JPH0449263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photoelectric conversion device, and more particularly to a photoelectric conversion device that accumulates carriers generated by incident light and reads out signals based on the accumulated carriers.

[Prior Art] In recent years, research on photoelectric conversion devices, particularly solid-state imaging devices, has been actively conducted along with the progress of semiconductor technology, and some of them have begun to be put into practical use.

These solid-state imaging devices can be broadly classified into
It is classified into two types: CCD type and MOS type. A CCD type imaging device forms a potential well under a MOS capacitor electrode, stores charges generated by incident light in this well, and during readout, these potential wells are sequentially moved by pulses applied to the electrode. The principle is that the accumulated charge is transferred to the output amplifier section and read out. Also
Some CCD-type imaging devices use a pn junction diode structure for the light receiving section and a CCD structure for the transfer section. On the other hand, in a MOS type imaging device, charges generated by incident light are accumulated in each photodiode made of a pn junction that constitutes the light receiving section, and when reading out, the MOS switching transistor connected to each photodiode is activated. It uses the principle that the accumulated charge is read out to the output amplifier section by sequentially turning on the transistors.

CCD type imaging device has a relatively simple structure,
In addition, considering the noise that can be generated, only the capacitance value of the charge detector consisting of the floating diffusion in the final stage contributes to random noise, so it is a relatively low-noise imaging device and is capable of low-light photography. be. However, due to process constraints in manufacturing CCD type imaging devices, MOS is used as the output amplifier.
Since the type amplifier is on-chip, 1/f noise, which is easily noticeable on images, is generated from the interface between silicon and SiO ₂ film. Therefore, although it is said to have low noise, there are limits to its performance. Furthermore, if the number of cells is increased to achieve higher density in order to achieve higher resolution, the maximum amount of charge that can be stored in one potential well will decrease, making it impossible to maintain a dynamic range. This becomes a big problem as resolution increases. Furthermore, since a CCD-type imaging device transfers accumulated charge by sequentially moving the potential wells, even if there is a defect in one of the cells, charge transfer may stop at that point, or It also has the disadvantage that the manufacturing yield cannot be improved.

On the other hand, MOS type imaging devices are structurally
Although it is a little more complicated than a CCD type imaging device, especially a frame transfer type device, it has the advantage of being able to be configured to have a large storage capacity and having a wide dynamic range. Furthermore, even if one of the cells has a defect, because of the X-Y addressing method, the defect does not affect other cells, which is advantageous in terms of manufacturing yield. However, this
In MOS type imaging devices, wiring capacitance is connected to each photodiode during signal readout, which causes an extremely large signal voltage drop and a drop in the output voltage.The wiring capacitance is large, which causes random noise. It also has disadvantages such as fixed pattern noise mixed in due to variations in the parasitic capacitance of each photodiode and MOS switching transistor for horizontal scanning, and that low-light photography is difficult compared to CCD type imaging devices. have.

Furthermore, in the future, as the resolution of imaging devices increases, the size of each cell will be reduced and the amount of accumulated charge will decrease. On the other hand, the wiring capacitance, which is determined by the chip size, does not decrease much even if the line width is made thinner. For this reason, the MOS type imaging device becomes increasingly disadvantageous in terms of S/N.

Although CCD type and MOS type imaging devices have the above-mentioned advantages and disadvantages, they are gradually approaching the level of practical use. However, it can be said that there are essentially major problems in promoting the higher resolution that will be required in the future.

On the other hand, regarding solid-state imaging devices,
−150878 Publication “Semiconductor Imaging Device”, Japanese Unexamined Patent Publication No. 1983-
Publication No. 157073 “Semiconductor imaging device”, Japanese Patent Application Laid-open No. 1983-
A new method is proposed in Publication No. 165473 "Semiconductor imaging device". CCD type and MOS type imaging devices are
Charges generated by incident light are transferred to the main electrode (e.g.
In contrast, the method proposed here stores the charge generated by incident light on the control electrode (e.g., the base of a bipolar transistor, the SIT (static induction transistor) or the MOS transistor). gate)
It is based on a new concept of controlling the flowing current using the charges accumulated in the light and generated by light. In other words, whereas the CCD type and MOS type read out the accumulated charge itself to the outside, the method proposed here amplifies the charge using the amplification function of each cell and then reads out the accumulated charge. If you look at it from another perspective, it is read out as a low impedance output through impedance conversion. Therefore, the method proposed here has high output, wide dynamic range, and low noise, and because the carriers (charges) excited by the optical signal accumulate on the control electrode, non-destructive readout is possible. It has several advantages such as: Furthermore, it can be said that this method has the potential for higher resolution in the future.

[Technical Problems to be Solved by the Invention] However, this method is basically an X-Y addressing method, and the element structure described in the above publication is a bipolar transistor in each cell of a conventional MOS type imaging device. The basic configuration is a combination of amplification elements such as , SIT transistors, etc.
Therefore, it has a relatively complicated structure, and although it has the possibility of achieving high resolution, there is a limit to how high resolution can be achieved as it is.

There are also limitations in the points described below. The above-mentioned Japanese Patent Application Publication No. 150878, Japanese Patent Application Publication No. 56-1508-
No. 157073, Japanese Patent Application Laid-open No. 165473, and “Application to SIT (Static Injection Transistor) Image Sensor, Technical Report of the Television Society (hereinafter referred to as
``TV Society Journal'' is a typical example of the prior art in which one of the inventors of the present invention was involved.

JP-A-56-150878 and JP-A-56-157073 disclose that charges are added to the P ⁺ region of a hook structure consisting of N ⁺ , P ⁺ , I (or P ^- , N ^- ), and N ⁺ regions. accumulate,
N ⁺ forming a capacitor with ground potential
A configuration is described in which the potential of a region is read out using a switching transistor.

However, with this configuration, high-speed readout with good linearity cannot be performed. Also, in the reset operation after reading, only the P ⁺ region is grounded, so many noticeable afterimages occur and fixed pattern noise is large.

On the other hand, Japanese Patent Application Laid-open No. 56-165473 describes the N ⁺ region,
N + , P ⁺ , I (or P ^{- ,} N ^- ), N ⁺ , consisting of a floating P ⁺ region, a high resistance region and an N ⁺ region connected to a transparent electrode to which a pulsed voltage is applied. The hook structure of the region is shown. The floating N ⁺ region also serves as one of the main electrode regions of the readout transistor, and during readout, the transistor is turned on and electrons flow into the positively charged N ⁺ region, and the voltage change is used as a signal. Perform reading. However, this method also does not provide a high-speed output signal with good linearity. Further, in the reset operation after reading, the N ⁺ region on the transparent electrode side is simply set to 0 or a slightly negative potential, resulting in many noticeable afterimages.

The TV Society Journal describes gate storage type photocells and base storage type photocells. Among these, the gate storage type photocell has a configuration in which the gate is placed in a floating state, the gate region is reverse biased to a predetermined voltage in advance via a refresh line via an insulating film, and the voltage is read out to an output circuit of a source-grounded resistive load. However, in this configuration, since there is no reset means on the output circuit side, the reset operation is insufficient and many afterimages occur.

Moreover, on the other hand, the base storage type photocell has N ⁺ ,
It has a P ⁺ , N ^- , N ⁺ phototransistor structure, and includes a floating base (P ⁺ ), a collector (N ⁺ ) to which a pulsed voltage is applied, a capacitor, and a switching MOSFET. It consists of an emitter (N ⁺ ) to which the output circuit of the emitter follower is connected. However, in this configuration, since reading is performed by applying a voltage to the collector, it is difficult to ensure linearity in high-speed operation, as will be described later with reference to FIGS. 4 and 5.

In addition to the above-mentioned conventional technology, there is also a U.S. patent
In the specification of No. 3624428 and Japanese Patent Publication No. 50-38531, an output circuit with a grounded emitter resistor load is connected to a transistor whose base is provided with an electrode through an insulating layer, and the base is reverse biased to perform storage operation. A configuration is shown in which the current is read out using the output circuit of the emitter-grounded resistive load. However, since it is a destructive current readout, linearity and afterimage characteristics are poor. Since the base and collector are connected to each other with a relatively high impurity concentration, the sensitivity, particularly the blue sensitivity, is low.

[Object of the Invention] An object of the present invention is to provide a new photoelectric conversion device that has an amplification function in each cell but has an extremely simple structure and can sufficiently cope with future increases in resolution.

Another object of the present invention is to provide a photoelectric conversion device with excellent high-speed performance that can obtain an output signal with good linearity with respect to irradiated light in a very short time.

Still another object of the present invention is to provide an excellent photoelectric conversion device in which afterimages and fixed pattern noise are hardly a problem even when performing high-speed readout with good linearity.

Still another object of the present invention is to provide a photoelectric conversion device that is sensitive even to blue light. This purpose includes: a collector region made of a first conductivity type semiconductor electrically connected to the collector electrode; and a high-resistance semiconductor region disposed adjacent to the collector region and having a higher resistivity than the collector region. and a base region made of a semiconductor of a second conductivity type different from the first conductivity type, which is disposed adjacent to the high-resistance semiconductor region and is disposed with an insulating region between the electrodes. an emitter region made of a semiconductor of a first conductivity type and electrically connected to an emitter electrode disposed adjacent to the base region and electrically connected to an output circuit including a capacitive load; In the photoelectric conversion device, the base region is configured such that carriers generated by received light energy are accumulated in the base region by controlling the potential of the base region with the electrodes. An output signal corresponding to the carrier is read out to the emitter electrode side as a voltage at the capacitive load, and the accumulated carrier is then placed in a floating state to be refreshed via the emitter electrode. This is achieved by a photoelectric conversion device.

[Function] According to the present invention, the potential of the base region can be controlled independently of the emitter and collector regions during each of storage, readout, and refresh operations.
During storage, the junction between the base region and the emitter region connected to the output circuit changes from a reversely biased state to the potential of the base region to the potential of the emitter region as charge accumulates. Therefore, since the saturation voltage is determined by the bias voltage at this time, a desired saturation voltage can be ensured. During the next readout, the junction can be deeply biased in the forward direction. In this way, it is possible to obtain an output signal with good linearity for the irradiated light in an extremely short period of time. Also, when refreshing,
As in the case of readout, by independently controlling the potential of the base region and deeply biasing the junction between the base region and the emitter region in the forward direction, refresh can be performed through the emitter region connected to the output circuit, eliminating image retention with high-speed operation. and noise removal is possible.

[Example] Hereinafter, embodiments of the present invention will be described in detail using the drawings.

FIG. 1 is a diagram illustrating the basic structure and operation of a photosensor cell that constitutes a photoelectric conversion device according to an embodiment of the present invention.

FIG. 1a shows a plan view of the optical sensor cell, FIG. 1b shows a sectional view of a section AA' in the plan view of FIG. 1a, and FIG. 1c shows an equivalent circuit thereof. In addition, the same numbers are given to the parts common to FIGS. 1a, b, and c in each part.

Although FIG. 1 shows a plan view of the aligned layout method, it goes without saying that the pixel shifting method (interpolation layout method) can also be used to increase the horizontal resolution.

