CS266957B1 - A method for producing MESFET transistor electrodes - Google Patents

Abstract

The solution concerns the field of microwave semiconductor component technology. It solves the problem of manufacturing MESFET transistors on gallium arsenide active layers. The aim of the solution is to simplify technological processes with the possibility of forming ohmic contacts and Schottky gates independently of their mutual order, to increase the accuracy of the concealment of individual metallization levels and to improve the basic electrical parameters of ohmic contacts and Schottky gate barriers. The stated purpose can be achieved by the fact that the formation of fused ohmic contacts and the formation of the Schottky gate barrier is the last technological operation, in which both metallization layers are simultaneously annealed in a reducing hydrogen atmosphere by a rapid temperature cycle. The solution can be used in the field of manufacturing discrete MESFET transistors on gallium arsenide active layers.

Description

2 CS 266 957 Bl

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing electrodes of MESFET type transistors to active layer of gallium galenium, GaAs, prepared by iraplantation of silicon ions into semi-insulated, non-doped gallium arsenide substrates.

So far known MESFET transistors are using different technological processes using different metallization systems. From the point of view of the function of the said transistor type, it is important to achieve optimum electrical parameters not only for the active layer of gallium arsenide, but especially for soft contacts and Schottky gate interfaces. Ohmiccontacts are most often prepared by casting technology based on metallization system consisting of gold, germanium and nickel. The Schottky gate barrier is most often formed by a metallization system consisting of titanium, platinum and gold. The use of a lift-off technique is advantageous for micro-molding of complex metallization systems. The disadvantage of the said micro-molding technique is that, when used, it is not possible to completely purify the surface metal of the gallium before deposition of said metallization systems, since the metallization system can be deposited at room temperature or at room temperature. at temperatures below 80 ° C.

Residual residues, which are therefore present on the surface of the gallium arsenide after the photolytic processing of the photoresist and the subsequent chemical etching in the form of oxide-like layers and various carbon compounds, substantially influence the electrical parameters of the formed molded ohmic contacts and, in particular, the Schottky barriers, in commonly used technological In the process of manufacturing MESFET transistors using said metallization systems, the Schottky gate shaping process takes place after the casting-ohm process. The Schottky gate barrier formed on such an imperfectly cleaned surface is characterized by an increased value of the ideal coefficient, a lower potential barrier height, and reduced thermal stability. Temperature regimens used for optimum bonding of ohmic contacts often do not allow the Schottky casting process to be selected prior to the forming and molding of ohmic contacts due to the possible degradation of the Schottky gates barrier during this casting process. Also, in the aforementioned conventional method, problems may arise in the concatenation of given metallization levels, since the metallization edges for the ohmic contact on the cover marks after the casting process are blurred.

The above-mentioned disadvantages are substantially eliminated by the process of producing the MESFET transistor electrodes according to the invention, wherein the metallization layers of the ohmic contacts and gates are annealed at a temperature of 400-520 ° C in a hydrogen reducing atmosphere at a heating rate of 20-200 ° C and subsequently cooled at least 50 ° Cs \ t

The main precision of the invention is that it allows to produce transistors that have a resistive contact resistance rating of ohmic contacts of less than 0.05 µm, a potential barrier height of Schottky gate interface of greater than 0.74 V, and an ideality ratio of 1.08. The transistors prepared in this way are characterized by improved unidirectional as well as high-frequency electrical properties and, moreover, a very good thermal stability of the Schottky gate interface. A further advantage is the ability to select the molding process and ohmic contacts process independently of each other and to conceal said metallization levels with substantial greater precision, since the metallization system for ohmic contact is cast in the concave to achieve perfect edge sharpness on the cover marks. The process for producing the MESFET transistors of the present invention can be applied in conventional laboratory conditions, it is not demanding the often complex chemical purification processes of the surface arsenide via the deposition of the Schottky metallization system, since the effect of the oxide interlayers is minimized by the application of the physical-chemical processes on the Schottky gate interface. . Since the casting of the ohmic contacts and the formation of the Schottky gate is another technological operation, it is possible to carry out the process of optimally casting and forming said contacts directly on the individual chips after breaking.

Claims (4)

In the accompanying drawing, there is shown schematically a method for producing electrodes of the transistor type MESFET, wherein FIG. 1 shows the deposition and shaping of the Schottky metallization layer of the slab, FIG. 2 depicts and shapes the metallizing layer of ohmic contacts; FIG. 3 depicts and shapes the contact metallization layer; and FIG. 4 annealing said metallization. On the undissolved semi-insulating substrate 1 according to FIG. 1, an active layer 2 is formed, on which the gate metalizing layer 2 is deposited. The active layer 2 is formed on the semi-insulating substrate of gallium arsenide 1 by direct implanting of silicon ions to a depth of 300 nm. The Schottky metallization layer 2 of the titanium, platinum and gold based gate is deposited by electron gun on the surface of the active layer 2 in the depth of 150 nm and shaped by a lift-off technique. Referring to FIG. 2, a metallization layer of ohmic contacts on the active layer 2 is formed on the system of FIG. After deposition and shaping of the Schottky gate metalization layer 3, the metallic, metallic, nickel and nickel-based ohmic contacts are deposited and shaped by a shift-off technique. Referring to FIG. 3, the contact metalization layer 5 formed on the system of FIG. 2 is further provided with a metallization layer of 4 ohmic contacts. The following technological operation consists of forming a layer 5 of contact metalized base of titanium and gold. 4, the system of FIG. 3 is placed in an annealing furnace. The metallization layer 3, 3 and the contact metallization layer 5 are annealed in a reducing hydrogen atmosphere at a temperature of 400-520 ° C with a heating rate of 20-100 ° C / s and subsequently cooled at a rate of at least 50 ° C / s. The annealing process involves the process of bonding the ohmic contacts and at the same time forming the properties of the Schottky barrier. The invention can be used to find a widespread industrial application in the production of discrete transistors of MESFET on active layers of gallium arsenide. It can also be used in the production of analog and logic integrated circuits. OBJECT OF THE INVENTION A method of manufacturing MESFET type electrodes on an active layer of gallium arsenide consisting of deposition and shaping of a metallic, metallic, metallic, titanium, platinum and gold-based metallization layer of ohmic, nickel and Schottky metallization layers; (3, 4) ohmic contacts and gates are annealed in a hydrogen reduction atmosphere at 400-520 ° C with a heating rate of 20-100 ° C 1 and then cooled at a rate of at least 50 ° C 1 drawing