RU2797136C1 - Method for manufacturing planar diode with anode whisker and air lead using “mesa-mesa” technology - Google Patents

Abstract

FIELD: diode manufacturing.

SUBSTANCE: according to the "Mesa-Mesa" method, it is proposed to manufacture a planar diode with an anode terminal in form of an air bridge with a whisker, including deposition of a dielectric film on the surface of the heteroepitaxial structure, in which windows of the ohmic contact of the cathode are created by chemical or physical etching on the resist mask by chemical or physical etching at least up to a highly doped U-shaped cathode layer along with a rectangular window for forming an anode contact pad in the same plane coaxially with it, simultaneous formation of low-resistance ohmic contacts in both windows by explosive lithography or electrochemical metallization methods, followed by annealing and their galvanic thickening, formation using thin (<1 mcm) micron or submicron rectifying barrier anode contact masks.

EFFECT: advantage of the proposed method for manufacturing a diode with an anode terminal in form of an air bridge with a whisker to the anode contact according to the “Mesa-Mesa” method is that the anode and cathode contact pads are located in the same plane as the anode contact.

1 cl, 2 dwg

Description

The invention relates to semiconductor electronics, to devices with bulk and beam leads, and is intended to create both discrete microwave (MW), extremely high frequency (EHF) and terahertz (THz) diodes, and monolithic integrated circuits (MIS) of modulators, mixers, multipliers , switches, attenuators, phase shifters, detectors, etc. based on them.

A known method of creating a microwave plenary diode, manufactured by the method of "Mesa-Mesa" with an anode output in the form of an air bridge [1]. The well-known "Mesa-Mesa" method was implemented by forming a local region on the surface of a planar-doped (PL) heteroepitaxial structure (Heterostructure-Barrier) by etching the n-GaAs layer along the resist mask to the layer of highly doped n ⁺ -GaAs located below. Then, windows to the n ⁺ - GaAs layer were created using photolithography methods. The first U-shaped window ^was formed in the resist mask on the surface of the n ⁺ -GaAs layer around the local n-GaAs region; bridge l _br . After that, low-resistance ohmic contacts (OC) to the n ⁺ -GaAs layer were simultaneously formed in the windows of the resist mask, followed by removal of the resist mask and high-temperature annealing. Then, in the center of the local region of n-GaAs between the protrusions of the U-contact - the cathode, at a distance Δx _R from the edge of the U-shaped contact, using lithography methods, a rectifying barrier contact - an anode was formed, a round shape of a given diameter D. Insulation of the anode and cathode contact pads from anode and cathode was carried out by etching the mesa on the mask of the resist or dielectric in the n ⁺ -GaAs layer both around the rectangular contact area (Mesa 1) and around the area with barrier and ohmic U-shaped contacts located on it (Mesa 2), at least to the i-GaAs semi-insulating layer. After the formation of the mesa insulation, the connection of the barrier contact with its cathode contact pad located on the adjacent mesa in the form of a rectangular contact was carried out by a metal air bridge formed using thick-layer resistive masks. This method involves the formation of an expanded contact (equal to or greater than its diameter) at the junction of the barrier contact with the air bridge. The anode was connected to its contact pad either by a metal air bridge or by a metal bus lying on the surface of the passivating dielectric layer covering the side surfaces of the mesa and the surface of the i-GaAs semi-insulating layer.

A disadvantage of the known "Mesa-Mesa" method with an air bridge output and an extended contact is the need to use thick-layer resists in their manufacture, usually exceeding the mesa height (for example, h _M > 5 μm), which is not compatible with the technology of forming micron and submicron contacts and for this reason leads to the formation of an extended contact, the extended fields l _p ≈3-10 μm, the caps of which, firstly, form a parasitic MIS capacitance (MIS - metal-insulator-semiconductor) C _mis , and, secondly, do not allow to shorten the distance Δx _R between the anode and cathode contacts, which largely determines the series resistance R _s ~R _s (Δx _R ) of a planar diode design.

