JPH07120780B2 - Method of manufacturing solid-state image sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a solid-state imaging device including a step of forming a metal film such as a spin-on-glass film and an aluminum film and performing heat treatment.

[Prior Art] Conventionally, an N ^- P junction type photodiode has been used in a light receiving portion of a solid-state imaging device in order to improve a charge reading characteristic from the light receiving portion to the charge transfer portion. In this N ^- P junction type photodiode, the dark current component increases due to the surface level at the Si-SiO ₂ interface by completely emptying the surface of the N ^- region.

As a method of reducing this dark current, Philips Res.Repts.20 p
p.568-594 `` EFFCTS OF LOW-TEMPERATURE HEAT TREATM
ENTS ON THE SURFACE PROPERTIES OF OXIDIZED SILICO
N), a metal film such as an aluminum film is formed on the oxide film and heat treated to cause hydrogen to be generated by causing hydrogen to react with the adsorbed water or OH groups in the oxide film.
It is known that the method of reducing the surface level of the O ₂ interface is effective.

A conventional manufacturing method using this method will be described with reference to FIGS. 3 and 4.

FIG. 3 is a plan view of the solid-state image sensor, and FIG.
6A to 6D are cross-sectional views showing the order of steps in the cross section taken along the line AA ′.

First, after the P-type well layer 2 is formed in the N-type semiconductor substrate 1, the N-type regions 5 and 6 to be the photoelectric conversion unit 3 and the charge transfer unit 4 are formed.
P-type regions 8 to be the channel stop portions 7 are selectively formed, and the N-type semiconductor substrate 1 is subjected to an oxidation treatment to grow a first gate oxide film on the surface. A first transfer gate electrode 10 made of polycrystalline silicon is formed on the upper surface by CVD and photolithography.
Then, using the first transfer gate electrode 10 as a mask, the first
A part of the gate oxide film is removed, and the second gate oxide film 11 is grown around the exposed N-type semiconductor substrate 1 and the first transfer gate electrode 10 by performing the thermal oxidation process again. After that, the second transfer gate electrode 12 made of polycrystalline silicon is formed on the second gate oxide film 11 by the CVD method and the photo-etching method.
It is formed on top [Fig. 4 (a)].

Then, an interlayer insulating film 13 is deposited on the entire surface by a CVD method, a contact hole is opened in the interlayer insulating film 13, and then a first aluminum film 14 is deposited on the entire surface of the interlayer insulating film 13, and this is photoetched. Patterning is performed to form a wiring portion and a light shielding portion [FIG. 4 (b)].

Next, an oxide film 15 is deposited on the entire surface of the interlayer insulating film 13 including the first aluminum film 14 by a plasma CVD method, and then a silica film forming material is spin-coated and baked to form a spin-off glass film 16. After the formation, a second aluminum film 17 is deposited on the entire surface, and subsequently, a heat treatment is performed at a temperature of about 400 ° C. for about 10 minutes in a mixed gas atmosphere of H ₂ and N ₂ , and at the Si-SiO ₂ interface. Decrease surface level [4th
Figure (c)].

Finally, the second aluminum film 17 is removed, and the manufacturing process of the solid-state image sensor is completed [FIG. 4 (d)].

[Problems to be Solved by the Invention] In the method for manufacturing a solid-state imaging device described above, a spin-on-glass film is formed in order to improve the step coverage of an aluminum film and increase the dark current reducing effect. After the series of steps is completed, the concave lens shape is left on the solid-state image sensor as shown in FIG. 4 (d). Therefore, light is refracted by this film and leaks into the charge transfer section. Therefore, particularly in the case of a high-luminance subject, a false signal is generated on the screen in the vertical direction due to smearing, and the video signal is significantly deteriorated.

[Means for Solving the Problems] In the method for manufacturing a solid-state imaging device according to the present invention, after the required diffusion step, transfer electrode forming step, interlayer insulating film forming step, light-shielding film and wiring layer forming step are completed, , Through the following steps.

Step of sequentially forming CVD oxide film, non-single crystal silicon film and spin-on-glass film on the entire surface, step of forming metal film such as aluminum film on the entire surface, non-oxidizing atmosphere (in H ₂ gas, N ₂ gas) Or H ₂ ,
Heat treatment at a relatively low temperature (350 to 450 ° C) in N ₂ mixed gas), and etching and removal of the metal film and spin-on-glass film.

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings.

1 (a) to (d) and FIGS. 2 (a) to (d) are cross-sectional views of a cell portion showing the order of steps in one embodiment of the present invention.
3A and 3B respectively show cross sections taken along the lines AA 'and BB'.

First, the P-type well layer 2 is formed in the N-type semiconductor substrate 1,
After that, the N-type regions 5 and 6 to be the photoelectric conversion unit 3 and the charge transfer unit 4 and the P-type region 8 to be the channel stop unit 7 are selectively formed. Next, the N-type semiconductor substrate 1 is thermally oxidized to grow a first gate oxide film 9 on the surface, and the first gate oxide film 9 is made of polycrystalline silicon by the CVD method and the photoetching method. The first transfer gate electrode 10 is formed. Then, using the first transfer gate electrode 10 as a mask, a part of the first gate oxide film 9 is removed, and heat treatment is performed again to expose the exposed N-type semiconductor substrate 1 and the first
A second gate oxide film 11 is grown around the transfer gate electrode 10 of FIG. After that, a second transfer gate electrode 12 made of polycrystalline silicon is formed on the second transfer gate electrode 12 by the CVD method and the photoetching method.
Is formed on the gate oxide film 11 of [FIG. 1 (a), second
(A)].

