JP2007012676A - Process for fabricating solid state image sensor and solid state image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state image sensor exhibiting high sensitivity and high reliability even in case of high degree scaling-down. <P>SOLUTION: In the process for fabricating a solid state image sensor having a lens formed in the layer to correspond with a photoelectric converting section, the process for forming a lens in the layer comprises a step for forming a translucent insulating film composed of a high refractive index material on the surface of a substrate where the photoelectric converting section and a charge transfer section are formed, a step for forming a resist pattern protruding upward by forming a resist pattern of first resist material on the translucent insulating film to face on the photoelectric converting section and then melting the resist pattern, a step for forming a resist pattern composed of the first and second resist materials by coating the resist pattern protruding upward with a second resist material to have a uniform thickness and then hardening the resist material, and a step for transferring the resist pattern to the high refractive index material by performing etching such that the etch selectivity of the first and second resist materials and the high refractive index material becomes 1:1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solid-state image pickup device and a solid-state image pickup device, and more particularly to a method for manufacturing a solid-state image pickup device having a structure capable of increasing the thickness and condensing property of an in-layer lens to withstand miniaturization.

  A solid-state imaging device using a CCD used for an area sensor or the like includes a photoelectric conversion unit such as a photodiode and a charge transfer unit including a charge transfer electrode for transferring a signal charge from the photoelectric conversion unit. A plurality of charge transfer electrodes are arranged adjacent to each other on a charge transfer path formed on the semiconductor substrate, and are sequentially driven.

  In recent years, demands for higher resolution and higher sensitivity have been increasing in solid-state imaging devices, and the number of imaging pixels has been increasing to more than gigapixels. Under such circumstances, in order to obtain high resolution without increasing the chip size, it is necessary to reduce the area per unit pixel and achieve high integration. As miniaturization progresses in this way, it has become difficult to maintain sensitivity and smear, and there is an increasing demand for a lens shape capable of obtaining sufficient light condensing performance.

  In a conventional method for forming an inner lens in a manufacturing process of a solid-state imaging device, a lens material film constituting an inner lens is formed on a surface on which a planarizing film is formed, and a predetermined lens is formed on the lens material film. A step of forming a resist having a shape, a step of transferring the lens shape of the resist to a lens material film, and forming a layer of the same lens material film on the lens material film to which the lens shape has been transferred The method of manufacturing using the process of forming an inner lens is taken (patent document 1).

JP 2002-26716 A

  However, it is difficult to obtain a sufficiently gentle shape with the above-mentioned intralayer lens, the light condensing property is not sufficient, and further improvement of the light condensing rate is demanded.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solid-state imaging device having high sensitivity and high reliability even at high miniaturization.

  Therefore, a method for manufacturing a solid-state imaging device according to the present invention includes, on a substrate, a photoelectric conversion unit, and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit. In the method of manufacturing a solid-state imaging device in which an inner lens is formed on the upper layer so as to correspond to the photoelectric conversion unit, the inner lens forming step is performed on the surface of the substrate on which the photoelectric conversion unit and the charge transfer unit are formed. Forming a translucent insulating film made of a high refractive index material, and forming a resist pattern made of a first resist material on the translucent insulating film so as to face the photoelectric conversion portion; A step of forming an upward convex resist pattern by melting, and applying and curing a second resist material on the upward convex resist pattern so that the film thickness is uniform; Second Etching such that a resist pattern composed of a resist material is formed, and the etching selectivity between the first and second resist materials and the high refractive index material is 1: 1, and the high refractive index Transferring the resist pattern to a material.

  If only the resist pattern made of the first resist material is melted, gaps are formed between the patterns, and it is difficult to obtain a sufficiently desirable shape. A desired shape can be obtained by applying a resist made of the second resist material to the substrate, and this shape can be transferred to a high refractive index material by etching back, so that an inner lens having a desired shape can be efficiently obtained. Can be obtained. In addition, since an intra-layer lens can be formed by forming a high refractive index material directly on the surface of the substrate on which the charge transfer electrode is formed and processing the shape, it is possible to reduce the thickness of the entire solid-state imaging device. Become.

  Further, in the method for manufacturing a solid-state imaging device of the present invention, the step of forming the light-transmitting insulating film includes the step of forming a silicon nitride film on the surface of the substrate on which the photoelectric conversion unit is formed by a plasma CVD method. Including some.

  According to this configuration, it is possible to form an in-layer convex lens that can form a film having a high refractive index, high passivation, and good flatness.

