JPH0766391A - Ohmic electrode - Google Patents

Abstract

PURPOSE:To prevent mutual diffusion between an electrode and a semiconductor layer, and form a stable electrode, by using high melting point metal as the electrode metal of an nonalloy ohmic electrode. CONSTITUTION:A source electrode 18 and a drain electrode 19 are formed on an N-type InGaAs cap layer 17. High melting point metal whose melting point is higher than or equal to 1200 deg.C is used for the ohmic electrodes 18, 19. A Schottky gate electrode 20 is formed in a recessed part wherein the part between the electrodes 18 and 19 is etched and eliminated until the middle part of an undoped InAlAs Schottky layer 16. As to the ohmic metals 18, 19, the interface lowermost layer metals are Mo 18a, 19a, on which Ti 18b, 19b, Pt 18c, 19c, and Au 18d, 19d are laminated in order. A device is formed by using the above multilayered structure. Thereby the heat treatment in the case of usual alloy ohmic is made unnecessary, and an ohmic electrode having excellent ohmic property can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-resistance ohmic electrode, which can be applied to a semiconductor device which operates at high speed in the microwave and millimeter wave wavelength regions.

[0002]

2. Description of the Related Art As an alloy type ohmic electrode,
It was produced by vapor-depositing a metal on the surface of a semiconductor and performing high-temperature heat treatment to make the contact between the metal and the semiconductor interface ohmic contact. The non-alloy ohmic electrode has a Schottky contact at the metal-semiconductor interface, but its Schottky barrier height is low, or the semiconductor layer forming the Schottky is small in thickness, so that it is electrically connected to the channel due to the tunnel effect and thermionic emission. Shows the obtained structure.
As a typical structure of this, for example, Japanese Journal of Applied Physics (Japane)
se Journal of Applied Phi
ss) 1988 Vol 27 No. 9 1718 Ni
Several studies have been published, including the paper by ttono et al. By providing a high-concentration layer of InGaAs on a GaAs substrate, the height of the Schottky barrier is kept small, and good ohmic characteristics are obtained. By adopting the non-alloy ohmic as described above, the heat treatment step of the ohmic electrode is omitted, and therefore, the field effect transistor can be manufactured without causing the deterioration of the gate electrode due to the heat treatment.

When a gate electrode is formed on a Schottky layer made of a semiconductor having a band gap larger than that of a cap layer and an electron affinity smaller than that of the cap layer, tunnel efficiency is improved. There is an example in which a second cap layer composed of a high In composition layer is provided on the substrate, and the ohmic electrode is formed on the first cap layer formed on the surface side of the semiconductor layer. An example in which such a structure is applied to an InAlAs / InGaAs HEMT on an InP substrate is, for example, IEE
E-Electron Device Letters, Volume 11,
No. 11, p. 502 (IEEE ELECTRON D
EVICE LETTERS, VOL. 11, NO. 1
1, P.I. 502) to Enoki et al. (T. Enokie e.
t al. ) Has been reported. Here, the first cap layer is an InGaAs layer, and the second cap layer is I
The nAlAs layer is used. In this report, AuGe / Ni is used in the non-alloy state as the electrode metal, and the contact resistance of the ohmic electrode is 0.14Ω.
-Mm is obtained. In such a structure, although the ohmic electrode is in Schottky contact with the cap layer, the barrier of the Schottky layer is thin, so that tunnel efficiency is improved, and an ohmic electrode having low source resistance and low drain resistance can be manufactured.

[0004]

The alloy type ohmic electrode represented by AuGe / Ni, which is generally used, lacks thermal stability, and the high temperature treatment causes mutual diffusion of metal and semiconductor, resulting in contact resistance. There was a problem such as deterioration. Although thermal stability is improved by using a metal such as W as the non-alloy ohmic electrode, further improvement in reliability is desired, and when these refractory metals are used for the electrode, workability is improved. There are many restrictions and problems in that the sputtering method must be used.

[0005]

[MEANS FOR SOLVING THE PROBLEMS] By using a refractory metal having excellent thermal stability and excellent workability as the non-alloy type ohmic electrode metal, the metal does not interdiffuse with the semiconductor even in the heat treatment. Maintaining stable contact enables highly reliable electrode formation.

According to the present invention, in the ohmic electrode in which the metal provided on the semiconductor substrate is in electrical contact with the active layer, the lowermost layer is a high melting point metal having a melting point of more than 1200 ° C. It is characterized in that it is composed of at least one or more layers. The refractory metal is Mo, Cr, P
t, Pd, Ni, Re, Os, Ta, Nb, Ir, R
It is characterized in that it is one of the elements u and Rh.

[0007]

By using the refractory metal as the electrode metal of the non-alloy ohmic electrode, stable electrode formation can be achieved without mutual diffusion with the semiconductor layer. Generally, refractory metals do not react well with semiconductor materials and are not suitable for alloy ohmic use, but when used as a non-alloy type ohmic electrode material, a thermally stable electrode can be obtained. In addition, each material such as Mo can be formed relatively easily by the electron gun vapor deposition method.

