JP5319370B2 - Imaging device pixel structure structure determination method, imaging device pixel structure structure determination program, and imaging device pixel structure structure determination device - Google Patents

Description

  The present invention relates to an image sensor pixel structure structure determination method, an image sensor pixel structure structure determination program, and an image sensor pixel structure structure determination apparatus.

  Conventionally, solid-state imaging devices such as a CCD (Charge Coupled Device) and a CMOS (Complementary Metal Oxide Semiconductor) are known as area image sensors for capturing an optical image. Such a solid-state imaging device is widely used in imaging devices such as video cameras and digital cameras. The solid-state image sensor includes a light-receiving pixel section in which a plurality of light-receiving pixels that photoelectrically convert an optical image of a subject formed through an imaging lens into an electric signal for each light-receiving pixel on the same semiconductor substrate, and each light-receiving pixel And a signal readout circuit portion that outputs the electrical signal to the outside of the semiconductor substrate after performing predetermined signal processing.

In recent years, in order to reduce the size of a solid-state imaging device, the pixel structure of the solid-state imaging device tends to be miniaturized and complicated. Along with this, there is a concern about sensitivity reduction and noise increase in the pixel structure, and there is an increasing need to optimize the structure of the pixel structure of the solid-state imaging device. Here, the pixel structure of the solid-state image sensor is a structure in which the light incident on the solid-state image sensor affects the propagation characteristics shown inside the solid-state image sensor. Specifically, for example, a structure having a microlens, a wiring, or the like Is the body.
Optimizing the structure of the pixel structure means obtaining values of the shape / size and characteristic values of the structure that affect the imaging result, such as the amount of light received by a photodiode on which an optical image is formed.

  In general, in order to optimize the structure of the pixel structure, first, an evaluation index of the pixel structure is obtained by simulation. Next, the pixel structure is corrected based on an empirical rule, and the evaluation index of the pixel structure is confirmed again by simulation. As described above, the optimization of the conventional pixel structure is performed by repeating the correction based on the empirical rule and the confirmation thereof, and searches for the optimal pixel structure by trial and error.

  As a method for performing the above-mentioned simulation, a simulation by optical analysis and a simulation by electromagnetic field analysis are roughly classified.

  As an example of optical analysis, Non-Patent Document 1 discloses optimization of the structure of a solid-state imaging device based on optical analysis. Non-Patent Document 1 describes an FT (Frame Transfer) image sensor provided with a microlens for condensing light in a light receiving region. According to the FT image sensor provided with this microlens, the sensitivity of light is increased. Can do.

  As an example of electromagnetic field analysis, Patent Document 1 describes a method of configuring pixels so as to optimize the structure of pixels (pixel structures) in an integrated waveguide. In the method described in Patent Document 1, an electromagnetic field analysis is performed by an FDTD method using an electromagnetic field simulation tool, and an interaction between elements constituting a pixel and light incident on the pixel is simulated. According to this method, it is possible to design an integrated waveguide in which light can suitably reach the photodetector in the pixel.

JP 2006-157001 A

N. Daemen and H.L.Peek, MICROLENSES FOR IMAGE SENSORS, Philips Journal of Research Vol.48 No.3 281-297 1994

  However, in the case of optimization by optical analysis as described in Non-Patent Document 1, although the analysis result can be obtained in a short calculation time, the calculation accuracy is relatively low. Therefore, there is a possibility that an optimal pixel structure cannot be obtained. In particular, when optical analysis is applied to a fine pixel with a structure with a length equal to or less than the wavelength of light, there is a significant difference between the parameters obtained by optical analysis and the actually optimal structure. There was a problem that a great divergence occurred.

  On the other hand, in the case of optimization by electromagnetic field analysis as described in Patent Document 1, the calculation accuracy is relatively higher than that of optical analysis, but the calculation time is relatively long. In the process of optimizing the pixel structure, it is necessary to repeat the electromagnetic field analysis based on various initial values. For this reason, if the range of the initial values to be specified is wide, there has been a problem that the number of calculations required to determine the optimal solution increases and the time required for the calculation becomes enormous. In addition, there may be no optimal solution for the specified initial value. In this case, there is a problem that a very inefficient result is that the pixel structure cannot be determined after a huge calculation time is spent. It was.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to determine a structure of an image sensor pixel structure, which can quickly and reliably determine the structure of the image sensor pixel structure, and an image sensor pixel. The object is to provide a structure determination program for a structure and a structure determination apparatus for an image sensor pixel structure.

