JPH06296008A - Manufacture of solid-state image pickup element - Google Patents

Abstract

PURPOSE:To simplify the manufacturing process of a solid-state image pickup element provided with a transfer electrode whose thickness is different in a light receiving region and in its peripheral region. CONSTITUTION:A plurality of isolation regions 31 are formed in the light receiving region of a silicon substrate 30, and similarly an isolation region 32 is formed in the peripheral region surrounding the isolation regions 31. An insulating film 34, a polycrystalline silicon film 35, and a nitride film 36 are formed in order. The nitride film 36 of the light receiving region part is eliminated and the residual part is made the mask of selective oxidation. The thickness of the polycrystalline silicon film 35 of the light receiving region part is reduced by selectively oxidizing the polycrystalline silicon film 35. A transfer electrode traversing the light receiving region in the direction crossing the isolation regions 31 is obtained by patterning the polycrystalline silicon film 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state image pickup device having an image pickup area covered with transfer electrodes.

[0002]

2. Description of the Related Art In a frame transfer type CCD solid-state image pickup device, an image pickup portion which receives light from an object accumulates information charges generated in response to the applied light, and at the same time, accumulates information charges accumulated for a predetermined period. Is transferred to the storage unit and output. Therefore, transfer electrodes for transferring and driving information charges are also provided in the light receiving region.

FIG. 5 shows a frame transfer type CCD.
It is a top view which shows the outline of a solid-state image sensor. The imaging unit 1
Comprised of a plurality of CCD shift registers that are continuous in the vertical direction, the information charges generated according to the amount of incident light are accumulated in each bit during the light receiving period, and the information charges are transferred and output according to the vertical transfer clock φ _V during the transfer period. To do. The storage unit 2 is
The shift register of the image pickup unit 1 is composed of a continuous CCD shift register, receives the storage transfer clock φ _S , and takes in and accumulates the information charges output from the image pickup unit 1 during the transfer period. The horizontal transfer unit 3 is a row of CCDs that are continuous in the horizontal direction.
It is composed of a shift register (two or more columns in some cases), receives the output of the shift register of the storage unit 2 for each bit, and outputs the information charges in horizontal line units in accordance with the horizontal transfer clock φ _H. The output unit 4 includes a floating diffusion (electrically independent diffusion region) that converts a charge amount into a voltage value and an amplifier that extracts a potential fluctuation of the floating diffusion, and information output from the horizontal transfer unit 4 in 1-bit units. The charges are sequentially converted into voltage values and output as video signals. For example, as shown in FIG. 6, the output unit 4 includes a floating diffusion 10 that receives the CCD output of the horizontal transfer unit 3, a transistor 11 that resets the potential of the floating diffusion 10 according to a reset clock φ _R, and a source follower-connected amplifier. And a video signal responsive to a change in the amount of information charges output from the horizontal transfer section 3 is output.

FIG. 7 is a plan view showing the structure of the image pickup section 1 of the solid-state image pickup device, and FIG. 8 is a sectional view taken along line XX thereof.
The P-type silicon substrate 20 has P
A plurality of isolation regions 21 into which high-concentration type impurities are implanted are arranged in parallel to each other, and similarly, isolation regions 22 containing high-concentration P-type impurities are formed in the peripheral region so as to surround the light receiving region. It The channel region 23 between the isolation regions 21 has a buried channel structure in which N-type impurities are diffused in the substrate surface portion. On the silicon substrate 20 on which the isolation region 21 and the channel region 23 are formed, a plurality of transfer electrodes 25 made of polycrystalline silicon via the insulating film 24 are formed in the light receiving region in a direction intersecting the channel region 23. Is located across and across to the peripheral region. On these transfer electrodes 25, a second-layer transfer electrode 26 also made of polycrystalline silicon is arranged so as to cover the gap between the first-layer transfer electrodes 25 to form a two-layer structure. Each of the transfer electrodes 25 and 26 is formed to have a smaller film thickness on the light receiving region than on the peripheral region, so that light can easily pass through the transfer electrodes 25 and 26 and enter the channel region 23 in the light receiving region. ing. Then, the aluminum wiring 28 is arranged on the transfer electrodes 25 and 26 in the peripheral region portion via the insulating film 27, and the transfer electrodes 2 are formed through the contact holes 29 provided in the insulating film 28.
5, 26 are connected. This aluminum wiring 28 is
It is provided corresponding to the number of phases of the transfer clocks supplied to the transfer electrodes 25 and 26. In the case of a four-phase clock, four lines are arranged and every three lines are connected to the transfer electrodes 25 and 26. . Here, since the transfer electrodes 25 and 26 are formed to have a large film thickness at the portion to which the aluminum wiring 28 is connected, it is difficult for the contact to penetrate.

