure being disposed on heater surface. In the course of annealing temperature of GaN/AlGsN semiconductor heterostructure is controlled to ensure reproducibility of its parameters.

EFFECT: facilitated procedure, reduced time requirement, enhanced quality of heterostructure.

1 cl

 

The invention relates to a technology of forming ohmic contacts to semiconductor structures of GaN/AlGaN and can be used in the manufacture of microelectronics devices, particularly field-effect transistors UHF range.

A known method of making ohmic contacts to semiconductor heterostructures, including the deposition of metal layers on the surface of the heterostructure and its rapid thermal annealing using radiation heating with quartz lamps described in particular in US 4482393.

The disadvantages of the methods containing the operation rapid thermal annealing using a quartz lamp are:

the uneven heating of the heterostructure due to differences absorbing properties different topological areas formed on its surface, which leads to uneven resistance area ohmic contact;

- high temperature quartz lamps, complicating the measurement of the temperature of the heterostructure in the annealing process, which leads to deterioration of its quality and hinders the reproduction of its parameters.

There is also known a method of making ohmic contacts to semiconductor heterostructure GaN/AlGaN, including preliminary formation on the surface of the AlGaN layer heterostructures deepening strictly specified dimensions through the om etching. The recess allows to make ohmic contact to the heterojunction between the layers of AlGaN and GaN, which reduces the contact resistance of the ohmic contact US 6897137 B2. In place of education deepening produce sequential sputtering of Ti, Al, Ni, Au. Then produce a rapid thermal annealing using a quartz lamp.

This solution is accepted as the prototype of the present invention.

The disadvantage of the prototype is the need for education deepening strictly specified dimensions on the surface of a semiconductor heterostructure, which significantly complicates and lengthens the process of making contacts; in addition, as noted above, the implementation of rapid thermal annealing using a quartz lamp causes the unevenness of the resistance area of the ohmic contact, and also makes it difficult to control the temperature of the heterostructure in the process of annealing, which leads to deterioration of the quality of heterostructure and hinders the reproduction of its parameters. Possible overheating of the semiconductor heterostructure, which leads to its degradation.

The present invention is to simplify and reduce the time of the process of making ohmic contacts to semiconductor heterostructure GaN/AlGaN, and improving the quality of heterostructures and support in the production of its parameters by controlling its temperature in the annealing process.

According to the invention in the method of making ohmic contacts to semiconductor heterostructure GaN/AlGaN, including sequential sputtering of Ti, Al, Ni, Au on the surface of the layer of AlGaN and rapid thermal annealing of semiconductor heterostructures, rapid thermal annealing to produce a contact method using a graphite resistance heater, when this semiconductor heterostructure disposed on the surface of the heater.

The applicant has not identified the sources containing information about technical solutions, identical to the present invention, which allows to make a conclusion about its compliance with the criterion of "novelty".

Thanks to the implementation of the distinguishing features of the invention is a uniform contact heating heterostructures, because it eliminates the dependence of the temperature of the heat absorbing properties of various topological areas heterostructures; this also eliminates the uncertainty in the temperature measurement heterostructures, due to the influence of background thermal radiation of the quartz lamp.

The control parameters of the process of making ohmic contacts to semiconductor heterostructures according to the claimed method eliminates the need of prior learning deeper under the ohmic contact, as is what NRN heating and strict control of the temperature of the heterostructure in the process of rapid thermal annealing allows control of diffusion of the metals, forming ohmic contacts in a given place heterostructure to a predetermined depth; in addition, ensure the specified quality heterostructures due to uniform resistance area ohmic contact; the controllability of the temperature of the heterostructure in the process of rapid thermal annealing leads to the constancy playback parameters.

The applicant has not found any sources of information containing data about the impact of an alleged distinguishing signs on achieved as a result of their implementation of the technical result. This, according to the applicant demonstrates compliance with this technical solution, the criterion of "inventive step".

Method of making ohmic contact of the semiconductor heterostructure of GaN/AlGaN is implemented as follows.

The vacuum chamber is placed heterostructure GaN/AlGaN formed with its surface elements on the instrument cluster topology. On a given area (or multiple areas) of the surface of the AlGaN layer using electron-beam spraying sprayed successive layers of Ti, Al, Ni, Au given thickness. After that, the semiconductor heterostructure move the camera rapid thermal annealing and come to the surface in the camera graphite resistive heater, representing the FDS is the first layer of graphite, deposited on a substrate made of pyrolytic boron nitride in the form of a flat spiral with current leads. Produce the pumping of air from the chamber and serves instead of a stream of inert gas, in particular nitrogen. Then heat the heterostructure at a speed of not less than 100°C/s to a temperature of 850-950°and maintain this temperature for 20-40 seconds. The temperature control is performed using thermocouple and pyrometer. Then conduct rapid cooling heterostructures by forced blow an inert gas. In the process of rapid thermal annealing is melting aluminum and its reaction with other components of ohmic contacts, the result is a connection of complex composition, forming ohmic contacts with a uniform resistance over the surface.

EXAMPLE 1.

By molecular-beam epitaxy on sapphire substrate grown semiconductor heterostructure field of microwave transistor comprising a base layer of variable composition AlxGa1-xN (0<x<1), the channel layer of GaN with a thickness of 100 nm and a barrier layer of Alfor 0.3Ga0,7N thickness of 25 nm (all layers are not doped). On the pre-formed topological surface barrier layer of Alfor 0.3Ga0,7N by electron beam deposition cause a sequence of metal layers of Ti (20 is m), Al (200 nm), Ni (50 nm), Au (nm). Next, perform a rapid thermal annealing of the entire heterostructure in order to obtain ohmic contacts at a temperature of 900°C for 30 seconds. On the resulting ohmic contact measurements of the contact resistance (Rcusing the method of long lines, which amounted to 0.12 Ohm·mm

EXAMPLE 2.

Same as in example 1, but the barrier layer Alfor 0.3Ga0,7N a total thickness of 25 nm consists of three sublayers: (1) non-alloy layer with a thickness of 1 nm, (2) doped Si (5·1018cm-3layer thickness of 10 nm, and (3) non-alloy layer with a thickness of 14 nm. Rapid thermal annealing is conducted at a temperature of 900°within 20 seconds. The obtained value of Rc=0.1 Ohm·mm

EXAMPLE 3.

Same as in example 2, but the barrier layer with a total thickness of 25 nm (also consisting of three sublayers) has the composition Alfor 0.4Gafor 0.6N. Rapid thermal annealing conducted at a temperature of 900°C for 40 seconds. The obtained value of Rc=0,14 Om·mm

For the way of analog value Rcis usually from 0.2 Ohm·mm version with earthing contact (Prototype) to 0.6-2.0 o·mm in the usual form of rapid thermal annealing with a mercury lamp.

Method of making ohmic contacts to semiconductor heterostructure GaN/AlGaN, including consecutive napaloni is Ti, Al, Ni, Au on the surface of the layer of AlGaN and rapid thermal annealing of the semiconductor heterostructure, wherein the rapid thermal annealing to produce a contact method using a graphite resistance heater, when this semiconductor heterostructure disposed on the surface of the heater.



 

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