JPH07283422A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To achieve a Schottky diode with a high-frequency high-breakdown voltage by forming a microelectrode precisely on an element with a step, at the same time improving the adhesion property of metal wiring for it, and achieving wire bonding for a device, and reducing element capacity. CONSTITUTION:A impurity concentration n-type GaAs layer 12 and an n-type GaAs layer 13 are formed on GaAs substrate 11, a Schottky electrode 17 is formed on the GaAs layer 13, at the same time an ohmic electrode 14 is formed on the GaAs layer 12, where the step generated by forming the GaAs layers 12 and 13 is flattened by a polyimide layer 16 and then the Schottky electrode 17 is formed. Also, a metal wiring 18 is formed on the GaAs substrate 11 and the polyimide layer 16 and wire bonding is performed at a part where the metal wiring 18 is formed on the GaAs substrate 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a Schottky diode and its manufacturing method.

[0002]

2. Description of the Related Art In recent years, the development of a technique for transmitting energy by microwaves has been advanced, and it has been attempted to use this technique for supplying power to an autonomous traveling inspection module in a circular metal pipe. Here, when the diameter of the pipe is 10 mm, the frequency of the microwave that can be stably propagated in the pipe is 21 GHz, and it is necessary to convert into a high DC voltage in order to drive the actuator of the module using this microwave. is there.

It has been considered to use a planar Schottky barrier diode as a rectifying element for converting a microwave into a direct current. However, there is no planar Schottky diode that has both high breakdown voltage and high frequency operation. This is because, when the breakdown voltage of the planar Schottky diode is increased, a large step is generated on the semiconductor surface, and this step causes a problem.

For example, when manufacturing such a planar Schottky diode, a photolithography process is used. In this process, the exposure intensity does not match above and below the step, the development degree is different, and the size of the resist opening is different. It will be different, ie the problem of loss of resolution will occur. This means that when a microelectrode is formed on the top of a high step with a high-frequency Schottky diode, it is difficult to form it due to the loss of resolution in the photolithography process described above. This is the reason why it is difficult to develop a high frequency and high breakdown voltage Schottky diode.

There is also known a method of flattening a step over the entire sample by using an insulating organic film. However, the insulating organic film has a coefficient of thermal expansion larger than that of a semiconductor, that is, an inorganic material by one digit, and there is a concern that the wafer may warp when formed on the entire surface of the wafer. In addition, the insulating organic film generally has poor adhesion to the semiconductor and the metal film, and when the insulating organic film is formed on the entire surface of the wafer and the metal wiring is formed thereon, Moreover, due to poor adhesion, peeling from the semiconductor layer and peeling of the metal film formed thereon are likely to occur. Further, the metal wiring is generally bonded to the mounting portion by ultrasonic wire bonding, but with the metal wiring formed on the insulating organic film, ultrasonic waves escape to the insulating organic film, which makes wire bonding difficult. Become. Particularly in the case of a flat type high breakdown voltage diode, the step is large, and as a result, the film thickness of the insulating organic film for flattening becomes large, and wire bonding becomes more difficult.

As another technique, a method of using glass as a flattening material is disclosed in JP-A-58-18943. Although this method does not cause the problems peculiar to the organic insulating film described above, this method cannot be used for a high frequency semiconductor device. The reason is that the semiconductor material and glass are heated to 900 ° C. or higher. The semiconductor material flattened by this heating is limited to one having a melting point sufficiently higher than the softening point of glass. G that can be used for high frequency devices
Since a compound semiconductor having a high mobility such as aAs, InAs, InP has a melting point of 900 ° C. or lower, planarization using glass cannot be used. 400 for GaAs
At a temperature of ℃ or more, As of the sublimable substance begins to come off and destroys the crystallinity, which is dangerous. Further, even silicon or the like having a relatively high melting point is not suitable for a device that requires a sharp change in impurity concentration due to diffusion of impurities in a semiconductor layer due to heat.