In order to solve the above problems, the present invention proposes the following means.
The method for determining the structure of an image sensor pixel structure according to the present invention shows the size, relative positional relationship, or physical property information of the elements arranged in the image sensor pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. A first determination step of determining a first information group by optical analysis; and subsequent to the first determination step, physical property information of each of the elements in more detail than the initial conditions of the elements used in the first determination step And a second determination step of determining a second information group indicating the dimension, relative positional relationship, or physical property information of the element by electromagnetic field analysis using the first information group and the first information group as initial conditions.

  According to the present invention, since optical analysis is used in the first determination step, structure determination based on light transmission and refraction is performed. Further, in the second determination step, structure determination is performed by further adding physical property information of the imaging pixel structure by electromagnetic field analysis. At this time, the first information group determined as the optimum structure in the first determination step is used as an initial value for the electromagnetic field analysis requiring complicated calculation. Therefore, the number of trials in the electromagnetic field analysis can be reduced. Further, a condition close to the optimal image sensor pixel structure is determined in the first determination step. Therefore, it is suppressed that the calculation becomes impossible due to the solution divergence in the second determination step, and the possibility that the image sensor pixel structure can be determined increases.

In the method for determining the structure of the image sensor pixel structure according to the present invention, the optical analysis is preferably an optical analysis based on a paraxial theory.
In the method of determining the structure of the image sensor pixel structure according to the present invention, the optical analysis may be an optical analysis based on geometric optics.
In the method for determining the structure of the image sensor pixel structure according to the present invention, the optical analysis may be an optical analysis based on wave optics.

The structure determination program for an image sensor pixel structure according to the present invention is a size, relative positional relationship, or physical property information of an element disposed in an image sensor pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. A first determination step of determining a first information group indicating optical analysis, and subsequent to the first determination step, each of the elements more detailed than the initial conditions of the elements used in the first determination step A second determination step of determining, by an electromagnetic field analysis, a second information group indicating the dimension, relative positional relationship, or physical property information of the element using the physical property information and the first information group as initial conditions; It is a feature.

  According to the present invention, since the determination of the pixel structure of the image sensor can be performed on the electronic computer, it is possible to save the trouble of making a prototype of the actual optical element. In addition, since both the first determination step and the second determination step are performed by an electronic computer, iterative calculation for determining the image sensor pixel structure can be quickly performed.

An image sensor pixel structure structure determining apparatus according to the present invention indicates the size, relative positional relationship, or physical property information of an element disposed in an image sensor pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. A first determination unit for determining a first information group by optical analysis, and initial information on each physical property information of the element and the first information group, which are more detailed than the initial condition of the element used in the first determination unit. And a second determination unit that determines a second information group indicating the dimension, relative positional relationship, or physical property information of the element as a condition by electromagnetic field analysis.

  According to the present invention, the imaging element pixel structure can be determined by the first determination unit and the second determination unit. In addition, since the first determination unit and the second determination unit are provided separately, the first determination unit can be used while the second determination unit is being used to advance subsequent imaging element pixel determination. it can.

  According to the structure determination method of the image sensor pixel structure, the image sensor pixel structure determination program, and the structure determination device of the image sensor pixel structure of the present invention, the optical analysis and the optical analysis performed in advance are determined. By performing electromagnetic field analysis in which the obtained value is used as an initial value, the structure of the image sensor pixel structure can be determined quickly and reliably.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus whose structure is determined by a structure determination method for an image sensor pixel structure according to a first embodiment of the present invention. FIG. It is sectional drawing which expands and shows the image sensor in the imaging device. It is a flowchart which shows the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows a part of process in the structure determination method of the image pick-up element pixel structure of the embodiment. (A) thru | or (D) is a figure which shows typically one process of the structure determination in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a figure which shows typically one process of the structure determination in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows a part of process in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows a part of process in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows a part of process in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows a part of process in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a flowchart which shows the modification in the structure determination method of the image pick-up element pixel structure of the embodiment. It is a block diagram which shows schematic structure of the image pick-up element pixel structure determination program and image pick-up element pixel structure determination apparatus of 2nd Embodiment of this invention.

