JPH11135765A - Solid-state image-pickup device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image-pickup device which, without deteriorating the characteristics, comparatively simply reduces the smear due to light multiply reflected in the gap between a light-proof metal film and substrate surface. SOLUTION: The image-pickup device comprises a light-receiving charge storage 1 having an opening which is sectioned by a light-proof material 6 for converting a light received at the opening into a signal charge to be stored therein and a charge transfer part 2 for reading and transferring the signal charges stored in the storage 1 with the application of voltages to first transfer electrodes 3 for reading the signal charges from the storage 1 and to second transfer electrodes 4 which is not used for the reading. A distance d2 between the second transfer electrode 4 and an opening is greater than d1 between the first transfer electrode 3 and the opening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device such as a CCD imaging device, and more particularly to a device for reducing smear.

[0002]

2. Description of the Related Art A phenomenon called smear is one of the phenomena which cause deterioration of image quality when photographing using a CCD image pickup device. This is a phenomenon in which white linear noise appears above and below a high-luminance illuminant such as the sun or a car headlight in a subject. There are three possible causes of smear, and as a prerequisite for listing them, the pixel structure and transfer method of the CCD image sensor will be described.

FIG. 10A shows an example of a sectional structure of one pixel of a CCD image pickup device, and FIG. 10B is a potential diagram thereof. In the vicinity of the surface of the silicon substrate 11, a sensor section (photoelectric charge storage section) 12 composed of a photodiode, a readout gate (ROG) 13, a vertical CCD (charge transfer section)
14 are formed in order. A common transfer electrode 15 made of polysilicon or the like is provided above the ROG 13 and the charge transfer section 14. The ROG 13, the charge transfer section 14 and the transfer electrode 15 are covered with a light-shielding metal film 16 made of aluminum or the like. ing. The light-shielding metal film 16 defines an opening of the light-receiving charge accumulation section 12.

[0004] In the light receiving charge storage section 12, the light L received at the opening is converted into signal charges and stored. This signal charge is applied to the ROG by applying a pulse voltage to the transfer electrode 15.
By making the potential of the reference 13 deeper than that of the light-receiving charge storage unit 12 and the potential of a specific portion of the charge transfer unit 14 (the state indicated by the broken line in FIG. 10B), the data is read out to the charge transfer unit 14. The signal charges read out in this manner are transferred in the transfer electrodes 15 by controlling the potentials of the respective portions of the charge transfer section 14 by applying a pulse voltage to the transfer electrodes 15 and are transferred to a horizontal CCD (not shown). Moved. The signal charges transferred to the horizontal CCD are transferred inside the horizontal CCD, transferred to an output unit (not shown), converted into electric signals at the output unit, and output to the outside.

[0005] The causes of smear occurrence are listed below with reference to FIG. 10 as an example. (A) Part of the light L received at the opening of the received charge accumulation unit 12 directly enters the charge transfer unit 14 due to multiple reflection in the gap between the light-shielding metal film 16 and the surface of the silicon substrate 11. thing. (B) Deep portion of photoreception charge storage section 12 (near P-Well)
That the signal charge photoelectrically converted in the step (d) is diffused into the charge transfer unit 14. (C) The light incident on the light-shielding metal film 16 is
And penetrates directly into the charge transfer section 14.

[0006] Among these causes, the occurrence of smear due to the cause (b) is sufficiently avoided by a P-Well potential barrier in a CCD imaging device having a structure called a HAD sensor which is currently mainstream. Has become possible. The generation of smear due to the cause (c) can be avoided by improving the method of forming the light-shielding metal film. Therefore, the largest cause of smear at present is the multiple reflection of light in the gap between the light-shielding metal film and the surface of the silicon substrate as shown in FIG.

Conventionally, in order to reduce smear caused by multiple reflection of light in the gap between the light-shielding metal film and the surface of the silicon substrate, for example, in the example of FIG. It is proposed to reduce the amount of light reaching the charge transfer unit 14 by covering the position as far as possible from the unit 14 with the light-shielding metal film 16 (that is, increasing the distance between the charge transfer unit 14 and the opening). It had been.

