JPH0524671B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a photoelectric conversion element, a charge transfer means for transferring signal charges of the photoelectric conversion element, and an output circuit for extracting the transferred signal charges as a voltage signal. and a conductive light shielding film that shields incident light and electrically shields it.

[Technical background of the invention and its problems]

A conventional solid-state imaging device is shown in FIGS. 1 and 2.
This solid-state imaging device includes a plurality of photoelectric conversion elements 1,
A charge transfer device 2 that transfers the signal charge of this photoelectric conversion element 1, and an output circuit 3 that extracts the signal charge transferred by this charge transfer device 2 as an output voltage.
The portion other than the photoelectric conversion element 1 is shielded by a light shield film 4. This optical shield film 4 is formed as a film of a conductive material such as aluminum, and also plays the role of an electromagnetic shield. Since it is necessary to make the signal charge transfer path as short as possible, the output circuit 3 is arranged near the photoelectric conversion element 1. Therefore, the output circuit 3 also has a light shield film 4.
covered with

The output circuit 3 of this solid-state imaging device has a cross-sectional structure as shown in FIG. 2a. The transfer electrode 8 of the charge transfer device 2 is formed on the semiconductor substrate 5 with an oxide film 24 interposed therebetween. The output gate electrode 7 is formed adjacent to the transfer electrode 8 and forms a barrier potential between the charge transfer device 2 and the output circuit 3. The reset electrode 9 is for electrically connecting the charge detection bonding layer 6 and the bonding layer 10 at a predetermined potential, and resetting the charge detection bonding layer 6 to a predetermined potential. The conductive line 11 is connected to the input gate 12 of the potential source follower circuit of the charge detection junction layer 6. The source follower circuit has this input gate 12, a drain junction layer 13 set to the power supply voltage, a source junction layer 16 of the load transistor, a gate 15, and an output junction layer 14 for taking out the output voltage. . The conductive light shield film 4 is formed to cover the insulating layer 24 and is set to a substrate voltage.

To explain the charge detection operation of this solid-state imaging device, when the reset electrode 9 is turned on, the potential under the reset electrode 9 becomes as shown by the broken line 25 as shown in FIG. 2b, and the potential of the charge detection junction layer 6 becomes Bonding layer 1
It becomes the same potential as the potential 27 of 0. Reset electrode 9
When turned off, the potential under the reset electrode 9 becomes the broken line 26.
The charge detection junction layer 6 is in a floating state as shown in FIG. In this state, the charge 29 transferred by the charge transfer device 2 exceeds the barrier potential 30 of the output gate electrode 7 and flows in, changing the potential of the charge detection junction layer 6 as shown by a solid line 28. This potential change is input to the source follower circuit to obtain an output.

The potential change Vs of the charge detection junction layer 6 is determined by the total capacitance _CT of the charge detection junction layer 6 and the amount of transferred charge Qs, and is expressed as Vs=Qs/ _CT . Therefore, in order to increase the detection sensitivity, it is necessary to make the total capacitance _CT sufficiently small. The total capacitance C _T of the charge detection junction layer 6 is equal to the capacitance C _FR between the charge detection junction layer 6 and the semiconductor substrate 5 and the output gate electrode 7 .
The capacitance C _FO between , the capacitance C _FR between the reset electrode 9 , the capacitance C _FL1 between the light shield film 4 , and the ground capacitance C _FL2 of the conductive wire 11 , It is expressed as the sum total with the ground capacitance C _G1 of the input gate 12.
That is, C _T =C _FS +C _FO +C _FR +C _FL1 +C _FL2 +C _G1 (1). Here, the values of C _FL1 , C _FL2 , and C _G1 are large,
For this reason, it has not been possible to sufficiently increase the charge detection sensitivity. Furthermore, the ground capacitance C _LO of the output line of the output junction layer 14 is also large, resulting in the problem that the output load capacity equivalently increases and the frequency response deteriorates.

[Purpose of the invention]

The present invention was made in consideration of the above circumstances, and
An object of the present invention is to provide a solid-state imaging device with high charge detection sensitivity and good frequency response.

[Summary of the invention]

In order to achieve this object, the solid-state imaging device according to the present invention includes an opening in the area above the photoelectric conversion element of the conductive light shielding film, and an opening in at least a part of the area above the output circuit. Features.

