JP2571011B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a charge coupled device (CC).
D) and a method for manufacturing a semiconductor device such as a solid-state imaging device.
In particular, the present invention relates to a method for manufacturing a semiconductor device capable of forming a charge transfer electrode in a single layer without deteriorating the charge transfer speed.

[0002]

2. Description of the Related Art As a transfer electrode structure at the beginning of the development of a charge-coupled device, a single-layer structure shown in FIG. 7 has been proposed. That is, as shown in the figure, a first charge transfer electrode 204a and a second charge transfer electrode 204 made of polysilicon or the like are formed on a semiconductor substrate 201 via a gate oxide film 203.
b is formed. However, in this electrode structure,
There is a distance a between the first charge transfer electrode and the second charge transfer electrode, which is the resolution limit of lithography (about 1-2 μm),
Since no electric field is applied here, a transfer failure occurs when the transfer speed increases.

For this reason, a transfer electrode having this structure is not employed in a product, and a multilayer electrode structure such as a two-layer polysilicon electrode structure shown in FIG. 8 is actually used. In a two-layer charge coupled device, the semiconductor substrate 30
The first and third charge transfer electrodes 304a, 304c are formed on the first charge transfer layer 304 by a first layer polysilicon through a gate oxide film 303.
The second and fourth charge transfer electrodes 30 are made of second layer polysilicon.
4b and 304d are formed, whereby the distance at which the electric field between the transfer electrodes is not applied can be sufficiently reduced, and high-speed charge transfer can be performed.

Conventionally, a two-layer polysilicon electrode structure has been adopted also in a solid-state image sensor which is an application element of a charge-coupled device, as shown in FIG. FIG. 9A is a plan view of a cell portion of a conventional two-dimensional solid-state imaging device.
(B) is a sectional view taken along line AA. As shown in FIG. 9, an n-type charge transfer region 402, a photoelectric conversion region 413, and a p ⁺ -type diffusion layer 414 are formed in a surface region of a p-type semiconductor substrate 401, and a gate is formed on the semiconductor substrate. Through an oxide film, first and third charge transfer electrodes 404a and 404c are formed of first layer polysilicon, and second and fourth charge transfer electrodes 404b and 404d are formed of second layer polysilicon. On top of that, a metal light-shielding film 417 having an opening 417a formed on the photoelectric conversion region 413 via an interlayer insulating film 416 is attached.

[0005]

The above-described conventional two-layer electrode structure has the following disadvantages, particularly in a two-dimensional solid-state image pickup device. In a conventional solid-state imaging device, FIG.
C, the first charge transfer electrode 404a formed of the first-layer polysilicon and the third charge transfer electrode 404b formed of the second-layer polysilicon overlap, and the material of the metal light-shielding film is formed. Since the coverage of Al is not so good, the side wall of the photoelectric conversion region is not covered by FIG.
As shown by D, uncoated portions and thin film portions are likely to occur. Therefore, light enters the charge transfer region from the D portion,
Deteriorate smear characteristics. Further, since the height of the side wall at the portion where the polysilicon layer overlaps the two layers is high, the light reflected therefrom enters the charge transfer region as oblique light, deteriorating smear characteristics. Further, in the case of a conventional two-layer electrode structure, two depositions of polysilicon, two thermal oxidation steps of polysilicon, and two photolithography steps are required to form an electrode, which increases the number of steps. There was a problem.

[0006]

According to the present invention, a gate insulating film (103), a polycrystalline silicon film (104) and a mask material layer (105) are formed on a semiconductor substrate (101). ) Sequentially, and an ion implantation mask material (106) selectively on the mask material layer
Forming, ion-implanting boron using the ion-implanted mask material as a mask, and forming the mask material layer (10) using the ion-implanted mask material (106) as a mask.
5) By etching and removing the mask material layer immediately below the ion implantation mask material by a predetermined distance, the surface of the polycrystalline silicon film to which boron is added and a part of the polycrystalline silicon film to which boron is not added Exposing the surface of the polycrystalline silicon film (107) to which boron is not added by using hydrazine to selectively remove the polycrystalline silicon film (104) from the plurality of transfer electrodes (104a). To 104d), and a step of etching and removing the mask material layer (105).

