JP4758170B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device having a T-type gate electrode having a two-layer structure and a manufacturing method thereof.

For example, in a high-frequency semiconductor device, when heat treatment is performed after the formation of the gate electrode, the gate electrode material diffuses into the semiconductor substrate and the gate characteristics deteriorate. For this reason, deterioration of gate characteristics is prevented by using a gate electrode having a two-layer structure of a refractory metal layer (barrier layer) such as WSi and a low resistance metal layer such as Au.
The gate electrode having a two-layer structure is formed by sequentially depositing a refractory metal material layer and a low resistance metal material layer on a semiconductor substrate, and then performing unnecessary ion milling using an etching mask and an unnecessary refractory metal material layer and a low resistance metal material. The layer is removed and formed. Usually, the gate electrode is formed as a T-shaped gate electrode having a T-shaped cross section.

FIG. 4 is a cross-sectional view of a semiconductor device having a T-type gate formed by ion milling, the whole being represented by 500. The semiconductor device 500 includes the semiconductor substrate 1. A T-type gate electrode 2 having a two-layer structure of a refractory metal layer 21 such as WSi and a low resistance metal layer 22 such as Au is provided on the semiconductor substrate 1. A source electrode 3 and a drain electrode 4 are formed on the surface of the semiconductor substrate 1, and the surface is covered with a passivation film 5.
Japanese Patent Laid-Open No. 8-45962

  As shown in FIG. 4, in the semiconductor device 500, the end portion 23 of the refractory metal layer 21 protrudes at an acute angle in the umbrella portion of the T-type gate electrode 2. That is, in the vertical cross section of the T-type gate electrode 2 in the gate length direction, the inner angle of the end portion 23 of the refractory metal layer 21 is an acute angle. This is because, when the refractory metal layer 21 and the low resistance metal layer 22 are etched simultaneously by ion milling, the refractory metal layer 21 is etched slightly isotropically, so that the refractory metal that has been etched first is started. This is probably because the surface portion of the layer 21 is also etched in the lateral direction.

Thus, when an acute-angled protrusion is formed at the end 23 of the refractory metal layer 21, the passivation film 5 formed thereon becomes thin at the tip of the protrusion, and the protection performance of the passivation film 5. There was a problem of deterioration.
Moreover, as a result of performing a high temperature and high humidity test, it was confirmed that moisture permeates from the passivation film 5 in the vicinity of the protrusion and the refractory metal layer 21 is corroded.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor device having a two-layer T-type gate electrode, which has high moisture resistance and does not deteriorate protection performance, and a method for manufacturing the same.

  The present invention covers a semiconductor substrate, a T-type gate electrode provided on the semiconductor substrate, the umbrella portion of which includes a refractory metal layer and a low-resistance metal layer formed thereon, and covers the T-type gate electrode A semiconductor device including a passivation film, wherein an inner angle of the refractory metal layer is approximately 90 ° or more at an end portion of the umbrella portion.

  As is clear from the above description, in the semiconductor device according to the present invention, it is possible to obtain a highly reliable semiconductor device in which the passivation film has good moisture resistance.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of the semiconductor device according to the first embodiment, the whole being represented by 100. The semiconductor device 100 includes a semiconductor substrate 1 such as GaAs. The semiconductor substrate 1 has a recess structure in which a recess 11 is formed. A T-type gate electrode 2 having a two-layer structure of a refractory metal layer (barrier layer) 21 and a low resistance metal layer 22 is provided on the semiconductor substrate 1. As the refractory metal layer 21, WSi, WSiN, Ta, TaN or the like is used. As the low resistance metal layer 22, Au or the like is used.

  A source electrode 3 and a drain electrode 4 made of, for example, Au are formed on the surface of the semiconductor substrate 1. Finally, the surface of the semiconductor substrate 1 or the like is covered and protected by a passivation film 5 made of, for example, SiN or SiO. The thickness of the passivation film 5 is about 50 nm to about 1 μm.

  In the semiconductor device 100, the internal angle of the end portion 23 of the refractory metal layer 21 is substantially perpendicular in the vertical cross section including the gate length direction (direction parallel to the paper surface) of the T-type gate electrode 2.

  Here, the “inner angle” refers to an angle between a bottom surface and a side surface sandwiching the end portion 23 of the refractory metal layer 21 in a vertical cross section including the gate length direction of the T-type gate electrode 2. As will be described later, when the bottom surface or the side surface is curved outward, it refers to the angle formed by the bottom surface tangent and the side surface tangent at the end 23.

  The passivation film 5 that covers the gate electrode 2 and the like is formed by, for example, a plasma CVD method. Generally, the passivation film 5 is formed on a bent portion or a protruding portion, a lower portion of an umbrella portion of the gate electrode, or the like as compared with a flat portion. Hard to form. For this reason, when there is an acute-angled protrusion at the end 23 of the gate electrode 2 as in the conventional semiconductor device 500, the thickness of the passivation film 5 is reduced in the vicinity of the protrusion, or the composition of the film is chemical. There was a problem that the film quality deteriorated due to deviation from the stoichiometric composition.