As shown in Figure 1a and b, this photo sensor cell is made of silicon that forms the collector and is doped with impurities such as phosphorus (P), antimony (Sb), and arsenic (As) to make it n-type or n ⁺ type. On board 1, usually
A passivation film 2 made of a PSG film or the like; an insulating oxide film 3 made of a silicon oxide film (SiO ₂ ); made of SiO ₂ or Si ₃ N ₄ or the like for electrically insulating between adjacent photosensor cells An element isolation region 4 made of an insulating film or a polysilicon film, etc.; an n ^- region 5 as a high-resistance semiconductor region with a low impurity concentration and higher resistivity than the substrate 1 formed by epitaxial technology; p region 6 which is the base of a bipolar transistor doped with an impurity such as boron (B) using an impurity diffusion technique or an ion implantation technique; becomes
n ⁺ region 7; Wiring 8, which is made of a conductive material such as aluminum (Al), Al-Si, Al-Cu-Si, etc. and partially serves as an emitter electrode, for reading signals to the outside; Insulating film 3, an electrode 9 as an electrode for applying a pulse to the p-region 6 in a floating state; its wiring 10; an impurity formed by impurity diffusion technology etc. to make ohmic contact with the back surface of the substrate 1; It consists of a highly concentrated n ⁺ region 11; an electrode 12 as a collector electrode formed of a conductive material such as aluminum for providing a substrate potential, that is, a collector potential of a bipolar transistor;

Note that 19 in FIG. 1A is a contact portion for connecting the n ⁺ region 7 and the wiring 8. Also wiring 8
The alternating portions of the wiring 10 are so-called two-layer wiring, and are insulated from each other by insulating regions formed of an insulating material such as SiO ₂ . That is, it has a two-layer metal wiring structure.

The capacitor Cox 13 in the equivalent circuit of ^FIG .
It is composed of an n ^- region 5 having a low impurity concentration and an n or n ⁺ region 1 serving as a collector.
As is clear from these drawings, p region 6 is made into a floating region.

The second equivalent circuit in Figure 1c shows the bipolar transistor 14 with a base-emitter junction capacitance Cbe.
15. Base-emitter pn junction diode Dbe
16. It is expressed using a base-collector junction capacitance Cbc17 and a base-collector pn junction diode Dbc18.

Here, as the original equivalent circuit diagram, pn junction diode Dbe16 and pn junction diode Dbc18
Symbols indicating two different orientations of current sources that should be written in parallel with are omitted.

The circuit configuration will be described with reference to FIGS. 2 and 3. An output circuit is connected to the emitter region of a photoelectric conversion cell including a transistor as shown by the reference numeral 30 in FIG. This output circuit consists of vertical lines 38, 38', 38'', horizontal shift register 39, MOS transistors 40, 40', 4
0'', output line 41, MOS transistor 42,
It is composed of an output transistor 44, a load resistor 45, etc., and each of the vertical lines 38, 38', 38'' has a wiring capacitance as a capacitive load.

Further, a vertical shift register 32, a buffer MOS transistor 33, a vertical shift register 32, a buffer MOS transistor 33,
33'33'', terminal 34, horizontal line 31, 31',
31'' is provided.

The potential of the base region, which is a control electrode region, is controlled by a reading means independently of the emitter and collector regions, which are main electrode regions. The operation at this time will be explained with reference to FIG. At the time of reading, a positive voltage V _R is independently applied from the wiring 10 to the emitter as a main electrode region in a floating state and the collector as a main electrode region held at a positive potential, thereby changing the emitter potential. On the other hand, by increasing the base potential, the forward potential of the junction between the control electrode region (base region) and the main electrode region (emitter region) connected to the output circuit is biased in the positive direction. In this way, a current flows until the emitter potential becomes equal to the base potential, that is, the accumulated voltage generated by light irradiation, but the time required at this time is shortened by the action of the voltage _VR , even in high-speed readout. Excellent linearity can be ensured.

On the other hand, the emitter as the first main electrode region is connected to the MOS transistors 48 and 4 as switching means.
8', 48'' is connected to a first reference voltage source indicated with a ground symbol and grounded.

At this time, the collector as the second main electrode region is connected to the second reference voltage source, that is, set to a positive potential or ground potential.In this state, a voltage of positive potential _VRH is applied to the collector as the control electrode region. By controlling the potential, at least the base-emitter region is forward biased, holes accumulated in the base region flow out, electrons flow into the base region, and the accumulated charges disappear. As a forward bias means for applying such a forward bias, in addition to the above reading means, for example, the buffer MOS transistors 35 and 3 shown in FIG.
5', 35'', terminals 36, 37, etc.

The basic operation of the optical sensor cell will be explained below with reference to FIG.

The basic operation of this photosensor cell consists of a charge accumulation operation by light incidence, a readout operation, and a refresh operation.

First, charge storage operation will be explained.

In charge storage operation, for example, the emitter is
It is grounded through a wiring 8, and its collector is biased to a positive potential through a wiring 12. In addition, the base is connected to the capacitor Cox13 in advance by wiring 1.
It is assumed that by applying a positive pulse voltage through 0, the emitter 7 is at a negative potential, that is, the emitter 7 is brought into a reverse bias state. The operation of biasing the base 6 to a negative potential by applying a pulse to the Cox 13 will be explained in detail later when the refresh operation is explained.

In this state, when light 20 enters from the front side of the photosensor cell as shown in FIG. 1, electron-hole pairs are generated within the semiconductor.
Of these, electrons flow toward the n-region 1 side because the n-region 1 is biased to a positive potential, but holes are rapidly accumulated in the p-region 6. Due to the accumulation of holes in the p region, the potential of the p region 6 gradually changes toward a positive potential.

In Figures 1a and 1b, the lower surface of the light-receiving surface of each sensor cell is mostly occupied by the p region, and some n ⁺
It has become area 7. Naturally, the concentration of electron-hole pairs excited by light increases as it approaches the surface. Therefore, many electron-hole pairs are excited in the p-region 6 by the light.
The photoexcited electrons in the p region immediately flow out of the p region 6 without recombining, and the n
If the structure is such that the holes are absorbed by the p-region 6, the holes excited in the p-region 6 will be accumulated as they are,
P region 6 is changed to a positive potential direction. When the impurity concentration in p region 6 is made uniform, electrons excited by light are diffused and are distributed between p region 6 and p region 6.
It flows to the pn ^- junction with the n ^- region 5, and is then absorbed by the n collector region 1 due to drift due to the strong electric field applied to the n ^- region. . Of course, it is possible for electrons to travel within the p region 6 by diffusion alone, but if the structure is configured so that the p-based impurity concentration decreases from the surface to the inside, this impurity concentration difference , an electric field Ed, Ed=1/W _B・kT/q・lnN _AS /N _Ai , is generated in the base from the inside toward the surface. Here, W _B is the depth from the light incident surface of the p region 6, k is the Boltzmann constant, T is the absolute temperature, q is the unit charge, N _AS is the surface impurity concentration of the p base region 6, and N _Ai is the p Region 6 n ^- High resistance region 5
is the impurity concentration at the interface with

Here, if N _AS /N _Ai >3, the movement of electrons in p region 6 will be performed by drift rather than diffusion. That is, in order to effectively operate carriers excited by light in p-region 6 as signals, the impurity concentration of p-region 6 must decrease from the light-incidence side surface toward the inside. is desirable. When p region 6 is formed by diffusion, its impurity concentration decreases toward the inside compared to the light incident side surface.

A portion below the light-receiving surface of the sensor cell is occupied by the n ⁺ region 7 . The depth of n ⁺ region 7 is typically 0.2
Since the thickness is designed to be about 0.3 μm or less, the amount of light absorbed by the n ⁺ region 7 is not so large to begin with, so there is no problem. just,
For light on the short wavelength side, especially blue light, the presence of the n ⁺ region 7 causes a decrease in sensitivity. The impurity concentration of the n ⁺ region 7 is usually designed to be about 1×10 ²⁰ cm ⁻³ or more. The diffusion distance of holes in the n ⁺ region 7 doped with impurities at such a high concentration is about 0.15 to 0.2 μm. Therefore, in order to effectively flow the holes optically excited in the n ⁺ region 7 into the p region 6, the n ⁺ region 7 must also have a structure in which the impurity concentration decreases from the light incident surface toward the inside. desirable. If the impurity concentration distribution in the n ⁺ region 7 is as described above, a strong drift electric field will be generated from the surface on the light incidence side toward the inside, and the holes photoexcited in the n ⁺ region 7 will immediately become p
Flows into area 6. If the impurity concentration of both the n ⁺ region 7 and the p region 6 decreases from the light incident side surface toward the inside, then the n ⁺ region 7 and the p region existing on the light incident side surface side of the sensor cell 6
All optically excited carriers function effectively as optical signals. If this n ⁺ region 7 is formed by impurity diffusion from a silicon oxide film or polysilicon film doped with As or P at a high concentration, it is possible to obtain an n ⁺ region with the desired impurity gradient as described above. It is.

Eventually, the accumulation of holes will cause the base potential to change to the emitter potential, in this case to ground potential, where it will be clipped.
More precisely, the base and emitter are biased deeply in the forward direction, and the holes accumulated in the base are clipped at a voltage that begins to flow to the emitter. That is, the saturation potential of the photosensor cell in this case is approximately given by the potential difference between the bias potential when p region 6 is initially biased to a negative potential and the ground potential. When n ⁺ region 7 is not grounded and accumulates charges generated by optical input in a floating state, p region 6 can accumulate charges to approximately the same potential as n region 1 .

The above is a qualitative and general explanation of the charge accumulation operation, but a more specific and quantitative explanation will be given below.

The spectral sensitivity distribution of this optical sensor cell is given by the following equation.

S (λ) = λ/1.24・exp(−αx) × {1−exp(−αy)}・T [A/W] However, λ is the wavelength of light [μm], and α is the light wavelength in the silicon crystal. Attenuation coefficient [μm ^-1 ] x is the thickness of the "dead layer" on the semiconductor surface that causes recrystallization loss and does not contribute to sensitivity [μm], y is the thickness of the epitaxial layer [μm], T represents the transmittance, that is, the ratio of the amount of light that effectively enters the semiconductor, taking into account reflection and the like, relative to the amount of incident light. Spectral sensitivity S(λ) of this optical sensor cell
The photocurrent Ip is calculated using the following equation and the irradiance Ee (λ).

Ip=∫ ^∞ _p S(λ)・Ee(λ)・dλ [μA/cm ² ] However, the irradiance Ee(λ) [μW・cm ⁻²・nm ⁻¹ ] is given by the following formula.

Ee(λ)=Ev・P(λ)/6.80∫ ^∞ / _p V(λ)P(λ
)・dλ [μW・cm ^-2・nm ^-1 ] However, Ev is the illuminance of the sensor's light receiving surface [Lnx], P
(λ) is the light distribution that is incident on the light receiving surface of the sensor,
V(λ) is the specific luminous efficiency of the human eye.

Using these equations, for an optical sensor cell with an epitaxial layer thickness of 4 μm, when irradiated with light source A (2854°K) and the sensor light receiving surface illuminance is 1 [Lux], approximately
A photocurrent of 280 nA/cm ^-2 flows, and the number of incident photons or the number of generated electron-hole pairs is about 1.8×10 ¹² /cm ² ·sec.

Also, at this time, the potential Vp generated by the accumulation of holes excited by light in the base is Vp=
It is given by Q/C. Q is the amount of accumulated hole charge, and C is the junction capacitance that is the sum of Cbe15 and Cbc17.

Now, the impurity concentration of n ⁺ region 7 is 10 ²⁰ cm ^-3 , the impurity concentration of p region 6 is 5×10 ¹⁶ cm ^-3 , the impurity concentration of n ^- region 5 is 10 13 cm -3 , and the impurity concentration of n ⁺ region 7 is 10 ¹³ cm ^-3 . The area is 16μm ² , p
When the area of region 6 is 64 μm ² and the thickness of n ^- region 5 is 3 μm, the junction capacitance is approximately 0.014 pF. On the other hand, the number of holes accumulated in p region 6 is determined by the accumulation time 1/ 60sec, effective light receiving area, i.e. p region 6
The area obtained by subtracting the area of electrodes 8 and 9 from the area of
If it is about 56μm ² , it will be 1.7×10 ⁴ pieces. Therefore, the potential Vp generated by light incidence is about 190 mV.

