JPH06237005A - Photodetector element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a photodetector element, whose dark current is decreased with respect to the photodetector element such as a photodiode. CONSTITUTION:Impurities, whose conductivity type is reverse with respect to a one-conductivity type HgCdTe substrate (P type) 1, are introduced into a specified pattern. An n-type layer (pixel region) 11 comprising a p-n junction region is provided in a photodetector element. In this photodetector element, the distribution of the concentration of the impurity carrier in the n-type layer 11 is made steep at the central part of the p-n junction region but gentle at the peripheral part of the p-n junction part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light sensing element and a method for manufacturing the same, and more particularly to mercury-cadmium-tellurium (HgCd).
Te), an infrared detector provided on a compound semiconductor substrate, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional photovoltaic infrared detecting element formed by implanting impurity atoms of a conductivity type opposite to that of a p-type HgCdTe substrate in a prescribed pattern in a prescribed region will be described.

As shown in FIG. 8 (a), a p-type HgCdTe substrate 1 is used.
Boron (B ⁺ ) ions, which are n-type impurities, are added to the resist film.
Using an ion implantation method (not shown) as a mask, an n ⁺ layer 2 is formed.

Then, as shown in FIGS. 8 (b) and 8 (d), the Hg
A surface protective film 3 of zinc sulfide (ZnS) is formed on the CdTe substrate 1 by vapor deposition or the like, a connection hole 4 is formed at a predetermined position of the surface protective film 3, and then an electrode 5 of gold, indium or the like is vapor deposited, And a lift-off process using a resist film.

In addition to the above-mentioned method, as shown in FIG. 8 (c), after ion implantation of boron, the HgCdTe substrate is heated at a predetermined temperature to diffuse the ion-implanted boron atoms to n ^+. There is also a method of expanding layer 2.

As another method, when the photodiode formed by providing the n ⁺ layer 2 is irradiated with infrared rays for detection, the infrared rays are photoelectrically converted to cross the minority carriers. In order to prevent the talk phenomenon, cross talk between pixels is prevented by forming an n ⁺ layer in a lattice shape at a peripheral portion of a pn junction region formed by the n ⁺ layer with a predetermined interval by an ion implantation method. The method is adopted.

[0007]

However, when formed by the conventional method, when a reverse bias voltage is applied to operate this photodiode, as shown in FIG. As shown, a surface leak current is often generated, and this surface leak current becomes noise and causes a dark current.

In order to reduce the surface leak current, it is advisable to expand the region where the voltage is actually applied, that is, the depletion layer in the pn junction region of the photodiode 6 to reduce the electric field strength applied to the pn junction region. . For that purpose, the HgCdTe substrate 1 on which the pn junction region is formed is heat-treated at a temperature of 200 ° C, and the pn junction region is graded with a gentle concentration gradient.
I recommend setting it to ion.

However, if the entire pn junction at the boundary between the n ⁺ layer 2 and the p-type HgCdTe substrate 1 is made a graded junction,
The dark current generated from the n ⁺ layer 2 increases and the characteristics of the photodiode 6 deteriorate. The reason is that when the carrier concentration of the n ⁺ layer 2 decreases, the concentration of minority carriers increases,
In addition, the dark current described above increases because the diffusion length increases as the flight time of minority carriers increases.

[0010] In conventional methods, in the structure surrounding the pn junction region by a lattice-like n ⁺ layer, as the width of the lattice-like n ⁺ layer is wide, the cross-talk is reduced, but the n ⁺ layer Therefore, the photocurrent also decreases.

Therefore, the required performance of the infrared detecting element,
At present, a method is employed in which the width of the n ⁺ layer is controlled depending on the type to control the amount of optical signal and the degree of crosstalk to predetermined values.

However, in the above method, the signal amount and the degree of occurrence of crosstalk are determined by the composition of the HgCdTe crystal, crystal parameters such as the amount of impurity atoms introduced, and various parameters in the manufacturing process of the infrared detection element. It is difficult to control, etc. to a predetermined value.

The present invention solves the above problems and provides a graded junction structure in which the carrier concentration gradient in the peripheral portion of the pn junction region, which causes the generation of surface leakage current, is made gentle.
It is an object of the present invention to provide a photodetection element in which surface leak current is prevented from occurring while preventing an increase in dark current generated in the n ⁺ layer, and a method for manufacturing the same.

