JP2902889B2 - Light-shielding film of solid-state image sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CC formed on a substrate.
The present invention relates to a light-shielding film that blocks unnecessary light rays entering a solid-state imaging device such as D, and more particularly, to a light-shielding film using a high melting point metal.

[0002]

2. Description of the Related Art It is known to use a high melting point metal silicide, Al, or an Al alloy as a light shielding film of a solid-state imaging device such as a CCD.

[0003] As a high melting point metal silicide used as a light shielding film, when X is a high melting point metal such as Mo,
XSi ₂ which is disilicide is used as a light shielding film.

[0004]

However, if a high-melting metal silicide is used as a light-shielding film and heat treatment is performed in a process after the formation of the light-shielding film, the light-shielding characteristics of the light-shielding film are significantly deteriorated, There is a problem that the smear resistance performance of the image sensor is reduced.

FIG. 8 shows MoSi ₂ which is a disilicide.
4 shows the heat treatment dependence of the transmittance of the light-shielding film when a light-shielding film is formed and then heat-treated. a shows the transmittance immediately after forming the light-shielding film by sputtering MoSi ₂ ,
b, c, and d show the transmittance after annealing at 900 ° C. for 1 hour, 2 hours, and 4 hours, respectively, and e and f show the transmittance after annealing at 950 ° C. for 1 hour and 2 hours, respectively. a
As shown in the figure, the light-shielding film immediately after the formation of MoSi ₂ has good light-shielding properties over the entire wavelength range,
It can be seen that after the above heat treatment step, the transmittance is significantly increased in the wavelength region of 550 nm or more, and the light shielding characteristics in the long wavelength region deteriorate.

The reason why the heat treatment deteriorates the light-shielding property is that amorphous silicon having a high melting point is crystallized by the heat treatment and Si atoms are regularly arranged. Therefore, in a light-shielding film using silicide, deterioration of light-shielding characteristics due to heat treatment is inevitable. It should be noted that there is a report similar to the case of MoSi _{2 in} the case where the light shielding film is formed using disilicide WSi _{2 in} which the high melting point metal is W (IEEE Trans. Elec. Div.
vol. 38, no. 5, p965).

It is conceivable to use a high melting point metal itself as a light shielding film instead of silicide, which is inevitable to deteriorate light shielding characteristics due to heat treatment.

However, in this case, there are the following problems. (1) High affinity with oxygen. Therefore, the high melting point metal is easily oxidized, and is easily oxidized even at about 500 to 600 ° C., and a volatile oxide is formed. Then, the light-shielding film volatilizes, and the smear performance decreases. (2) The bonding strength is poor. Since a high melting point metal has a larger coefficient of thermal expansion than Si or SiO ₂ , a large internal stress is generated at the time of film formation or subsequent heat treatment, and the film is easily peeled. (3) Poor chemical resistance.

Therefore, it is not appropriate to use the high melting point metal itself as a light shielding film instead of silicide.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to improve the smear resistance of the solid-state imaging device without basically changing the manufacturing process of the conventionally used solid-state imaging device. It is to provide a light-shielding film that can be used.

[0011]

In order to achieve the above object, a light-shielding film according to the present invention is a light-shielding film which is formed on a substrate and shields unnecessary light rays entering a solid-state imaging device. A high-melting point metal thin film, a high-melting point metal silicide or nitride, a protective film laminated on the high-melting point metal thin film, and a high-melting point metal silicide or nitride; And a bonding film laminated below the metal thin film.

[0012]

The light-shielding film according to the second aspect of the present invention is a light-shielding film formed on a substrate for shielding unnecessary light rays entering the solid-state image pickup device. X3Si with a lower Si composition ratio than silicide
2. A silicide which is a high melting point metal compound such as X3Si is generated in advance, and the generated silicide which is a high melting point metal compound is laminated on the substrate by sputtering.

In this light-shielding film, the refractory metal is Mo,
Preferably it is W, Ti or Ta.

[0015]

In the light-shielding film according to the first aspect, since a protective film made of a silicide or nitride of a high-melting-point metal is laminated on a thin film of a high-melting-point metal, even if the light-shielding film is heat-treated, the high-melting-point metal is used. The thin film is not easily oxidized.

