JP4909538B2 - Microlens, manufacturing method thereof, solid-state imaging device using microlens, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a microlens, a manufacturing method thereof, a solid-state imaging device using the microlens, and a manufacturing method thereof, and particularly relates to a shape of the microlens.

  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, in a solid-state imaging device, pixel miniaturization has progressed due to downsizing of the solid-state imaging device and an increase in the number of imaging pixels. Along with this, miniaturization of the photoelectric conversion unit has progressed and it has become difficult to maintain high sensitivity. In order to improve the sensitivity, as shown in FIG. 8, various structures have been proposed in which the inner lens 20 and the microlens 60 are provided in the upper layer of the pixel to increase the light collection efficiency to the photodiode (note that Details of the solid-state imaging device will be described later).

  In such a conventional solid-state imaging device, the two condensing lenses of the in-layer lens and the microlens (on-chip lens) are both configured by a resist pattern or a resist pattern is formed and transferred. For example, an on-chip lens is manufactured as follows.

  First, a photodiode portion, a charge transfer portion, and a (third) planarization layer 61 are formed on the surface of the semiconductor substrate, and then a resist pattern R1 is formed on the planarization layer 61 as shown in a schematic diagram of FIG. The resist pattern R1 is formed and reflowed and cured to obtain a desired curvature (FIG. 9B).

  Alternatively, there is a method of transferring using a resist pattern formed in this way. In this method, first, a photodiode portion, a charge transfer portion, and a planarization layer 61 are formed on the surface of a semiconductor substrate, and then a silicon nitride film that becomes a lens base is formed as shown in a schematic diagram in FIG. A resist pattern R1 is formed on the upper layer, the resist pattern R1 is reflowed and cured to obtain a desired curvature (FIG. 10B), and anisotropic etching is performed using the resist pattern R1 as a mask. By transferring the surface shape of R1 to a lens substrate made of silicon nitride, an on-chip lens 60 having the same curvature as the resist pattern R1 is formed (FIG. 10C).

However, there is a problem that the sensitivity becomes non-uniform in the chip due to the incident angle of light (shading effect). In order to suppress this shading effect, a method of increasing the opening area of the light receiving portion from the center of the imaging region to the periphery has been proposed (Patent Document 1).
In addition, a method has been proposed in which the center axis of the microlens is shifted from the center of the light receiving portion opening (Patent Document 2).

Japanese Patent Laid-Open No. 7-50401 Japanese Patent Laid-Open No. 10-229180

As described above, various methods have been proposed in order to suppress the shading effect. However, in the conventional method shown in Patent Document 2 as described above, the shape obtained by reflowing the resist pattern R1 can be obtained. Although it is the outer shape of the condenser lens as it is, it is extremely difficult to shift the optical axis.
In the method disclosed in Patent Document 1, fine adjustment is difficult, and it is extremely difficult to adjust the mask by changing the shape of the resist pattern.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a microlens that is easy to manufacture and can perform desired light collection.
It is another object of the present invention to provide a solid-state imaging device that suppresses shading effects and has high sensitivity and uniform imaging characteristics.

Therefore, the microlens of the present invention includes a lens body formed to have a desired curvature, and an auxiliary lens unit including a concave portion or a convex portion locally provided on the lens body.
According to this configuration, by adjusting the number, arrangement, size, and the like of the auxiliary lens portions, it is possible to provide a micro lens having a fine structure that can be easily adjusted to the pixel size or the chip size.

Further, in the above micro-lens, the auxiliary lens unit is composed of a plurality of protrusions or a plurality of recesses provided in the lens body.
According to this configuration, adjustment is easy, and it is also possible to perform fine adjustment by adding or deleting convex portions or concave portions . Moreover, when comprised by a recessed part, the possibility of drop-off is reduced compared with the case where a local convex part is provided.

Further, the present invention includes the above microlens in which the auxiliary lens portion is made of a material having a refractive index different from that of the lens body.
According to this configuration, fine adjustment is possible by adjusting the refractive index in addition to the number, arrangement, and size of the auxiliary lens portions.

The present invention includes the microlens in which the auxiliary lens portion is formed in the same process as the lens body.
According to this structure, manufacture is easy and there is no fear of the convex part falling off by peeling.

The present invention also includes the above microlens in which the auxiliary lens portion has a different size on the same lens body.
According to this configuration, fine adjustment becomes easier.

Further, the present invention includes the above microlens in which the auxiliary lens portion is constituted by a plurality of concave portions provided in the lens body.
According to this configuration, fine adjustment is possible, and the risk of dropout is reduced as compared with the case where a local convex portion is provided.