Further, according to the present invention, as a method for manufacturing a solid-state imaging device, a step of forming a photoelectric conversion region (113) and a charge transfer region (102) in a surface region of a semiconductor substrate (101); Gate insulating film (1
03), a step of sequentially forming a polycrystalline silicon film (104) and a mask material layer (105), a step of selectively forming an ion implantation mask material (106) on the mask material layer, and the ion implantation mask Ion-implanting boron using the material as a mask;
Using the mask 6) as a mask, the mask material layer (105) is removed by etching, and the mask material layer immediately below the ion implantation mask material is side-etched for a predetermined distance to remove the surface of the boron-added polycrystalline silicon film and boron. Exposing a part of the surface of the non-added polycrystalline silicon film; and selectively removing the exposed polycrystalline silicon film (107) to which boron is not added by using hydrazine. The film is transferred to a plurality of transfer electrodes (104
a to 104d), and a method of manufacturing a semiconductor device including a step of etching and removing the mask material layer.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a plan view of a two-dimensional solid-state imaging device formed according to the first embodiment of the present invention.
(B) is a sectional view taken along line AA. FIG.
FIGS. 2A to 2C to 3C are main process cross-sectional views of the present embodiment along the line BB in FIG. 1A. First, as shown in FIG. 2A, an n-type impurity is diffused in a surface region of a p-type semiconductor substrate 101 to form a charge transfer region 102. Next, a gate oxide film 103 is formed on the semiconductor substrate by about 500.degree.
4 is approximately 5000 °, and the silicon nitride film 105 is approximately 1000
膜厚 is formed in order.

[0009] Next, as shown in FIG.
A photoresist film 106 is formed on the region to be the charge transfer electrode and the second charge transfer electrode, and boron is added using the photoresist film as a mask to a concentration of about 1 × 10 ¹⁸ cm ⁻³ . Activate boron by annealing at low temperature. Next, as shown in FIG. 2C, the silicon nitride film 10 is
5 is etched. At this time, the silicon nitride film 105 immediately below the photoresist by about 0.4 μm from the end of the photoresist film is side-etched to form a non-doped polysilicon exposed region 107 to which boron is not added.

Next, as shown in FIG. 3 (a), the polysilicon film in the non-doped polysilicon exposed region 107 is etched with a mixed solution of hydrazine and isopropyl alcohol using the remaining silicon nitride film 105 as a mask.
8, the polysilicon film 104 is separated into a first charge transfer electrode 104a, a second charge transfer electrode 104b, and a third charge transfer electrode 104c, and then the silicon nitride film 105 is removed. In the treatment with hydrazine, the polysilicon film to which boron is added is hardly etched.
Here, the width of the separation groove 108 is optimally about 0.4 μm.

Next, in order to remove an unnecessary portion of the polysilicon film, a photoresist film (not shown) is formed on the unnecessary portion of the polysilicon film. ^After adding the photoresist film to a concentration of ¹⁸ cm ⁻³ or more and removing the photoresist film, boron is activated by a low-temperature annealing treatment. Next, processing is again performed with a mixed solution of hydrazine and isopropyl alcohol to remove unnecessary portions of the polysilicon film by etching.

Next, as shown in FIG. 3B, after removing the exposed gate oxide film 103, a heat treatment is performed in an oxidizing atmosphere to form a film having a thickness of about 500 on the surface of each transfer electrode.
The thermal oxide film 109 of Å is formed, and then the SOG film 110 is formed.
Is formed by spin coating and heat treatment to planarize the surface. Next, as shown in FIG. 3C, a contact hole 111 is formed on the first charge transfer electrode 104a and the third charge transfer electrode 104c, and a metal wiring 112 (metal light shielding) for supplying a voltage for charge transfer is formed. To form a device. Here, the supply of the transfer voltage to the other charge transfer electrodes is similarly performed from the peripheral portion of the device (not shown).

Returning to FIG. 1, as shown in FIGS. 1A and 1B, an opening 112a is provided in the metal wiring 112 also serving as a light shielding film on the photoelectric conversion region. FIG.
As shown in (b), in this light receiving opening,
Unlike the case of the conventional example shown in FIG. 9, since there is no overlap of the transfer electrodes, the height of the opening can be reduced.
Therefore, according to the structure of this embodiment, it is possible to reduce leakage of light into the charge transfer region due to reflection on the side wall of the opening and to improve the step coverage of the metal light shielding film (metal wiring). Light leakage due to the incomplete light-shielding film can also be suppressed. Therefore,
The smear characteristics can be remarkably improved as compared with the case of the conventional example shown in FIG.