What should be noted here is that as the resolution increases and the cell size decreases, the amount of light incident on each photosensor cell decreases, and the amount of accumulated charge Q also decreases. As the cell size decreases, the junction capacitance also decreases in proportion to the cell size, so the potential Vp generated by light incidence remains almost constant. This is because the optical sensor cell according to the present invention has an extremely simple structure, as shown in FIG. 1, and has the possibility of having an extremely large effective light-receiving surface.

This is one of the reasons why the photoelectric conversion device of the present invention is advantageous compared to the case of an interline type CCD. If an attempt is made to ensure this, the area of the transfer section becomes relatively large, which reduces the effective light-receiving surface, resulting in a decrease in sensitivity, that is, the voltage generated by light incidence. In addition, in an interline type CCD type imaging device, the saturation voltage is limited by the size of the transfer section and gradually decreases, whereas in the optical sensor cell of the present invention, as mentioned earlier, the saturation voltage The saturation voltage is determined by the bias voltage when p-region 6 is biased to a negative potential, and a large saturation voltage can be ensured.

The operation of reading out the voltage generated by the charges accumulated in p region 6 as described above to the outside will be described next.

In the read operation state, the emitter and wiring 8 are held in a floating state, and the collector is held at a positive potential Vc.c.

Figure 2 shows an equivalent circuit.

Also here, symbols indicating two current sources in different directions that should originally be written in parallel with the pn junction diode Dbe16 and the pn junction diode Dbc18 as an equivalent circuit are omitted.

Now, if the potential when the base 6 is biased to a negative potential before light irradiation is -V _B , and the accumulated voltage generated by light irradiation is V _P , then the base potential is
The potential is −V _B +V _P. In this state, a positive voltage V _R for reading is applied to the electrode 9 through the wiring 10.
is applied, this positive potential V _R increases the oxide film capacitance
Cox13 and base-emitter junction capacitance Cbe1
5. The capacitance is divided by the base-collector junction capacitance Cbc7, and the voltage Cox/Cox+Cbe+Cbc·V _R is added to the base. Therefore, the base potential becomes −V _B +V _P +Cox/Cox+Cbe+Cbc·V _R. Here, if the condition -V _B +Cox/Cox+Cbe+Cbc·V _R =O is satisfied, the base potential becomes the accumulated voltage V _P generated by light irradiation. When the base potential is biased in a positive direction with respect to the emitter potential in this way, electrons are injected from the emitter to the base, and since the collector potential is positive, they are accelerated by the drift electric field and flow into the collector. reach. The current flowing at this time is given by the following equation.

i=A _j・q・Dn・n _pe /W _B (1+lnN _Ae /N _Ac ) × {expq/kT (V _p −V _e )−1} However, A _j is the junction area between the base and emitter, q
is the unit charge (1.6×10 ^-19 coulombs), D _o is the electron diffusion constant in the base, n _pe is p
Electron concentration as a minority carrier at the base emitter end, W _B is the base width, N _Ae is the acceptor concentration at the base emitter end, N _Ac
is the acceptor concentration at the collector end of the base,
k is Boltzmann's constant, T is absolute temperature, and V _e is emitter potential.

This current has an emitter potential V _e as a base potential,
In other words, here the accumulated voltage generated by light irradiation
It is clear from the above equation that the flow continues until it becomes equal to V _P. At this time, the temporal change in the emitter potential V _e is calculated using the following formula.

CS・dV _e /dt= i=A _j・q・Dn・n _pe /W _B (1+lnN _Ae /N _AC ) × {expq/kT (V _p −V _e )−1} However, here, the wiring capacitance CS is the capacitance 21 of the wiring 8 connected to the emitter.

FIG. 4 shows an example of a temporal change in emitter potential calculated using the above formula.

According to FIG. 4, it takes about 1 second for the emitter potential to become equal to the base potential. This is because when the emitter potential V _e approaches V _p , less current flows. Therefore, the means to solve this problem is to set the condition −V _B +Cox/Cox+Cbe+Cbc·V _R =O when applying the positive voltage V _R to the electrode 9, but instead of this condition − One possible method is to insert the condition that V _B +Cox/Cox+Cbe+Cbc・V _R =V _Bias and bias the base potential by V _Bias in the forward direction.
The current flowing at this time is given by the following equation.

i=A _j・q・Dn・n _pe /W _B (1+lnN _Ae /N _Ac ) x {expq/KT (V _P +V _Bias −V _e )−1} In Figure 5a, V _Bias = 0.6V and In this case, after a certain period of time, the V _R applied to the electrode 9 is returned to zero volts, and the flowing current is stopped. The relationship between the read voltage, that is, the emitter potential, and the accumulated voltage V _p is shown below. However, in FIG. 5a, the read voltage is always added with a constant potential depending on the read time due to the bias voltage component, but the value obtained by subtracting the gain is plotted. When the positive voltage V _R applied to the electrode 9 is returned to zero volts, a voltage of -Cox/Cox+Cbe+Cbc・V _R is added to the base potential, which is the opposite of when it was applied, so the base potential becomes the positive voltage V It becomes the state before applying _R , that is, -V _B , and the emitter is reverse biased, so the flow of current stops. According to Figure 5a, if the readout time is about 100ns or more (that is, the time during which V _R is applied to the electrode 9), the linearity of the accumulated voltage V _p and the readout voltage can be ensured over a range of about 4 digits. This shows that high-speed reading is possible. In Figure 5a, the 45° line is the result when sufficient time is taken for reading.In the above calculation example, the capacitance CS of the wiring 8 is set to 4 pF, which is 0.014 of the junction capacitance of Cbe + Cbc. Although it is approximately 300 times larger than pF, the accumulated voltage V _p generated in p region 6 is not attenuated in any way and is read out at extremely high speed due to the effect of the bias voltage. FIG. 5a shows. This is because the amplification function, that is, the charge amplification function, of the photosensor cell according to the above configuration is working effectively.

On the other hand, in a conventional MOS type imaging device, the accumulated voltage V _p is Cj・V _p /(Cj + Cs) (however, Cj
is the pn junction capacitance of the light-receiving part of the MOS type image pickup device), which has the disadvantage that the readout voltage value decreases by two orders of magnitude. For this reason, in MOS type imaging devices, fixed pattern noise due to variations in parasitic capacitance of switching MOS transistors for external readout, or random noise generated due to large wiring capacitance, that is, output capacitance, is large.
There was a problem that the S/N ratio could not be obtained, but the first
In the optical sensor cell with the configuration shown in Figures a, b, and c, p
The accumulated voltage itself generated in region 6 is read out to the outside, and since this voltage is quite large, fixed pattern noise and random noise caused by the output capacitance are relatively small, resulting in a signal with an extremely good S/N ratio. It is possible to obtain

Previously, we showed that when the bias voltage V _Bias is set to 0.6 V, linearity of about 4 orders of magnitude can be obtained with a high-speed readout time of about 100 nsec, but the relationship between this linearity, readout time, and bias voltage V _Bias is The calculated results are shown in more detail in Figure 5b.

In Figure 5b, the horizontal axis is the bias voltage V _Bias
, and the vertical axis indicates the readout time.
In addition, the parameters are, when the accumulated voltage is 1mV,
It shows the time dependence until the read voltage reaches 80%, 90%, 95%, and 98% of 1 mV. As shown in Figure 5a, when the storage voltage is 80%, 90%, 95%, and 98%, respectively, at a storage voltage of 1 mV, it is clear that the values are even better at higher storage voltages. it is obvious.

According to FIG. 5b, the bias voltage V _Bias is
At 0.6V, the readout time is 0.12μs for the readout voltage to be 80% of the storage voltage, and the readout time to be 90% is
0.27μs, 95% is 0.54μs, 98% is
It can be seen that the time is 1.4μs. Also, the bias voltage
This shows that even higher speed reading is possible if V _Bias is made larger than 0.6V. Like this,
Once the readout time and required linearity are determined from the overall design of the imager, the required bias voltage V _Bias can be determined by using the graph of FIG. 5b.

Another advantage of the optical sensor cell according to the above configuration is that the probability of recombination of electrons and holes in the p region 6 is extremely small for the holes accumulated in the p region 6, and the capacitive load voltage connected to the emitter is read out. This means that it can be read out non-destructively. That is, when the voltage V _R applied to the electrode 9 during readout is returned to zero volts, p
The potential of region 6 is in the reverse bias state before voltage V _R is applied, and the accumulated voltage generated by light irradiation is
V _P remains intact unless it is exposed to new light. This means that when the optical sensor cell according to the above configuration is configured as a photoelectric conversion device, new functions can be provided in terms of system operation.

The time during which the accumulated voltage V _p can be held in the p region 6 is extremely long, and the maximum holding time is rather limited by the dark current thermally generated in the depletion layer of the junction. In other words, this thermally generated dark current saturates the optical sensor cell. However, in the optical sensor cell having the above configuration, the region in which the depletion layer spreads is the n ⁻ region 5 which is the low impurity concentration region 5, and this n ⁶ region 5 has a width of 10 ¹² cm ⁻³ to 10 ¹⁴ cm ⁻ It has an extremely low impurity concentration of about ³ , so its crystallinity is good.
Compared to MOS and CCD type imaging devices, fewer electron-hole pairs are thermally generated. Therefore, the dark current is small compared to other conventional devices. That is, the optical sensor cell according to the above configuration essentially has a structure with low dark current noise.

Next, the operation of refreshing the charges accumulated in p region 6 will be explained.

In the optical sensor cell having the above configuration, as already mentioned, the electricity accumulated in the p region 6 does not disappear during the read operation. Therefore, in order to input new optical information, a refresh operation is required to eliminate the previously accumulated charges. At the same time, it is necessary to charge the potential of p region 6, which is in a floating state, to a predetermined negative voltage.

In the optical sensor cell having the above configuration, the refresh operation is also performed by applying a positive voltage to the electrode 9 through the wiring 10, similarly to the read operation. At this time, the emitter is grounded through the wiring 8. The collector is grounded or at a positive potential through the electrode 12. FIG. 6 shows an equivalent circuit for refresh operation. However, an example is shown in which the collector side is grounded.

When a positive voltage V _RH is applied to the electrode 9 in this state, the oxide film capacitance Cox1 is applied to the base 22.
3. Due to the capacitance division of the base-emitter junction capacitance Cbe15 and the base-collector junction capacitance Cbc17, a voltage of CoxCox+Cbe+Cbc·V _RH is instantaneously applied as in the previous read operation. Due to this voltage, the base-emitter junction diode Dbc16 and the base-collector junction diode Dbc18 are forward biased and become conductive, current begins to flow, and the base potential gradually decreases.

At this time, the change in the potential V of the base in a floating state is approximately expressed by the following equation.

(Cbe + Cbc) dV/dt = - (i ₁ + i ₂ ) However, i ₁ = Ab (qD _{p poe} / Lp + qD _o n _pe / W _B ) × {exp (q / kTV) - 1} i ₂ = AeqD _o n _pe /W _B ×{exp(q/kTV)−1} i ₁ is the current flowing through the diode Dbc, and i ₂ is the current flowing through the diode Dbe. A _b is the base area,
Ae is the emitter area, Dp is the hole diffusion constant in the collector, p _oe is the hole concentration in the collector at thermal equilibrium, Lp is the mean free path of holes in the collector, n _pe is the electron concentration in the base at thermal equilibrium It is. i ₂ ,
The current due to hole injection from the base side to the emitter can be ignored because the impurity concentration of the emitter is sufficiently higher than that of the base.

The above equation is an approximation of a stepwise junction, and the actual device deviates from a stepwise junction, and the base is thin and has a complicated concentration distribution, so it is not exact. , the refresh operation can be explained with a fair approximation.

