JPH07335852A - Manufacture of photoelectric conversion element and solid-state image sensing element - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method of a photoelectric conversion element having sensitivity to X-rays and ultraviolet rays. CONSTITUTION:In the manufacturing process of a photoelectric conversion element, a light receiving part diffusion region 13a of a first conducting type for performing photoelectric conversion is formed on a semiconductor substrate 11 in a process (a), and an impurity layer 12 of a second conducting type with which the surface of the light receiving part diffusion region is covered is stuck and formed on the light receiving part diffusion region in a process (b). Thereby, the impurity layer 12 of a second conducting type is thinly formed as compared with the conventional technique.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a photoelectric conversion element and a solid-state image pickup element including a plurality of photoelectric conversion elements manufactured by the manufacturing method.

[0002]

2. Description of the Related Art With the progress of semiconductor technology, a one-dimensional solid-state image pickup device for detecting light or recording an image and a two-dimensional solid-state image pickup device have been developed and are now put to practical use in the visible light region. The solid-state image pickup device detects a one-dimensional or two-dimensional image by a light receiving section in which photoelectric conversion elements are arranged,
The output is transferred and read in series.

In recent years, in order to obtain a light intensity distribution as an image, a plurality of photoelectric conversion elements are arranged in rows or in a vertical / horizontal matrix, and one-dimensional or means provided with means for reading out signal charges. A two-dimensional solid-state image pickup device has been developed and used for industrial purposes to consumer use for capturing a visible image. FIG. 6 shows a conceptual diagram of an interline transfer CCD as an example of a two-dimensional solid-state image sensor.

In the interline transfer CCD, photoelectric conversion elements 121 are arranged in a vertical / horizontal matrix, and a charge coupled element which is a vertical signal charge transfer means 122 and a horizontal signal charge transfer means 123, and a photoelectric conversion element. Conversion element 12
1 and the like (not shown) for controlling the readout of the signal charges from the vertical charge coupled device.

Here, FIG. 7 shows an example of a photoelectric conversion element used for detecting the presence or absence of light and its intensity. In FIG. 7, the photoelectric conversion element uses, for example, a P-type silicon substrate as a semiconductor substrate 61, and a P-type diffusion region 62 having a high P-type impurity concentration and LOCOS (Local oxid) for element isolation.
of silicon, a thick silicon oxide film 68 is formed, and then N-type impurities are diffused in the light receiving portion diffusion region 63 where photoelectric conversion is performed in the photoelectric conversion portion 66. Thereafter, the light receiving portion diffusion region 63 is covered with a silicon oxide film 68a, and metal wirings (64, 67) for reading out signal charges are formed.
It was created by forming.

By the way, the characteristics of the solid-state image sensor, especially S
In order to improve the / N (Sampling / Noise) ratio, it is necessary to reduce the dark current that becomes noise. This is for the following reason. An interface level exists on the surface of the photoelectric conversion portion, that is, the interface between the silicon on the silicon substrate side and the silicon oxide film, and a current is generated through this interface level. This current is a current that occurs when there is no incident light and is called a dark current. If the dark current varies among the elements, unevenness in the image occurs, which is one of the causes of deteriorating the S / N ratio. Furthermore, it has been a factor of narrowing the dynamic range.

Therefore, in order to eliminate such an influence, for example, a photoelectric conversion element called a so-called embedded photodiode having a structure as shown in FIG. 8 is adopted. That is, N-type impurities are diffused in the P-type silicon substrate 71 to form the light-receiving part diffusion region 73 of the photoelectric conversion part 7,
A P-type diffusion layer 71 having a conductivity type opposite to that of the light receiving portion diffusion region 73 is formed on the surface thereof by ion implantation and annealing (heat treatment for recovering crystal defects caused by ion implantation). In FIG. 8, it is connected to the diffusion layer 75 for element isolation, but only the place where the diffusion depth is shallow is used as the P-type diffusion layer 71. Here, the P-type diffusion layer 71 can shield a region on the surface of the photoelectric conversion unit where the recombination rate is high. As described above, it is possible to manufacture a photoelectric conversion element and a solid-state image pickup element that are sufficiently practical in the visible light region.

[0008]

However, the detection and imaging of low-energy X-rays called soft X-rays in the ultraviolet region and the X-ray region, especially in the X-ray region, are performed by using the semiconductor photoelectric conversion element or the photoelectric conversion device as described above. There is a problem that the solid-state imaging device including the conversion device does not have sufficient sensitivity, and for example, detection or imaging of X-rays having a wavelength of 30 to 50Å is almost impossible.