[0014]

According to a first aspect of the present invention, there is provided a pn junction region in which a one-conductivity type semiconductor substrate is doped with impurities of a reverse conduction type to the semiconductor substrate of a one-conductivity type in a predetermined pattern. In the photo-detecting element provided with the pixel region, the impurity carrier concentration distribution in the pixel region is steep in the central portion of the pn junction region and is gentle in the peripheral portion of the pn junction region. To do.

According to a second aspect of the present invention, the width or the depth is provided in any of the peripheral area of the pixel area, the central area between the pixel areas, or the central area between the peripheral area of the pixel area and the pixel area. A reverse conductivity type layer of the semiconductor substrate that can be controlled.

According to a third aspect of the present invention, the reverse conductivity type layer of the semiconductor substrate is provided by heating the anodic oxide film formed on the semiconductor substrate. According to a fourth aspect of the present invention, there is provided a method of manufacturing a photodetecting element by introducing an impurity of a conductivity type reverse to that of a semiconductor substrate of one conductivity type into a predetermined pattern and providing a pixel region including a pn junction region. In the peripheral area of the pixel area, the central area between the pixel areas, or the central area between the peripheral area of the pixel area and the pixel area, an anodic oxide film is formed, and then the substrate is formed. Is heat-treated to introduce mercury in a mercury-rich layer formed at the interface between the substrate and the anodic oxide film into the substrate to fill the mercury vacancies in the substrate with the mercury to form a reverse conduction type layer of the substrate. It is characterized in that impurity atoms having a conductivity type opposite to that of the substrate are introduced into the central portion of the pixel region.

According to a fifth aspect of the present invention, after forming an anodic oxide film in the central region between the pixel regions, an impurity atom having a conductivity type opposite to that of the substrate is introduced into the central region of the pixel region to form the pixel region. Formed, and then a protective film is formed on the substrate to form a connection hole in the protective film, and then an electrode is formed to form a photodetection element, and then the substrate on which the photodetection element is formed is subjected to heat treatment. The mercury in the mercury-rich layer formed at the interface between the substrate and the anodic oxide film is introduced into the substrate to fill the mercury holes in the substrate with the mercury to form the reverse conduction type layer of the substrate. It is characterized in that the current and the amount of crosstalk can be controlled.

[0018]

The central portion of the pn junction region is formed as usual, and the concentration gradient of the junction at the peripheral portion of the pn junction, which causes the leakage current, is made gentle to form a graded junction. As a result, the surface leak current can be reduced without substantially increasing the dark current generated in the n ⁺ layer. How to the peripheral portion of the pn junction region Graded Junction, after ion implantation in the peripheral portion of the formation region of the n ⁺ layer, Grad peripheral portion is heat-treated
After the ed junction, ions are implanted in the central part of the pn junction region.

After forming the anodic oxide film around the pn junction region, heat treatment is performed at about 100 ° C. for a predetermined time to form an n layer, the anodic oxide film is removed, and impurity atoms are ion-implanted. When the anodic oxide film is formed in this way, a mercury-rich layer containing a large amount of Hg is formed at the interface between the anodic oxide film and the HgCdTe substrate surface. When the substrate is heat-treated, Hg diffuses into the HgCdTe crystal substrate and fills the Hg holes that serve as acceptors in the p-type HgCdTe crystal.
^It can be converted to an n-type layer of ¹⁴ / cm ³ . This has been confirmed by experiments.

It is also possible to introduce Hg into the p-type HgCdTe crystal to form the n-layer by heat-treating the p-type HgCdTe crystal in the Hg gas, but to prevent passage of the Hg gas. There is no suitable mask, and it is difficult to control the amount of Hg diffusion. Furthermore, since the connection between the n-type layer formed on the HgCdTe crystal and the metal film for the electrode connected to the n-type layer is not good, this method is not practical at present.

FIG. 7 shows the carrier concentration in the HgCdTe substrate after ion implantation of such impurity atoms into the HgCdTe substrate, and further after ion implantation and diffusion, and the anodic oxide film of the substrate is formed on the HgCdTe substrate. After that, a concentration distribution diagram of carrier concentration in the HgCdTe substrate when the substrate is heat-treated is shown.

