JPH0412067B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in charge transfer type image sensors.

[Technical background of the invention]

Recently, charge transfer type image sensors, particularly interline transfer type image sensors, have been attracting attention as solid-state image sensors. Conventionally, this is the first image sensor using the interline transfer method.
The devices shown in FIGS. 5 to 5 are known.

1 in the figure is, for example, a p-type semiconductor substrate. On the surface of this substrate 1, an n
A photosensitive section consisting of shaped photosensitive pixels 2 ₁ , 2 ₂ , . . . is provided two-dimensionally. A vertical register 3 is provided between each pixel column of these photosensitive sections to vertically transfer signal charges accumulated in the pixels 2 ₁ , 2 ₂ . . . . An n-type charge transfer channel 4 forming a part of the vertical register 3 is provided between the pixel columns. Further, on the surface of the substrate 1, a horizontal register (not shown) is provided for converting the signal charges transferred by the vertical register 3 into parallel and serial signals for each scan, transferring them in the horizontal direction, and reading out the signals to the outside. . On the surface of the substrate 1 except for the pixels 2 ₁ , 2 _{2 .} . . , the charge transfer channel 4 and the gate region 5, p
+-type channel blocking regions 6 are provided.
An insulating film 7 is provided on the substrate 1 including the pixels _{2 1 ,} 2 ₂ . They are set apart. On the insulating film 7 are the pixels 2 ₁ , 2 _{2 .} . . and the pixels 2 ₁ , 2 _{2 .} . . in each pixel column.
A light shielding film 9 is provided so as to exclude a portion corresponding to the intermediate portion.

Next, the operation of the image sensor having the above-described structure will be explained.

First, when light enters, for example, the pixel 2 ₂ , charges are generated and accumulated as signal charges. After a certain period of time,
When a large positive voltage (V ₁ ) is applied to the transfer electrode 8 ₂ , the signal charge accumulated in the pixel 2 ₂ is transferred to the potential well of the charge transfer channel 4 through the gate region 5 . Note that signal charges are generated in other pixels 2 ₁ , 2 ₃ , 2 _{4 .} . . and similarly transferred to the charge transfer channel 4. Subsequently, by applying a clock pulse sufficiently smaller than V ₁ to the transfer electrode (not shown) of the vertical register 3, the signal charge is transferred in the vertical direction, and further the signal charge is read out through the horizontal register. Note that during this readout period, signal charges for the next screen are accumulated in pixels 2 ₁ , 2 ₂ .
Since the voltage of the clock pulse applied to the vertical register 3 is small, the signal charges newly accumulated in the pixels 2 ₁ , 2 _{2 .} . . are not immediately transferred to the vertical register 3. Furthermore, after a certain period of time, the newly accumulated signal charge is transferred to the vertical register 3 by applying voltage V ₁ to the transfer electrode of the vertical register 3. Thereafter, by repeating the same operation as described above, signals for new screens are successively read out.

[Problems with background technology]

However, in the image sensor having the above-described structure, a charge transfer channel 4 is formed in the channel blocking region 6 so that the channel blocking region 6 does not become a potential well.
Contains impurities of opposite conductivity type higher than the impurity concentration of... Therefore, the impurities in the channel blocking region 6 are diffused laterally during the high temperature heat treatment process when forming the pixels 2 ₁ , 2 ₂ . 6, 6, the width of the charge transfer channel 4 becomes narrower than the designed value. As a result, vertical register 3
The drawback was that the maximum amount of charge that could be carried by the sensor was reduced, and the dynamic range of the image sensor was reduced.

Further, as shown in FIG. 3, since there is no channel blocking region 6 in the gate region 5 between the pixel 2 ₂ and the charge transfer channel 4, the charge transfer channel 4 in this portion
has channel blocking regions 6 on both sides as shown in FIG.
It becomes wider in the horizontal direction compared to when there is. As a result, the charge transfer channel 4 portion in FIG.
The narrow channel effect is small and the potential well is deeper compared to the charge transfer channel 4 in FIG.
Therefore, a part of the signal charge remains in this deep potential well portion, resulting in a decrease in the transfer efficiency of the vertical register 3 and a disadvantage in that the resolution as an image sensor is degraded.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a charge transfer type image sensor with improved dynamic range and resolution.

[Summary of the invention]

The present invention includes a plurality of photosensitive pixels that generate and accumulate signal charges in response to optical input in one surface of a semiconductor substrate of a first conductivity type, and a signal of the photosensitive pixels transferred via a gate region. In a charge transfer type image sensor comprising a charge transfer type shift register that transfers charges along a charge transfer channel and sequentially reads out charges, an insulating film is provided in a region between the photosensitive pixel and the charge transfer channel except for the gate region. Improving characteristics such as resolution by providing a barrier electrode through the barrier electrode and applying a DC voltage to the barrier electrode to form a potential barrier against the signal charge near the surface of the semiconductor substrate under the barrier electrode. The main point is to aim for the following.