  In addition, the method for manufacturing a solid-state imaging device of the present invention includes a step of forming a silicon nitride film as an antireflection film prior to the step of forming the light-transmitting insulating film.

  According to this configuration, the high refractive index film can be formed directly on the antireflection film, and the thickness can be further reduced.

  Moreover, the manufacturing method of the solid-state image sensor of this invention includes the process of forming a color filter layer on the said inner lens.

  According to this configuration, since the color filter layer is formed on the flattened surface, the thickness can be further reduced.

  Moreover, the manufacturing method of the solid-state image sensor of this invention includes the process of forming the opening for performing a hydrogen termination process prior to the process of forming the said color filter layer.

  According to this configuration, hydrogen termination treatment can be performed efficiently.

  The solid-state imaging device of the present invention includes a photoelectric conversion unit on a substrate and a charge transfer unit including a charge transfer electrode that transfers a charge generated in the photoelectric conversion unit, and further on the upper layer. A solid-state imaging device in which an inner lens is formed so as to correspond to the photoelectric conversion unit, and an upward convex light transmission made of a high refractive index material on the photoelectric conversion unit so as to face the photoelectric conversion unit An insulating film is formed.

  According to this configuration, an in-layer lens having a desired shape can be obtained, so that a solid-state imaging device with high light collecting property, high sensitivity, and low smear can be obtained. In addition, it is possible to reduce the thickness of the entire solid-state imaging device.

  In the solid-state imaging device of the present invention, the light-transmitting insulating film is a silicon nitride film formed by a plasma CVD method.

  According to this configuration, it is possible to obtain a dense insulating film having high flatness and a high refractive index.

  The solid-state imaging device of the present invention includes one in which the silicon nitride is directly disposed on the photoelectric conversion unit.

  According to this configuration, the thickness can be further reduced.

  In the solid-state imaging device of the present invention, the translucent insulating film is disposed on an antireflection film that covers the photoelectric conversion portion.

Moreover, the solid-state image sensor of this invention contains what formed the color filter layer so as to oppose the said photoelectric conversion part.
According to this configuration, the thickness can be further reduced.

  According to the above configuration, by forming the aspherical inner lens, incident light at the pixel end can be efficiently collected on the photoelectric conversion unit, the light collection efficiency can be improved, and a highly sensitive sensor can be obtained. Can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)

  As shown in FIGS. 1 and 2 (FIG. 1 is a diagram showing a cross section AA in FIG. 2), the solid-state imaging device of the present embodiment includes a photoelectric conversion unit and charges generated in the photoelectric conversion unit. In the solid-state imaging device including the charge transfer unit including the charge transfer electrode for transferring the inner layer, the inner lens is formed of an aspherical upward convex lens. The aspherical upward convex lens can be formed by melting and curing a resist pattern to be a mask pattern, applying a resist to the upper layer again, and then etching back. That is, the upper convex lens on the aspherical surface includes a step of forming a translucent insulating film made of a high refractive index material on the surface of the substrate on which the photoelectric conversion unit and the charge transfer unit are formed, and an upper surface of the translucent insulating film. Forming a resist pattern made of a first resist material so as to oppose the photoelectric conversion portion, and forming an upward convex resist pattern by melting; and an upper convex resist pattern A step of applying a resist material of 2 to make the gap fill film thickness uniform and curing to form a resist pattern composed of the first and second resist materials; and the first and second resist materials And etching so that the etching selection ratio with the high refractive index material becomes 1: 1, and transferring the resist pattern to the high refractive index material.

As shown in FIGS. 1 and 2, the silicon substrate 1 has a plurality of photodiode regions 30 constituting a photoelectric conversion unit, and a charge transfer unit 40 for transferring signal charges detected by the photodiode. , Formed between the photodiode regions 30.
About parts other than a charge transfer part, it forms similarly to a usual solid-state image sensor.

  Here, the effective imaging region is composed of a light receiving region including a photoelectric conversion unit and a vertical transfer path (a part of the charge transfer unit) and a horizontal transfer path (a part of the charge transfer unit), and a peripheral circuit outside thereof. As an output circuit.

  Here, the gate oxide film 2 is formed to have a total film thickness of about 50 nm of the radical oxide film and the CVD film. Although not shown, a horizontal transfer register, a signal processing circuit, and wiring for transferring signal charges in the horizontal direction are formed on the non-imaging region of the silicon substrate 1 and the element isolation region of the charge transfer unit.

