JPH0777223B2 - Method for forming protective film for stabilizing surface of compound semiconductor device - Google Patents

Description

The present invention relates to a method for forming a surface stabilizing protective film for a compound semiconductor device.

[Conventional technology]

Conventionally, indium phosphide (InP) and gallium arsenide (GaAs)
When forming a surface stabilizing protective film (hereinafter referred to as a passivation film) of an element using a P / N junction or a Schottky junction formed on a III-V group compound semiconductor plate, etc., the surface of the compound semiconductor substrate is forced. Not oxidize, or anodic oxidation method (eg H. Hasegawa et.al., JEC
S. 123 713 (1976)), oxygen plasma oxidation method (eg,
T.Sugano et.al., JECS 121 113 (1974)), photo-assisted oxidation method (eg T. Suzuki et.al., APL, 31 473).
(1977)), the surface of the substrate was forcibly oxidized to form a so-called CVD protective film (passivation film) such as a silicon oxide film or a silicon nitride film.

[Problems to be Solved by the Invention]

In the conventional passivation film formation method described above, the reproducibility and uniformity of the oxide composition of the compound semiconductor constituent elements on the surface of the compound semiconductor and its depth direction distribution are not good, or the oxide layer is once formed with good controllability. However, since a CVD protective film such as a plasma CVD (silicon) nitride film or a photo-assisted CVD nitride film is not continuously grown, ionic impurities such as sodium ion (Na ⁺ ) and copper ion (C
u ⁺ ), etc., is taken in, or the oxide layer is scraped or a composition change occurs during the subsequent cleaning step of the compound semiconductor substrate or CVD film formation, which causes reproducibility and It has the drawback of poor uniformity.

An object of the present invention is to provide a method for forming a surface stabilizing protective film for a compound semiconductor element, which solves the above problems.

[Differences from the Prior Art of the Invention]

The present invention is different from the above-described conventional method for forming a surface stabilizing protective film in that element characteristics are stabilized by steam oxidation in the same furnace before forming a passivation film.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides indium phosphide (In
P) or gallium arsenide (GaAs), etc. Surface stabilizing protective film of compound semiconductor element for forming surface stabilizing protective film of element using P / N junction or Schottky junction formed on III-V compound semiconductor plate In the forming method, the element surface of the compound semiconductor substrate is steam-oxidized in an atmosphere kept at a predetermined steam concentration, and continuously plasma CVD nitride film or silicon oxide film or photo-assisted CVD nitride film or silicon oxide is formed in the same furnace. A surface stabilizing protective film such as a film is formed.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

The present invention is applied to indium phosphide (InP) and gallium arsenide (GaA
In forming a passivation film of an element using a P / N junction or a Schottky junction formed on a III-V group compound semiconductor plate such as s), the element surface of the compound semiconductor substrate is steam-oxidized, and the same in the same furnace. Continuously, plasma CV
D (silicon) nitride film, silicon oxide film or optical assist C
A passivation film such as a VD (silicon) nitride film or a silicon oxide film is formed.

During steam oxidation, the element surface of the compound semiconductor substrate is kept at a constant temperature (50 ° C to 400 ° C) in an atmosphere of a predetermined steam concentration.
(C)) to form an oxide layer composed of the compound semiconductor constituent elements whose composition is controlled at a low temperature by oxidization under a low temperature. By forming a so-called CVD protective film (passivation film), so-called plasma damage due to exposure of the substrate surface to a plasma state is not induced, and introduction of ionic impurities and oxide transformation due to continuous growth are prevented. . Further, when heat-treating the compound semiconductor substrate in a water vapor atmosphere, the heat treatment is performed from a constant temperature side to a high temperature side (within a range from room temperature to 400 ° C. as an upper limit) at a predetermined heating rate to obtain a III-V group compound semiconductor. The formation of the oxide layer having a predetermined thickness is controlled while the evaporation of the group V element, which is a disadvantage, is covered and protected by the oxide layer formed of the compound semiconductor constituent element formed by the heat treatment on the low temperature side.

Next, examples of the present invention will be described.

(Embodiment 1) FIG. 1 (a) is a longitudinal sectional view of an avalanche photodiode (APD) using an indium phosphide (InP) compound semiconductor substrate, which is Embodiment 1 of the present invention, FIG. 1 (b)-
(D) is a longitudinal sectional view showing the present invention in the order of manufacturing steps.

