JP2004235621A - Back-illuminated image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent signal charges from being mixed in a backside illuminated imaging device.
A backside illuminated imaging device includes a conversion layer, a charge collection unit, and suppression regions. The conversion layer 23 is provided on the side of the incident surface 102 on which the incident lines are incident, converts the incident lines into signal charges, and is provided for each of a plurality of pixels forming a two-dimensional array. The charge collection unit 24 extends from the conversion layer 23 to the surface 22 opposite to the incident surface 8 and collects signal charges generated in the conversion layer 23. The suppression regions 23 and 29 are provided between the conversion layer 23 and the peripheral circuit 26, and suppress the inflow of signal charges from the conversion layer 21 to the peripheral circuit 26.
[Selection diagram] Fig. 1

Description

  The present invention relates to a backside illumination type imaging device. In particular, the present invention relates to a back-illuminated imaging device suitable for imaging for measurement purposes in the fields of science and technology.

  2. Description of the Related Art A back-illuminated imaging device in which an incident line of visible light or the like is incident from a surface (back surface) opposite to a surface (front surface) on which electrodes and the like of a chip are arranged (see Patent Document 1). In this back-illuminated imaging device, a conversion unit for each pixel (for example, a photoelectric conversion unit when the incident light is visible light) is provided on the back side of the chip, and the conversion unit such as an A / D converter or a signal storage unit is provided. A portion that performs some processing on the signal charges (charge processing unit) is provided on the front surface side of the chip.

  Since the back-illuminated imaging device can obtain an aperture ratio close to 100%, extremely high sensitivity can be realized. Therefore, in applications requiring high sensitivity, such as in the fields of astronomy and electron microscopes, back-illuminated imaging devices are often used. A back-illuminated imaging device having high sensitivity is also suitable for high-speed shooting in which the exposure time per image is short.

  The main problem in the back-illuminated imaging device is the mixing of signal charges into the charge processing section. More specifically, signal charges such as photoelectrons generated in the conversion unit are mixed into a portion of the charge processing unit where the signal charges should not flow due to diffusion or wraparound. The mixed signal charges hinder the function of the charge processing unit.

  Another problem with the back-illuminated imaging device is light transmission. In the back-illuminated imaging device, it is necessary to reduce the thickness of the chip as much as possible. This is because, when the chip is thick, signal charges are mixed between adjacent pixels while the charges generated in accordance with the incident line reach the functional area, or noise due to crystal defects in the chip is mixed into the signal charges. Because you do. Since the thickness of the chip is thin, light of a long wavelength having high transmittance (having a small absorption coefficient) reaches the functional region on the front surface side, and generates unwanted unwanted charges in the functional region. This charge also impairs the function of the element provided in the functional region.

  The present inventors have developed a pixel peripheral recording type image pickup device (In-situ Storage Image Sensor: ISIS) having a linear signal accumulation unit in or near a pixel (for example, Patent Document 2, Non-Patent Document 1) And Non-Patent Document 2). When the backside illumination structure is employed in the pixel peripheral recording type image pickup device, the above-described problems caused by mixing of signal charges and transmission of light are particularly significant.

JP-A-9-331052 JP 2001-345441 A Goji Eto et al., "A CCE Image Sensor of 1M frames / s for Continuous Image Capturing of 103 Frames", Digest of Technical Papers 2002, 2002 IEEE International Solid-State Circuits Conference, 2002, Vol. 45, p. 46-47 Goji Eto, 4 others, "1,000,000 Images / Second Image Sensor with Oblique Line CCD Type Pixel Peripheral Recording Area", Journal of the Institute of Image Information and Television Engineers, The Institute of Image Information and Television Engineers, 2002, Vol. 56, No. No. 3, p. 483-486

  SUMMARY OF THE INVENTION It is an object of the present invention to prevent signal charges from being mixed in a backside illuminated imaging device and to prevent generation of unnecessary charges due to light transmission.

  In the present specification, the term “incident line” refers to a flow of energy or particles to be detected that enters the image sensor, and includes ultraviolet light, visible light, and electromagnetic waves including light such as infrared light, electrons, ions, And the flow of charged particles, such as holes, and radiation, including alpha, gamma, beta, and neutron radiation in addition to x-rays.