Of the current i ₁ flowing between the base and the collector in the above equation, q·Dp· _poe /Lp indicates a current due to holes, that is, a component in which holes flow from the base to the collector side. In order to facilitate the flow of current due to these holes, in the optical sensor cell having the above configuration, the impurity concentration of the collector is designed to be slightly lower than that of a normal bipolar transistor.

FIG. 7 shows an example of the time dependence of the base potential calculated using this formula. The horizontal axis shows the passage of time from the moment when the refresh voltage V _RH was applied to the electrode 9, that is, the refresh time, and the vertical axis shows the base potential. In addition, the initial potential of the base is used as a parameter. The initial potential of the base is the potential exhibited by the base in a floating state at the moment the refresh voltage V _RH is applied, and V _RH ,
Depends on Cox, Cbe, Cbc and the charges stored in the base.

Looking at FIG. 7, the potential of the base always decreases following a straight line on the semi-logarithmic graph after a certain amount of time has passed, regardless of the initial potential.

FIG. 7b shows experimental values of base potential change with respect to refresh time. Compared to the calculation example shown in Figure 7a, the test device used in this experiment has a much larger dimension, so although the absolute value does not match the calculation example, the base potential change with respect to the refresh time is semi-logarithmic. It has been demonstrated that it changes linearly on the graph. This experimental example shows the value when both the collector and emitter are grounded.

Now, set the maximum value of the accumulated voltage V _p due to light irradiation to 0.4
[V], and the voltage V applied to the base by the refresh voltage V _RH is 0.4 [V], as shown in Figure 7, the maximum value of the initial base potential is 0.8 [V], and after the refresh voltage is applied, the voltage V is ^0.4 [V]. After [sec], the base potential begins to fall in a straight line and becomes 10 ^-5
After [sec], the potential change coincides with that when no light was applied, that is, when the initial base potential was 0.4 [V].

There are two ways in which the p region 6 can be charged to a negative potential by applying a positive voltage for a certain period of time through the MOS capacitor Cox and removing the positive voltage.
One is an operation in which holes with positive charges flow from p region 6 to n region 1 which is mainly in a grounded state, thereby accumulating negative charges.

In order to prevent holes from flowing unilaterally from p-region 6 to n-region 1 and to prevent electrons from n-region 1 from flowing into p-region 6 too much, the impurity density of p-region 6 must be set to the impurity density of n-region 1. It should be higher. On the other hand, electrons from n ⁺ region 7 and n region 1 are
By flowing into the p region 6 and recombining with holes, negative charges can also be accumulated in the p region 6. In this case, the impurity density of n region 1 is higher than that of p region 6. The operation of accumulating negative charges due to holes flowing out from p-region 6 is much faster than the operation of accumulating negative charges due to electrons flowing into the base of p-region 6 and recombining with holes. However, according to experiments conducted so far, it has been confirmed that even the refresh operation in which electrons flow into the p region 6 exhibits a sufficiently fast time response for the operation of the photoelectric conversion device.

When a photoelectric conversion device is constructed by arranging a large number of optical sensor cells according to the above configuration in the XY direction, the image shows that the accumulated voltage V _P of each sensor cell varies between 0 and 0.4 [V] in the above example. , 10 ^-5 [sec] after applying the refresh voltage V _RH , a constant voltage of approximately 0.3 [V] remains at the base of all sensor cells, but all changes in the accumulated voltage V _p due to the image disappear. I understand that. That is, in the photoelectric conversion device using optical sensor cells according to the above configuration, there is a complete lift mode in which the base potential of all sensor cells is brought to zero volts by a refresh operation (in this case, in the example of FIG. 7a, 10
[sec]), and a transient refresh mode in which a certain constant voltage remains at the base potential but the fluctuation component due to the accumulated voltage V _p disappears (in this case, as shown in Figure 7a), there are two modes: In the example,
Refresh pulse of 10 [μsec] to 10 [sbc]). In the above example, the voltage V _A applied to the base by the refresh voltage V _RH was set to 0.4 [V], but if this voltage V _A is set to 0.6 [V], the above transient refresh mode According to Figure 7, 1 [nsec]
, and can be refreshed extremely quickly. The choice of whether to operate in the complete refresh mode or the transient refresh mode is determined by the purpose of use of the photoelectric conversion device.

If the voltage remaining at the base in this transient refresh mode is V _k , then the refresh voltage V _RH
In the transient state at the moment when V _RH is returned to zero volts after applying V RH, a negative voltage of -Cox/Cox+Cbe+Cbc・V _RH is added to the base, so the base potential after the refresh operation by the refresh pulse is V _k -Cox /Cox + Cbe + Cbc・V _RH , and the base becomes reverse biased with respect to the emitter.

It was explained earlier that during the accumulation operation of accumulating carriers excited by light, the base is in a reverse bias state in the accumulation state, but this refresh operation brings the refresh and base to a reverse bias state. These two operations are performed simultaneously.

FIG. 7c shows experimental values of changes in the base potential V _k −Cox/Cox+Cbe+Cbc·V _RH after the refresh operation with respect to the refresh voltage V _RH . The parameter Cox value is set from 5pF to 100pF. The circles are experimental values, and the solid lines are calculated values calculated from V _k −Cox/Cox+Cbe+Cbc·V _RH . At this time
V _k =0.52V, and Cbc+Cbe=4pF. However, the probe capacity of the observation oscilloscope
13pF is connected in parallel to Cbc + Cbe. In this way, the calculated values and experimental values are in complete agreement, and the refresh operation has been experimentally confirmed.

In the above refresh operation, an example has been described in which the collector is grounded as shown in FIG. 6, but it is also possible to perform the refresh operation with the collector at a positive potential. At this time, even if a refresh pulse is applied, the base-collector junction diode Dbc18 becomes non-conductive if the positive potential applied to the collector is higher than the potential applied to the base by the refresh pulse. As it remains in this state, current flows only through the base-emitter junction diode Dbe16. For this reason,
Although the base potential decreases relatively more slowly than when the collector is grounded, basically the same high-speed refresh operation as described above is performed.

In other words, in the relationship between the base potential and the refresh time shown in FIG. 7a, the diagonal straight line when the base potential decreases in FIG. 7a shifts to the right, that is, in a direction that requires more time. Therefore, if you use the same refresh voltage V _RH as when the collector is grounded, it will take time to refresh, but if you slightly increase the refresh voltage V _RH , you can achieve a high-speed refresh just like when the collector is grounded. Operation is possible.

The above is an explanation of the basic operations of the photosensor cell according to the above configuration, which consists of a charge accumulation operation, a readout operation, and a refresh operation by light incidence.

As explained above, the basic structure of the optical sensor cell according to the above configuration is disclosed in the above-mentioned Japanese Patent Application Laid-Open No.
Publication No. 157073, Japanese Patent Publication No. 157073, Japanese Patent Publication No. 157073-
Compared to Publication No. 165473, it has an extremely simple structure and is fully compatible with future higher resolutions, as well as its excellent characteristics of low noise, high output, wide dynamic range, and non-destructive amplification function. The advantages of reading etc. are preserved as they are.

Next, an embodiment of the photoelectric conversion device of the present invention, which is configured by two-dimensionally arranging the optical sensor cells according to the configuration described above, will be described with reference to the drawings.

FIG. 3 shows a circuit configuration diagram of a photoelectric conversion device in which basic optical sensor cell structures are two-dimensionally arranged in a 3×3 arrangement.

The basic photosensor cell 30 surrounded by the dotted line already described (this time indicates that the collector of the bipolar transistor is connected to the substrate and the substrate electrode), and the horizontal line 31 for applying read pulses and refresh pulses. ,31',3
1'', vertical shift register 32 for generating read pulses, buffer MOS between vertical shift register 32 and horizontal lines 31, 31', 31''
Terminal 34 for applying pulses to the gates of transistors 33, 33', 33'', buffer MOS transistors 35, 35', 35'' for applying refresh pulses, and terminals for applying pulses to their gates. 36, a terminal 37 for applying a refresh pulse, a vertical line 38, 3 for reading out the stored voltage from the basic photosensor cell 30;
8', 38'', horizontal shift register 39 that generates pulses for selecting each vertical line, gate MOS transistors 40, 40', 40'' for opening and closing each vertical line, and reading the accumulated voltage to the amplifier section. An output line 41 for outputting the output, and an output line 41 for refreshing the charge accumulated in the output line after reading.
MOS transistor 42, MOS transistor 42
Terminal 4 for applying refresh pulse
3. Bipolar for amplifying the output signal,
Transistors 44 such as MOS, FET, J-FET,
A load resistor 45, a terminal 46 for connecting the transistor and the power supply, an output terminal 47 of the transistor, and vertical lines 40, 40', 4 in the read operation.
0″ to refresh the charge accumulated in
MOS transistors 48, 48', 48'', and
This photoelectric conversion device is constituted by a terminal 49 for applying a pulse to the gates of MOS transistors 48, 48', 48''.

The operation of this photoelectric conversion device will be explained using pulse timing diagrams shown in FIGS. 3 and 8.

In FIG. 8, a section 61 corresponds to a refresh operation, a section 62 corresponds to an accumulation operation, and a section 63 corresponds to a read operation.

At time _t1 , the substrate potential, that is, the collector potential 64 of the photosensor cell portion is kept at the ground potential or positive potential, and FIG. 8 shows that it is kept at the ground potential. Regardless of whether it is at ground potential or positive potential, as already explained, the only difference is the time required for refreshing.
There is no change in the basic operation. The potential 65 of the terminal 49 is
is in a high state, and the MOS transistors 48, 4
8', 48'' are kept conductive and each photosensor cell is grounded through a vertical line 38, 38', 38''. In addition, a voltage that makes the buffer MOS transistor conductive as shown by a waveform 66 is applied to the terminal 36, and the buffer MOS transistors 35, 35', and 35'' for refreshing the entire screen at once are in a conductive state. When a pulse as shown in waveform 67 is applied to the terminal 37, a voltage is applied to the base of each photosensor cell through the horizontal lines 31, 31', 31'', and as explained above, a refresh operation is entered and the previously accumulated data is The charge that has been stored is refreshed according to the complete refresh mode or the transient refresh mode. The pulse width of the waveform 67 determines whether the mode is a complete refresh mode or a transient refresh mode.

At time _t2 , as already explained, the base of the transistor of each photosensor cell is reverse biased with respect to the emitter, and the next accumulation period 62
Move to. In this refresh section 61,
As shown in the figure, all other applied pulses are kept low.

In the accumulation operation section 62, the substrate voltage, that is, the transistor collector potential waveform 64 is set to a positive potential. This allows electrons among electron-hole pairs generated by light irradiation to flow quickly toward the collector side. but,
Keeping this collector potential at a positive potential is not an essential condition because the base is biased in the reverse direction with respect to the emitter, that is, images are taken with a negative potential.Even if the collector potential is at ground potential or a slightly negative potential, it is not an essential condition. There is no change in storage behavior.

In the storage operation state, the potential 6 of the gate terminal 49 of the MOS transistors 48, 48', 48''
5 is kept high as in the refresh section,
Each MOS transistor is kept conductive. For this reason, the emitter of each photosensor cell is grounded through vertical lines 38, 38', 38''. Due to strong light irradiation, holes are accumulated in the base,
When it becomes saturated, that is, when the base potential becomes forward biased with respect to the emitter potential (ground potential), the holes move along the vertical lines 38, 38',
38", where the base potential change stops and becomes clipped. Therefore,
Even if the emitters of vertically adjacent optical sensor cells are commonly connected by the vertical lines 38, 38', 38'', the vertical lines 38, 38', 38''
If 38'' is grounded, no blooming phenomenon will occur.