In addition, the method of the present invention includes a step of forming a base material to be a lens body, a step of forming a resist pattern on the surface of the base material, and forming a plurality of concave portions or a plurality of convex portions locally on the resist pattern. A resist pattern correcting step, and etching the base material using the resist pattern as a mask, and transferring the resist pattern onto the base material, so that a plurality of concave portions or a plurality of convex portions are locally formed on the lens body. And a step of forming a microlens having an auxiliary lens portion.
According to this configuration, it is possible to more easily form a microlens having a plurality of concave portions or a plurality of convex portions locally by adjusting the resist pattern.

In the method of the present invention, the resist pattern correcting step includes a step of forming a minute resist pattern on the resist pattern by photolithography.
According to this configuration, it is possible to adjust with high accuracy by forming a minute resist pattern by photolithography.

In the method of manufacturing a microlens, the resist pattern correcting step includes a step of forming a fine resist pattern by potting on the resist pattern.
According to this configuration, it is possible to adjust the size and position of the minute protrusions very easily by dropping the resist material onto the resist pattern to form the minute resist pattern.

In the method of manufacturing a microlens, the resist pattern correcting step includes a step of locally removing the resist pattern from the resist pattern surface.
According to this configuration, it is only necessary to form the recesses by locally removing the resist pattern, and adjustment can be easily performed. For removal, various methods such as electron beam irradiation, sputtering, and chemical etching can be applied. It is also possible to adjust the light condensing property by simply forming irregularities by roughening treatment.

Furthermore, the present invention includes a reflow process in which the resist pattern is heated and fluidized after the resist pattern correction process in the method for manufacturing a microlens.
According to this configuration, it is possible to realize a gentle condensing characteristic and to obtain a good strength.

The solid-state imaging device according to the present invention includes a step of processing a shape of a lens base to form a lens body, a step of simulating the light collection characteristics of the lens body, and the light collection characteristics in the microlens manufacturing method. And a step of forming an auxiliary lens portion including a plurality of concave portions or a plurality of convex portions on the surface of the lens body.
According to this configuration, points to be adjusted are calculated by simulation, and adjustment with high accuracy and good reproducibility is possible.

Further, 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 a microlens is provided corresponding to the photoelectric conversion unit. The formed solid-state imaging device, wherein the microlens includes a lens body formed to have a desired curvature, and an auxiliary lens including a plurality of concave portions or a plurality of convex portions locally provided on the lens body. It consists of parts.
According to this configuration, in addition to the above effects, it is easy to adjust the light collection characteristics in accordance with the characteristics of the solid-state imaging device. In addition, an auxiliary lens unit can be provided so as to compensate for characteristic variations of the solid-state imaging device.

  Further, the present invention includes the above-described solid-state imaging device in which the auxiliary lens unit is configured by a plurality of convex portions provided on the lens body.

The present invention includes the solid-state imaging device in which the auxiliary lens unit is made of a material having a refractive index different from that of the lens body.
According to this configuration, the light collection characteristic can be adjusted also by selecting the refractive index of the auxiliary lens unit, and the characteristic adjustment range can be increased.

  The present invention also includes the solid-state imaging device in which the auxiliary lens portion is formed in the same process as the lens body.

The present invention includes the solid-state imaging device in which the auxiliary lens unit has a different size on the same lens body.
According to this configuration, it is easy to adjust the condensing characteristic on the surface of the solid-state imaging device.

  The present invention includes the solid-state imaging device in which the auxiliary lens unit is configured by a plurality of concave portions provided in the lens body.

Further, the method of the present invention includes a step of 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 substrate, and an upper layer thereof. Forming a microlens composed of a lens body formed to have a desired curvature and a plurality of concave portions or a plurality of convex portions locally provided on the lens body. Including.
According to this configuration, it is possible to provide a solid-state imaging device including a microlens having excellent light collecting characteristics very easily.

Further, according to the method of the present invention, in the method of manufacturing a solid-state imaging device, the step of forming the microlens forms a lens base on the substrate surface on which the photoelectric conversion unit and the charge transfer unit are formed. A step of forming a lens body by processing, a step of simulating the light condensing characteristic of the lens main body at the photoelectric conversion unit, and a plurality of concave portions or a plurality of convex portions on the surface of the lens main body according to the light condensing characteristic Forming an auxiliary lens portion comprising:

  With this configuration, the condensing characteristic of the lens body once formed is simulated, and the auxiliary lens portion is formed according to the condensing characteristic, so that fine adjustment is possible and the light collecting characteristic does not depend on the shape of the lens body. Since the optical characteristics can be controlled, a lens shape with excellent controllability can be obtained.