If no flattening is performed,
Since the problem of photolithography described above occurs, it is difficult to form a fine electrode on the top of the step, and further, an electric capacitance is generated between the n-type semiconductor layer and the high impurity concentration n-type semiconductor layer and the metal wiring. The capacitance has a great adverse effect on the efficiency and cutoff frequency of the high frequency device.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. It is possible to solve the problem of photolithography and form fine electrodes on the top of a step with good accuracy, and to improve the adhesion of metal wiring. It is an object of the present invention to provide a semiconductor device having a Schottky diode and a method of manufacturing the same, which enables wire bonding to a device.

[0009]

In order to achieve the above-mentioned object, in the invention according to claim 1, a first semiconductor layer and an impurity concentration lower than that of the first semiconductor layer are formed on a semiconductor substrate. A second semiconductor layer, and a Schottky electrode for forming a Schottky diode with the second semiconductor layer on the second semiconductor layer, and
In a semiconductor device in which an ohmic electrode is formed on the first semiconductor layer and a compound semiconductor is used as these semiconductors, the first and second semiconductor layers are formed except for the Schottky electrode and the ohmic electrode. An insulating film formed to cover the insulating film, an insulating layer formed on the insulating film to flatten a step formed by the first and second semiconductor layers with respect to the semiconductor substrate, the semiconductor substrate and the insulating film And a metal wiring connected to the Schottky electrode and the ohmic electrode via a layer.

The invention described in claim 2 is characterized in that, in contrast to the invention described in claim 1, the insulating layer is formed of an insulating organic film. In the invention described in claim 3, in contrast to the invention described in claim 2, the insulating organic film is made of polyimide. Further, in the invention according to claim 4, there is provided a method of manufacturing a semiconductor device using a compound semiconductor as a semiconductor material, wherein a first semiconductor layer is formed on a predetermined portion of a semiconductor substrate, and the first semiconductor layer is formed. Partially forming a second semiconductor layer having an impurity concentration lower than that of the first semiconductor layer, and forming an ohmic electrode on the first semiconductor layer. The first to the semiconductor substrate,
A step of forming an insulating film on the surface of the step formed by the second semiconductor layer, and an insulating layer formed on the entire surface of the semiconductor substrate on which the insulating film is formed, and the surface is flattened to the top of the step on which the insulating film is formed. And a step of removing the insulating film on the top of the step and forming a Schottky electrode in that portion, and a step of removing the insulating layer and the insulating film on the semiconductor substrate and the ohmic electrode, And a step of forming a wiring connected to the Schottky electrode and the ohmic electrode via the insulating layer and the semiconductor substrate from which the insulating film is removed by the removing step and the insulating layer. There is.

[0011]

According to the present invention as set forth in claims 1 to 3, an insulating layer is provided for a step generated by the first and second semiconductor layers formed on the semiconductor substrate for forming the Schottky diode. Since it is formed and flattened, it is possible to accurately form a fine electrode on the top of such a high step, and the insulating layer is formed not on the entire surface of the semiconductor substrate but on the region where the element is formed. Since the metal wiring is formed on the semiconductor substrate and the insulating layer, by forming the metal wiring on the semiconductor substrate, the adhesion of the metal wiring is improved and the wire bonding can be performed in that portion. As a result, wire bonding to the device can be enabled.

Further, since the metal wiring is formed on the first and second semiconductor layers via the insulating film and the insulating layer for planarization, the electric capacitance generated between the semiconductor layer and the metal wiring is reduced. It is possible to realize a Schottky diode that achieves both high breakdown voltage and high frequency operation. According to the invention described in claim 4, there is an effect that the manufacture of the semiconductor device having the Schottky diode can be realized.

[0013]

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 and 2. The structure of the high frequency high breakdown voltage Schottky diode according to the present invention will be described with reference to FIG. C
Semi-insulating GaA doped with rO of about 1 × 10 ¹⁵ cm ^-3
On the s substrate 11 (semiconductor substrate), Si is 2.5 × 10 ¹⁸
High impurity concentration n-type GaAs layer 12 doped to about cm ^-3
An n-type GaAs layer 1 having a (first semiconductor layer) formed to a thickness of about 3 μm and doped with S at a concentration of about 1.5 × 10 ¹⁶ cm ⁻³ 1
3 (second semiconductor layer) is formed to a thickness of about 2.7 μm.

