JP2012070005A - Solid photographing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the probability that in a conventional back-illuminated type solid photographing device, stray light enters a semiconductor substrate having a light receiving part disposed thereon, from a surface (front surface) on the opposite side of a back surface as a photographing surface.SOLUTION: A solid photographing device 1 includes a semiconductor substrate 10, a light receiving part 14, and a light shielding film 20. The solid photographing device 1 is of the back-illuminated type. The light from a photographing object which has entered a back surface S2 of the semiconductor substrate 10 is subjected to photoelectric conversion in the inside of the semiconductor substrate 10, and an electric charge generated by the photoelectric conversion is received by the light receiving part 14, thereby photographing the photographing object. The light receiving part 14 constitutes a PN junction diode together with the semiconductor substrate 10. The light shielding film 20 is disposed to cover the light receiving part 14 on a front surface S1 of the semiconductor substrate 10. The light shielding film 20 is for shielding light that tends to enter from the outside of the solid photographing device 1 to the front surface S1.

Description

  The present invention relates to a solid-state imaging device.

  Patent Document 1 describes a back-illuminated solid-state imaging device. In the solid-state imaging device, light from the imaging target incident on the back surface of the semiconductor substrate is photoelectrically converted inside the semiconductor substrate. And a to-be-photographed object is imaged when the light-receiving part receives the electric charge which arises by it.

  In addition to Patent Document 1, Patent Documents 2 and 3 are cited as prior art documents related to the present invention.

JP 2002-33469 A JP 2000-252452 A Japanese Patent Laid-Open No. 3-148172

  However, the present inventors have found that such a solid-state imaging device has the following problems. That is, in the solid-state imaging device, stray light may enter the semiconductor substrate provided with the light receiving unit from the surface (front surface) opposite to the back surface that is the imaging surface. When stray light enters, a false signal is generated, thereby deteriorating the captured image.

  A solid-state imaging device according to the present invention is a solid-state imaging device that images an object to be imaged by photoelectrically converting light incident on the back surface of a semiconductor substrate, and is provided in the semiconductor substrate and is a PN junction diode together with the semiconductor substrate And a light receiving portion that receives the signal charges generated by the photoelectric conversion, and is provided to cover the light receiving portion on the surface side of the semiconductor substrate, and is incident on the surface from the outside of the solid-state imaging device And a light-shielding film that shields the light.

  In this solid-state imaging device, a light shielding film is provided on the surface side of the semiconductor substrate. Thereby, stray light can be prevented from entering the semiconductor substrate from the surface.

  ADVANTAGE OF THE INVENTION According to this invention, the solid-state imaging device which can obtain a favorable captured image is implement | achieved.

It is sectional drawing which shows 1st Embodiment of the solid-state imaging device by this invention. It is sectional drawing which shows 2nd Embodiment of the solid-state imaging device by this invention. It is sectional drawing which shows 3rd Embodiment of the solid-state imaging device by this invention.

Hereinafter, preferred embodiments of a solid-state imaging device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted.
(First embodiment)

  FIG. 1 is a cross-sectional view showing a first embodiment of a solid-state imaging device according to the present invention. The solid-state imaging device 1 includes a semiconductor substrate 10, a light receiving unit 14, and a light shielding film 20. The solid-state imaging device 1 is a back-illuminated type, and photoelectrically converts light from the imaging target incident on the back surface S2 of the semiconductor substrate 10 inside the semiconductor substrate 1 and charges generated by the photoelectric conversion are received by the light receiving unit 14. And picks up an image of the object. The imaging is preferably performed in a state where the imaging target is in direct contact with the back surface S2. Further, the imaging target is, for example, a finger.

  In the present embodiment, the semiconductor substrate 10 is a P-type silicon substrate. The semiconductor substrate 10 includes a P-type well region 12, and a light receiving portion 14 is formed in the P-type well region 12. The light receiving unit 14 is an N-type impurity diffusion layer (first impurity diffusion layer), and constitutes a PN junction diode together with the semiconductor substrate 10.