The way to avoid this blooming phenomenon is to
Even if the transistors 48, 48', 48'' are in a non-conductive state and the vertical lines 38, 38', 38'' are in a floating state, the substrate potential, that is, the collector potential 64, is kept at a slightly negative potential to prevent hole accumulation. When the base potential changes in the positive potential direction,
This can also be achieved by allowing the flow to flow toward the collector side before the emitter.

Following the accumulation section 62, a readout section 63 begins at time _t3 . At this time _t3 , the potential 65 of the gate terminal 49 of the MOS transistors 48, 48', 48'' is set to low, and the horizontal lines 31, 31',
31″ buffer MOS transistors 33, 33′,
The potential 68 of the gate terminal 33'' is set high to bring each MOS transistor into a conductive state.However, it is not an essential condition that the potential 68 of the gate terminal 34 is set high at time _t3 . It would be better if the time was earlier than that.

At time _t4 , among the outputs of the vertical shift register 32, those connected to the horizontal line 31 have waveform 6.
Since the MOS transistor 33 is in a conductive state at this time, each of the three photosensor cells connected to this horizontal line 31 is read out. This readout operation is as described above, and the signal voltage generated by the signal charge accumulated in the base region of each photosensor cell appears as it is on the vertical lines 38, 38', 38''. As shown in FIG. 5, the pulse width of the pulse voltage from the shift register 32 is set to a pulse width that maintains a sufficient linearity between the read voltage and the accumulated voltage. As shown above, the emitter is adjusted to be forward biased by V _Bias .

Next, at time _t5 , among the outputs of the horizontal shift register 39, the one connected to the vertical line 38
Only the output to the gate of the MOS transistor 40 becomes high as shown in the waveform 70, the MOS transistor 40 becomes conductive, and the output signal passes through the output line 41, enters the output transistor 44, is current amplified, and is output from the output terminal 47. . After the signal is read out in this way, signal charges due to the wiring capacitance remain in the output line 41, so that at time t ₆
, the gate terminal 4 of the MOS transistor 40
3, apply a pulse as shown in pulse waveform 71,
By turning on the MOS transistor 42 and grounding the output line 41, the remaining signal charges are refreshed. Similarly, the switching MOS transistors 40, 4
0', 40'' are connected in sequence to form vertical lines 38, 3.
8', 38'' is read out. After reading out the signals from each horizontally arranged line of photosensor cells in this way, the signals from the vertical lines 38, 38', 3
Similar to the output line 41, signal charges due to the wiring capacitance of the output line 8'' remain, so the MOS connected to each vertical line 38, 38', 38''
Transistors 48, 48', and 48'' are turned on by having their gate terminals 49 high, as shown by waveform 65, to refresh this residual signal charge.

Next, at time _t8 , among the outputs of the vertical shift register 32, the output connected to the horizontal line 31' becomes high as shown by waveform 69', and the accumulated voltage of each photosensor cell connected to the horizontal line 31' increases. The signals are read out to the vertical lines 38, 38', and 38''. Thereafter, signals are sequentially read out from the output terminal 47 by the same operation as before.

In the above explanation, we have explained the operation applied to application fields where the storage section 62 and the readout section 63 are clearly separated, for example, still video, which has been actively researched and developed recently. The present invention can also be applied to fields of application where the operation in the storage section 62 and the operation in the readout section 63 are performed simultaneously, by changing the pulse timing shown in FIG. 8. However, the refresh function at this time is not a one-time refresh function for the entire screen, but requires a refresh function for each line. For example, after the signal of each photosensor cell connected to the horizontal line 31 is read out, at time t ₇
In order to erase the charge remaining on each vertical line, the MOS transistors 48, 48', and 48'' are made conductive. At this time, a refresh pulse is applied to the horizontal line 31. That is, in the waveform 69, even at time _t7 , a refresh pulse is applied to the horizontal line 31. Similar to time _t4 , this can be achieved by using a vertical shift register configured to generate pulses with different pulse voltages and pulse widths. This can also be achieved by installing a second vertical shift register on the right side, similar to the one on the left side, instead of the device installed on the right side that applies a batch refresh, and operating it while shifting the timing from the vertical register installed on the left side. It is possible.

At this time, in the accumulation state as described above, the degree of freedom in controlling the blooming by controlling the potentials of the emitter and collector of each photosensor cell is reduced. However, as explained in the basic operation section, in the read state, the base
Since the configuration is such that high-speed reading is possible when a bias voltage of V _Bias is applied, as can be seen from the graph in Figure 4, when V _Bias is not applied,
Due to the saturation of each photosensor cell, vertical lines 28,
The signal charges flowing out to 28' and 28'' are extremely small, and the blooming phenomenon does not pose a problem at all.

Moreover, the photoelectric conversion device according to this embodiment can obtain extremely excellent characteristics with respect to the smear phenomenon. Smear phenomenon is an operational and structural problem that occurs in CCD type imaging devices, especially frame transfer type, in which charge is transferred to the area irradiated with light. This problem occurs because carriers generated deep in the semiconductor due to light are accumulated in the charge transfer section.

Furthermore, in MOS type imaging devices, this problem arises because carriers generated deep in the semiconductor due to long wavelength light are accumulated on the drain side of the switching MOS transistor grounded in each photosensor cell.

On the other hand, in the photoelectric conversion device according to this embodiment, the smear phenomenon that occurs due to its operation and structure does not easily occur, and the phenomenon that carriers generated deep in the semiconductor due to long wavelength light are accumulated does not occur. . However, there is a concern that electrons will accumulate among the electrons and holes generated relatively near the surface of the emitter of the optical sensor cell. Therefore, electrons are not accumulated and smear phenomenon does not occur. In addition, during the line refresh operation applied to ordinary television cameras, during the horizontal blanking period, the vertical line is grounded and refreshed before reading out the accumulated voltage on the vertical line, so at the same time the emitter The electrons accumulated during one horizontal scanning period flow out, and therefore almost no smear phenomenon occurs. As described above, in the photoelectric conversion device according to this embodiment, the smear phenomenon occurs to an essentially negligible extent due to its structure and operation, which is one of the major advantages of the photoelectric conversion device according to this embodiment. It is one.

Further, although the operation of suppressing the blooming phenomenon by manipulating the emitter and collector potentials in the storage operation state has been described above, it is also possible to control the Υ characteristic using this.

In other words, during the storage operation, the potential of the emitter or collector is temporarily set to a certain negative potential, and of the carriers accumulated in the base, the holes that are accumulated in a greater number than the number of carriers that give this negative potential are transferred to the emitter or collector. It causes the flow to flow to the collector side. As a result, the relationship between the accumulated voltage and the amount of incident light shows the characteristic of Υ=1 of silicon crystal when the amount of incident light is small,
In areas where the amount of incident light is large, Υ exhibits a characteristic such that it becomes smaller than 1. In other words, it is possible to provide the characteristic of Υ=0.45, which is normally required for television cameras, using a polygonal approximation. If the above operation is performed once during the storage operation, it becomes a one-fold line approximation, and if the negative potential applied to the emitter or collector is changed twice as appropriate, it is also possible to have a two-fold line type Υ characteristic.

Further, in the above implementation, the silicon substrate is used as a common collector, but a structure may be adopted in which a buried n ⁺ region is provided like a normal bipolar transistor and the collector is divided for each line.

In addition to the pulse timing shown in FIG. 8, clock pulses for driving the vertical shift register 32 and the horizontal shift register 39 are required for actual operation.

FIG. 9 shows an equivalent circuit related to the output signal.
The capacitance C _v 80 is the wiring capacitance of the vertical lines 38, 38', 38'', and the capacitance C _H 81 is the wiring capacitance of the output line 41
shows the wiring capacitance of each. The equivalent circuit on the right side of FIG. 9 is in a read state, and the switching MOS transistors 40, 4
0' and 40'' are in a conductive state, and the resistance value in the conductive state is shown by a resistor R _M 82. Also, the amplifying transistor 44 is shown by an equivalent circuit using a resistor r _e 83 and a current source 84. The MOS transistor 42 for refreshing the charge accumulation caused by the wiring capacitance of the output line 41 is non-conductive in the read state and has high impedance, so it is omitted in the equivalent circuit on the right side.

Each parameter of the equivalent circuit is determined by the size of the photoelectric conversion device actually constructed. For example, the capacitance C _v 80 is about 4 pF, and the capacitance C _H 81
The following is an example of calculating the output signal waveform observed at the output terminal 47, assuming that the conduction state resistance R _M 82 of the MOS transistor is about 3K, and the current amplification factor β of the bipolar transistor 44 is about 100. It is shown in Figure 10.

In FIG. 10, the horizontal axis represents the time [μs] from the moment the switching MOS transistors 40, 40', 40'' became conductive, and the vertical axis represents the time from the moment when the switching MOS transistors 40, 40', 40'' became conductive.
The output voltage [V] appearing at the output terminal 47 when a signal charge is read from each photosensor cell and a voltage of 1 volt is applied to the wiring capacitance C _v 80 of 8' and 38'' is shown, respectively.

The output signal waveform 85 shows that the load resistance R _E 45 is 10K,
86 is load resistance R _E 45 is 5K〓, 87 is load resistance
These are the values when R _E 45 is 2K〓, and in both cases, the peak value is about 0.5 V due to the capacitance division between C _v 80 and _CH 81. Naturally, the larger the load resistance R _E 45 is, the smaller the amount of attenuation is, resulting in a desirable output waveform. The rise time is approximately 20nsec when the above parameter values are used.
And it is fast. Resistance R _M of switching MOS transistors 40, 40', 40'' in conduction state
By reducing the wiring capacitance C _v ,
By reducing _CH , even faster reading is possible.

In a photoelectric conversion device using photosensor cells with the above configuration, the voltage appearing at the output is large due to the amplification function of each photosensor cell, so the final stage amplification amplifier is also quite simple compared to a MOS type imaging device. That's fine. In the above example, a one-stage bipolar transistor type was used, but it is of course possible to use other systems, such as a two-stage structure. If a bipolar transistor is used as in this example, the CCD
1/f, which is easily noticeable on images, is generated from the MOS transistor of the final stage amplifier in an imaging device.
The problem of noise does not occur in the photoelectric conversion device of this embodiment, and it is possible to obtain image quality with an extremely good S/N ratio.

As mentioned above, in a photoelectric conversion device using a photosensor cell with the above configuration, the amplification amplifier in the final stage can be extremely simple, so the configuration shown in FIG. 3 in which only one amplification amplifier in the final stage is provided Instead of the type shown in the embodiment shown, it is also possible to install a plurality of amplifiers so that one screen can be divided into a plurality of parts and read out.

FIG. 11 shows an example of a divided readout method. The embodiment shown in FIG. 11 is an example in which the horizontal direction is divided into three parts and three final stage amplifiers are installed. The basic operation is almost the same as that explained using the embodiment shown in FIG. 3 and the timing diagram shown in FIG.
In the embodiment shown in FIG. 11, three equivalent horizontal shift registers 100, 101, and 102 are provided, and when a starting pulse is input to the terminal 103 for applying these starting pulses, the 1st column and (n+1) column are eye,
The outputs of the sensor cells connected to the (2n+1)th column (n is an integer, and in this embodiment, the number of picture elements in the horizontal direction is 3n) are read out simultaneously. At the next point in time, the second column, (n+2) column,
The (2n+2)th column will be read.

According to this embodiment, when the time to read out one horizontal line is fixed, the horizontal scanning frequency is 1/3 compared to the system with one final stage amplifier. A high-speed analog-to-digital converter is unnecessary for applications where the frequency is sufficient, the horizontal shift register is simple, and the output signal from a photoelectric conversion device is converted from analog to digital for signal processing. This is a major advantage of the readout method.