  On the other hand, as in the semiconductor device 100, by setting the inner angle of the end portion 23 of the refractory metal layer 21 to a substantially right angle, the passivation film 5 formed thereon has a substantially uniform film thickness and a chemical thickness. It can be formed without much deviation from the stoichiometric composition.

  The moisture resistance of the semiconductor device 100 depends on the thickness and quality of the passivation film 5. The thicker the passivation film 5 is, the longer it takes for moisture to diffuse through the film and reach the semiconductor substrate 1 and the like, thereby improving the moisture resistance. In addition, a denser film with a closer stoichiometric composition has a slower moisture diffusion rate in the film and improves moisture resistance.

  As described above, in the semiconductor device 100 according to the first embodiment, since the end portion 23 has no protrusion, the film thickness and film quality of the passivation film 5 in the vicinity of the end portion 23 can be prevented from being deteriorated. As compared with the semiconductor device 100, the moisture resistance is improved and the highly reliable semiconductor device 100 can be obtained.

An accelerated test in a high temperature and high humidity state was performed on the conventional semiconductor device 500 and the semiconductor device 100 of the present invention. The experimental conditions were a temperature of 130 ° C., a humidity of 85% RH, and a holding time of 300 hours.
As a result of this test, in the conventional semiconductor device 500, moisture entered from the vicinity of the acute-angled end 23, and the entire refractory metal layer 21 of WSi was oxidized or hydroxylated by moisture to swell. Then, the semiconductor device 500 has malfunctioned.
On the other hand, in the semiconductor device 100, the refractory metal layer 21 did not change, and the performance degradation of the semiconductor device 100 was not recognized. This is presumably because the semiconductor device 100 has good moisture resistance without deterioration of film quality or reduction in film thickness even in the vicinity of the end 23.

  Next, a method for manufacturing the semiconductor device 100 will be described with reference to FIG. This manufacturing method includes the following steps 1 to 4.

  Step 1: As shown in FIG. 2A, a semiconductor substrate 1 such as GaAs is prepared. A source region and a drain region (not shown) are formed in the semiconductor substrate 1. Subsequently, the surface of the semiconductor substrate 1 is partially etched to produce a recess 11, and further a mask 12 is made of a silicon oxide film. A part of the semiconductor substrate 1 is etched using the mask 12.

  Step 2: As shown in FIG. 2B, a refractory metal material layer 21 'such as WSi is deposited by sputtering. Further, a low resistance metal material layer 22 'such as Au is deposited by sputtering and plating.

  Step 3: As shown in FIG. 2C, after forming a resist mask 24 with a photoresist, the refractory metal material layer 21 ′ and the low-resistance metal material layer 22 ′ are formed by dry etching using the resist mask 24. Are continuously etched in one step, and a T-type gate electrode 2 having a two-layer structure of a refractory metal layer (barrier layer) 21 and a low-resistance metal layer 22 is produced.

For dry etching, ECR plasma etching or reactive ion etching (RIE) is used. As the etching gas, a chlorine-based reactive gas such as Cl ₂ is used.
The variation in the incident angle of the etching ions 25 is preferably suppressed within 10 ° from the normal direction of the semiconductor substrate 1.

  When ECR plasma etching is used, it is preferable to provide a mesh-shaped converging grid between the ion generation source and the etching chamber to control the incident angle of the etching ions to the semiconductor substrate 1.

Step 4: As shown in FIG. 2D, after removing the resist mask 24 and the mask 12, the source electrode 3 and the drain electrode 4 made of, for example, Au are produced.
Finally, a passivation film 5 made of SiN or SiO is formed using, for example, a plasma CVD method so as to cover the surface of the semiconductor substrate 1 and the gate electrode 2.

  The semiconductor device 100 is completed through the above steps.

  In addition, as a manufacturing process of the semiconductor device 100, after the semiconductor device 500 is manufactured by the same manufacturing method as the conventional method, the protruding portion of the end portion 23 of the refractory metal layer 21 may be selectively removed.

  In such a manufacturing method, after performing the above-described Steps 1 and 2, in Step 3, the refractory metal material layer 21 ′ and the low-resistance metal material layer 22 ′ are etched by ion milling using Ar gas to obtain a high melting point. A T-type gate electrode 2 having a two-layer structure of a metal layer (barrier layer) 21 and a low resistance metal layer 22 is produced. At this time, a protrusion is formed on the end 23 of the refractory metal layer 21.

  Subsequently, a passivation film 5 is produced in step 4. As a result, a semiconductor device 500 as shown in FIG. 4 is obtained.

