JPH04212447A - Compound semiconductor integrated circuit device and its manufacture - Google Patents

Abstract

PURPOSE:To increase the capacitance per unit area of a capacitor, and obstruct the gate current of a compound semiconductor field effect transistor. CONSTITUTION:An oxide film 7 formed by directly oxidizing a compound semiconductor substrate 1 is used as the dielectric film of a capacitor. Thereby a very thin dielectric film can be formed, as compared with the one formed by an ordinary CVD method, so that a capacitor having large capacitance can be realized. By using a GaAs oxide film formed by projecting a light in an oxygen atmosphere as a gate insulating film, the gate current is obstructed. Hence the surface level is lowered, and characteristics control of a transistor is enabled.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound semiconductor integrated circuit device in which a circuit including a capacitor or a compound semiconductor field effect transistor is integrated on a compound semiconductor substrate, and a method for manufacturing the same.

0002

[Background Art] In recent years, with the increase in the amount and sophistication of information,
Demand for higher speed, larger capacity semiconductor integrated circuits is increasing. Under these circumstances, gallium-arsenic (G
BACKGROUND ART Compound semiconductor devices mainly based on aAs) are being actively researched in various places as next-generation devices. FIG. 5 shows the structure of a capacitor conventionally used in this type of circuit device. This is because a dielectric film 4 is formed between the first and second metal electrodes 2 and 3 formed on a semi-insulating GaAs substrate 1.
MIM (Metal Ins
The first and second input/output terminals 5 and 6 are connected to the first and second metal electrodes 2 and 3, respectively, and the electric charge is transferred to the side of the dielectric film 4. is stored on the surfaces of two metal electrodes 2 and 3. Such a capacitor is formed as follows. That is, as shown in FIG. 6, a metal electrode 2 made of a material such as Au is formed on a GaAs substrate 1 by a metal vapor deposition method (
(a) in the same figure), then after forming a dielectric film 4 using a normal CVD method ((b) in the same figure), a method is adopted in which a metal electrode 3 is formed again using a metal vapor deposition method. (Same figure (c)
)).

On the other hand, as a transistor made of GaAs, MESFET (Metal Semi
MESFETs (conductor junction FETs) are almost at the practical stage, but since MESFETs have a Schottky junction between the gate and channel, the voltage Vgs (Vgd) between the gate and source (drain) is less than the clamp voltage (0
．． 7 to 0.8 V) or higher, a current flows between the gate and the channel. This creates constraints on the operation of logic circuits,
For example, a DCFL (Direct Coupled
FET Logic) has a logic amplitude of only about 0.5V, and therefore cannot secure a sufficient noise margin, resulting in a circuit with very little operating margin.

[0004] In order to overcome these difficulties, GaAs/A
MISFET (Meta
l Insulator Semiconductor
Development is underway to manufacture FETs. MISFET
In the case of AlGaAs heterojunction with channel semiconductor
A semi-insulating semiconductor made by et al. is used as a gate insulating film.
An example is shown in FIG. In the figure, a non-doped GaAs layer 32 deposited on a semi-insulating GaAs substrate 11 is used as a channel layer, and an MB layer is formed on this non-doped GaAs layer 32.
A non-doped AlGaAs layer 35 is deposited with lattice matching using a method such as E.
After forming the s-layer 16, a gate electrode 17, a drain electrode 18, and a source electrode 19 are formed respectively to form a MISFET.
is configured. Ohmic contact is obtained between the drain electrode 18 and the source electrode 19 by the n+ contact layer 13 into which impurities are implanted at a high concentration to lower the resistance. A two-dimensional electron gas layer 34 is directly below the i-AlGaAs layer 35.
is formed and a channel is generated.

FIG. 8 shows n which becomes the gate of the above MISFET.
The band structure when a positive voltage is applied to +-GaAs is shown. Here, a two-dimensional electron gas is induced at the heterojunction interface of the i-AlGaAs layer 35/i-GaAs layer 32 by the positive potential of the gate, a channel is formed, and a current flows. At this time, n+-GaAs layer 16/i-AlGaAs layer 35
Ionized donors are also induced at the interface. MISFE
In T, there is an i-AlGaAs layer 35 between the gate and the channel, so as shown in FIG.
acts as a barrier and blocks gate current.