  As described above, in the present invention, the in-layer lens or the on-chip lens is not only controlled by the curvature and material of the lens body, but also by the lens body and the auxiliary lens part, so that the condensing characteristic is controlled with good controllability. It can be adjusted and an excellent microlens can be formed. Also, using this microlens, a highly sensitive solid-state imaging device can be obtained very easily with good workability.

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

(Embodiment 1)
FIG. 1 is a cross-sectional view showing the main part of a solid-state image sensor, and FIG. 2 is an explanatory view showing the top surface of a microlens formed on the solid-state image sensor. This solid-state imaging device is locally provided on a lens body 60S in which a microlens 60 to be formed has a desired curvature on a photodiode unit 30 as a photoelectric conversion unit, and the lens body. And an auxiliary lens portion 62 formed of a convex portion, which is characterized in that the light collecting characteristic is enhanced.

  According to this configuration, by adjusting the number, arrangement, size, and the like of the auxiliary lens portions, it is possible to provide a micro lens having a fine structure that can be easily adjusted to the pixel size or the chip size.

  Above the image pickup unit of the solid-state image pickup device, a layer formed of a silicon nitride film so as to serve also as a passivation film via a first planarization layer 10 made of a BPSG film formed through a silicon oxide film. A lens 20 is formed, and a second planarization layer 22, a color filter 50, a third planarization layer 61, and a microlens 60 are sequentially stacked on the upper layer.

  As shown in FIG. 1, the solid-state imaging device includes a photodiode portion 30 formed on the silicon substrate 1 and having a pn junction, and a charge transfer electrode 3 formed on the gate oxide film 2, and includes a photodiode portion. And a charge transfer unit 40 for transferring the charges generated at 30.

  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.

  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 charge transfer channel 33 composed of an n region is formed with a slight distance. A charge readout region 34 is formed in the p-well layer 1P between the n region 30b and the charge transfer channel 33.

A charge transfer electrode 3 is formed on the charge readout region 34 and the charge transfer channel 33 via the gate oxide film 2. An interelectrode insulating film 4 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.

  The upper layer of the charge transfer electrode 3 is made of a silicon oxide film 5 (passivation film), a first planarization layer 10 made of BPSG (borophospho silicate glass), an in-layer lens 20 made of P-SiN, a transparent resin, or the like. A second planarizing layer 22 is formed as a planarizing layer under the filter. Above these, a color filter 50 (red filter 50R, green filter 50G, blue filter 50B) and a micro lens 60 are provided.

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.
Needless to say, the present embodiment is not limited to a so-called honeycomb-structured solid-state imaging device, but can also be applied to a square lattice type solid-state imaging device.

Next, the manufacturing process of this solid-state imaging device will be briefly described.
The photodiode and the charge transfer unit are formed by a usual method although the explanation is omitted.
Then, a silicon oxide film (not shown) is formed on the surface of the substrate 1 on which the photodiode and the charge transfer electrode are formed by plasma CVD, and a BPSG film (10) having a thickness of 300 nm is formed by atmospheric pressure CVD. Form. Then, it heats to 700-850 degreeC by furnace annealing, reflows a BPSG film | membrane, planarizes, and obtains the 1st planarization layer 10 (refer FIG. 1).

  Then, a silicon nitride film as an inner lens 20 that also serves as a passivation film is formed on this upper layer by plasma CVD, and after shape processing, a second planarizing layer 22 is formed, and a filter layer 50 is formed. After that, a third flattening layer 61 is formed as a flat layer on the filter.

  Thereafter, the process of forming a microlens is started. First, a lens base 60 made of a silicon nitride film having a thickness of about 0.3 μm is formed by plasma CVD. (Here, only the upper layer than the third planarization layer 61 is shown, but the filter layer 50 shown in FIG. 1 is formed in this lower layer.)

  Further, a resist is applied to the upper layer and patterned by photolithography to form a resist pattern R1 as shown in FIG. Thereafter, a resist is applied again, and patterning is performed by photolithography as shown in FIG. 3B to form a minute resist pattern R2. Then, for example, heat treatment at 120 to 140 ° C. is performed to reflow, the corner portions of the resist pattern R1 and the minute resist pattern R2 are rounded by surface tension, and cooled and cured (FIG. 3C).

  Thereafter, etching is performed so that the etching selectivity ratio between the resist pattern and the silicon nitride film as the lens base is 1: 1, and as shown in FIG. A microlens provided with the auxiliary lens unit 62 is formed, and the solid-state imaging device shown in FIG. 1 is formed.

  According to this method, a microlens having an auxiliary lens portion can be formed very easily and with good controllability.