[Embodiments of the invention]

An interline transfer type image sensor, which is an embodiment of the present invention, will be explained based on FIGS. 6 to 10. Note that the same components as the image sensor shown in FIGS. 1 to 5 are denoted by the same reference numerals, and the description thereof will be omitted.

In the figure, 1 is a p-type semiconductor substrate. On the surface of this substrate 1, pixels 2 ₁ , 2 _{2 .} . . , a vertical register 3, a charge transfer channel 4, and a horizontal register (not shown) are provided, similar to the image sensor shown in FIGS. 1 to 5. There is. An insulating film 7 is provided on the substrate 1. and the charge transfer channel 4
Barrier electrodes 21 are provided on both sides of the insulating film 7, excluding the gate region 5, through the first layer film of the insulating film 7. In the second layer within the insulating film 7, second, fourth, and fifth transfer electrodes 8 ₂ , 8 ₄ , and 8 ₅ are provided spaced apart from each other. In the third layer within the insulating film 7, first and third transfer electrodes 8 ₁ and 8 ₃ are provided spaced apart from each other. A light shielding film 9 of Al is formed on the insulating film 7 so as to exclude the portions corresponding to the pixels 2 ₁ , 2 _{2 .} . . and the portions between the pixels 2 ₁ , 2 _{2 .} . . in each pixel column. It is provided.

Next, a method of manufacturing the image sensor having the above-described structure will be explained based on FIGS. 11a and 11b to 14a and 14b.

() First, the first insulating film 7 ₁ was formed on the p-type semiconductor substrate 1 . Subsequently, a conductor layer serving as a barrier electrode is deposited on the insulating film ₇₁ , and then patterned by photolithography to form a conductor layer pattern in which holes are formed in areas corresponding to areas where pixels are to be formed and charge transfer channels are to be formed. 22 was formed. Next, using this conductor layer pattern 22 as a mask, phosphorus was ion-implanted into the substrate 1 under predetermined conditions and heat treatment was performed to form pixels (2 ₁ ), 2 ₂ , 2 ₃ . . . and a charge transfer channel 4 (first (Illustrated in Figures 11a and b). Next, a conductor layer pattern 22 corresponding to the gate region 5 between the pixel 2 ₂ and the charge transfer channel 4 is formed.
The barrier electrode 21 is removed by etching using a conventional method.
was formed (as shown in FIGS. 12a and 12b).

() Next, after selectively etching and removing the first insulating film 7 ₁ using the barrier electrode 21 as a mask, a second insulating film 7 ₂ was formed on the entire surface (the first
(Illustrated in Figures 3a and b). Next, by repeating the deposition and patterning of a conductive layer (not shown) on the entire surface by a conventional method, the first to fifth transfer electrodes (8 ₁ ), 8 ₂ , 8 ₃ , (8 ₄ ) are formed at desired locations. , (8 ₅ ) were formed, respectively. Next, a third insulating film ₇₃ was formed over the entire surface.
After this, Al was deposited on the entire surface and patterned to form holes in the areas corresponding to the pixels 2 ₁ , 2 ₂ ... and the areas between the pixels 2 ₁ , 2 ₂ ... in each pixel column.
A light shielding film 9 made of Al was formed, and a desired interline transfer type image sensor was manufactured (as shown in FIGS. 14a and 14b). In addition, the first to third
An integrated insulating film 7 ₁ to 7 ₃ corresponds to the insulating film 7 in FIGS. 7 to 10.

Next, the operation of the image sensor of the present invention will be explained. Since operations such as light incidence on the pixels 2 ₁ , 2 _{2 .} . . and generation of signal charges are the same as in the conventional example, only the differences will be explained. That is, the barrier electrode 21 is operated by applying the same voltage as the substrate 1 or a constant DC voltage V _B. Here, V _B is selected to be a voltage at which the surface of the substrate 1 under the barrier electrode 21 becomes a potential barrier with respect to the charge transfer channel 4 .

According to the image sensor having the above-described structure, the charge transfer channel 4 is formed by introducing phosphorus into the substrate 1 using the conductor layer pattern 22 serving as the barrier electrode 21 as a mask, and then diffusing the phosphorus in the lateral direction by heat treatment. A wide charge transfer channel 4 can be formed. Therefore, the maximum amount of signal charge that the vertical register 3 can carry increases, and the dynamic range increases.

Furthermore, since there is no channel blocking region on the surface of the substrate 1 on both sides of the charge transfer channel 4 as in the conventional case,
The potential wells of the charge transfer channel 4 are the first to fifth wells.
It is uniquely determined by the voltage applied to the transfer electrodes 8 ₁ to 8 ₅ , and the wells do not become deeper depending on the location as in the conventional case. Therefore, charge transfer by the vertical register 3 is performed efficiently, and the resolution of the image sensor is improved.