[0008]

As a specific method for covering the surface of the silicon substrate 11 up to a position as far as possible from the charge transfer section 14 with the light-shielding metal film 16, first, as shown in FIG. It is conceivable to increase the area of. However, in this method, on the contrary, the area of the opening of the light receiving charge storage section 12 is reduced (that is, the aperture ratio is reduced), so that the sensitivity, which is an important characteristic of the CCD image sensor, is reduced.

Therefore, instead of increasing the area of the light-shielding metal film 6, the width (length in the direction orthogonal to the transfer direction) of the charge transfer section 14 is reduced, so that the charge transfer section 14 is consequently reduced. It is also conceivable to increase the distance between 14 and the opening. However, the width of the charge transfer unit 14 is closely related to the amount of charge that can be transferred by the charge transfer unit 14, and the smaller the width, the smaller the amount of charge that can be transferred. Therefore, in this method, the output level decreases due to the decrease in the amount of transfer charges.

As described above, increasing the distance between the charge transfer portion and the opening portion has a disadvantage that sensitivity and output level, which are important characteristics of the image pickup device, decrease.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been described, without these inconveniences, and relatively simply, because of the multiple reflections of light at the gap between the light-shielding metal film and the silicon substrate surface. It is an object of the present invention to provide an image sensor capable of reducing smear and a method of manufacturing such an image sensor.

[0012]

According to the present invention, there is provided a solid-state image pickup device having a light-receiving material which has an opening defined by a light-shielding material, converts light received at the opening into signal charge, and stores the signal charge. The signal charges accumulated in the light receiving charge accumulating portion are applied by applying a voltage to a first transfer electrode used for reading the signal charge from the light receiving charge accumulating portion and a second transfer electrode not used for the reading. In the solid-state imaging device having a charge transfer unit that reads and transfers from the received light charge storage unit, the distance between the second transfer electrode and the opening is larger than the distance between the first transfer electrode and the opening. It is characterized by increasing the distance.

In this image pickup device, first, without increasing the distance between the charge transfer section and the opening (ie, without reducing the area of the opening or reducing the width of the charge transfer section), The distance between the transfer electrode and the opening (that is, the distance between the transfer electrode and the edge of a light-shielding material such as a light-shielding metal film that defines the opening) is made larger than that of the conventional image sensor. I have. 10 as an example, the transfer electrode 15
FIG. 11 shows a state in which the distance between the light-shielding metal film 16 and the edge of the light-shielding metal film 16 is increased (the width of the transfer electrode 15 is reduced without increasing the area of the light-shielding metal film 16). As is clear from the comparison of the figures, the greater the distance between the transfer electrode and the end of the light-shielding metal film, the greater the number of multiple reflections of light in the gap between the light-shielding metal film and the surface of the silicon substrate.

Assuming that the attenuation rate of the light intensity when the light is reflected once is α (0 <α <1), the intensity after the light is reflected n times is n times the α of the first light. Therefore, the degree of smear due to the light incident on the charge transfer unit also increases to the n-th power of α (that is, the smear decreases as the number of multiple reflections increases). Therefore, by increasing the distance between the transfer electrode and the opening in this manner, the gap between the light-shielding metal film and the silicon substrate surface can be reduced without lowering the sensitivity and output level, which are important characteristics of the image sensor. Smear due to multiple reflections of the light is reduced.

However, as shown in FIG. 11, when the width of the transfer electrode 15 is reduced, the width of the ROG 13 below the transfer electrode 15 must be reduced. Since the readout gate has a role as a potential barrier between the received charge storage section and the charge transfer section, if the width is narrowed, this role is sufficient when the received charge storage section receives excessive light. However, there is a disadvantage that the charge overflows into the charge transfer section without performing the above operation. It should be noted that even if the width of the read gate is reduced in this manner,
At the same time, if the impurity concentration is increased, the read gate can sufficiently serve as a potential barrier. However, while the read gate has a role as a potential barrier, it also has a role as a read path for signal charges to the charge transfer section. The inconvenience of not fulfilling the function sufficiently occurs.

Further, at the time of manufacturing the image pickup device, the readout gate is formed by ion implantation (ion implantation method).
And a transfer electrode formed by etching polysilicon or the like. Therefore, the width of the read gate varies due to variations and deviations in the width of the charge transfer portion and the transfer electrode.