  A light shielding film 20 is provided on the surface S <b> 1 side of the semiconductor substrate 10 so as to cover the light receiving unit 14. The light shielding film 20 covers the entire region where the light receiving unit 14 is provided. Particularly in the present embodiment, substantially the entire surface S <b> 1 of the semiconductor substrate 10 is covered with the light shielding film 20. The light shielding film 20 blocks light that enters the surface S1 from the outside of the solid-state imaging device 1.

  A wiring layer 30 is provided on the semiconductor substrate 10, and the above-described light shielding film 20 is provided in the wiring layer 30. The wiring layer 30 includes wirings 32, 34, and 36. The light shielding film 20 is formed of the same material as these wirings 32, 34, and 36. Examples of such a material include Al, Cu, W, and Ti.

  A gate insulating film 42 is formed on the surface S <b> 1 of the semiconductor substrate 10. The gate insulating film 42 is provided adjacent to the light receiving unit 14 described above. A gate electrode 44 connected to the wiring 34 is formed on the gate insulating film 42. The gate insulating film 42 and the gate electrode 44 are made of, for example, silicon oxide and polysilicon, respectively.

  Further, an N-type impurity diffusion layer 46 (second impurity diffusion layer) is formed on the opposite side of the light receiving portion 14 with the gate insulating film 42 and the gate electrode 44 interposed therebetween. The N-type impurity diffusion layer 46 is connected to the wiring 36. The gate insulating film 42, the gate electrode 44, and the N-type impurity diffusion layer 46 together with the light receiving portion 14 constitute a field effect transistor (FET). In this FET, the gate electrode 44 and the N-type impurity diffusion layer 46 function as a reset gate and a reset drain, respectively. The FET is separated from other elements by an element isolation region 62. The element isolation region 62 is, for example, a LOCOS (Local Oxidation of Silicon) region or an STI (Shallow Trench Isolation) region.

  A source follower amplifier 50 is connected to the light receiving unit 14 via a wiring 64. The wiring 64 is also a wiring formed in the wiring layer 30. In FIG. 1, the wiring 64 and the source follower amplifier 50 are shown in a circuit diagram.

The source follower amplifier 50 includes a selection switch FET 52, a detection FET 54, and a load FET 56. These are provided between the high potential side power supply terminal (V _dd ) and the low potential side power supply terminal (V _ss ). Specifically, the detection FET 54, the selection switch FET 52, and the load FET 56 are provided in series in this order from the power supply terminal (V _dd ) to the power supply terminal (V _ss ). The output terminal 58 of the source follower amplifier 50 is connected to the drain terminal of the load FET 56 (terminal on the selection switch FET 52 side).

  Next, the operation of the solid-state imaging device 1 will be described. First, a high pulse is applied to the gate electrode 44 to reset the potential of the light receiving unit 14. Next, a low pulse is applied to the gate electrode 44, whereby charges generated by photoelectric conversion are accumulated in the light receiving unit 14. Then, the potential of the light receiving unit 14 becomes a value depending on the accumulated charge amount, and is output from the output terminal 58 of the source follower amplifier 50.

  Next, effects of the solid-state imaging device 1 will be described. In the solid-state imaging device 1, a light shielding film 20 is provided on the surface S <b> 1 side of the semiconductor substrate 10. Thereby, stray light can be prevented from entering the semiconductor substrate 10 from the surface S1. Therefore, the solid-state imaging device 1 capable of obtaining a good captured image is realized.

  Since the entire region where the light receiving unit 14 is provided is covered with the light shielding film 20, it is possible to effectively prevent deterioration of the captured image due to stray light. Furthermore, in the present embodiment, since substantially the entire surface S1 of the semiconductor substrate 10 is covered with the light shielding film 20, stray light can be further reliably prevented from entering the semiconductor substrate 10.

