JPS63174376A - Manufacture of infrared detector - Google Patents

Abstract

PURPOSE:To eliminate the hollow part between a semiconductor crystal layer and a substrate and to prevent an electrode from being disconnected by a method wherein the semiconductor crystal layer adhered on the substrate is developed after the rear of the crystal layer is exposed from the rear of the substrate at the same time as the crystal layer is exposed from its upper surface through a photo mask. CONSTITUTION:An HgCdTe crystal layer 2 is adhered on an insulative substrate 1, which transmits ultraviolet rays, with a bonding agent 3 and after the layer 2 is formed into a thin layer, the unnecessary bonding agent 3 is removed. Then, a P-type photo resist 4 is applied. Then, the layer 2 is exposed with ultraviolet rays 9 from its upper surface side through a photo mask 5. Subsequently, by performing an exposure on the whole surface from the rear of the substrate 1, the resist to intrude into the overhang part on the peripheral part of the layer 2 is exposed. After that, a developing processing is performed to form a prescribed resist pattern 8 for lift-off.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing an infrared detection element using a semiconductor.

[Conventional technology]

In general, semiconductor crystal layers such as HgCdTe, Pb5nTe, and In5b are known as materials for high-intensity infrared detection elements, and elements using these are basically 10μ thick.
This device is configured to form electrode terminals on a semiconductor crystal layer of approximately m thickness, and to detect resistance changes therebetween. A conventional method for manufacturing an infrared detecting element, for example, an infrared detecting element using a Hg Cd Te crystal layer, includes the following main steps.

First, as shown in FIG. 2(a), Hg is placed on the insulating substrate 1.
After bonding the CdTe crystal layer 2 with an adhesive 3, as shown in FIG. 2(b), it is polished and etched to a predetermined thickness, usually about 10 μm, and its edges 11 are smoothed. do. Next, as shown in FIG. 2(C), the unnecessary adhesive 3 exposed on the substrate 1 is removed by etching using oxygen plasma. This is because if unnecessary adhesive is left behind, the electrode film that will be laminated later is likely to peel off or breakage due to cracks will occur. Next, Figure 2(d)
As shown in FIG. 2, a resist pattern 8 is formed to set a wide photosensitive region to be the photosensitive portion of the Hg Cd Te crystal layer 2, and using this as a mask, the Hg Cd Te crystal layer 2 is exposed.
After lightly etching the surface, a conductive film 13, which is an electrode material, is formed by a so-called lift-off method, as shown in FIG. 2(e). The reason why the surface of the crystal layer is lightly etched here is to remove the oxide film formed on the surface.

Next, as shown in FIG. 2(f), a resist pattern 14 is formed.
By performing ion milling etching using the mask as a mask, no infrared detecting element was manufactured as shown in FIG. 2(g).

[Problem that the invention seeks to solve]

However, as infrared detecting elements manufactured in this way are cooled to liquid nitrogen temperature and repeatedly used, some conductivity failures occur, and as a result of investigation, the following problems were found.

That is, a detailed view of the peripheral edge of the crystal layer of an infrared detecting element manufactured by the conventional method is shown in FIGS. 3(a) to 3(d). As shown in FIG. 3(a), the conductor film 13 of the electrode is floating in a tunnel shape from the substrate 1 at the stepped portion of the adhesive 3, and this portion is disconnected due to stress during cooling, etc. Met.

Furthermore, this tunnel-shaped hollow part 15 was formed as follows.

That is, (i) when the adhesive is etched with oxygen plasma, the adhesive layer 3 becomes HgC as shown in FIG. 3(a).
The undercut is made to the bottom of the dTe crystal layer 2. (ii
) When forming the resist pattern 8 for lift-off, the area under the crystal layer is not exposed in the case of a positive resist, so that a resist residue 7 is left after development, as shown in FIG. 3(b). (iii) Subsequently, when light ion etching is performed to remove the oxide film on the surface of the crystal layer, the remaining resist 7 is exposed, and the conductive film 13 is laminated thereon as shown in FIG. 3(C). be done. (iv) Next, when the resist pattern 8 is removed or when an organic solvent is used in a subsequent process, the remaining resist 7 is dissolved away, as shown in FIG.
A hollow 15 shown in d) is formed.

These problems do not occur if the resist is negative in these processes, but negative resists are not easy to peel off after use, and when processing semiconductor crystal layers such as HgCdTe, they may deteriorate due to the chemicals used and the processing temperature. There are drawbacks that make it difficult to use.

Such a state in which the conductor film is separated from the substrate tends to cause disconnection, and even if it does not lead to disconnection, it limits the amount of current that can be applied to the element, greatly reducing reliability.

An object of the present invention is to provide a highly reliable method of manufacturing an infrared detection element that eliminates the occurrence of such hollow portions and prevents disconnection of electrodes.

[Means for solving problems]

The method for manufacturing an infrared detecting element of the present invention involves bonding a semiconductor crystal layer onto an insulating substrate that transmits ultraviolet rays, forming an R layer on the layer, removing unnecessary adhesive, and then forming an electrode terminal portion using a lift-off method. In the method for manufacturing an infrared detection element, when forming a photoresist pattern for setting a photosensitive area on the crystal layer, exposing the crystal layer from the upper surface side through a photomask of the resist pattern and , the method is characterized in that at least a peripheral edge of the crystal layer is exposed from the back surface of the substrate and then developed.

