JP4500667B2 - Solid-state imaging device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid-state imaging device and a method for manufacturing the same, and more particularly to improving the reliability of a solid-state imaging device having a fine structure.

  A solid-state imaging device using a CCD, which is an imaging device such as an area sensor, has, as a basic structure, a photoelectric conversion unit such as a photodiode, a charge readout unit from the photoelectric conversion unit, and a charge transfer for transferring the readout charge. And a charge transfer portion including an electrode. A plurality of these charge transfer electrodes are arranged adjacent to each other on a charge transfer channel formed on the surface of the semiconductor substrate, and are sequentially driven by a clock signal.

  In recent years, in a solid-state imaging device, pixel miniaturization has progressed due to an increase in the number of imaging pixels. Along with this, miniaturization of the photoelectric conversion part has progressed and it has become difficult to maintain high sensitivity.

  Therefore, various methods for efficiently condensing the light that has reached the periphery of the opening on the photoelectric conversion unit have been proposed.

  For example, an optical waveguide is formed by forming a hole in the planarizing film immediately above the light receiving unit, and then embedding a high refractive index material in the hole, and the high refractive index film and the planarizing film that become the optical waveguide A technique is disclosed in which light is totally reflected at the interface with the light and taken into the light receiving unit. Also, in Patent Document 1, a light receiving section formed on a substrate, and an optical waveguide configured to confine and propagate incident light and guide it to the light receiving section in an interlayer film formed on the substrate. In an imaging apparatus, a structure has been proposed in which a gap is formed between an optical waveguide and the interlayer film to further improve the light guiding function (for example, Patent Document 1).

JP 2003-60179 A

However, when forming the gap, it is extremely difficult to form a fine gap with high accuracy, and there is a limit to miniaturization. There is also a problem that the gap is collapsed when forming an upper layer inner lens or the like.
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a solid-state imaging device with excellent optical characteristics by further improving the light collection efficiency even when miniaturized, reducing the oozing of incident light. And
It is another object of the present invention to provide a method for manufacturing a solid-state imaging device that is easy to manufacture and highly reliable.

The solid-state imaging device according to the present invention includes a photoelectric conversion unit and a charge transfer unit including a charge transfer electrode that transfers a charge generated in the photoelectric conversion unit, and confines and propagates incident light to transmit the photoelectric conversion unit. A solid-state imaging device having an optical waveguide guided to a conversion unit, wherein the optical waveguide is formed on the photoelectric conversion unit, has a predetermined refractive index, and has a columnar first translucency having a light guiding function A film and a second light-transmitting film having a void layer formed in a groove having an aspect ratio of 1.5 or more formed around the first light-transmitting film , In the groove, the second light-transmitting film is formed under the condition that the film forming speed on the vertical plane is lower than that on the horizontal plane .
With this configuration, since the void layer is used as an air gap layer with a low refractive index, the air gap layer has an extremely small width, improving the mechanical strength and ensuring the air gap layer without being buried. Can do. Also, the positional accuracy is high, and the solid-state imaging device can be miniaturized. In addition, a void can be formed in the second light-transmitting film with good workability.

In the solid-state imaging device of the present invention, the first light-transmitting film includes a material having a higher refractive index than that of the second light-transmitting film.
With this configuration, the light collection rate can be further increased.

In the solid-state imaging device of the present invention, the first light-transmitting film is a silicon nitride film and the second light-transmitting film is a silicon oxide film.
With this configuration, since a silicon oxide film having a void layer is formed around silicon nitride which is a high refractive index material, the light collection rate can be further increased. Here, examples of the anisotropic process include sputtering, thermal CVD, and plasma CVD (PECVD).

In the solid-state imaging device of the present invention, the first light-transmitting film includes a shape processed so that the upper surface has a convex lens shape.
With this configuration, a chip-on lens is not necessary, and further downsizing and thinning can be achieved, so that a solid-state imaging device with higher light collecting property can be formed.

The solid-state imaging device manufacturing method of the present invention includes a step of forming, on a semiconductor substrate, a photoelectric conversion unit and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit, Forming a columnar first translucent film in a region corresponding to a light receiving region of the photoelectric conversion unit, and forming a groove having an aspect ratio of 1.5 or more around the first translucent film; And a step of forming a second light-transmitting film in the groove while leaving a void layer under a condition that a film forming speed on a vertical plane is lower than a horizontal plane.
With this configuration, the second light-transmitting film is formed under film-forming conditions such that the gap has anisotropy, so that a fine void layer (air gap layer) can be accurately formed. it can.