In the embodiment shown in FIG. 11, three equivalent horizontal shift registers are provided, but the same function can be provided with only one horizontal shift register. The example in this case is shown in the 12th example.
As shown in the figure.

The embodiment of FIG. 12 uses the horizontal switching MOS transistor of the embodiment shown in FIG.
Only the middle part of the final stage amplifier is shown, and the other parts are omitted because they are the same as the embodiment shown in FIG.

In this example, one horizontal shift register 1
04 in the 1st column, (n+1) column, (2n
+1) are connected to the gates of the switching MOS transistors in the column so that those lines can be read out simultaneously. . At the next point in time, the second column, (n+
The second column and (2n+2) column are read out.

According to this embodiment, although the number of wirings to the gate of each switching MOS transistor increases,
It is possible to operate with only one horizontal shift register.

In the examples shown in FIGS. 11 and 12, three output amplifiers are provided, but it goes without saying that this number may be increased depending on the purpose.

In both the embodiments shown in FIGS. 11 and 12, the starting pulses and clock pulses for the horizontal shift register and vertical shift register are omitted, but they are provided in the same chip like other refresh pulses. clock pulse generator or
It is supplied from a clock pulse generator on another chip.

In this split readout method, when the horizontal line or the entire screen is refreshed at once, the storage time is slightly different between the light sensor cells in the n-th column and the (n+1)-th column, which causes dark current components and signal components to Although there is a possibility that a slight discontinuity may occur and be noticeable on the image, the amount of this is small and poses no problem in practice. Furthermore, even if this exceeds the allowable limit, correcting it using an external circuit will generate a square wave, subtracting this from the dark current component, and multiplying and dividing this by the signal component. This is easily possible using conventional correction techniques.

When capturing a color image using such a photoelectric conversion device, a stripe filter or a mosaic filter is placed on-chip on top of the photoelectric conversion device, or a separately manufactured color filter is attached to the photoelectric conversion device. It is possible to get a signal.

As an example, when R, G, and B stripe filters are used, in a photoelectric conversion device using a photosensor cell according to the above configuration, the R signal, G signal, and B signal can be obtained from separate final stage amplifiers. It is possible. An example of this is shown in FIG. Like FIG. 12, FIG. 13 also shows only the area around the horizontal shift register. The rest is the same as Fig. 3 and Fig. 11, except that the first column is an R color filter, the second column is a G color filter,
It is assumed that color filters are installed in the third column, such as the B color filter and the fourth column, the R color filter. As shown in Figure 13, the first row,
Each vertical line of the 4th column, 7th column, etc. is connected to an output line 110, which takes out the R signal. Further, each vertical line of the second column, fifth column, eighth column, . . . is connected to an output line 111, which takes out the G signal. In the same way, 3rd row, 6th row, 9th row...
The B signal connected to each vertical line 112 of... is taken out. Output lines 110, 111, and 112 are each on-chip refresh MOS
It is connected to a transistor and a final stage amplifier, such as an emitter follower type bipolar transistor, and each color signal is output separately.

FIG. 14 shows a diagram for explaining the basic structure and operation of another example of a photosensor cell constituting a photoelectric conversion device according to another example of the present invention. In addition, the equivalent circuit and the overall circuit configuration diagram are shown in Figure 15a.
Shown below.

The optical sensor cell shown in FIG. 14 is an optical sensor cell that can simultaneously perform a read operation and a line refresh using the same horizontal scan pulse. In Figure 14, the first
The difference from the configuration shown in the figure is that in the case of FIG. 1, there is only one MOS capacitor electrode 9 connected to the horizontal line wiring 10, but there are also MOS capacitor electrodes 120 on the sides of the vertically adjacent optical sensor cells. When viewed from one photosensor cell, the emitters 7 and 7' of the vertically adjacent photosensor cells in the figure are wires 8 and 121, which are two-layer wiring. In Fig. 14, the vertical line appears to be one, but two lines are arranged through an insulating layer).
The difference is that emitter 7' is connected to wiring 8 through contact hole 19, and emitter 7' is connected to wiring 121 through contact hole 19'.

This becomes clearer when looking at the equivalent circuit shown in FIG. 15a. That is, the MOS capacitor 150 connected to the base of the optical sensor cell 152 is connected to the horizontal line 31, and the MOS capacitor 151 is connected to the horizontal line 31'. Furthermore, in the diagram of the optical sensor cell 152, the MOS capacitors 150' of the adjacent optical sensor cells 152' below are connected to a common horizontal line 31'.

The emitter of the optical sensor cell 152 is on the vertical line 3.
8, the emitters of the photosensor cells 152' are connected alternately to the vertical line 138, and the emitters of the photosensor cell 152'' are connected to the vertical line 38, respectively.

The equivalent circuit shown in FIG. 15a differs from the image pickup device shown in FIG. 3, other than the basic photosensor cell section described above, in that it has a switching MOS transistor 48 for refreshing the vertical line 38 and a vertical line 138. In addition to the switching MOS transistor 148 for refreshing and the switching MOS transistor 40 for selecting the vertical line 38, a switching MOS transistor 140 for selecting the vertical line 138 is added, and one output amplifier system is added. . The configuration of this output system consists of 4 switching MOS transistors for refreshing each line.
8 and 148 are connected, and a switching MOS for horizontal scanning is also installed.
It is also possible to use only one output amplifier as shown in FIG. 15b using transistors. FIG. 15b shows only the vertical line selection and output amplifier system portions of FIG. 15a.

This optical sensor cell in FIG. 14 and FIG. 15a
According to the embodiment shown in , the following operations are possible. That is, when the readout operation of each optical sensor cell connected to the horizontal line 31 is completed and the horizontal blanking period in the TV operation is in progress, the output pulse from the vertical shift register 32 is outputted to the horizontal line 31' by the MOS capacitor. 151, the optical sensor cell 152 that has been read is refreshed. At this time, the switching MOS transistor 48 is made conductive, and the vertical line 3
8 is grounded.

Further, the output of the photosensor cell 152' is read out to the vertical line 138 through the MOS capacitor 150' connected to the horizontal line 31'. At this time, naturally, the switching MOS transistor 148 is rendered non-conductive, and the vertical line 138
is in a floating state. In this way, with one vertical scan pulse, it is possible to simultaneously refresh the optical sensor cells that have already been read out and read out the optical sensor cells of the next line using the same pulse. At this time, as already explained, the voltage at the time of refreshing and the voltage at the time of reading are different because a bias voltage is applied at the time of reading due to the necessity of high-speed reading. This is achieved by changing the areas of the electrode 9 and the MOS capacitor electrode 120 so that even if the same voltage is applied to each electrode, different voltages are applied to the base of each photosensor cell.

That is, the area of the refresh MOS capacitor is smaller than the area of the read MOS capacitor. As in this example, when refreshing one line at a time instead of refreshing all sensor cells at once, the first
Although the collector may be formed of an n-type or n-substrate as shown in FIG. b, it may be desirable to separate the collectors for each horizontal line. When the collector is a substrate, the collectors of all the photosensor cells are a common area, so that a constant bias voltage is applied to the collectors in the storage and light reception/readout states. Of course, as explained above, floating-based refresh can be performed between the emitters even when a bias voltage is applied to the collector. However, in this case, there is a drawback that at the same time that the base region is refreshed, a wasteful current flows between the emitter collector of the cell to which the refresh pulse is applied, increasing power consumption.
In order to overcome these drawbacks, instead of making the collectors of all the sensor cells a common area, the collectors of the sensor cells arranged in each horizontal line are common, but the collectors of each horizontal line are structured to be separated from each other. That is, in connection with the structure shown in FIG. 1, the substrate is of a p-type, and the p-type substrate has a structure in which n ⁺ buried regions separated from each other are provided for each horizontal line of the collector. The n ⁺ buried regions of adjacent horizontal lines may be separated by a structure in which a p region is interposed therebetween. Dielectric isolation is better for reducing collector capacitors embedded along horizontal lines. In FIG. 1, since the collector is comprised of a substrate, all isolation regions surrounding the sensor cell are provided to approximately the same depth. On the other hand, in order to separate the collectors of each horizontal line from each other, the separation area in the horizontal line direction is made deeper than the separation area in the vertical line direction by a necessary value.

If the collector is separated for each horizontal line, if the voltage of the collector of that horizontal line is grounded when reading is finished and the refresh operation starts, the emitter-collector current as described above will not flow, and the consumption will be reduced. Does not result in an increase in power. When the refresh ends and the charge storage operation starts based on the optical signal, a predetermined bias voltage is applied to the collector region again.

According to the equivalent circuit shown in FIG. 15a, the outputs are alternately output to the output terminals 47 and 147 for each horizontal line. As already explained, it is also possible to take out the output from one amplifier by using the configuration as shown in FIG. 15b.

As explained above, according to this embodiment, line refresh is possible with a relatively simple configuration.
It can also be applied to fields of application such as ordinary television cameras.

As another embodiment of the present invention, an optical sensor cell may be provided with a plurality of emitters, or one emitter may be provided with a plurality of contacts.
A type that takes out multiple outputs from one optical sensor cell is considered.

This is because each optical sensor cell of the photoelectric conversion device according to the present invention has an amplification function, so even if multiple wiring capacitors are connected to each optical sensor cell in order to extract multiple outputs from one optical sensor cell, the optical sensor cell This is due to the fact that the internally generated accumulated voltage V _p can be read out to each output without attenuating too much.

In this way, by having a configuration in which multiple outputs can be taken out from each optical sensor cell, many advantages can be added to the photoelectric conversion device formed by arranging a large number of each optical sensor cell in terms of signal processing, noise countermeasures, etc. is possible.

Next, an example of a method for manufacturing a photoelectric conversion device according to the present invention will be described. Figure 16 shows selective epitaxial growth (N. Endo et al, “Novel device isolation
technology with selected epitaxial growth”
An example of the manufacturing method using Tech.Dig.of 1982 IEDM, pp.241-244) is shown below.

An n ⁺ region 11 for contact is formed on the back side of an n-type Si substrate 1 with an impurity concentration of about 1 to 10 × 10 ¹⁶ cm ^-3 .
Provided by diffusion of As or P. In order to prevent autodoping from the n ⁺ region, an oxide film and a nitride film (not shown) are usually provided on the back surface.

The substrate 1 used has impurity concentration and oxygen concentration controlled to be uniform. That is, a crystal wafer having a sufficiently long and uniform carrier line time is used. For example, such a thing
Crystals produced by the MCZ method are suitable. An oxide film of about 1 μm is formed on the surface of the substrate 1 by wet oxidation. That is, H ₂ O atmosphere or (H ₂
+O ₂ ) oxidizes in the atmosphere. High-pressure oxidation at a temperature of about 900°C is suitable for obtaining a good oxide film without producing stacking faults.