  That is, as shown in FIG. 1 and FIG. 2, a schematic cross-sectional view and a plan view of the solid-state imaging device chip (FIG. 1 is a cross-sectional view taken along line AA in FIG. 2). ) Are formed with a photoelectric conversion part and a charge transfer part provided with a photodiode, and the upper layer thereof is covered with an insulating film.

  The charge transfer unit 40 is formed in the upper layer of a plurality of vertical charge transfer channels 33 formed in the column direction of the surface portion of the silicon substrate 1 corresponding to each of the plurality of photodiode columns, and the vertical charge transfer channel 33. The charge transfer electrode 3 and a charge read region 34 for reading the charge generated in the photodiode 30 to the vertical charge transfer channel 33 are included. The charge transfer electrode 3 has a meandering shape extending in the row direction as a whole between a plurality of photodiode rows composed of a plurality of photodiodes 30 arranged in the row direction. Further, the vertical charge transfer channel 33 through which the signal charge transferred by the charge transfer electrode moves is formed in a direction crossing the direction in which the charge transfer unit 40 extends.

  As shown in FIG. 1, a p well layer 1P is formed on the surface of the silicon substrate 1, an n region 30b for forming a pn junction is formed in the p well layer 1P, and a p region 30a is formed on the surface. The photodiode 30 is configured, and the signal charge generated in the photodiode 30 is accumulated in the n region 30b.

  On the right side of the photodiode 30, a vertical charge transfer channel 33 composed of an n region is formed a little apart. A charge readout region 34 is formed in the p-well layer 1P between the n region 30b and the vertical charge transfer channel 33.

A charge transfer electrode 3 is formed on the charge readout region 34 and the vertical charge transfer channel 33 via the gate oxide film 2. An interelectrode insulating film 5 is formed between the electrodes. A channel stop 32 made of a p ⁺ region is provided on the right side of the vertical transfer channel 33, and is separated from the adjacent photodiode 30.

  On top of the charge transfer electrode 3, a silicon oxide film 7, a (passivation film), an insulating film 8 made of BPSG (borophosphosilicate glass), an inner lens 73 made of P-SiN, a flat under filter made of transparent resin, etc. A chemical film 74 is formed. Above these, a color filter 50 (red filter 50R, green filter 50G, blue filter: not shown) and a microlens 60 are provided.

  Although FIG. 2 shows a so-called honeycomb-structured solid-state imaging device, it is needless to say that the present invention can also be applied to a square lattice type solid-state imaging device.

Next, the manufacturing process of the solid-state imaging device according to the present embodiment will be described with reference to FIGS. 3 to 8 are explanatory views taken along the line BB in FIG.
First, an n-type silicon substrate 1 is prepared, and an n having an impurity concentration of about 1.0 × 10 ¹⁶ cm ^{−3 in} which the charge transfer channel 33, the channel stop region 32, and the charge readout region 34 illustrated in FIG. 1 are formed. A gate oxide film 2 having a two-layer structure is formed on the surface of the silicon substrate 1 of the mold, which is composed of a silicon oxide film having an oxide film thickness of 15 to 35 nm by radical oxidation by low-temperature plasma and a silicon oxide film by CVD.

  Subsequently, a doped amorphous silicon film D1 is formed on the gate oxide film 2 by a low pressure CVD method, and a two-layer film D4 of a silicon oxide film and a silicon nitride film 5 is formed by a low pressure CVD method. A resist pattern R1 is formed (FIG. 3A). This resist pattern is formed so as to correspond to the pattern of every other charge transfer electrode.

  Subsequently, the two-layer film D4 is etched by reactive ion etching to form a mask pattern for patterning the doped amorphous silicon film D1 (FIG. 3B).

  Then, the resist pattern is removed by ashing (FIG. 3C).

  Subsequently, radical oxidation by low-temperature plasma is performed on the surface of the electrode pattern and film formation is performed by the CVD method to form an interelectrode insulating film 5 made of a silicon oxide film having the same thickness as the gate oxide film having a two-layer structure (exactly here Then, a portion 5a serving as the core of the interelectrode insulating film 5 is used as the interelectrode insulating film 5) (FIG. 4A).

  Subsequently, a doped amorphous silicon film D2 is formed again by the low pressure CVD method and planarized by CMP (FIG. 4B). Thereafter, the doped amorphous silicon film D2 is patterned and etched to form the charge transfer electrode by photolithography (FIG. 4C).