The GaAs layer 13 has a circular shape with an upper bottom having a diameter of about 22 μm and a lower bottom having a diameter of about 30 μm and a height of about 2.7 μm. On this GaAs layer 13, a Schottky electrode 17 in which Pt is stacked 20 nm on Ti 100 nm is formed, and Schottky contact is obtained between the GaAs layer 13 and the Schottky electrode 17. This Schottky electrode 17
Although a depletion layer spreads in the GaAs layer 13 when a reverse bias is applied to the GaAs layer 13, the GaAs layer 13 is formed with a height of about 2.7 μm so as to withstand a high reverse bias (for example, 25 V).

Au 150 nm / Ni 20 nm / Au-Ge 6 is formed on the GaAs layer 12 at a portion different from the GaAs layer 13.
An ohmic electrode 14 of 0 nm is formed. Ga
An insulating thin film 15 made of silicon nitride (or a silicon oxide film) is formed on the As layers 12 and 13 except the Schottky electrode 17 and the ohmic electrode 14. Furthermore, Au 1 μm is formed on the Schottky electrode 17 and the ohmic electrode 14.
The metal wiring 18 is formed. This metal wiring 1
Electric power is injected into the Schottky electrode 17 and the ohmic electrode 14 through 8. In addition to the insulating thin film 15, a polyimide insulating layer 16 which is an organic insulating film is formed between the metal wiring 18 and the GaAs layers 12 and 13.

The metal wiring 18 is formed on the GaAs substrate 11 except in the vicinity of the GaAs layers 12 and 13. As a result, the adhesion is improved as compared with the case where it is formed only on the insulating layer 16 of polyimide. . In addition, the metal wiring 18 is Ga
The presence of the portion formed on the As substrate 11 enables wire bonding to the metal wiring 18 at this portion. That is, wire bonding can be performed on the device. At the same time, GaAs
Since the polyimide insulating layer 16 is present in the vicinity of the layers 12 and 13, the metal wiring 18 and the GaAs layer 12 were a big problem when the metal wiring 18 was formed on the insulating thin film 15.
The capacitances between and 13 became negligibly small. With this structure, a Schottky diode that operates at a high frequency (21 GHz or higher) and has a high breakdown voltage (25 V or higher) was realized.

Next, the manufacturing method will be described with reference to FIG. Note that 21 to 27 in FIG. 2 are the same as those shown in 11 to 17 in FIG. CrO 1 x 10 ¹⁵ cm
^-3 on the GaAs substrate 21 doped with ^-3 to 2.5x Si
A high impurity concentration n-type GaAs layer 22 doped to about 10 ¹⁸ cm ^{-3 is} epitaxially grown to a thickness of about 3 μm, and S is doped thereon to a concentration of about 1.5 × 10 ¹⁶ cm ^-3 to a high impurity concentration n-type G.
The aAs layer 23 is epitaxially grown to about 2.7 μm,
The structure of FIG. 2A was formed.

A resist film having a diameter of 30 μm is formed on this, and it is immersed in an etching solution of H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 4: 1: 90 (volume ratio) for 50 minutes to form an n-type GaAs layer. Two
A portion other than the desired portion of 3 was removed to form the shape of FIG. A resist film is formed on this shape, and etching is performed for 55 minutes as in the case of FIG.
Other than the desired portion of the above was removed, and the ohmic electrode 24 was further formed on the GaAs layer 22 to form the structure of FIG.

In order to form the step shape in FIGS. 2B and 2C, the resist film is formed by using the photolithography technique. Further, in the step of forming the first semiconductor layer and the second semiconductor layer described in the claims, after forming the n-type GaAs layers 22 and 23 in FIG. 2A, they are removed. Figure 2
2B and 2C are applicable, but GaAs
After forming the n-type GaAs layer 22 on the substrate 21 and removing the predetermined portion, the n-type GaAs layer 23 is formed on the entire surface, and then the predetermined portion is left and removed. You may make it obtain the structure as shown in (c).

Next, the silicon nitride film 2 is formed by a plasma CVD apparatus.
5 is formed to a thickness of 250 nm, a polyimide solvent is applied on this, and the film is thermally cured at 200 to 350 ° C. to form a polyimide film 26.
Is formed to flatten the step generated in the semiconductor layer, as shown in FIG.
Formed the shape of. O ₂ flow rate 2000 sccm, gas pressure 2 Torr, microwave power 400 W, substrate temperature 200 °
C is ashing back to expose the top of the step, and FIG. 2 (e)
Formed the shape of. The top of the step may be exposed by etching back instead of ashing back.