In the light-shielding film according to the present invention, a bonding film made of a refractory metal silicide or nitride is laminated below the refractory metal thin film, and the refractory metal silicide or nitride is formed. Since the bonding film made of is excellent in adhesion to the SiO ₂ layer, the light-shielding film is made of SiO _{2 in} a high-temperature heat treatment.
It is difficult to peel off from the layer.

In the light-shielding film according to the present invention, when X is a refractory metal, the disilicide XSi ₂
Since it is made of a silicide such as X ₃ Si ₂ or X ₃ Si having a small composition ratio, the degree of regular arrangement of Si atoms by heat treatment is small, and the increase in transmittance due to the heat treatment is small and the light shielding characteristics are excellent.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a light-shielding film of a solid-state imaging device according to the present invention will be described in detail with reference to the drawings. FIG. 2 shows a light shielding structure of the CCD area sensor. Reference numeral 1 denotes a Si substrate. An SiO ₂ layer 2 as an insulating layer is laminated on the Si substrate 1, and Poly electrodes 3 and 4 are embedded in the SiO ₂ layer 2. On the surface of the SiO ₂ layer 2, a light shielding film 5 according to the present embodiment is provided. After the light-shielding film 5 is provided, a passivation film 6 is provided on the light-shielding film 5, and an Al-Si light-shielding film 7 is formed on a flat upper portion of the passivation film 6. The Al-Si light shielding film 7 can be omitted by appropriately selecting the thickness of the light shielding film 5.

The structure of the light shielding film 5 will be described in detail with reference to FIG. The light shielding film 5 provided on the SiO ₂ layer 2
a high melting point metal thin film 11 made of any of high melting point metals such as o, W, Ti, and Ta; a protective film 12 provided on the high melting point metal thin film 11; And the bonding film 13 provided. Both the protective film 12 and the bonding film 13 are made of silicide or nitride of refractory metal, that is, MoSi ₂ , WSi ₂ , TiSi ₂ , TaS
_{i 2, MoN, WN, TiN} , consisting of TaN or the like.

It should be noted that the types of the high melting point metal constituting the high melting point metal thin film 11, the protective film 12, and the bonding film 13 may or may not be the same. The thicknesses of the refractory metal thin film 11, the protective film 12, and the bonding film 13 may or may not be the same. Also, the bonding film 13
Can be omitted. Further, the light-shielding film 5 can be formed of four or more layers by laminating a plurality of refractory metal thin films 11, protective films 12, or bonding films 13.

Next, the operation of this embodiment will be described. Since the protective film 12 is provided on the refractory metal thin film 11, the refractory metal thin film 11 does not come into direct contact with the oxidizing atmosphere during the heat treatment after the formation of the light shielding film 5, so that oxidation is prevented.

Further, the refractory metal thin film 11 is not directly laminated on the SiO ₂ layer 2 as an insulating layer but is laminated via a bonding film 13 and is formed of a refractory metal silicide or nitride. Since the film 13 has excellent adhesion to the SiO ₂ layer 2, the light-shielding film 5 is
It is not peeled off from the _two layers 2.

Next, a specific example of the present embodiment will be described below. The refractory metal thin film 11 is formed of Mo having a thickness of 1150 Å, the protective film 12 is formed of MoSi ₂ having a thickness of 720 Å, and the bonding film 13 is formed of MoSi ₂ having a thickness of 720 Å.
oSi ₂ / Mo / MoSi ₂ ) = (720/1150 /
720).

FIG. 3 shows the light-shielding characteristics (a) of the light-shielding film 5 having the above-described structure.
Shows the results of a comparison shielding characteristics (b) of the conventional light-shielding film formed only with Si _2. FIG. 3 shows the transmittance after annealing both the light-shielding film 5 and the conventional light-shielding film formed of MoSi _{2 in} a nitrogen atmosphere at 900 ° C. for 2 hours. While the conventional light-shielding film has deteriorated light-shielding characteristics in a long wavelength region of 550 nm or more, the light-shielding film 5 according to the present embodiment has 550 n
Even in a long wavelength region of m or more, the transmittance shows almost zero within the detection sensitivity of the spectroscope, and shows good light-shielding characteristics.