The curve a in the figure is a carrier concentration distribution chart of the HgCdTe substrate immediately after the boron (B ⁺ ) ion is ion-implanted into the p-type HgCdTe substrate, and the curve b is the boron (B ⁺ ) ion-implanted after the ion implantation. Further, the carrier concentration distribution diagram of the HgCdTe substrate when the HgCdTe substrate is further heat-treated, the curve c is the carrier concentration distribution diagram of the HgCdTe substrate when the substrate is heat-treated after the anodic oxide film of the substrate is formed on the HgCdTe substrate, d is
It is the carrier concentration of HgCdTe.

According to the above carrier concentration distribution chart, an anodic oxide film is formed in a grid pattern so as to surround pixels, a photodiode is manufactured, and then heat treatment is performed at 100 ° C. to form an interface between the anodic oxide film and the HgCdTe substrate. By diffusing the mercury-rich layer described above, an n-type lattice-shaped reverse conduction type layer can be formed.

When the photocurrent value of the photodiode or the amount of crosstalk generated reaches a predetermined value, the heat treatment work for diffusing Hg is stopped. After the photodiode is once formed, the photodiode after the formation is further formed. It is also possible to control the characteristics of the diode.

By selectively forming the graded junction only in the peripheral portion of the pn junction region where the pixel is formed, the dark current component generated in the n-type layer is hardly increased and the surface leak current is reduced. Can be reduced.

Further, an anodic oxide film having a predetermined width and depth is formed in a lattice shape on the periphery of the pn junction region to form a photodiode once, and after the photodiode is formed, the substrate is heat treated to form a photo diode. It is possible to control the amount of diode crosstalk to an optimum value.

[0027]

Embodiments of the present invention will be described in detail below with reference to the drawings. 1 (a) and 1 (b) are a cross-sectional view and a plan view of a first embodiment of a photo-detecting element of the present invention. As shown,
p-type B ⁺ ions in a predetermined pattern HgCdTe substrate 1 is in the n ⁺ layer 2 is formed the ion implantation, the low-concentration n-type layer of so as to surround the periphery of the pixel region of the n ⁺ layer 2 in a lattice 11 are formed.

The low-concentration n-type layer 11 may be formed by selectively implanting B ⁺ ions in a lattice shape so as to surround the pixel region and then thermally diffusing the HgCdTe substrate 1. After the HgCdTe anodic oxide film is selectively formed in a lattice pattern so as to surround the pixel region, the HgCdTe substrate 1 is heat-treated to diffuse the mercury-rich layer formed on the interface between the anodic oxide film and the HgCdTe substrate. You may form.

Further, a surface protective film 3 of ZnS is formed on the HgCdTe substrate 1.
Is provided, a connection hole 4 is provided in the surface protection film 3, and a gold or In electrode 5 is provided to form a photodetection element. By doing so, since the peripheral portion of the pn junction is a graded junction, the electric field strength applied to the pn junction region can be reduced, the surface leakage current can be reduced, and the dark current can be reduced.

2 (a) and 2 (b) are a sectional view and a plan view of a second embodiment of the photo-detecting element of the present invention. The present embodiment differs from the first embodiment in that the n-type layer 11 is provided in a state of being separated from the pixel region of the n ⁺ layer 2 by a predetermined distance. If this structure is adopted, the effect of preventing the generation of dark current is inferior to that of the first embodiment, but there is the effect of preventing the crosstalk phenomenon that occurs between pixels.

3 (a) and 3 (b) are a sectional view and a plan view of a third embodiment of the photo-detecting element of the present invention. This embodiment is a combination of the first embodiment and the second embodiment, and has a structure in which the n-type layer 11 is provided in the peripheral portion of the pixel region of the n ⁺ layer 2 and at a position separated from the pixel region by a predetermined distance. Although the number of steps is larger than in the first and second embodiments, it is most effective in preventing dark current and crosstalk.

Next, the manufacturing process of the photo-detecting element of the present invention will be described. As a first embodiment, as shown in FIG. 4A, a p-type HgCd film is formed by using a resist film (not shown) as a mask.
B ⁺ ions are ion-implanted into the peripheral portion of the region where the pn junction is to be formed on the Te substrate 1 to form an n-type ion implantation layer 12.

