JPH0450753B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a method for manufacturing a frame transfer type semiconductor solid-state imaging device, and in particular, when pixels are densely arranged on the same semiconductor substrate, the signal of each pixel is The present invention relates to a manufacturing method that can form a charge weir so that it can be reliably decomposed.

(b) Technical background In recent years, significant progress in semiconductor technology has led to the development of multi-component semiconductors, such as mercury cadmium tellurium (HgCdTe).
It has been noted that the mobility of charge in materials such as alloys is much higher than that of conventionally used materials such as silicon (Si). This is done using semiconductors.

(c) Conventional technology and problems Frame transfer type (hereinafter referred to as FT type)
The solid-state imaging device shown in FIG. Transparent electrodes are arranged in a periodic arrangement among the plurality of transfer electrodes 3 of the CCD. However, FIG. 1 is a sectional view of the charge transfer path viewed from the longitudinal direction. In such a device, a charge weir must be provided between each adjacent charge transfer path 6, which is a common characteristic of imaging devices.
Since the diffusion coefficient of impurities in HgCdTe is extremely large, it is impossible to construct a charge weir consisting of a high carrier concentration region of the same conductivity type as a low carrier concentration substrate in such a semiconductor substrate, for example, by diffusion. .

Therefore, in the past, the properties of the so-called _MIS structure as shown in FIG. The charge transfer paths 6 have been separated by using a flat band state or an accumulation state. However, 8 is a potential well (hereinafter referred to as a well) forming the charge transfer path 6.

Although not shown in the figure, if the field plate 7 cannot be formed, increasing the thickness of the insulating film in that area increases the number of positive fixed charges near the interface between the insulating film 2 and the semiconductor. The thickness of the insulating film has been increased, and the portion directly under the insulating film is placed in, for example, an accumulation state to separate the charge transfer paths 6.

However, if the former field plate 7 is formed, the number of electrodes to be provided increases, which has the drawback of lowering the yield. Also, in both the former method and the latter method of increasing the thickness of the insulating film, the charge transfer path 6
If the separation between the charge transfer paths 6, that is, the isolation, is not sufficient, and if excessive signal light is incident, the charges in each charge transfer path 6 will immediately mix together.
This has the disadvantage of causing so-called crosstalk.

(d) Purpose of the Invention The present invention has been made in view of the above-mentioned conventional drawbacks, and utilizes the heat treatment properties unique to HgCdTe as a substrate material to allow relatively easy escape and re-introduction of Hg atoms from the surface layer of the substrate. The purpose of the present invention is to provide a method for manufacturing a solid-state imaging device in which a high carrier concentration of the same conductivity type as the substrate is formed only in a predetermined portion using the process described above, thereby forming a reliable charge dam. It is something to do.

(e) Structure of the Invention According to the present invention, an object of the present invention is to provide a method for manufacturing a solid-state imaging device using a mercury cadmium telluride semiconductor substrate as a material, the semiconductor substrate containing a low concentration of acceptor impurities. A process of once increasing the carrier concentration by subjecting the substrate to high-temperature heat treatment in a mercury atmosphere and extracting the mercury from the surface layer of the substrate, and providing a diffusion mask material having a window in the area where the charge transfer path is to be formed on the surface thereof. process and
A low-temperature treatment is performed in mercury vapor to introduce mercury into the surface layer of the substrate that is not covered with the diffusion mask material to lower the carrier concentration in the surface layer, resulting in a high carrier concentration remaining directly under the diffusion mask material. This is achieved by a method for manufacturing a solid-state imaging device characterized by including the step of forming a charge dam by a portion.

(f) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 2a, an HgCdTe substrate 1 is prepared. During the crystal production of the substrate 1, a low concentration of acceptor impurities, such as silver (Ag), is added in advance.
is added, and this wafer is heat-treated in Hg vapor at a low temperature, for example, 250° C., for about 10 days. In this way, the vacancies of the metal sites are filled with Hg atoms even deep in the substrate 1, and as a result, the acceptor impurity added in advance dominantly determines the conductivity type. As a result, the entire substrate 1 becomes p-type with a low carrier concentration as shown in FIG. 2a.

Next, this substrate 1 is heat-treated at a high temperature, for example, 500° C., for about 30 minutes. In this way, for example, the surface layer of the substrate 1 can be
Mercury atoms up to a depth of 5 μm escape, creating metal site vacancies and forming a p ⁺ -type layer 9 with a high carrier concentration as shown in FIG. 2b.