FIG. 4 shows (MoSi ₂ / Mo / Mo
Si ₂ ) = light-shielding film 5 represented by (720 / t / 720)
The results of measuring the transmittance T of the refractory metal thin film 11 made of Mo for various thicknesses t are shown. As can be seen from FIG. 5, the light-shielding film 5 shows high light-shielding characteristics even after the heat treatment. (MoSi ₂ / Mo / MoSi ₂ ) =
The transmittance T of the light-shielding film 5 which is (720/1150/720) is 1/500 of the transmittance of the conventional light-shielding film formed of only 3000 Å-thick MoSi ₂ .
The light-shielding film 5 has sufficient light-shielding characteristics for smear caused by transmitted light.

The light-shielding film 5 is made of S
It was recognized that the iO ₂ layer 2 was not peeled off.

Next, a second embodiment of the present invention will be described. FIG. 7 is a phase diagram of silicide shown when the refractory metal is Mo. As shown in FIG. 7, it has been confirmed that the refractory metal silicide forms silicide X ₃ Si ₂ , X ₃ Si or the like having a lower Si composition ratio than disilicide XSi _{2, in} addition to disilicide XSi ₂ (M ．Hansen, Construction o
f Binary Alloys, McGraw-Hi
11, 1985, p 974).

The light-shielding film 5 according to this embodiment is different from the conventional light-shielding film made of disilicide XSi ₂ when X is a high-melting point metal, and X ₃ Si ₂ , X ₃ having a smaller Si composition ratio than disilicide. It is made of silicide such as Si.

In the light shielding film 5 of this embodiment, X ₃ Si ₂ ,
The film such as X ₃ Si can be formed by a sputtering method. Further, using a target having an area ratio determined so as to obtain a predetermined composition ratio of the high melting point metal X and Si, X ₃ Si
₂ , a film of X ₃ Si or the like may be formed.

X ₃ Si ₂ , X ₃ Si and the like have a Si composition ratio of 1 / 1.6 to 1 / 2.6 lower than that of disilicide.
For this reason, when the light-shielding film is formed with the same thickness as that in the case of using disilicide, the transmittance of the light-shielding film is 40% to 60%.
To decrease.

FIG. 5 shows the relationship between the thickness t of the disilicide MoSi ₂ and the transmittance T when the refractory metal is Mo. Referring to the straight line (a) in FIG. 5 showing the relationship between the film thickness t and the transmittance T after heat treatment of the light-shielding film under various conditions, the decrease in the transmittance from 40% to 60% indicates that the die This corresponds to the film thickness t of silicide MoSi ₂ being approximately doubled.

FIG. 6 shows the relative smear relative to each wavelength λ when the smear at wavelength λ = 500 nm is set to 1 for the light-shielding films of various thicknesses t of disilicide MoSi ₂ . The fact that the film thickness t of the disilicide MoSi ₂ becomes about twice as large improves the smear resistance ratio about twice as shown in FIG.

According to the structure of this embodiment, the light shielding film 5 has a lower Si composition ratio than that of disilicide, that is, X ₃ Si ₂ and X ₃ S.
Since it is formed of silicide such as i, even after the light-shielding film 5 is heat-treated, the regular arrangement of Si atoms due to the heat-treatment is less likely to occur than in the case of di-silicide, so that the transmittance does not increase and good light-shielding characteristics are obtained. Can be. Further, in the silicide sputtering process, the same process as in the case of using disilicide can be used only by changing the Si composition ratio of the target without changing other processes. Therefore, it is possible to provide a light-shielding film capable of improving the smear resistance of the solid-state imaging device without basically changing the manufacturing process of the conventionally used solid-state imaging device.

[0034]

As described above, according to the present invention,
In the light-shielding film according to the first aspect, the protective film made of silicide or nitride of the high-melting-point metal is laminated on the thin film of the high-melting-point metal. It is hard to be done.

