JP2001196572A - Photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of a charge in a charge transfer means, adjoining a photoelectric conversion part of a photoelectric conversion device and to reduce or suppress generation of a dark current in the photoelectric conversion part. SOLUTION: In a photoelectric conversion device of a structure where the device has at least a photoelectric conversion part 201, which generates charge by an optical pumping and stores the charge, and a charge transfer means 202 adjoining the part 201 and the means 202 consists of a p-type conduction d semiconductor base body 401, an insulating film 403 provided on the base body 401 and a conductor 402 provided on the film 403, the value of the work function of the conductor 402 is set at least higher than or lower than the value of the work function of an intrinsic polycrystalline semiconductor material, consisting of a semiconductor material which is the same material as that for the base body 401.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage-type photoelectric conversion device in which a current generated in a light receiving portion in a dark state is suppressed.

[0002]

2. Description of the Related Art CCDs used in digital still cameras and digital video cameras, and recently developed CCDs,
In a photoelectric conversion device (image sensor) using a solid-state imaging device such as an active pixel sensor (for example, a CMOS image sensor) that is being commercialized, reduction of dark current is one of the most important issues. Is given.

Hereinafter, various photoelectric conversion devices will be described.
The problems of the prior art will be described with respect to a storage type photodiode which is almost the mainstream at present, that is, a type in which a PN junction of the photodiode is reverse-biased to accumulate photoexcited charges for a certain period of time and perform photoelectric conversion.

FIG. 15 shows a conventional photoelectric conversion device,
It is a figure explaining D. A pixel 101 mainly composed of a photodiode and a vertical transfer unit serving as a charge transfer unit is
An area-shaped sensor array is formed by regularly arranging the sensor array vertically and horizontally. The light incident on the opening 102 is transferred to its own vertical transfer unit after a certain charge accumulation time Tacc has elapsed, and is sequentially sent to the horizontal transfer unit.

FIG. 16 is a sectional view taken along the line AA ′ shown in FIG. Note that FIG. 16 shows only parts necessary for explanation.

[0006] The pixel 101 mainly receives light, exchanges the received photons for electric charge, and stores a photodiode 201 provided in the opening 102 having a function of accumulating the light. It comprises charge transfer means 202. In the CCD, electrons are selected as charges to be accumulated for reasons such as mobility of the charges. For this reason, the photodiode 201 and the charge transfer means 202 are formed on a substrate 203 having a p-well. The charge transfer means 202 is a capacitor having a so-called MIS structure, and has a gate electrode 2
The potential applied to the lower part of the gate electrode 205 is controlled by the voltage applied to the transistor 04 to perform charge accumulation and transfer.

[0007] 20 just below the gate electrode of the charge transfer means 202
5, a current 206 generated due to the defect occurs.
When it reaches the photodiode 201, it generates what is called a dark current. Although such a generated current is generated in all MIS capacitors, the MIS capacitor of the charge transfer means 202 causes an inherent problem due to a special structure in which the MIS capacitor is particularly adjacent to the photodiode 201. The dark current becomes noise in the sensor output and needs to be reduced. In the CCD, the capacitor having the MIS structure of the charge transfer means 202 is made of p-substrate-n ⁺ polysilicon, and a voltage lower than the substrate voltage (normally 0 V) is applied to the gate electrode 204 during photocharge accumulation. This suppresses the current generated below the gate electrode.

However, applying a negative voltage to the gate electrode 204 means that the amplitude of the voltage applied to the gate electrode 204 becomes large, and there is a problem of an increase in power consumption due to charge and discharge of the capacitance. Therefore, the gate electrode 2
It is desirable not to apply a negative voltage to the gate electrode 04, but if only 0 V is applied to the gate electrode 204, the region under the gate electrode will be in a weak inversion state, and cannot be in a strong accumulation state for suppressing dark current.

Here, as a method of suppressing a current generated during accumulation in the charge transfer means without applying a negative voltage to the gate electrode 204, there is a method of increasing the impurity concentration of silicon below the gate electrode. By increasing the impurity concentration, the inversion threshold value of the MIS capacitor can be increased, and a strong accumulation mode can be provided under the gate when 0 V is applied effectively.

[0010] However, although this method is theoretically feasible, in actuality, an impurity implantation technique in the current semiconductor process, for example, ion implantation or diffusion, determines the impurity concentration on the outermost surface of the substrate and the generated current. It was found that it was difficult to increase the density before suppression. It is difficult to achieve a substrate concentration that can suppress the current generated on the outermost surface of the MIS capacitor on the substrate side when n ⁺ polysilicon is used as a gate material and 0 V is applied to the gate electrode by the impurity implantation technique. is there. This is a conventional problem.