〔Example〕

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

FIGS. 1(a) to 1(d) are cross-sectional views showing an embodiment of the method for manufacturing an infrared detecting element of the present invention in the order of steps, which is basically similar to the conventional method shown in FIG. However, the main difference lies in the use of an insulating substrate that is transparent to ultraviolet light and the method of forming the photoresist pattern during the lift-off process shown in FIG. 2(d). Therefore, the case where HgCdTe is used will be explained, focusing on the process of forming the photoresist for lift-off.

First, HgCdTe is placed on an insulating substrate 1 that transmits ultraviolet rays.
After bonding the crystal layer 2 with an adhesive 3 and thinning it, unnecessary bonding is removed by etching with oxygen plasma. The process up to this point is exactly the same as in Figures 2 (a) to (e), except that a substrate that transmits ultraviolet rays is used.Next, as the lift-off resist pattern forming process, first, as in the conventional method, , as shown in FIG. 1(a), apply a positive photoresist 4. At this time, the adhesive 3 is Hg
There is an undercut inside the Cd Te crystal layer 2, and the photoresist also penetrates into the overhang part. Subsequently, as in the prior art, exposure to ultraviolet rays 9 is performed from the upper surface side of the HgCdTe crystal layer 2 through a photomask 5 covering the photosensitive region of the element, as shown in FIG. 1(b). As a result, the photoresist 4 changes so that the exposed portion 6 melts during development, but the HgCdT
The photoresist 7 directly under the overhang portion of the e-crystal layer 2 remained unexposed, and this residue caused a decrease in reliability.

In this embodiment, in order to remove this, as shown in FIG. 1(c).
As shown in FIG. 2, the entire surface of the substrate 1 is exposed to ultraviolet light from the back side. At this time, the overhanging unexposed resist 7 is exposed to the ultraviolet light that has passed through the substrate 1, while the lift-off resist pattern 8 for setting the photosensitive area is affected by the HgCdTe crystal layer 2 blocking the ultraviolet light. Not allowed. Thereafter, development is carried out in the same manner as in the prior art, thereby forming a predetermined lift-off resist pattern with no resist remaining in the overhang portion of the crystal layer 2, as shown in FIG. 1(d).

The subsequent steps are performed in the same manner as the conventional method shown in FIG. That is, similar to the method shown in FIGS. 2(d) to (g), a conductor as an electrode/material is formed by the so-called lift-off method, and then the shape is processed by ion milling etching to obtain an infrared detection element. It will be done.

In contrast to conventional devices, where the electrode conductor film was separated from the substrate and caused a decrease in reliability due to disconnection, etc., the device thus obtained was able to remove the unexposed photoresist in the overhang of the crystal layer, which was the cause of this problem. This eliminates these problems, making it a highly reliable device.

In the above embodiments, the entire surface of the substrate is exposed to ultraviolet light from the back surface, but essentially it is sufficient to expose only the peripheral portion of the crystal layer where an overhang of the crystal layer is formed.

It is easiest to expose the entire surface because it does not require a mask, but in that case, all the photoresist in areas where there is no crystal layer will be removed, so for example, a place outside the crystal store for subsequent mask exposure will be removed. In the case where an alignment mark is provided for the purpose of alignment, it is necessary to expose the area so as to cover it.

In addition, in this example, HgCdTe is used as the semiconductor crystal layer.
The same applies to Pb5nTe and InSb. The substrate is made of sapphire, which transmits ultraviolet rays and has good thermal conductivity, and the photoresist may be any ordinary positive type resist such as Microposit manufactured by Shipley. Further, as the conductive film, a stack of Cr and An, In, A47, etc. are suitable.

〔Effect of the invention〕

As explained above, according to the present invention, when forming a resist pattern for a lift-off resist, the unexposed photoresist under the semiconductor crystal layer can be exposed and removed from the back surface of the substrate, so that a layer can be stacked on top of it. It is possible to manufacture a highly reliable infrared detecting element in which the conductive film does not come loose from the substrate and is less likely to be disconnected.

[Brief explanation of the drawing]

1(a) to 1(d) are cross-sectional views showing the lift-off resist pattern forming process according to an embodiment of the present invention in order of process;
Figures (a) to (g) are cross-sectional views showing the conventional manufacturing method in order of process, and Figures 3 (a) to (d) are cross-sectional views showing the lift-off process of the manufacturing method of Figure 2 in order of process. ...Insulating substrate that transmits ultraviolet rays, 2...HgC
dTe crystal layer, 3... Adhesive, 4... Photoresist, 5... Photomask, 6... Photoresist in the exposed part, 7... Photoresist under the crystal layer,
8... Resist pattern for lift-off, 9... Ultraviolet light, 11... Edge of crystal layer, 13... Conductor film of electrode, 14... Resist pattern, 15... Hollow part. 2 HgCt Te Close & Go 1 Figure 2

Claims (1)

[Claims] In a method for manufacturing an infrared detecting element, which involves bonding a semiconductor crystal layer onto an insulating substrate that transmits ultraviolet rays, thinning the layer, removing unnecessary adhesive, and then forming electrode terminal portions by a lift-off method. , when forming a photoresist pattern for setting a photosensitive area on the crystal layer, exposure is performed from the upper surface side of the crystal layer through a photomask of the resist pattern, and at least the photoresist pattern is exposed from the back surface of the substrate. A method for manufacturing an infrared detecting element, comprising exposing a peripheral edge of a crystal layer to light and then developing it.