This is because the P-type diffusion layer 71 having a conductivity type opposite to that of the light-receiving portion diffusion region 73 formed by the conventional manufacturing method is formed by ion implantation in which impurity ions penetrate deeply, so that for X-rays and ultraviolet rays. This is because it is too thick to penetrate it. In such an ion implantation / annealing method which has been conventionally used, the impurity layer is reduced to 0.
The limit was to form a thin film of about 2 to 0.3 μm.

Here, FIG. 5 shows how the X-rays irradiated on the silicon substrate are absorbed. In this diagram, the horizontal axis is the depth from the silicon surface, and the vertical axis is the wavelength λ = 4.
It is the absorption ratio for X-rays of 5Å, the ratio of X-rays absorbed by the width of the horizontal axis is shown by the prism, and the broken line shows the total amount of light absorbed from the silicon surface to its depth.

As is clear from FIG. 5, at a depth of 0.2 μm, which is the limit of the conventional method, the X-rays are absorbed by almost 90%. Therefore, in a photoelectric conversion element in which an impurity diffusion layer of a conductivity type opposite to that of the light receiving portion diffusion region is formed in the upper layer with such a thickness, only about 10% of X-rays can reach the light receiving portion diffusion region.

Further, as shown in FIG. 8, a silicon oxide film 78 is usually formed on the light receiving portion diffusion region 73 to be thicker than the impurity diffusion layer 71 having a conductivity type opposite to that of the light receiving portion diffusion region 73. X-ray absorption also occurs in this silicon oxide film 78. For example, the absorption length of the silicon oxide film is 3.4 × 10 ⁻⁵ cm for a wavelength of 45 Å X-ray, and the absorption length of silicon is 1.2 × 10 ⁻⁵ cm. Therefore, it is more easily absorbed in the silicon oxide film than in silicon. As described above, in the conventional photoelectric conversion element, almost no X-ray can reach the light receiving portion diffusion region, and it is impossible to photoelectrically change the X-ray.

Regarding the sensitivity to ultraviolet rays, for example, when the silicon substrate is irradiated with ultraviolet rays having a wavelength of 0.365 μm, the amount of light is attenuated to 1/100 at a depth of 0.050 μm from the surface. Therefore, in the prior art, even if the thickness of the impurity layer of the second conductivity type is as thin as about 0.2 μm, it is almost impossible for ultraviolet rays to reach the light receiving portion diffusion region. The photoelectric conversion device cannot detect ultraviolet rays or take an image.

In view of the above problems, the main object of the present invention is to obtain a method for manufacturing a photoelectric conversion element having sensitivity to X-rays and ultraviolet rays. Another object of the present invention is to obtain a method for manufacturing a photoelectric conversion element capable of controlling the thickness of an impurity diffusion layer having a conductivity type opposite to that of the light receiving portion diffusion region. Further, the present invention is
An object of the present invention is to obtain a solid-state imaging device having pixels that are photoelectric conversion elements having sensitivity to X-rays and ultraviolet rays.

[0015]

In order to achieve the above object, in the method of manufacturing a photoelectric conversion element according to the present invention, the first method for performing photoelectric conversion on a semiconductor substrate is provided.
A method of manufacturing a photoelectric conversion element, which includes a step a of forming a conductive type light receiving portion diffusion region and a step b of forming a second conductive type impurity layer on the light receiving portion diffusion region so as to cover the surface of the light receiving portion diffusion region. In the step b, the step b includes a step of forming the second conductivity type impurity layer on the surface of the light receiving portion diffusion region by deposition.

According to a second aspect of the present invention, there is provided a method of manufacturing a photoelectric conversion element according to the first aspect, wherein in the step b, the impurity layer of the second conductivity type is used. The thickness is 0.1 μm or less.

Further, in the method for manufacturing a photoelectric conversion element according to the invention described in claim 3, in the method for manufacturing the photoelectric conversion element according to claim 1, in the step b, the impurity layer of the second conductivity type is used. The thickness is 0.01 μm or less.

Further, in the method of manufacturing a photoelectric conversion element according to the invention described in claim 4, in the method of manufacturing the photoelectric conversion element according to claim 1 or 2, the surface of the impurity layer of the second conductivity type The method further includes the step c of forming a silicon oxide film layer having a thickness of 0.01 μm or less.