  The present invention provides a conversion unit, which is provided on an incident surface side on which an incident line is incident, converts the incident line into a signal charge, and is provided for each of a plurality of pixels forming a two-dimensional array. A charge collection unit extending to a surface side opposite to the incident surface and collecting signal charges generated in the conversion unit; and a charge processing unit provided on the surface side and processing signal charges collected by the charge collection unit And a suppression region provided between the conversion unit and the charge processing unit and configured to suppress the inflow of the signal charge from the conversion unit to the charge processing unit. I will provide a.

  Since the suppression region is provided between the conversion unit and the charge conversion unit, it is possible to prevent the signal charges generated in the conversion processing unit from flowing into the charge processing unit instead of the charge collection unit due to diffusion or wraparound. Therefore, it is possible to prevent the occurrence of noise or the like due to the mixing of the signal charges into the charge processing unit.

  Specifically, the conversion section, the charge collection section, the charge processing section, and the suppression region are made of a semiconductor material, the conversion section has a first conductivity type, and the charge collection section has a second conductivity type. And the suppression region has the first conductivity type, but has a higher conductivity type impurity concentration than the conversion unit, the signal charge processing unit is embedded therein, and the signal charge The collection unit includes a charge blocking layer penetrating therethrough.

  When the signal charge is an electron, the first conductivity type is p-type and the second conductivity type is n-type. When the signal charges are holes, the first conductivity type is n-type and the second conductivity type is p-type.

  Preferably, the suppression region has a second conductivity type, is interposed between the conversion unit and the charge blocking layer, and is continuous with the charge collection unit and an end on the incident surface side. Is further provided.

  The signal charge generated in the conversion unit is once collected in the charge collection layer, and the signal charge in the second suppression unit moves in the horizontal direction and is collected in the charge collection unit. Therefore, the provision of the charge collection layer can more effectively prevent signal charges from being mixed into the charge processing portion.

  The function and structure of the charge processing unit are not particularly limited. For example, the charge processing unit is an A / D converter that converts the signal charge from an analog signal to a digital signal.

  The present invention can also be applied to a pixel peripheral recording type imaging device. That is, the charge processing unit may be a signal charge storage unit that is provided inside or near each pixel and stores the signal charge. It has both high sensitivity, which is a feature of the backside illumination type, and extremely high shooting speed, which is a feature of the pixel peripheral recording type, and can prevent the occurrence of noise due to the mixing of signal charges into the signal charge storage section. .

  When the incident line is light, the incident line is disposed on the incident surface, and transmits light from the incident surface to the charge processing unit to block light having a wavelength that generates the same kind of signal charge as the signal charge in the charge processing unit. An optical filter may be further provided. It is possible to prevent unnecessary light from being generated by direct light reaching the charge processing unit and causing deterioration in image quality.

  Further, the present invention provides an electron microscope and a photographing apparatus including the back-illuminated imaging device.

  In the back-illuminated imaging device of the present invention, since the suppression region is provided between the conversion unit and the charge processing unit, the signal charges generated in the conversion unit flow into the charge processing unit instead of the charge collection unit due to diffusion or sneak. Can be prevented. Therefore, it is possible to prevent the occurrence of noise or the like due to the mixing of the signal charges into the charge processing unit.

  Next, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

(1st Embodiment)
FIG. 1 shows a transmission electron microscope 2 including a back-illuminated imaging device 1 according to a first embodiment of the present invention. The transmission electron microscope 2 irradiates a sample 5 with an electron stream 4 (incident line) from an electron gun 3, and forms an image of the transmitted electron stream 4 on a back-side illuminated imaging device 1. 6A to 6C are magnetic lenses. The inside of the transmission electron microscope 2 in which the electron gun 3, the sample 5, the back-side illuminated imaging device 1, and the magnetic lenses 6A to 6C are arranged is maintained at a required degree of vacuum by a vacuum pump 7.

  2 to 4, a fluorescent film 9 on which the electron flow 4 transmitted through the sample 5 is incident is disposed on the back surface or the incident surface 8 side of the back-illuminated imaging device 1. 8 is optically connected by a fiber glass 10. The fluorescent film 9 emits light at a luminance corresponding to the intensity of the incident electron flow 4, and light 11 emitted from the fluorescent film 9 enters the incident surface 8.

  As shown in FIG. 2, a plurality of pixels 13 are two-dimensionally arranged on the incident surface 8 of the backside illumination type imaging device 1. In FIG. 2, for simplicity, only nine (3 rows × 3 columns) pixels 13 are shown, but the number of rows and columns of the pixels 13 may be two or more.

