JP2895894B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly, to a method for laminating a surface protection film for protecting the surface of a solid-state imaging device.

(B) Conventional technology An interline solid-state imaging device will be described with reference to FIGS. 3 and 4. FIG. FIG. 4 shows A in FIG.
FIG. 4 is a cross-sectional view taken along a line A.

FIG. 3 shows an interline solid-state imaging device (hereinafter, referred to as an “inline type”).
The CCD (11) is a light receiving unit (12 ₁₁ ) to (12 _mn ) that performs a photoelectric conversion of an optical image in a matrix arrangement, and a light receiving unit in each column. (12
photocharge _lj) ~ (12 _mj) are parallel input, a vertical transfer register for transferring it to the drawing the vertical direction _{(13 l) ~ (13 n} ) , of the vertical transfer register _{(13 l) ~ (13 n} ) The output comprises a horizontal transfer register (14) for inputting in parallel and transferring it in the right direction in the drawing.

The light receiving sections (12 _lj ) to (12 _mj ) are arranged in a matrix of, for example, about 400 × 500 pixels, and the light receiving sections (12 _lj ) to (12 _lj ) are arranged.
First, the two-dimensional image information photoelectrically converted by (12 _mj )
By the transfer operation of the vertical transfer registers ( _13l ) to ( _13n ), n
It is converted into bit serial image information. Next, the outputs of the vertical transfer registers (13 _l ) to (13 _n ) are converted into serial image information by a transfer operation of a horizontal transfer register (14) which receives the outputs in parallel, and are serially output via an output circuit (not shown).

The sectional structure of the above-mentioned light receiving sections (12 _lj ) to (12 _mj ) and the vertical transfer registers (13 _l ) to (13 _n ) is as shown in FIG. 4, and such a sectional structure is n-type. Si substrate (21)
A p-type impurity is implanted and diffused into the surface layer of the first step to form a first-stage p-well (22) and a second-stage p-well (23).
An n-type impurity is implanted into the well (22) to form an n-layer (24) constituting a photodiode, and an n-type impurity is implanted into the two-stage p-well (23) to form a vertical transfer register (13 _l ) to (1
An n ⁻ layer (25) constituting a buried channel of 3 _n ) is formed, and a p-type impurity is further implanted into a two-step p well (23) to form p ⁺ (26) serving as a channel stopper and the like.
The Si surface of the substrate (21) is obtained by, for example to form a transfer electrode (27) by using the polysilicon through the S _i O ₂ film. The structure indicated by reference numeral 28 in the figure is a light shield using pure Al.

In the CCD (11) having the above-described structure, electric charges are excited in the light receiving sections (12 _lj ) to (12 _mj ) in accordance with the amount of incident light, and this is the n ⁻ layer (25) where the buried channel of the vertical transfer register is formed. Then, an operation of transferring the data up to a predetermined bit of the horizontal transfer register indicated by reference numeral 4 in FIG. 3 is performed by well-known transfer means. Therefore, the upper surface of the n-layer (24) constituting the photodiode should be as light rays (3
0) is incident, while the n ⁻ layer (25) where the buried channel of the vertical transfer register is formed is completely light-shielded by pure Al.

Silicon nitride film (29) is 3SiH in plasma CVD.
₄ + 4NH ₃ → Si ₃ N ₄ + 12H ₂ formed by the reaction, CCD (1
In addition to protecting the uppermost layer of 1), hydrogen radicals generated by NH ₃ excitation in the above reaction terminate dangling bonds at the Si—SiO ₂ interface, thereby reducing dark current.

(C) Problems to be solved by the invention In a CCD in which the uppermost layer is protected by a silicon nitride film (29), the silicon nitride film (29) has a high refractive index of about 2.0, so that the silicon nitride film (29) There is a problem that the reflection or interference of light on the surface is large and the loss of the incident light amount is large. For this reason, there is a problem that the dark current reducing effect of the silicon nitride film (29) is reduced and the S / N is not improved. Also, since the size of the light receiving unit cannot be reduced,
This is an obstacle to increasing the number of pixels.

An object of the present invention is to provide a solid-state imaging device in which an improvement in light sensitivity and a reduction in dark current are achieved, thereby achieving a good S / N ratio. And

(D) Means for Solving the Problems The above-mentioned problems are achieved by an image pickup unit that picks up a two-dimensional optical image and performs photoelectric conversion on the semiconductor substrate to obtain photocharges, and a transfer that transfers the photocharges of the image pickup unit. And an output unit for converting an output charge of the transfer unit to a voltage value, and then forming the surface protection layer covering the imaging unit, the transfer unit, and the output unit. At the start of lamination, the surface protective layer supplies SiH ₄ and NH _3, and supplies N ₂ O while increasing the flow rate over time.
The problem is solved by a method for manufacturing a solid-state imaging device characterized by being formed by a method.