[0008]

EXAMPLE 1 An example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of a main part showing an example of a structure in which the ohmic electrode of the present invention is applied to a field effect transistor.

Non-doped I on the semi-insulating InP substrate 11
n _0. In _{5 2} Al _{0. 4 8} As layer 12 to a thickness of 800 nm, a non-doped _{Ni 0. 5 3 Ga 0.} 4 7 The As channel layer 13 with a thickness of 40 nm, undoped In _{0. 5 2} A
l _0. In _{4 8} As layers 14 of 3nm thickness, 2 × 10 ^{1 8}
cm _^-. In ₀ which is Si-doped n-type to a concentration of ³ ₅₂
In Al _{0. 4 8} As the thickness of 30nm electron supply layer 15,
_.. Non-doped In _{0 52} Al _{0 4 8} with As Shot key layer 16 of 20nm ^{thickness, 2 × 10 1 9 cm -} .. In 0 which is Si-doped n-type to a ^third concentration _{5 3} Ga _{0 4 7}
The As cap layer 17 was sequentially grown with a thickness of 30 nm.

A source electrode 18 and a drain electrode 19 are formed on the n-type InGaAs cap layer 17. The Schottky gate electrode 20 is formed between the ohmic electrodes 18 and 19 in the recess region which is removed by etching up to the middle of the non-doped InAlAs Schottky layer 16.

Mo (10 nm) in which the interface lowermost layer metal is Mo (molybdenum) as the ohmic metals 18 and 19
(18a, 19a) / Ti (50 nm) (18b, 19
b) / Pt (50 nm) (18c, 19c) / Au (1
(00 nm) (18d, 19d), a device was manufactured, and the ohmic electrode had good ohmic characteristics without heat treatment like normal alloy ohmic, and the contact resistance was 0.075Ω · mm. Was obtained.

A heat resistance test was conducted, and the results (open circles) are shown in FIG. 2. Almost no deterioration was observed in the Mo / Ti / Pt / Au structure even after annealing at 350 ° C. for 10 minutes. A contact resistance of 0.078 Ω · mm is obtained. Ti (50nm) / Pt (5
The results of the heat resistance test (dots with black circles) when a laminated structure of 0 nm) / Au (100 nm) is used are also shown.
Contact resistance is greatly deteriorated by heat treatment at 50 ° C,
A value of 0.2 Ω · mm or more is obtained. The above results indicate that the deterioration due to the heat treatment in Ti / Pt / Au ohmic is due to the mutual diffusion of the metal and the semiconductor, and the interdiffusion of Ti and the semiconductor is suppressed by sandwiching Mo, which is a refractory metal, at the interface. It is shown that.

The In composition of the InGaAs layer 17 used for the cap is set to 0.53 in this embodiment, but the present invention does not limit this In composition ratio to this value. The In composition ratio can be further increased as long as the strained layer does not cause misfit transition. Further, the In composition ratio in the cap InGaAs layer does not have to be uniform, and if at least one portion having a large In composition exists in the layer, the conduction band of the cap InGaAs layer has a uniform In composition of 53%. Since it is smaller than when set, the effect of reducing ohmic resistance can be confirmed. In this embodiment, Mo is used as the refractory metal, but this Mo contains Cr, Pt, Pd, Ni,
The same effect of the invention can be obtained even if it is replaced with another refractory metal such as Re, Os, Ta, Nb, Ir, Ru.

(Embodiment 2) FIG. 3 is a cross-sectional view of a main part showing another example of the structure of a semiconductor device to which the ohmic electrode of the present invention is applied.

Non-doped I on the semi-insulating InP substrate 31
n _0. In _{5 2} Al _{0. 4 8} As layer 32 a thickness of 800 nm, a non-doped _{In 0. 5 3 Ga 0.} 4 7 The As channel layer 33 with a thickness of 40 nm, undoped In _{0. 5 2} A
l _0. In _{4 8} As layers 34 of 3nm thickness, 2 × 10 ^{1 8}
cm _^-. In ₀ which is Si-doped n-type to a concentration of ³ _{5 2}
In Al _{0. 4 8} As the thickness of the electron supply layer 35 30 nm,
Doped _{In 0. 5 2 Al 0.} 4 8 As Shot key layer 36 with a thickness of ^{20nm, 5 × 10 1 8 cm} In 0 which is Si-doped n-type to a concentration of _{^-3. 5 2} Al _{0. 4 8}
The As cap layer 37 with a thickness of 30 nm is 5 × 10 ¹⁸
cm ⁻³ Concentration n-type Si-doped In _0.53 G
a _0. In _{4 7} As cap layer 38 of 10nm thickness were sequentially grown respectively.

A source electrode 39 and a drain electrode 40 are formed on the n-type InGaAs cap layer. A Schottky gate electrode 41 is formed between the ohmic electrodes 39 and 40, inside the recess region which is etched and removed halfway through the non-doped InAlAs Schottky layer 36.

Mo (10 nm) in which the interface lowermost layer metal is Mo (molybdenum) as the ohmic metals 39 and 40
(39a, 40a) / Ti (50 nm) (39b, 40
b) / Pt (50 nm) (39c, 40c) / Au (1
(00 nm) (39d, 40d), a device was manufactured, and the ohmic electrode had good ohmic characteristics without heat treatment like normal alloy ohmic, and the contact resistance was 0.45Ω · mm. Was obtained.

A heat resistance test was conducted, and the result (open circles) is shown in FIG. 4. The Mo / Ti / Pt / Au structure showed almost no deterioration even after annealing at 350 ° C. for 10 minutes. A resistance of 0.048 Ω · mm is obtained. Ti (50nm) / Pt (50
nm) / Au (100 nm) laminated structure is also used, the result of the heat resistance test (dots in black) is also shown.
Contact resistance is greatly deteriorated by heat treatment at 0 ° C,
A value of 0.1 Ω · mm or more is obtained. The above results indicate that the deterioration due to the heat treatment in Ti / Pt / Au ohmic is due to the mutual diffusion of the metal and the semiconductor, and the interdiffusion of Ti and the semiconductor is suppressed by sandwiching Mo, which is a refractory metal, at the interface. It is shown that.

The In composition of the InGaAs layer 38 used for the cap is set to 0.53 in this embodiment, but the present invention does not limit this In composition ratio to this value. The In composition ratio can be further increased as long as the strained layer does not cause misfit transition. Further, the In composition ratio in the cap InGaAs layer does not have to be uniform, and if at least one portion having a large In composition exists in the layer, the conduction band of the cap InGaAs layer has a uniform In composition of 53%. Since it is smaller than when it is set, the effect of reducing ohmic resistance can be confirmed. In this embodiment, Mo is used as the refractory metal, but this Mo contains Cr, Pt, Pd, Ni,
The same effect can be obtained by substituting other refractory metals such as Re, Os, Ta, Nb, Ir and Ru.

[0021]

According to the present invention, an ohmic electrode having excellent reliability such as heat resistance can be obtained. It has been confirmed by experiments that the deterioration of contact resistance does not change up to at least 350 ° C. This reliability is due to the use of a refractory metal such as Mo at the interface between the semiconductor and the ohmic metal, and it is possible to obtain a highly reliable ohmic electrode with low resistance when used in combination with a semiconductor laminated structure suitable for non-alloy. It will be possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a semiconductor device of an embodiment to which the present invention is applied.

FIG. 2 is a diagram for explaining the effect of the present invention.

FIG. 3 is a diagram showing a structure of a semiconductor device of another embodiment to which the present invention is applied.

FIG. 4 is a diagram for explaining the effect of the present invention.

[Explanation of symbols]

11 InP substrate 12 doped _{In 0. 5 2 Al 0.} 4 7 As layer 13 doped _{In 0. 5 3 Ga 0.} 4 7 As layer 14 doped _{In 0. 5 2 Al 0.} 4 7 As layer 15 Si doped In _{0 . 5 2 Al 0. 4 7} As layer 16 doped _{In 0. 5 2 Al 0.} 4 7 As layer 17 Si doped _{In 0. 5 3 Ga 0.} 4 7 As layer 18 source electrode 18a source electrode (molybdenum) 18b source Electrode (titanium) 18c Source electrode (platinum) 18d Source electrode (gold) 19 Drain electrode 19a Drain electrode (molybdenum) 19b Drain electrode (titanium) 19c Drain electrode (platinum) 19d Drain electrode (gold) 20 Gate electrode 31 InP substrate 32 doped _{In 0. 5 2 Al 0.} 4 7 As layer 33 doped _{In 0. 5 3 Ga 0.} 4 7 As layer 34 doped _{In 0. 5 2 Al 0.} 4 7 As layer 35 Si doped _{In 0. 5 2 Al 0.} 4 7 As layer 36 doped _{In 0. 5 2 Al 0.} 4 7 As layer 37 Si doped _{In 0. 5 3 Al 0.} 4 7 As layers 38 SI-doped In _{0. 5 3 Ga 0. 4} 7 As layer 39 source electrode 39a source electrode (molybdenum) 39 b a source electrode (titanium) 39c source electrode (platinum) 39d source electrode (gold) 40 source electrode 40a drain electrode (molybdenum) 40b drain electrode (Titanium) 40c Drain electrode (platinum) 40d Drain electrode (gold) 41 Gate electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 29/43

Claims (2)

[Claims] 1. In an ohmic electrode in which a metal provided on a semiconductor substrate is in electrical contact with an active layer, the ohmic electrode metal is a refractory metal having a melting point of 1200 ° C. or higher as a lowermost layer. An ohmic electrode having a laminated structure of at least one layer. 2. The refractory metal is Mo, Cr, Pt, P.
d, Ni, Re, Os, Ta, Nb, Ir, Ru, Rh
The ohmic electrode according to claim 1, wherein the ohmic electrode is any one or a plurality of the metals.