Furthermore, in the method for manufacturing a photoelectric conversion element according to the invention described in claim 5, in the method for manufacturing a photoelectric conversion element according to claim 1 or claim 2, claim 3, or claim 4, Before the step b, after forming the first conductive type light receiving part diffusion region in the step a, a photoelectric conversion element structure such as an insulating layer, an electrode, a metal wiring layer, a silicon oxide film layer is formed on the semiconductor substrate. A step of forming and removing an upper layer within a predetermined range of the first-conductivity-type light receiving portion diffusion region,
And a step of exposing the surface of the light receiving portion diffusion region.

Further, in the solid-state image pickup device according to the invention of claim 6, the first conductivity type light receiving part diffusion region provided on the semiconductor substrate and the second conductivity type covering the surface of the light receiving part diffusion region. In the solid-state imaging device having a photoelectric conversion element having the impurity layer of 1. as a pixel, the second conductivity type impurity layer is formed on the first conductivity type light receiving portion diffusion region with a thickness of 0.1 μm or less. It is what

[0021]

According to the first aspect of the present invention, in the step a, a light receiving portion diffusion region of the first conductivity type for performing photoelectric conversion is formed, and in the step b, the light receiving portion is formed on the light receiving portion diffusion region. A second conductivity type impurity layer covering the surface of the diffusion region is formed by deposition. Therefore, the second conductivity type impurity layer can be formed to have an arbitrary thickness. For example, MBE (Molecular, Beam E
pitaxy: line-of-sight epitaxial growth method) and the like, the impurity concentration is 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm 2.
² found that a thin film impurity layer can be formed on the light receiving portion diffusion region in the range of 0.2 μm to 0.005 μm.

This makes it possible to control the film thickness of the second-conductivity-type impurity layer so that the X-rays and the ultraviolet rays can be photoelectrically converted so that they can reach the light receiving portion diffusion region. . Therefore, according to the manufacturing method of the present invention, X
It is possible to obtain a photoelectric conversion element that has sensitivity to rays and ultraviolet rays and can detect these. Moreover, since the impurity layer of the second conductivity type is formed by deposition, the impurity concentration distribution can be changed steeply, so that an ideal step junction can be approximated, and the depletion layer at the junction has the second conductivity type. Almost does not spread to the impurity layer side. Therefore, also from this point, the thickness of the second conductivity type impurity layer can be made as thin as possible.

In forming the second-conductivity-type impurity layer, specific values such as the impurity concentration and the thickness of the impurity layer can be set to optimum conditions depending on the wavelength of the target light source. is there. Therefore, the second step in step b
When the conductive type impurity layer is formed by deposition to have a thickness of 0.1 μm or less as described in claim 2, it becomes possible to manufacture a photoelectric conversion element having sufficient sensitivity to X-rays.
This can be seen from the relationship between the silicon substrate depth and the X-ray absorption ratio shown in FIG.
Å) is transparent. Therefore, if 40% or more of incident X-rays, especially soft X-rays, which were difficult to detect, can be detected, the photoelectric conversion element for X-rays is more effective than ever before.

Further, regarding the production of the photoelectric conversion element for ultraviolet rays, when the film thickness of the impurity layer of the second conductivity type is set to about 0.01 μm, 40% of the incident ultraviolet ray amount is transmitted, so that the third aspect of the present invention is described. As described above, if the film thickness of the second conductivity type impurity layer formed in step b is 0.01 μm or less, the sensitivity is sufficient as compared with the conventional case, the dark current is small, and the characteristic variation is small, and the ultraviolet rays are small. An effective photoelectric conversion element can be obtained.

As described above, the lower limit of the film thickness of the second-conductivity-type impurity layer for both X-rays and ultraviolet rays is such that the region where the recombination rate is high on the surface of the photoelectric conversion portion can be shielded. do it.

When a silicon oxide film layer is formed as a protective film on the surface of the second conductivity type impurity layer, the film thickness is 0.01 μm in step c as described in claim 4.
It is formed as follows. This is because, as described above, since the silicon oxide film also absorbs X-rays, the absorption of X-rays by the silicon oxide film is caused by the entire upper layer of the first-conductivity-type light receiving section diffusion region (second-conductivity-type impurity layer). And the proportion of X-ray absorption by the silicon oxide film) is small, and the X-rays of these upper layers as a whole are thin enough to reach the light receiving portion diffusion region by sufficient photoelectric conversion. To control. Of course, it is necessary to make this silicon oxide film as thin as possible,
Further, in consideration of X-ray absorption in the silicon oxide film, the film thickness of the second-conductivity-type impurity layer formed in the step b may be set thin in advance.

