JPH077830B2 - Solid-state image sensor for radiation detection - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a solid-state imaging device, and in particular, a device structure that suppresses background noise caused by unnecessary light and radiation is formed, and highly accurate radiation measurement is possible. The present invention relates to a solid-state image sensor for detecting radiation.

[Prior Art] A conventional solid-state image sensor mainly senses an electromagnetic wave wavelength region from ultraviolet light to infrared light, and basically, a light receiving region is not shielded, and other regions are low energy radiation. Even against it, it was shielded by a thin film of Al material or the like, which has a low shielding effect.

FIG. 2 is a cross-sectional view of a semiconductor chip showing an example of a conventional solid-state imaging device that mainly detects light from ultraviolet light to infrared light. An insulating oxide film 2 is formed on one main surface of a semiconductor substrate 1. , The polysilicon electrode 3 and the phosphorous glass layer 4 are sequentially formed, and the Al layer 6 is usually formed on the phosphorous glass layer 4 by deposition.
Was configured to be an opening. Conventional solid-state imaging devices that mainly sense light from ultraviolet light to infrared light generate signal charges when electromagnetic waves / charged particles enter, similar to the case when light enters, so electromagnetic waves / charged particles It can be used to detect and measure. It is desirable that the solid-state imaging device used for such radiation measurement does not sense light outside the measurement target. In radiation measurement, there is radiation called background radiation that comes from other than the sample to be measured. This may be due to the radioactivity contained in the detector or sample stage, that which is incident directly from an external radiation source or that is scattered by surrounding substances, and that which is caused by cosmic rays or other natural radiation. , Its energy distribution is wide, but the intensity of low-energy radiation is particularly strong.

[Problems to be Solved by the Invention] However, this background radiation becomes background noise when performing radiation measurement, and makes it difficult to detect radiation for measurement purposes. Therefore, in the solid-state image sensor for detecting radiation, the background noise caused by light and low-energy radiation that is not light-shielded like the conventional solid-state image sensor or unnecessary in the formation of a light-shielding thin film such as an Al material is suppressed. It was not possible to measure radiation with high precision. Also, when trying to shield low energy radiation of background radiation using Al material etc., there is a problem that the film thickness of the light shielding film becomes thick and the industrial productivity is poor, so far it has been suitable for radiation detection. No fixed image sensor has been obtained.

The present invention has been made in consideration of the conventional circumstances described above, and an object thereof is to provide a solid-state imaging device for radiation detection in which background noise caused by unnecessary light and low-energy radiation is suppressed. And

[Means for Solving Problems] According to the present invention, in a solid-state imaging device for radiation detection, a light receiving area is formed in a main surface of a semiconductor substrate, and a light receiving area and means for transferring signal charges to the outside are integrated. The solid-state imaging device for radiation detection is characterized in that the entire main surface is covered with a light-shielding film made of Pb material.

[Function] Since the light-shielding film has an element structure formed of Pb material, unnecessary low-energy radiation can be shielded with a thinner film thickness than that formed of conventional Al material and the light-receiving region is also shielded by Pb material. Since it is covered with a film, it is possible to prevent the incidence of light or the like.
Therefore, the absorption of light and low energy radiation that does not require measurement in the semiconductor substrate is suppressed, and the generation of charges is suppressed, so that background noise is suppressed and high-precision radiation measurement becomes possible.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a cross-sectional view of a semiconductor chip of a CCD image pickup device, showing an insulating oxide film 2, a CCD shift register transfer polysilicon electrode 3 and a phosphorus glass layer 4 on a radiation incident surface on a semiconductor substrate 1 on which an impurity region is formed.
Are sequentially formed, and a Pb layer 5 having a light-shielding effect and a large radiation-shielding effect is formed on the entire surface of the phosphorous glass layer 4 by adhesion. The Pb layer 5 of the present embodiment does not have an opening in the imaging region, blocks low-energy component radiation having particularly high intensity, out of the light outside the measurement target and the background radiation, and reduces background noise.

The effective thickness of the Pb layer 5 depends on the type and energy of the radiation to be measured and the energy spectrum of the background radiation. In other words, the effective thickness of the Pb layer 5 depends on the purpose of measurement as to which radiation is blocked up to what level of energy, and therefore cannot be uniquely determined here.