  The light shielding film 20 is provided in the wiring layer 30 and is formed of the same material as the wirings 32, 34, and 36. Thereby, since formation of the light shielding film 20 can be performed by a wiring formation process, formation of the light shielding film 20 and, in turn, manufacture of the solid-state imaging device 1 is facilitated. For example, the light shielding film 20 can be formed simultaneously with an electrode pad (not shown).

  The light receiving unit 14, the gate insulating film 42, the gate electrode 44, and the N-type impurity diffusion layer 46 constitute an FET. Thereby, a structure for resetting the potential of the light receiving unit 14 can be realized with a simple configuration.

  By the way, Patent Document 3 discloses a solid-state imaging device in which a light shielding film is provided on the surface side of a semiconductor substrate. However, the solid-state imaging device is different from the solid-state imaging device 1 in which a PN junction diode is employed in that a Schottky barrier diode is employed in the light receiving unit. In the solid-state imaging device of this document, the light used is limited to infrared light (having a wavelength of about 5 μm or less), so a PN junction diode cannot be used. That is, if a PN junction diode is used, the band gap is wide and the light receiving part cannot receive infrared light sufficiently.

  Moreover, since the solid-state imaging device of the same literature targets infrared light as described above, it exhibits sensitivity to heat rays. Therefore, when the imaging target is a finger, it is affected by heat rays from the entire finger. Therefore, this solid-state imaging device is not suitable for fingerprint imaging. In this regard, the solid-state imaging device 1 can be suitably applied to fingerprint imaging.

Moreover, since the solid-state imaging device of the same document is a CCD (Charge Coupled Device) type, the wiring layer is a single layer. Therefore, the space in the wiring layer is limited, and it is difficult to form the light shielding film in the wiring layer. Actually, in the solid-state imaging device, a light shielding film is provided on the wiring layer. Therefore, unlike the solid-state imaging device 1, since the light shielding film cannot be formed by the wiring formation process, the number of steps increases by the amount of forming the light shielding film.
(Second Embodiment)

  FIG. 2 is a cross-sectional view showing a second embodiment of the solid-state imaging device according to the present invention. In the solid-state imaging device 2, the light shielding film 20 is formed integrally with the wiring 34. That is, the light shielding film 20 is a part of the wiring in the wiring layer 30 and has both a function as a light shielding film and a function as a wiring. Other configurations and operations of the solid-state imaging device 2 are the same as those of the solid-state imaging device 1.

According to the solid-state imaging device 2 having such a configuration, since the light shielding film 20 can be formed simultaneously with the wiring 34, the number of manufacturing steps can be reduced. Other effects of the solid-state imaging device 2 are the same as those of the solid-state imaging device 1. In the present embodiment, it goes without saying that the light shielding film 20 may be formed integrally with wirings other than the wirings 34 in the wiring layer 30 (for example, the wirings 32 and 36).
(Third embodiment)

  FIG. 3 is a cross-sectional view showing a third embodiment of the solid-state imaging device according to the present invention. In the solid-state imaging device 3, an N-type impurity diffusion layer 48 (second impurity diffusion layer) is formed in the surface layer on the surface S1 side of the semiconductor substrate 10. The N-type impurity diffusion layer 48 is provided adjacent to the light receiving unit 14. A gate insulating film 42 is formed on the surface S <b> 1 of the semiconductor substrate 10 so as to be adjacent to the N-type impurity diffusion layer 48. A gate electrode 44 is formed on the gate insulating film 42. Further, an N-type impurity diffusion layer 46 (third impurity diffusion layer) is formed on the opposite side of the N-type impurity diffusion layer 48 across the gate insulating film 42 and the gate electrode 44.

