JP3353764B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device with improved high-frequency characteristics in a high-power GaAs MESFET for wireless communication.

[0002]

2. Description of the Related Art High-power GaAs MESFET for wireless communication
In many cases, a structure called a recess is provided between a drain electrode and a source electrode, and a gate electrode is provided in the recess. And this GaAs
In order to increase the output of the MESFET, it is necessary to improve the breakdown voltage. For that purpose, it is effective to provide a field plate between the gate and the drain.

Hereinafter, a conventional semiconductor device (GaAs MES) will be described.
FET) and its manufacturing method will be described with reference to the drawings. 6A to 6C are cross-sectional views in the order of steps showing a conventional method for manufacturing a semiconductor device. FIG. 7 is a sectional view (D) showing a conventional method of manufacturing a semiconductor device in the order of steps,
(E) and (F). A desired resist pattern is formed on the GaAs operation layer 412 formed on the GaAs substrate 411 by photolithography, and wet etching is performed to form a wide recess 412a between the source region SS and the drain region DD. Is formed (FIG. 6A).

A SiN film 413 is formed on the entire upper surface of the substrate formed as shown in FIG. 6A by plasma CVD or the like (FIG. 6B). The thus formed SiN film 41
3, a resist pattern having an opening for forming a gate electrode in a portion where a gate is to be formed in a region of a wide recess 412a is formed, and a SiN film 413 is formed from the opening. Then, a reactive dry etching is performed to form a dry etching opening 415a (FIG. 6C).

After forming as shown in FIG. 6C, the photoresist 415 is removed, a WSi film 417 is formed on the entire upper surface by sputtering, and the formed WSi film 417 is formed.
Au film 418 by plating or sputtering
(FIG. 7D).

A portion where a gate is to be formed is covered with a photoresist 419 on a substrate formed as shown in FIG. 7D by means of a stepper or the like, and ion milling is performed using the photoresist 419 as a mask. Alternatively, the WSi film 417 and the Au film 418 other than the portion where the gate electrode is formed are removed by reactive dry etching (FIG. 7E).

After the formation as shown in FIG. 7E, the photoresist 419 left on the gate electrode forming portion is removed.
A source electrode S and a drain electrode D are formed in the source region SS and the drain region DD, respectively (FIG. 7).
(F)). Through these steps, a semiconductor device 40 as shown in FIG. 8 is completed.

[0008]

In a semiconductor device 40 formed as shown in FIG. 8, a GaAs substrate 41 is formed.
1 and a contact layer 41 appropriately formed to obtain an ohmic contact on the GaAs operation layer 412 formed on the GaAs operation layer 412.
A source electrode S and a drain electrode D are formed on 2s and 412d, respectively, and a gate electrode G is formed in the center of the wide recess 412a.

In the region where the gate electrode G is formed,
On the drain electrode side, a metal layer (WSi film 417) acting as a field plate 417a for improving withstand voltage and the like.
And the Au film 418) overhangs the surface protective film 413 toward the drain electrode. However, since an alignment margin is required in a process using a stepper or the like, a certain amount of overhang portion 417b is also formed on the source electrode side. Will occur. The overhanging portion 417b has a problem that the capacitance between the gate and the source is increased and the high-frequency characteristics are deteriorated.

The present invention has been made in view of the above-mentioned conventional problems, and a desired field plate for improving withstand voltage and the like is formed on the drain electrode side.
On the source electrode side, an object is to provide a semiconductor device and a method for manufacturing the same, in which a protruding portion that increases the capacitance between the gate and the source is eliminated and high-frequency characteristics are improved.

[0011]

That is, a semiconductor device according to the present invention can achieve the above object by having the following features. 1: forming a recess region between a source region and a drain region of a GaAs operation layer formed on a GaAs substrate; forming a surface protection film on the entire upper surface of the GaAs substrate; A step of forming an insulating film on the protective film, a step of forming a photoresist on the insulating film, forming a pattern for forming a gate electrode on the photoresist, and forming a first pattern by reactive dry etching. The step of forming an opening, the step of covering the upper surface and the side surface of the first opening with a photoresist on the source region side, and adjusting the dimensions so as to form a desired field plate on the drain region side By performing a process of covering with photoresist and wet etching,
Forming a second opening by removing a part of the insulating film in a portion following the first opening to the drain region side, removing a photoresist, and forming a metal layer;
For the metal layer, a step of covering a portion where a gate electrode is to be formed with a photoresist, a step of removing the metal layer in a portion excluding a portion where the gate electrode is formed, and a step of forming a gate electrode; A step of removing the remaining photoresist, a step of removing all insulating films on the surface protective film by etching, and a step of forming a source electrode and a drain electrode through a contact layer appropriately formed to obtain ohmic contact. The above object can be attained by having a step of forming by (claim 1).