Next, a CMOS image sensor, which is another typical image sensor, will be described.

FIG. 17 is a schematic diagram showing the pixel structure of a CMOS sensor, and FIG. 18 is a schematic sectional view of the pixel structure of a CMOS sensor. FIG. 18 schematically shows the cross-sectional structure and connection relationship of each component of the CMOS sensor.
It does not show a cross section of an actual pixel. As a CMOS image sensor, a photodiode 301 serving as a photoelectric conversion unit, a transfer MOS transistor 302 serving as charge transfer means for transferring signal charges from the photodiode 301,
The floating diffusion 303 serving as an input part of the source follower transistor, the reset MOS transistor 304 serving as reset means for initializing the voltage of the floating diffusion 303, and the floating diffusion 30 in which the transferred signal charges are stored.
3, a source follower transistor 305 serving as amplifying means for reading the voltage and a selection transistor 306 serving as a selecting means for selecting the source follower are given as examples here. These MOS transistors are on a p-type conductive silicon substrate 307, and are all nMOS
It is composed of transistors. The CMOS image sensor is characterized by utilizing a logic process, and the gate electrodes of the nMOS transistors are all n ⁺ polysilicon. Here, a generated current is generated immediately below the gate electrodes of all the MOS transistors, as in the description of the CCD. However, in the transfer MOS transistor 302, the transfer MOS transistor 302 The current generated at the time of accumulation under the gate electrode 307 becomes a problem.

NMOS in CMOS image sensor
Since the transistor uses n ⁺ polysilicon for the gate electrode, similarly to the above-described problem, it is difficult to suppress the generated current by using an impurity implantation technique under the condition that 0 V is applied to the gate electrode.

[0014]

As described above, the charge transfer means adjacent to the photodiode must take into account the requirement of a dark current reduction, which is a design requirement different from other MIS devices. . An object of the present invention is to suppress a current generated in a charge transfer unit without applying a negative voltage.

[0015]

In view of the above problems, the present invention has at least a photoelectric conversion unit for generating a charge by photoexcitation and storing the charge, and a charge transfer unit adjacent to the photoelectric conversion unit. And the charge transfer means is p
In a photoelectric conversion device including a semiconductor substrate of a conductivity type of n-type or n-type, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, a work function value of the conductor Is at least equal to or less than the work function of an intrinsic polycrystalline semiconductor of a semiconductor of the same material as the semiconductor substrate.

Further, in the present invention, at least a photoelectric conversion unit that generates a charge by photoexcitation and stores the charge, a charge transfer unit adjacent to the photoelectric conversion unit, and a charge transfer unit that transfers the charge to the input unit. Wherein said charge transfer means comprises a plurality of pixels each having: an amplifying means for amplifying a voltage generated in said input means; a selecting means for selectively activating said amplifying means; and a reset means for initializing a voltage generated in said input section. Is p
In a photoelectric conversion device including a semiconductor substrate of a conductivity type of n-type or n-type, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, a work function value of the conductor Is at least equal to or less than the work function of an intrinsic polycrystalline semiconductor of a semiconductor of the same material as the semiconductor substrate.

Further, according to the present invention, at least a photoelectric conversion unit for generating a charge by photoexcitation and storing the charge, and a charge transfer unit adjacent to the photoelectric conversion unit, wherein the charge transfer unit is a first charge transfer unit. A photoelectric conversion device comprising a semiconductor substrate of the first conductivity type, an insulating film provided on the semiconductor substrate, and a polycrystalline semiconductor of the second conductivity type provided on the insulating film. And the second conductivity type are the same, and are formed on the surface of the semiconductor substrate where the charge transfer means is inverted.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) In a first embodiment of the present invention, the present invention is applied to the CCD shown in FIGS. FIG. 1 is a schematic sectional view of a CCD according to a first embodiment of the present invention. The same parts as those in FIG. 16 are denoted by the same reference numerals. The material of the gate electrode 402 of the charge transfer means 202 adjacent to the photodiode 201 formed in the p-type conduction type substrate 401 is made of p ⁺ conduction type poly such that the work function is higher than intrinsic polysilicon. The use of silicon is a feature of this embodiment. By using this structure, the dark current caused under the gate electrode can be reduced below the detection limit compared with the conventional structure under the condition that the same voltage (normally 0 V) as that of the base 401 is applied to the gate electrode to accumulate photocharges. Was reduced to 0%.