(First embodiment)
The structure determination method for the image sensor pixel structure according to the first embodiment of the present invention will be described below with reference to FIGS.
(Configuration of pixel structure)
First, the configuration of the pixel structure will be described by taking an imaging device including the pixel structure of the present embodiment as an example.
FIG. 1 is a block diagram illustrating a schematic configuration of an imaging apparatus whose structure is determined by the structure determination method of the imaging element pixel structure according to the present embodiment.

  As shown in FIG. 1, the imaging apparatus 1 includes an imaging optical system 2 that collects light incident from the outside at a predetermined imaging position, and a light receiving region 3 a that receives the light collected by the imaging optical system 2. And an image pickup device 3 for picking up an optical image, a circuit 4 such as CDS (Correlated Double Sampling) / AGC (Automatic Gain Control) / ADC (Analog to Digital Converter), and the optical image read out by the circuit 4 An image processing circuit 5 for processing a digital signal, a display unit 6 capable of displaying captured image information, and a storage medium 7 having, for example, a nonvolatile memory for storing the captured image information are provided.

  FIG. 2 is a cross-sectional view showing the image sensor 3. As shown in FIG. 2, the image sensor 3 of the present embodiment is a CMOS area image sensor. In addition, the image pickup device 3 has a plurality of pixels (pixel structures) arranged side by side like the pixels 31, 32, 33,. Although not shown in detail, in the imaging device 3, the pixels are arranged in a lattice pattern along the surface of the light receiving region 3a.

Hereinafter, the configuration of the pixel 31 (see FIG. 1) located near the center of the light receiving region 3a will be described. The schematic configuration is the same for the other pixels.
The pixel 31 includes elements 12 to 21 arranged in the thickness direction so as to overlap with the imaging element forming region 11 configured on the semiconductor substrate 10 and the imaging element forming region 11. Specifically, a photodiode (element 12) that is a light receiving element and an FD (Floating Diffusion) (element 13) that detects charges accumulated in the photodiode are provided in the imaging element formation region 11. ing.

  Further, as a specific example of the element arranged so as to overlap the imaging element forming region 11, a polysilicon transfer electrode (element 14) arranged on the surface of the semiconductor substrate 10 and an insulating interlayer insulating film (element) 15), a wiring layer (elements 16, 17, 18) which is a wiring circuit arranged via an interlayer insulating film, a protective film (element 19) laminated on the wiring layer, and further laminated on the protective film A color filter (element 20) and a microlens (element 21) which are optical systems.

  The elements 12 to 21 are elements that require optimization of the arrangement, shape, and physical properties in order to efficiently receive light incident on the pixels 31.

  As shown in FIG. 2, light enters the pixel 31 from the microlens (element 21) side. For example, the incident light beam 22 to the pixel 31 is refracted by the microlens (element 21), passes through the gap between the multilayer wiring layers (elements 16, 17, and 18), is received by the photodiode (element 12), and is photoelectrically converted. The

Here, the opening angle α 0 of the incident light beam 22 is determined by the F number of the imaging optical system 2.
In FIG. 2, the incident light beam 22 is shown as an example of light incident on the pixel 31, but the incident light beam is not limited to the incident light beam 22. That is, there is an incident light beam incident from another position of the microlens.

  Although details are not shown, in the image sensor 3, the incident light beam travels substantially along the normal direction of the surface of the light receiving region 3a at the center of the light receiving region 3a. Further, the incident light flux has an angle with respect to the normal of the surface of the light receiving region 3a as it goes from the center to the periphery of the light receiving region 3a. For this reason, the incident light flux in the pixels in the periphery of the light receiving area 3a enters the pixel with a light flux tilt angle (for example, a light flux tilt angle β0) corresponding to the position on the light receiving area 3a.

(Structure determination method of image sensor pixel structure)
Hereinafter, a method for determining the structure of the above-described imaging element pixel structure (pixels 31, 32, 33,...) Will be described with reference to FIGS.
The structure determination of the pixel structure is to determine the optimum condition of the structure (size, arrangement, physical properties) of the elements 12 to 21 in the pixel. Here, the optimum condition is a condition in which the sensitivity of light in the photodiode (element 12) is the highest.

  FIG. 3 is a flowchart showing an outline of the structure determination method of the image sensor pixel structure according to the present embodiment. As shown in FIG. 3, the structure determination method for the image sensor pixel structure according to the present embodiment includes a first determination step S <b> 1 and a second determination step S <b> 2 executed subsequent to the first determination step S <b> 1. .