FIG. 4A is a plan view for explaining a second embodiment of the present invention, and FIG. 4B and FIG.
4C is a cross-sectional view taken along line AA and line BB in FIG. In the second embodiment, the metal wiring for supplying the transfer voltage to the first and third charge transfer electrodes and the light shielding film are formed by separate metal films. In FIG. 4C, the SOG film 110 and the thermal oxide film 10
Since the steps up to the formation of the contact hole 111 in 9 are the same as in the case of the first embodiment, a description thereof will be omitted.

After the formation of the contact hole 111, the first and third charge transfer electrodes 104 are formed as shown in FIG.
a, a metal wiring 115 for supplying a voltage to 104c is formed. At this time, the photoelectric conversion region 113 of the metal wiring 115
The closer end is formed sufficiently inward from the end of the charge transfer electrode. Next, after forming an interlayer insulating film 116, a metal light-shielding film 117 provided with an opening 117a on the photoelectric conversion region 113 is formed, thereby completing the formation of the device. Also in this embodiment, unlike the conventional structure, the transfer electrode is a single layer in the light receiving opening, so that the step coverage is good and the smear characteristic is improved similarly to the previous embodiment.

FIGS. 5 and 6 are plan views showing modifications of the second embodiment of the present invention shown in FIG. In the example of FIG. 5, the second and fourth charge transfer electrodes 104b and 104d
However, the transfer voltage is supplied by the metal wiring 115, and the first and third charge transfer electrodes 104a and 104c are configured to receive the transfer voltage by the metal wiring 112 also serving as the metal light shielding film. Second and fourth charge transfer electrodes 1
04b and 104d are metal wirings 115 every few blocks.
Connected to In the modification of FIG. 6, the first and third charge transfer electrodes 104a and 104c receive supply of a transfer voltage via the metal wiring 115a, and the second and fourth charge transfer electrodes 104b and 104d are connected with the metal wiring 115b. It is configured to receive the supply of the transfer voltage.
A metal light-shielding film 117 having an opening 117a is formed on the light receiving region via an interlayer insulating film on the layers 15a and 115b.

While the preferred embodiment has been described above,
The present invention is not limited to these embodiments, and various changes can be made within the gist of the present invention described in the claims. For example, in the embodiment, the unnecessary portion of the polysilicon film is removed after forming the separation groove between the transfer electrodes. However, instead of this method, the polysilicon other than the transfer electrode portion may be removed before forming the separation groove. The film can be removed. Further, in the embodiments, the two-dimensional solid-state imaging device has been described, but the present invention is applicable to a one-dimensional solid-state imaging device and further to a general charge-coupled device.

[0018]

As described above, according to the method of manufacturing a semiconductor device of the present invention, the polysilicon film is selectively doped with boron and the silicon nitride film covering the polysilicon film is side-etched. According to the present invention, the non-doped polysilicon film is exposed and is removed by etching to separate the transfer electrodes. Will be able to Therefore, according to the present invention, the electric field between the transfer electrodes does not weaken without using the transfer electrodes having a multilayer structure, and the charge transfer can be performed sufficiently quickly by the single-layer transfer electrodes. Therefore, it is possible to form a charge transfer device having good transfer efficiency with a small number of man-hours, and in a solid-state imaging device, it is possible to reduce the step of the light-receiving opening, and to use a transfer electrode. It is possible to significantly improve the smear characteristics that have been deteriorated by overlapping.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view of a solid-state imaging device formed according to a first embodiment of the present invention.

FIG. 2 is a part of a process cross-sectional view for explaining the first embodiment of the present invention.

FIG. 3 is a part of a process cross-sectional view for explaining the first embodiment of the present invention.

FIG. 4 is a plan view and a cross-sectional view of a solid-state imaging device for explaining a second embodiment of the present invention.

FIG. 5 is a plan view for explaining a modification of the second embodiment of the present invention.

FIG. 6 is a plan view for explaining another modification of the second embodiment of the present invention.

FIG. 7 is a sectional view of a first conventional example.

FIG. 8 is a sectional view of a second conventional example.

FIG. 9 is a plan view and a cross-sectional view of a conventional solid-state imaging device.