For these reasons, when designing the read gate, the width and the impurity concentration are determined in a well-balanced manner in consideration of both the role as the potential barrier and the role as the read path, and the manufacturing process is performed. It is necessary to determine the width in consideration of a margin for variation and deviation of the width. Therefore, it is not appropriate to reduce the width of the read gate too much for the purpose of improving smear.

By the way, in an image pickup device employing a drive system other than the single-phase drive system (two-phase drive system, three-phase drive system and four-phase drive system), a plurality of transfer electrodes are provided for each pixel. Some of the transfer electrodes read both signal charges from the light receiving charge storage section to the charge transfer section and transfer signal charges in the charge transfer section (that is, control of the potential of the read gate and charge transfer). The remaining transfer electrodes are not used for this readout, but are used only for transferring signal charges (that is, only for controlling the potential of the charge transfer unit).

In other words, in such an image sensor,
The readout gate exists only below the transfer electrode used for both reading out the signal charge from the light receiving charge storage unit to the charge transfer unit and transferring the signal charge in the charge transfer unit. The lower part of the transfer electrode, which is used only for, serves only as a potential barrier. Therefore, in this portion, it is not necessary to determine the width and the impurity concentration in a very well-balanced manner as compared with the read gate.
It suffices that the charge does not overflow into the charge transfer section even when excessive light is received by the received charge accumulation section.

In view of this point, the present invention is directed to a transfer electrode (first transfer) used for reading signal charges from a light-receiving charge storage section in an image pickup device employing a drive method other than the single-phase drive method. The distance between the electrode and the opening is almost the same as before (or slightly larger than before, as long as the role of the readout gate is not impaired). The distance between the unused transfer electrode (the second transfer electrode) and the opening is made larger (i.e., the width of the first transfer electrode is almost the same as the conventional one or slightly larger). In this case, the width of the second transfer electrode is smaller than the width of the first transfer electrode.

According to this imaging device, the distance between the second transfer electrode, which is not used for reading out the signal charge from the received charge storage portion, and the opening is considerably larger than in the prior art. Between the transfer electrode and the opening, the number of multiple reflections of light in the gap between the light-shielding metal film and the surface of the silicon substrate increases. Therefore, smear due to multiple reflection of light in the gap between the light-shielding metal film and the surface of the silicon substrate is reduced.

Further, the distance between the first transfer electrode used for reading out the signal charge from the light receiving charge storage portion and the opening is almost the same as the conventional one (or is slightly larger than the conventional one). The read gate can sufficiently fulfill both the role as a potential barrier and the role as a read path.

Moreover, the imaging device having such a structure can be manufactured relatively easily based on the fact that the width of the second transfer electrode is determined to be larger than the width of the first transfer electrode at the time of design. is there. Therefore, smear reduction can be realized relatively easily.

In this image pickup device, it is preferable that the side of the second transfer electrode in the direction of transfer of the charge transfer section is longer than the side of the first transfer electrode in the direction of transfer. is there. Thereby, the ratio of the light that is multiple-reflected between the second transfer electrode and the opening portion (that is, the multiple reflection) of the light that is multiply reflected at the gap between the light-shielding metal film and the silicon substrate surface and directly enters the charge transfer portion is (The ratio of light having a large number of times) increases, so that smear is further reduced.

Moreover, in the image pickup device having such a structure, in addition to determining the width of the second transfer electrode to be larger than the width of the first transfer electrode at the time of designing, the image pickup device has the following structure. Based on the determination that the side of the second transfer electrode is longer than the side, the manufacture can also be performed relatively easily.

In this imaging device, the lower portion of the second transfer electrode (that is, only the role as a potential barrier) is lower than the impurity concentration of the lower portion of the first transfer electrode (that is, the read gate). It is preferable to increase the impurity concentration of the portion having the same. As a result, the impurity concentration of a portion having only a role as a potential barrier increases,
Even if the width of this portion is further reduced (that is, the distance between the second transfer electrode and the opening portion is further increased), the portion sufficiently serves as a potential barrier. Therefore, smear is further reduced.

