JPH04124854A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a high resistance layer capable of sufficiently isolating elements from each other even if a high electric field is applied on a board by forming an active layer containing n-type GaAs on a substantially insulating GaAs substrate, and by ion-implanting boron of a specific amount or less in a specific depth from the surface of the active layer. CONSTITUTION:A process of forming an active layer 2 made of semiconductor including n-type GaAs on a substrate 1 made of substantially insulating GaAs semiconductor, and a process of ion-implanting boron of 1/10 or less of carrier concentration of the layer 2 in a depth of 2.5 times as deep as that of the layer 2 from the surface of the layer 2 are provided. For example, Si<+> ions are implanted into one main surface of the substrate 1 to form an n-type active layer 2. The ion implanting condition includes 100keV of acceleration voltage, 5X10<12>/cm<2> of dose, and annealing after ion implanting. Then, with an ohmic electrode 3 as a mask B<+> ions are implanted in the layer 2 to form a high resistance layer 4. The ion implanting conditions include 4X10<11>/cm<2> of dose and 160keV of an acceleration voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and in particular to a method for manufacturing a semiconductor device.
The present invention relates to a method of forming a high resistance layer for equal isolation between elements on a semiconductor substrate using S.

[Prior Art] When configuring a plurality of elements on a semiconductor substrate using GaAs, an electrical isolation structure is required between the elements or within the element. In particular, on the entire surface of a semi-insulating GaAs substrate,
When the active layer is formed by epitaxial growth, the isolation structure is, for example, the following structure (1) or (2).

■Mesa-etch the active layer to electrically isolate it using a mesa structure.

(2) Form a high resistance layer in a desired region of the active layer by ion implantation.

Comparing the above-mentioned two key structures (1) and (2), the structure (2) has a flat surface and a Brainer structure, so it is generally considered to be advantageous for high integration and complex structures.

Conventionally, the method for forming a high-resistance layer to realize the isolation structure (2) was to deposit a layer of 1/10 of the carrier concentration of the active layer from the surface of the active layer to a depth approximately twice the depth of the active layer. Ion implantation of ions such as H''' B+ 01 at a dose (implantation amount) of about 100 to 100 m is being carried out (Asai, Ohata, IEICE Technical Report ED89-91.p25).

[Problem to be solved by the invention] The high-resistance layer formed by the conventional method to realize the isolation structure in (2) above exhibits high resistivity at low electric field strength;
At high electric field strengths, the resistivity decreases. For this reason,
It is not possible to shorten the distance between electrodes (between elements) due to high integration, or increase the applied voltage due to high output, etc.
There was a problem that it was insufficient for electrical isolation between elements or within an element.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a semiconductor device that can provide a high resistance layer on a substrate that can sufficiently isolate elements even when a high electric field is applied.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides (a) an n-type GaAs semiconductor substrate on a substrate made of a substantially insulating GaAs semiconductor;
Step of forming an active layer made of a semiconductor containing As, (b
) The method comprises the step of implanting boron ions having a carrier concentration of 1/10 or less of the active layer to a depth of 2.5 times or more the depth of the active layer from the surface of the active layer.

Note that the depth of the active layer refers to the depth from its surface to a carrier concentration point that is 1/e lower than the maximum carrier concentration of the active layer (the carrier concentration point on the deep side from the surface), and The value of e is e-2 to ]0 depending on the formation method such as the ion implantation method or the epitaaxial growth method when the active layer is formed.
is chosen as the value of Furthermore, in general, the carrier concentration in the active layer is expressed per unit volume, and the ion implantation amount is expressed per unit area, so the carrier concentration in the active layer is ]/10
The following ion implantation amount is 1/1 of the amount obtained by integrating the carrier concentration of the active layer from its surface to the depth of the active layer described above.
Refers to the amount of ions less than 0.

[Operation] When boron ions are implanted into the active layer, the implanted region becomes highly resistive due to carrier traps formed by the ion implantation. The conductive mechanism of the high resistance layer in this case is the first
As shown in the figure, it is divided into a niomic region, b = trap filling region C: space charge limited region. A current of 1 ohm in the ohmic region a is expressed by the following equation, assuming that the effective current path is d (see FIG. 2).

Engineering Ohm! qIlno 11μ00v/d...
(1) where q: charge element no: equilibrium carrier concentration μ0 of high resistance layer: electron mobility of high resistance layer V: applied voltage. In Fig. 2, 1 is a semi-insulating GaAs substrate, 2 is an active Layer 3 is an ohmic electrode for characteristic evaluation, and layer 4 is a high resistance layer.

Further, the boundary voltage vc between the ohmic region a and the trap filling region is expressed by the following equation.

