JPH0744262B2 - Method of manufacturing solid-state imaging device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device having a light shielding film as a part of a photoelectric conversion element.

Conventional Example and Configuration and Problems Thereof A solid-state imaging device is composed of a plurality of photoelectric conversion elements arranged in an array on a semiconductor substrate and a reading means for reading out the accumulated charges in time series. .

Conventionally, as this type of solid-state imaging device, a device using a PN junction diode as a photoelectric conversion element is generally used. The accumulated charge is photoelectrically converted by the PN junction diode and
A time-series electric signal is taken out from the scanning circuit using the transistor by using the charge transfer element.

In such a solid-state imaging device, thermally generated charges (so-called dark current) are integrated even when there is no light incident on the PN junction diode. This dark current has the property of increasing and decreasing in response to temperature. Therefore, when the charge that responds to the light incident on the PN junction diode is integrated, the dark current described above causes mixing with the signal charge that responds to the light, and a video signal that accurately responds to the incident image is obtained. Absent.

Therefore, a means for shielding the light incident on at least a part of the PN junction diodes that are predetermined in the PN junction diode array, that is, a light shielding film is provided, and only the dark current is provided by the light shielded PN junction diodes. Accumulate. In a PN junction diode without a light shielding film, the signal output is a mixture of integrated signal charges and dark current in response to light, but the signal output of the light shielded PN junction diode corresponds to the reference signal level. By doing so, a stable video signal independent of temperature can be taken out.

Conventionally, as a method of providing a light shielding film, a method of providing a light shielding film after forming a passivation protective film of a semiconductor element is used. In this case, after forming the passivation protective film, a method of forming an opaque film and forming a pattern of only a necessary portion, and separately forming a pattern of a light shielding film on a glass substrate in advance and bonding the semiconductor element with the pattern. There is a way. In the former method, after forming the passivation protective film,
Since a light shielding film such as an aluminum (AL) film is formed,
Since there is no protective film on the light shielding film, there is a problem in reliability. Regarding the latter, it is difficult to accurately align the light shielding pattern on the glass substrate with the PN junction diode on the semiconductor element, which is a big problem in manufacturing.

It is desirable to form the passivation protective film after forming the light shielding film, but the biggest reason why this method cannot be taken is that when the light shielding film is formed, the PN junction diode under the light shielding film and the light shielding film are formed. This is because the amount of dark current generated varies with the PN junction diode that is not provided. Therefore, the signal of the PN junction diode provided with the light shielding film cannot be used as the reference level of the signal.

There is a light shielding film on the PN junction diode, and a PN junction diode on which a passivation protection film is formed,
This is because the effect of the passivation protective film is different from that of the PN junction diode in which the passivation protective film is formed without the light shielding film. Various methods of forming a passivation protective film have been attempted to improve this, but a method of forming a passivation protective film that can be solved has not been found, and the method of forming a light shielding film after the formation of the passivation protective film as described above has to be adopted. I am in a situation where I do not get.

An object of the present invention is to provide a method for manufacturing a solid-state imaging device, which can form a light shielding film before forming a passivation protective film and can improve the change in device characteristics due to the influence of the formation of the passivation protective film.

According to the present invention, a first photoelectric conversion element group and a second photoelectric conversion element group are formed on a semiconductor substrate, and a light shielding film is formed on the front surface side of the second photoelectric conversion element group, and then, A method for manufacturing a solid-state imaging device, comprising forming a passivation protective film on the surfaces of the first photoelectric conversion element group and the second photoelectric conversion element group, and then performing heat treatment in a hydrogen atmosphere. Improves the change in the interface state due to the formation of the passivation protection film, eliminates the difference in dark current due to the difference in the structure under the passivation protection film, and lowers the dark current level of the entire device, which deteriorates the characteristics due to dark current. Will also improve.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a configuration diagram of a charge transfer type solid-state image pickup device embodying the present invention, in which reference numerals 1 are photoelectric conversion element arrays composed of PN junction diodes, and 2 is vertical transfer. Charge transfer element array 3 indicates a charge transfer element array for horizontal reading. Further, in this solid-state imaging device, the output detection unit 4 is provided adjacent to the charge transfer element array 3. The number of photoelectric conversion element columns 1 is, for example, 404 rows in the horizontal direction and 496 rows in the vertical direction, and a light shielding film is formed by an AL film 5 (shown by a hatched portion) in which a predetermined portion of these is used for the AL wiring. That is, a first photoelectric conversion element group including a plurality of photoelectric conversion elements without the light shielding film 5 and a second photoelectric conversion element group including a plurality of photoelectric conversion elements covered with the light shielding film 5 are configured. .