In the photoelectric conversion element for ultraviolet rays, it is desirable to control the thickness so that the silicon oxide film functions as an antireflection film. This is because, when used for ultraviolet rays, unless an antireflection film is provided on the semiconductor surface, reflection occurs on the semiconductor surface and the amount of signal light entering the semiconductor substrate such as silicon decreases.

The impurity layer of the second conductivity type may be formed as described in claim 5.
As described above, after forming the first-conductivity-type light receiving portion diffusion region in step a, an element forming portion such as an insulating layer, an electrode, or a metal wiring layer, a light shielding layer, a silicon oxide film layer is formed on the semiconductor substrate. Then, the stacked layer of the oxide film or the like on the first-conductivity-type light receiving portion diffusion region is removed to expose the surface of the light receiving portion diffusion region within a predetermined range, and is formed on the exposed surface. By doing so, it becomes easier to control the film thickness of the second conductivity type impurity layer.

This is because, in the process of manufacturing a photoelectric conversion element, an electrode layer, a light-shielding layer, and a metal wiring via an insulating layer are formed on a semiconductor substrate on which a light receiving portion diffusion region of the first conductivity type is formed below the surface. There are steps involving heating, such as formation of layers and the like, and further formation of a silicon oxide film layer thereabove. However, if these steps are performed after the second conductivity type impurity layer is formed,
This is because the influence of heating extends to the second-conductivity-type impurity layer, and the impurity layer formed thinly is spread by heating.

Therefore, as described above, after the process involving heating required for manufacturing the photoelectric conversion element is first completed, the surface of the light receiving portion diffusion region in the range where the second conductivity type impurity layer is to be formed is exposed. To remove the upper layer,
When the conductive type impurity layer is formed, it is not necessary to consider the spread of the impurity layer due to the influence of heating, and the film thickness control is simple. In the formation of the second-conductivity-type impurity layer in the step b, if the impurity layer is stacked on the peripheral portion other than the necessary area, the unnecessary portion is removed by an etching technique after the step b. May be further provided.

Further, according to the sixth aspect, the impurity layer of the second conductivity type is formed on the light-receiving part diffusion region of the first conductivity type.
If a solid-state image sensor is configured by using a photoelectric conversion element formed to have a thickness of 1 μm or less as a pixel, the solid-state image sensor can be used to detect and image X-rays that could hardly be detected in the past. realizable. Further, if the second conductivity type is made up of a photoelectric conversion element having a thickness of 0.01 μm or less, a solid-state image pickup element that is particularly effective against ultraviolet rays can be obtained.

[0032]

EXAMPLES The present invention will be described in detail below with reference to examples. (Embodiment 1) As a first embodiment of the present invention, a method of manufacturing a photoelectric conversion element of an interline transfer type CCD solid-state image pickup element for X-ray in which an impurity layer of the second conductivity type is formed by MEB will be described. The CCD solid-state image sensor manufactured in the present embodiment has a vertical charge transfer path (vertical CC) that shields the signal charges converted / accumulated by the photoelectric conversion unit according to incident X-rays from the X-rays.
D), and the signal charges transferred from the vertical CCD are sequentially read. FIG. 1 is a sectional view showing a part of a photoelectric conversion part of a CCD solid-state image pickup device and a vertical CCD.

First, below the surface of the P-type silicon substrate 11,
P-type impurity diffusion region 15 and LO for element isolation
A thick silicon oxide film was formed by COS oxidation. Next, the N-type impurity was diffused by ion implantation to form the light receiving portion diffusion region 13. Here, as the N-type impurity, A
Using s (arsenic), ion implantation was performed under the condition of a dose amount of 1 × 10 ¹² / cm ² . Further, the diffusion region 14 of the vertical CCD made of N-type impurities was also formed.

After that, a polycrystalline silicon layer was formed on the entire surface of the silicon substrate 11 via an insulating film and patterned to form a CCD electrode 16. Furthermore, C
VD (Chemical Vapor Deposition)
Then, a silicon oxide film 18a is formed, a light-shielding layer is formed on the vertical CCD region by a sputtering method, and the light-shielding portion 17 is formed by patterning. A silicon oxide film 18b was formed on the uppermost layer by CVD (FIG. 1).
(A)). The above operation is the same as the conventional method for manufacturing a visible light image pickup device, except that the impurity layer of the opposite conductivity type is not formed on the light-receiving diffusion region 13.