In the solid-state imaging device manufacturing method of the present invention, the step of forming the second light-transmitting film includes a sputtering step.
In the sputtering process, since the coverage of the vertical surface is poor compared to the horizontal surface, the void layer can be formed efficiently.

In the solid-state imaging device manufacturing method of the present invention, the step of forming the second light-transmitting film includes a CVD step.
By selecting the conditions, it is possible to make the coverage of the vertical plane worse than the horizontal plane, so that the void layer can be formed efficiently. It is desirable to use a thermal CVD method or a plasma CVD method.

Moreover, the manufacturing method of the solid-state image sensor of this invention includes what includes the process of forming a color filter and a micro lens on a said 1st translucent film | membrane.
According to this method, it is possible to efficiently stack the optical systems.

The solid-state imaging device of the present invention is covered with a light-shielding film having an opening in the light receiving region of the photoelectric conversion unit, and the opening is a high refractive index film having a columnar single layer structure as a first light-transmitting film. The periphery of the high refractive index film may be covered with an insulating film having a lower refractive index than the high refractive index film and having a planarized surface.
With this configuration, the opening is covered with a high refractive index film having a single layer structure, so that light in a long wavelength region can also be efficiently collected in the light receiving region, and there is little decrease in sensitivity at low illuminance. Even in the case of oblique incident light, total reflection occurs at the interface between the insulating film and the high refractive index film, and most of the incident light is collected on the photodiode. Further, the shape is simple, and the size can be reduced. Furthermore, since the surface of the insulating film is flattened, even when a wiring is formed in this upper layer, it can be formed without causing a decrease in pattern accuracy.

  Further, a high refractive index film having a refractive index of 1.9 or more can be obtained by using a silicon nitride film formed by plasma CVD as the first light-transmitting film.

  Further, it is desirable to use a tungsten film as the light shielding film. With this structure, it is possible to serve as a local wiring pattern of the peripheral circuit portion, and a wiring pattern having a high light shielding property and a low resistance can be formed in the same process.

  As described above, in the present invention, the incident light guided into the waveguide can reduce total reflection or bleeding at the interface of the void layer that is an air gap, thereby improving the light collection rate, Light in the long wavelength region can also be efficiently collected on the light receiving region, and most of the incident light is collected on the photodiode even at low illumination or obliquely incident light. In addition, the shape is simple and downsizing is possible. Accordingly, a high-speed shutter can be used, and an image with less camera shake and subject blur can be obtained.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
This solid-state imaging device has a p-well (not shown) and an n-type semiconductor layer (not shown) formed on the surface thereof as shown in FIG. 1 and FIG. A plurality of charge transfer electrodes 3 (3a, 3b) arranged on the surface of the silicon substrate 1 via the gate oxide film 2 are formed by an interelectrode insulating film 4 formed on the gate oxide film 2 at a predetermined interval. The solid-state imaging device is formed by separating the charge transfer electrodes and covering the light receiving region of the photodiode 30 as the photoelectric conversion portion with a light shielding film 7, and the opening portion is formed on the silicon nitride and the upper layer thereof. The first translucent film 20 made of a high refractive index film having a columnar structure made of the formed BPSG film is covered, and the first translucent film 20 is surrounded by the first translucent film. The refractive index is lower than that of the film 20, and the void layer g is It characterized in that it is coated with a second light-transmitting film 9 made of a silicon nitride film.

The silicon nitride film having the void layer is an NSG film formed by atmospheric pressure CVD in the trench T formed around the first light-transmitting film 20 made of a columnar high refractive index film. _Two- diluted SiH ₄ gas and oxygen gas were flowed at 900 ccm and 800 ccm, respectively, and film formation was performed at a dispersion head exhaust pressure of 70 to 150 Pa, a housing exhaust pressure of 5 to 15 Pa, and a susceptor temperature of 380 to 450 ° C. The film speed is sufficiently larger than the film forming speed on the vertical surface, and the film is formed so as to have a void layer. At this time, since the aspect ratio of the groove greatly affects the formation of the void layer, it is desirable to set the aspect ratio to about 1.5 or more. Other regions are formed in the same manner as a usual solid-state imaging device.

  The upper layer of the first translucent film 20 is made of a silicon nitride film formed by a plasma CVD method, forming a lens 10 having a convex surface, and its periphery is made of a translucent organic film. Covered with a planarizing film 70.