A resist film 29 having an opening with a diameter of 2 μm was formed on the top of the step. Since the high step formed by the n-type semiconductor layer and the high-impurity-concentration n-type semiconductor layer is flattened, such a minute shape can be accurately formed. HF: NH ₄ F: H ₂ O = 1: 10: 1
2 (f) was obtained by immersing in 1 (volume ratio) for 6 minutes to perform etching to form an opening in the silicon nitride film 25.

With the resist film 29 as it is, H ₂ SO
After dipping in ₄ : H ₂ O ₂ : H ₂ O = 4: 1: 90 (volume ratio) for 10 seconds and performing light etching, Ti100 nm / Pt20
nm is vacuum-deposited, soaked in acetone and lifted off to remove the Schottky electrode 27 as shown in FIG. 2 (g).
Was formed. This has been a problem in the past.
The microelectrode could be formed on the top of the step formed by the n-type semiconductor layer and the high-concentration n-type semiconductor layer. A resist film was formed on a desired portion of the semiconductor layer in the vicinity of the semiconductor layer where it should be left, and the resist film was etched with a polyimide-dedicated etching solution to obtain the shape shown in FIG. A metal wiring Au having a thickness of 1 μm was formed thereon by a lift-off method, and a high frequency and high breakdown voltage Schottky diode could be manufactured as shown in FIG.

Although the semiconductor device using GaAs has been described in the above embodiments, it may be applied to compound semiconductors such as InAs and InP.

[Brief description of drawings]

FIG. 1 is a sectional view of a Schottky diode showing an embodiment of the present invention.

FIGS. 2A to 2H are manufacturing process diagrams showing a method of manufacturing the Schottky diode shown in FIG.

[Explanation of symbols]

 11 GaAs substrate 12 n-type GaAs layer with high impurity concentration 13 n-type GaAs layer 14 ohmic electrode 15 silicon nitride film 16 polyimide layer 17 Schottky electrode 18 metal wiring

Claims (4)

[Claims] 1. A first semiconductor layer and a second semiconductor layer having an impurity concentration lower than that of the first semiconductor layer are formed on a semiconductor substrate, and the second semiconductor layer is formed on the second semiconductor layer. A Schottky electrode for forming a Schottky diode with a semiconductor layer is formed, an ohmic electrode is formed on the first semiconductor layer, and a semiconductor device using a compound semiconductor as these semiconductors is used. An insulating film formed to cover the first and second semiconductor layers except the key electrode and the ohmic electrode, and the first and second semiconductors formed on the insulating film with respect to the semiconductor substrate. A semiconducting device, comprising: an insulating layer for flattening a step formed by a layer; and a metal wiring connected to the Schottky electrode and the ohmic electrode via the semiconductor substrate and the insulating layer. Body device. 2. The semiconductor device according to claim 1, wherein the insulating layer is formed of an insulating organic film. 3. The semiconductor device according to claim 2, wherein the insulating organic film is polyimide. 4. A method of manufacturing a semiconductor device using a compound semiconductor as a semiconductor material, comprising forming a first semiconductor layer on a predetermined portion of a semiconductor substrate and lowering an impurity concentration lower than that of the first semiconductor layer. Partially forming a second semiconductor layer having a layer on the first semiconductor layer; forming an ohmic electrode on the first semiconductor layer; 1. A step of forming an insulating film on the surface of the step formed by the second semiconductor layer, and an insulating layer is formed on the entire surface of the semiconductor substrate on which the insulating film is formed, and the surface is extended to the top of the step where the insulating film is formed. A step of flattening, a step of removing the insulating film on the top of the step and forming a Schottky electrode thereover, a step of removing the insulating layer and the insulating film on the semiconductor substrate and the ohmic electrode And this excluding A step of forming a wiring connected to the Schottky electrode and the ohmic electrode through the insulating layer and the semiconductor substrate from which the insulating film has been removed by the step and the insulating layer. Device manufacturing method.