Then, as shown in FIG. 2c, a diffusion mask material 10 such as zinc sulfide is applied to the surface of the substrate.
is formed on one side, and a window W is formed only in the area where the charge transfer path is planned to be formed.
open. Furthermore, Hg
When the same low-temperature heat treatment as described above is applied in steam, the surface layer of the window W where there is no diffusion mask material will be covered again.
As a result of Hg being diffused and filling the vacancies in the metal sites, as shown in FIG. Returning to the mold, only the p ⁺ layer 11, which acts as a charge weir, remains.

After that, the diffusion mask material 10 is removed and an insulating film 12 with a thickness of, for example, about 1200 mm is provided on the exposed substrate surface, and a field insulating layer 1 is further formed in a predetermined portion.
3, the result will be as shown in Figure 2e.

Then, by disposing a conductive film 14 of nickel (Ni) or chrome (Cr) on one surface and creating a separation region shown as W' at a predetermined portion, the conductive film 14 divided into two parts as shown in FIG. CCD transfer electrode 3
Therefore, all that is left to do is to perform bonding wiring to the conductive film 14 to complete the FT type solid-state imaging device.

In this case, the part of the substrate surface covered with the diffusion mask material 10 in FIG. 2d is shown as 11.
Although the p ⁺ semiconductor region remains,
This region will act as a metallurgically created charge weir, thus defining here the charge transfer path shown as 6 in FIG. 2f.

Figures 3a to 3f show the manufacturing process of a modified embodiment of the present invention, and the contrast with the process shown in Figures 2a to 3e is as shown in Figure 3a. mold
The point is that a wafer is used in which a p ^- type HgCdTe layer 15 is stacked on an HgCdTe substrate 1a by epitaxial technology. In this case, when stacking the p ^- type HgCdTe growth layer 15, a low concentration of acceptor impurity such as silver (Ag) is added in advance.

If this wafer is heat-treated at high temperature in Hg vapor, p ^-
Hg atoms in the HgCdTe layer escape and the layer 15 becomes p ⁺ conductivity type as shown in FIG. Arrange it like this.

After this, if this sample is also subjected to low-temperature heat treatment in Hg vapor, the portion 16 of the surface of the growth layer 15 that is not covered with the diffusion mask 10 is p ^-
In the part that was covered by the diffusion mask 10, p ⁺ type HgCdTe remains as shown as 17 in FIG. 3d.

Therefore, an insulating film 1 is formed on this as shown in FIG. 3e.
2 and further form a field insulating layer 13, and then a conductive film 14 as shown in FIG. 3f, a semiconductor of the same conductivity type as that shown in FIGS. A solid-state imaging device is completed.

That is, according to the present invention, the charge weir is significantly different from the conventional one in that it is not made by an electric field induction method but by a metallurgical method. Since a pn junction exists directly under each charge transfer path,
Even if charges overflow from the transfer path when strong light is incident, they will be pulled toward the substrate 1a by the built-in electric field of the pn junction, so there is no possibility that charges will mix into the adjacent charge transfer path. It is convenient that this will not occur.

(g) Effects of the Invention As explained in detail above, if the method for manufacturing a solid-state imaging device of the present invention is used, the charge weir is made by a metallurgical method, so that In order to achieve perfect isolation,
Great practical effects can be expected.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a conventional solid-state imaging device, FIG. 2 is a manufacturing process diagram of the device according to the present invention, and FIG. 3 is a manufacturing process diagram of a modified embodiment of the present invention. In the figure, 1 is a semiconductor substrate, 2 is an insulating film, and 3 is a semiconductor substrate.
is a transfer electrode, 6 is a charge transfer path, 7 is a field plate, 8 is a potential well, and 9 is a high carrier concentration
10 is a p ⁺ layer, 10 is a diffusion mask material, 11 is a p ⁺ layer serving as a charge weir, 12 is an insulating film, 13 is a field insulating layer, and 14 is a conductive film.

Claims (1)

[Claims] 1. A method for manufacturing a solid-state imaging device using a mercury-cadmium-tellurium semiconductor substrate, comprising: subjecting the semiconductor substrate containing a low concentration of acceptor impurities to high-temperature heat treatment in mercury vapor; A step of temporarily increasing the carrier concentration by removing mercury from the surface layer of the substrate, a step of disposing a diffusion mask material having a window in the area where the charge transfer path is to be formed on the surface, and a low-temperature treatment in mercury vapor. Then, mercury is introduced into the surface layer of the substrate not covered with the diffusion mask material to lower the carrier concentration in the surface layer, and a charge weir is formed by the high carrier concentration portion left directly under the diffusion mask material. A method for manufacturing a solid-state imaging device, comprising the steps of: