JPH0917985A - Image pickup element and manufacturing method thereof - Google Patents

Abstract

PURPOSE: To provide an image pickup element the smear characteristic of which is improved and manufacturing method thereof. CONSTITUTION: An image pickup element 21 has a light reception part 4 for performing the photoelectric conversion linearly formed on a surface layer of a Si substrate 21, vertical transfer part 22 disposed linearly on the side of the part 4 along the length thereof and screen film 15 opened just above the reception part on the Si substrate. The surface of the substrate 21 locate just above the reception part 4 is formed lower than the surfaced of the substrate 21 located just above a laterally central part of the transfer part 22 and the surface of the substrate 21 located between these surfaces of the substrate 21 is made curved. A manufacturing method of an image pickup element having such a constitution is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device having a light receiving portion for photoelectric conversion, and more particularly to an image pickup device having improved smear characteristics and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, CCD (Charge-Coupled Device)
) Type image pickup device having a structure shown in FIG. 5, for example, is known. In FIG. 5, reference numeral 1 is an image pickup device. In this image pickup device 1, an overflow barrier 3 is formed on a surface layer portion of a silicon substrate 2, light receiving portions 4 are linearly arranged on the overflow barrier 3, and the light receiving portion 4 is further formed. 4, the hole accumulating portion 5 is formed. A p-well 6 is arranged on one side of the light-receiving section 4 via a reading section 9, and a vertical transfer section 7 is arranged in a line on the p-well 6. Further, a channel stop 8 is arranged on the other side of the light receiving section 4, another vertical transfer section 7 is formed on the side of the channel stop 8, and further on the side of the vertical transfer section 7. A reading section 9 and a light receiving section (not shown) are sequentially arranged.

An insulating film 10 is formed on the surface of the silicon substrate 2, and a transfer electrode 11 is formed on the insulating film 10 so as to cover a position directly above the vertical transfer portion 7. An oxide film 12 is formed on the transfer electrode 11 so as to cover it, and an insulating oxide film 13 is formed on the insulating film 10 so as to cover the oxide film 12. An interlayer insulating film 14 is formed on the insulating oxide film 13, and the light shielding film 15 is formed on the insulating film 13 while covering the transfer electrode 11 and opening the upper portion of the light receiving portion 4. And a transparent insulating layer (not shown) is formed on the light shielding film 15.

[0004] With such a configuration, the image pickup device 1
The incident light that has passed through the transparent insulating layer (not shown) is received by the light receiving section 4, and photoelectrically converted into electric charges. Then, the obtained charges are sent to the vertical transfer unit 7 via the readout unit 9, further moved in the vertical transfer unit 7 by driving the transfer electrode 11, and output as a signal via the horizontal transfer unit (not shown). .

In order to manufacture the image pickup device 1 having such a structure, first, the overflow barrier 3 is formed on the silicon substrate 2, and then p-type impurities are implanted at a predetermined position on the surface layer portion of the silicon substrate 2. Then, the channel stop 8 and the reading section 9 are formed with a predetermined space therebetween, and the p-well 6 is formed. Separately from this, an n-type impurity is implanted into the p-well 6 outside the channel stop 8 and the reading section 9 to form the vertical transfer section 7 in a line shape. Next, the insulating film 10 is formed on the surface of the silicon substrate 2 by a thermal oxidation method, and then a polysilicon film (not shown) is formed on the insulating film 10. Then, this polysilicon film is patterned by a well-known lithography technique and etching technique to form a transfer electrode 11 made of polysilicon in a line shape at a position substantially above the vertical transfer portion 7.

Next, a polysilicon oxide film 12 is formed on the surface of the transfer electrode 11 by a thermal oxidation method, and subsequently, a self-alignment is performed using the formed transfer electrode 11 as a mask so that the surface of the silicon substrate 2 is relatively deep. An n-type impurity is implanted, and the light receiving sections 4 are formed in a line between the read section 9 and the channel stop 8. Further, similarly, using the transfer electrode 11 as a mask, a p-type impurity is implanted at a relatively shallow position in the surface layer portion of the silicon substrate 2, and the hole accumulation portion 5 is formed immediately above the light receiving portion 4. Then, a Si film is formed on the insulating film 10 by CVD or the like so as to cover the polysilicon oxide film 12.
An insulating oxide film 13 made of O ₂ is deposited and formed.