The above object can be achieved by the method for manufacturing a semiconductor device according to the present invention having the following features. 2: The wet etching is wet etching using buffered hydrofluoric acid (claim 2). 3: In the step of removing all the insulating films on the surface protective film by etching, wet etching with buffered hydrofluoric acid or vapor phase etching with hydrofluoric acid vapor is used. 4: The surface protection film is a SiN film (Claim 4). 5: The insulating film is a SiO ₂ film. 6: The insulating film is a photosensitive organic film (claim 6). 7: The photosensitive organic film is a polyimide (claim 7). 8: The metal layer is formed of a two-layer film composed of a WSi film and an Au film. 9: After the WSi film is sputtered, an Au film is formed by plating or sputtering (claim 9).

(Operation) According to the configuration of the semiconductor device,
On the drain side of the gate portion, there is an overhanging portion of the gate portion serving as a field plate on the surface protection film, which effectively acts for improving withstand voltage and the like. Since there is no overhang, no unnecessary gate-source capacitance is generated and the high-frequency characteristics are not deteriorated. Further, according to the above manufacturing method, at the time of forming the metal layer serving as the gate electrode, the insulating film prevents the metal layer from being formed on the surface protection film on the source electrode side of the opening for forming the gate electrode. On the drain electrode side of the opening, a field plate is formed because a part of the insulating film following the opening is removed and a metal layer is formed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a structure of a semiconductor device according to one embodiment of the present invention. FIG.
4A to 4C are cross-sectional views in the order of steps showing a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG.
4A to 4F are cross-sectional views (D), (E), and (F) in a process order showing a method for manufacturing a semiconductor device according to an embodiment of the present invention.
4A to 4H are sectional views (G) and (H) illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps. FIG.
7 is a graph showing high frequency characteristics of the present invention and a conventional example.

In the semiconductor device 10 shown in FIG.
A GaAs operation layer 112 is formed on the substrate 111, and a wide recess 112a (see FIG. 2A) is formed at the center thereof. On the GaAs operation layer 112 on both sides of the wide recess 112a, contact layers 112s and 112d for obtaining ohmic contact as in the related art are formed.
And a source electrode S and a drain electrode D thereon, respectively.
Are formed. On the contact layers 112s and 112D not covered with the source electrode S and the drain electrode D, and on the GaAs operation layer 112 on which the WSi film for the gate electrode is not directly formed, a surface protective film is formed. 113 (for example, a SiN film) is formed.

In the central portion of the wide recess 112a, a WSi film is formed on the GaAs operation layer 112,
By forming an Au film thereon, the WSi film 11 is formed.
The gate electrode G is formed of a two-layer metal layer including the gate electrode 7 and the Au film 118. In this case, on the source electrode side, the WSi film 117 rises perpendicular to the surface protection film 113 and along the side wall of the gate electrode, and on the drain electrode side, the WSi film 117 is formed of the Au film 118 and the surface protection film. 113, and extends horizontally over the surface protection film 113 by a predetermined distance.
3 and rises vertically along the side wall of the gate electrode.

As is apparent from such a structure, the semiconductor device 10 is a MES type field effect transistor (F
ET), where the gate electrode G on the opening of the surface protection film 113 overlaps the surface protection film 113 and projects horizontally by a predetermined distance, forms a field plate 117a to improve the breakdown voltage. And it is effective for gate lag control. On the other hand, on the source electrode side of the opening, the gate electrode G does not protrude horizontally above the surface protective film 113, so that unnecessary increase in capacitance does not occur and good high-frequency characteristics and high output characteristics are obtained. Can be obtained.

Next, a manufacturing process of the semiconductor device 10 will be described with reference to FIGS. A desired resist pattern is formed on the GaAs operation layer 112 formed on the GaAs substrate 111 by photolithography, and a wide recess 112a is formed between the source region SS and the drain region DD by performing wet etching. Is formed (FIG. 2A).

An SiN film 113 is formed on the entire upper surface of the substrate formed as shown in FIG. 2A by plasma CVD or the like, and an SN film 113 is formed thereon by thermal CVD or plasma CVD.
An iO ₂ film 114 is formed (FIG. 2B).