Subsequently, as shown in FIG. 4 (b), the HgCdTe substrate 1 having the ion-implanted layer 12 is heat-treated at a temperature of 200 ° C. for 1 hour, and a predetermined grading is formed on the peripheral portion of the region where the pn junction is to be formed. N-type layer 11 (Graded Junction)
ction) is formed.

Then, as shown in FIG. 4 (c), a resist film is formed.
As shown by an arrow, B ⁺ ions are ion-implanted in a region where a pn junction is to be formed using (not shown) as a mask, and further heat treatment is performed to form an ion-implanted layer into the n ⁺ layer 2.

Finally, as shown in FIG. 4 (d), after the surface protective film 3 of ZnS film is formed on the surface of the p-type HgCdTe substrate 1 by vapor deposition,
After forming the connection hole 4 in the surface protective film 3, In or gold is vapor-deposited, and the vapor-deposited film is formed into a predetermined pattern by a lift-off method or the like to form the electrode 5.

As a second embodiment, as shown in FIG. 5A, the anodic oxide film of the p-type HgCdTe substrate 1 is formed on the entire surface of the substrate.
After forming 13, the resist film 14 is formed on the anodic oxide film 13 in a region other than the region where the pn junction is to be formed, and the anodic oxide film is formed by using the resist film 14 as a mask and a mixed solution of hydrofluoric acid and ammonium fluoride. 13 is selectively etched and removed, and further the resist film 14 is removed. This state is shown in FIG. 5 (b).

Next, as shown in FIG. 5 (c), the HgCdTe substrate 1
Is heat-treated for a predetermined time to diffuse the Hg-rich layer 15 formed at the interface between the anodic oxide film 13 and the HgCdTe substrate 1 to form the n-type layer 11 as shown in FIG. Has a certain gradual carrier concentration gradient in the periphery of the planned formation region
A graded junction is formed, and then the anodic oxide film 13 is removed by etching.

Then, as shown in FIG. 5 (e), B ⁺ ions are ion-implanted in a region where a pn junction is to be formed as shown by an arrow using a resist film (not shown) as a mask, and further heat-treated and implanted. The ion implantation layer is formed on the n ⁺ layer 2.

As a third embodiment, as shown in FIG. 6A, the anodic oxide film 13 of the p-type HgCdTe substrate 1 is formed on the entire surface of the substrate 1.
After the formation, the resist film 14 is used as a mask to selectively etch the anodic oxide film 13 in the region other than the inter-pixel region with the above-described etching solution.

Then, as shown in FIG. 6 (b), the anodic oxide film is formed.
While leaving 13, the B ⁺ ions are ion-implanted into the pixel formation planned region as shown by the arrow to form the n ⁺ layer 2. A Hg rich layer 15 is formed on the boundary surface between the anodic oxide film 13 and the HgCdTe substrate 1.

Subsequently, as shown in FIG. 6C, the HgCdTe substrate 1
A surface protective film 3 of ZnS film is formed on the surface by vapor deposition. Next, as shown in FIG. 6 (d), the surface protection film 3 is provided with a connecting hole 4
After formation of In, gold or In is vapor-deposited, the vapor-deposited film is formed into a predetermined pattern by a lift-off method or the like, and the electrode 5 is provided to form a photodiode.

Then, as shown in FIG. 6E, the HgCdTe substrate 1 having the photodiode thus formed is heat-treated by controlling the heat treatment temperature and the heat treatment time to diffuse the Hg of the Hg rich layer 15 described above. Then, the n-type layer 11 is formed to form a photodetector having a predetermined optical signal amount and a predetermined crosstalk generation amount.

[0043]

As described above, according to the photodetector of the present invention and the manufacturing method thereof, the dark current generated in the n-type layer is the same as in the case of the conventional method, and the dark current It is possible to obtain a light-sensing element with less generation. Further, by forming the anodic oxide film between the pixels, the amount of crosstalk generated can be controlled to a predetermined value after the photodetector element is formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a plan view of a first embodiment of a photo-detecting element of the present invention.

FIG. 2 is a cross-sectional view and a plan view of a second embodiment of the photo-detecting element of the present invention.