Then, PSG (phosphosilicate glass) is deposited by the CVD method or the like to form an interlayer insulating film 14 on the insulating oxide film 13. After that, an Al film (not shown) is formed on the interlayer insulating film 14, and the Al film is further patterned by a known lithography technique or etching technique.
The light-shielding film 15 is formed by patterning the light-receiving portion 4 so that the upper portion thereof is open. Then, a transparent insulating layer (not shown) made of a transparent resin or the like is formed to cover the light shielding film 15 and the interlayer insulating film 14, and a color filter (not shown) and an on-chip lens (not shown) are formed by a known method. Then, the image pickup device 1 is obtained.

[0008]

However, the image pickup device 1 having the above structure has the following disadvantages. In the image pickup device 1, the light receiving part 4 and the vertical transfer part 7 are formed on the silicon substrate 2.
Since it is formed on the same plane in the surface layer part of, the part of the light entering the light receiving part 4 at a large incident angle by being refracted and reflected is directly or directly on the light shielding film 15 and the surface of the silicon substrate 2. The vertical transfer unit 7 by reflecting between
Alternatively, it reaches its vicinity and is photoelectrically converted there. Then, a part of the charges generated by the photoelectric conversion is taken into the vertical transfer unit 7 and becomes smear signal charges, so that the smear characteristic deteriorates. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image sensor having improved smear characteristics and a method for manufacturing the same.

[0009]

According to the image pickup device of the present invention,
A light receiving portion for performing photoelectric conversion is formed in a line shape on the surface layer portion of the silicon substrate, and a vertical transfer portion is arranged in a line along the line direction on the side of the light receiving portion, and the light receiving portion is formed on the silicon substrate. A light-shielding film is provided in a state in which the light-shielding film is provided substantially directly above, and the silicon substrate surface located directly above the light-receiving portion is located above the silicon substrate surface immediately above the center portion in the width direction of the vertical transfer portion. It is a means for solving the above-mentioned problem that the substrate surface is formed low and the surface of the substrate located between these silicon substrate surfaces is curved.

In the method of manufacturing an image pickup device of the present invention, a step of forming an oxide film on the surface of a silicon substrate, a silicon nitride film is formed on the oxide film, and the silicon nitride film is linearly patterned to form a plurality of vertical films. A step of forming a silicon nitride film pattern immediately above the transfer portion forming portion, and the oxide film at a portion other than the portion where the silicon nitride film pattern is formed by oxidizing the surface of the silicon substrate on which the silicon nitride film pattern is formed To increase the thickness thereof, a step of removing the silicon nitride film pattern, a step of removing an oxide film on the silicon substrate, and a step of removing the silicon nitride film pattern on the surface layer portion of the silicon substrate. A step of injecting an impurity into each of the formed portions to form a plurality of vertical transfer portions in a line, and a step of forming a first insulating film on the surface of the silicon substrate, A step of forming a transfer electrode on the first insulating film substantially directly above the vertical transfer portion, a step of forming a second insulating film on the surface of the transfer electrode, and an impurity between the transfer electrodes. And a step of forming a light receiving portion by injecting the solution.

[0011]

According to the image pickup device of the present invention, the surface of the silicon substrate directly above the light receiving portion is formed lower than the surface of the silicon substrate directly above the center portion in the width direction of the vertical transfer portion. Since the surface of the silicon substrate located between them is formed to be curved, when light enters the light receiving section at a large incident angle, this light is vertically transferred to a position higher than the light receiving section. Incident below. Therefore, even if photoelectric conversion is performed to generate charges, the charges are hardly taken into the vertical transfer unit. Further, since the silicon substrate surface located directly above the light receiving portion and the silicon substrate surface located directly above the center portion in the width direction of the vertical transfer portion are curved, the silicon between them is formed as in the conventional case. Compared with the case where the surface of the substrate is flat, the substantial area is increased particularly on the upper surface side of the vertical transfer portion, which increases the amount of charge handled. Similarly, the length of the read path from the light receiving portion to the vertical transfer portion, that is, the width of the read portion is widened as compared with the case where the surface of the silicon substrate is flat, and therefore the read potential difference margin is increased.