Next, an interlayer insulating film 13 is deposited on the entire surface by a CVD method, a contact hole is formed in the interlayer insulating film 13, and then a first aluminum film 14 is deposited on the entire surface of the interlayer insulating film 13 and is patterned by photo-etching. To form the wiring portion and the light shielding portion [FIG. 1 (b), FIG. 2 (b)].

Next, an oxide film 15 is deposited on the entire surface of the interlayer insulating film 13 including the first aluminum film 14 by a plasma CVD method, and then an amorphous silicon film 18 is deposited on the entire surface of the oxide film 15 by a sputtering method. Subsequently, the silica film forming material is spin-coated and baked to form the spin-on-glass film 16. A second aluminum film 17 is deposited on the entire surface, and then heat treatment is performed at a temperature of about 400 ° C. for about 10 minutes in a mixed gas atmosphere of H ₂ and N ₂ [FIG. Figure (c)].

Finally, after removing the second aluminum film 17, the spin-on-glass film 16 is removed by using the amorphous silicon film 18 as a stopper, and then the amorphous silicon film 18 is removed by etching by a wet method [FIG. 1 (d)]. ,
FIG. 2 (d)].

In this embodiment, the silicon film is formed by the sputtering method, but this method enables the film formation by the good coverage method at a relatively low temperature. Further, since this film has a different etching property from the underlying oxide film 15, the surface of the oxide film 15 is not roughened when the amorphous silicon film 18 is etched. The silicon film 18 may be left unremoved if there is no particular problem in terms of the characteristics of the solid-state image sensor.

Further, although the amorphous silicon film 18 deposited by the sputtering method is used as the stopper when removing the spin-on-glass film in the above embodiment, it may be replaced with a polycrystalline silicon film deposited by the sputtering method.

Further, although aluminum is used as the second metal film in the above-mentioned embodiment, this can be replaced with another metal film such as an aluminum alloy film.

Further, although the solid-state image pickup device having the buried channel has been described in the above description, the present invention is not limited to this, and the same applies to a solid-state image pickup device having a surface channel or a MOS type solid-state image pickup device. Can be applied. Further, the second aluminum film does not have to be removed in the optically black portion on the image sensor.

As described above, according to the present invention, the CVD oxide film, the non-single-crystal silicon film, the spin-on-glass film, and the metal film are sequentially formed, and the heat treatment is performed in a non-oxidizing atmosphere. Since the spin-on-glass film is removed, according to the present invention, the spin-on-glass film does not function as a concave lens and smearing can be significantly reduced. Furthermore, since the silicon film has etching selectivity with respect to the spin-on-glass film and the CVD oxide film,
The base is not damaged when the spin-on-glass film or the silicon film is removed by etching.

[Brief description of drawings]

FIG. 3 is a plan view of the solid-state image pickup device, FIGS. 1 (a) to (d), and FIGS. 2 (a) to (d) are lines AA ′ and BB in FIG. 3, respectively. 4A to 4D are sectional views showing the process steps of one embodiment of the present invention in a section taken along the line ', showing the conventional example in the section taken along the line AA' in FIG. It is sectional drawing which shows a process step. 1 ... N-type semiconductor substrate, 2 ... P-type well layer, 3 ... photoelectric conversion part, 4 ... charge transfer part, 5 ... N-type region (photoelectric conversion part), 6 ... N-type region (charge Transfer part), 7 ... channel stop part, 8 ... P-type region (channel stop part), 9 ... first gate oxide film, 10 ... first transfer gate electrode, 11 ... second gate Oxide film, 12 ... second transfer gate electrode, 13 ... interlayer insulating film, 14 ... first aluminum film, 15 ... oxide film, 16 ... spin-on-glass film,
17: second aluminum film, 18: amorphous silicon film.

Claims (3)

[Claims] 1. A step of forming a photoelectric conversion region on a surface of a semiconductor substrate and a region receiving signal charges transferred from the photoelectric conversion region, a step of forming a gate insulating film and a gate electrode on the semiconductor substrate, and the gate. Forming an interlayer insulating film on the gate insulating film including an electrode; depositing a first metal film on the interlayer insulating film and patterning the first metal film to form a wiring and a light shielding film; Sequentially forming an oxide film, a non-single-crystal silicon film, and a spin-on-glass film on the entire surface of the interlayer insulating film including the metal film, and forming a second metal film on the entire surface of the spin-on-glass film to form a non-oxidizing gas. A method of manufacturing a solid-state imaging device, comprising: a step of performing heat treatment in an atmosphere; and a step of removing the second metal film and the spin-on-glass film. 2. The method for manufacturing a solid-state image sensor according to claim 1, wherein the non-single crystal silicon film is formed by a sputtering method. 3. The method for manufacturing a solid-state imaging device according to claim 1, wherein the non-single crystal silicon film is removed by a wet etching method after the step of removing the spin-on-glass film.