As a prototype, a method for manufacturing a planar diode with a whisker and an anode terminal in the form of an air bridge, manufactured by the Mesa-Substrate method [2], is considered. The prototype under consideration is devoid of the above disadvantages inherent in the known method [1], since its design and manufacturing method practically exclude the possibility of an expanded contact and the occurrence of parasitic capacitance C _mis . In addition, the prototype manufacturing method allows creating air terminals of various thickness d _br , width W _br and length l _br to anode contacts of micron and submicron sizes, and also allows you to significantly reduce the distance Δx _R between the barrier (anode) and ohmic (cathode) contacts. This method of manufacturing planar diodes is characterized by the fact that the connection of the anode with its contact pad lying on the substrate in a parallel plane located below the plane of the mesa surface is carried out by means of an air bridge hanging over the surfaces of both levels through the Whisker. The whisker is a metal sharp truncated cone, the smaller base of which is connected to the barrier contact, and the opposite wide base is connected to the end of the air bridge hanging over it. The diameter of the smaller base is usually commensurate with the diameter of the barrier contact, which prevents the formation of protruding edges - fields, and prevents the formation of an expanded contact cap and prevents the appearance of parasitic capacitance C _mis , and also allows to reduce the distance Δx _R between the anode and cathode contacts and significantly reduce the series resistance R _s ~R _s (Δx _R ) of a planar diode design "Mesa-substrate".

A method for manufacturing a diode with a "Mesa-Substrate" whisker, which includes applying a dielectric film 0.1-0.5 μm thick to the surface of a heteroepitaxial structure, in which a U-shaped cathode contact window is created by chemical or physical etching to a highly doped cathode layer along the photoresist mask, forming in it metallization of a low-resistance ohmic cathode contact with subsequent removal of the resist, annealing and galvanic thickening, formation of an anode contact window of micron or submicron diameter D between the U-protrusions of the cathode using thin resist masks on the surface of active layers, removal of a dielectric layer in the anode contact window, finishing chemical treatments, the formation of metallization of the anode contact, the removal of the resist, the formation of a metal whisker on the anode contact with a height h _W , which is an inverted truncated metal cone with a cross section connected to the anode contact, the formation of a dielectric mask for etching the mesa around the area with the anode and cathode located on it, etching mesa at least to a semi-insulating i-layer of a heteroepitaxial structure, forming anode and cathode contact pads on it from different sides of the mesa base, connecting the whisker to the anode contact pad with a metal air bridge with a thickness d _br , a width W _br and a length l _br , and a cathode with a cathode contact pad with a metal air bridge or a busbar lying on the surface with a thickness d _oc , a width W _oc and a length l _oc , galvanic thickening of the anode and cathode contact pads up to a thickness d _c , sticking the plate face down on a mechanical carrier, thinning the plate from the side of the semi-insulating substrate to approximately 50 µm, transmission lithography and etching into individual crystals, removal of the resist and peeling off the crystals from the mechanical carrier, washing.

The disadvantage of the prototype is that the anode and cathode, as well as their contact pads, are located in different planes with a sufficiently large (several microns) gap between them, which makes it difficult to match such a planar diode in a monolithic integrated circuit (MIS). This undesirable effect is greatly enhanced with an increase in the operating frequency to the millimeter frequency range and above. The same disadvantage is the reason for the impossibility to carry out "Flip chip" - installation of a planar diode upside down if it is necessary to use it in hybrid integrated circuits.

The aim of the invention is to eliminate these disadvantages. This goal is achieved due to the fact that in the known method of manufacturing a diode - the prototype, the anode and cathode, together with their contact pads, are located in the same plane. This manufacturing method allows the use of thinner layers of resists to form barrier contacts of micron and nanosizes, since the formation of mesa insulation is carried out after the formation of the whisker and the air outlet - the bridge. The proposed method combines the design, technological and functional advantages of planar diodes with an expanded contact and an anode air terminal made using the well-known Mesa-Mesa method, as well as the advantages of a prototype made using another well-known Mesa-Substrate technology with a whisker and an anode air outlet. These advantages provide easier matching of the diode in the microwave path, the formation of reliable leads to micron and nano-contacts, reduce parasitic parameters, and also allow flip-chip mounting of a planar diode with a whisker and an anode air lead upside down.

The technical result is achieved by the fact that in the well-known method of manufacturing a prototype diode, which includes applying a dielectric film to the surface of a heteroepitaxial structure, in which U-shaped ohmic contact windows - the cathode - are created along the resist mask by chemical or physical etching at least to a highly doped cathode layer, and a rectangular window coaxially with it for forming an anode contact pad in the same plane, simultaneous formation in both windows by explosive lithography, or by electrochemical methods of metallization of low-resistance ohmic contacts with subsequent annealing and their galvanic thickening, formation using thin (<<1 μm) resistive masks of a micron or submicron rectifying barrier contact - anode, diameter D between the U-protrusions of the cathode _; , length l _br , width W _br and height h _W and connecting the whisker with the anode contact pad is carried out before the mesa insulation is etched, and the mesa insulation is etched at least to the semi-insulating i-layer using a dielectric mask under the already formed air bridge. Then the galvanic thickening of the anode and cathode pads is carried out to the thickness d _c . At the end of the technological process, the plate is glued face down onto a mechanical carrier and thinned from the side of the semi-insulating substrate to 50 µm. After transmission lithography, etching into individual crystals, the crystals are peeled off from the mechanical carrier and washed.