FIG. 1b is a schematic sectional view taken along the line AA ′ of FIG. As the passivation protective film 6, phosphorus glass (PSG) is deposited by 5000Å and silicon dioxide film is deposited by 3000Å by vapor phase growth (CVD). After this, 40% of nitrogen gas containing 5% hydrogen
Heat treatment was performed for about 30 minutes in an atmosphere of 0 ° C.

As another example, heat treatment was performed in hydrogen gas at the same temperature for 30 minutes.

In FIG. 1b, reference numerals in the figure denote 7 as a vertical transfer charge transfer electrode, 8 as an electrode for transferring the signal charge of a PN junction diode to the vertical transfer charge transfer element, 9 as a vertical transfer charge transfer region, and 10 Is a PN junction diode, 11 is a semiconductor substrate, 12 is a channel stopper, and 13 is an insulating oxide film.

Conventionally, heat treatment was sometimes performed in a hydrogen atmosphere after forming the AL film, but the heat treatment effect in the hydrogen atmosphere after forming the passivation protective film was not considered.

In order to see the effect of the present invention, the temperature is changed to 25 ° C., 40 ° C., 60 ° C., 80 ° C., and the difference between the signal output from the light-shielded PN junction diode and the signal output from the non-light-shielded PN junction diode is measured. It was measured.

FIG. 2 shows 1 of a light-shielded PN junction diode and a non-light-shielded PN junction diode existing in the vicinity of the light-shielded PN junction diode in the charge transfer type solid-state imaging device having the configuration shown in FIG. In the signal output of the horizontal component, when the signal V ₁ from the light-shielded PN junction diode is compared with the signal V ₂ which is not light-shielded in the dark, the difference (signal amount) ΔV
Is a conventional one, it was 2 mV at 25 ° C and 50 mV at 80 ° C, but by performing the processing of the present invention, there is no difference at 25 ° C, and the change in the noise signal level at 80 ° C Was recognized, and it was at a level where there was no problem in practical use.

It was also found that the processing of the present invention can reduce the dark current of the solid-state imaging device. Especially when only hydrogen gas was used, the reduction effect was remarkable, and it was half that of the conventional method. Specifically, in the present invention, what was 70 nA at 80 ° C. was 30 nA in the present invention. In the present invention, it is an essential requirement to perform heat treatment in a hydrogen atmosphere after forming the passivation protective film. Therefore, it does not deny the conventional step of performing heat treatment in a water atmosphere after forming the AL film (light shielding film), and it is also possible to perform the heat treatment in a hydrogen atmosphere after forming each of the shielding film and the passivation film. Of course.

The present invention can be applied not only to the solid-state image pickup device other than the charge transfer type solid-state image pickup device but also to other semiconductor elements, and its application range is extremely wide.

As described above, according to the present invention, the light shielding film is formed on the surface side of the photoelectric conversion element group in a predetermined portion on the semiconductor substrate, and then the heat treatment is performed in the hydrogen atmosphere after forming the passivation protective film covering the whole. Thereby, the change in the interface state due to the formation of the passivation protective film can be improved.

[Brief description of drawings]

FIG. 1a is a configuration diagram of a charge transfer type solid-state imaging device embodying the present invention, FIG. 1b is a schematic sectional view of a PN junction diode having a light shielding film, and FIG. 2 is a signal light of one horizontal component. It is a signal output diagram near the shielded PN junction diode. 5 ... AL film, 6 ... passivation protection film, 7 ... vertical transfer charge transfer electrode, 8 ... electrode for transferring signal charge of PN junction diode to vertical transfer charge transfer element array, 10 ... PN junction diode, 11 …… Semiconductor substrate, 12 …… Channel stopper, 13 …… Insulating oxide film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-40831 (JP, A) JP-A-50-48876 (JP, A) Actual development-Sho 55-45223 (JP, U) JP-B 53- 11436 (JP, B1)

Claims (3)

[Claims] 1. A first photoelectric conversion element group and a second photoelectric conversion element group are formed on a semiconductor substrate, a light-shielding film is formed on the surface side of the second photoelectric conversion element group, and then the above-mentioned A method for manufacturing a solid-state imaging device, comprising forming a passivation protective film on the surfaces of the first photoelectric conversion element group and the second photoelectric conversion element group, and then performing heat treatment in a hydrogen atmosphere. 2. The solid-state image pickup device according to claim 1, further comprising the step of forming a light-shielding film on the surface side of the second photoelectric conversion element group and then performing a heat treatment in a hydrogen atmosphere. Production method. 3. A photoelectric conversion element in each of the first photoelectric conversion element group and the second photoelectric conversion element group is a PN junction diode, according to claim (1) or (2). Manufacturing method of solid-state imaging device.