On top of that, for example, a layer with a thickness of about 2 to 4 μm is added.
Deposit the SiO ₂ film by CVD. (N ₂ + SiH ₄ + O ₂ ) to the desired thickness at a temperature of about 300 to 500℃ using a gas system.
Deposit the _SiO2 film. The molar ratio of O ₂ /SiH ₄ is set to about 4 to 40, although it depends on the temperature. Through the photolithography process, the oxide film in the areas that will become the isolation regions between cells is left behind, and the oxide film in other areas is (CF ₄ +
H ₂ ), C ₂ F ₄ , CH ₂ F _2, etc. (step a in Figure 16). For example, when one pixel is provided in 10 x 10 μm ² , Leave a SiO ₂ film in the form of a mesh with a pitch of 10 μm. The width of the SiO ₂ film is selected to be, for example, about 2 μm.
After removing the damaged layer and contaminant layer on the surface caused by reactive ion etching by Ar/Cl ₂ gas plasma etching or wet etching, the atmosphere is sufficiently cleaned by evaporation in an ultra-high vacuum or by using a load lock method. _{The amorphous} silicon 3
01 (step b in Figure 16), CBrF ₃ ,
By anisotropic etching using reactive ion etching using gases such as CCl ₂ F ₂ and Cl ₂ .
Remove the amorphous silicon other than that deposited on the side of the SiO ₂ layer (step c in Figure 16). After sufficiently removing the damaged layer and contamination layer as before,
Thoroughly clean the silicon substrate surface and remove (H ₂ +
The silicon layer is selectively grown using a gas system (SiH ₂ , Cl ₂ +HCl). Growth is performed under reduced pressure of several tens of Torr, the substrate temperature is set at 900 to 1000°C, and the molar ratio of HCl is set to a value higher than a certain level. If the amount of HCl is too small, selective growth will not occur. A silicon crystal layer grows on the silicon substrate, but since the silicon on the SiO ₂ layer is etched by HCl, no silicon is deposited on the SiO ₂ layer (FIG. 16d). The thickness of the n ^- layer 5 is, for example, about 3 to 5 μm. Impurity concentration is preferably between 10 ¹² and 10 ¹⁶ cm
Set it to about ^-3 . Of course, it is possible to deviate from ^{this range} , but the impurity concentration and It is preferable to choose the thickness.

Since commonly available HCl gas contains a large amount of water, an oxide film is constantly formed on the surface of the silicon substrate, making it impossible to expect high-quality epitaxial growth. watery
When HCl is in the cylinder, it reacts with the cylinder material and contains a large amount of heavy metals, mainly iron, which tends to result in an epitaxial layer with heavy metal contamination. Since it is desirable for the epitaxial layer used in the optical sensor cell to have as little dark current component as possible, it is necessary to suppress contamination by heavy metals to the utmost. Of course, ultra-high purity materials are used for SiH ₂ Cl, but HCl has a particularly low moisture content, preferably with a moisture content of at least 0.5 ppm.
Use the following: Of course, the lower the water content, the better. To further improve the quality of the epitaxial growth layer, the substrate is first treated at a high temperature of about 1150 to 1250°C to remove oxygen from near the surface, and then
It is also extremely effective to generate a large number of micro-defects inside the substrate by heat treatment at about 800° C. for a long time to make the substrate capable of intensive gettering with a denuded zone.
Since epitaxial growth is performed in the presence of the SiO ₂ layer 4 as the isolation region,
In order to reduce the uptake of oxygen from SiO ₂ ,
The lower the growth temperature, the more desirable. With the commonly used high-frequency heating method, there is a lot of contamination from the carbon susceptor, making it difficult to lower the temperature further. The wafer direct heating method using lamp heating, which does not involve bringing a carbon susceptor into the reaction chamber, provides a clean growth atmosphere and allows high-quality epitaxial layers to be grown at low temperatures.

Ultra-high purity fused sapphire, which has a lower vapor pressure, is suitable for the wafer support in the reaction chamber. The wafer direct heating method using lamp heating allows for easy preheating of the raw material gas and makes it easy to uniformize the temperature within the wafer surface even when a large flow of gas is flowing.In other words, the wafer direct heating method using lamp heating generates almost no thermal stress. suitable for obtaining. UV irradiation of the wafer surface during growth further improves the quality of the epitaxial layer.

Amorphous silicon is deposited on the sidewalls of the SiO ₂ layer forming the isolation region 4 . (Step c in Figure 16). Since amorphous silicon is easily formed into a single crystal by solid phase growth, the crystal near the interface with the SiO ₂ separation region 4 becomes very good. High resistance n ^- layer 5
After forming by selective epitaxial growth (step d in Fig. 16), a P region 6 with a surface concentration of about 1 to 20 × 10 ¹⁶ cm ^-3 is formed by diffusion from doped oxide or by low-dose ion implantation. The layer is formed to a predetermined depth by diffusion using the layer as a source. The depth of p region 6 is, for example, about 0.61 μm.

The thickness and impurity concentration of p region 6 are determined based on the following considerations. If you want to increase the sensitivity, p region 6
It is desirable to reduce Cbe by lowering the impurity concentration. Cbe is approximately given as follows.

Cbe=Ae〓(q・N _A /2〓Vbi) ^1/2 However, Vbi is the emitter-base diffusion potential and is given by Vbi=kT/q1nN _D N _A /n _i ² . Here, 〓 is the dielectric constant of the silicon crystal, N _D is the impurity concentration of the emitter, N _A is the impurity density of the portion of the base adjacent to the emitter, and n _i is the intrinsic carrier concentration. The smaller N _A is, the more Cbe
As N A becomes smaller, the sensitivity increases, but if N _A is made too small, the base region will be completely depleted in the operating state, resulting in a punch-through state, so it cannot be made too low. It is set to such an extent that the base region is not completely depleted and a punch-through state occurs.

Thereafter, a thermal oxide film 3 having a thickness of several tens of angstroms to several hundreds of angstroms is formed on the surface of the silicon substrate by (H ₂ +O ₂ ) gas-based steam oxidation at a temperature of approximately 800 to 900°C. On top of that, (SiH ₄ +NH ₃ ) system gas
A nitride film (Si ₃ N ₄ ) 302 is formed to a thickness of about 500 to 1500 Å by CVD. The formation temperature is about 700-900℃. NH ₃ gas, along with HCl gas, also contains a large amount of water in commonly available products. If NH ³ gas with a high moisture content is used as a raw material, the result will be a nitride film with a high oxygen concentration, resulting in poor reproducibility and an inability to obtain a selective etching ratio with the SiO ₂ film. _NH3 gas also
The moisture content should be at least 0.5 ppm or less. It goes without saying that the lower the water content, the more desirable it is. A PSG film 3 is further formed on the nitride film 302.
00 is deposited by CVD. For the gas system, for example, (N ₂ + SiH ₄ + O ₂ + PH ₃ ) is used,
With a thickness of about 2000 to 3000 Å at a temperature of about 450℃
A PSG film is deposited by CVD (step e in Figure 16). By a photolithography process including two mask alignment processes, an As-doped polysilicon film 304 is deposited on the n ⁺ region 7 and on the refresh and read pulse application electrodes. In this case, a p-doped polysilicon film may be used. For example, by two photolithography steps,
The PSG film, Si ₃ N ₄ film, and SiO ₂ film were all removed from the emitter, leaving the underlying SiO ₂ film in the area where the refresh and readout pulse application electrodes were to be provided.
Only the PSG film and Si ₃ N ₄ film are etched. after that,
As-doped polysilicon (N ₂ + SiH ₄ +
AsH ₃ ) or (H ₂ +SiH ₄ +AsH ₃ ) gas
Deposited by CVD method. Deposition temperature is 550℃~700℃
The film thickness is about 1000 to 2000 Å. Of course, non-doped polysilicon may be deposited by the CVD method and then As or P may be diffused. After the mask alignment photolithography process, the polysilicon film in other parts except on the emitter, refresh and readout pulse application electrodes is removed by etching. Furthermore, when the PSG film is etched,
Due to lift-off, the polysilicon deposited on the PSG film is removed in a self-aligned manner. (Step f in Figure 16). The polysilicon film is etched using a gas system such as C ₂ Cl ₂ F ₄ or (CBBrF ₃ +Cl ₂ ), and the Si ₃ N ₄ film is etched using a gas such as CH ₂ F ₂ .

Next, a PSG film 305 is deposited by the gas-based CVD method as described above, and then a contact hole is formed on the polysilicon film for the refresh pulse and read pulse electrodes by a mask alignment process and an etching process. Under these conditions, Al,
Deposition of metals such as Al-Si, Al-Cu-Si, etc. by vacuum evaporation or sputtering, or plasma using (CH ₃ ) ₃ Al or ACl ₃ as raw material gas.
CVD method or Al-C of the above raw material gas
Al is deposited using the light irradiation CVD method, which cuts the bond or Al-Cl bond by direct light irradiation.
When carrying out the above-mentioned CVD method using (CH ₃ ) ₃ Al or AlCl ₃ as the raw material gas, a large excess of hydrogen is allowed to flow. For narrow and steep contact holes
An excellent method for depositing Al is the CVD method, which raises the substrate temperature to a film thickness of 300 to 400°C in a clean atmosphere that does not contain moisture or oxygen. After completing the patterning of the metal wiring 10 shown in FIG.
An interlayer insulating film 306 is deposited by CVD. 306
is the aforementioned PSG film or CVD SiO ₂ B film,
Alternatively, if it is necessary to take water resistance into consideration, an Si ₃ N ₄ film formed by a (SiH ₄ +NH ₃ ) gas-based plasma CVD method is used. In order to keep the hydrogen content in the Si ₃ N ₄ film low, (SiH ₄ + N ₂ )
Use the plasma CV method in a gas system.

In order to increase the electrical withstand voltage of the Si ₃ N ₄ film formed by reducing the damage caused by the plasma CVD method and to reduce the leakage current, the photo CVD method is used.
The Si ₃ N ₄ film is excellent. There are two methods for optical CVD. (SiH ₄ + NH ₃ + Hg) gas system with 2537 Å ultraviolet rays from a mercury lamp from the outside, and (SiH ₄ + NH 3 + Hg) ₃ gas system with 1849 Å ultraviolet rays from a mercury lamp.
This is a method of irradiating UV rays. In both cases, the substrate temperature is about 150 to 350°C.

Through the mask alignment process and etching process,
An insulating film 305,
After drilling a contact hole through 306 using a reactive ion etching method, use the method described above.
Deposit metals such as Al, Al-Si, Al-Cu-Si, etc.
In this case, since the aspect ratio of the contact hole is large, deposition by CVD is superior. After patterning the metal wiring 8 in Fig. 1, a final passivation film is formed.
A Si ₃ N ₄ film or a PSG film 2 is deposited by the CVG method (FIG. 16g).

In this case as well, the film produced by the photo-CVD method is superior. 12 is a metal electrode made of Al, Al-Si, etc. on the back surface.

The method for manufacturing the photoelectric conversion device of the present invention involves a wide variety of steps, and FIG. 16 shows only one example.

The important point of the photoelectric conversion device of the present invention is that the p region 6
The problem lies in how to suppress leakage current between the and n ^- regions 5 and between the p region 6 and the n ⁺ region 7. n ^-
It goes without saying that dark current can be reduced by improving the quality of the region 5, but the problem lies in the interface between the isolation region 4 made of an oxide film or the like and the n ^- region 5. In FIG. 16, for this purpose, the separation area 4 is
We have explained a method in which amorphous Si is deposited on the sidewalls of the substrate and then epitaxially grown. In this case, amorphous Si is made into a single crystal by solid phase growth from the substrate Si during epitaxial growth. Epitaxial growth is performed at a relatively high temperature of about 850°C to 1000°C. Therefore, the board
Before the amorphous Si becomes single crystallized by solid phase growth from Si, microcrystals often begin to grow in the amorphous Si, which causes poor crystallinity. The lower the temperature, the faster the solid-phase growth becomes relatively faster than the speed at which microcrystals begin to grow in amorphous Si. Therefore, before performing selective epitaxial growth, it is necessary to If the amorphous Si is made into a single crystal during processing, the characteristics of the interface will be improved. At this time, if there is a layer such as an oxide film between the substrate Si and the amorphous Si, the start of solid phase growth will be delayed, so an ultra-high cleanliness process is required to prevent such a layer from being included at the boundary between the two.