(E) in the top layer is a plasma CVD action solid-state imaging device, SiH ₄
And is formed under the control of the gas flow rate of NH ₃ and N ₂ O, and is protected by the Si _x O _y N _z film (y ≠ 0), so that reflection and interference of incident light are reduced and light sensitivity is improved. . Further, the interface state density of the solid-state imaging device substrate decreases, and the dark current decreases. And S / N is improved by those effects.

(F) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Note that the present invention relates to a method for laminating a protective layer formed on the uppermost layer of a CCD, and the description of the planar structure of the CCD is omitted since it is not different from the conventional example.

FIG. 4 differs from FIG. 4 used in the description of the conventional example only in the composition of the protective layer formed on the top layer of the CCD. The cross-sectional structure of the transfer register is as shown in the figure, and such a cross-sectional structure is obtained by injecting and diffusing a p-type impurity into the surface layer of the n-type Si substrate (1) and diffusing it into a one-step p-well (2). And a two-stage p-well (3) are formed, and the one-stage p-well (2) is formed.
N to form a photodiode by injecting n-type impurities into
A layer (4) is formed, an n-type impurity is implanted into the two-stage p-well (3) to form an n ⁻ layer (5) that forms a buried channel of the vertical transfer register, and further a two-stage p-well (3) is formed. ) transferred using the polysilicon through the S _i O ₂ film on the Si surface of the substrate (1) to form a p-type impurity serving as a channel stopper are implanted p ⁺ layer (6) or the like in the electrode ( 7) is obtained. The structure indicated by reference numeral 8 in the figure is a light shield using pure Al.

Conventional CCDs have a plasma CVD
_{SiH 4 + 4NH 3 → Si 3} N 4 + 12H but by ₂ becomes the reaction is the Si ₃ N ₄ layer is formed, the CCD in the plasma CVD of the present _{invention, SiH 4 + NH 3 + N} 2 O → Si x O y N z nitride oxide _{(9) (S ix O y} N z) is formed by the reaction. Note that x, y, z
Is a constant and can be changed by controlling the flow rate of each gas during the reaction in plasma CVD. Therefore, in the present invention, the supply of the N ₂ O gas is interrupted at the beginning of the formation of the nitrided oxide film (9) by the above reaction, so that the conventional nitride film is formed, and the supply of the N ₂ O gas is sequentially increased to increase the nitridation. An oxide film (9) is formed. The nitrided oxide film (9) thus formed has both the characteristics of reducing the Si—SiO ₂ interface state density of the nitride film and the high light transmission characteristics of the nitrided oxide film described later.

FIG. 2 shows the light transmission characteristics of the nitride film (Si _x N _y ) having a refractive index of 2.0 and the nitrided oxide film (Si _x O _y N _z ) having a refractive index of 1.6 with respect to each wavelength. As shown in the figure, the light transmittance of the nitrided oxide film (Si _x O _y N _z ) is higher than that of the nitride film (Si _x N _y ) in the entire wavelength range shown in the figure, as well as the wavelength. The change of the transmittance with respect to the change is minute. Therefore, the CCD in which the Si _x O _y N _z film (9) is formed on the uppermost part of the final protective layer has excellent optical characteristics and S / N is improved due to an increase in light sensitivity.

(G) According to the present invention as mentioned effects or more inventions, be a nitride film having excellent reduction properties of S _i -S _i O ₂ interface state density at the lower part as the protective layer of the uppermost layer of the solid-state imaging device In addition, since the nitrided oxide film which becomes the nitrided oxide film having excellent light transmission characteristics is used in the upper layer, the light sensitivity is increased, the dark current is reduced, and the S / N is improved.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a solid-state imaging device illustrating an embodiment of the present invention, FIG. 2 is a diagram illustrating light transmission characteristics of a Si _x N _y film and a Si _x O _y N _z film, and FIG. FIG. 4 is a conceptual diagram illustrating a planar structure of the solid-state imaging device. FIG. 4 is a cross-sectional view taken along the line AA of FIG. 1... N-type Si substrate, 2... 1-step P well, 3.
Well, 4 ... n layer, 5 ... n ^- layer, 6 ... P ⁺ layer, 7 ...
Transfer electrode, 8 ... Light shield, 9 ... Nitride oxide film (Si _x O
_y N _z ).

Claims (1)

(57) [Claims] 1. An imaging section for capturing a two-dimensional optical image on a Si substrate and performing photoelectric conversion to obtain photocharges, a transfer section for transferring the photocharges of the imaging section, and an output charge of the transfer section. A method of manufacturing a solid-state image sensor that forms an output unit that converts a voltage value into a voltage value, and then forms the nitrided oxide film covering the imaging unit, the transfer unit, and the output unit. The output unit includes a SiO ₂ film in contact with the Si substrate, and the nitrided oxide film supplies SiH ₄ and NH ₃ at the start of lamination, and supplies N ₂ O while increasing the flow rate with time. A method for manufacturing a solid-state imaging device, wherein an oxygen component is continuously increased from a substrate side to a surface side by a plasma CVD method.