  Although a plan view is omitted, a plurality of photodiodes 30 are formed on the silicon substrate 1, and the charge transfer unit 40 for transferring signal charges detected by the photodiodes has a meandering shape between the photodiodes 30. It is formed to exhibit. Although not shown, the charge transfer channel through which the signal charge transferred by the charge transfer unit 40 moves is formed to have a meandering shape in a direction intersecting with the direction in which the charge transfer unit 40 extends.

  A photodiode 30 having a pn junction, a charge transfer channel, a channel stop region, and a charge readout region are formed in the silicon substrate 1 in which the p-well is formed. A gate oxide film 2 is formed on the surface of the silicon substrate 1. Is formed. On the surface of the gate oxide film 2, an interelectrode insulating film 3 made of a silicon oxide film and a charge transfer electrode 3 (charge transfer portion 40) are formed. Here, the gate oxide film is composed of a three-layer film of a silicon oxide film formed by thermal oxidation, a silicon nitride film formed by low pressure CVD, and an HTO film formed by thermal oxidation.

  Further, as shown in an enlarged view of the main part of the charge transfer unit 40, a gate oxide film 2 is formed on the surface of the silicon substrate 1 as shown in FIG. On the surface of the gate oxide film 2, a first electrode made of the first layer doped amorphous silicon film 3a constituting the charge transfer electrode and a second electrode made of the second layer doped amorphous silicon film 3b are formed from the silicon oxide film. These are laminated via an interelectrode insulating film 4 to form a multilayer electrode structure.

  A silicon nitride film 6 having a film thickness of 30 nm is formed on the second electrode via a silicon oxide film 5, and an HTO film 6S having a film thickness of 50 nm is formed on the upper layer. The HTO thin film 6S is a film for forming a path for supplying hydrogen to the photodiode (part) 30 during sintering. The upper layer is formed with a tungsten thin film 7 having a thickness of 200 nm as a light shielding layer through a titanium nitride layer 7S having a thickness of 50 nm formed by sputtering.

  As described above, the light-shielding film 7 having an opening formed in the region corresponding to the photodiode 30 is provided above the solid-state imaging device, and the photodiode region has a high height through the insulating film 21 made of a silicon oxide film. A first light-transmitting film 20 that is a refractive index film is formed in a columnar shape and is surrounded by a second light-transmitting film 9 having a void layer g. The upper layer is provided with a color filter 50 and a microlens 60 through an in-layer convex lens 10 and a planarizing film 70. Since these are the same as the usual ones, a description thereof will be omitted.

  Here, the first light-transmitting film is composed of a two-layer film of silicon nitride and a BPSG film, but it may be planarized by an etch-back process or a CMP process after the silicon nitride film is formed.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the above embodiment, a charge transfer element having a two-layer electrode structure has been described. In this embodiment, a charge transfer element having a single-layer electrode structure will be described. In this solid-state imaging device, as shown in a cross-sectional view of the main part in FIG. 3, the charge transfer electrode is a first amorphous silicon layer 3a as a first electrode and a second amorphous silicon layer 3b as a second electrode. Is different from the first embodiment in that the surface of the charge transfer electrode has a flat structure, but basically has the same structure. Have.

  A plurality of charge transfer electrodes (3a, 3b) arranged on the surface of the silicon substrate 1 via the gate oxide film 2 are formed by an interelectrode insulating film 4 formed on the gate oxide film 2 at a predetermined interval. A solid-state imaging device that is separately formed in a plurality of charge transfer electrodes and is covered with a light-shielding film 7 having an opening in a light receiving region of a photodiode 30 as a photoelectric conversion portion, wherein the opening has a columnar single layer structure The first light-transmitting film 20 made of a silicon nitride film, which is a high refractive index film, is covered, and the periphery of the first light-transmitting film 20 is refracted more than the first light-transmitting film 20. It is characterized by being covered with a second translucent film 9 made of a silicon oxide film having a low rate and having a void layer g. Other areas are the same as those of a conventional solid-state imaging device.

Next, the manufacturing process of this solid-state image sensor will be described.
First, a charge transfer electrode having a single-layer electrode structure is formed by a normal method. That is, a 25-nm-thick silicon oxide film, a 50-nm-thick silicon nitride film, and a 10-nm-thick silicon oxide film are formed on the surface of an n-type silicon substrate 1 having an impurity concentration of about 1.0 × 10 ¹⁶ cm ^−3. Then, a gate oxide film 2 having a three-layer structure is formed.

Subsequently, a phosphorus-doped first layer doped amorphous silicon film 3a having a film thickness of 0.25 μm is formed on the gate oxide film 2 by low pressure CVD using PH ₃ , N _2, and SiH ₄ . The substrate temperature at this time shall be 500-600 degreeC.