According to the method of manufacturing an image pickup device of the present invention, a silicon nitride film is formed on an oxide film on a surface of a silicon substrate, and the silicon nitride film is patterned in a line shape to form a silicon nitride film pattern. The surface of the silicon substrate on which the silicon nitride film pattern is formed is oxidized, and the oxide film is grown at a position other than the position where the silicon nitride film pattern is formed to increase its thickness, and then the silicon nitride film pattern, Since each of the oxide films is removed, a concave portion gently curved is formed between the portions of the surface of the silicon substrate where the silicon nitride film pattern is formed as apexes. Then, the vertical transfer portion is formed on the surface layer portion of the silicon substrate at the apex portion, and the light receiving portion is formed at the recess forming portion between the vertical transfer portions, so that the image pickup device is obtained.

[0013]

The present invention will be described below in more detail with reference to examples. FIG. 1 is a diagram showing an embodiment in which the image pickup device of the present invention is applied to a CCD type image pickup device, and in this figure, reference numeral 20 is an image pickup device. In the image sensor 20 shown in FIG. 1, the same components as those of the image sensor 1 shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. This image pickup device 20 is basically different from the image pickup device 1 shown in FIG. 5 in that a silicon substrate (silicon substrate) is used.
The surface shape of 21 is not flat but curved. That is, in the image pickup device 20, the silicon substrate 21 has a planar shape along the direction orthogonal to the line direction of the light receiving portion 4 and the vertical transfer portion 22, which are formed in a linear shape.
The point directly above the center of the vertical transfer section 22 is the apex, and the point directly above the center of the light-receiving section 4 is curved as the lowest point, that is, the point directly above the center of the vertical transfer section 22 is the apex. A gently curved concave portion is formed between the vertices.

As described above, the light receiving portion 4 is formed immediately below the center of the concave portion, and the vertical transfer portion 22 is formed immediately below the apex, so that the vertical transfer portion 22 is formed.
Is not only located on the side of the light receiving portion 4 as in the conventional case, but is also arranged at a sufficiently high position. Further, the surface of the silicon substrate 2 immediately above the center portion in the width direction of the vertical transfer portion 22 is the apex, and the surface of the silicon substrate 2 gradually curves from the apex to the left and right and becomes lower. Therefore, as shown in a manufacturing method to be described later, the vertical transfer portion 22 has its central portion as the uppermost portion and is gradually curved downward as it goes to the left and right.

Similarly, the p-well 23 formed immediately below the vertical transfer portion 22 has its central portion as the uppermost portion,
It gradually curves downward as it goes to the left and right. On the contrary, the hole accumulating portion 24 formed on the light receiving portion 4 has its central portion as the lowermost portion and is gradually curved upward as it goes to the left and right. further,
The reading section 25 formed between the light receiving section 4 and the vertical transfer section 22 on one side, and the channel stop 26 formed between the light receiving section 4 and the vertical transfer section 22 on the other side,
In each case, the curved surface of the silicon substrate 2 immediately above is inclined with a downward slope from the transfer electrode 22 side toward the light receiving portion 4 side. In addition, the insulating film 10, the transfer electrode 11, the oxide film 12, the insulating oxide film 13, the interlayer insulating film 14, the light-shielding film 15, etc. formed on the silicon substrate 21 having the curved planar shape as described above are all Is also formed and arranged in a shape corresponding to the surface shape of the silicon substrate 21.