Next, the surface of the light receiving diffusion region 13 was exposed by removing the silicon oxide film (18a, 18b) on the light receiving diffusion region 13 by a photolithographic etching technique (FIG. 1B). This silicon oxide film (18a, 1
8b) is etched, in order to fix the potential of the P-type impurity layer 12 having a conductivity type opposite to that of the light receiving portion diffusion region 13, which is formed thereafter, the light emitting portion diffusion region 13 and the element isolation diffusion region 15 are formed together. Part 15a is exposed.

After that, a P-type impurity film 51 was deposited on the entire surface of the silicon substrate including the exposed surface of the light-receiving diffusion region 13. Molecular beam epitaxial growth (MBE) was used as the deposition method. This is to place a silicon substrate in a high vacuum, heat the separately provided silicon with an electron beam to evaporate the silicon, and deposit silicon atoms on the entire surface of the silicon substrate to crystallize the silicon. In the present embodiment, when silicon is deposited, impurities are simultaneously deposited at an impurity concentration of 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ² to deposit a P-type impurity having a thickness of about 0.05 μm. The film 10 was formed (FIG. 1 (c)).

Further, the impurity diffusion film 10 other than the photoelectric conversion region 1 is removed by a photolithographic etching technique or a lift-off technique to form a desired region on the light receiving region diffusion region 13 with a conductivity type opposite to that of the light receiving region diffusion region 13. Then, the P-type impurity layer 12 was formed. After that, the P-type impurity layer 12
15 between the light receiving part diffusion region 13 and the element isolation region 15
In order to improve the bonding characteristics between a, 4 in a nitrogen atmosphere
Heat treatment was performed at a relatively low temperature of 50 ° C. for 30 minutes. Further, a silicon oxide film layer 19 having a thickness of 0.01 μm is formed on the surface of the P-type impurity region 12 by CVD (FIG. 1).
(D)).

In the photoelectric conversion part 1 of the solid-state image pickup device of the present embodiment manufactured by the above steps, the surface of the light receiving part diffusion region 13 in which the interface state causing the dark current exists is of the opposite conductivity type. Since the impurity layer 12 is covered with the impurity layer 12 and the impurity layer 12 has the substrate potential, the dark current is suppressed from flowing into the light receiving portion diffusion region 13. Therefore, the dark current suppressing effect of the photoelectric conversion portion of the device according to the present embodiment will be described below with reference to FIG.

FIG. 2 shows the potential distribution in the section AB of FIG. 1D, where the horizontal axis represents the depth direction and the vertical axis represents the potential depth. As can be seen from FIG. 2, the P-type impurity layer 12 is set to the potential of the semiconductor substrate via the element isolation diffusion region 15 in the immediate vicinity of the surface of the semiconductor substrate. The P-type impurity layer 12 is not depleted. The light receiving diffusion region 13 and the semiconductor substrate are reverse biased, and the light receiving diffusion region 13 is completely depleted. Therefore, if there is an interface order on the surface of the P-type impurity layer 12 and a dark current is generated due to this interface order, the holes are recombined with the holes in the P-type impurity layer 12 to disappear, and the P-type impurity layer 12 disappears. It does not affect the light receiving part diffusion region 13 region below the impurity layer 12.

The distribution of the potential in the depth direction at the light receiving portion has the minimum value Φmin in the light receiving portion diffusion 13, and the signal charges generated by the irradiation light are accumulated at the position of this minimum value Φmin. Therefore, since the signal charge is held at a position away from the semiconductor substrate of the photoelectric conversion unit 1 having a high surface recombination speed, the problem of disappearance of the signal charge due to surface recombination can be avoided.

(Embodiment 2) As a second embodiment of the present invention, a method of manufacturing a photoelectric conversion element of an interline transfer type CCD solid-state image pickup element for ultraviolet rays in which a second conductivity type impurity layer is formed by MEB will be described. . C manufactured in this example
The CD solid-state image pickup device transfers the signal charges converted / accumulated by the photoelectric conversion unit in accordance with incident ultraviolet rays to a vertical charge transfer path (vertical CCD) shielded from ultraviolet rays, and further the vertical CCD
The signal charges transferred from are read out sequentially. Figure 3
Is a photoelectric conversion unit of a CCD solid-state image sensor and a vertical CCD
2 is a cross-sectional view of a part of FIG.