On FIG. 1 shows the main key points of a possible variant of the proposed method for manufacturing a planar diode with a whisker using the Mesa-Mesa technology, which eliminates the disadvantages of the prototype

On FIG. 1a) shows a diagram of the cross-section A-A of an epitaxial semiconductor nn ⁺ -structure containing a semi-insulating i-layer substrate with a buffer layer 1 located on it with an epitaxial highly doped cathode n ⁺ -layer 2, a barrier n-layer 3, a protective layer of dielectric SiO ₂ or SiN _x 4, photoresist mask 5, windows in the resist for the formation of cathode 6 and anode 7 pads, metallization of ohmic contacts (OC) 8.

On FIG. 1b) shows a cross-sectional diagram A-A of an epitaxial n- n ⁺ - structure with a formed metallization 8 of the ohmic contact of the cathode and the same metallization 8 of the anode contact pad with galvanic thickenings of the cathode 9 and anode 10 contact pads.

On FIG. 1c) shows a cross-sectional diagram of the A-A heterostructure after the formation of the metallization of the Schottky rectifying barrier contact (anode) 11 located at a distance Δx _R from the galvanic thickening of the cathode metallization 9, the window 12 in the dielectric mask SiO ₂ or SiN _x determining the lateral (in the plane (x ,y)) the dimensions of the mesa (shown by the dotted line) with the length Δx _M .

On FIG. 1d) shows a cross-sectional diagram of the A-A heterostructure after the formation of a rectifying contact of the whisker 13 with a height h _W above the metallization, the formation of an air bridge 14 with a thickness d _br , a length l _br and a width W _br and a protrusion l _p connecting the upper expanded free end of the whisker 13 with the metallization anode contact pad 10 and simultaneous similar thickening 14-1 of the metallization of the cathode contact pad 9, etching under the mesa air bridge with a depth of h _M along in the window 12 of the dielectric mask at least to a semi-insulating i-layer 1, galvanic thickening of the anode 15 and cathode 16 contact pads up to given thickness d _c .

On FIG. 1e) shows a diagram of a top view of a planar diode with an anode terminal in the form of an air bridge with a whisker in accordance with the Mesa-Mesa manufacturing method.

Example. Planar Schottky diodes with whiskers were fabricated using the "Mesa-Mesa" method (Fig. 2) based on semiconductor epitaxial nn ⁺ InP structures on a semi-insulating i-GaAs {100} substrate, the main manufacturing steps of which are shown in Fig. 1.

For the manufacture of planar Schottky diodes using the "Mesa-Mesa" technology with an anode terminal in the form of an air bridge with a whisker, an epitaxial structure was used, which is a semi-insulating substrate of gallium arsenide i-GaAs {001} 450 μm thick (Fig. 1, a, 1) with grown on it by MOS-hydride epitaxy with a contact n ⁺ -InP layer with a thickness of at least 5 μm (Fig. 1, a, 2) and a barrier n-InP layer of indium phosphide with a thickness of 0.2 μm (Fig. 1, a, 3). The electron concentration in the n ⁺ -InP layer was 2×10 ¹⁸ cm ^-3 , and in the n-InP layer - 6×10 ¹⁶ cm ^-3 .