FIG. 12 is a graph plotting the work function difference between the p-type substrate and the gate electrode on the horizontal axis and the dark current on the vertical axis. Temperature is room temperature, substrate concentration is 1 × 10 ¹⁶
/ Cm ³ . Here, the same voltage as that of the substrate is applied to the gate electrode. When the work function difference is 0 or less, the substrate side is in an accumulation state, and no dark current is generated. As the work function difference progresses more positively from 0, the dark current sharply increases.
As in the conventional case, when the gate material is made of n ⁺ polysilicon, the dark current is set to 1, and the dark current is reduced by one digit (10
%), The boundary line is (A). By selecting at least intrinsic polysilicon as the gate material, the conventional dark current value can be reduced by one digit. As a more preferable material, p ⁺ polysilicon capable of completely accumulating the surface is used in this embodiment. This result is merely an example, and the value slightly increases or decreases due to a change in the work function on the substrate side due to a change in temperature, substrate concentration, or the like.
It is about eV, and does not essentially deny the effect of the present invention.

Here, a thermal oxide film of silicon was used for the insulating film 403 of the charge transfer means constituting the MIS capacitor. By reacting the silicon of the base in an oxygen atmosphere to form a thin film of an insulator of SiO ₂ , the defect density at the silicon-oxide film interface was reduced, and the dark current was reduced. Here, the insulating film 403 is not limited to the silicon thermal oxide film, and is, for example, a silicon nitride film, an ON film in which a silicon nitride film and a silicon oxide film are stacked, an ONO film in which a silicon nitride film is sandwiched between silicon oxide films, and the like. May be. The effect of the present invention is obtained by controlling the work function, and it is apparent that the effect does not depend on the composition of the insulator interposed therebetween.

Here, the substrate 401 is a p-type conductive substrate, but may be a p-type silicon substrate, for example.
It may be a p-type well formed in a silicon substrate. The substrate is not limited to a silicon substrate, but may be a substrate using another compound semiconductor. This embodiment is not limited to the structure of the base.

The structure of the photodiode 201 may be, for example, a PIN junction photodiode, a PN junction photodiode, or, for example, a photogate. An object of the present invention is to reduce dark current generated in the charge transfer means, and does not depend on the structure of the photodiode.

Although the gate electrode 402 of the charge transfer means is made of a single p ⁺ polysilicon, the invention is not limited to this. The part in contact with the insulating film, which determines the difference in work function between the substrate and the gate electrode, may have any of the above structures. For example, the resistance of the gate electrode is reduced on p ⁺ silicon having a certain thickness. For this purpose, aluminum or tantalum may be laminated. Alternatively, a portion in contact with the insulating film may be polysilicon which does not give an impurity as described later, or another metal.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic sectional view of a CCD according to a second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals. The difference from the first embodiment is that the gate electrode 501 is made of polysilicon to which no impurities are added. As can be seen from FIG. 12, the gate electrode 501 has
Under the condition that the same voltage as that of 01 (normally 0 V) was applied to accumulate the photocharge, the dark current caused by the portion under the photodiode and the gate electrode could be reduced to 6% which is one digit or less of the related art.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic sectional view of a CCD according to a third embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals. The feature of the present embodiment, which is different from the first embodiment, is that the gate electrode 601 is formed of an alloy 603 of p ⁺ polysilicon 602 and a metal laminated thereon.
It has a layered structure. The work function difference that determines the accumulation / reversal state under the gate electrode depends on the portion in contact with the insulating film, and does not depend on the alloy laminated thereon.
By using this structure, the dark current caused under the gate electrode can be reduced by 0% as compared with the conventional structure, as in the first embodiment.
% Could be reduced. As for the method of forming the alloy, for example, a silicidation technique conventionally used may be used. Although it is an alloy metal, molybdenum or tantalum is preferable in consideration of the heat process after the gate is formed, but any other material that can withstand the heat process after the gate is formed may be used. By using this structure,
Along with the effect of the first embodiment, that is, the reduction of dark current, the resistance of the gate material can be reduced, and high-speed driving has become possible.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic sectional view of a CCD according to a fourth embodiment of the present invention. The same parts as those in FIG. 3 showing the third embodiment are denoted by the same reference numerals. The feature of the present embodiment, which is different from the third embodiment, is that the gate electrode 701 is composed of an alloy 703 of polysilicon 702 to which impurities are not added and a metal laminated thereon.
With this structure, the dark current caused by the portion under the photodiode and the gate electrode could be reduced to 6% as in the second embodiment. The method and material for forming the alloy are the same as in the third embodiment. Polysilicon to which no impurity is added has a high resistance, and by adopting this structure, the gate material can be reduced in resistance in addition to the effect of the second embodiment, that is, the dark current can be reduced. Became possible.

(Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a schematic sectional view of a CCD according to a fifth embodiment of the present invention. The same parts as those in FIG. 1 showing the first embodiment are denoted by the same reference numerals. In this embodiment, an n-type conductive silicon substrate 801 is used, and the charges stored in the photodiode are holes. Dark current is generated under the gate electrode of the charge transfer means 802 irrespective of the conductivity type of the substrate, but n ⁺ polysilicon whose work function is equal to or less than that of intrinsic polysilicon should be selected as the material of the gate electrode 803. Thus, even when the same voltage (normal power supply voltage) as that of the base 801 was applied to the gate electrode to accumulate photocharges, the dark current could be reduced to 0% which is below the detection limit as compared with the conventional case.

FIG. 13 shows an n-type substrate.
It is a graph in which the horizontal axis represents the work function difference Φms and the vertical axis represents the dark current. When the work function difference is 0 or more, the substrate side is in an accumulation state, and no dark current occurs. As the work function difference progresses more positively from 0, the dark current sharply increases. As in the conventional case, the dark current when p ⁺ polysilicon is used as the gate material is 1, and the boundary line when the dark current is improved by one digit (10%) is (A). By selecting intrinsic polysilicon as the gate material, the value of the conventional dark current can be reduced by one digit. In this embodiment, as a more preferable material, n ⁺ polysilicon capable of completely accumulating the surface is used. This result is merely an example, and the value slightly increases or decreases due to a change in the work function on the substrate side due to a change in the temperature, the substrate concentration, etc., but at most about 0.1 eV in a practical range. It does not deny the effects of the invention.

(Sixth Embodiment) A sixth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a schematic sectional view of a CCD according to a sixth embodiment of the present invention. The same parts as those in FIG. 5 showing the fifth embodiment are denoted by the same reference numerals. In this embodiment, intrinsic polysilicon is used as the material of the gate electrode 802 used for the charge transfer means 802, so that the same voltage (normal power supply voltage) as that of the base 801 is applied to the gate electrode to accumulate photocharges. However, the dark current caused by the charge transfer means could be reduced to one digit or less, that is, 6% as compared with the conventional method.

(Seventh Embodiment) A seventh embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic sectional view of a CCD according to a seventh embodiment of the present invention. The same parts as those in FIG. 5 showing the fifth embodiment are denoted by the same reference numerals. In this embodiment, the gate electrode 1002 constituting the charge transfer means 1001 is composed of a thin n ⁺ polysilicon 1004 deposited on the insulating film 1003 and an alloy 1 deposited thereon.
005. The composition and manufacturing method of the alloy are the same as in the third embodiment.

By doing so, the dark current can be reduced to 0% as in the fifth embodiment, and at the same time, the gate resistance can be reduced and the circuit can be speeded up.

(Eighth Embodiment) An eighth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a schematic sectional view of a CCD according to an eighth embodiment of the present invention. The same parts as those in FIG. 6 showing the sixth embodiment are denoted by the same reference numerals. In this embodiment, the gate electrode 1102 constituting the charge transfer means 1101 is made of a thin, undoped polysilicon 1104 deposited on the insulating film 1103 and an alloy 1105 deposited thereon. is there. The composition and manufacturing method of the alloy are the same as in the third embodiment.

In this manner, as in the sixth embodiment, the dark current can be reduced to 6%, the gate resistance can be reduced, and the circuit can be operated at higher speed.

(Ninth Embodiment) A ninth embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is applied to a CMOS sensor. FIG. 9 is a schematic sectional view of a CMOS sensor according to a ninth embodiment of the present invention. A feature of this embodiment is that p ⁺ conductive type polysilicon is used for the gate electrode 1201 of the transfer MOS transistor 302. In this embodiment, similar to the first embodiment,
The dark current could be reduced to 4%.

(Tenth Embodiment) A tenth embodiment of the present invention will be described with reference to FIG. The gate electrode 1201 includes
As in the second embodiment, intrinsic polysilicon was used. As in the second embodiment, the dark current could be reduced to 6%.

(Eleventh Embodiment) An eleventh embodiment of the present invention will be described with reference to FIG. The gate electrode 1201 includes
As in the third embodiment, an alloy of p ⁺ polysilicon and silicon deposited thereon was used. As in the first embodiment, the dark current was reduced to 0%, and the gate resistance was also reduced.

(Twelfth Embodiment) A twelfth embodiment of the present invention will be described with reference to FIG. The gate electrode 1201 includes
As in the fourth embodiment, an alloy of intrinsic polysilicon and silicon deposited thereon was used. As in the second embodiment, the dark current was reduced to 6%, and the gate resistance was also reduced.

(Thirteenth Embodiment) A thirteenth embodiment of the present invention will be described with reference to FIG. FIG. 10 shows a thirteenth embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of a CMOS sensor according to the example of FIG. A hole accumulation type photodiode 1302, a transfer MOS transistor 1303, and a floating diffusion 1 are formed on an n-type conductive silicon substrate 1301.
304, a reset switch transistor 1305, a source follower transistor 1306, and a select transistor 1307, all of which are pMOS transistors.