In order to manufacture the image pickup device 20 having such a structure, as shown in FIG. 2A, a silicon substrate 21 having an overflow barrier (not shown) formed therein is prepared as in the conventional case, and the surface thereof is prepared. The oxide film 30 is formed by the thermal oxidation method. Then, on this oxide film 30, a silicon nitride (Si) film having a thickness of about 10 to 1000 nm is formed by atmospheric pressure CVD or the like.
N) A film 31 is deposited and formed. Next, the silicon nitride film 31 is linearly patterned by a known lithography technique and etching technique to form a silicon nitride film pattern 31a ... As shown in FIG. 2 (b). Here, the silicon nitride film pattern 31a is formed so as to be disposed immediately above the planned formation portion of the vertical transfer portion (22) to be formed later, and the vertical transfer portion (22) to be formed.
It is also formed to correspond to the width of.

Then, the silicon nitride film pattern 31a is formed.
2 is formed by strongly oxidizing the surface of the oxide film 30 on the silicon substrate 21 on which the ... Is formed, for example, by a pyrogenic oxidation method at a temperature of about 950 to 1100.degree.
As shown in (c), the oxide film 30 is grown at a portion other than the portion where the silicon nitride film pattern 31a is formed, and the thickness of the central portion between the silicon nitride film patterns 31a and 31a is set to 10
It should be about 0 to 2000 nm. That is, the series of processing steps up to this point are so-called LOCOS processing, and in this embodiment, the silicon substrate 2 is used.
70% or more of the cell area in No. 1 is oxidized and grown by the LOCOS method.

Next, the silicon nitride film patterns 31a, 31a are removed using a phosphoric acid solution or the like, and the oxide film 30 is removed by etching using an appropriate etching material. Then, as shown in FIG. 3A, the surface of the silicon substrate 2 has a shape in which the central portion of the portion where the silicon nitride film pattern 31a is formed has an apex and the apex is curved to form a concave portion. . Here, when the thickness of the oxide film 30 grown and formed by the LOCOS method is set to, for example, 100 nm, the surface of the silicon substrate 21 located directly above the light receiving portion 4 is located directly above the vertical transfer portion 22.
When the silicon nitride film pattern 31a is recessed from the surface by about 450 nm, the width of the silicon nitride film pattern 31a is set to 1.0 μm, and the thickness thereof is set to 100 nm, the flat portion of the surface of the silicon substrate 21 immediately above the vertical transfer portion 22, that is, The width at the apex is about 0.5 μm.

Then, n-type impurities are implanted into the surface of the silicon substrate 21 where the silicon nitride film pattern has been formed by ion implantation or drive-in, respectively, and vertical transfer is performed as shown in FIG. 3 (b). A plurality of parts 22 are formed in a line. Prior to this, the silicon substrate 2
A p-type impurity is implanted at a predetermined position in the surface layer portion of, the channel stop 26 and the reading portion 25 are formed with a predetermined gap, and the p well 23 is formed.

Next, as shown in FIG. 3B, an insulating film (first insulating film) 10 made of SiO ₂ is formed on the surface of the silicon substrate 21 by a thermal oxidation method, and then, as shown in FIG.
As shown in (c), a polysilicon film 32 is deposited and formed on the insulating film 10 by a low pressure CVD method or the like. And P
850 for dry oxidation by adding 1-100 cc of OCl ₃ etc.
Phosphorus (P) is implanted into the polysilicon film 32 by performing the process at a temperature of about 1000 ° C. Next, this polysilicon film 32 is patterned by a known lithography technique as in the conventional technique and a dry etching technique using CHCl ₃ or the like as an etchant, and as shown in FIG. 4A, substantially directly above the vertical transfer portion 22. A transfer electrode 11 made of polysilicon is formed in a line shape at the position.