Next, in the method of manufacturing a solid-state imaging device according to the present invention, as described above, the received charge storage section and the signal charges stored in the received charge storage section are transferred to the first transfer electrode and the second transfer electrode.
A charge transfer unit that reads out and transfers a charge from a light-receiving charge storage unit by applying a voltage to a transfer electrode of the solid-state imaging device (that is, an imaging device that employs a driving method other than the single-phase driving method). In the step of introducing an impurity into a portion where a storage portion is to be formed, a portion below the second transfer electrode (that is, a portion having only a role as a potential barrier)
In addition, impurities are introduced.

According to this method of manufacturing the image pickup device, in the step of forming the light-receiving charge storage portion, the impurity is introduced into the portion having only the role of the potential barrier, so that the impurity concentration in this portion is reduced. Get higher. As a result, even if the width of this portion is further narrowed (that is, the distance between the second transfer electrode and the opening portion is further increased) as described above, this portion sufficiently serves as a potential barrier. In particular, according to this manufacturing method, the impurity concentration of a portion having only a role as a potential barrier is increased by using a process of forming a light receiving charge storage portion, so that it is necessary to add a new process. Disappears. Therefore, it is possible to easily manufacture an imaging device in which the impurity concentration of a portion having only a role as a potential barrier is increased.

In the case where the step of forming the light-receiving charge accumulating portion includes a plurality of steps of introducing different kinds of impurities, the impurities are also added to the portion having only a role as a potential barrier in all the steps. Conversely, if the impurity concentration is introduced, the impurity concentration in this portion may not be able to be increased. Therefore,
In such a case, an impurity is introduced together with this part only in some of the plurality of steps (that is, only some kinds of impurities are introduced together with this part). Is preferred.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a CCD which drives a charge transfer unit by a four-phase drive system and transfers signal charges from a pixel to an output unit by an interline transfer (IT) system.
An example in which the present invention is applied to an image sensor will be described.

FIG. 1 shows an example of the surface structure of the image pickup surface of such a CCD image pickup device (in FIG. 1, the positional relationship of each part in the vertical direction (direction perpendicular to the drawing) is omitted, and the horizontal position is omitted). Only the positional relationship is shown). Used for both reading out signal charges from a sensor unit (light receiving charge storage unit) 1 comprising a photodiode to a vertical CCD (charge transfer unit) 2 and transferring signal charges in the charge transfer unit 2 for each pixel. A transfer electrode 3 made of polysilicon or the like and a transfer electrode 4 made of polysilicon or the like that is not used for reading and is used only for transferring signal charges are provided.
A read gate (R) (not shown) is provided in the lower portion of the transfer electrode 3 near the surface of the silicon substrate of the CCD image sensor.
OG) is formed.

ROG, charge transfer section 2 and transfer electrodes 3 and 4
Are covered with a light-shielding metal film (not shown), and the light-shielding metal film defines an opening portion of the light-receiving charge accumulation section 1. A channel separation region 5 is provided between each pixel column in the vertical transfer direction (vertical direction in the figure). This CCD
The cross-sectional structure along the horizontal transfer direction (horizontal direction in the drawing) at the transfer electrode 3 portion of each pixel of the image sensor is the same as that shown in FIG.

FIGS. 2 and 3 show an example of a signal charge readout operation of such a CCD image pickup device in a field readout system (two-pixel mixed readout system). FIG. FIG. 3 is a potential diagram of a lower portion of the transfer electrodes 3 and 4 of two pixels adjacent to each other in the vertical transfer direction. FIG.
6 is a timing chart showing a change in the level of a voltage applied to the power supply. In these figures, of the transfer electrodes 3 and 4 of two adjacent pixels, the transfer electrodes 3 and 4 of one pixel (pixel (A)) are electrodes (1) and (2), respectively. Transfer electrodes 3 and 4 of the remaining one pixel (pixel (B)) are electrodes (3) and (4), respectively.

As shown in FIG. 3, first, at time T0, the level of the voltage applied to the electrodes (1), (2), (3) and (4) is changed to a predetermined intermediate level M and low levels L and M, respectively. , L, and at time T1, the level of the voltage applied to the electrode (1) is set to a predetermined high level H, so that in the pixel (A), the lower side of the electrode (1) in the charge transfer section 2 And the potential of the ROG are deepened. As a result, as shown in FIG. 2, in the pixel (A), the signal charges are read out from the light receiving charge accumulating section 1 and the charge
Of the electrode (1).

