JPH10261658A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the surface protection film of a semiconductor device for improving the reliability of an element. SOLUTION: The alloy protection film 107 of a coarse film quality is patterned on a semiconductor substrate 105 containing an epitaxial layer 104. Ohmic electrodes 101, 102, 112 and 113 are formed and an alloy treatment is executed. The interlayer-insulating film 108 of dense film quality is formed, after the alloy treatment and it is patterned. Then, the ohmic electrodes are exposed and a wiring treatment is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device including a field effect transistor FET, a resistance element and the like formed on a semiconductor substrate. In particular, the present invention relates to a method for forming a protective film of a field effect transistor FET using a compound semiconductor such as GaAs (gallium arsenide).

[0002]

2. Description of the Related Art Heretofore, a Schottky barrier gate field effect transistor (MESFET) has been formed with a simple structure using a Schottky junction formed by contact between a metal and a semiconductor as a gate electrode. A surface protection film is provided on the surface of such a semiconductor element in order to improve the reliability of the semiconductor element.

FIG. 8 is a cross-sectional view of a conventional GaAs compound semiconductor device described in Japanese Patent Application Laid-Open No. 5-335345. In the figure, a compound semiconductor device has a source electrode 1, a drain electrode 2, a gate electrode 3, an epitaxial layer 4, and a semi-insulating GaAs substrate 5, and this semiconductor element is formed by first and second SiN films 7, 8. The surface protection film prevents moisture from entering from outside the element and improves moisture resistance. Further, due to the good step coverage between the semiconductor element and the first SiN film directly adhered and the good adhesion between the first and second SiN films, the overall adhesion on the semiconductor element surface is improved. I was letting it.

[0004]

However, in the above-mentioned semiconductor device, an HEMT having an epitaxial layer 4 grown thereon and a source electrode 1, a drain electrode 2 and a gate electrode 3 formed on the surface thereof is prepared. After depositing the surface protective films 7 and 8 for protecting the substrate by a plasma CVD method and then performing a heat treatment for increasing the ohmic property between each electrode and the epitaxial layer, for example, the ohmic property is obtained by a heat treatment at 400 ° C. for one minute. In this case, as shown in the cross-sectional view of FIG. 9, since the surface protection films 7 and 8 of SiN are damaged by the heat treatment, as shown in the cross-sectional view of FIG. The surface protection films 7 and 8 are peeled off together with the bonding electrode pad portions 9 metal-wired on the surface protection films 7 and 8 to form peeled portions 10. There has been a drawback.

Further, as a result of the reduced adhesion between the damaged surface protective films 7 and 8 and the wiring electrode 6, the wiring electrode 6 peels off due to mechanical stress such as ultrasonic vibration or thermal cycling. There was also.

Further, in order to solve the above-mentioned problem, it is possible to remove the surface protection films 7 and 8 of the SiN film damaged by the thermal stress by a wet etching method and to form a new SiN film which is not subjected to the thermal stress. However, there has been a defect that the ohmic electrode peripheral portions 1 and 2 are abnormally etched, and undesired grooves are formed on the surface of the semiconductor element, thereby deteriorating the electrical characteristics of the MESFET and the resistor.

[0007]

According to a first aspect of the present invention, there is provided a method for solving the above-mentioned problems.
A method for manufacturing a semiconductor device, comprising: a semiconductor substrate; a semiconductor element formed on the surface of the semiconductor substrate; and first and second protective films provided on the surface of the semiconductor element and having different film qualities. Forming a first protective film on the surface and then etching the first protective film on the contact region of the semiconductor device; depositing and patterning an ohmic metal layer on the contact region; Forming a second protection film having a film quality denser than that of the first protection film on the first protection film, and then forming the second protection film on the ohmic metal layer. And removing the protective film by etching.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device having a semiconductor substrate, a semiconductor element formed on the surface of the semiconductor substrate, and a protective film provided on the surface of the semiconductor element. Forming a protective film on the contact region of the semiconductor device, etching the protective film on the contact region of the semiconductor device, depositing and patterning an ohmic metal layer on the contact region exposed by the etching, and contacting the ohmic metal layer with the ohmic metal layer. A step of alloying the region with heat treatment, a step of etching and removing the protective film, a step of forming a new protective film on the entire surface of the semiconductor substrate, and then etching and removing a new protective film on the contact region. And the step of performing

[0009]

In the present invention having the above structure, a first protective film is formed, the ohmic metal layer and the contact region are alloyed by heat treatment, and then a second protective film having a dense film quality is formed. Therefore, improvement in moisture resistance and adhesion between the protective film and the semiconductor substrate can be ensured.

Further, since a new protective film is formed after removing the protective film damaged by the heat treatment, the adhesion between the semiconductor substrate and the protective film is ensured.

[0011]

Preferred embodiments of the present invention will be described below with reference to the drawings. This semiconductor manufacturing method includes:
Although not particularly limited, a field effect transistor FET using a compound semiconductor such as GaAs (gallium arsenide)
And a protective film for the resistance element.

FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention. In the figure, a semiconductor device includes an n-type GaAs substrate 105 including an epitaxial layer 104 having a carrier density of 2 × 10 ¹⁷ cm ⁻³ and an alloy protective film 10.
7, has a multilayer structure of an interlayer insulating film 108 and a wiring electrode 106, and includes a field effect transistor (FET section) 100 and a resistor 110 formed on the epitaxial layer 104. Alloy ohmic electrodes 101, 102, and 11 in the FET section 100 formed on the epitaxial layer 104.
When the alloys 2 and 113 are alloyed, the epitaxial layer 10 is protected by an alloy protective film 107 for protecting the surface of the semiconductor substrate.
4 is protected. Since the interlayer insulating film 108 is formed on the alloy protective film 107, the step coverage with the wiring electrode 106 can be improved and the intrusion of contaminants from the outside can be prevented. And the epitaxial layer 104 can also be improved in adhesion.

FIG. 2 is a cross-sectional view of the substrate showing a starting step of the semiconductor device. n conductivity type, carrier density 2 × 10
^The GaAs substrate 105 including the ¹⁷ cm ^-3 epitaxial layer 104 is etched into a mesa shape through a photolithography process to isolate the FET unit 100 and the resistor 110 from each other.

FIG. 3 is a sectional view of a substrate on which an alloy protective film is patterned. An alloy protective film 107 such as an SiN film is deposited on the GaAs substrate 105 and the epitaxial layer 104 from which the elements have been separated by a plasma chemical vapor deposition PCVD method. As the SiN film, for example, a SiN film formed in a process in which the refractive index is 1.8 or less and the buffered HF rate is 2 nm or more per second can be used. The SiN film deposited in such a process can obtain a coarser and sparser film quality than the SiN film formed with a refractive index of 1.9 to 2.1 and a buffered HF rate of 1 nm per second in a normal SiN forming process. it can. The alloy protective film of this embodiment may be a protective film having a film quality capable of relieving thermal stress. In addition to the above-described forming method, the substrate temperature during the film forming process of the PCVD method may be lower than the normal SiN film forming temperature. 5
The temperature may be lowered from 0 ° C. to about 100 ° C., and a sparse film quality can be obtained in any case by using a technique such as increasing the film forming rate faster than usual. Next, the deposited alloy protective film 107 is subjected to photolithography and etching steps to form the FET portion 1.
After the contact region of the resistor 110 is opened, AuGe is deposited on the entire surface of the substrate by electron beam evaporation, although there is no particular limitation.
A metal layer having a / Ni / Au structure is deposited. The deposited metal layer is formed by ohmic electrodes 101, 102,
After the formation of the ohmic electrodes 101, 102, and 102, heat treatment is performed at a temperature of about 400 ° C. for 10 to 60 seconds in an atmosphere of an inert substance such as hydrogen H ₂ or nitrogen N ₂ . Alloy treatment for increasing the ohmic properties of the electrodes 112 and 113 can be performed.

FIG. 4 is a cross-sectional view of the substrate on which the interlayer insulating film 108 has been formed after the above alloy processing. Interlayer insulating film 10
Numeral 8 is formed on the alloy-treated ohmic electrode and the alloy protective film 107 by the PCVD method, and the film quality is formed so as to be denser than the alloy protective film 107. That is, since the alloy protective film 107 is formed more sparsely than a normal SiN film, an interlayer insulating film having a normal film quality with a refractive index of 1.9 to 2.1 and a buffered HF rate of 1 nm or less per second is used. However, the same effect can be obtained by using an interlayer insulating film having a higher density than usual.

FIG. 5 is a sectional view of a substrate in which openings 115 to 121 are formed in desired regions of the FET section 100 and the resistor 110. The interlayer insulating film 108 is patterned and subjected to a photolithography process and an etching process to form the ohmic electrodes 101, 102, 112, and 1 described above.
13 can be removed to form openings 115 to 121, and the opening 116
The gate electrode 103 of the portion 100 can be provided. More specifically, in order to obtain desired electrical characteristics of the FET, the exposed protective film for alloy 107 is patterned, recess-etched to the surface of the GaAs epitaxial layer 104 immediately below, and the gate electrode 103 is deposited. The gate electrode 103 is selectively formed in a desired region by a lift-off method.
Can be provided. Further, a wiring material such as T
The semiconductor device can be completed by depositing the metal layer 106 having the i / Pt / Au structure and patterning the wiring layer by a photolithography method, an etching method, and a lift-off method. FIG. 1 shows a cross section of the completed semiconductor device.

In the above embodiment, the step of removing the interlayer insulating film 108 on the ohmic electrodes 101 and 102 and the step of removing the interlayer insulating film 1 in the region where the gate electrode 103 is provided are described.
08 at the same time, but instead of this,
Interlayer insulating film 108 in a region where gate electrode 103 is provided
After the removal, the interlayer insulating film 108 on the ohmic electrodes 101 and 102 may be removed, or vice versa. As described above, when the step of removing the interlayer insulating film 108 is performed independently, the step of obtaining desired FET characteristics and the step of simply obtaining the interlayer insulating film 108 can be performed.
Can be separated from the step of removing, so that more accurate recess etching can be performed, and thus, an FET having excellent electrical characteristics can be obtained. In the above embodiment, a wiring layer patterning step such as a lift-off method is used. However, it is a matter of course that another wiring layer forming method such as an ashing method can be used. Furthermore, Si
As a method for forming an N film and a method for depositing an ohmic electrode, other known methods such as a molecular vapor deposition method can be applied.