Thereafter, the first layer doped amorphous silicon film 3a is patterned by photolithography to form a first electrode, and the surface of the first electrode is thermally oxidized to form a silicon oxide film 4a having a thickness of 80 to 90 nm. Form. In this patterning, reactive ion etching using a mixed gas of HBr and O ₂ is performed to form wirings for the first electrode and the peripheral circuit. Here, it is desirable to use an etching apparatus such as an ECR (Electron Cyclotoron Resonance) system or an ICP (Inductively Coupled Plasma) system.

Similarly, a 0.6 μm-thick phosphorus-doped second-layer doped amorphous silicon film 3b is formed on this upper layer by low-pressure CVD using PH ₃ , N _2, and SiH ₄ , and CMP (chemical mechanical polishing) is performed. ) Method is used to form a second electrode in which the first and second electrodes are juxtaposed on the gate oxide film 2. Further, a silicon oxide film 4b having a thickness of 80 to 90 nm is formed on the upper layer after thermal oxidation. At this time, it is desirable to cover the first layer doped amorphous silicon film 3a with a silicon nitride film so as not to be excessively oxidized.

  Then, after removing the silicon nitride film on the photodiode, an HTO thin film of 10 nm is formed on this upper layer by a low pressure CVD method, and further, an antireflection film 5 made of a silicon nitride film having a thickness of 30 nm is formed by the CVD method, This is patterned (FIG. 4A).

  Subsequently, a silicon oxide film 7 is formed on the upper layer by CVD (FIG. 4B), and a titanium nitride layer as the adhesive layer 8 and a tungsten film as the light shielding layer 7 are formed (FIG. 4). (C)).

  Then, as shown in FIG. 5D, a positive resist R1 is applied so as to have a thickness of 0.5 to 1.4 μm, exposed using a desired mask by photolithography, developed and washed with water. A pattern R1 is formed.

Then, the light shielding film 7 and the adhesive layer 8 are patterned using the resist pattern R1 as a mask.
Then, the resist pattern R1 is ashed using oxygen plasma (FIG. 5E).

Thereafter, as shown in FIG. 6F, a silicon oxide film 22a having a thickness of 100 nm is formed by PECVD using SiH ₄ gas for preventing the light-shielding film from being altered.
Thereafter, as shown in FIG. 6G, a BPSG film 22b having a film thickness of 300 nm is formed by atmospheric pressure CVD and heated to 800 to 850 ° C. by furnace annealing to flatten the surface.

Thereafter, as shown in FIG. 7 (h), after patterning the BPSG film 22b by photolithography so that the edge is located on the charge transfer electrode, the silicon oxide film 22a and the like are further etched, and on the surface of the photodiode, Etching is performed using the antireflection film 5 as an etching stopper. At this time, the etching is performed by high-density plasma using C ₄ F ₆ .

  Then, as shown in FIG. 7 (i), a first light-transmitting film 20 made of a silicon nitride film is formed by plasma CVD, and then flattened by etchback or CMP to fill the opening on the photodiode. . Alternatively, the coating film may be formed after silicon nitride is formed by plasma CVD.

  Thereafter, as shown in FIG. 8J, a resist pattern R2 is formed by photolithography. Then, as shown in FIG. 8 (k), using this resist pattern R2 as a mask, the BPSG film 22b and the silicon oxide film 22a have an etching condition with a high etching selectivity with respect to the first light-transmitting film made of the silicon nitride film. Etching is performed to form a groove T.

Thereafter, as shown in FIG. 9L, the silicon oxide film 9 is formed as the second light-transmitting film while forming the void layer g by the plasma CVD method. At this time, the film formation conditions were TEOS: 1.2 to 1.5 ml / min, N ₂ O: 5 to 10 SLM, O ₂ : 0 to 5 SLM, susceptor temperature: 300 to 420 ° C., pressure: 1.0 to 3 0.0 Torr, high frequency RF (13.56 MHz): 0 to 1.0 kW, low frequency RF (50 to 500 kW): 0 to 1.0 kW.

Finally, as shown in FIG. 9M, the surface is flattened by resist etch back or CMP.
Thus, after forming a solid-state image sensor, a color filter, a microlens, etc. are formed, and a solid-state image sensor is completed.

  According to this method, a void layer is formed by forming a silicon oxide film in the trench T by plasma CVD, and this void layer is used as an air gap. An extremely small void layer is accurately formed. It can be formed and has high mechanical strength and is not buried.