Then, as shown in FIG. 4 (b), the temperature is 850 to 1000 ° C., for example, by the pyrogenic oxidation method.
The polysilicon oxide film (second insulating film) 12 is formed on the surface of the transfer electrode 11 by being oxidized to a certain degree, thereby forming a smooth polysilicon / SiO ₂ interface.
Then, by self-alignment using the formed transfer electrode 11 as a mask, an n-type impurity is injected into a relatively deep position of the surface layer of the silicon substrate 21, and the light receiving section 4 is lined between the read section 25 and the channel stop 26. To form an array. Further, similarly, using the transfer electrode 11 as a mask, a p-type impurity is implanted at a relatively shallow position of the surface layer of the silicon substrate 2, and the hole accumulating portion 24 is formed immediately above the light receiving portion 4. Then, the insulating film 10 is covered to cover the polysilicon oxide film 12.
An insulating oxide film 13 made of SiO ₂ is deposited and formed thereon by a CVD method or the like.

Next, PSG (phosphosilicate glass) is deposited by the CVD method or the like to form an interlayer insulating film 14 on the insulating oxide film 13. After that, an Al film (not shown) is formed on the interlayer insulating film 14, and the Al film is further patterned by a known lithography technique or etching technique.
The light-shielding film 15 is formed by patterning the light-receiving portion 4 so that the upper portion thereof is open. Then, a transparent insulating layer (not shown) made of a transparent resin or the like is formed to cover the light shielding film 15 and the interlayer insulating film 14, and a color filter (not shown) and an on-chip lens (not shown) are formed by a known method. Then, the image pickup device 20 shown in FIG. 1 is obtained.

In the image pickup device 20 thus obtained, the surface of the silicon substrate 21 located directly above the light receiving portion 4 is located directly above the center portion of the vertical transfer portion 22 in the width direction. Since the surface of the silicon substrate 21 is formed to be lower than the surface and is located between the surfaces of the silicon substrate 21, the surface of the silicon substrate 21 is curved. Therefore, when the light enters the light receiving portion 4 at a large incident angle, This light enters below the vertical transfer portion 22 formed at a position higher than the light receiving portion 4. Therefore, even if charges are generated by photoelectric conversion here, the charges are hardly taken into the vertical transfer unit 22, and thus excellent smear characteristics can be obtained.

Further, since the surface of the silicon substrate 21 located directly above the light receiving section 4 and the surface of the silicon substrate 21 located directly above the center of the vertical transfer section 22 in the width direction are curved, As compared with the case where the surface of the silicon substrate is flat as described above, the substantial area on the upper surface side of the formed vertical transfer portion 22 increases even if impurities are injected under the same conditions particularly when the vertical transfer portion 22 is formed. This can increase the amount of charge handled. Similarly,
Compared with the case where the surface of the silicon substrate 21 is flat, the length of the read path from the light receiving section 4 to the vertical transfer section, that is, the width of the read section 25, becomes wider, and therefore the read potential difference margin can be increased.

Further, since the surface of the silicon substrate 21 located immediately above the light receiving portion 4 is loose but is curved in a state of being depressed downward, the area of the upper surface side of the hole accumulating portion 24 is increased, which results in dark current. Is reduced. Similarly, the light receiving portion 4 located immediately below the hole accumulating portion 24 also has a slight increase in the area on the upper surface side thereof, whereby the hole accumulating portion 2 is formed.
Since the junction area with 4 increases, the amount of accumulated charge, that is, Qs (Handled Chargein Sensor) increases.

[0026]