First, below the surface of the P-type silicon substrate 21,
P-type impurity diffusion region 25 and LO for element isolation
A thick silicon oxide film was formed by COS oxidation. Next, the N-type impurity was diffused by ion implantation to form the light receiving portion diffusion region 23. Here, As is used as the N-type impurity.
Ion implantation was performed using (arsenic) under the condition of a dose amount of 1 × 10 ¹² / cm ² . Vertical C due to N-type impurities
The CD diffusion region 24 was also formed.

Then, a polycrystalline silicon layer was formed on the entire surface of the silicon substrate 21 with an insulating film interposed therebetween, and patterned to form a CCD electrode 26. Furthermore, C
The silicon oxide film 28a is formed by the VD method, and the vertical CC
A light shielding layer was formed on the D region by a sputtering method and patterned to form a light shielding portion 27 for ultraviolet rays. The silicon oxide film 2 is formed on the uppermost layer by the CVD method.
8b was formed (FIG. 3 (a)). The above operation is the same as the conventional method for manufacturing a visible light image pickup device except that the impurity layer of the opposite conductivity type is not formed on the light receiving diffusion region 23.

Next, the surface of the light receiving diffusion region 23 was exposed by removing the silicon oxide film (28a, 28b) on the light receiving diffusion region 23 by a photolithographic etching technique (FIG. 3B). This silicon oxide film (28a, 2
8b) is etched, in order to fix the potential of the P-type impurity layer 22 having a conductivity type opposite to that of the light receiving portion diffusion region 23, which is formed thereafter, the light receiving portion diffusion region 23 and the element isolation diffusion region 25 are formed together. Part 25a is exposed.

After that, the P-type impurity film 20 is formed on the entire surface of the silicon substrate including the exposed surface of the light receiving portion diffusion region 23.
It was deposited using the molecular beam epitaxial growth method (MBE). This is because the silicon substrate is placed in a high vacuum and the separately provided silicon is heated with an electron beam to evaporate the silicon,
Although silicon atoms are deposited on the entire surface of the silicon substrate to crystallize the silicon, in this embodiment, when depositing silicon, the impurity concentration is 1 × 10 5.
By simultaneously depositing impurities at ¹⁸ to 1 × 10 ²⁰ / cm ² , the P-type impurity deposition film 2 having a thickness of about 0.01 μm 2
0 was formed (FIG. 3 (c)).

Further, the impurity exhibiting film 20 other than the photoelectric conversion region 2 is removed by a photolithography etching technique or a lift-off technique to form a desired conductivity type on the light receiving part diffusion region 23 and a conductivity type opposite to that of the light receiving part diffusion region 23. Thus, the P-type impurity layer 22 was formed. After that, the P-type impurity layer 22
And a contact point 25 between the light receiving portion diffusion region 23 and the element isolation region 25
In order to improve the bonding characteristics between a, 4 in a nitrogen atmosphere
A relatively low temperature heat treatment was performed at 50 ° C. for 30 minutes. Further, a silicon oxide film layer 29 having a thickness of 0.01 μm as an antireflection film was formed on the surface of the P-type impurity region 22 by the CVD method (FIG. 3D).

Although the above first and second embodiments have been described with respect to the manufacture of the interline transfer type two-dimensional CCD image pickup device, the present invention is applicable to various other reading / reading operations.
It can be applied to manufacture of a transfer type solid-state imaging device. For example, M
It is also possible to combine it with an XY address reading method called an OS type. Furthermore, although the two-dimensional solid-state image pickup device has been described, it goes without saying that the present invention can be applied to a one-dimensional sensor and a point sensor used to detect the presence or absence of light or the intensity of light.

(Embodiment 3) FIG. 4 shows an X-ray point sensor manufactured by the method for manufacturing a photoelectric conversion element according to a third embodiment of the present invention. First, a P-type diffusion region 32 having a high impurity concentration and a thermal oxide film 38 for element isolation are formed below the surface of a P-type silicon semiconductor substrate 31. Next, the N-type impurities were diffused to form the light receiving portion diffusion region 33 for performing photoelectric conversion in the photoelectric conversion portion 3. Next, the silicon oxide film 39 is formed on the light receiving portion diffusion region 33.
a, a metal layer is laminated on top of it, and metal wiring (34, 3
7) was formed, and a silicon oxide film 39b was further formed.