[Embodiment of the Invention] A solid-state imaging device according to a first embodiment of the invention is shown in FIG. This solid-state imaging device includes a plurality of photoelectric conversion elements 1, a charge transfer device 2 that transfers signal charges of the photoelectric conversion elements 1, and an output circuit that extracts the signal charges transferred by the charge transfer device 2 as an output voltage. 3, and is covered with a conductive light shield film 4 having an opening on the photoelectric conversion element 1. This embodiment is characterized in that an opening 30 is provided in the light shield film 4 also in the region above the output circuit 3.

This output circuit 3 is shown in detail in FIGS. 4 and 5. FIG. 4 shows the planar configuration of this output circuit 3,
FIG. 5 shows a cross-sectional configuration. However, the cross-sectional configuration in FIG. 5 has been modified to make it easier to understand this embodiment, and there are some differences from the actual cross-section. The output circuit 3 of this embodiment consists of a floating junction type charge detection circuit and a two-stage source follower circuit. Output gate electrode 7 is transfer electrode 8
is formed adjacent to and forms a barrier potential. The reset electrode 9 is for electrically connecting the charge detection bonding layer 6 and the bonding layer 10 at a predetermined potential, and resetting the charge detection bonding layer 6 to a predetermined potential. A conductive line 11 connects the potential of the charge detection junction layer 6 to the input gate 12 of the source follower circuit. The source follower circuit has a two-stage configuration. The first stage source follower circuit is composed of a drain junction layer 10, an input gate 12, an output junction layer 14, a source junction layer 32 and a gate 31 of a load transistor, and a second stage source follower circuit is the drain junction layer 10, the input gate 34, the output junction layer 35, and the source junction layer 3 of the load transistor.
2 and a gate 31. The output junction layer 14 of the first stage source follower circuit and the input gate 34 of the second stage source follower circuit are connected to the conductive wire 36.
connected with. Since the conductive line 45 uses the source junction layer 32 of the source follower circuit as a reference potential, it is normally grounded to the potential of the semiconductor substrate 5. Conductive wire 46
is the output of the source follower circuit, that is, output circuit 3
It extracts the output of The conductive wire 47 supplies power supply voltage.

The conductive light shield film 4 does not cover the entire surface as in the conventional case, but has an opening 100. In this embodiment, the opening 100 is provided above a part of the floating junction type charge detection circuit and the first stage source follower circuit in the output circuit 3. Specifically, they are a part of the output gate electrode 7, the charge detection junction layer 6, the junction layer 10, a part of the reset electrode 9, the conductive line 11, and the upper part of the input gate 12.

In this way, in this embodiment, a part of the optical shield film 4 is removed, so that the total capacitance C _T of the charge detection junction layer 6 is equal to the capacitance C _FS between the charge detection junction layer 6 and the semiconductor substrate. Capacitance C _FO between output gate electrode 7 and capacitance C _FR between reset electrode 9
and the capacitance C _FD of the input gate 12. That is, _CT = C _FS + C _FO + C _FR + C _FD (2). In other words, as can be seen by comparing with the conventional equation (1), the capacitance between the light shielding film and
C _FL1 and C _FL2 disappear, and the capacitance C _T becomes smaller. Therefore, the potential change of the charge detection junction layer 6
The charge detection sensitivity Vs/Qs=1/ _CT , which is the ratio between Vs and the transferred charge amount Qs, becomes very high.

To explain the operation of this embodiment, the reset electrode 9
When turned on, the potential under the reset electrode 9 becomes high, and the potential of the charge detection junction layer 6 becomes the same as the potential of the junction layer 10. When the reset electrode 9 is turned off,
The potential under the reset electrode 9 becomes low, and the charge detection junction layer 6 enters a floating state. In this state, the charge transferred from the charge detection device is transferred to the output gate electrode 7.
The potential of the inflow charge detection junction layer 6 is changed beyond the barrier potential of . This potential change V _s is detected by a two-stage source follower circuit. As mentioned above, in this embodiment, the total capacitance C _T of the charge detection junction layer 6
is small, the potential change Vs becomes larger than the transferred charge Qs, and the detection sensitivity becomes higher.