The difference of this embodiment from the conventional one is that the transfer MOS
This embodiment is characterized in that n ⁺ conductive type polysilicon is used for the gate electrode 1308 of the transistor 1303. As in the fifth embodiment, the dark current could be reduced to 0%.

(Fourteenth Embodiment) A fourteenth embodiment of the present invention will be described with reference to FIG. As the gate electrode 1308, as in the sixth embodiment, polysilicon without using impurities was used. As in the sixth embodiment, the dark current could be reduced to 6%.

(Fifteenth Embodiment) A fifteenth embodiment of the present invention will be described with reference to FIG. As in the seventh embodiment, n ⁺ polysilicon and an alloy of metal and silicon deposited thereon were used for the gate electrode 1308. As in the seventh embodiment, the dark current can be reduced to 0%,
In addition, the gate resistance could be reduced.

(Sixteenth Embodiment) A sixteenth embodiment of the present invention will be described with reference to FIG. As in the eighth embodiment, polysilicon without using impurities and an alloy of metal and silicon deposited thereon are used for the gate electrode 1308. As in the eighth embodiment, the dark current can be reduced to 6%, and the gate resistance can be reduced.

(Seventeenth Embodiment) A seventeenth embodiment of the present invention will be described with reference to FIG. FIG. 11 shows a seventeenth embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view of a CMOS sensor according to the example of FIG. The same parts as those in FIG. 9 showing the ninth embodiment are denoted by the same reference numerals. This embodiment is characterized in that the gate electrode 17 of each of the MOS transistors 302, 304, 306, and 305 is provided.
The structures 01, 1702, 1703, and 1704 are all of the same composition. In this embodiment, p ⁺ polysilicon is used, and the dark current can be reduced to 0% as in the first embodiment.

The gate electrode is not limited to p ⁺ polysilicon,
For example, as shown in the second, third, and fourth embodiments, polysilicon to which no impurity is added, or p ⁺ polysilicon / polysilicon and metal alloy to which no impurity is added may be used.

The effect of this embodiment is that, in addition to the reduction of dark current, the gate electrode film can be made of one kind of layer.
This means that the process steps can be simplified. Therefore, the type of the gate electrode is not limited to polysilicon, and if the gate material capable of suppressing the dark current described in the above embodiment is selected, the effect of this embodiment can be obtained with any other material.

In this embodiment, for example, a CMOS sensor is assumed. In the CMOS sensor, a light receiving element, that is, a region where pixels are gathered, and a signal obtained from the pixel are processed (for example, noise removal, an amplifier, A / D
There is an advantage that the peripheral part to be converted can be integrated on one chip. Since the material used for the gate electrodes of the MOS transistors in the peripheral portion is not limited in the present invention, it may be of the same conductivity type as the charge transfer means in the present embodiment.

In this embodiment, the conductivity type of the substrate 307 is p-type, but is not limited to p-type and may be n-type. First
By selecting the gate structure described in the third to fifteenth embodiments, the dark current can be similarly reduced even if the MOS transistor is formed of pMOS.

(Eighteenth Embodiment) Eighteenth Embodiment of the Present Invention
An example will be described with reference to FIG. The feature of this embodiment is that
Structure of gate electrode 1701 of MOS transistor 302
And other MOS transistors 304, 306, 30
5 gate electrodes 1702, 1703 and 1704
It is different. In each of the embodiments described above,
Transfer MOS transistor or charge transfer means
Gate material is selected only for the purpose of suppressing dark current.
Have been. However, in other MOS transistors,
It is not necessary to control the flow. Rather
When considering current-voltage characteristics, other M
OS transistor is n⁺Use polysilicon as gate
Is preferred. In this embodiment, the transfer MOS
The gate electrode 1701 of the transistor is used to reduce dark current.
P⁺Polysilicon and n for the other gate electrodes ⁺
It is characterized by using polysilicon. This embodiment
Optimizes current-voltage characteristics and reduces dark current
It became possible to make it.

The gate electrode of the transfer MOS transistor is p
⁺ Not limited to polysilicon, for example, as shown in the second, third, and fourth embodiments, polysilicon without adding impurities,
p ⁺ polysilicon / polysilicon and metal alloy to which no impurity is added may be used.

Here, a method of providing a plurality of gate electrode structures is described. For example, in a two-layer polysilicon process, the first-layer polysilicon is used for forming other MOS transistors as n ⁺ polysilicon, and the second-layer polysilicon is formed. Polysilicon was realized by using it as p ⁺ polysilicon for forming a transfer MOS transistor. It goes without saying that the order of the first and second layers may be reversed. Further, for example, a polysilicon layer to which no impurity is added is formed on the entire surface, and a p-type impurity is selectively formed in a portion constituting the transfer MOS transistor using masking with a photoresist, and an n-type impurity is formed in other portions. May be selectively implanted.