In the light-shielding film, a bonding film made of a refractory metal silicide or nitride is laminated below a refractory metal thin film, and the bonding film made of the refractory metal silicide or nitride is made of SiO. _Because of the excellent adhesion to the _two layers, the light-shielding film is not easily peeled off from the SiO ₂ layer during the high-temperature heat treatment.

In the light-shielding film according to the third aspect, when X is a high melting point metal, the disilicide XSi ₂
Since it is made of a silicide such as X ₃ Si ₂ or X ₃ Si having a small composition ratio, the degree of regular arrangement of Si atoms by heat treatment is small, and the increase in transmittance due to the heat treatment is small and the light shielding characteristics are excellent.

The protective film, the refractory metal thin film, the bonding film, and X ₃ having a lower Si composition ratio than disilicide XSi ₂
Since a thin film of silicide such as Si ₂ or X ₃ Si can be formed without basically changing the manufacturing process of a conventionally used solid-state imaging device, light shielding that can improve the smear resistance of the solid-state imaging device can be improved. The membrane can be provided efficiently.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a light shielding film according to the present invention.

FIG. 2 is a sectional view showing a light shielding structure of a CCD area sensor using a light shielding film according to the present invention.

[3] The light shielding properties of the light-shielding film according to the first embodiment of the present invention (a), the thickness of 3000 Å MoSi ₂
FIG. 9 is a diagram showing a comparison with a light-shielding characteristic (b) of a conventional light-shielding film formed only by using a light-shielding film.

FIG. 4 (MoSi ₂ / Mo / MoSi ₂ ) = (720)
/ T / 720) shows the relationship between the transmittance T and the various thicknesses t of the refractory metal thin film made of Mo after heat treatment of the light-shielding film represented by (/ t / 720).

FIG. 5 shows the thickness t and transmittance T of disilicide MoSi ₂ .
FIG. The straight line (a) shows the relationship between the film thickness t and the transmittance T after heat treatment of the light-shielding film under various conditions,
The straight line (b) shows the relationship between the film thickness t immediately after the formation of the light-shielding film and the transmittance T.

FIG. 6 shows that the smear at a wavelength λ = 500 nm of light shielding films of various thicknesses t of disilicide MoSi ₂ is 1
The figure which shows the smear relative ratio with respect to each wavelength (lambda) at the time of.

FIG. 7 is a phase diagram of the atomic ratio of silicide and the temperature, in the case where the high melting point metal is Mo.

FIG. 8 shows the dependence of the transmittance of the light-shielding film on the heat treatment when a light-shielding film is formed using MoSi ₂ as a disilicide and then heat-treated. a indicates the transmittance immediately after the formation of the light-shielding film by sputtering MoSi ₂ , and b, c, and d indicate 9;
The transmittance after annealing at 00 ° C. for 1 hour, 2 hours, and 4 hours, respectively, is shown.
The transmittance after annealing for an hour is shown.

[Explanation of symbols]

1 Si substrate 2 SiO ₂ layer 3 Poly electrode 4 Poly electrode 5 light shielding film 6 passivation film 7 Al-Si light shielding film 11 the refractory metal film 12 protective film 13 bonding film

Claims (3)

(57) [Claims] 1. A light-shielding film formed on a substrate for blocking unnecessary light rays entering a solid-state image sensor, comprising a high-melting-point metal thin film and a high-melting-point metal silicide or nitride. A light-shielding film, comprising: a protective film laminated on the metal film; and a bonding film made of silicide or nitride of a refractory metal and laminated below the refractory metal thin film. 2. A light-shielding film formed on a substrate for shielding unnecessary light rays entering a solid-state imaging device, wherein X3S having a Si composition ratio smaller than that of disilicide when X is a high melting point metal.
A light-shielding film, wherein a silicide which is a high melting point metal compound such as i2 or X3Si is generated in advance, and the generated silicide which is a high melting point metal compound is laminated on the substrate by sputtering. 3. The high melting point metal is Mo, W, Ti or T.
3. The light-shielding film according to claim 1, wherein the light-shielding film is a.