Subsequently, at time T2, the voltage level applied to the electrode (1) is returned to M, and then at time T3, the voltage level applied to the electrode (3) is set to H. The potential of the portion below the electrode (3) in the charge transfer section 2 and the potential of the ROG are increased. As a result, as shown in FIG. 2, in the pixel (B), the signal charge is read out from the light receiving charge storage unit 1 and stored in the lower part of the electrode (3) in the charge transfer unit 2.

In this manner, only (1) and (3) of the electrodes (1) to (4) (that is, only three of the transfer electrodes 3 and 4) are transferred from the light receiving charge storage unit 1 to the charge transfer unit. It is used for reading out signal charges to the section 2.

Subsequently, at time T4, the voltage level applied to the electrode (3) is returned to M, and then at time T5, the voltage level applied to the electrode (2) is increased to M, whereby the charge transfer unit 2 The potential of the lower part of the electrode (2) is deepened. As a result, as shown in FIG. 2, the signal charge stored in the lower part of the electrode (1) and the signal charge stored in the lower part of the electrode (3) in the charge transfer unit 2 are: The mixture spreads over the lower portions of the electrodes (1) to (3) (that is, the signal charges of the adjacent pixels (A) and (B) are mixed).

At time T6, the level of the voltage applied to the electrode (3) is lowered to L, so that the signal charges in the lower portions of the electrodes (1) to (3) are reduced as shown in FIG. Move to the lower part of (2) and (3). Hereinafter, by changing the level of the voltage applied to each of the electrodes (1) to (4) individually between M and L as shown in the timing chart of FIG. Will be transferred.

FIG. 5 shows an example of the surface structure of one pixel when the present invention is applied to the CCD image pickup device of FIG. 1. The same parts as those in FIG. Is omitted. (In the figure, the positional relationship of each part in the vertical direction is neglected, and only the peripheral part of the light receiving charge accumulation part is illustrated for the light-shielding metal film. The same applies to FIGS. 6 and 7 described later. .) In this example, the light receiving charge storage section 1
The distance d1 between the transfer electrode 3 used for reading signal charges from the substrate and the opening of the light-receiving charge storage section 1 defined by the light-shielding metal film 6 is substantially the same as that of the related art (that is, the distance d1 of the transfer electrode 3) Although the width is almost the same as the conventional case, the distance d2 between the transfer electrode 4 not used for reading out the signal charges and the opening is larger than the distance d1 (that is, the width of the transfer electrode 4). Is smaller than before.)

Incidentally, the conventional CCD image pickup device shown in FIG.
FIG. 6 shows the surface structure of the pixel in comparison with FIG. 5, and the distance between the transfer electrode 3 and the opening and the distance between the transfer electrode 4 and the opening are the same size d. (That is, the width of the transfer electrode 3 is equal to the width of the transfer electrode 4).

According to the example of FIG. 5, the distance d2 between the transfer electrode 4 and the opening is considerably larger than in the prior art, so that the light-shielding metal film and the silicon substrate are provided between the transfer electrode 4 and the opening. The number of multiple reflections of light at the gap with the surface increases. Therefore, smear due to multiple reflection of light in the gap between the light-shielding metal film and the surface of the silicon substrate is reduced.

Since the distance between the charge transfer section 2 and the opening is not increased (that is, the area of the opening is not reduced or the width of the charge transfer section 2 is not reduced), the importance of the image sensor is increased. The sensitivity and output level, which are important characteristics, do not decrease. Also, the distance d2 between the transfer electrode 3 and the opening portion
Is almost the same as the conventional one, so that the ROG can sufficiently fulfill both the role as a potential barrier and the role as a readout path.

Further, the CCD image pickup device having the structure as shown in FIG. 5 can be manufactured relatively easily based on the fact that the width of the transfer electrode 4 is determined to be larger than the width of the transfer electrode 3 at the time of design. It is. Therefore, smear reduction can be realized relatively easily.