[Description of Reference Numerals] 101, 401 p-type semiconductor substrate 201, 301 semiconductor substrate 102, 402 charge transfer region 103, 203, 303, 403 gate oxide film 104 polysilicon film 104a-104d, 304a-304d, 404a-
404d First to fourth charge transfer electrodes 204a, 204b First and second charge transfer electrodes 105 Silicon nitride film 106 Photoresist film 107 Non-doped polysilicon exposed region 108 Separation groove 109 Thermal oxide film 110 SOG film 111 Contact hole 112 Metal wiring 112a openings 113, 413 photoelectric conversion regions 114, 414 p ⁺ -type diffusion layers 115, 115a, 115b metal wirings 116, 416 interlayer insulating films 117, 417 metal light shielding films 117a, 417a openings

Claims (5)

(57) [Claims] A step of sequentially forming a gate insulating film, a polycrystalline silicon film, and a mask material layer on a semiconductor substrate; a step of selectively forming an ion implantation mask material on the mask material layer; A step of ion-implanting boron using a mask material as a mask, and etching away the mask material layer using the ion-implantation mask material as a mask, and side-etching the mask material layer immediately below the ion-implantation mask material by a predetermined distance. Exposing the surface of the polycrystalline silicon film to which boron is added and a part of the surface of the polycrystalline silicon film to which boron is not added; and exposing the polycrystalline silicon film to which boron is not added by using hydrazine. Selectively dividing the polycrystalline silicon film into a plurality of transfer electrodes, and etching away the mask material layer. And a method of manufacturing a semiconductor device. 2. The method according to claim 1, wherein said mask material layer is a silicon nitride film. 3. a step of sequentially forming a gate insulating film, a polycrystalline silicon film and a mask material layer on a semiconductor substrate; and a step of selectively forming a first ion implantation mask material on the mask material layer. A step of ion-implanting boron using the first ion-implanted mask material as a mask, and etching and removing the mask material layer using the first ion-implanted mask material as a mask; Exposing the surface of the polycrystalline silicon film to which boron is added and a part of the surface of the polycrystalline silicon film to which boron is not added by side-etching the mask material layer for a predetermined distance, and exposing using hydrazine. Selectively removing the polycrystalline silicon film to which the boron is not added and dividing the polycrystalline silicon film into a plurality of transfer electrodes; and Etching the material layer, covering unnecessary portions of the polycrystalline silicon film with a second ion implantation mask material, and adding boron to the polycrystalline silicon film using the second ion implantation mask material as a mask. A method of manufacturing a semiconductor device, comprising: a step of adding; and a step of removing the second ion implantation mask material and removing an exposed polycrystalline silicon film to which boron is not added using hydrazine. 4. A step of forming a photoelectric conversion region and a charge transfer region in a surface region of a semiconductor substrate; a step of sequentially forming a gate insulating film, a polycrystalline silicon film, and a mask material layer on the semiconductor substrate; A step of selectively forming an ion implantation mask material on the mask material layer, a step of implanting boron ions using the ion implantation mask material as a mask, and etching the mask material layer using the ion implantation mask material as a mask Removing and side-etching the mask material layer immediately below the ion-implanted mask material for a predetermined distance to expose the surface of the polycrystalline silicon film to which boron is added and a part of the surface of the polycrystalline silicon film to which boron is not added. And selectively removing the exposed polycrystalline silicon film to which boron is not added by using hydrazine to form the polycrystalline silicon film. A method of manufacturing a semiconductor device, comprising: a step of dividing a recon film into a plurality of transfer electrodes; and a step of etching and removing the mask material layer. 5. A step of forming a photoelectric conversion region and a charge transfer region in a surface region of a semiconductor substrate; a step of sequentially forming a gate insulating film, a polycrystalline silicon film, and a mask material layer on the semiconductor substrate; Selectively forming a first ion-implanted mask material on the mask material layer;
Implanting boron using the ion implantation mask material as a mask, etching the mask material layer using the first ion implantation mask material as a mask, and removing the mask immediately below the first ion implantation mask material. Exposing the surface of the polycrystalline silicon film to which boron is added and a part of the surface of the polycrystalline silicon film to which boron is not added by side-etching the material layer for a predetermined distance; and exposing the boron exposed using hydrazine. Selectively removing the polycrystalline silicon film to which no silicon is added to divide the polycrystalline silicon film into a plurality of transfer electrodes, etching the mask material layer, and eliminating the need for the polycrystalline silicon film. Covering a portion with a second ion implantation mask material; and forming a portion on the polycrystalline silicon film using the second ion implantation mask material as a mask. Adding an Ron, the second
Removing the ion implantation mask material and removing the exposed polycrystalline silicon film to which boron is not added using hydrazine.