  Then, radical oxidation is performed to form a silicon oxide film 4S (FIG. 5A), and after forming a silicon nitride film as the antireflection film 6, ion implantation is performed to form a photodiode portion. Thereafter, flash lamp annealing is performed to activate the implanted ions. Then, a silicon oxide film 7 is formed on the surface by the CVD method (FIG. 5B).

  Then, a BPSG film 8 having a thickness of 700 nm is formed on this upper layer, and is reflowed and flattened at 850 ° C. (FIG. 5C).

  Next, CMP is performed using the silicon nitride film 6 as an antireflection film as a polishing prevention layer. Thereafter, the silicon nitride film and the silicon oxide film are etched away by anisotropic etching (FIG. 6A), and the exposed doped amorphous silicon layers D1 and D2 are etched away (FIG. 6B). A shape in which the charge transfer electrode formation region is exposed across the inter-layer insulating film 5a is obtained.

  Subsequently, after radical oxidation by low-temperature plasma, a silicon nitride film 5b is formed by plasma CVD, and the surface of the silicon nitride film 5b is radically oxidized to form a silicon oxide film 5c, thereby forming an interelectrode insulating film 5. (FIG. 6C).

  Next, a two-layer film of a TiN layer and a W layer is formed by the CVD method, and planarized by the CMP method to form the metal electrode 3. At this time, after removing the silicon nitride film 5b as an anti-polishing layer in the CMP process, a silicon oxide film 7 is formed by plasma CVD (FIG. 7).

  Then, a silicon nitride film 73 as a lens material is formed by a plasma CVD method after forming a silicon oxide film (not shown) as a passivation film. Then, a resist is applied, a pattern is formed by photolithography, heated and melted, and then the lens-shaped first resist pattern R1 is cured by ion implantation (FIG. 8A).

  Thereafter, a second resist pattern R2 is formed to form an aspherical outer surface (FIG. 8B). Then, the silicon nitride film 73 having the same etching rate as that of the surface member made of the first and second resist patterns is etched back to form an in-layer lens (FIG. 8C). Then, after removing the silicon nitride from the pad portion and performing a hydrogen termination process, a planarizing film 74, a color filter 50, a microlens 60, and the like are formed, and a solid-state imaging device as shown in FIGS. 1 and 2 is obtained. In FIG. 2, only the main part is shown.

  According to this configuration, since the in-layer lens is composed of an aspherical convex lens having a desired curvature, it is possible to obtain a solid-state imaging device with improved light collecting performance and high sensitivity and low smear. In this embodiment, since the charge transfer electrode is made of a metal material, a light-shielding film is not required, the thickness can be reduced, and the light collecting property is extremely high. In addition, the light-receiving area is defined in a self-aligned manner with the edge of the charge transfer electrode while realizing reliable light shielding by the low-resistance charge transfer electrode made of a metal material. Therefore, it is possible to increase the amount of light.

  According to this method, in forming the in-layer lens, the resist pattern R1 made of the first resist material is melted, and then the resist R2 made of the second resist material is applied to the upper layer, thereby forming a desired shape. By transferring this shape to a high refractive index material by etch back, an intralayer lens having a desired shape can be obtained efficiently such as gapless. In addition, since an intra-layer lens can be formed by forming a high refractive index material directly on the surface of the substrate on which the charge transfer electrode is formed and processing the shape, it is possible to reduce the thickness of the entire solid-state imaging device. Become.

  In the present embodiment, the following effects are achieved in forming the charge transfer electrode. Since the interelectrode gap is determined by the interelectrode insulating film based on the insulating film formed by oxidation of a silicon-based conductive film such as doped amorphous silicon, it is possible to form a fine interelectrode gap beyond the resolution limit. it can. In addition, a dense and high withstand voltage insulating film can be obtained while using low-temperature oxidation by using radical oxidation, so that the diffusion length is prevented from increasing and a highly accurate and reliable solid-state imaging device is formed. be able to. In particular, since the inter-electrode insulating film including the gate oxide film is formed by the two-layer film of the silicon oxide film and the CVD film by radical oxidation by low-temperature plasma, it can be formed at a low temperature without causing an increase in the base diffusion length. A high-quality insulating film can be formed, an interelectrode insulating film with high accuracy and high withstand voltage can be formed, and a solid-state imaging device with high reliability can be formed. Further, since radical oxidation is a low-temperature process, the diffusion length is hardly increased even if it is repeated many times, and a high breakdown voltage can be reliably achieved.