  According to this method, it is possible to improve the light condensing performance with better controllability. At this time, the convex portion as the auxiliary lens portion may be formed by using the same material as the lens base while changing the film formation conditions, or another material may be used.

  In addition, the profile differs between the center and the peripheral part of the substrate, and the height of the central axis of the lens tends to be low and the curvature tends to vary in the peripheral part. It is also possible to reduce the internal variation.

  Thereby, since the light collection efficiency can be further increased, the sensitivity of the solid-state imaging device can be increased.

In the embodiment described above, the fine resist pattern R2 having the same composition as the resist pattern R1 is formed by photolithography, but a resist having a different composition may be used.
Further, the present invention is not limited to photolithography, and a fine resist pattern may be formed by potting.
Furthermore, the resist may be potted after the lens body is formed by pattern transfer.

  Furthermore, as shown in FIG. 4, a plurality of different positions and shapes of the auxiliary lens portions may be formed.

  In addition, it goes without saying that the microlens of the present embodiment may be used as an in-layer lens.

(Embodiment 2)
Next, a second embodiment of the present invention will be described.
In the above embodiment, the case where the auxiliary lens portion is a convex portion has been described. However, as shown in FIG. 5, the auxiliary lens portion 63 may be formed to be a concave portion.

  In manufacturing, as described in the first embodiment, a silicon nitride film (60) serving as a lens base is formed on the third planarizing layer 61, and then a resist is applied and patterned by photolithography. As shown in FIG. 6A, after forming the resist pattern R1, for example, heat treatment at 120 to 140 ° C. is performed to reflow, and the corners of the resist pattern R1 are rounded by surface tension, and cooled and hardened. (FIG. 6B).

  Thereafter, minute concave portions C are formed in the resist pattern R1 by electron beam etching (FIG. 6C).

  Thereafter, etching is performed so that the etching selection ratio between the resist pattern and the silicon nitride film as the lens substrate is 1: 1, and a concave portion is formed on the lens body 60S as shown in FIG. A microlens provided with the auxiliary lens unit 63 is formed to complete a solid-state imaging device.

  According to this method, since the auxiliary lens portion is formed of a concave portion, optical control is easy, and the risk of dropping is reduced compared to the convex portion.

  In the above embodiment, the concave portion is formed in the resist pattern by electron beam etching, and the lens main body portion and the auxiliary lens portion are formed by transferring the concave portion to the lens base using this as a mask. It is also effective to roughen the surface by sputtering or plasma treatment.

(Embodiment 3)
Next, a third embodiment of the present invention will be described.
In the present embodiment, as shown in the flowchart in FIG. 7, the condensing characteristic of the lens body in the photoelectric conversion unit is simulated, and a concave or convex portion is formed on the lens body surface according to the condensing characteristic obtained by the simulation. The auxiliary lens part which consists of is formed.

First, from the layout information, the light collection characteristic on the light receiving part of the photodiode part of the solid-state imaging device is simulated (step 101).
From this simulation result, the shape information of the auxiliary lens unit is calculated so as to adjust the variation on the wafer (step 102).
Considering the auxiliary lens portion based on the calculation result, the resist pattern R1 for forming the pattern of the main body portion and the minute resist pattern information for forming the auxiliary lens portion are calculated (step 103).
Based on the obtained information, a solid-state image sensor is manufactured (step 104).

And the condensing characteristic of a solid-state image sensor is measured (step 105).
From the measurement result, it is determined whether or not the error in the light collection efficiency is within the range of the reference value (step 106). If it exceeds the reference value, trimming is performed (step 107). This trimming is performed by forming a concave portion by laser irradiation or forming a convex portion by potting (for example, dropping a resist).
When the light collection efficiency error is within the range of the reference value, the process is completed (step 108).

  According to the above method, since the condensing characteristic of the lens body once formed is simulated and the auxiliary lens portion is formed according to the condensing characteristic, fine adjustment is possible, and it does not depend on the shape of the lens body. Since the condensing characteristic can be controlled, it is possible to obtain a lens shape with excellent controllability. In this way, it is possible to form a solid-state imaging device having a uniform light collection characteristic efficiently.

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

  As described above, since the microlens of the present invention can improve the light collection efficiency and make the light collection characteristics uniform, it can be used for a small image pickup device used for a digital camera, a mobile phone, or a facsimile. It is extremely effective as a condensing lens for various devices such as a reading element.