[0006]

However, such conventional compound semiconductor field effect transistors have the following problems. In other words, since a semi-insulating semiconductor such as an i-AlGaAs layer is used as the gate insulating film, unlike a silicon MOS transistor, a voltage above a certain level (potential barrier built using a semi-insulating semiconductor) is used as the gate insulating film. Since a gate current flows at a voltage higher than that, the transistor does not exhibit the characteristics of a perfect MOS transistor. Furthermore, in order to form a heterojunction, a sophisticated epitaxial growth technique such as the above-mentioned MBE or MOCVD is required, making it unsuitable for mass production. On the other hand, in a conventional capacitor, since it is formed by the method shown in FIG. 6, the dielectric film is at least several tens of nanometers thick. As is well known, the capacitance of a capacitor is inversely proportional to the thickness of the dielectric film, so there is a problem in that if the dielectric film is thick, a capacitor with a large capacity cannot be obtained.

In view of the above points, the present invention has been made to solve these problems, and its purpose is to improve the integration of compound semiconductors by using a homogeneous oxide film with high dielectric strength as a dielectric film. The objective is to dramatically increase the capacitance per unit area of a capacitor integrated into a circuit device. Another object of the present invention is to completely block the gate current of a compound semiconductor field effect transistor by using a homogeneous oxide film with high dielectric strength as a gate insulating film, and to eliminate the need for advanced epitaxial growth technology. The first objective is to improve the mass productivity of compound semiconductor integrated circuit devices.

[0008]

A compound semiconductor integrated circuit device according to the present invention uses an oxide film of a compound semiconductor obtained by oxidizing the surface of a compound semiconductor substrate as a dielectric film of a capacitor. Further, in a method for manufacturing a compound semiconductor integrated circuit device according to another aspect of the present invention, when forming a capacitor, an oxide film of a compound semiconductor is formed by irradiating the surface of a compound semiconductor substrate with light in an oxygen atmosphere. It is something. Further, a compound semiconductor integrated circuit device according to still another aspect of the present invention includes an oxide film of the compound semiconductor formed by oxidizing the surface of the compound semiconductor substrate.
This was used as a gate insulating film for a compound semiconductor field effect transistor. Further, in a method for manufacturing a compound semiconductor integrated circuit device according to still another aspect of the present invention, in forming a gate insulating film of a field effect transistor,
A compound semiconductor oxide film is formed by irradiating the surface of a compound semiconductor substrate with light in an oxygen atmosphere.

[0009]

[Operation] In the present invention, CV
An extremely thin dielectric film can be obtained by using a film formed by oxidizing the surface of the compound semiconductor substrate itself, rather than a film newly deposited by the D method or the like. In this case, an oxide film as thin as 1 nm can be uniformly formed by exposure in an oxygen atmosphere. In addition, in another invention of the present invention, a GaAs oxide film formed by irradiating light in an oxygen atmosphere is used as the gate insulating film, so that gate current can be completely blocked, and even more advanced epitaxial growth can be achieved. Since no technology is required, a compound semiconductor field effect transistor with excellent mass productivity can be obtained.

0010

Embodiments Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is a sectional view of a capacitor showing one embodiment of the present invention. The same reference numerals as in FIG. 5 indicate the same or corresponding parts, but the capacitor of this embodiment uses an extremely thin GaAs oxide film 7 as a dielectric film, and the n-type GaAs region 8 and metal electrode 3 are connected to the GaAs oxide film 7. It has a structure sandwiching the . The GaAs oxide film 7 is formed on the GaAs substrate 1.
The surface of the GaAs region 8 itself is oxidized. Next, the manufacturing method will be explained using FIG. 2.