So, below, about some radiation energy,
An example of the effect of the Pb layer 5 as a radiation shielding film and the effect of shielding the radiation of the Al layer, which is conventionally used as a light shielding film, will be compared. Let t be the thicknesses of the Pb layer and the Al layer, respectively. The intensity and range of radiation is "Science chronology 1980 edition"
Calculated based on data from (Tokyo Observatory compilation).

First, γ rays will be described. _Let E _{γ be} the energy of γ rays. When γ-rays pass through a substance, the intensity of γ-rays decreases exponentially as the passage distance increases. Let I ₀ and I be the intensities of γ rays before and after passing through the Pb layer or Al layer, respectively, and I / I ₀ is the attenuation of γ rays due to passage through the Pb layer or Al layer, that is, the degree of shielding. Represents

When E _γ = 0.05 MeV and t = 10 μm, I / I ₀ is ₀ for the Pb layer.
6, 1.0 for Al layer, I / I ₀ is ₀ for Pb layer when E _γ = 0.02MeV and t = 10μm.
1, 1.0 for Al layer, and E / = ₀ for Pb layer when E _γ = 0.02 MeV and t = 5 μm.
3, 1.0 for Al layer.

Thus, for γ rays with E _γ <0.1 MeV, Pb of t / 10 μm
The layer has a greater shielding effect than the Al layer.

Next, β rays will be described. Let E _{β be} the energy of β rays. When β rays, that is, electrons pass through a substance, it is difficult to determine the average range as in the case of heavy charged particles because the absorption curve is blunt, so the intensity is usually extended by extending the steep part with a straight line. The distance that becomes 0 is defined as the practical electron range (referred to as Reff). The range of charged particles is inversely proportional to the electron concentration in the passing substance. The electron concentrations of ₈₂ Pb ²⁰⁷ and ₁₃ Al ²⁷ are 27 × 10 ²⁴ / cm ³ and 7.8 × 10 ²³ / cm ³ , respectively.

When E _β = 0.08 MeV, Reff is 10 μm for the Pb layer and 35 μm for the Al layer, and when E _β = 0.01 MeV, Reff is 2 μm for the Pb layer and 7.3 μm for the Al layer.

Next, α rays will be described. Let E _{α be} the energy of α rays. Like α rays, α rays are also charged particles, and the average range (denoted by R) is inversely proportional to the electron concentration in the passing substance.

When E _α = 1MeV, R is 0.8μm for Pb layer and 2.8 for Al layer
When E _α = 10 MeV, R is 14 μm for Pb layer and 50 for Al layer
μm.

Thus, the range of charged particles such as β rays and α rays is about 1 / 3.5 of that of Al in Pb, and the film thickness required to obtain the same shielding effect is about 1 / 3.5 of that of Pb. Than. Pb layer of t ~ 10 μm is E
There is a sufficient shielding effect for β rays of _β <0.1 MeV and α rays of E _α <10 MeV.

[Advantages of the Invention] As described above, according to the element structure of the present invention, light incident on the semiconductor substrate from the radiation incident surface is eliminated, and the film thickness is thinner than that formed by a conventional Al material or the like, which is unnecessary. Solids for radiation detection that can shield high-precision radiation measurement by shielding the low-energy radiation, and by suppressing the absorption and charge generation of these low-energy radiation that does not require measurement in the semiconductor substrate. An image sensor can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor chip showing an embodiment of the present invention, and FIG. 2 is a sectional view of a semiconductor chip showing an example of a conventional solid-state imaging device. 1 ... semiconductor substrate, 2 ... insulating oxide film 3 ... polysilicon electrode, 4 ... phosphorus glass layer 5 ... Pb layer, 6 ... Al layer 7 ... light receiving part

Claims (1)

[Claims] 1. A solid-state imaging device for radiation detection, comprising: a semiconductor substrate having a main surface on which a light-receiving region and means for transferring signal charges to the outside are integrated, and the entire main surface on which the light-receiving region is formed is made of Pb material. A solid-state imaging device for radiation detection, which is covered with the formed light-shielding film.