Next, FIG. 7 shows another example of the surface structure of one pixel when the present invention is applied to the CCD image pickup device of FIG. 1, and the same portions as FIG. 1 and FIG. The same reference numerals are given and duplicate explanations are omitted. In this example, the distance d2 between the transfer electrode 4 and the opening is larger than the distance d1 between the transfer electrode 3 and the opening as in the example of FIG. Transfer electrode 3 above
The length n2 of the side of the transfer electrode 4 in this direction is longer than the length n1 of the side. Incidentally, in the conventional CCD imaging device of FIG. 1, as shown in FIG. 6, the sides of the transfer electrodes 3 and 4 have the same length n.

According to the example of FIG. 7, of the light that is multiple-reflected at the gap between the light-shielding metal film and the surface of the silicon substrate and directly enters the charge transfer section, multiple-reflected between the transfer electrode 4 and the opening. Since the ratio of light (that is, the ratio of light having a large number of multiple reflections) is increased, smear is further reduced.

In addition, the imaging device having the structure as shown in FIG.
At the time of designing, in addition to determining the width of the transfer electrode 4 to be larger than the width of the transfer electrode 3, based on determining the side of the transfer electrode 4 to be longer than the side of the transfer electrode 3,
Again, production is relatively easy.

Next, FIG. 8 shows another example of the surface structure for one pixel when the present invention is applied to the CCD image pickup device of FIG. 1, and the same portions as FIG. 1 and FIG. The same reference numerals are given and duplicated explanation is omitted (in the same figure, the positional relationship of each part in the vertical direction is omitted). In this example, similarly to the example of FIG. 5, the distance between the transfer electrode 4 and the opening is larger than the distance between the transfer electrode 3 and the opening, and the lower part of the transfer electrode 3 ( That is, the impurity concentration of the portion p1 near the light-receiving charge accumulation portion 1 in ROG) is higher than the impurity concentration.
The impurity concentration at the portion p2 of the lower portion of the transfer electrode 4 (that is, the portion having only a role as a potential barrier) near the light-receiving charge accumulation portion 1 is higher. Incidentally, in the conventional CCD image pickup device shown in FIG. 1, the impurity concentrations at these portions are equal.

According to the example of FIG. 8, since the impurity concentration of the portion only serving as the lower potential barrier on the lower side of the transfer electrode 4 is increased, the width of this portion can be further reduced (that is, the transfer electrode 4 can be further narrowed). 4. Even if the distance between the openings is further increased)
This portion sufficiently serves as a potential barrier. Therefore, smear is further reduced.

In the example of FIG. 8, as in the example of FIG. 7, the length of the side of the transfer electrode 4 in the transfer direction of the charge transfer section 2 is longer than the length of the side of the transfer electrode 3 in the transfer direction. Needless to say, the length can be longer.

Next, an example of a method for increasing the impurity concentration of a portion having only a role as a potential barrier as in the example of FIG. 8 will be described. FIG. 9 shows an example of the impurity distribution (impurity distribution in the case of using an N-type silicon substrate and having a vertical overflow drain structure) of the CCD image pickup device of FIG. In the light-receiving charge accumulation section 1, there is a deep P-type impurity region for suppressing dark current shot noise near the substrate surface, and an N-type impurity region for accumulating signal charges below the substrate surface. doing. After the formation of the transfer electrodes 3 and 4, the light-receiving charge accumulation section 1 having such an impurity distribution has two steps: a step of introducing an N-type impurity by ion implantation; and a step of introducing a dense P-type impurity by ion implantation. It is formed through two steps.

When manufacturing a CCD image sensor having an impurity distribution as shown in FIG. 9, in order to increase the impurity concentration of a portion having only a role as a potential barrier as shown in FIG. In the step of introducing a dense P-type impurity into a portion where the accumulation portion 1 is to be formed by ion implantation, a light-receiving charge accumulation portion of a portion below the transfer electrode 4 (that is, a portion having only a role as a potential barrier) is formed. This dense P-type impurity is also introduced into a portion adjacent to the portion where the film 1 is to be formed (the portion p1 in FIG. 8).