After that, the silicon oxide film (38, 39a, 39b) on the light receiving portion diffusion region 33 is removed by etching to expose the surface of the light receiving portion diffusion region 33. At this time, part of the element isolation diffusion region 32 is exposed. The P-type impurity layer 30 is formed only on the exposed surface of the light receiving portion diffusion region 33 by the MBE method in the same manner as in the first and second embodiments, and the P-type impurity layer 30 is formed to 0.1.
μm was formed. The potential distribution of the cross section AB of the photoelectric conversion unit 3 of the point sensor obtained by the above process was the same as that shown in FIG.

In the above embodiment, the MBE method is used for forming the second conductivity type impurity layer. This MBE method has excellent controllability of the film thickness, and can grow a thin film of several tens of angstroms, for example. However, in the present invention, the method of depositing the second conductivity type impurity layer is not limited to MBE, and any method having excellent controllability of the film thickness and the impurity concentration can be adopted.

When forming a thin silicon oxide film on the surface of the second conductivity type impurity layer, in order to prevent the impurity layer from spreading due to the influence of heat, the silicon oxide film is formed at a relatively low temperature by, for example, the CVD method. A method capable of forming is preferred. Further, in the above-described embodiment, the impurity layer of the second conductivity type is formed by forming another photoelectric conversion element such as an electrode, a light-shielding film, a silicon oxide film, or a component part of the solid-state imaging device on the semiconductor substrate. It was carried out after the step involving heating for heating was completed first. This is because when the steps involving heating are performed after the second-conductivity-type impurity layer is formed, it is possible to avoid the possibility that the impurity layer formed thin due to the influence of heating in these steps expands. The order of the steps is not limited to this as long as the impurity layer of the second conductivity type is not affected by heating after the impurity layer of the second conductivity type is formed, for example, the above steps are performed at a relatively low temperature.

[0052]

As described above, in the photoelectric conversion element according to the manufacturing method of the present invention, the impurity layer formed on the light receiving portion diffusion region for photoelectric conversion can be made thinner than ever before. Therefore, in a state where the interface state is confined by the impurity layer, and the depth of penetration of X-rays or ultraviolet rays into the semiconductor substrate, which cannot be detected by the photoelectric conversion element manufactured by the conventional technique, is shallow. It also has sufficient sensitivity to, and is capable of photoelectric conversion.

Therefore, by applying the present invention to a photoelectric conversion element or a solid-state image pickup element, even if an optical signal having a short penetration depth into a semiconductor substrate, such as ultraviolet rays or soft X-rays, is detected by the conventional visible light. Similar to the photoelectric conversion device for light and the solid-state imaging device, the unevenness of the image can be reduced because the variation of the dark current can be reduced, and the S / N ratio can be improved. Therefore, the photoelectric conversion device and the solid-state imaging device with good stability can be obtained. Can be obtained. Also, the dynamic range can be widened.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method of manufacturing an X-ray solid-state image pickup device according to a first embodiment of the present invention, and FIGS. 1A to 1D are cross-sectional views showing the state of the device in each step.

2 is a diagram showing a potential distribution of a photoelectric conversion unit of the solid-state image pickup device for X-rays of FIG. 1, in which the horizontal axis represents the depth direction of the device and the vertical axis represents the potential depth.

FIG. 3 is a schematic view showing a method of manufacturing a solid-state image pickup device for ultraviolet light according to the second embodiment of the present invention, and (a) to (d) are cross-sectional views showing the state of the device in each step.

FIG. 4 is a schematic diagram showing an X-ray point sensor according to a third embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the depth of a silicon substrate and the X-ray absorption rate for explaining the operation of the present invention, where the horizontal axis is the silicon depth (μm) and the vertical axis is the X-ray absorption rate (%). Is.

FIG. 6 is a schematic diagram of an interline transfer CCD as an example of a two-dimensional solid-state image sensor.

FIG. 7 is a cross-sectional view of a photoelectric conversion element according to a conventional technique.

FIG. 8 is a cross-sectional view of a photoelectric conversion element according to a conventional technique.