  The N-type impurity diffusion layer 48, the gate insulating film 42, the gate electrode 44, and the N-type impurity diffusion layer 46 constitute an FET. Also in this FET, the gate electrode 44 and the N-type impurity diffusion layer 46 function as a reset gate and a reset drain, respectively. Other configurations and operations of the solid-state imaging device 3 are the same as those of the solid-state imaging device 1. The effect of the solid-state imaging device 3 is the same as that of the solid-state imaging device 1. Also in this embodiment, the light shielding film 20 may be formed integrally with the wiring in the wiring layer 30 as in the second embodiment.

  The solid-state imaging device according to the present invention is not limited to the above embodiment, and various modifications are possible. For example, although a P-type semiconductor substrate and an N-type light receiving unit are illustrated, an N-type semiconductor substrate and a P-type light receiving unit may be used.

DESCRIPTION OF SYMBOLS 1 Solid-state imaging device 2 Solid-state imaging device 3 Solid-state imaging device 10 Semiconductor substrate 12 P-type well area | region 14 Light-receiving part 20 Light-shielding film 30 Wiring layers 32, 34, 36 Wiring 42 Gate insulating film 44 Gate electrode 46 N-type impurity diffusion layer 48 N Type impurity diffusion layer 50 source follower amplifier 58 output terminal 62 element isolation region 64 wiring 52 selection switch FET
54 Detection FET
56 Load FET
S1 Front side S2 Back side

Claims (11)

A solid-state imaging device that images an object to be imaged by photoelectrically converting light incident on a back surface of a semiconductor substrate,
A light receiving portion provided in the semiconductor substrate, constituting a PN junction diode together with the semiconductor substrate, and receiving a signal charge generated by the photoelectric conversion;
A light-shielding film that is provided on the surface side of the semiconductor substrate so as to cover the light-receiving unit, and shields light from entering the surface from the outside of the solid-state imaging device;
A solid-state imaging device comprising: The solid-state imaging device according to claim 1,
The light-shielding film is a solid-state imaging device that covers the entire region where the light-receiving unit is provided. The solid-state imaging device according to claim 2,
The solid-state imaging device, wherein the light shielding film covers substantially the entire surface of the semiconductor substrate. The solid-state imaging device according to any one of claims 1 to 3,
A wiring layer provided on the surface of the semiconductor substrate and including wiring;
The light-shielding film is a solid-state imaging device formed of the same material as the wiring. The solid-state imaging device according to claim 4,
The light shielding film is a solid-state imaging device provided in the wiring layer. The solid-state imaging device according to claim 5,
The light shielding film is a solid-state imaging device which is a part of the wiring. The solid-state imaging device according to any one of claims 1 to 6,
The solid-state imaging device, wherein the back surface of the semiconductor substrate is a surface in direct contact with the object to be imaged. The solid-state imaging device according to any one of claims 1 to 7,
The imaging object is a solid-state imaging device that is a finger. The solid-state imaging device according to any one of claims 1 to 8,
The light receiving unit is a solid-state imaging device which is a first impurity diffusion layer. The solid-state imaging device according to claim 9,
On the surface of the semiconductor substrate, a gate insulating film provided adjacent to the light receiving unit,
A gate electrode provided on the gate insulating film;
A second impurity diffusion layer provided on the opposite side of the light receiving portion across the gate insulating film and the gate electrode,
The solid-state imaging device in which the light receiving unit, the gate insulating film, the gate electrode, and the second impurity diffusion layer form a field effect transistor. The solid-state imaging device according to claim 9,
A second impurity diffusion layer provided adjacent to the light receiving portion in the semiconductor substrate;
A gate insulating film provided adjacent to the second impurity diffusion layer on the surface of the semiconductor substrate;
A gate electrode provided on the gate insulating film;
A third impurity diffusion layer provided on the opposite side of the second impurity diffusion layer across the gate insulating film and the gate electrode,
The solid-state imaging device in which the second impurity diffusion layer, the gate insulating film, the gate electrode, and the third impurity diffusion layer constitute a field effect transistor.

Images