As shown in FIGS. 3 and 4, a p ⁻ type conversion layer 21 is provided on the incident surface 8 side of the chip 14. Further, ap ⁺ type charge blocking layer 23 is provided on the surface 22 side of the chip 14 with respect to the conversion layer 21.

An n ⁻ type charge collecting unit 24 for collecting signal charges generated in the conversion layer 21 is provided for each pixel 13. One end of the charge collecting section 24 is located in the conversion layer 21 and extends from the conversion layer 21 to the surface 22 of the chip 14. An n-type input region 25 is provided at the other end of the charge collection unit 24 located on the surface 22 side of the chip 14. The charge collecting portion 24 extends through the charge blocking layer 23, and the input region 25 is embedded in the charge blocking layer 23.

In a region on the surface 22 side of the charge blocking layer 23, various peripheral circuits 26 (charge processing units) including an A / D converter are provided for each pixel 13. These peripheral circuits 26 are embedded in the charge blocking layer 23. 3 and 4, reference numeral 27 denotes an electrode of the peripheral circuit 26, and reference numeral 28 denotes an electrode for transmitting signal charges from the input region 25 to the peripheral circuit 26. As schematically shown in FIG. 5, the serial A / D converter 31 included in the peripheral circuit 26 includes a comparator 32 and a counter 33. With a voltage V _in is input a signal charge from the input region 25 to the comparator 32, the comparison voltage V _ref is input, the output of the comparator 32 is output to the counter 33. The output of the counter 33 is output to the controller 34 (see FIG. 1) as an image signal. The controller 34 includes various elements including a memory, an image processing circuit, and the like, and the controller 34 outputs a captured image to the display device 35. As described above, the A / D converter 31 is provided for each pixel 13, but the reset signal output from the controller 34 and the comparison voltage V _ref are common to all the pixels 13.

The conversion layer 21, the charge blocking layer 23, the charge collection unit 24, and the input region 25 of the back-side illuminated imaging device 1 are, for example, p ^- type and impurity concentration 1 respectively having an impurity concentration of 1 × 10 ¹⁰ to 1 × 10 ¹⁵ cm ^−3. A p ⁺ type of × 10 ¹⁵ to 1 × 10 ¹⁶ cm ^−3, an n type of impurity concentration of 1 × 10 ¹³ to 1 × 10 ¹⁶ cm ^{−3, and} an n of impurity concentration of 1 × 10 ¹⁶ to 1 × 10 ²⁰ cm ^{−3 It} is made of a semiconductor material mainly composed of ⁺ type silicon. In this case, the p ^- type substrate can be manufactured by performing ion implantation of boron and phosphorus using a photoresist as a mask and then performing thermal diffusion.

When the electron flow 4 transmitted through the sample 5 enters the fluorescent film 9, the fluorescent film 9 emits light. Light 11 generated by the fluorescent film 9 is incident on the back-illuminated imaging device 1 via the fiber glass 10. The light 11 incident from the incident surface 8 reaches the conversion layer 21 and generates pairs of electrons and holes. Among them, the electrons have negative charges, so that they collect in the n ⁻ type charge collecting section 24 and further accumulate in the n type input region 25. The holes are continuously discharged out of the chip through the p ⁻ type conversion layer 21. The electrons integrated in the input area 25, that is, the signal charges, are output to the peripheral circuit 26 and subjected to various processes including conversion of an analog signal into a digital signal by the A / D converter 31, and then to the controller 34 as an image signal. Is output.

The p ⁻ type conversion layer 21 and the peripheral circuit 26 are separated from each other by the p ⁺ type charge blocking layer 23. Therefore, it is possible to prevent the electrons generated in the conversion layer 21 from directly reaching the peripheral circuit 26 without going through the charge collection unit 24 and the input region 25 due to diffusion or wraparound. Therefore, it is possible to prevent noise from being generated in the peripheral circuit 26 due to mixing of signal charges. The charge blocking layer 23 also has a function of electrically separating adjacent peripheral circuits 26 from each other.