In this embodiment, for example, a CMOS sensor is assumed. In the CMOS sensor, a light receiving element, that is, a region where pixels are gathered, and a signal obtained from the pixel are processed (for example, noise removal, an amplifier, A / D
There is an advantage that the peripheral part to be converted can be integrated on one chip. Since the material used for the gate electrodes of the MOS transistors at the peripheral portions is not limited in the present invention, the present embodiment may have the same conductivity type as the charge transfer means, or the opposite conductivity type (for example, n) to the charge transfer means.
(Contrary to each other, such as shape and p-type), or a metal whose conductivity type is not determined. Since the effect of the present invention is only the suppression of the dark current of the transfer means, for example, the gate electrode corresponding to the function may be independently selected for the amplifying means and the AD conversion means, and the gate electrode of the peripheral MOS transistor may be selected. Anything is fine.

The effect of the present embodiment is obtained by considering the difference in properties between the transfer MOS transistor and the other MOS transistors and by forming gate electrodes suitable for each of them. The transfer MOS transistor is not limited to a gate material capable of suppressing dark current, and other M
For the OS transistor, any other material or manufacturing method may be used as long as a gate material is selected in consideration of current-voltage characteristics.

In this embodiment, the conductivity type of the substrate 307 is p-type, but is not limited to p-type and may be n-type. First
The dark current can be similarly reduced by selecting the gate structure described in the embodiments 3 to 15 and appropriately changing the polarity of the conductivity type.

Further, as a modified example of the configuration of the CMOS sensor described above, as shown in FIG. 14, two photoelectric conversion units 301-1 and 301-2, and each of the photoelectric conversion units 301-1 and 301-3.
0-2, two transfer MOS transistors 302-1 and 302-2 serving as charge transfer means, a MOS transistor 304 serving as reset means, a MOS transistor 306 serving as selection means, and a MOS serving as a source follower input. And a common circuit unit provided with a single transistor 305, and a MOS transistor 305 which receives signals from the photoelectric conversion units 301-1 and 301-2 as one source follower input. The present invention can be applied to a photoelectric conversion device of a common amplifier system in which an amplifier is shared by sequentially transferring data to a gate. In this case, a unit cell is considered to be a group of two pixels. Of course, a common amplifier type photoelectric conversion device may be configured by providing three or more photoelectric conversion units and three or more charge transfer units.

[0056]

As described above, according to the present invention, as described above, generation at the charge transfer means adjacent to the photoelectric conversion unit is suppressed, and the dark current in the photoelectric conversion unit is reduced or suppressed. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a CCD according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a CCD according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a CCD according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a CCD according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a CCD according to a fifth embodiment of the present invention.

FIG. 6 is a schematic sectional view of a CCD according to a sixth embodiment of the present invention.

FIG. 7 is a schematic sectional view of a CCD according to a seventh embodiment of the present invention.

FIG. 8 is a schematic sectional view of a CCD according to an eighth embodiment of the present invention.

FIG. 9 is a schematic sectional view of a CMOS sensor according to a ninth embodiment of the present invention.

FIG. 10 is a schematic sectional view of a CMOS sensor according to a thirteenth embodiment of the present invention.

FIG. 11 is a schematic sectional view of a CMOS sensor according to a seventeenth embodiment of the present invention.

FIG. 12 is a graph in which a horizontal axis represents a work function difference of a gate electrode and a vertical axis represents a dark current in a p-type substrate.

FIG. 13 is a graph plotting a work function difference of a gate electrode on a horizontal axis and a dark current on a vertical axis in an n-type substrate.

FIG. 14 is a schematic diagram showing a modification of the configuration of the CMOS sensor.

FIG. 15 is a schematic plan view showing a configuration of a CCD.

FIG. 16 is a sectional view taken along line AA ′ of FIG.

FIG. 17 is a schematic diagram showing a pixel structure of a CMOS sensor.

FIG. 18 is a schematic sectional view of a pixel structure of a CMOS sensor.