In FIG. 1 (b), high-concentration N-type indium phosphide (n ⁺
Low concentration n ^- indium gallium arsenide (n ^- I) on the InP substrate 1.
A substrate having an epitaxial growth layer composed of an nGaAs) layer 2 and an n-type indium phosphide (InP) layer 3 is formed by a CVD method on a silicon oxide film or a silicon oxide film containing phosphorus pentoxide (CVD).
After the SiO ₂ ) film 9 is grown, a desired region of the CVD SiO ₂ film 9 is opened by ordinary photolithography and an aqueous solution of hydrofluoric acid, and then a predetermined process is performed by a sealed tube diffusion method using a zinc compound containing phosphorus. High-concentration P-type diffusion layer (p ⁺ Zn) after heat treatment
4 to form a PN junction. Then, as shown in FIG. 1 (c), after removing the CVD SiO ₂ film 9 with a hydrofluoric acid aqueous solution,
The surface stabilizing protective film according to the present invention is formed in the following manner.

That is, a predetermined amount of nitrogen gas is bubbled in a pure tank at a predetermined temperature connected to a plasma CVD nitride film growth device (not shown), so that nitrogen gas containing a constant concentration of water vapor is flown into the growth device. As shown in c),
The temperature of the substrate in the plasma CVD nitride film growth apparatus is raised from room temperature to 300 ° C. at a predetermined heating rate, and In ₂ O ₃ , In (PO ₃ ) ₃ and In
Indium phosphide tank consisting of In and P such as PO ₄ (p ⁺ InP
Layer 5 is formed with a predetermined thickness and a predetermined composition mixture ratio, and then the steam atmosphere is completely replaced with a nitrogen atmosphere, and then a nitrogen mixture of monosilane gas (SiH ₄ ) and ammonia gas (NH ₃ ) is added. A so-called plasma CVD nitride film 6 which is plasma-discharged in a gas atmosphere is grown.

Then, as shown in Fig. 1 (d), p ⁺
A part of the InP layer 5 and the plasma CVD nitride film 6 is opened by ordinary photolithography and hydrofluoric acid aqueous solution or hot phosphoric acid, and titanium is inserted through an ohmic electrode for the P-type InP layer such as gold zinc (AuZu). An anode electrode 7 of platinum and gold (Ti / pt / Au) is formed. Then, as shown in FIG. 1 (a),
N consisting of gold, germanium alloy and nickel on the n ⁺ InP side
The cathode electrode 8 made of titanium, gold or the like is formed through the mold solution ohmic electrode to complete the avalanche photodiode.

As described above, according to Example 1, after the element surface of the indium phosphide (InP) compound semiconductor substrate is oxidized in a water vapor atmosphere to form an oxide layer of indium phosphide composed of the constituent elements of the compound semiconductor substrate, Consecutively in the same furnace
By forming the CVD nitride film 6, it is possible to stabilize the reverse breakdown voltage of the APD and reduce the leak current.

(Embodiment 2) FIG. 2A shows a Schottky junction type electric field transistor using a gallium arsenide (GaAs) compound semiconductor substrate which is a second embodiment of the present invention as a basic active element, and other passive elements such as resistors. 2 is a vertical cross-sectional view showing an integrated circuit element made of, and FIGS. 2B to 2E are vertical cross-sectional views showing a method for forming the integrated circuit element of FIG.