It is a cross-sectional schematic diagram of the solid-state image sensor obtained by the method of Embodiment 1 of this invention. It is a top view which shows the micro lens used in Embodiment 1 of this invention. It is sectional drawing which shows a part of manufacturing process of the solid-state image sensor of Embodiment 1 of this invention. It is sectional drawing which shows the modification of the microlens used with the solid-state image sensor of Embodiment 1 of this invention. It is sectional explanatory drawing which shows the microlens used with the solid-state image sensor of Embodiment 2 of this invention. It is sectional explanatory drawing which shows a part of manufacturing process of the solid-state image sensor of Embodiment 2 of this invention. It is a flowchart which shows the manufacturing process of the solid-state image sensor of Embodiment 3 of this invention. It is a cross-sectional schematic diagram of the solid-state image sensor of a prior art example. It is sectional explanatory drawing which shows a part of manufacturing process of the solid-state image sensor of a prior art example. It is sectional explanatory drawing which shows a part of manufacturing process of the solid-state image sensor of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate oxide film 3 Charge transfer electrode 4 Interelectrode insulating film 5 Passivation film 10 1st planarization layer 20 Intralayer lens R1 Resist pattern R2 Small resist pattern 20 Passivation film 30 Photodiode part 40 Charge transfer part 50 Color Filter 60 Micro lens 60S Lens body 61 Third flattening layer 62 Auxiliary lens part 63 Auxiliary lens part

Claims (16)

A microlens composed of a lens body formed to have a desired curvature, and an auxiliary lens part including a plurality of concave portions or a plurality of convex portions locally provided on the lens body. The microlens according to claim 1,
  A microlens in which the auxiliary lens portion is made of a material having a refractive index different from that of the lens body. The microlens according to claim 1,
  A microlens in which the auxiliary lens portion is formed in the same process as the lens body. The microlens according to any one of claims 1 to 3,
  A microlens in which the auxiliary lens part has different sizes on the same lens body. Forming a substrate to be a lens body;
  Forming a resist pattern on the substrate surface;
  A resist pattern correction step for locally forming a plurality of concave portions or a plurality of convex portions in the resist pattern,
  Using the resist pattern as a mask, the base material is etched, and the resist pattern is transferred onto the base material, whereby an auxiliary lens portion consisting of a plurality of concave portions or a plurality of convex portions locally on the lens body. Forming a microlens having a microlens. It is a manufacturing method of the micro lens according to claim 5,
  The said resist pattern correction process is a manufacturing method of the microlens including the process of forming a micro resist pattern on the said resist pattern by photolithography. It is a manufacturing method of the micro lens according to claim 5,
  The method of manufacturing a microlens, wherein the resist pattern correcting step includes a step of forming a minute resist pattern on the resist pattern by potting. It is a manufacturing method of the micro lens according to claim 5,
  The method of manufacturing a microlens, wherein the resist pattern correcting step includes a step of locally removing the resist pattern from the resist pattern surface. A method of manufacturing a microlens according to any one of claims 5 to 8,
  A microlens manufacturing method including a reflow process in which the resist pattern is heated and fluidized after the resist pattern correction process. Forming a lens body by processing the shape of the lens substrate;
  Simulating the condensing characteristics of the lens body;
  Forming an auxiliary lens portion including a plurality of concave portions or a plurality of convex portions on the surface of the lens body in accordance with the light condensing characteristics. A solid-state imaging device including 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 a microlens is formed corresponding to the photoelectric conversion unit. There,
  The microlens is a solid-state imaging device including a lens body formed to have a desired curvature, and an auxiliary lens unit including a plurality of concave portions or a plurality of convex portions locally provided on the lens body. . The solid-state imaging device according to claim 11,
  A solid-state imaging device in which the auxiliary lens unit is made of a material having a refractive index different from that of the lens body. The solid-state imaging device according to claim 11,
  A solid-state imaging device in which the auxiliary lens unit is formed in the same process as the lens body. The solid-state imaging device according to any one of claims 11 to 13,
  A solid-state imaging device in which the auxiliary lens unit has different sizes on the same lens body. 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 substrate;
  A lens body formed to have a desired curvature above the photoelectric conversion section and the charge transfer section, and an auxiliary lens section comprising a plurality of concave portions or a plurality of convex portions locally provided on the lens body. And a step of forming a microlens composed of the solid-state imaging device. It is a manufacturing method of the solid-state image sensing device according to claim 15,
  The step of forming the microlens includes
  Forming a lens body on the surface of the substrate on which the photoelectric conversion unit and the charge transfer unit are formed, and processing the shape thereof to form a lens body;
  Simulating the condensing characteristic of the lens body in the photoelectric conversion unit;
  Forming an auxiliary lens portion including a plurality of concave portions or a plurality of convex portions on the surface of the lens main body in accordance with the light condensing characteristics.

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