[Explanation of symbols]

 101 pixel 102 opening 201, 301 photodiode 202, 802, 1001, 1101 charge transfer means 203, 307, 401, 801, 1301 substrate 204 gate electrode 302 transfer MOS transistor (charge transfer means) 303 floating diffusion 304 reset MOS transistor ( Reset means) 305 source follower transistor (amplification means) 306 selection transistor (selection means)

Claims (45)

[Claims] 1. At least a photoelectric conversion unit that generates a charge by photoexcitation and stores the charge, and a charge transfer unit adjacent to the photoelectric conversion unit, wherein the charge transfer unit has a p-type conductivity. In a photoelectric conversion device including a semiconductor substrate, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, a work function value of the conductor is at least the same as that of the semiconductor substrate. A photoelectric conversion device characterized by having a work function that is equal to or higher than a work function of an intrinsic polycrystalline semiconductor of a material semiconductor. 2. The photoelectric conversion device according to claim 1, wherein a p-type conductivity type polycrystalline semiconductor is used at least in a portion in contact with the insulating film as the conductor. 3. An alloy of at least a p-type conduction type polycrystalline semiconductor as said conductor and a metal and said p-type conduction type polycrystalline semiconductor on said p-type conduction type polycrystalline semiconductor. The photoelectric conversion device according to claim 1, wherein: 4. The photoelectric conversion device according to claim 1, wherein an intrinsic polycrystalline semiconductor is used as at least a portion in contact with the insulating film as the conductor. 5. The method according to claim 1, wherein at least the intrinsic polycrystalline semiconductor and an alloy of a metal and the intrinsic polycrystalline semiconductor on the intrinsic polycrystalline semiconductor are used as the conductor. The photoelectric conversion device as described in the above. 6. The photoelectric conversion device according to claim 3, wherein tungsten is used as the metal. 7. The photoelectric conversion device according to claim 3, wherein molybdenum is used as the metal. 8. The photoelectric conversion device according to claim 5, wherein tungsten is used as the metal. 9. The photoelectric conversion device according to claim 5, wherein molybdenum is used as said metal. 10. The photoelectric conversion device according to claim 1, wherein a silicon oxide film is used as the insulating film. 11. At least a photoelectric conversion unit that generates a charge by photoexcitation and stores the charge, and a charge transfer unit adjacent to the photoelectric conversion unit, wherein the charge transfer unit has an n-type conductivity type. In a photoelectric conversion device including a semiconductor substrate, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, a work function value of the conductor is at least the same as that of the semiconductor substrate. A photoelectric conversion device characterized in that the work function is equal to or less than a work function of an intrinsic polycrystalline semiconductor of a material semiconductor. 12. The photoelectric conversion device according to claim 11, wherein an n-type conductivity type polycrystalline semiconductor is used at least in a portion in contact with the insulating film as the conductor. 13. An n-type polycrystalline semiconductor having at least an n-type conductive type as said conductor, and an alloy of a metal and said n-type conductive type polycrystalline semiconductor on said n-type conductive type polycrystalline semiconductor The photoelectric conversion device according to claim 11, wherein: 14. The photoelectric conversion device according to claim 11, wherein an intrinsic polycrystalline semiconductor is used as the conductor at least in a portion in contact with the insulating film. 15. The semiconductor device according to claim 11, wherein at least the intrinsic polycrystalline semiconductor and an alloy of a metal and the intrinsic polycrystalline semiconductor on the intrinsic polycrystalline semiconductor are used as the conductor. The photoelectric conversion device as described in the above. 16. The photoelectric conversion device according to claim 13, wherein tungsten is used as said metal. 17. The photoelectric conversion device according to claim 13, wherein molybdenum is used as said metal. 18. The photoelectric conversion device according to claim 15, wherein tungsten is used as said metal. 19. The photoelectric conversion device according to claim 15, wherein molybdenum is used as said metal. 20. The photoelectric conversion device according to claim 11, wherein a silicon oxide film is used as said insulating film. 21. At least a photoelectric conversion unit for generating a charge by photoexcitation and storing the charge, a charge transfer unit adjacent to the photoelectric conversion unit, and a voltage for transferring the charge to an input unit and generating a voltage at the input unit. A plurality of pixels having amplifying means for amplifying, selecting means for selectively activating the amplifying means, and reset means for initializing a voltage generated at the input section, wherein the charge transfer means is a p-type In a photoelectric conversion device comprising a semiconductor substrate of the conductivity type, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, the work function value of the conductor is at least the A photoelectric conversion device having a work function that is equal to or higher than a work function of an intrinsic polycrystalline semiconductor of a semiconductor made of the same material as a semiconductor substrate. 22. The photoelectric conversion device according to claim 21, wherein a p-type conduction type polycrystalline semiconductor is used at least in a portion in contact with the insulating film as the conductor. 23. An alloy of at least a p-type conductive polycrystalline semiconductor and a metal and a p-type conductive polycrystalline semiconductor on the p-type conductive polycrystalline semiconductor as the conductor. 