JPH021137A - Metallized contact for iii-v device - Google Patents

Abstract

PURPOSE: To reduce an area needed for contact by providing a direct short- circuit contact structure consisting of a composite metal layer and bringing a source or drain area and gate metal into ohmic contact with each other. CONSTITUTION: Direct metal contact is formed between the gate 22 and source 10 or/and drain 12 of an FFT. That is, the direct short-circuit contact is formed by an ohmic contactor 18' directly on the gate 22 and the ohmic contactor 18' and gate 22 are both patterned by etching or peeling under specific metallization and processing conditions. Consequently, a layout area is reduced and the gate and ohmic contactor for mutual contact metallization are used effectively to improve circuit density.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to ■-V devices, such as GaAs devices, and more particularly to improved contact metallization for such devices.

In many device applications, the source (or drain, or both) of a FET (field effect transistor)
is desired to be shorted to the gate.

Previous gate-to-source contact methods require a contact hole to be drilled in the first dielectric layer and an actual metal connection to be made between the source (or drain) and gate.

However, as the density of devices packaged on a single wafer increases, previous approaches have been found to inappropriately waste surface area. Therefore, there is a need to develop techniques to achieve the desired contact in a reduced area.

In accordance with the present invention, high density devices on a wafer are achieved by directly contacting the gate metal to the source (or drain) metal.

A direct shorting contact structure consisting of a composite metal layer is provided that provides ohmic contact between the source or drain region and the gate metal.

Direct contact between the source or train and the region gate metal reduces the additional area required for such contact and eliminates the need for another metal second layer required for such contact. .

The composite metal layer has good electrical conductivity, is thermally stable, and covers the entire top layer 171, the first layer being a gold-germanium layer that contacts the source or drain region and the gate metal. It consists of a second layer that resists movement.

Such composite layers avoid step coverage problems present with other metallization techniques.

The best explanation below is for gallium arsenide devices. However, the technique of the present invention can be applied to semiconductor devices of the ■-■ group.

Each element of the drawing is provided with a reference numeral.

A conventional shorting contact is shown in FIGS. 1 and 2. Here, each of the source and drain regions 10.12 is -
It is formed on the V substrate 14. A channel head 16 is connected to the source and drain regions 10.12. The source and drain regions 10.12 are, as is known, of one conductivity type, the opposite conductivity type, or formed in large areas of semi-insulating material.

Each of the source and drain regions 10.12 is in contact with each of the ohmic contacts 18.20. gate metal 22
forms a Schottky contact with the semiconductor substrate 14. Its gate 22 is located remote from the source and drain contacts 18.20.

For some device applications, it may be desirable to short the source 10 to the gate 22. As shown in FIGS. 1 and 2, another metal layer 24 interconnects the source contact 18 and gate 22. used to connect. This connection forms a suitable opening in the dielectric layer 26 and the gold rA layer 24.
This is done by routing the gate (metal) contact area 28 to the gate (metal) contact area 28.

Of course, the same approach is taken when shorting both the drain or source and the train to the gate 22.

As can be seen in FIGS. 1 and 2, the previous approach requires a large area to make contact between source 10 and gate 22. Additionally, other levels of metallization are required to form the interconnects. This defines an opening in the dielectric [26] prior to the deposition of the contact metal 24;
This means that an additional processing step of etching is required.

In accordance with the present invention, the required interconnections can be made without using large areas or requiring other levels of metal. In the present invention, direct shorting contacts are made.

The structure of the direct shorting contact is the gate 22 and source 1 of the FFT.
0 (or drain 12, or both).

It is particularly advantageous for, but not limited to, MES'FETs (metal-semiconductor FETs).

In that FET, both a gate 22 (to form a Schottky contact) and an ohmic contact 18°, 20 (to form an ohmic contact) are used.

As shown in FIGS. 3 and 4, a direct shorting contact is formed by superposing the ohmic contact 18' directly onto the gate 22. Both the ohmic contact 18° and the gate 22 can be patterned by etching or stripping under certain metallization and processing conditions. The direct shorting contacts of the present invention include an oxide spacer (indicated by diagonal lines 30) at the edge of the gate. can be produced with or without

Forming a direct shorting contact requires only a single change in the FET layout and does not require any other additional processing steps.

Therefore, direct shorting contacts substantially reduce layout area and improve circuit density by making better use of gate and ohmic contacts (metal) for interconnect metallization.

There are potential problems with the direct shorting contacts of the present invention which require the use of other contact metallizations.

As is well known, a typical conventional contact metallization consists of a first layer of gold-germanium alloy in contact with the semiconductor substrate, followed by a second layer of nickel overlying it, and a thick third layer of gold.

However, the inventive step contact would have poor step coverage or poor reliability if insufficient metallization was done, and furthermore, there would be large currents through the step; is an electric transfer (electnomiBr) if there is bad step coverage.
ation) will quickly lead to dire consequences.

These problems are solved by two layers: a first layer of gold-germanium alloy 18°a to form an ohmic contact;
and the use of a novel contact 18' consisting of a second layer 18°b of a thermally stable electromigration resistant gold layer with good electrical conductivity to prevent device failure. It is solved by doing.

The gold-germanium 18A is formed to a thickness of about 500-700mm. The thickness of this layer is selected to match the thickness of the source and drain connections to achieve the lowest contact resistance. This layer can be formed by any process known in the art.