VC-(q-Nt/2ε) ・d2 ・-(
2) Here, Nt Nidrap concentration: Even if a high electric field is applied to a high resistance layer formed with a dielectric constant, in order to obtain the required high resistivity, it is necessary that Iohm be small and the boundary voltage VC be large. For this purpose, the effective current path d
is large, that is, the ion implantation depth (ion penetration distance RP
) is necessary. Ion penetration distance RP
It has been found that when the depth of the active layer is made 2.5 times or more, the boundary voltage VC becomes about twice or more compared to the conventional technology.
By making the ion implantation depth 2.5 times or more deeper than the active layer, it is possible to obtain the required high resistivity even when a high electric field is applied to the high resistance layer. If the active layer is thick, 2.
Since the implantation depth is five times or more, there is a concern that if ions are implanted with high energy, damage to the surface of the active layer will increase and surface leakage will increase. This case can be solved by using multiple injections. On the other hand, if the amount of ion implantation becomes too large, damage to the surface of the active layer increases, the electrical resistance of the ohmic region a decreases, and leakage current increases.

The leakage current begins to increase as the amount of ion implantation increases when the concentration of boron ions exceeds approximately 1/10 of the carrier concentration of the active layer. Therefore, the amount of boron ions to be implanted is 1/ of the carrier concentration in the active layer.
It can be suppressed to 1.0 or less. As described above, boron ions with a carrier concentration of 1/10 or less of the active layer are ion-implanted from the surface of the active layer to a depth of 2.5 times or more the depth of the active layer. Even if a high electric field is applied to the high-resistance layer, the required high resistivity can be obtained, making it possible to sufficiently isolate elements.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 3(A), 2981+ ions are implanted into one main surface of the semi-insulating GaAs substrate 1 to form an n-type active layer 2. As shown in FIG. The conditions for ion implantation are an acceleration voltage of 100
keV, a dose of 5×10 12 /c−, and annealing was performed after ion implantation. The depth of the active layer 2 obtained under these conditions was 850A. A pair of ohmic electrodes 3 were formed on the surface of the active layer 2 with an interval of 2 μm in order to evaluate the electrical characteristics of the high resistance layer to be formed.

Next, using the ohmic electrode 3 as a mask, a layer of 1 is applied to the active layer 2.
184 ions are implanted to form a high resistance layer 4 (
Figure 3 (B)). The conditions for ion implantation are a dose of 4X1.
01'/c-, and the acceleration voltage was 50~1 for the purpose of characteristic evaluation.
It varied between 60 keV. Accelerating voltage 160keV,
The depth of ion implantation is 2.5 times or more the depth of the active layer 2.

FIG. 4 shows the measurement results of the acceleration voltage dependence of the boundary voltage VC for the sample formed as described above. The accelerating voltage in the prior art is at most 100 keV. On the other hand, if ions are implanted at an acceleration voltage of 160 keV and the ion implantation depth is 2.5 times or more the depth of the active layer 2, the boundary voltage VC is found to be approximately 2.5 times that of the conventional technique. Ru.

In addition, FIG. 5 shows the depth of ion implantation and the ohmic electrode 3.
．． 3 shows the measurement results of the relationship between the leakage current and the leakage current.

The applied electric field is IOV/2 μm.

The measurement results show that for a depth of 850 people in the active layer 2, when the ion implantation depth is increased to 210 OA or more, which is approximately 2.5 times that depth, the leakage current decreases to about 1.0 x 1 O-7 A or less. When the leakage current is reduced to a value that can be used in practical use and exceeds 290OA, which is more than three times as much, the leakage current becomes 2
It becomes saturated at about -8A.

From this example, by ion-implanting 11B+ ions with a carrier concentration of 1/10 or less of the carrier concentration of the active layer 2 from the surface of the active layer 2 to a depth of 2.5 times or more the depth of the active layer 2, It can be seen that even when a high electric field is applied, a high-resistance layer 4 is obtained on the GaAs substrate 1, which allows sufficient isolation between elements.

[Effects of the Invention] As explained above, according to the present invention, a carrier concentration of 1/10 or less of the carrier concentration of the active layer is formed from the surface of the active layer to a depth of 2.5 times or more the depth of the active layer. Since boron ions are implanted, a high-resistance layer can be formed on the substrate with little leakage current even when a high electric field is applied, and which can sufficiently isolate elements.

[Brief explanation of drawings]

1 and 2 are for explaining the characteristics of the high resistance layer formed by the method for manufacturing a semiconductor device according to the present invention, and FIG. 1 is for explaining the applied voltage vs. current characteristics for explaining the conduction mechanism. FIG. 2 is a longitudinal cross-sectional view for explaining the effective current path, FIGS. 3 to 5 are for explaining the invention in detail, and FIG. 3 is a diagram showing the formation of the high resistance layer. A process diagram for explaining the process, Figure 4 is a characteristic diagram showing the acceleration voltage dependence of the boundary voltage in the formed high resistance layer, and Figure 5 is the relationship between the depth of ion implantation and the leakage current of the high resistance layer. FIG. 1. Semi-insulating GaAs substrate, 2: Active layer, 4: High resistance layer.

Claims (1)

Scope of Claims: (a) a step of forming an active layer made of a semiconductor containing n-type GaAs on a substrate made of a substantially insulating GaAs semiconductor; (b) a step of forming an active layer made of a semiconductor containing n-type GaAs from the surface of the active layer; A method for manufacturing a semiconductor device, comprising the step of implanting boron ions with a carrier concentration of 1/10 or less of the active layer to a depth of 2.5 times or more.