JPH04106975A - Manufacture of solid state image sensor - Google Patents

Abstract

PURPOSE:To suppress irregularities in various characteristics such as a dark current, a light signal storage capacity, an after image, etc., for a solid state image sensor by providing a sidewall at the side of a charge transfer electrode, then ion implanting it, and forming a buried photodiode region. CONSTITUTION:Sidewalls 12-1, 12-2 are formed on the side of a charge transfer electrode 7 through a silicon oxide film 14 by anisotropically etching. Then, with the electrode 7 and the sidewalls 12-1, 12-2 as masks P-type impurity such as boron is ion implanted about 10<13>/cm<2> to form a P<+> type semiconductor layer 10a in a self-alignment manner. Since the width of the sidewall is reduced smoothly upward, an impurity concentration profile of the layer 10a has a trend for reducing toward the electrode 7 in the vicinity directly under the sidewall. Then, the sidewall is removed by wet etching, and a buried photodiode region 8'b can be formed with high reproducibility.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a solid-state imaging device.

[Conventional technology]

FIGS. 3(a) to 3(d) are cross-sectional views of semiconductor chips arranged in the order of steps for explaining a conventional method for manufacturing a CCD type solid-state imaging device having a vertical overflow drain structure and an embedded photodiode. .

First, as shown in FIG. 3(a), a dose of 1o12/cm2 is applied to the surface of an N-type semiconductor substrate 1 made of single crystal Si.
A P-type well 2 of approximately 10 cm is formed, a P+ type channel stopper 4 (dose of approximately 1013/cm2) is formed to perform device isolation, and an N-type charge transfer region 3 (dose of approximately 1013/cm2) is formed.
/cm2), and a charge transfer electrode 7 made of a phosphorus-doped polysilicon film with a thickness of 300 nm, which serves as an electrode for applying a charge transfer pulse, is formed. Next, as shown in FIG.
), using the charge transfer electrode 7 and the silicon oxide film on its surface as a mask, N-type impurity 'S (for example, phosphorus) is ion-implanted at a dose of IQ 12'cm'' to form the optical signal storage area. Form an N- type photodiode region 8. Next, as shown in FIG. 3(c), a P-type impurity (for example, holon) is ion-implanted using the photoresist film 9 as a mask to form a shallow P+-type semiconductor. After forming the layer 10, the photoresist film 9 is peeled off as shown in FIG. 3(d).

[Problems to be Solved by the Invention] According to the above-described conventional method for manufacturing a solid-state imaging device, since the P-type thick conductor layer 10 is formed by ion implantation using a photoresist film as a mask, the buried photodiode region 8
′, the area of the region where the P° type half body layer 10 is not formed on the surface is likely to vary from process to process due to misalignment in the alignment process of the photoresist film. For this reason, there is a drawback that variations in the characteristics such as dark current and afterimage of the optical signal storage capacitance cannot be avoided. A second conductivity type challel stopper is provided in the provided second conductivity type well to separate a photoelectric conversion region and a charge transfer region into three sections, a charge transfer electrode is formed on the charge transfer region via a gate insulating film, and a charge transfer electrode is formed on the charge transfer region via a gate insulating film. In the conversion region, the surface or the second region except for the vicinity of the charge transfer region
A method for manufacturing a solid-state imaging device in which a buried photodiode region of a first conductivity type is formed covered with a conductivity type semiconductor layer, wherein the second conductivity type semiconductor layer is formed in self-alignment with the charge transfer electrode. .

〔Example〕

FIGS. 1(a) to (d) are cross-sectional views of semiconductor chips arranged in the order of steps for explaining the first embodiment of the present invention.6 In the conventional example, FIGS. 3(a) and (b) After the process described with reference to FIG. 1(a), a polysilicon film 11 is deposited to a thickness of about 400 nm and phosphorus doped, as shown in FIG. 1(b). A sidewall 12112-2 is formed on the side surface of the charge transfer electrode 7 via the silicon oxide film 14 by performing diagonal machining and sawching. Next, as shown in FIG. P using wall 12-1.12-2 as a mask
A P+ type semiconductor layer 10a is formed in a self-aligned manner by ion-implanting type impurity S (for example, holon) to a depth of about 1013 cm2.

Since the width of the sidewall gradually decreases upward, the impurity concentration profile of the P'-type half layer 10a has a slope that decreases toward the charge transfer electrode 7 near just below the sidewall. . Next, Figure 1 (
As shown in d), remove the sidewall by wet etching.

Since the width of the sidewall is determined by the thickness of the polysilicon film 11, it can be controlled with high precision, and the buried phototiode region 8'b can be formed with good reproducibility.

FIGS. 2(a) to 2(c) are cross-sectional views of a semiconductor chip shown in order of steps for explaining a second embodiment of the present invention.

After forming the sidewalls in the same manner as in the first embodiment, as shown in FIG. Since the parts other than the wall 12-1 are unnecessary, the photoresist film 13 is used to shield the side wall 12-1 and the side wall 12-2 is removed by wet etching.Next, as shown in FIG.
), the electrode transfer electrode 7 and the sidewall 1
Using 2-1 as a mask, add a P-type impurity (for example, holon) to 1
Ions are implanted to a depth of about 0.013/cm2 to form a P+ type semiconductor layer 10b in a self-aligned manner. Next, as shown in FIG. 2(C), the sidewall 12-1 is removed by wet etching. In this embodiment, the sidewall 12-
Since the ion implantation is performed after etching the P+ type semiconductor layer 10b and the P+ type channel stopper 4, there is an advantage that sufficient overlap between the P+ type semiconductor layer 10b and the P+ type channel stopper 4 can be ensured and sufficient electrical continuity can be achieved.

3 Effects of the Invention] As explained above, the present invention provides the following steps: After providing a sidewall on the side of the charge transfer electrode, ions are implanted to form a P" type semiconductor layer to form a buried photodiode region. Since the P+ type semiconductor layer can be formed in self-alignment with the charge transfer region, it has the effect of suppressing variations in various characteristics such as dark current, optical signal storage capacity, and afterimage of the mass imaging device.

Iode region, 8', 8'a, 8'b...Buried photodiode region, 9.Photoresist film, ]0], Oa
, 10b P" type semiconductor layer, 11... polysilicon' film, 12-1.12-2... side wall, 13...
Photoresist film, 14... silicon oxide film.

Claims (1)

[Claims] 1. A photoelectric conversion region and a charge transfer region are defined by a second conductivity type channel stopper in a second conductivity type well provided on the surface portion of the first conductivity type semiconductor substrate, and a photoelectric conversion region and a charge transfer region are defined on the charge transfer region. a solid state in which a charge transfer electrode is formed through a gate insulating film, and a buried photodiode region of a first conductivity type whose surface is covered with a semiconductor layer of a second conductivity type except for the vicinity of the charge transfer region is formed in the photoelectric conversion region; A method for manufacturing a solid-state imaging device, characterized in that the second conductivity type semiconductor layer is formed in self-alignment with the charge transfer electrode. 2. The solid according to claim 1, wherein a sidewall is formed on the side surface of the charge transfer electrode via an insulating film, and then ion implantation is performed using the charge transfer electrode and the sidewall as a mask to form the second conductivity type semiconductor layer. A method for manufacturing an imaging device.