(2nd Embodiment)
The back-illuminated imaging device 1 according to the second embodiment of the present invention shown in FIGS. 6 and 7 includes an n ⁻ -type charge collection layer 29. The charge collecting layer 29 is interposed between the conversion layer 21 and the charge blocking layer 23 and is continuous with the end of the charge collecting unit 24 on the incident surface 8 side. The charges generated in the conversion layer 21 are once collected in the charge collection layer 29. The charges collected in the charge collection layer 29 move in the horizontal direction and are collected by the charge collection unit 24. Therefore, the provision of the charge collection layer 29 can more effectively prevent signal charges from being mixed into the peripheral circuit 26.

The back-illuminated imaging device 1 of the second embodiment is manufactured, for example, as follows. A thick n ⁻ layer having a depth of 2 to 8 μm is formed by high-energy ion implantation or thermal diffusion from the surface side of the p ⁻ type substrate. Next, a p + layer is formed at about 2 to 8 μm from the surface by the same method, and a peripheral circuit 26 is formed on the surface by ion implantation.

  Other configurations and operations of the second embodiment are the same as those of the first embodiment, and therefore, the same components are denoted by the same reference numerals and description thereof will be omitted.

(Third embodiment)
The back-illuminated imaging device 1 according to the third embodiment of the present invention shown in FIGS. 8 and 9 does not include the fluorescent film 9 and the fiber glass 10 (FIGS. 3, 4, 6, and 7). The electron flow 4 transmitted through the sample 5 is directly incident on the incident surface 8. Secondary electrons generated when the electron flow 4 reaches the conversion layer 21 become signal charges. This signal charge is accumulated in the charge collection unit 24 and sent to the peripheral circuit 26 via the input region 25. Since the charge blocking layer 23 is interposed between the conversion layer 21 and the peripheral circuit 26, secondary electrons generated in the conversion layer 21 can be prevented from reaching the direct product peripheral circuit 26.

  In the back-illuminated imaging device of the electron flow direct type as in the third embodiment, the device life tends to be shortened because the imaging device is directly exposed to the high-energy electron flow. Therefore, it is preferable to make the light incident on the incident surface 8 after weakening the current intensity by setting the magnetic lenses 6A to 6C (see FIG. 1).

  Since other configurations and operations of the third embodiment are the same as those of the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

(Fourth embodiment)
In the back-illuminated imaging device 1 according to the fourth embodiment of the present invention shown in FIGS. 10 and 11, the n ⁻ -type charge collection layer 29 continuous with the charge collection unit 24 between the conversion layer 21 and the charge blocking layer 23. Is interposed. By collecting the secondary electrons generated in the conversion layer 21 in the charge collection layer 29 and collecting the collected electrons in the charge collection unit 24, the mixing of signal charges into the peripheral circuit 26 can be more effectively prevented.

  Other configurations and operations of the fourth embodiment are the same as those of the third embodiment, and therefore, the same elements will be denoted by the same reference characters and description thereof will be omitted.

(Fifth embodiment)
The fifth embodiment of the present invention shown in FIGS. 12 to 17 is an example in which the present invention is applied to a pixel peripheral recording type image sensor (In-Situ Storage Image Sensor: ISIS).

  Referring to FIG. 12, a high-speed video camera 100 including a back-illuminated imaging device 101 according to the fifth embodiment includes a lens 104 that forms visible light 103 on an incident surface 102, and an analog signal output from the back-illuminated imaging device 101. And an A / D converter 106 for converting the amplified image signal into a digital signal, and a main memory 107 for storing the digital image signal. The image processing device 108 processes the image signal read from the main memory 107 and displays it on the display device 109. The controller 110 controls the operation of the entire video camera including the image sensor 101, the amplifier 105, and the A / D converter 106.

  FIG. 13 is a view of the back-illuminated imaging device 101 as viewed from the incident surface 102 (see FIGS. 15 to 17). In FIG. 13, for simplicity, only 12 (4 rows × 3 columns) pixels 121 are shown, but the number of rows and columns of pixels may be two or more. Further, FIG. 13 does not show an optical filter 130, a conversion layer 131, and a charge collecting unit 134 (see FIGS. 15 to 17) described later.

  With reference to FIG. 13, the structure of the back-illuminated type ISIS will be described. An input region 122 is provided for each pixel 121. The input region 122 and the pixels 121 including the input region 122 are arranged so that the row direction and the column direction are orthogonal to each other. A signal recording CCD 123 extending obliquely downward and leftward in the figure is provided for each input area 122. Further, a CCD (vertical readout CCD 124) extending in the vertical direction (column direction) in the figure is provided, one for each column of each input area 122. Further, a drain line 126 is provided adjacent to each vertical readout CCD 124. Further, a CCD (horizontal readout CCD 125) extending in the horizontal direction (row direction) in the figure is provided.