  In the above embodiment, the silicon nitride film is used to form the intralayer lens. However, the present invention is not limited to the silicon nitride film, and other high refractive index materials such as a resist may be used as the lens substrate. Needless to say.

(Embodiment 2)
In the above embodiment, the solid-state imaging device in which the charge transfer electrode is made of a metal material has been described. However, in this embodiment, the charge transfer electrode is made of doped amorphous silicon films 3a and 3b as shown in FIG. An example will be described. In this case, a light shielding film 71M for defining a light receiving region of the photodiode is formed. Other parts are the same as those in the first embodiment, and the description thereof is omitted.

  As described above, according to the method of the present invention, it is possible to provide a solid-state imaging device with high light collection efficiency and fine and high sensitivity.

  According to this configuration, the in-layer lens can be an aspheric lens, and a solid-state imaging device with high light condensing properties can be formed. Therefore, it is useful as a solid-state imaging device in electronic devices such as next-generation mobile phones and digital cameras. It is.

It is a figure which shows the solid-state image sensor of Embodiment 1 of this invention. It is a figure which shows the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is a figure which shows the solid-state image sensor of Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate oxide film 3 Vertical charge transfer electrode 3a, 3b Doped amorphous silicon layer 5a Silicon oxide film 5b Silicon nitride film 5c Silicon oxide film 5 Interelectrode insulating film 7 Silicon oxide film 8 BPSG film 30 Photoelectric conversion part 40 Charge Transfer unit 50 Color filter 60 Lens 71M Light shielding film 73 In-layer lens 74 Flattening film

Claims (10)

A photoelectric conversion unit and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit are provided on a substrate, and a layer corresponding to the photoelectric conversion unit is further formed thereon. In the manufacturing method of the solid-state imaging device in which the inner lens is formed,
The step of forming the intralayer lens includes
Forming a translucent insulating film made of a high refractive index material on the substrate surface on which the photoelectric conversion unit and the charge transfer unit are formed;
Forming a resist pattern made of a first resist material on the translucent insulating film so as to face the photoelectric conversion portion, and forming an upward convex resist pattern by melting;
Applying a second resist material on the upwardly convex resist pattern so that the film thickness is uniform and curing to form a resist pattern composed of the first and second resist materials;
Solid-state imaging including a step of etching the first and second resist materials and the high refractive index material so that an etching selection ratio is 1: 1, and transferring the resist pattern to the high refractive index material Device manufacturing method. It is a manufacturing method of the solid-state image sensing device according to claim 1,
The step of forming the light-transmitting insulating film is a method of manufacturing a solid-state imaging device, which is a step of forming a silicon nitride film by plasma CVD on the substrate surface on which the photoelectric conversion unit is formed. It is a manufacturing method of the solid-state image sensing device according to claim 1 or 2,
A method for manufacturing a solid-state imaging device including a step of forming a silicon nitride film as an antireflection film prior to the step of forming the light-transmitting insulating film. It is a manufacturing method of the solid-state image sensing device according to any one of claims 1 to 3,
A method for manufacturing a solid-state imaging device, including a step of forming a color filter layer on the intra-layer lens. It is a manufacturing method of the solid-state image sensing device according to claim 4,
Prior to the step of forming the color filter layer,
A method for manufacturing a solid-state imaging device, including a step of forming an opening for performing hydrogen termination. A photoelectric conversion unit and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit are provided on a substrate, and a layer corresponding to the photoelectric conversion unit is further formed thereon. A solid-state image sensor having an inner lens formed thereon,
A solid-state imaging device in which an in-layer lens made of a light-transmitting insulating film having an upward convex shape made of a high refractive index material is formed on a photoelectric conversion portion so as to face the photoelectric conversion portion. The solid-state imaging device according to claim 6,
The light-transmitting insulating film is a solid-state imaging device which is a silicon nitride film formed by a plasma CVD method. The solid-state imaging device according to claim 7,
The silicon nitride is a solid-state image sensor directly disposed in the photoelectric conversion unit. The solid-state imaging device according to claim 6,
The light-transmitting insulating film is a solid-state imaging device disposed on an antireflection film covering the photoelectric conversion unit. The solid-state imaging device according to any one of claims 6 to 9,
A solid-state imaging device formed by forming a color filter layer so as to face the photoelectric conversion unit.

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