According to the "Mesa-Mesa" method, the technological route for manufacturing Schottky diodes with an anode terminal in the form of an air bridge with a whisker included the following set of technological operations: deposition of a SiO ₂ dielectric film on the surface of the n-InP barrier layer (Fig. 1, a, 3) thickness d=0.2 μm (Fig. 1, a, 4), the formation of a resist mask on the SiO ₂ film (Fig. 1, a, 5) with a window that determines the location of the cathode contact (Fig. 1, a, 6), which differs in that that simultaneously with the window (Fig. 1, a, 6) another window was formed in the resist mask, which determines the location of the anode contact pad (Fig. 1, a, 7), in which the resist mask was chemically etched at least up to the highly alloyed cathode layer n ⁺ -InP, a U-shaped cathode contact window and a rectangular anode contact area were simultaneously created, the formation of metallizations of low-resistance ohmic contacts based on an AuGeNi alloy 0.15 µm thick and Au 0.3 µm thick by explosive lithography (Fig. 1, a, 8) with subsequent annealing in a hydrogen atmosphere at a temperature of 400°C and galvanic thickening of the cathode with gold 0.5 µm thick (Fig. 1, 6, 9) and the anode contact pad (Fig. 1, 6, 10), the formation of an anode Schottky contact with a diameter of D=2 μm to the n-InP barrier layer in the window of the dielectric mask between the U-protrusions of the cathode at a distance of Δx _R =5 µm by electrochemical deposition of palladium 0.1 µm thick Pd and 0.2 µm thick Au metallization (Fig. 1, c, 11), formation of windows around the contact pads in the dielectric mask to form mesoinsulation (Fig. 1, c, 12), formation on the anode contact whisker (Fig. 1, d, 13) with a height h _W =2 μm, the formation of an electrical connection of the free expanded end of the whisker with the anode contact pad with a gold air bridge 3 μm thick, l _br =150 μm long and W _br =21 μm wide (Fig. 1, c, 14) with a simultaneous thickening of the cathode contact pad (Fig. 1, c, 14-1), characterized in that the formation of meso-insulation by chemical etching of the mesa to a depth of h _M = 6 μm on a SiO ₂ dielectric mask was carried out under air bridge (Fig. 1, d, 14). After that, the galvanic thickening of the anode (Fig. 1, d, 15) and cathode (Fig. 1, d, 16) pads was carried out by d _c =3 μm, the plate was glued face down on the mechanical carrier, and its thinning from the side of the semi-insulating substrate to 50 µm, transmission lithography and etching into individual crystals, removal of the resist and peeling off the crystals from the mechanical carrier, washing.

Thus, the goal was achieved and, as a result, planar InP/GaAs Schottky diodes with whiskers and anode leads in the form of air bridges were obtained, made using the Mesa-Mesa technology (Fig. 2).

The advantage of the proposed method for manufacturing a diode with an anode terminal in the form of an air bridge with a whisker to the anode contact according to the Mesa-Mesa method is that the anode and cathode contact pads are located in the same plane as the anode contact. This manufacturing method allows the use of thinner layers of resists to form barrier contacts of micron and nanosizes, since the formation of mesa insulation is carried out after the formation of the whisker and air outlet. The proposed method combines the design, technological and functional advantages of planar diodes with an extended contact and an anode air lead made using the well-known Mesa-Mesa method [1] and the advantages of a prototype made using another well-known Mesa-Substrate technology with whisker and anode air outlet [2]. These advantages provide easier matching of the diode in the microwave path, the formation of reliable leads to micron and nano-contacts, reduce parasitic parameters, and also allow flip-chip mounting of a planar diode with a whisker and an anode air lead upside down.

Information sources:

[1]. B. Thomas, P. Landry, A. Maestrini, G. Beaudin. HBV DIODE MULTIPLIER DEVELOPMENTS FOR THZ APPLICATIONS. https://hal.archives-ouvertes.fr/tel-00392239/file/Annexe_D_These_HBV_report.pdf

[2]. Torkhov H.A. A method for manufacturing a diode with a terahertz whisker. Patent No. 2635853 dated November 16, 2017, application No. 2016102531 dated January 26, 2016

Claims (1)

A method for manufacturing a planar diode with an anode whisker and an air output using the Mesa-Mesa technology, which includes applying a heteroepitaxial nn ⁺ - or p-p ⁺ -structure of a dielectric film to the surface of an n- or p-layer, in which the resist mask is chemically or physically by etching at least to a highly alloyed cathode n ⁺ - or p ⁺ -layer, a cathode contact window of a given shape is created and at a certain distance from it in the same plane another window of a given shape is created to form an anode contact pad, simultaneous formation in both windows by explosive lithography or methods of electrochemistry of metallization of low-resistance ohmic contacts with subsequent annealing, the formation of an anode contact of a micron or submicron size, the formation of a dielectric mask for mesa etching, characterized in that the formation of a whisker and an air bridge of a given thickness, length, width and height on the anode contact is carried out before etching the mesa insulation, and the etching of the mesa insulation is carried out under the formed air bridge connecting the whisker with the anode pad.

Images