Note that the charge transfer type image sensor according to the present invention is not limited to the structure described above, and may have the structure shown below.

As shown in FIG. 15, the substrate 1 under the barrier electrode 21
It has a structure in which a p+ type semiconductor region 23 is formed on the surface. In the image sensor having such a structure, the pixels (2 ₁ ), 2 ₂ , 2 ₃ . . . and the charge transfer channel 4 are formed by introducing p-type impurities into the surface of the substrate 1 and then forming conductors in the same manner as in the embodiment described above. A layer pattern 22 was formed, and then, using this pattern 22 as a mask, a large amount of n-type impurity was introduced and heat treatment was performed.

According to the image sensor shown in FIG.
3 is formed, even if the voltage of the barrier electrode 21 changes due to the induction of the applied pulse of the third transfer electrode 21, the threshold voltage of the semiconductor region 23 is high and the potential barrier is maintained.

Further, as shown in FIG. 16, a predetermined barrier electrode 2
1, an n-type semiconductor region 24 containing an extremely low concentration of n-type impurities on the surface of the substrate 1 below the substrate 1, and an n+-type drain region 25 containing a high concentration of n-type impurities on the surface of the substrate 1 adjacent to this semiconductor region 24. It may also have a structure in which it is provided with. In the image sensor having such a structure, when excessive charge is accumulated in the pixel 2 ₃ , it is discharged through the potential well formed in the semiconductor region 24 of the potential barrier 21 to the drain region 25 having a deeper well.

According to the image sensor shown in FIG. 16, since the barrier electrode 21 is formed integrally with the control gate that controls the discharge of excess charge to the drain region 25,
Manufacturing can be simplified.

In the above embodiments, the case where the substrate is p-type has been described, but the substrate is not limited to this, and may be n-type.

Further, in the above embodiment, the photosensitive pixel is a photodiode, but the application is not limited to this, and the same can be applied to a photosensitive pixel using an MCS type diode in which a transparent electrode is provided via an insulating film or a photoconductive film. .

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a highly reliable charge transfer type image sensor such as an interline transfer type image sensor, which has improved dynamic range and resolution compared to the conventional one.

[Brief explanation of drawings]

Fig. 1 is a plan view of a conventional interline transfer type image sensor, Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1, and Fig. 3 is a cross-sectional view taken along line B-B in Fig. 1. , FIG. 4 is a sectional view taken along line C-C in FIG. 1,
5 is a cross-sectional view taken along line D-D in FIG. 1, FIG. 6 is a plan view of an interline transfer type image sensor according to an embodiment of the present invention, and FIG. 7 is a cross-sectional view taken along the line D-D in FIG.
-A sectional view taken along line A, Figure 8 is a sectional view taken along line B-B in Figure 6, Figure 9 is a sectional view taken along line C-C in Figure 6, and Figure 10 is a sectional view taken along line C-C in Figure 6. The cross-sectional views taken along the line D-D, FIGS.
6, and FIGS. 15 and 16 are cross-sectional views of interline transfer type image sensors showing other embodiments of the present invention, respectively. It is a diagram. DESCRIPTION OF SYMBOLS 1...p-type semiconductor substrate, ₂₁ , ₂₂ , ₂₃ ...photosensitive pixel, 3...vertical register, 4...charge transfer channel, 5...gate region, 6...channel blocking region, 7... Insulating film, 8 ₁ to 8 ₅ ... Transfer electrode, 9
... Light shielding film, 21 ... Barrier electrode, 22 ... Conductor layer pattern, 23 ... P + type semiconductor region, 24
. . . n − type semiconductor region, 25 . . . n + type drain region.

Claims (1)

[Scope of Claims] 1. A plurality of photosensitive pixels that generate and accumulate signal charges in response to optical input within one surface of a semiconductor substrate of a first conductivity type, and the photosensitive pixels transferred via a gate region. In a charge transfer type image sensor comprising a charge transfer type shift register that transfers pixel signal charges along a charge transfer channel and sequentially reads them out, the area between the photosensitive pixel and the charge transfer channel excluding the gate region. A barrier electrode is provided through an insulating film, and a DC voltage is applied to the barrier electrode to form a potential barrier against the signal charge near the surface of the semiconductor substrate under the barrier electrode. Transfer type image sensor. 2. Claim 1, characterized in that the charge transfer channel is formed by ion-implanting a second conductivity type impurity into the surface of the semiconductor substrate using a conductor pattern serving as a barrier electrode as a mask. charge transfer type image sensor. 3. The charge according to claim 1, wherein the barrier electrode is formed integrally with a control gate that controls discharge of excess charge to a drain region provided in the vicinity of the photosensitive pixel. Transfer type image sensor.