As a result, the impurity concentration of a portion having only a role as a potential barrier is increased. Therefore, even if the width of this portion is further reduced (ie, the distance between the transfer electrode 4 and the opening portion is further increased). Also, this part sufficiently plays a role as a potential barrier. In particular, according to this method, the impurity concentration of a part having only a role as a potential barrier is utilized by utilizing the process of forming the photoreceptor charge storage unit 1. , It is not necessary to increase the number of new processes. Therefore,
It is possible to easily manufacture an imaging device in which the impurity concentration of a portion having only a role as a potential barrier is increased.

Here, of the two steps for forming the light-receiving charge accumulating portion 1, the impurity is introduced together with the portion having only the role of a potential barrier only in the step of introducing a deep P-type impurity. The reason is that the P-type impurity and N
This is because the impurity concentration of this part cannot be increased if both impurities are introduced into a portion having only a role as a potential barrier. As described above, when the formation process of the light-receiving charge accumulation section 1 includes a plurality of steps of introducing different types of impurities, the impurities having a role only as a potential barrier in all the steps are added together. On the contrary, it may not be possible to increase the impurity concentration in this portion by introducing, so that it is preferable to introduce the impurity into this portion only in some steps.

As shown in the above examples, according to the present invention, the read gate sufficiently fulfills both the role as a potential barrier and the role as a read path without deteriorating the characteristics of the image sensor. In addition, it is possible to reduce smear caused by multiple reflection of light in a gap between the light-shielding metal film and the surface of the silicon substrate, and it is possible to relatively easily reduce such smear.

In each of the above examples, the present invention is applied to a CCD image pickup device in which the charge transfer section is driven by a four-phase drive method. However, the present invention is not limited to this. The present invention may be applied to a CCD imaging device driven by a phase driving method.

In each of the above examples, the present invention is applied to a CCD image pickup device which transfers signal charges by an interline transfer method. However, the present invention is not limited to this. For example, a signal charge is transferred by a frame interline transfer (FIT) method. The present invention may be applied to a CCD image pickup device that transfers the image data.

In each of the above embodiments, the present invention is applied to a CCD image sensor, but the present invention may be applied to other solid-state image sensors. In addition, the present invention is not limited to the above-described embodiments, and may take various other configurations without departing from the gist of the present invention.

[0058]

As described above, according to the solid-state imaging device according to the present invention, the distance between the second transfer electrode, which is not used for reading out the signal charge from the light receiving charge accumulating portion, and the opening is larger than that of the conventional device. Becomes considerably large, so that the number of times of multiple reflection of light in the gap between the light-shielding metal film and the silicon substrate surface between the transfer electrode and the opening increases, so that the light-shielding metal film and the silicon substrate surface can be separated. There is an effect that smear caused by multiple reflection of light in the gap can be reduced.

Further, the distance between the charge transfer portion and the opening is not increased (that is, the area of the opening is not reduced or the width of the charge transfer portion is not reduced).
Therefore, the sensitivity and output level, which are important characteristics of the image sensor, are not reduced. Further, the distance between the first transfer electrode used for reading out the signal charge from the light receiving charge storage section and the opening is almost the same as that of the related art (or is slightly larger than that of the related art). Can sufficiently fulfill both the role as a potential barrier and the role as a readout path.

Moreover, the imaging device having such a structure can be manufactured relatively easily based on the fact that the width of the second transfer electrode is determined to be larger than the width of the first transfer electrode at the time of design. is there. Therefore, smear can be relatively easily reduced.

In such an image sensor, when the side of the second transfer electrode in the transfer direction of the charge transfer section is longer than the side of the first transfer electrode in the transfer direction, The ratio of the light that is multiple-reflected between the second transfer electrode and the opening portion of the light that directly enters the charge transfer portion after multiple reflection at the gap between the light-shielding metal film and the silicon substrate surface (that is, the number of times of multiple reflection is (The ratio of a large amount of light) increases, so that smear can be further reduced.

In addition, in the image pickup device having such a structure, in addition to determining the width of the second transfer electrode to be larger than the width of the first transfer electrode at the time of designing, the image pickup device has the following structure. Based on the determination that the side of the second transfer electrode is longer than the side, the manufacture can also be performed relatively easily.