Note that since there is no light shield film 4, incident light causes photoelectric conversion to occur at the Pn junction consisting of the charge detection bonding layer 6, the bonding layer 10, and the semiconductor substrate 5, and charges are generated; however, the transfer charge cannot be detected and reset. If this is operated periodically at a high speed of 1 MHz or higher, for example, this charge can be almost ignored, so there is no problem.

An output circuit 3 of a solid-state imaging device according to a second embodiment of the present invention is shown in FIGS. 6, 7, and 7. This example is the first
The shape of the opening 101 of the light shield film 4 is different from that of the embodiment. That is, a wider area of the light shield film 4 is removed than the opening 101 in the first embodiment. Specifically, in addition to a part of the output gate 7, the charge detection junction layer 6, the junction layer 10, a part of the reset electrode 9, and the area above the conductive line 11, the first stage A conductive wire 36 connecting the output junction layer 14 of the source follower circuit and the input gate 34 of the second stage source follower circuit, and the input gate 36 of the second stage source follower circuit and the output junction layer 3
The light shielding film 4 in the upper region with 5 has been removed. In this embodiment, in addition to the capacitances C _FL1 and C _FL2 , the ground capacitance of the output conductive wire 36 of the output junction layer 14 is
_CLO will also be eliminated. Therefore, the charge detection sensitivity is increased, and the frequency response, which has been degraded due to the presence of the capacitance 10, is improved.

Note that FIG. 8 is an equivalent circuit of the output circuits shown in FIGS. 4 to 7. It can be seen that if an opening is provided as in the first embodiment, the capacitance C _FL (=C _FL1 +C _FL2 ) indicated by reference numeral 61 is eliminated, so that the detection sensitivity is improved. Furthermore, it can be seen that if an opening is provided as in the second embodiment, the capacitance C _LO indicated by reference numeral 62 is further eliminated, so that the frequency response is improved.

In the above embodiments, the output circuit is a floating junction type detection circuit, but the present invention can also be applied to a floating gate type or other capacitance storage type detection circuit. Furthermore, by removing the light shielding film on other circuits of the solid-state imaging device, the frequency response of that circuit can be improved.

〔Effect of the invention〕

As described above, according to the present invention, a solid-state imaging device having an output circuit with high charge detection sensitivity can be realized without impairing the light shielding function of the conductive light shielding film. Furthermore, the frequency response can be improved by removing the light shielding film from the region.

[Brief explanation of drawings]

FIG. 1 is a plan view of a conventional solid-state imaging device, FIG. 2a is a sectional view of an output circuit of the solid-state imaging device, FIG. 2b is a potential diagram showing the operation of the output circuit, and FIG. 3 is a diagram of the present invention. FIG. 4 is a plan view of the output circuit of the solid-state imaging device according to the first embodiment of the invention, FIG. 5 is a sectional view of the output circuit, and FIG. FIG. 7 is a plan view of the output circuit of the solid-state imaging device according to the embodiment, FIG. 7 is a sectional view of the output circuit, and FIG. 8 is a circuit diagram of the output circuit. DESCRIPTION OF SYMBOLS 1... Photoelectric conversion element, 2... Charge transfer device, 3... Output circuit, 4... Light shield film, 5... Semiconductor substrate, 6
... Charge detection junction layer, 7... Output gate electrode, 8... Transfer electrode, 9... Reset electrode, 10... Bonding layer, 11
...Conductive line, 12...Input gate, 13...Drain junction layer, 14...Output junction layer, 15...Gate, 16...
Source junction layer, 24... Insulating layer, 31... Gate, 3
2... Source junction layer, 34... Input gate, 35... Output junction layer, 36... Conductive line, 100... Opening, 10
1...Opening.

Claims (1)

[Claims] 1. A plurality of photoelectric conversion elements that generate signal charges according to incident light, a charge transfer means that transfers the signal charges generated by these photoelectric conversion elements, and a charge transfer means that transfers the signal charges generated by the photoelectric conversion elements. an output circuit having a charge detection section that detects a signal charge detected by the charge detection section and an amplification section that amplifies the detection signal of the charge detection section and takes it out as a voltage signal; a conductive light shielding film that shields incident light and electrically shields it; , wherein the conductive light shielding film has an opening in a region above the photoelectric conversion element and has an opening in at least a region above the charge detection section among the regions above the output circuit. Imaging device.