22. The photoelectric conversion device according to claim 21, wherein: 24. The photoelectric conversion device according to claim 21, wherein an intrinsic polycrystalline semiconductor is used as at least a portion in contact with the insulating film as the conductor. 25. The method according to claim 21, wherein at least the intrinsic polycrystalline semiconductor and an alloy of a metal and the intrinsic polycrystalline semiconductor on the intrinsic polycrystalline semiconductor are used as the conductor. The photoelectric conversion device as described in the above. 26. The photoelectric conversion device according to claim 23, wherein tungsten is used as the metal. 27. The photoelectric conversion device according to claim 23, wherein molybdenum is used as said metal. 28. The photoelectric conversion device according to claim 25, wherein tungsten is used as the metal. 29. The photoelectric conversion device according to claim 25, wherein molybdenum is used as said metal. 30. The photoelectric conversion device according to claim 21, wherein a silicon oxide film is used as the insulating film. 31. At least one of the amplifying means, the reset means, and the selecting means includes a semiconductor substrate of p-type conductivity, an insulating film provided on the semiconductor substrate, and The conductor constituting at least one of the amplifying unit, the resetting unit, and the selecting unit has the same composition as the conductor constituting the charge transfer unit. The photoelectric conversion device according to claim 21, wherein: 32. At least one of the amplifying means, the reset means, and the selecting means includes a semiconductor substrate of p-type conductivity, an insulating film provided on the semiconductor substrate, and A conductor provided in the amplifying unit, the reset unit, and the selecting unit, wherein the conductor constituting at least one of the selecting unit has a different composition from the conductor constituting the charge transfer unit. 22. The photoelectric conversion device according to claim 21, wherein 33. A photoelectric conversion unit for generating a charge by photoexcitation and accumulating the charge, a charge transfer unit adjacent to the photoelectric conversion unit, and a voltage generated at the input unit when the charge is transferred to the input unit. A plurality of pixels each including an amplifying unit for amplifying, a selecting unit for selectively activating the amplifying unit, and a reset unit for initializing a voltage generated at the input unit, wherein the charge transfer unit is an n-type. A conductive type semiconductor substrate, an insulating film provided on the semiconductor substrate, and a conductor provided on the insulating film, wherein the work function value of the conductor is at least the semiconductor A photoelectric conversion device having a work function value equal to or less than a work function of an intrinsic polycrystalline semiconductor of a semiconductor of the same material as a base. 34. The photoelectric conversion device according to claim 33, wherein an n-type conduction type polycrystalline semiconductor is used at least in a portion in contact with the insulating film as the conductor. 35. An n-type polycrystalline semiconductor having at least an n-type conductive type as the conductor, and an alloy of a metal and the n-type conductive type polycrystalline semiconductor on the n-type conductive type polycrystalline semiconductor 34. The photoelectric conversion device according to claim 33, wherein: 36. The photoelectric conversion device according to claim 33, wherein an intrinsic polycrystalline semiconductor is used as at least a portion in contact with the insulating film as the conductor. 37. The method according to claim 33, wherein at least the intrinsic polycrystalline semiconductor and an alloy of a metal and the intrinsic polycrystalline semiconductor on the intrinsic polycrystalline semiconductor are used as the conductor. The photoelectric conversion device as described in the above. 38. The photoelectric conversion device according to claim 35, wherein tungsten is used as the metal. 39. The photoelectric conversion device according to claim 35, wherein molybdenum is used as said metal. 40. The photoelectric conversion device according to claim 37, wherein tungsten is used as the metal. 41. The photoelectric conversion device according to claim 37, wherein molybdenum is used as said metal. 42. The photoelectric conversion device according to claim 33, wherein a silicon oxide film is used as said insulating film. 43. At least one of the amplifying means, the reset means, and the selecting means includes: an n-type conductive semiconductor substrate; an insulating film provided on the semiconductor substrate; The conductor constituting at least one of the amplifying unit, the resetting unit, and the selecting unit has the same composition as the conductor constituting the charge transfer unit. The photoelectric conversion device according to claim 33, wherein: 44. At least one of the amplifying unit, the reset unit, and the selecting unit includes: an n-type conductive semiconductor substrate; an insulating film provided on the semiconductor substrate; A conductor provided in the amplifying unit, the reset unit, and the selecting unit, wherein the conductor constituting at least one of the selecting unit has a different composition from the conductor constituting the charge transfer unit. 34. The photoelectric conversion device according to claim 33, wherein: 45. At least a photoelectric conversion unit that generates a charge by photoexcitation and accumulates the charge, and a charge transfer unit adjacent to the photoelectric conversion unit, wherein the charge transfer unit has a first conductivity type. In a photoelectric conversion device including a semiconductor substrate, an insulating film provided on the semiconductor substrate, and a polycrystalline semiconductor of a second conductivity type provided on the insulating film, the first conductivity type and the second conductivity type Is the same as the conduction type of
And an inversion region of the charge transfer means formed on the surface of the semiconductor substrate.