[Explanation of symbols]

1, 2, 3: Photoelectric conversion section 11, 21, 31: Semiconductor substrate 13, 23, 33: (first conductivity type) light receiving section diffusion region 10, 20: Shower film of reverse conductivity type impurity layer 12, 22, 30: (second conductivity type) reverse conductivity type impurity layer 14, 24: vertical CCD (buried channel) diffusion region 15, 25, 32: element isolation diffusion region 16, 26: CCD electrode 17, 27: light shielding film 18a, 18b , 19, 28a, 28b, 29, 38,
39a, 39b: oxide film 37: metal wiring layer

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[Procedure amendment]

[Submission date] July 22, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

Therefore, in order to remove such an influence, for example, a photoelectric conversion element called a so-called embedded photodiode having a structure as shown in FIG. 8 is adopted. That is, N-type impurities are diffused in the P-type silicon substrate 71 to form the light-receiving part diffusion region 73 of the photoelectric conversion part 7,
The light receiving section diffusion region 73 on the surface is obtained by forming the opposite conductivity type of the P-type diffusion layer 7 2 ion implantation and annealing (heat treatment for recovering crystal defects generated by ion implantation). It is connected to the diffusion layer 75 for the FIG. 8, element isolation but only depth shallower diffusion and P-type diffusion layer 7 2. Here by the P-type diffusion layer 7 2, it is possible to shield the region recombination rate is high photoelectric conversion surface. As described above, it is possible to manufacture a photoelectric conversion element and a solid-state image pickup element that are sufficiently practical in the visible light region.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

Further, as also shown in FIG. 8, usually, a silicon oxide film 78 is formed on the light receiving portion diffusion region 73 to be thicker than the impurity diffusion layer 71 having a conductivity type opposite to that of the light receiving portion diffusion region 73. X-ray absorption also occurs in this silicon oxide film 78. For example, the absorption length of the silicon oxide film is 2.3 × 10 ⁻⁵ cm for a wavelength of 45 Å X-ray, and the absorption length of silicon is 1.2 × 10 ⁻⁵ cm. since it is, Ru is absorbed similarly in silicon in the silicon oxide film. in this way,
In the conventional photoelectric conversion element, almost no X-ray can reach the light-receiving part diffusion region, and it is impossible to photoelectrically change the X-ray.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

After that, a P-type impurity film 10 was formed by depositing on the entire surface of the silicon substrate including the exposed surface of the light receiving portion diffusion region 13. Molecular beam epitaxial growth (MBE) was used as the deposition method. This is to place a silicon substrate in a high vacuum, heat the separately provided silicon with an electron beam to evaporate the silicon, and deposit silicon atoms on the entire surface of the silicon substrate to crystallize the silicon. In the present embodiment, when depositing silicon, impurities are simultaneously deposited at an impurity concentration of 1 × 10 ¹⁸ to 1 × 10 ²⁰ / cm ² , so that P having a thickness of about 0.05 μm is deposited.
The type impurity deposition film 10 was formed (FIG. 1 (c)).

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

Claims (6)

[Claims] 1. A step a of forming a light-receiving part diffusion region of a first conductivity type for performing photoelectric conversion on a semiconductor substrate, and a second step of covering the surface of the light-receiving part diffusion region on the light-receiving part diffusion region. In the method for manufacturing a photoelectric conversion element, which includes the step b of forming a conductivity type impurity layer, the step b includes a step of forming the second conductivity type impurity layer on the surface of the light receiving part diffusion region by deposition. A method for manufacturing a photoelectric conversion element, comprising: 2. The method for manufacturing a photoelectric conversion element according to claim 1, wherein in the step b, the thickness of the second conductivity type impurity layer is set to 0.1 μm or less. 3. The method of manufacturing a photoelectric conversion element according to claim 1, wherein in the step b, the thickness of the second conductivity type impurity layer is set to 0.01 μm or less. 4. The surface of the impurity layer of the second conductivity type has a resistance of 0.
The method for producing a photoelectric conversion element according to claim 1 or 2, further comprising a step c of forming a silicon oxide film layer having a thickness of 01 µm or less. 5. The first step in the step a before the step b
Forming a photoelectric conversion element configuration such as an insulating layer, an electrode, a metal wiring layer, and a silicon oxide film layer on the semiconductor substrate after forming the conductive type light receiving section diffusion region; Removing the upper layer within a predetermined range of the diffusion region and exposing the surface of the light receiving portion diffusion region. A method for manufacturing the photoelectric conversion element according to 1. 6. A light receiving part diffusion region of a first conductivity type provided on a semiconductor substrate, and a second surface covering the surface of the light receiving part diffusion region.
In a solid-state imaging device having a photoelectric conversion element having a conductivity type impurity layer as a pixel, the second conductivity type impurity layer is deposited on the first conductivity type light receiving part diffusion region with a thickness of 0.1 μm or less. A solid-state imaging device characterized by being formed.