JPH0473313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photodetecting element using a Schottky barrier diode.

In general, Schottky barrier diodes are often used as photodetecting elements, especially in the infrared region, and can also be used to form one-dimensional or two-dimensional imaging elements using silicon LSI technology.

FIG. 1 is a schematic cross-sectional view showing a conventional Schottky type photodetecting element. In the same figure, 1 is several Ωcm
2 is a metal side electrode of a Schottky junction formed by depositing a metal such as platinum silicide, gold, or a metal silicide on this P-type silicon substrate 1, and 3 is the P-type silicon substrate. This is a Schottky junction formed at the interface between No. 1 and this metal side electrode.

Next, the operation of the Schottky type photodetecting element having the above configuration will be explained. First, when light in the infrared region is incident from either the silicon substrate 1 side or the metal side electrode 2 side, electron-hole pairs are formed in the metal side electrode. Of these holes, those with energy exceeding the Schottky barrier flow toward the silicon substrate 1 side and flow as a photocurrent. The magnitude of this photocurrent is determined by the area of the element (area of the shot key barrier 3), quantum efficiency, and amount of incident light. However, the amount of incident light is the amount of light incident on the shot key barrier 3, excluding reflections from the silicon surface or the metal side electrode surface. The photocurrent is proportional to the area of the shot key barrier 3, but in one-dimensional and two-dimensional image sensors, the area for one pixel is limited by the overall dimensions of the image sensor, so the photocurrent per unit area is It needs to be bigger. For this purpose, it is important to increase the quantum efficiency or the amount of incident light.

However, in conventional Schottky type photodetecting elements, when light is incident from the silicon substrate side, extra adhesive is required around the element when adhering the image sensor to a package or frame, which reduces the element size. Enlarge. In addition, when testing the device, since the back side of the device formation surface is the incident surface, it is difficult to handle. Furthermore, when light is incident from the metal electrode 2 side, since the incident surface is metal, there is a drawback that reflection on the surface is large and the amount of light reaching the Schottky barrier 3 is reduced.

The purpose of the present invention is to facilitate the handling by allowing light to enter from the element formation side, eliminate the need for extra glue, and form first and second shot key barriers to form the photodetector element. To provide a Schottky-type photodetecting element that is easy to handle and has high performance by increasing the effective area and reducing light reflection on the incident surface to increase the photocurrent per unit area. It is.

In order to achieve this purpose, this invention
Polycrystalline or single crystal silicon is formed on the metal side electrode of the Schottky junction, and between this polycrystalline or single crystal silicon film and the metal side electrode,
A second Schottky junction is formed and an anti-reflection film is formed on the polycrystalline or single crystal silicon film, and will be described in detail below using examples.

FIG. 2 is a schematic sectional view showing an embodiment of the Schottky type photodetecting element according to the present invention. In the same figure, reference numeral 6 is formed on the metal side electrode 2 by a sputtering method that can be formed at a relatively low temperature, and doped with a P-type impurity such as boron by ion implantation or the like to form a P-type silicon substrate 1. 7 is a second shot key barrier formed at the interface between the metal side electrode 2 and this polycrystalline silicon film 6, and 8 is the polycrystalline silicon film having an impurity concentration similar to that of the polycrystalline silicon film. This is a silicon oxide film (SiO) formed on a film using a sputtering method.

Next, the operation of the Schottky type photodetecting element having the above configuration will be explained. First, both the first Schottky junction 3 and the second Schottky junction 7 are reverse biased. The light enters from the side of the second Schottky junction 7. The light passes through the antireflection film 8 and the polycrystalline silicon film 6 while minimizing loss due to reflection, forming electron-hole pairs in the metal electrode 2. Since the holes formed by this incident light move in all directions, the holes that flow over the first shot-key barrier 3 as well as the holes that flow over the second shot-key barrier 7 Holes are also present. The total photocurrent I is therefore the sum of the current I 1 flowing through the first shot key barrier ₃ and the current I ₂ flowing through the second shot key barrier 7 . On the other hand, since the first shot key barrier 3 and the second shot key barrier 7 are integrated in the vertical direction, the device area does not increase. Furthermore, since light can be incident from the element forming surface side, handling is easy, and by forming an antireflection film on polycrystalline silicon, loss due to reflection of incident light can be prevented. When this anti-reflection film is a single layer film, as is well known, refractive index: n=√ _{0 1} film thickness: dλ/4n. Here, n ₀ is the refractive index of vacuum, n ₁ is the refractive index of polycrystalline silicon, and λ is the wavelength of incident light. In a Schottky junction between silicon and gold (Au) or platinum silicide, the Schottky barrier height determines the cutoff wavelength for photodetection, which is 4.92 μm for gold and 4.47 μm for platinum silicide. Therefore, Schottky type photodetecting elements are commonly used for detecting infrared rays in the 3-5 μm band, which is called the atmospheric window. If λ
= Considering incident light with a wavelength of 4 μm, n = 1.85, d =
It becomes 0.54μm. A substance that satisfies this requirement is
Examples include silicon oxide (SiO) and silicon nitride (SiN).
Further, this antireflection film may be a multilayer film, for example, 2
As a layer film, the lower layer is TiO ₂ (n=2.48, d=
0.40μm) MgF ₂ (n=1.38, d=0.73μm) in the upper layer,
As a three-layer film, TiO ₂ (n=2.48, d=
0.40), CaO (n=1.84, d=0.54), MgF ₂ (n=
1.38, d=0.73).

Further, the crystallinity of the polycrystalline silicon 6 can be further improved by laser annealing, and detection sensitivity can be improved. It goes without saying that by arranging the photodetecting elements constructed in this way in a one-dimensional or two-dimensional matrix and combining them with charge-coupled devices or the like, an efficient imaging device can be produced.

As described above in detail, according to the shot key type photodetecting element according to the present invention, by creating the first shot key barrier and the second shot key barrier, the effective area of the element can be increased. However, by forming an antireflection film on silicon, it is possible to prevent loss due to reflection when light is incident on the element surface, and to provide a Schottky type photodetector element that is easy to handle and has high detection sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a conventional Schottky type photodetecting element, and FIG. 2 is a schematic sectional view showing an embodiment of the Schottky type photodetecting element according to the present invention. 1...P-type silicon substrate, 2...metal side electrode, 3...
shot key barrier, 4... guard ring (N type region), 6... polycrystalline silicon film, 7... second shot key barrier, 8... antireflection film. Note that the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a photodetecting element that uses a Schottky junction formed by joining metal or metal silicide and silicon for light detection, a polycrystalline silicon or single crystal silicon film is formed on the metal side electrode of the Schottky junction. , a second shot junction is formed between the polycrystalline or single-crystalline silicon film and the metal electrode, and a light antireflection film is provided on the polycrystalline or single-crystalline silicon film. Schottky type photodetector. 2 Anti-reflection film has a refractive index of 1.8 to 1.9 and a film thickness of 0.04 μm to
The Schottky type photodetecting element according to claim 1, characterized in that it is a single layer film of 0.68 μm. 3 The antireflection film has a lower layer with a refractive index of 2.45 to 2.52 and a film thickness of 0.35 to 0.50 μm, and an upper layer with a refractive index of 1.30 to 1.45 and a film thickness.
The Schottky type photodetecting element according to claim 1, characterized in that it is a two-layer film with a thickness of 0.65 to 0.80 μm.