  Each signal recording CCD 123 has one end connected to a corresponding input area 122 via an input gate (not shown), and the other end connected to a vertical readout CCD 124. The other end of the signal recording CCD 123, one end of which is connected to the input area 122 forming the same column, merges with the vertical readout CCD 124 corresponding to that column. In other words, all the signal recording CCDs 123 connected to the input area 122 constituting the same column join the same vertical readout CCD 124. Of the signal recording elements or elements 124a provided in the vertical readout CCD 124, an element 124a on the upstream side of the element 123a where the signal recording CCD 123 joins is connected to a drain line 126 via a drain gate 127. The lower end of each vertical readout CCD 124 in the figure is connected to the horizontal readout CCD 125.

  In the back-illuminated imaging device 101 of the fifth embodiment, continuous overwriting is performed during shooting. Referring to FIG. 14, as indicated by arrow Y1, signal charges are sequentially transferred from input area 122 to element 123a of signal recording CCD 123 during shooting. Assuming that signal charges are accumulated in each element 123a numbered from “1” to “26” at a certain moment, the smaller the number assigned to each element 123a, the more signal charges correspond to an older image. The larger the number is, the more the signal charge corresponds to a new image. At the next moment after the state shown in FIG. 14, the signal charge is discharged from the element 123a numbered "1" to the drain line 126 via the drain gate 127, and the input area is transferred to the element 123a numbered "26". From 122, the signal charge corresponding to the latest 27th image is input. The signal charges corresponding to the second to 26th images are sent one by one to the downstream element 123a. Therefore, signal charges corresponding to the second to 27th images are recorded on the signal recording CCD 123. During the photographing, the continuous overwriting process continues.

  When occurrence of a phenomenon to be photographed is confirmed, continuous overwriting is stopped. The operation of reading out the stored signal charges is generally as follows. (1) The charge transfer in the signal recording CCD 123 is stopped, the charge transfer is performed only on the vertical reading CCD 124 as indicated by an arrow Y2, and the signal charge is sent to the horizontal reading CCD 125. With this operation, the CCD 124 for vertical reading becomes empty. (2) The charge is transferred from the signal recording CCD 123 to the vertical reading CCD 124 to fill the vertical reading CCD 124.

  In FIG. 12, if the signal recording CCD 123 does not extend obliquely downward, the signal recording CCD 123 connected to one input area 122 interferes with the input area 122 immediately below the input area 122, and The recording CCD 123 cannot be made sufficiently long. In order to make the signal recording CCD 123 sufficiently long, the signal recording CCD 123 may be extended right below by gradually shifting the input area 122 rightward toward the lower side. In this case, the center point of the input area 122 that forms the pixel axis is a rhombus without forming a square lattice or a rectangular lattice. In order to eliminate such a rhombic lattice, the position of the input area 122 may be slightly shifted upward. When the resulting layout is slightly rotated clockwise, the layout shown in FIG. 12 is obtained. This is the reason why the signal recording CCD 123 is skewed with respect to the pixel axis.

  12 and 13, signal charges corresponding to 26 images are accumulated in the signal recording CCD 123 and the vertical reading CCD 124 for simplification. However, if the number of these elements 123a and 124a is increased, the number of images that can be continuously shot can be increased. For example, if 103 elements are provided around each pixel, an image photographed at a photographing speed of 1 million frames / second can be reproduced as a moving image of 10 seconds at a reproduction speed of 10 frames / second.

Referring to FIGS. 15 to 17, an optical filter 130 is disposed on the incident surface 102 of the chip 128. A p ⁻ type conversion layer 131 is provided on the incident surface 102 side of the chip 128, and a p ⁺ type charge blocking layer 133 is provided on the surface 132 side of the chip 128 with respect to the conversion layer 131.

An n ⁻ type charge collecting unit 134 for collecting signal charges generated in the conversion layer 131 is provided for each pixel 121. One end of the charge collecting portion 134 is located in the conversion layer 131 and extends from the conversion layer 131 to the surface 132 of the chip 128. An n-type input region 122 is provided at the other end of the charge collection unit 134 located on the surface 132 side of the chip 128. The charge collecting portion 134 extends through the charge blocking layer 133, and the input region 122 is embedded in the charge blocking layer 133.