[0005]

In the solid-state image pickup device as described above, the transfer electrodes 25 and 26 having different film thicknesses in the light receiving region and the peripheral region are formed by temporarily covering the entire surface of the polycrystalline silicon film to be the transfer electrodes 25 and 26. It is obtained by removing only the light-receiving region portion after forming the above-mentioned structure, and forming a polycrystalline silicon film over the entire surface again. In this case, the process of forming the polycrystalline silicon film is required twice, and the processing time in the manufacturing process becomes long. Especially in the second polycrystalline silicon film formation,
Processing at low temperature is required to prevent natural oxidation, and it takes a long time to bring the polycrystalline silicon film to a predetermined thickness. In addition, when removing the light receiving region of the polycrystalline silicon film that is initially formed, there is a risk that a part of the insulating film below the polycrystalline silicon film may be removed by overetching, resulting in a decrease in device reliability. There is a problem.

It is therefore an object of the present invention to shorten the processing time of the manufacturing process and to improve the efficiency of light incident on the image pickup section while preventing the reliability of the device from being lowered.

[0007]

The present invention has been made in order to solve the above-mentioned problems, and is characterized in that charges move to a range that becomes a light-receiving region on a surface portion of a semiconductor substrate. Forming a plurality of isolation regions parallel to each other, forming a conductive layer on the semiconductor substrate, and selectively oxidizing the conductive layer corresponding to the range of the light receiving region; After removing the oxidized portion of the layer, a step of etching the conductive layer to obtain a plurality of transfer electrodes that cross the light receiving region in a direction intersecting the isolation region, and forming a transfer electrode in the peripheral region portion of the light receiving region. Forming a connected power supply line.

[0008]

According to the present invention, the step of forming the polycrystalline silicon film is performed once by selectively oxidizing the thickly formed polycrystalline silicon film to partially reduce the film thickness. Processing time for forming is reduced. Also,
Since the thickness of the polycrystalline silicon film is reduced by the selective oxidation, the insulating film below the polycrystalline silicon film is less likely to be affected by the manufacturing process, and the reliability is maintained.

[0009]

1 to 4 are sectional views showing steps of a method of manufacturing a solid-state image pickup device according to the present invention, showing an image pickup portion of the device.
First, P-type impurities such as boron are implanted at a high concentration into the light-receiving region of the P-type silicon substrate 30 to form the isolation regions 31 and 32. Similarly, P-type impurities are implanted into the peripheral region as well. To form the isolation region 32. Further, N-type impurities such as phosphorus are implanted between the isolation regions 31 to form a channel region 33 having a buried channel structure. These implantation steps are performed using a resist pattern having a desired shape obtained by a well-known photolithography technique as a mask.

Therefore, as shown in FIG.
An oxide film 3 to be a gate insulating film by thermal oxidation is formed on the silicon substrate 30 on which the channel regions 33 and 1 and 32 are formed.
4 is formed, a polycrystalline silicon film 35 to be a transfer electrode and a nitride film 36 to be a mask for selective oxidation are formed by a CVD method.
Are sequentially formed. Then, as shown in FIG. 2, a resist pattern 42 having an opening in the light receiving region is formed on the nitride film 36, and the nitride film 36 is etched using the resist pattern 37 as a mask. As a result, the nitride film 36 serving as an oxidation mask is left in the portion except the light receiving region. Therefore, as shown in FIG. 3, the polycrystalline silicon film 35 is selectively oxidized to form an oxide film 38 in the light receiving region. In this selective oxidation, the polycrystalline silicon film 35 is left with a predetermined film thickness, and the oxide film 38 is replaced by the polycrystalline silicon film 3
The processing conditions are set so as not to reach the insulating film 34 below 5. Then, when the nitride film 36 and the oxide film 38 on the polycrystalline silicon film 35 are removed, as shown in FIG. 4, the polycrystalline silicon film 35 is formed to be thin in the light receiving region and thick in the peripheral region. After this, the polycrystalline silicon film 3
5 is patterned to cross the light receiving region in a direction intersecting with the channel region 31 to form a first-layer transfer electrode extending to the peripheral region.