In FIG. 2, n is formed on the surface of the GaAs substrate 1.
An n-type GaAs region 8 is formed by implanting a type of impurity (FIG. 4(a)). Next, without using the CVD method, n
A part of the surface of the GaAs type region 8 is directly oxidized to form GaAs.
An s oxide film 7 is formed (FIG. 2(b)). As a result, C
A thinner capacitor dielectric film can be obtained than by using the VD method. In semiconductor devices using Si, a thermal oxidation method is normally used to form an oxide film. However, since the thermal oxidation method performs heat treatment in an oxygen atmosphere, in the case of GaAs, the As element peels off, resulting in poor quality of the formed film and making it impractical. On the other hand, in the method using light irradiation, Ga
Since the As substrate does not reach a high temperature, the As element does not dissociate, and a high quality GaAs oxide film can be obtained. For example, 4 in the June 1990 issue of "Science" published by Nikkei Science.
On page 5, it is reported that an extremely thin and homogeneous GaAs oxide film of 1 nm was obtained in high purity oxygen at 10 Torr. Specifically, in this example, n-type GaAs
After forming the region 8, a resist is applied to the entire surface of the GaAs substrate, and the resist in the region where the GaAs oxide film 7 is to be formed is removed. In this state, by irradiating the entire surface of the GaAs substrate with light in an oxygen atmosphere, a GaAs oxide film 7 is selectively formed only in the region where the GaAs surface is exposed. Thereafter, two metal electrodes 2 and 3 are formed using a metal vapor deposition method (FIG. 4(c)). Metal electrodes 2 and 3 are input/output terminals 5
, 6, and charges are stored on the side of the n-type GaAs region 8 and the metal electrode 3 that are in contact with the GaAs oxide film 7.

By using the GaAs oxide film obtained by directly oxidizing the surface of the GaAs substrate in this way, the film thickness can be easily controlled and is several tenths thinner than the conventional film using the CVD method. Capacitors with dielectric films can be formed. In addition, in the above-mentioned embodiment, a method of forming an oxide film by selective oxidation was explained, but if the atmosphere is GaA
A method may also be used in which an oxide film is formed by irradiating the entire surface of the s-substrate with light, and then unnecessary portions of the oxide film are selectively etched and removed.

FIG. 3 is a sectional view showing an embodiment in which the present invention is applied to a channel inversion type compound semiconductor field effect transistor. In FIG. 3, this field effect transistor has a p-type GaAs layer 12 formed by ion implantation on a semi-insulating GaAs substrate 11 as a channel layer, and this G
A gate oxide film 15 is formed on the aAs layer 12 using a GaAs oxide film formed by irradiating light in an oxygen atmosphere, and then a gate electrode 17, a drain electrode 18, and a source electrode 19 are formed respectively. Ru. At this time, ohmic contact is obtained between the drain electrode 18 and the source electrode 19 by the n+ contact layer 13 into which impurities are implanted at a high concentration to lower the resistance. Directly below the gate oxide film 15, a channel inversion layer 14 is formed by applying a positive voltage to the gate, creating a channel and allowing current to flow.

The gate oxide film in this example has a thickness of 10T.
A GaAs substrate is placed in a high-purity oxygen atmosphere of about
) to form. According to this method, an extremely homogeneous and stable ultra-thin oxide film can be obtained, so it is suitable as a gate oxide film. This point will be explained in detail below.

First, as a gate insulating film, the conventional i-A
Since an oxide film is used instead of a semi-insulating semiconductor such as a GaAs layer, insulation between the gate and channel can be maintained. Therefore, the gate current does not flow at Vgs above a certain level, and the gate current is blocked up to a voltage that destroys the gate oxide film, which has the same characteristics as a MOS transistor. In particular, G created by irradiating light in an oxygen atmosphere
By using the aAsxO(1-X) film, a homogeneous and stable insulating film can be obtained, so compared to insulating films created by other methods, the same thickness can withstand breakdown at higher voltages. can. Furthermore, since the oxide film can be formed without thermal oxidation, arsenic does not evaporate and the surface state can be kept low, making it possible to control the characteristics of the transistor. In addition, since there is no exposure to the atmosphere from the cleaning stage of the substrate surface before oxide film formation to the formation of the oxide film, the surface state does not change.
Also from this point of view, the characteristics of the transistor can be easily controlled.

FIG. 4 shows another embodiment in which the present invention is applied to a depletion type compound semiconductor field effect transistor. In FIG. 4, the compound semiconductor field effect transistor of FIG. 3 has a channel layer of n-type G
The aAs layer 22, the GaAs substrate 1 directly under the gate.
The difference is that a buried p layer 26 of p+ type GaAs is provided between the channel layer 22 and the channel layer 22. In this embodiment, the gate voltage controls the depletion layer 24 extending from the gate oxide film 15 to the channel layer 22, thereby controlling the current. Note that the buried p layer 26 has the effect of reducing the subthreshold current and suppressing the short channel effect.

In this embodiment as well, the gate current is blocked as in the embodiment of FIG. 3, and the surface state is kept low.
It becomes possible to control the characteristics of transistors. In the above embodiments, an n-channel type (electrons are electrically conductive carriers) has been described, but it goes without saying that the present invention can be applied to other conduction types as well.

[0018]

As described above, according to the present invention, by using an oxide film obtained by directly oxidizing a compound semiconductor substrate as a dielectric film, it is possible to realize a large capacitance capacitor in a compound semiconductor integrated circuit device. have In particular, by using a method of irradiating light in an oxygen atmosphere as an oxidation method, an extremely thin dielectric film can be formed compared to the case where a CVD method is used. According to another aspect of the present invention, since a GaAs oxide film formed by irradiating light in an oxygen atmosphere is used as the gate insulating film, gate current is blocked and the surface level can be kept low. This has the effect of making it possible to control the characteristics of the transistor.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a capacitor according to an embodiment of the invention.

FIG. 2 is a process cross-sectional view showing the manufacturing method of the embodiment of FIG. 1;

FIG. 3 is a cross-sectional view of a compound semiconductor field effect transistor according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a compound semiconductor field effect transistor according to yet another embodiment of the present invention.

FIG. 5 is a sectional view of a conventional capacitor.

6 is a process sectional view of the conventional example shown in FIG. 5. FIG.

FIG. 7 is a cross-sectional view of another conventional compound semiconductor field effect transistor.

FIG. 8 is a band structure diagram for explaining the operation of the transistor in FIG. 7;

[Explanation of symbols]

1 GaAs substrate 2 Metal electrode 3 Metal electrode 7 GaAs oxide film 8 N-type GaAs region 11 GaAs substrate 12 P-type GaAs channel layer 13 N+ contact layer 14 Channel inversion layer 15 Gate oxide film (GaAs oxide film) 17 Gate electrode 18 Drain electrode 19 Source electrode 22 N-type GaAs channel layer 24 Channel inversion layer

Claims (4)

[Claims] Claim 1: A first and a second semiconductor substrate are provided on a compound semiconductor substrate.
A compound semiconductor integrated circuit device that integrates a circuit having a capacitor made of a dielectric film sandwiched between conductor regions, which includes a capacitor whose dielectric film is an oxide film of a compound semiconductor formed by oxidizing the surface of a compound semiconductor substrate. A compound semiconductor integrated circuit device characterized by: 2. In a method for manufacturing a compound semiconductor integrated circuit device including a step of forming a capacitor on a compound semiconductor substrate, the step of forming the capacitor includes a step of forming a first conductor region and a step of forming the capacitor in an oxygen atmosphere. forming an oxide film of the compound semiconductor in contact with a first conductor region by irradiating the surface of the compound semiconductor with light; and forming a second oxide film in contact with the oxide film and away from the first conductor region. 1. A method for manufacturing a compound semiconductor integrated circuit device, the method comprising: forming a conductor region. 3. In a compound semiconductor integrated circuit device in which a compound semiconductor field effect transistor is integrated on a compound semiconductor substrate, the compound semiconductor field effect transistor includes a channel layer formed on the substrate and a surface of the channel layer that is oxidized. a gate oxide film formed using a GaAs oxide film, a gate electrode formed on the gate oxide film, and a drain electrode and a source electrode formed on the channel layer, respectively. Semiconductor integrated circuit device. 4. A method for manufacturing a compound semiconductor integrated circuit device including a step of forming a field effect transistor on a compound semiconductor substrate, wherein the step of forming the field effect transistor comprises a step of forming a channel layer on the substrate. a step of forming an oxide film of the compound semiconductor in contact with the channel layer by irradiating the surface of the compound semiconductor with light in an oxygen atmosphere; a step of forming a gate electrode on the oxide film; 1. A method for manufacturing a compound semiconductor integrated circuit device, comprising the step of forming an ohmic junction thereon to form a drain electrode and a source electrode.