  A signal recording CCD 123 is provided in a region on the surface 132 side of the charge blocking layer 133. These signal recording CCDs 123 are embedded in the charge element layer 133. 15 to 17, reference numeral 135 denotes an electrode for driving the signal recording CCD 123, and reference numeral 136 denotes an electrode for transmitting signal charges from the input area 122 to the signal recording CCD 123. In the present embodiment, since the signal recording CCD 123 is driven in four phases, four electrodes 135 are provided for each element 123a as shown in FIG.

The conversion layer 131, the charge collection unit 134, the input region 122, and the charge blocking layer 133 of the back-side illuminated imaging device 101 are, for example, p ^- type impurities having an impurity concentration of 1 × 10 ¹⁰ to 1 × 10 ¹⁵ cm ⁻³ , respectively. P ⁺ type with a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁶ cm ⁻³ , n-type with an impurity concentration of 1 × 10 ¹³ to 1 × 10 ¹⁶ cm ⁻³ , and an impurity concentration of 1 × 10 ¹⁶ to 1 × 10 ²⁰ cm ⁻³ Made of a semiconductor material mainly composed of n ⁺ type silicon. In this case, the p ^- type substrate can be manufactured by performing ion implantation of boron and phosphorus using a photoresist as a mask and then performing thermal diffusion.

Light 137 incident from the incident surface 102 via the optical filter 130 reaches the conversion layer 131 and generates pairs of electrons and holes. Among them, the electrons have negative charges, so that the electrons are collected in the n ⁻ -type charge collection unit 134 and further accumulated in the n-type input region 122. The holes are continuously discharged out of the chip through the p ^- type conversion layer 131. The electrons accumulated in the input area 122, that is, signal charges, are output to the corresponding signal recording CCD 123.

The p ⁻ type conversion layer 131 and the n type signal recording CCD 123 are separated from each other by a p ⁺ type charge blocking layer 133. Therefore, it is possible to prevent the electrons generated in the conversion layer 131 from directly reaching the signal recording CCD 123 without going through the charge collection unit 134 and the input region 122 due to diffusion or wraparound. Accordingly, it is possible to prevent noise from being generated in the signal recording CCD 123 due to mixing of signal charges. The charge blocking layer 133 also functions as a channel stop for electrically separating the adjacent signal recording CCDs 123 from each other.

  Next, the optical filter 130 will be described. Table 1 shows the relationship between the thickness of the chip and the transmittance calculated from the wavelength of the incident light and the absorption coefficient with respect to the silicon single crystal wafer used in the manufacture of the ordinary CCD type image pickup device. In the case of the back-illuminated type, a chip having a thickness of about 20 μm is used in the thinnest case.

  In the backside illuminated pixel peripheral recording type imaging device, it is desirable that the light transmittance be 1/10000 or less. For example, as described above, when signal charges corresponding to 100 images can be stored in the signal recording CCD 123 and the vertical readout CCD 124, when one image is captured, the signal charge of the image is up to 99 sheets. Are held until the image of (1) is taken. When light reaches the CCD 123 for signal recording and the CCD 124 for vertical reading, electric charges are generated. If the ratio (transmittance) of the light incident from the incident surface 102 to the signal recording CCD 123 on the front surface 132 side is 1/10000, every time one image is captured, 1/10000 of the original signal charge is obtained. A signal is added to the signal charge. Therefore, 1/1000 × 100 (sheets) = 1/00, that is, 1% of unnecessary signals are added to the original signal charges during 100 images. When this ratio exceeds a few percent, a phenomenon of very unsightly smear occurs.

From Table 1, the transmittance of light at 600 nm passing through a silicon single crystal having a thickness of 20 μm is 6.692 × 10 ⁻⁵ , and the transmittance of light having a wavelength of 650 nm passing through a silicon single crystal having a thickness of 30 μm is 7. It is 59 × 10 ⁻⁵ . Therefore, in these cases, the above-mentioned condition of the transmittance of 1/10000 or less is satisfied. On the other hand, the transmittance of 650 nm light passing through a 20 μm thick silicon single crystal is 0.00179, and the transmittance of 700 nm light passing through a 30 μm thick silicon single crystal is 0.001393. In these cases, the condition for the transmittance of 1/10000 or less is not satisfied. For example, when light of 700 nm is incident on a silicon single crystal having a thickness of 30 μm, the transmittance is 0.001933, which is 0.19393 when multiplied by 100. Accordingly, 13.93% of unnecessary charges are added to the signal charges during photographing of 100 sheets.