In addition to the above-mentioned furnace growth, effective solid-phase growth of amorphous Si is a rapid annealing technique in which the substrate is kept at a certain temperature and heated by a fuselage lamp or an infrared lamp for, for example, several seconds to several tens of seconds. When using such techniques, the Si deposited on the sidewalls of the SiO ₂ layer may be polycrystalline. However, polycrystalline Si needs to be deposited using a very clean process and does not contain oxygen, carbon, etc. at the grain boundaries of the polycrystalline material.

After the Si on these SiO ₂ sides is single-crystalized, the Si
This will result in selective growth.

When leakage current at the interface between the SiO ₂ isolation region 4 and the high resistance n ^- region 5 becomes a problem, the high resistance n ^-
Only the part of region 5 adjacent to SiO ₂ separation region 4,
This problem of leakage current can be avoided by increasing the n-type impurity concentration. For example, only the region with a height of about 0.3 to 1 μm of the n ^- region 5 that contacts the isolated SiO ₂ region 4, for example, about 1 to 10 × 10 ¹⁶ cm ^-3
This increases the impurity concentration in the shape. This configuration can be formed relatively easily. After forming a thermal oxide film with a thickness of about 1 μm on the substrate 1, it is deposited thereon by CVD. First, the SiO ₂ film is made into a SiO ₂ film having a required thickness and containing a predetermined amount of P. Furthermore, a separation region 4 is created by depositing SiO ₂ thereon by CVD. In the subsequent high-temperature process, phosphorus is diffused from the phosphorus-containing SiO ₂ film that exists in the form of a sandwich in the separation region 4 into the high-resistance n ^- region 5, resulting in a good impurity distribution with a high impurity concentration even at the interface. make.

In other words, the structure is as shown in FIG. 17. The isolation region 4 has a three-layer structure, in which 308 is a thermal oxide film SiO ₂ , 309 is a CVD SiO ₂ film containing phosphorus, and 301 is a CVD SiO ₂ film. Adjacent to the separation region 4 and between the n ^- region 5 and the n-region 307, an SiO ₂ film 309 containing phosphorus is formed.
Formed by diffusion from 307 is formed all around the cell. With this structure, the base
Although the collector capacitance Cbc increases, the base
The leakage current between the collectors is drastically reduced.

In FIG. 16, an example was explained in which the isolation insulating region 4 was formed in advance and selective epitaxial growth was performed.
After epitaxial growth of the n ^-layer ,
U-group separation technology (A.
Hayasaka et al, “U-groove isolation
technique for high speed bipolar VLSI′S”，
Tech.Dig.of IEDM.P.62, 1982).

A photoelectric conversion device according to the present invention forms a bipolar transistor in which a base region, most of which is adjacent to the semiconductor wafer surface, is in a floating state in a region surrounded by an isolation region made of an insulator, This device performs photoelectric exchange of optical information by controlling the potential of a floating base region with an electrode provided on a part of the base region via a thin insulating layer. An emitter region made of a high impurity concentration region is provided in a part of the base region, and this emitter is connected to a MOS transistor operated by a horizontal scan pulse.
The aforementioned electrode provided on a portion of the floating base region via a thin insulating layer is connected to a horizontal line. The collector provided inside the wafer is
Depending on the purpose, it may be composed of a high-resistance substrate of an opposite conductivity type and high-concentration impurity buried regions separated for each horizontal line. The pulse voltage applied when reading out a signal is substantially larger than the pulse voltage when refreshing the floating base region using the electrode provided through the insulating layer. In fact, a pulse train that waits for two types of voltages may be used, or as explained in the double capacitor structure, the capacitance C _px of the readout MOS capacitor electrode may be made larger than the capacitance C _px of the refresh MOS capacitor electrode. You can leave it there. By applying a refresh pulse, optically excited carriers are accumulated in the floating base region, which is brought into a reverse bias state, and a signal based on the optical signal is stored. When reading out the signal, the base-emitter is deeply biased in the forward direction. The feature is that a readout pulse voltage is applied so that signals can be read out at high speed. As long as it has these characteristics, the photoelectric conversion device of the present invention may be realized in any structure, and it is needless to say that it is not limited to the structure described in the above embodiments.

For example, the same applies to a structure in which the conductivity type is completely reversed from that described in the above embodiment. However, at this time, it is necessary to completely reverse the polarity of the applied voltage. In a structure in which the conductivity types are completely reversed, the region becomes n-type. That is, the impurities constituting the base are As and P. When the surface of a region containing As or P is oxidized, As or P becomes Si/SiO ₂
Pile up on the Si side of the interface. That is, a strong drift electric field is generated inside the base from the surface to the inside, and the optically excited holes immediately escape from the base to the collector side, and electrons are efficiently accumulated in the base.

If the base is p-type, the commonly used impurity is boron. When the surface of the p-region containing boron is thermally oxidized, boron is incorporated into the oxide film, so the boron concentration in the Si near the Si/SiO ₂ interface becomes slightly lower than the boron concentration inside. This depth depends on the oxide film thickness, but is usually several hundred angstroms.
A reverse drift electric field for electrons is generated near this interface, and electrons photoexcited in this region tend to be collected on the surface. If this continues, the region where this reverse drift electric field is generated will become a dead region, but since the photoelectric conversion device of the present invention has an n ⁺ region along a part of the surface, the p-region Si/ Electrons gathered at the SiO ₂ interface flow into this n ⁺ region before being recombined. Therefore, even if there is a region where, for example, boron is reduced near the Si/SiO ₂ interface and a reverse drift electric field occurs, it hardly becomes a dead region. Rather, if such a region exists at the Si/SiO ₂ interface, the accumulated holes will be transferred to the Si/SiO ₂
By separating the holes from the interface and making them exist inside, the effect of holes disappearing at the interface is eliminated, and the effect of accumulating holes at the base of the p-layer becomes good, which is extremely desirable.

As described above, the photoelectric conversion device of the present invention accumulates carriers excited by light in the base region, which is the control electrode region in a floating state. i.e. Base Store Image
It is a device that should be called a Sensor, and is abbreviated as BASIS.

In addition to the solid-state imaging device described above, the photoelectric conversion device according to the present invention can also be used, for example, an image input device,
It can also be applied to image input devices such as facsimiles, workstations, digital copying machines, and word processors, OCR, barcode reading devices, and photoelectric conversion object detection devices for autofocus such as cameras, video cameras, and 8mm cameras.

[Effects of the Invention] According to the present invention, since the potential of the base region is controlled independently of the collector region and emitter region, high-speed readout is possible while ensuring good linearity of the output voltage signal. becomes.

Also, during storage, the saturation voltage can be determined by the voltage that reverse biases the base region with respect to the emitter region, and during refresh, the base region can be biased deeply in the forward direction with respect to the emitter region.
It operates at high speed, has a wide dynamic range, and can provide a good output signal with no afterimage or noise.
Furthermore, blue sensitivity characteristics are improved.

Since the photoelectric conversion device of the present invention can configure one pixel with one transistor, it is extremely easy to increase the density, and at the same time, due to its structure, there is little blooming and smearing, and it has high sensitivity. Its dynamic range is wide, and since it has an internal amplification function, it generates a large signal voltage regardless of wiring capacitance, so it has the characteristics of low recording and easy peripheral circuitry. For example, its industrial value as a future high-quality solid-state imaging device is extremely high.

[Brief explanation of the drawing]

Figures 1, 2, and 4 to 7 are
1 is a diagram for explaining the main structure and basic operation of an optical sensor cell according to an embodiment of the present invention. FIG. 1A is a plan view, b is a sectional view, and c is an equivalent circuit diagram; FIG. 2 is an equivalent circuit diagram during read operation; FIG. 4 is a graph showing the relationship between read time and read voltage; Figure 5a is a graph showing the relationship between storage voltage and readout time, Figure 5b is a graph showing the relationship between bias voltage and readout time, Figure 6 is an equivalent circuit diagram during refresh operation, and Figures 7a to c. is a graph showing the relationship between refresh time and base potential. FIG. 3 is a circuit diagram of a photoelectric conversion device constructed from the optical sensor shown in FIG. 1. FIG. 8 to FIG. 10 are explanatory diagrams of the photoelectric conversion device of FIG. 3 configured by the optical sensor shown in FIG.
The figure is a pulse swimming diagram. FIG. 9 is an equivalent circuit diagram related to the output signal, and FIG. 10 is a graph showing the output voltage from the moment of conduction in relation to time. 11, 12 and 13 are circuit diagrams showing other photoelectric conversion devices. FIG. 14 is a plan view for explaining the main structure of a modified example of the present invention. FIG. 15 is a circuit diagram of a photoelectric conversion device constituted by the optical sensor cell shown in FIG. 14. FIGS. 16 and 17 are cross-sectional views showing an example of a method for manufacturing a photoelectric conversion device of the present invention. 1...Silicon substrate, 2...PSG film, 3...
Insulating oxide film, 4... element isolation region, 5... n ^- region (collector region), 6... p region (base region), 7, 7'... n ⁺ region (emitter region), 8...
...Wiring, 9...Electrode, 10...Wiring, 11...
n ⁺ region, 12...electrode, 13...capacitor,
14... Bipolar transistor, 15, 17...
...Junction capacitance, 16, 18...Diode, 19,
19'...Contact part, 20...Light, 28...
Vertical line, 30...Photo sensor cell, 31...Horizontal line, 32...Vertical shift register, 33,
35...MOS transistor, 36, 37...terminal, 38...vertical line, 39...horizontal shift register, 40...MOS transistor, 41...
Output line, 42...MOS transistor, 43
... terminal, 44 ... transistor, 45 ... load resistance, 46 ... terminal, 47 ... terminal, 48 ...
MOS transistor, 49... terminal, 61, 62,
63... section, 64... collector potential, 67...
Waveform, 80, 81... Capacity, 82, 83... Resistance, 84... Current source, 100, 101, 102...
...Horizontal shift register, 111, 112...Output line, 138...Vertical line, 140...
MOS transistor, 148...MOS transistor, 150, 150'...MOS capacitor, 15
2,152'... Optical sensor cell, 300... Amorphous silicon, 302... Nitride film, 303...
...PSG film, 304...Polysilicon, 305...
...PSG film, 306...Interlayer insulating film.

Claims (1)

[Claims] 1. A first electrode electrically connected to the collector electrode.
a collector region made of a conductive type semiconductor; a high-resistance semiconductor region disposed adjacent to the collector region and having a higher resistivity than the collector region; and a high-resistance semiconductor region disposed adjacent to the high-resistance semiconductor region. , a base region made of a semiconductor of a second conductivity type different from the first conductivity type and disposed with respect to the electrode via an insulating region; and an output circuit disposed adjacent to the base region and including a capacitive load. An emitter region made of a first conductivity type semiconductor electrically connected to an emitter electrode electrically connected to a bipolar transistor, the photoelectric conversion device including a bipolar transistor having: By controlling the potential of the base region, carriers generated by received optical energy are accumulated, and an output signal corresponding to the carriers accumulated in the base region is applied to the emitter electrode as a voltage at the capacitive load. 1. A photoelectric conversion device characterized in that the photoelectric conversion device is in a floating state so that carriers read out to the side and subsequently accumulated are refreshed via the emitter electrode. 2. Claim 1, characterized in that a semiconductor layer region of the first conductivity type is interposed in a portion along the interface between the insulating layer provided on the control electrode region and the control electrode region. The photoelectric conversion device described in . 3. The photoelectric conversion device according to claim 1, wherein the bipolar transistor is integrally formed with a semiconductor substrate made of a first conductivity type semiconductor. 4. The photoelectric conversion device according to claim 1, wherein the bipolar transistor is formed on a semiconductor substrate made of a second conductivity type semiconductor. 5. The photoelectric conversion device according to claim 1, wherein a plurality of the bipolar transistors are two-dimensionally arranged and integrally provided on a semiconductor substrate.