In such an image sensor, the lower portion of the second transfer electrode (that is, only the role as the potential barrier) is lower than the impurity concentration of the lower portion of the first transfer electrode (that is, the read gate). In the case where the impurity concentration of the portion having the second transfer electrode is higher, the impurity concentration of the portion having only a role as a potential barrier becomes higher. Even if the distance between the opening and the opening portion is further increased), this portion sufficiently serves as a potential barrier. Therefore, smear can be further reduced.

Next, according to the method of manufacturing the solid-state imaging device according to the present invention, the impurity concentration of the portion having only the role of a potential barrier is increased by utilizing the process of forming the light-receiving charge accumulation portion. There is an effect that an imaging element in which a portion having only a role as a potential barrier has a high impurity concentration can be easily manufactured without adding new steps.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an example of a surface structure of an imaging surface of a CCD imaging device.

FIG. 2 is a potential diagram of a portion corresponding to two adjacent pixels in a charge transfer unit.

FIG. 3 is a timing chart showing a change in the level of a voltage applied to a transfer electrode of two adjacent pixels.

FIG. 4 is a timing chart showing a change in the level of a voltage applied to a transfer electrode of two adjacent pixels.

FIG. 5 is a plan view showing an example of a surface structure for one pixel of the CCD image sensor according to the present invention.

FIG. 6 is a plan view showing an example of a surface structure for one pixel of a conventional CCD image sensor.

FIG. 7 is a plan view showing another example of the surface structure for one pixel of the CCD image sensor according to the present invention.

FIG. 8 is a plan view showing another example of the surface structure for one pixel of the CCD image sensor according to the present invention.

FIG. 9 is a cross-sectional view illustrating an example of an impurity distribution of a CCD image sensor.

FIG. 10 is a cross-sectional view illustrating an example of a cross-sectional structure for one pixel of a CCD image sensor, and a potential diagram thereof.

11 is a cross-sectional view showing a state where the width of a transfer electrode is reduced in the CCD imaging device of FIG.

[Explanation of symbols]

1,12 received light charge storage unit, 2,14 charge transfer unit,
3, 4, 15 transfer electrodes, 5 channel separation regions,
11 silicon substrate, 13 read gate,
6,16 shading metal film

Claims (5)

[Claims] An opening is defined by a light-shielding material, a light receiving charge accumulating portion for converting light received at the opening into signal charge and storing the signal charge, and a signal charge stored in the light receiving charge accumulating portion. Charges applied to the first transfer electrode used for reading out signal charges from the light receiving charge accumulating section and the second transfer electrodes not used for reading out, and read and transferred from the light receiving charge accumulating section. A solid-state imaging device having a transfer unit, wherein a distance between the second transfer electrode and the opening is larger than a distance between the first transfer electrode and the opening. Characteristic solid-state imaging device. 2. The solid-state imaging device according to claim 1, wherein a side of the second transfer electrode in the direction of transfer of the charge transfer unit is larger than a side of the first transfer electrode in the direction of transfer. A solid-state imaging device characterized by having a longer one. 3. The solid-state imaging device according to claim 1, wherein an impurity concentration of a portion located on said second transfer electrode is higher than an impurity concentration of a portion located below said first transfer electrode. A solid-state imaging device characterized by having a higher height. An opening portion defined by a light shielding material, a light receiving charge accumulating portion for converting light received at the opening portion into a signal charge and storing the signal charge, and a signal charge stored in the light receiving charge accumulating portion. Charges applied to the first transfer electrode used for reading out signal charges from the light receiving charge accumulating section and the second transfer electrodes not used for reading out, and read and transferred from the light receiving charge accumulating section. In the method for manufacturing a solid-state imaging device having a transfer section, the step of introducing an impurity into a portion where the light-receiving charge accumulation section is to be formed, the step of introducing the impurity also into a portion below the second transfer electrode A method for manufacturing a solid-state imaging device. 5. The method of manufacturing a solid-state imaging device according to claim 4, wherein the step of introducing an impurity into a portion where the light-receiving charge accumulation section is to be formed comprises a plurality of steps of introducing different types of impurities. A method of manufacturing a solid-state imaging device, wherein an impurity is introduced into only a part of the plurality of steps together with a part below the second transfer electrode.