In this way, a high refractive index film having an air gap around it is formed on the light receiving portion, and it is possible to provide a solid-state imaging device with high light collection efficiency.
Further, the surface is flat, the wiring can be easily formed, and the manufacturing is easy and the reliability is high.
In addition, a series of manufacturing processes is made efficient, and manufacturing costs can be easily reduced.

  In the above-described embodiment, a doped polysilicon film formed by annealing a doped amorphous silicon layer is used as a conductive film for forming an electrode. However, a non-doped amorphous silicon layer is formed and then formed. Doping may be performed.

  Note that the formation of the second light-transmitting film having a void layer is not limited to atmospheric pressure CVD and plasma CVD, and a method such as forming a silicon oxide film using a sputtering method may be employed. Good. In addition to the silicon oxide film, aluminum oxide or the like may be used, but in some cases, the underlying gap may be exposed in the subsequent planarization process.

  Note that the present invention is not limited to the above-described embodiment, and can be appropriately made within the scope of the technical idea of the present invention.

  As described above, the solid-state imaging device of the present invention can increase the light collection efficiency even when miniaturized, and can be miniaturized and easily manufactured. It is extremely effective as a small-sized image sensor.

It is a cross-sectional schematic diagram of the solid-state image sensor of Embodiment 1 of the present invention. It is principal part sectional drawing of the solid-state image sensor of Embodiment 1 of this invention. It is principal part sectional drawing of the solid-state image sensor of Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing process of the solid-state image sensor of Embodiment 2 of this invention. It is sectional drawing of the manufacturing process of the solid-state image sensor explaining Embodiment 2 of this invention. It is sectional drawing of the manufacturing process of the solid-state image sensor explaining Embodiment 2 of this invention. It is sectional drawing of the manufacturing process of the solid-state image sensor explaining Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate oxide film 3 Charge transfer electrode 3a 1st layer amorphous silicon film 3b 2nd layer amorphous silicon film 4 Interelectrode insulating film 5 Antireflection film 6 Silicon nitride film 7 Light-shielding film 9 2nd translucent film | membrane R1 Resist pattern R2 Resist pattern 10 Lens 20 First translucent film (high refractive index film)
30 Photodiode 40 Charge Transfer Unit 50 Color Filter 60 Microlens 70 Flattening Layer

Claims (8)

A photoelectric transfer unit, and a charge transfer unit including a charge transfer electrode configured to transfer charges generated in the photoelectric conversion unit, and having an optical waveguide that confines and propagates incident light and guides the light to the photoelectric conversion unit A solid-state imaging device,
The optical waveguide is
A columnar first light-transmitting film formed on the photoelectric conversion unit, having a predetermined refractive index and having a light guiding function;
A second translucent film having a void layer formed in a groove having an aspect ratio of 1.5 or more formed around the first translucent film ;
The void layer is formed by forming the second light-transmitting film in the groove under a condition that a film forming speed on a vertical plane is lower than a horizontal plane . The solid-state imaging device according to claim 1,
The first light-transmitting film is a solid-state imaging device made of a material having a higher refractive index than that of the second light-transmitting film. The solid-state imaging device according to claim 1 or 2,
The first light-transmitting film is a silicon nitride film, and the second light-transmitting film is a silicon oxide film. The solid-state imaging device according to any one of claims 1 to 3,
The first light-transmitting film is a solid-state imaging device having a shape processed so that an upper surface forms a convex lens shape. Forming a photoelectric conversion unit and a charge transfer unit including a charge transfer electrode for transferring charges generated in the photoelectric conversion unit on a semiconductor substrate;
Forming a columnar first translucent film in a region corresponding to a light receiving region of the photoelectric conversion unit, and forming a groove having an aspect ratio of 1.5 or more around the first translucent film; ,
And a step of forming a second light-transmitting film while leaving a void layer under a condition that a film forming speed on a vertical surface is lower than a horizontal surface in the groove . It is a manufacturing method of the solid-state image sensing device according to claim 5 ,
The step of forming the second translucent film is a method for manufacturing a solid-state imaging device, which is a sputtering step. It is a manufacturing method of the solid-state image sensing device according to claim 5 ,
The step of forming the second translucent film is a method for manufacturing a solid-state imaging device, which is a CVD step. A method for manufacturing a solid-state imaging device according to any one of claims 5 to 7 ,
A method for manufacturing a solid-state imaging device, including a step of forming a color filter and a microlens on the first translucent film.

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