As described above, in the image pickup device of the present invention, the surface of the silicon substrate directly above the light receiving portion is formed lower than the surface of the silicon substrate directly above the center portion in the width direction of the vertical transfer portion. Since the surface of the silicon substrate located between these silicon substrate surfaces is curved, when the light enters the light receiving portion at a large incident angle, this light is formed at a position higher than the light receiving portion. It is possible to make the charges incident below the vertical transfer unit, and thus even if photoelectric conversion is performed here to generate electric charges, it is possible to prevent the electric charges from being taken in by the vertical transfer units.
Thereby, excellent smear characteristics can be obtained. In addition, since the silicon substrate surface located directly above the light receiving portion and the silicon substrate surface located directly above the widthwise central portion of the vertical transfer portion are curved, the silicon substrate surface between them as in the conventional case. In comparison with the case where the surface of the silicon substrate is flat, in particular, the substantial area on the upper surface side of the vertical transfer portion can be increased, thereby increasing the amount of charges handled. However, it is possible to increase the length of the read path from the light receiving unit to the vertical transfer unit, that is, the width of the read unit, and thus to increase the read potential difference margin. A method for manufacturing an image pickup device according to the present invention comprises forming a silicon nitride film on an oxide film on a surface of a silicon substrate, patterning this in a line shape to form a silicon nitride film pattern, and further forming the silicon nitride film pattern on the silicon nitride film pattern. The surface of the formed silicon substrate is oxidized to grow the oxide film at a location other than the location where the silicon nitride film pattern is formed to increase its thickness, and then the silicon nitride film pattern and the oxide film are removed respectively. Therefore, the surface of the silicon substrate can have a shape in which the portions where the silicon nitride film pattern is formed serve as the apexes and the gently curved concave portions are formed between the portions. Then, the vertical transfer portion is formed on the surface layer portion of the silicon substrate at the apex portion, and the light receiving portion is formed at the concave portion formation portion between the vertical transfer portions.
It is possible to reliably manufacture the image pickup device having the above-mentioned excellent effects.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an essential part showing a schematic configuration of an embodiment of an image pickup device of the present invention.

2A to 2C are side cross-sectional views of main parts for explaining the method of manufacturing the image pickup device shown in FIG. 1 in process order.

3 (a) to 3 (c) are views for explaining a method of manufacturing the image pickup device shown in FIG. 1 in order of process steps, and for explaining a manufacturing process subsequent to the process shown in FIG. 2 (c). FIG.

4A to 4C are views for explaining the method of manufacturing the image pickup device shown in FIG. 1 in the order of steps, and for explaining the manufacturing steps subsequent to the step shown in FIG. FIG.

FIG. 5 is a side sectional view of an essential part showing an example of a conventional image sensor.

[Explanation of symbols]

 4 Light-receiving part 10 Insulating film (first insulating film) 11 Transfer electrode 12 Oxide film (second insulating film) 15 Light-shielding film 20 Image sensor 21 Silicon substrate (silicon substrate) 22 Vertical transfer part 30 Oxide film 31 Silicon nitride film 31a Silicon nitride film pattern

Claims (2)

[Claims] 1. A light receiving portion for performing photoelectric conversion is formed in a line shape on a surface layer portion of a silicon substrate, and a vertical transfer portion is arranged in a line along the line direction on a side of the light receiving portion, An imaging device comprising a light-shielding film provided on a substrate in such a manner that the light-receiving unit is opened substantially directly above, and the silicon substrate surface located directly above the light-receiving unit has a center in the width direction of the vertical transfer unit. An image pickup device characterized in that it is formed lower than the surface of a silicon substrate located immediately above the portion, and the surface of the silicon substrate located between the surfaces of these silicon substrates is curved. 2. A step of forming an oxide film on the surface of a silicon substrate, and forming a silicon nitride film on the oxide film, and patterning the silicon nitride film in a line shape so that the silicon nitride film is formed directly above a plurality of vertical transfer portion formation locations. A step of forming a silicon nitride film pattern, and oxidizing the surface of the silicon substrate on which the silicon nitride film pattern is formed to grow the oxide film at a place other than the place where the silicon nitride film pattern is formed to reduce its thickness. Thickening, removing the silicon nitride film pattern, removing an oxide film on the silicon substrate, and injecting impurities into the silicon substrate surface layer portion where the silicon nitride film pattern is formed. Forming a plurality of vertical transfer portions in a line shape, forming a first insulating film on the surface of the silicon substrate, and forming a first insulating film on the first insulating film, Forming a transfer electrode substantially directly above the direct transfer portion, forming a second insulating film on the surface of the transfer electrode, and implanting an impurity between the transfer electrodes to form a light receiving portion. An image pickup element manufacturing method comprising: