JPH0153729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an infrared detection element.

Mercury cadmium telluride (Hg _1-X Cd _x Te) crystal can be made by changing the composition ratio of mercury and cadmium to increase the energy gap of the crystal from −0.3 eV.
It can be changed up to 1.6eV. In particular, a crystal with a composition of X=0.2 is important as a material for a 10 μm band infrared detection element. Such infrared detection elements are often used as an array by arranging a large number of detection elements in a line or two-dimensionally.

First, the structure of a conventional infrared detection element array will be described.

FIG. 1a shows a plan view of the photoconductive element array, and FIG. 1b shows a sectional view taken along line A--A in FIG. 1a. Here, 1 is a cadmium tellurium (CdTe) substrate, 2 is a mercury cadmium telluride crystal layer, 3 is an electrode made of a metal multilayer such as indium/gold (In/Au), 4 is a thin metal wire made of, for example, a gold wire, and 5
is the portion where the gold wire 4 is crimped onto the electrode 3.

The method for manufacturing the array will be described below. A mercury-cadmium-tellurium crystal layer 2 is formed on a semi-insulating cadmium tellurium (CdTe) substrate 1 by epitaxial growth using, for example, a well-known liquid phase epitaxial growth method. Thereafter, in order to separate the elements, a photoresist film is deposited, and a pattern is formed in the shape of the mercury-cadmium-tellurium crystal layer 2 and the electrode 3 shown in FIG. 1A using photolithography. Using the patterned resist film as a mask, the mercury-cadmium-tellurium crystal layer 2 is etched down to the cadmium-tellurium substrate 1 with a mixed solution of bromine and methyl alcohol. Thereafter, electrode metal layers are successively deposited on both ends of the mercury-cadmium-tellurium crystal layer 2 remaining after etching by a method such as vapor deposition to form the shape of the electrode 3 shown in FIG. 1a. After the above process is completed, the cadmium tellurium substrate 1 is set in a predetermined position, and wire bonding is performed using gold wires 4 in order to electrically connect it to an external terminal (not shown).

When manufacturing array elements using the conventional method as described above, the wire bonding process is the most problematic. The mercury-cadmium-tellurium crystal layer 2 is very fragile and easily damaged, and has the disadvantage that the gold wire 4 is easily detached. In order to improve this drawback, conventionally,
A device structure as shown in FIGS. 2a and 2b was devised. This structure is intended to form the bonding electrode 13 not on the fragile mercury-cadmium-tellurium crystal layer 2 but on the cadmium-tellurium substrate 1 which is harder than the mercury-cadmium-tellurium crystal layer 2. FIG. 2a is a plan view thereof, and FIG. 2b is a sectional view taken along line BB in FIG. 2a. Here, 13 is a bonding electrode made of, for example, indium/gold (In/Au), which also serves as an ohmic contact with the mercury-cadmium-tellurium crystal layer 2.

However, even in this conventional structure, as shown in Fig. 3, when the gold wire 4 is crimped and pulled up with the capillary 7 of the bonder, the electrode 13 is often pulled up together with it due to the fragility of cadmium tellurium. This is thought to be due to insufficient adhesion between the cadmium telluride and the electrode metal. In general, it is necessary to bond several tens to hundreds of elements in an array element, and even if one of them comes off, the array element cannot be used anymore, making it difficult to fabricate an array with the conventional structure described above. It's haunting me.

The present invention has been made in view of the above points, and includes forming an intermediate layer made of zinc sulfide or zinc selenide adjacent to a mercury-cadmium-tellurium crystal layer on a cadmium-tellurium substrate, and forming an interlayer between the mercury-cadmium-tellurium crystal layer and the ohmic layer. An object of the present invention is to provide an infrared detecting element in which an infrared detecting element array can be easily manufactured without peeling off the electrode during bonding by providing a wire bonding electrode that is in contact with the intermediate layer and a part of the electrode is attached on the intermediate layer. The purpose is

FIG. 4 is a sectional view of an infrared detection element according to an embodiment of the present invention. In the figures, the same reference numerals as in FIGS. 1 to 3 indicate the same or corresponding parts, and 8 is a zinc sulfide (ZnS) layer as an intermediate layer.

This structure is characterized in that a zinc sulfide layer 8 is deposited under at least a portion of the bonding electrode 13 of the element having the conventional structure shown in FIG.
The zinc sulfide layer 8 can be deposited by vapor deposition, sputtering, or chemical vapor deposition (CVD). Zinc sulfide is a material that is sufficiently harder than cadmium tellurium, and also has strong adhesion to cadmium tellurium and electrode metals. Therefore, it is possible to form a zinc sulfide layer 8 that can sufficiently withstand the pressure and tension during wire bonding, and the adhesion between the bonding electrode 13 attached on the zinc sulfide layer 8 and the zinc sulfide layer 8 is also sufficient. Therefore, it is possible to eliminate peeling of the electrode during wire bonding.

Although only the photoconductive type element has been described so far, it goes without saying that the present invention can also be applied to a photovoltaic type element.

Furthermore, the zinc sulfide layer as the intermediate layer described in the above embodiments may be as wide as it is as long as there is a contact area between the electrode and the mercury-cadmium-tellurium crystal layer.
Alternatively, it may be placed on a mercury cadmium telluride crystal layer. Further, the intermediate layer may be a zinc selenide (ZnSe) layer.

As described above, according to the infrared detection element according to the present invention, since the intermediate layer made of zinc sulfide or zinc selenide is deposited between the cadmium telluride substrate and the wire bonding electrode, there is no possibility of a single failure. A major advantage is that wire bonding can be performed and arrays of several hundred can be easily manufactured.

[Brief explanation of drawings]

Figure 1a is a plan view of a conventional photoconductive infrared detection element array, Figure 1b is a sectional view taken along line A-A in Figure 2a, and Figure 2a is another conventional photoconductive infrared detection element array. 2b is a sectional view taken along the line B-B in FIG. 2a, FIG. 3 is a diagram showing the state of wire bonding in FIG. 2b, and FIG. FIG. 3 is a cross-sectional view of a detection element. DESCRIPTION OF SYMBOLS 1... Cadmium tellurium substrate, 2... Mercury cadmium telluride crystal layer, 8... Intermediate layer (zinc sulfide layer), 13... Wire bonding electrode. In addition,
The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A mercury-cadmium-tellurium crystal layer formed on a cadmium-tellurium substrate; an intermediate layer made of zinc sulfide or zinc selenide deposited on the cadmium-tellurium substrate adjacent to the mercury-cadmium-tellurium crystal layer; An infrared detecting element comprising a wire bonding electrode that is in ohmic contact with a cadmium tellurium crystal layer and a part of the wire bonding electrode is attached on the intermediate layer.