By forming a photoresist 115 on the SiO ₂ film 114 thus formed, a pattern for forming a gate is formed in a portion where a gate is to be formed in a region of a wide recess 112a, and a reactive By performing dry etching or the like, the dry etching opening 115a is formed.
Is formed (FIG. 2C).

On the source region side of the substrate formed as shown in FIG. 2C, the top surface and the side surface of the opening (first opening) 115a formed by dry etching are covered with a photoresist 116, and on the drain region side, It is covered with a photoresist 116 whose dimensions are adjusted so that a desired field plate is formed.

Further, by performing wet etching with buffered hydrofluoric acid or vapor phase etching with hydrofluoric acid vapor, a portion of SiO ₂ from the opening (first opening) 115 a by dry etching to the drain region side is formed.
A part of the film 114 is removed to form an opening (second opening) 116a by wet etching (FIG. 3).
(D)). In this case, the Si under the SiO ₂ film 114
Since the N film 113 has a low etch rate due to, for example, buffered hydrofluoric acid, it remains without being etched like the SiO ₂ film 114.

After being formed as shown in FIG. 3D, the photoresist 116 is removed and the WSi film 117 is formed on the entire upper surface.
Is formed by sputtering, and an Au film 118 is formed on the WSi film 117 by plating or sputtering (FIG. 3E).

After the formation as shown in FIG. 3E, the portion where the gate is to be formed is covered with a photoresist 119, and the WSi film 117 and the portion excluding the gate formation portion are removed by ion milling or reactive dry etching. Au
The film 118 is removed, and the remaining WSi film 117 and Au film 11 are removed.
A gate electrode G made of two metal layers 8 is formed (FIG. 3F).

As shown in FIG. 3F, after removing the photoresist 119 remaining on the gate electrode G, the entire SiO ₂ film 114 on the SiN film 113 is removed by etching (FIG. 3F). 4 (G)).

As the etching method used in the above case, the above-described wet etching with buffered hydrofluoric acid or the vapor phase etching with hydrofluoric acid vapor is used. Thus, only the SiO ₂ film 114 can be selectively removed. Source region SS and drain region D
In D, ohmic electrodes serving as a source electrode S and a drain electrode D are respectively formed with contact layers 112s and 11 appropriately formed in order to obtain ohmic contact as in the related art.
It is formed via 2d (FIG. 4H). Thereafter, an upper wiring layer and the like (not shown) necessary for the semiconductor device are formed, and the semiconductor device is completed.

In the above-described manufacturing process, in the step of forming the SiN film 113 and the SiO ₂ film 114 after the formation of the recess (FIG. 2B), a photosensitive organic film such as polyimide is used instead of the SiO ₂ film. Is also good. In this case,
Damage to the WSi film 117 that occurs when removing SiO ₂ with buffered hydrofluoric acid (FIG. 4G) can be suppressed.

As described above, the semiconductor device 10 of FIG. 1 formed by including the steps shown in FIGS.
The gate electrode G overlaps the surface protection film 113 and extends horizontally to form a field plate 117a, which is effective for improving the breakdown voltage and suppressing the gate lag. On the other hand, on the source electrode side, the gate electrode G has the surface protection film. Since it does not protrude horizontally above 113, an unnecessary increase in capacitance does not occur, and good high-frequency characteristics and high output characteristics can be obtained.

FIG. 5 shows an example of improved characteristics of the semiconductor device 10 formed as described above. The high frequency characteristics of the semiconductor device 10 of FIG. 1 according to the present invention and a conventional semiconductor device are compared. It is a graph which shows a result. In FIG. 5, the vertical axis indicates the current gain, the horizontal axis indicates the frequency, and the intersection with the horizontal axis of the graph indicates the current gain cutoff frequency (f
T). From this graph, it can be confirmed that the semiconductor device 10 of the present invention has a current gain cutoff frequency (fT) improved by about 10% as compared with the conventional semiconductor device, and has a good high frequency characteristic. .