FIG. 3 is a cross-sectional view and a plan view of a third embodiment of the photo-detecting element of the present invention.

FIG. 4 is a cross-sectional view showing the manufacturing method of the first embodiment of the photodetecting element of the present invention.

FIG. 5 is a cross-sectional view showing the manufacturing method of the second embodiment of the light-sensing element of the present invention.

FIG. 6 is a cross-sectional view showing the manufacturing method of the third embodiment of the photodetecting element of the present invention.

FIG. 7 is a concentration distribution diagram of an n-type layer HgCdTe substrate of the present invention.

8A and 8B are a cross-sectional view and a plan view showing a conventional method for manufacturing a photodetecting element.

FIG. 9 is an explanatory view showing the inconvenience of the conventional photodetector.

[Explanation of symbols]

1 HgCdTe Substrate 2 n ⁺ Layer 3 Surface Protective Film 4 Connection Hole 5 Electrode 11 n-type Layer 12 Ion Implantation Layer 13 Anodized Film 14 Resist Film 15 Hg Rich Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Watanabe 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (5)

[Claims] 1. A photodetection device comprising a one-conduction type semiconductor substrate (1) having a pixel pattern (2) consisting of a pn junction region, which is obtained by introducing impurities of a reverse-conduction type to the substrate in a predetermined pattern. , The impurity carrier concentration distribution of the pixel region (2) is
A photodetection element, characterized in that the central part of the n-junction region is made steep and the peripheral part of the pn-junction region is made gentle. 2. A peripheral portion of the pixel region (2) according to claim 1,
The conductivity type of the semiconductor substrate (1) whose width or depth can be controlled either in the central region between the pixel regions (2) or in the central region between the peripheral region of the pixel region (2) and the pixel region A photo-detecting element, which is provided with a reverse conductivity type layer (11) different from the above. 3. The reverse conductivity type layer (11) according to claim 2, comprising a diffusion layer in which impurities of reverse conductivity type are introduced into a semiconductor substrate, or an anodic oxide film (13) formed on the semiconductor substrate. A photo-detecting element, which is provided by being heat-treated. 4. A photo-sensing element is manufactured by introducing an impurity of a conductivity type opposite to that of a semiconductor substrate (1) of one conductivity type into a predetermined pattern and providing a pixel region (2) consisting of a pn junction region. In the method, in the peripheral area of the pixel area (2), the central area between the pixel areas (2), or the central area between the peripheral area of the pixel area (2) and the pixel area (2). A anodic oxide film (13) is formed on any region, and then the semiconductor substrate (1) is heat treated to form a mercury-rich layer (15) formed at the interface between the semiconductor substrate (1) and the anodic oxide film (13). Of the reverse conductivity type layer of the semiconductor substrate (1) by introducing mercury of the above into the semiconductor substrate (1) and filling the mercury holes of the semiconductor substrate (1) with the above mercury.
(11) is formed, and an impurity atom of a conductivity type opposite to that of the semiconductor substrate (1) is introduced into the central portion of the pixel region (2). 5. An impurity of opposite conductivity type to the semiconductor substrate (1) is introduced into a predetermined pattern in the one conductivity type semiconductor substrate (1),
In a method of manufacturing a photodetector by providing a pixel region (2) consisting of a pn junction region, an anodic oxide film (13) is formed in a central region between the pixel regions (2), and then the pixel region (2) is formed. A pixel region (2) is formed by introducing impurity atoms of the opposite conductivity type to the semiconductor substrate (1) in the central part of 2), and then a surface protective film (3) is formed on the semiconductor substrate (1). After forming the connection hole (4) in the surface protective film (3), the electrode (5)
To form a photo-sensing element, and then heat-treating the semiconductor substrate (1) on which the photo-sensing element is formed to form a mercury-rich layer formed at the interface between the semiconductor substrate (1) and the anodized film (13). The mercury in the layer (15) is introduced into the semiconductor substrate (1) so that the mercury vacancies in the semiconductor substrate (1) are removed from the mercury-rich layer.
Manufacture of a photo-detecting element characterized in that the semiconductor substrate (1) is filled with mercury of (15) to form a reverse-conduction type layer (11), and the photocurrent and crosstalk amount of the photo-detecting element can be controlled. Method.