First, as shown in FIG. 2 (b), N-type impurity ions such as silicon are ion-implanted in a predetermined region on a semi-insulating gallium arsenide (GaAs) substrate 21, and activation annealing is performed to perform n-type gallium arsenide ( After forming the (GaAs) region 22, a normal CV
A silicon oxide film 23 is formed by the D method. Subsequently, a Schottky gate electrode 24 made of titanium, platinum and gold is formed by opening a predetermined region of the silicon oxide film 23. Then, as shown in FIG. 2C, a source ohmic electrode 25 and a drain for N-type GaAs made of gold, germanium alloy (AuGe) and nickel (Ni) are formed by a resist lift-off technique using the silicon oxide film 23 as a spacer layer. Ohmic electrode 26,
A resistance layer ohmic electrode 27 is formed. In particular, what is important here is that the silicon oxide film as the spacer layer is removed with a hydrofluoric acid aqueous solution, and then the Ga gas is removed with hot phosphoric acid or hydrochloric acid.
Sufficient removal of oxides such as a natural oxide layer on the exposed surface and removal of the silicon oxide film 23 in the so-called field region such as the surface of the semi-insulating GaAs substrate 21 other than the n-type active region are entirely removed. There is a need. Then, as shown in FIG. 2 (d), Ga, which is a constituent element of the compound semiconductor plate, is formed by the method of the present invention.
After a gallium arsenide oxide layer 28 made of As and As is formed in a water vapor atmosphere, a silicon oxide film (CVD SiO ₂ film) 29 is formed. Then, in accordance with the usual Schottky junction type GaAs field effect transistor manufacturing method, a predetermined position of the CVD SiO ₂ film 29 is opened to form a source electrode 30, a drain electrode 31 and a resistance electrode.
The Schottky junction type GaAs field effect integrated circuit device shown in FIG. 2 (a) is completed by connecting the 32 and the gate extraction electrode with titanium, platinum and even metal.

According to the present embodiment, by selectively controlling the composition ratio of only the surface of the semi-insulating GaAs substrate 21 to oxidize it with water vapor, the side gate which is the most problematic in the manufacture of the integrated circuit of the Schottky junction type GaAs field effect transistor. The effect is greatly improved, and the effect on the transistor due to the forced oxidation can be ignored.

〔The invention's effect〕

As described above, according to the present invention, the element surface of the compound semiconductor substrate is oxidized in a water vapor atmosphere to form an oxide layer composed of the constituent elements of the compound semiconductor substrate, and then plasma CVD silicon nitriding is continuously performed in the same furnace. By forming a film or a silicon oxide film or a CVD silicon oxide film, not only plasma damage is not induced on the element surface of the semiconductor substrate, but also the mixing of impurities such as ionic impurities is prevented and the structure of the compound semiconductor substrate is formed. Evaporation prevention of group V elements peculiar to III-V group compound semiconductors by low-temperature formation of oxide layers made of elements, reproducibility of interfacial characteristics between CVD silicon nitride film and silicon oxide film and compound semiconductors through the oxide layers, It has the effect that it can be uniformly and well controlled.

[Brief description of drawings]

FIG. 1 (a) is a longitudinal sectional view of an avalanche photodiode (APD) using an InP compound semiconductor substrate showing a first embodiment of the present invention, and FIGS. 1 (b) to (d) are FIG. FIG. 2A is a vertical cross-sectional view showing the method for forming an APD shown in a) in the order of steps, and FIG. 2A is a vertical cross-sectional view of a Schottky junction field effect transistor integrated circuit device using a GaAs compound semiconductor substrate according to a second embodiment of the present invention. Plan, FIG. 2 (b)-
(E) is a longitudinal sectional view showing a forming step of FIG. 2 (a). 1 ... High-concentration N-type indium phosphorus substrate 2 ... Low-concentration n ^- indium gallium arsenide layer 3 ... n-type indium phosphorus layer 4 ... High-concentration P-type diffusion layer 5 ... Indium phosphorus oxide layer 6 ... Plasma CVD (silicon) nitride film 7 …… Anode electrode, 8 …… Cathode electrode 9,23,29 …… Silicon oxide film 21 …… Semi-insulating gallium arsenide substrate 22 …… N-type gallium arsenide region 24 …… Schottky gate electrode 25 …… Source ohmic electrode 26 …… Drain ohmic electrode 27 …… Resistive layer ohmic electrode 28 …… Gallium arsenide oxide layer, 30 …… Source electrode 31 …… Drain electrode, 32 …… Resistive electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 29/812

Claims (1)

[Claims] 1. Indium phosphide (InP) and gallium arsenide (G)
P / formed on a III-V compound semiconductor substrate such as aAs)
In the method of forming a surface stabilizing protective film of a compound semiconductor element for forming a surface stabilizing protective film of an element using N-junction or Schottky junction, steam oxidize the element surface of the compound semiconductor substrate in an atmosphere kept at a predetermined water vapor concentration. , Surface stabilization of a compound semiconductor device characterized by continuously forming a surface stabilizing protective film such as a plasma CVD silicon nitride film or a silicon oxide film or an optically assisted CVD silicon nitride film or a silicon oxide film in the same furnace. Protective film forming method.