From the above examination, when the thickness of the chip is 30 μm, the optical filter 130 substantially blocks light having a wavelength of 700 to 1000 nm, specifically, when the transmittance of these lights is 1% or less. Preferably, there is. However, when the number of consecutive shots is less than 100, the transmittance of the light of the optical filter 130 may be 1% or more. Conversely, when the number of images exceeds 100, the transmittance of light is 1%. Must be less than In addition, a certain time is required from the stop of continuous shooting until the shutter (not shown) is closed and the light from the optical system does not enter the back-illuminated image sensor 101, and a large amount of light enters during this time. Specifically, photographing speed is the case of 1M sheets / sec, the light 10 ⁴ times the amount of incident light at the time of photographing to obtain the incident surface 102. Therefore, the light transmittance of the optical filter 130 needs to be set in consideration of the time from the stop of the continuous shooting to the stop of the incidence on the incident surface 102.

  By providing the optical filter 130 having an appropriately set light transmittance, it is possible to prevent the light from directly reaching the signal recording CCD 123 and generating unnecessary charges, thereby causing deterioration in image quality.

(Sixth embodiment)
The back-illuminated imaging device 101 according to the sixth embodiment of the present invention shown in FIGS. 18 to 20 includes an n ⁻ -type charge collection layer 138. The charge collection layer 138 is interposed between the conversion layer 131 and the charge blocking layer 133 and is continuous with the end of the charge collection unit 134 on the incident surface 102 side. The charges generated in the conversion layer 131 are temporarily collected in the charge collection layer 138. The charges collected in the charge collection layer 138 move in the horizontal direction and are collected by the charge collection unit 134. Therefore, the provision of the charge collection layer 138 can more effectively prevent signal charges from being mixed into the signal recording CCD 123.

The back-illuminated imaging device 101 of the sixth embodiment is manufactured, for example, as follows. A thick n ⁻ layer having a depth of 2 to 8 μm is formed by high-energy ion implantation or thermal diffusion from the surface of the p ⁻ type substrate. Next, a p + layer is formed at about 2 to 8 μm from the surface by the same method, and a peripheral circuit is formed on the surface by ion implantation.

  Other configurations and operations of the sixth embodiment are the same as those of the fifth embodiment, and therefore, the same elements will be denoted by the same reference characters and description thereof will be omitted.

  The present invention is not limited to the above embodiment, and various modifications are possible. For example, the incident rays may be electromagnetic waves other than light rays, flows of charged particles such as ion holes other than electron beams, and radiations including α-rays, γ-rays, β-rays, and neutron rays in addition to X-rays. Good. When the incident ray is radiation, a scintillator may be arranged on the incident surface side of the image sensor, and light rays generated by the scintillator according to the intensity of the radiation may be incident on the image sensor. In this case, from the viewpoint of the life of the imaging element, it is preferable to select a material that generates green or blue light, that is, light that has a relatively short wavelength, as the material of the scintillator. When color imaging is required, it is necessary to increase the thickness of the chip so that red light does not reach the recording CCD or the vertical reading CCD. Further, when performing high-resolution image analysis, it is sufficient to use green to yellow light, which has the highest energy of natural light, and block red to near-infrared light to reduce chromatic aberration.

