JPH02260468A - Infrared light detecting element - Google Patents

Abstract

PURPOSE:To reduce wavelength dependency of an effect due to a reflecting film and to improve detecting sensitivity in a wide wavelength range by forming the thickness of an insulating film in predetermined change. CONSTITUTION:A Schottky junction is formed of a P-type Si substrate 2, and a PtSi(platinum silicide) film 3 to compose an infrared light detector part. The thickness of an insulating film 5 on the detector part is formed irregularly with predetermined change. For example, the thickness of the film is changed between the maximum thickness and the minimum thickness respectively corresponding to infrared light wavelengths lambda and lambda2 to be detected. Thus, the wavelength dependency of the effect due to a reflecting film 6 is reduced, and detecting sensitivity of infrared light of wide wavelength range of lambda1 and lambda2 can be improved as a whole.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an infrared light detection element using, for example, a Schottky barrier diode, The present invention relates to an infrared light detection element having a reflective film on its surface.

[Prior art] Fig. 5 shows a conventional Schottky-type infrared light detection element 1.
0, in which 2 is a p-type Si substrate, 3 is a Pt5l (platinum silicide) film, and 4 is this Pt
A guard ring made of an n-type impurity layer formed to surround the Si film 3, 7 is a Si film for element isolation.
OxHs 6 is a reflective film made of At, 5° is, for example, S
This is an insulating film between the eyebrows made of i Os, S i O, and S ixNν.

An infrared light detection element l having such a configuration. When infrared light is incident on the substrate from the back side as shown by arrow A, the infrared light passes through the Si substrate 2 and reaches the PtSi film 3, forming a PtS
In the t-film 3, electron-hole pairs are generated. Among these holes, those with energy exceeding the Schottky barrier formed by the Pt Si film 3 and the Sl substrate 2 flow into the 81 substrate 2 and become photocurrent. The guard ring 4 has the function of alleviating electric field concentration at the edge portion and reducing leakage current.

In such an infrared light detection element I0, the above-mentioned reflection M6 is often formed in order to improve detection sensitivity.
This reflective film 6 reflects infrared light that has not been absorbed by the Pt Si film 3 and makes it enter the Pt Si film 3 again, thereby improving detection sensitivity.

FIG. 6 is a characteristic diagram showing the effect of the reflective film 6, and shows the ratio of photocurrent to wavelength λ of incident infrared light (Ir/io). Here, Ir is the photocurrent when the reflective film 6 is formed, and Io is the photocurrent when the reflective film 6 is not formed.

Due to the optical interference effect between the incident light and the reflected light, the photocurrent ratio (lr/Io) exhibits wavelength dependence and varies with wavelength, as shown in FIG.

Here, the refractive index of the interlayer insulating film 5° is nl, the film thickness is t,
If N is an integer, infrared light with a wavelength of λ=(4nt)/(2N+1) is reflected! Although the detection sensitivity can be improved by I6, the detection sensitivity cannot be improved by the reflective film 6 with infrared light having a wavelength of λ=2nt/N.

For example, in FIG. 6, in the case of infrared light of λ = 4 nt, the detection sensitivity can be expected to be improved by the reflective film 6, but in the case of 1 m-2 nt of infrared light, the detection sensitivity is expected to be improved due to the reflection film 6. This means that no improvement in detection sensitivity can be expected.

For this reason, conventionally, the refractive index n and the film thickness t of the interlayer insulating film 5° are set so that the peak occurs at the wavelength of the infrared light to be detected.

[Problems to be Solved by the Invention] However, in conventional infrared light detection elements, the effect of the reflective film is wavelength dependent, so the detection sensitivity is not affected by any of the wavelengths λ and λ mentioned above. It was not possible to improve.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to reduce the wavelength dependence of the effect of a reflective film and to improve detection sensitivity over a wide wavelength range.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention includes an infrared light detection section for photoelectrically converting infrared light on the front side of a semiconductor substrate, and an infrared light detection section on the infrared light detection section. In the infrared light detection element that detects infrared light incident from the back side of the semiconductor substrate, the infrared light detection element includes an insulating film formed on the insulating film and a reflective film formed on the insulating film. The film thickness is formed to have a required change in the region corresponding to the infrared light detection section.

[Function] According to the above configuration, the thickness of the insulating film on the infrared light detection section is
Since the film is formed non-uniformly with required changes, for example, the film thickness can be varied between the maximum film thickness and the minimum film thickness corresponding to the wavelengths λ1 and λ of the infrared light to be detected, respectively. Accordingly, the wavelength dependence of the effect of the reflective film can be reduced, and the detection sensitivity of infrared light in a wide wavelength range covering λ and λ can be improved overall.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. T is a sectional view of a Schottky-type infrared light detection element according to an embodiment of the present invention, and parts corresponding to the conventional example in FIG. 5 are given the same reference numerals.

This infrared light detection element l has a Pt5i (platinum silicide) film 3 formed on the surface side of a p-type Si substrate 2, and an n-type impurity layer surrounding the PtSi film 3. A guard ring 4 is formed. A Schottky junction is formed by the p-type Si substrate 2 and the Pt Si film 3 to constitute an infrared light detection section.

On this infrared light detection section, for example, S
Interlayer insulating film 5 made of iO*, SiO, 5izN
Further, a reflective film 6 made of Al is formed on this interlayer insulating film 5L to reflect infrared light and increase detection sensitivity. Note that 7 is sio for element isolation,
*It is.