  Next, the passivation film 5 near the end 23 is selectively removed using hydrofluoric acid. As described above, since the thickness of the passivation film 5 is thin and the film quality is poor in the vicinity of the end 23, the portion of the passivation film 5 is selectively removed, and the refractory metal layer 21 is exposed.

  Subsequently, the exposed refractory metal layer 21 is selectively removed with hydrofluoric acid. In this case, the refractory metal layer 21 exposed by the battery action is selectively etched by immersing the entire semiconductor device in hydrofluoric acid. Thereby, the internal angle of the refractory metal layer 21 at the end 23 becomes approximately 90 ° or more.

  Further, this portion can be selectively etched with hydrofluoric acid by subjecting the exposed high melting point metal layer 21 to high temperature and high humidity treatment to oxidize or hydroxylate.

  In this step, after selectively removing the protrusions of the refractory metal layer 21, the semiconductor device 100 can be obtained by forming the passivation film 5 again by plasma CVD or the like.

Embodiment 2. FIG.
FIG. 3 is a cross-sectional view of the semiconductor device according to the second embodiment, the whole being represented by 200. 3, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  In the semiconductor device 200, the internal angle of the end portion 23 of the refractory metal layer 21 (the bottom surface of the refractory metal layer 21 at the end portion 23) in a vertical cross section including the gate length direction (direction parallel to the paper surface) of the T-type gate electrode 2. And the side surface) are obtuse angles (angles greater than 90 °).

  In this way, by making the inner angle of the end portion 23 of the refractory metal layer 21 an obtuse angle, the passivation film 5 formed thereon has a substantially uniform film thickness and is not substantially deviated from the stoichiometric composition. Can be formed. As a result, a highly reliable semiconductor device 200 with excellent moisture resistance can be provided.

  In such a semiconductor device 200, after the low resistance metal material layer 22 ′ is etched in the manufacturing process 3 (FIG. 2C) of the semiconductor device 100 described above, the etching ions 25 are inclined from the normal direction of the semiconductor substrate 1. And the refractory metal material layer 21 ′ can be formed by etching while rotating the semiconductor substrate 1.

  In FIG. 3, in the end portion 23, the bottom surface and the side surface constituting the inner angle are expressed as flat surfaces, but may be curved surfaces so as to project outward. That is, if the inner angle is 90 ° or more, the film thickness and film quality of the passivation film 5 at the end portion 23 can be prevented from being lowered. Therefore, the bottom surface and the side surface sandwiching the inner angle may be rounded curved surfaces.

It is sectional drawing of the semiconductor device concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the semiconductor device concerning Embodiment 1 of this invention. It is sectional drawing of the semiconductor device concerning Embodiment 2 of this invention. It is sectional drawing of the conventional semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 Gate electrode, 3 Source electrode, 4 Drain electrode, 5 Passivation film, 11 Recess, 12 Mask, 21 Refractory metal layer, 22 Low resistance metal layer, 23 End, 24 Resist mask, 25 Etching ion, 100 Semiconductor device.

Claims (2)

A method of manufacturing a semiconductor device having a T-type gate electrode,
Preparing a semiconductor substrate;
Sequentially depositing a refractory metal material layer and a low resistance metal material layer on the semiconductor substrate;
Forming a resist mask on the low-resistance metal material layer;
Using the resist mask as an etching mask, the low-resistance metal material layer and the refractory metal material layer are continuously etched, and a T having an umbrella portion having a laminated structure of the refractory metal layer and the low-resistance metal layer. An etching process for producing a mold gate electrode;
Forming a passivation film covering the T-type gate,
The etching step, Ri dry etching process der using reactive etching gas, after etching the low-resistance metal material layer, along with rotating the semiconductor substrate, a predetermined angle from the normal direction of the semiconductor substrate A method of manufacturing a semiconductor device, comprising: etching ions incident on the semiconductor substrate from an inclined direction to etch the refractory metal material layer . A method of manufacturing a semiconductor device having a T-type gate electrode,
Preparing a semiconductor substrate;
Sequentially depositing a refractory metal material layer and a low resistance metal material layer on the semiconductor substrate;
Forming a resist mask on the low-resistance metal material layer;
Using the resist mask as an etching mask, the low-resistance metal material layer and the refractory metal material layer are continuously etched by ion milling, and an umbrella portion having a laminated structure of the refractory metal layer and the low-resistance metal layer Producing a T-type gate electrode having :
A film forming step of forming a passivation film covering the T-type gate;
A step of selectively etching the passivation after the film forming step to expose an end portion of the refractory metal layer included in the umbrella portion of the T-type gate electrode;
The edge of the refractory metal layer is selectively etched so that the angle between the bottom surface and the side surface of the refractory metal layer sandwiching the edge of the refractory metal is 90 ° or more. Process,
And a step of forming a passivation film so as to cover an end portion of the refractory metal .

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