Furthermore, after the surface portion of the transfer electrode of the first layer is thermally oxidized to form an interlayer insulating film, the polycrystalline silicon film is formed and the selective oxidation of the polycrystalline silicon film is similarly performed. Repeatedly, a polycrystalline silicon film whose thickness is thicker in the peripheral region than in the light receiving region is formed. Then, by patterning this polycrystalline silicon film, a second-layer transfer electrode that covers the gap between the first-layer transfer electrodes is formed.

After the two layers of transfer electrodes are formed as described above, aluminum wiring is formed in the peripheral region through an insulating film such as a nitride film, and the aluminum wiring is connected to each transfer electrode. The formation of the aluminum wiring is performed by forming a contact hole at a predetermined position of an insulating film covering each transfer electrode and then etching the aluminum film formed by sputtering or the like into a desired pattern. Therefore, it is possible to obtain a transfer electrode having a two-layer structure in which the film thickness becomes thin in the light receiving region and becomes thick in the peripheral region, and as a result, a solid-state imaging device having the same shape as the solid-state imaging device shown in FIG. It

Incidentally, the transfer electrodes of the storage section and the horizontal transfer section other than the image pickup section are not selectively oxidized like the polycrystalline silicon film 35 in the light receiving region, and are formed with the polycrystalline silicon film 35 formed first. It has an equivalent film thickness. Further, the gates of the transistors in the output section are formed in the same step as the transfer electrodes in the storage section and the horizontal transfer section, and have the same film thickness as the transfer electrodes in the peripheral area.

According to the above manufacturing steps, a transfer electrode having a different thickness in the light receiving region and the peripheral region can be obtained by forming the polycrystalline silicon film once, and further, the gate insulation under the polycrystalline silicon film can be obtained. The film is no longer etched.

[0015]

According to the present invention, a transfer electrode having a thin film thickness of the transfer electrode in the light receiving region of the image pickup portion can be obtained by forming the polycrystalline silicon film once, so that the polycrystalline silicon film is formed. The processing time for doing this is reduced. Also,
Since the insulating film under the polycrystalline silicon film is not etched when the polycrystalline silicon film is thinned in the light receiving region, the insulating film can be kept at a predetermined film thickness and the reliability of the device is deteriorated. Can be suppressed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first manufacturing process of a solid-state imaging device of the present invention.

FIG. 2 is a cross-sectional view showing a second manufacturing process of the solid-state imaging device of the present invention.

FIG. 3 is a cross-sectional view showing a third manufacturing process of the solid-state imaging device of the present invention.

FIG. 4 is a cross-sectional view showing a fourth manufacturing process of the solid-state imaging device of the present invention.

FIG. 5 is a schematic plan view of a frame transfer type CCD solid-state imaging device.

FIG. 6 is a circuit diagram of an output unit of a CCD solid-state image sensor.

FIG. 7 is a plan view showing an image pickup section of a conventional solid-state image pickup element.

8 is a cross-sectional view taken along line XX of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Imaging part 2 Storage part 3 Horizontal transfer part 4 Output part 20, 30 Silicon substrate 21, 22, 31, 32 Separation area 23, 33 Channel area 24, 27, 34, 37 Insulating film 25, 26, 35, 36 Transfer electrode 28 Aluminum wiring 29 Contact hole 36 Nitride film 37 Resist pattern 38 Oxide film

Claims (2)

[Claims] 1. A step of forming a plurality of separation regions in parallel with each other in the area of the surface portion of a semiconductor substrate, which is a light receiving region, and a step of forming a conductive layer on the semiconductor substrate. A step of selectively oxidizing a layer corresponding to the range of the light receiving region; and after removing an oxidized portion of the conductive layer, the conductive layer is etched to cross the light receiving region in a direction intersecting with the isolation region. A method for manufacturing a solid-state imaging device, comprising: a step of obtaining a plurality of transfer electrodes; and a step of forming a power supply line connected to the transfer electrodes in a peripheral region part of the light receiving region. 2. The step of forming the transfer electrode is repeated to form a first electrode arranged at a constant interval and a second electrode arranged so as to cover a gap between these first electrodes. The method for manufacturing a solid-state image sensor according to claim 3, wherein the method is obtained.