In the above-described embodiment, a method of manufacturing a semiconductor device in which the alloy protective film 107 having a low film quality and the interlayer insulating film 108 having a higher film quality are formed has been described. As shown in FIG. Protective film for alloy 1 on a GaAs substrate 105 including an epitaxial layer 104 from which elements have been separated
After the formation of the layer 07 and the alloying treatment, the protective film 107 for the alloy can be removed. In the figure, a substrate is an FET in which an element is separated on an epitaxial layer 104.
A photoresist 125 is patterned so as to cover the region of the portion 100 and the resistor 110, and an alloy protective film 107 to which thermal stress has been applied during alloying remains on the lower side wall of the patterned photoresist 125. In the process of removing the alloy protective film 107, chemicals such as an etchant are used by the remaining photoresist 125 to remove ohmic electrodes 101, 102, 112, and 113 in the step of removing the alloy protective film 107.
Can be effectively prevented from touching the periphery of the
The peripheral portion such as the ohmic electrode 101 is not abnormally etched. Therefore, an undesired groove is not formed in the ohmic electrode portion, and the electric characteristics of the FET are not deteriorated.

After the alloy protective film 107 is removed from the substrate surface, a new SiN film surface protective film 123 is formed, and then the wiring electrode 10 is formed on the surface protective film 123.
By forming 6, the GaAs semiconductor device shown in FIG. 7 can be completed.

In the above embodiment, the step of removing the interlayer insulating film 108 on the ohmic electrodes 101 and 102 and the step of removing the interlayer insulating film 1 in the region where the gate electrode 103 is provided are described.
08 at the same time.
3 is removed, the interlayer insulating film 108 on the ohmic electrodes 101 and 102 is removed.
Even if 8 is removed, the same effect provided by the new protective film 123 can be obtained in the reverse case. Further, in the above embodiment, a wiring layer patterning step such as a lift-off method may be used, or another wiring layer forming method such as another ashing method may be used. As the electrode deposition method, other known methods such as a molecular deposition method can be applied.

The embodiment of the present invention has been described with reference to the method of manufacturing a compound semiconductor device such as GaAs.
The present invention is, of course, applicable to methods for manufacturing silicon semiconductor devices, heterojunction semiconductor devices, and semiconductor laser devices other than the GaAs compound semiconductor devices described above. In addition, the same effect as described above can be obtained with one or two or more surface protective films. Furthermore, although the embodiment of the present invention is directed to a substrate including an epitaxial layer, it goes without saying that a single crystal substrate can be used in addition to this.

[0022]

As described above, according to the method of manufacturing a semiconductor device of the present invention, the adhesion between the substrate and the surface protective film can be improved, and the peeling of the surface protective film by the ordinary assembly process can be effectively performed. Can be prevented.

Also, since a new surface protective film is formed,
Separation of metal wiring can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 3 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 7 is a cross-sectional view of the substrate according to the embodiment of the present invention.

FIG. 8 is a cross-sectional view of a conventional semiconductor device.

FIG. 9 is a cross-sectional view of a conventional semiconductor device.

FIG. 10 is a cross-sectional view of a conventional semiconductor device.

[Explanation of symbols]

100 FET part, 101, 102 Ohmic electrode,
103 gate electrode, 104 epitaxial layer, 10
5 semiconductor substrate, 107 protective film for alloy, 108 interlayer insulating film, 110 resistor, 123 new protective film.

Claims (2)

[Claims] 1. A method for manufacturing a semiconductor device comprising a semiconductor substrate, a semiconductor element formed on the surface of the semiconductor substrate, and first and second protective films provided on the surface of the semiconductor element and having different film properties from each other. Forming a first protective film on a surface of a semiconductor substrate, and then etching the first protective film on a contact region of the semiconductor device; and depositing an ohmic metal layer on the contact region. A step of patterning, a step of alloying the ohmic metal layer and the contact region by heat treatment, and a step of forming a second layer having a denser film quality than the first protective film.
Forming a protective film on the first protective film, and then etching and removing the second protective film on the ohmic metal layer. 2. A method for manufacturing a semiconductor device, comprising: a semiconductor substrate; a semiconductor element formed on the surface of the semiconductor substrate; and a protective film provided on the surface of the semiconductor element. After forming, etching the protective film on the contact region of the semiconductor element, depositing and patterning an ohmic metal layer on the contact region exposed by the etching, and forming the ohmic metal layer and the contact region. Forming a new protective film over the entire surface of the semiconductor substrate, and then etching a new protective film on the contact region. Removing the semiconductor device.