In the infrared light detection element 1 of this embodiment, in order to improve the detection sensitivity over a wide wavelength range by the reflection 116, the thickness of the glabella insulating film 5 is set to the infrared light detection part. It is formed to have the required changes in the corresponding areas. The maximum and minimum thicknesses of this interlayer insulating film 5 are selected as follows.

That is, as explained based on FIG.
The photocurrent ratio (Ir/Io) showing the improvement in detection sensitivity due to
shows wavelength dependence, and when the refractive index of the interlayer insulating film 5 is nl, its film thickness is t, and N is an integer, for infrared light with a wavelength of λ=(4nt)/(2N+1), The improvement in detection sensitivity due to the reflective film 6 is maximized.

Therefore, for example, from λ1 in FIG. 6 to λ, (=λ.

/2) In order to improve the detection sensitivity over the wavelength range, the maximum film thickness t and the minimum film thickness t of the interlayer insulating film 5
, for example, l l=λ1/4n, Lx;λ,/4n
and may be changed between ti and [,.

As a result, infrared light with a wavelength of λ1 is transmitted to the maximum film thickness j+
The detection sensitivity is improved the most by the part with the minimum film thickness t, for infrared light with a wavelength of λ, and the detection sensitivity is improved the most by the part with the minimum film thickness t, and the infrared light with a wavelength of λ, ~λ , t, ~t
Detection sensitivity is improved depending on the thickness of the film.

Therefore, by varying the thickness of the interlayer insulating film between 1+ and t in the region corresponding to the infrared light detection section, as shown in the characteristic diagram of FIG.
The detection sensitivity can be improved overall over the wavelength range from λ to λμ = λI/2).

Formation of the glabellar insulating film 5 having a thickness varied in this manner is performed, for example, by photo-etching. That is, the portion having the maximum film thickness t may be masked with a resist, and if the interlayer insulating film is 5tO2, it may be etched to the minimum film thickness using an HF solution. Note that the reflective film 6 is formed with a uniform thickness by sputtering, as in the prior art.

When infrared light enters the infrared light detection element 1 having the above configuration from the back side as shown by the arrow A, the infrared light passes through the Si substrate 2 and passes through the Pt5t film 3. Finally,
In the PTSI film 3, electron-hole pairs are generated.

Among these holes, those with energy exceeding the Schottky barrier formed by the Pt St film 3 and the Si substrate 2 flow into the Si substrate 2 and become photocurrent. The guard ring 4 has the function of alleviating electric field concentration at the edge portion and reducing leakage current. The reflective film 6 is a PTST film 3
The infrared light that was not absorbed by the ptSi film 3 is reflected again.
This improves detection sensitivity.

Infrared light detection element of this example! Now, as described above, the thickness of the glabellar insulating film 5 is from t to t.

Since it is formed with the necessary changes between
As shown in the characteristic diagram of FIG. 2 corresponding to the figure, the wavelength dependence of the effect of the reflective film 6 is reduced, and the detection sensitivity is improved overall over a wide wavelength range from λ to λ. I can do it.

3 and 4 are cross-sectional views of other embodiments of the present invention, and parts corresponding to the embodiments described above are given the same reference numerals.

In these embodiments, the interlayer insulating film 5 is a first interlayer insulating film 5. with a uniform thickness. and a second interlayer insulating film 5 patterned by photoetching,
The overall film thickness is changed from t to t.

The interlayer insulating film shown in FIG. 3 is the first interlayer insulating film 5.
For example, a 5ins film with a uniform thickness is formed, and then a N) film is deposited on Si, and a 5ixN4 film is formed by photoetching using the required resist pattern as a mask, for example, by plasma etching using Freon gas. By patterning, the second interlayer insulating film 5
．． is formed.

The glabellar insulating film 5 shown in FIG. 4 is a second glabellar insulating film 115 patterned by photo-etching.
After forming 4, a first interlayer insulating film 5° is uniformly formed.
obtained by

Although in the above-mentioned embodiment, the infrared light detection section is of the Schottky barrier type, the present invention is not limited to this, and the present invention can be similarly applied to one using a compound semiconductor such as HgCdTe. It can be applied to

[Effects of the Invention] As described above, according to the present invention, since the insulating film is formed with the required change in film thickness, the wavelength dependence of the effect of the reflective film can be reduced. ,
It becomes possible to improve detection sensitivity over a wide wavelength range.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between the wavelength of incident infrared light and the ratio of photocurrent to explain the effects of the present invention, and FIG. Fig. 4 is a sectional view of another embodiment of the present invention, Fig. 5 is a sectional view of a conventional example, and Fig. 6 is a sectional view of another embodiment of the present invention.
The figure is a characteristic diagram showing the relationship between the wavelength of incident infrared light and the ratio of photocurrent in a conventional example. 1, la, 1b, 1. ---Infrared light detection element, 2-
8 L substrate, 3...Pt5i (platinum silicide) film,
5゜58...Interlayer insulating film, 6...Reflection film.

Claims (1)

[Claims] (1) An infrared light detection section that photoelectrically converts infrared light, an insulating film formed on the infrared light detection section, and a reflective film formed on this insulating film on the front side of the semiconductor substrate. In the infrared light detection element for detecting infrared light incident from the back side of the semiconductor substrate, the insulating film has a thickness that changes as required in a region corresponding to the infrared light detection section. An infrared light detection element characterized in that it is formed to have a