FIG. 1 is a schematic diagram showing a transmission electron electron microscope including a back-illuminated imaging device according to a first embodiment of the present invention. 1 is a schematic front view of a back-illuminated imaging device according to a first embodiment of the present invention. FIG. 3 is a sectional view taken along line III-III in FIG. 2. FIG. 4 is a sectional view taken along line IV-IV in FIG. 2. FIG. 2 is a schematic diagram of an A / D converter included in the back-illuminated imaging device according to the first embodiment. FIG. 3 is a cross-sectional view of the back-illuminated imaging device according to a second embodiment of the present invention, taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 2 showing a back-illuminated imaging device according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view of the back-illuminated imaging device according to a third embodiment of the present invention, taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2 showing a back-illuminated imaging device according to a third embodiment of the present invention. FIG. 3 is a cross-sectional view of the back-illuminated imaging device according to a fourth embodiment of the present invention, taken along line III-III in FIG. 2. FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 2 showing a back-illuminated imaging device according to a fourth embodiment of the present invention. FIG. 14 is a schematic diagram showing a high-speed camera including a back-illuminated imaging device according to a fifth embodiment of the present invention. FIG. 14 is a schematic front view showing a back-illuminated imaging device according to a fifth embodiment of the present invention. FIG. 14 is a partially enlarged view of FIG. 13. FIG. 14 is a sectional view taken along line XV-XV in FIG. 13. FIG. 14 is a sectional view taken along line XVI-XVI in FIG. 13. FIG. 14 is a sectional view taken along line XVII-XVII in FIG. 13. FIG. 14 is a cross-sectional view of the back-illuminated imaging device according to the sixth embodiment of the present invention, taken along line XV-XV in FIG. 13. FIG. 14 is a cross-sectional view taken along line XVI-XVI of FIG. 13 illustrating a back-illuminated imaging device according to a sixth embodiment of the present invention. FIG. 14 is a sectional view taken along line XVII-XVII of FIG. 13 illustrating a back-illuminated imaging device according to a sixth embodiment of the present invention.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 back-side illuminated image sensor 2 transmission electron microscope 3 electron gun 4 electron beam 5 sample 6A, 6B, 6C magnetic lens 7 vacuum pump 8 incident surface 9 fluorescent film 10 fiber glass 11 light 13 pixel 14 chip 21 conversion layer 22 surface 23 Charge blocking layer 24 Charge collecting unit 25 Input area 26 Peripheral circuit 27, 28 Electrode 29 Charge collecting layer 31 A / D converter 32 Comparator 33 Counter 34 Controller 35 Display device 100 High-speed video camera 101 Back-side illuminated imaging device 102 Incident surface 103 visible light 104 lens 105 amplifier 106 A / D converter 107 main memory 108 image processing device 109 display device 110 controller 121 pixel 122 input area 123 signal recording CCD
124 CCD for vertical reading
125 CCD for horizontal reading
126 drain line 127 drain gate 128 chip 130 optical filter 131 conversion layer 132 surface 133 charge blocking layer 134 charge collecting unit 135,136 electrode 137 light 138 charge collecting layer

Claims (8)

A conversion unit provided on an incident surface side on which an incident line is incident, converting the incident line into a signal charge, and provided for each of a plurality of pixels forming a two-dimensional array;
A charge collection unit that extends from the conversion unit to a surface side opposite to the incident surface and collects signal charges generated in the conversion unit;
A charge processing unit that is provided on the front surface side and processes signal charges collected by the charge collection unit;
And a suppression region provided between the conversion unit and the charge processing unit, the suppression region suppressing flow of the signal charge from the conversion unit to the charge processing unit. The conversion unit, the charge collection unit, the charge processing unit, and the suppression region is made of a semiconductor material,
The converter has a first conductivity type,
The charge collection unit has a second conductivity type, and the suppression region has the first conductivity type, but a concentration of a conductivity type impurity is higher than that of the conversion unit, and the signal charge processing unit is provided therein. A back-illuminated imaging device, comprising a charge blocking layer embedded in the substrate and penetrated by a signal charge collecting unit.   The suppression region has a second conductivity type, and further includes a charge collection layer interposed between the conversion unit and the charge blocking layer, and continuous with the charge collection unit and an end on the incident surface side. The backside illuminated imaging device according to claim 2, wherein:   The back-illuminated imaging according to any one of claims 1 to 3, wherein the charge processing unit is an A / D converter that converts the signal charge from an analog signal to a digital signal. element.   The back surface according to any one of claims 1 to 3, wherein the charge processing unit is a signal charge storage unit that is provided inside or near each pixel and stores the signal charge. Irradiation type imaging device. The incident line is light, and is disposed on the incident surface, and blocks light having a wavelength that transmits from the incident surface to the charge processing unit and generates charges of the same type as the signal charges in the charge processing unit. The back-illuminated imaging device according to any one of claims 1 to 5, further comprising an optical filter.   An electron microscope comprising the back-side illuminated imaging device according to claim 1.   An imaging device comprising the back-illuminated imaging device according to any one of claims 1 to 6.

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