Next, a second layer 18°b is deposited. Since Au-Ge is known to form balls and exhibit electrical transfer, the gold layer forming this layer must have properties that prevent this behavior. Examples of suitable gold layers that should be used include tungsten, tungsten nitride (WNX, where X ranges up to about 0.3), tungsten silicide (WSi, where X ranges up to about 2), ), other carbides (refracto
ry) There are metals, superhard metal silicides, and superhard metal nitrides. Examples of other such hard metals include molybdenum,
There is ditanium. Additionally, platinum, panidium and chromium are suitable for use as the second layer 18''b, as are their silicides and other known silicides.

Metal layers 18'a, 18[deg.]b are conveniently deposited by sputtering as nitrides or silicides formed in the presence of a nitrogen or silicon source. Alternatively, other materials may be deposited by vapor deposition.

Approximately 800-1,000 people [II
[] [7] Thickness 4: Attached. The minimum thickness of the 27118°b is determined by the relationship between allowable sheet resistance and step coverage. Its maximum thickness is determined by patterning performance. Thicker layers make patterning, either by etching or by life-oH, more difficult.

The direct shorting contact of the present invention is suitable for use with semiconductors, especially GaAs.
It can be used for devices.

Contacts are therefore provided to short the source and/or drain to the gate, avoiding complexity and saving space in the layout. Contact metallization techniques have also been demonstrated that produce good thread coverage, good morphology, and good ohmic contacts in GaAs.

It is obvious that various modifications and changes can be made without departing from the scope of the technical idea of the present invention, and such modifications and changes are included within the scope of the present invention as defined by the claims. .

Claims (1)

[Claims] [1] A reduced area contact for shorting at least one of the source or drain regions to a gate contact in a III-V semiconductor device, comprising: an ohmic metal contact; the source and drain regions; A contact comprising: a portion that makes contact with at least one of the gate contact; and a portion that makes direct contact with the gate contact. [2] The contact according to claim (1), wherein a first layer of a gold-germanium alloy contacts at least one of the source region or the drain region and the gate contact, and the first layer. A contact consisting of a composite contact with a second layer of metal formed throughout with good electrical conductivity, thermal stability and resistance to electromigration. [3] The contact according to claim (2), wherein the gold
A contact in which the germanium layer is formed to a thickness of about 500-700 Å. [4] The contactor according to claim (2), wherein the second
A contact in which the layers are formed to a thickness of about 800-1,000 Å. [5] The contact according to claim 2, wherein the second layer is a metal selected from the group consisting of platinum, palladium, and chromium, or a cemented carbide selected from the group consisting of tungsten, molybdenum, and titanium. , or their nitrides or silicides. [6] The contactor according to claim (5), wherein the second
A contact in which the layer consists of WN_X, where X ranges up to about 0.3. [7] The contactor according to claim (5), wherein the second
A contact in which the layer consists of WSi_X, where X ranges up to about 0.2. [8] In a III-V semiconductor device, a reduced area contact shorting at least one of the source or drain regions to a gate contact, the contact comprising an ohmic metal contact, the source region and the drain region. a gold-germanium alloy comprising a portion making contact with at least one of the regions and a portion making direct contact with the gate contact, the contact making contact between the gate contact and at least one of the source contact or the drain region; a first layer of
A contact comprising a second layer of tungsten or its nitride or silicide formed over the entire layer. 9. The contact of claim 8, wherein the gold-germanium alloy layer is formed to a thickness of about 500-700 Å. 10. The contact of claim 8, wherein the second layer is formed to a thickness of about 800-1,000 Å. (11) A composite ohmic contact for use in III-V semiconductor devices, which is made of a gold-germanium alloy and is formed on the first layer in contact with the semiconductor and the entire layer thereon, and has good electrical conductivity. , a contact consisting of a second layer of metal that is thermally stable and resistant to electromigration. 12. The contact of claim 11, wherein the gold-germanium layer is formed to a thickness of about 500-700 Å. (13) The contact of claim (11), wherein the second layer is formed to a thickness of about 800-1,000 Å.
However, the contact. (14) The contact according to claim (13), wherein the second layer is made of a metal selected from the group consisting of platinum, palladium, and chromium, a metal selected from the group consisting of tungsten, molybdenum, and titanium. Contacts made of hard metals, or their nitrides or silicides. 15. The contact of claim 14, wherein said second layer comprises WN_X, where X ranges up to about 0.3. 16. The contact of claim 14, wherein said second layer comprises WSi_X, where X ranges up to about 0.2. (17) A composite ohmic contact for use in a III-V semiconductor device, comprising a first layer in contact with the semiconductor made of a gold-germanium alloy, and a tungsten or A contact consisting of a second layer of nitride or silicide. 18. The contact of claim 17, wherein the gold-germanium layer is formed to a thickness of about 500-700 Å. (19) The contact of claim (17), wherein the second layer is formed to a thickness of about 800-1,000 Å.
However, the contact. (20) A method of forming a contact comprising an ohmic metal contact shorting one of the source or drain regions to a gate contact in a III-V semiconductor, the method comprising: contacting a first portion of a contact; and contacting the gate contact with a second portion of the contact, the contact contacting the first portion to reduce the area contact. and the second part are directly connected.