[0030]

As described above in detail, the method of manufacturing a semiconductor device according to the present invention comprises the steps of: providing a GaAs active layer formed on a GaAs substrate between a source region and a drain region;
Forming a recess region, forming a surface protection film on the entire top surface of the GaAs substrate, forming an insulating film on the surface protection film, and forming a photoresist on the insulating film Forming a pattern for forming a gate electrode on the photoresist and forming a first opening by reactive dry etching; and forming a first opening on the source region side by photolithography. A step of covering with a resist, a step of covering with a photoresist whose dimensions are adjusted so that a desired field plate is formed on the drain region side, and a step of wet etching to continue from the first opening to the drain region side Removing a part of the insulating film to form a second opening, removing a photoresist, and forming a metal layer; Covering the portion of the metal layer where the gate electrode is to be formed with photoresist, removing the metal layer in the portion except for the portion where the gate electrode is to be formed, and forming a gate electrode; Removing the exposed photoresist, removing all insulating films on the surface protective film by etching, and forming a source electrode and a drain electrode through a contact layer appropriately formed to obtain ohmic contact. Forming a gate electrode on the surface protective film at the source electrode side during the formation of the gate electrode. In order to suppress the deterioration of the characteristics, a protruding part of the gate is formed on the drain electrode side, and this part works as a field plate. Sex is improved, and a high output characteristic, in which it is possible to manufacture a semiconductor device excellent high-frequency characteristics can be obtained.

[0031]

[Brief description of the drawings]

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

FIGS. 2A to 2C are cross-sectional views in the order of steps showing a method for manufacturing a semiconductor device according to an embodiment of the present invention; FIGS.

3A to 3F are cross-sectional views (D), (E), and (F) in a process order illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention.

4A to 4H are sectional views (G) and (H) illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps.

FIG. 5 is a graph showing high frequency characteristics of the present invention and a conventional example.

FIGS. 6A to 6C are cross-sectional views in the order of steps showing a conventional method for manufacturing a semiconductor device.

FIGS. 7A to 7F are cross-sectional views (D), (E), and (F) in the order of steps showing a conventional method for manufacturing a semiconductor device.

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

[Explanation of symbols]

Reference Signs List 10 semiconductor device 111 GaAs substrate 112 GaAs operation layer 112a recess 112s, 112d contact layer 113 SiN film (surface protective film) 114 SiO ₂ film (insulating film) 115, 116, 119 photoresist 115a opening by dry etching (first opening) 116a Opening by wet etching (second opening) 117a Field plate 117 WSi film 118 Au film G Gate electrode S Source electrode D Drain electrode

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/338 H01L 29/812

Claims (9)

(57) [Claims] 1. GaAs formed on a GaAs substrate
Forming a recess region between the source region and the drain region of the operation layer; forming a surface protection film on the entire upper surface of the GaAs substrate; forming an insulating film on the surface protection film A step of forming a photoresist on the insulating film; a step of forming a pattern for forming a gate electrode in the photoresist, and forming a first opening by reactive dry etching; Performing a step of covering the upper surface and side surfaces of the first opening with a photoresist, a step of covering a drain region side with a photoresist whose dimensions are adjusted so as to form a desired field plate, and performing wet etching. Forming a second opening by removing a portion of the insulating film from the first opening to the drain region side; Removing a metal layer; forming a metal layer; covering a portion of the metal layer where a gate electrode is to be formed with a photoresist; removing the portion of the metal layer other than the gate electrode formation portion; ,
Forming a gate electrode; removing a photoresist remaining on the gate electrode; removing all insulating films on the surface protective film by etching; Forming via a contact layer appropriately formed to obtain contact. Wherein said wet etch method of manufacturing a semiconductor device according to claim 1, characterized in that the wet etching using buffered hydrofluoric acid. 3. A process of removing by etching all of the insulating film on the surface protective film, wet etching using buffered hydrofluoric acid or, claims, characterized in that using a vapor phase etching by hydrofluoric acid vapor One more
3. The method for manufacturing a semiconductor device according to item 2 . 4. A method of manufacturing a semiconductor device according to claim 1, wherein the surface protective film is a SiN film. 5. A method of manufacturing a semiconductor device according to claim 1, wherein the insulating film is a SiO ₂ film. 6. The method for manufacturing a semiconductor device according to claim 1 , wherein said insulating film is a photosensitive organic film. 7. The method according to claim 6 , wherein the photosensitive organic film is polyimide. 8. claims 1 to 7, characterized in that said metal layer is formed with a film of two layers of a WSi film and an Au film
The method for manufacturing a semiconductor device according to any one of the above. 9. After sputtering the WSi film,
9. The method for manufacturing a semiconductor device according to claim 8 , wherein the Au film is formed by plating or sputtering.