Below, 1st determination process S1 is explained in full detail.
The first determination step S1 is a step of determining a first information group indicating the dimensions, relative positional relationship, or physical property information of the elements 12 to 21 by optical analysis.

  FIG. 4 is a flowchart showing the first determination step S1. As shown in FIG. 4, the first determination step S1 includes a step S11 for determining the power arrangement of the microlens (element 21) and a step S12 for determining the arrangement of the wiring layers (elements 16, 17, and 18). ing. Step S11 and step S12 are both steps for determining the structure of a pixel (for example, pixel 31) located in the center of the light receiving region 3a.

  In addition, the optimum condition of the pixel structure is different between the center and the periphery of the light receiving region 3a due to the difference in the inclination of the incident light beam. For this reason, the first determination step S1 includes a step S13 of correcting the structure of pixels that are incident with a light beam tilt angle around the light receiving region 3a. In step S13, the pixel structure is corrected using the conditions determined in steps S11 and S12 as initial conditions.

Below, how to handle the incident light beam in the first determination step S1 will be described with reference to FIG. FIG. 5 is a schematic diagram schematically showing a state in which the first determination step S <b> 1 is applied to the pixel 31.
5A to 5C, in the first determination step S1, the incident light beam 22 incident on the outermost periphery of the micro lens (element 21) of the pixel 31 is opposite to the incident light beam 22 across the optical axis. An incident light beam 23 incident on the outermost periphery of the side microlens (element 21) and an incident light beam 24 incident near the optical axis of the microlens (element 21) are shown.

Here, the opening angles of the incident light beams 22, 23, and 24 are α0 in common. When the F number of the imaging optical system 2 is FN, α0 = sin ⁻¹ (1 / (2FN)). Further, as shown in FIG. 5D, the most peripheral rays incident from the X side are extracted from the incident light beams 22, 23, and 24, and these are considered as new incident light beams 25. In this way, the incident light fluxes 22, 23, and 24 collected at an angle of 2α0 toward the microlens (element 21) are incident light fluxes that are collimated light having an inclination angle of 2α0 toward the microlens (element 21). Replace with 25.

  FIG. 6 is a diagram schematically showing elements for which structure determination is performed in the first determination step S1. Here, each symbol shown in FIG. 6 will be described. P is a pitch indicating the width per pixel, W is the width of the photodiode (element 12), E1 and E2 are based on an axis (optical axis O1) passing through the top of the microlens (element 21) in the pixel 31 The distance between the wiring layers (elements 16, 17, and 18) measured as D, D is the total thickness of the interlayer insulating film (element 15) and the protective film (element 19), and R1 is the radius of curvature of the microlens (element 21) , H is the thickness of the microlens (element 21), G is a half value of the difference between the pitch P and the width W, and α1 is a microlens of light incident on the microlens (element 21) at an angle α0 (element 21). Refractive angles in element 21) are respectively represented.

  In determining the structure of a pixel such as the pixel 31, the adjustment range of elements 12 to 21 described below is limited in advance depending on conditions such as the specifications of the imaging device 1 or the manufacturing process of the imaging element 3.

  Specifically, the pitch P of the pixels 31 is already determined by the specifications of the imaging device. The width W of the photodiode (element 12) is determined by manufacturing process constraints. The materials of the other elements 13 to 21 are determined by the manufacturing process, and the refractive index and dispersion in the region through which the incident light beam 25 is transmitted are known. The lower limit value of the radius of curvature R1 of the microlens (element 21) is determined by the manufacturing process. When the curvature radius R1 is determined, the thickness H of the microlens is also uniquely determined by the manufacturing process. Further, the lower limit of the value G is also determined by the manufacturing process. Furthermore, the thickness of the color filter (element 20) is determined in advance by the color characteristics determined by the specifications of the imaging device 1.

  Therefore, the variable elements in the present embodiment are the dimensions and arrangement of the elements 16, 17, and 18 related to the size of the distances E1 and E2, the size and arrangement of the element 21 related to the size of the curvature radius R1, and the thickness. This is the thickness of the interlayer insulating film (element 15) and the protective film (element 19) related to the size of the thickness D.

Hereinafter, the process of determining the variable in the first determination process S1 will be described with reference to FIGS.
First, step S11 for determining the power arrangement of the microlens is performed. FIG. 7 shows a detailed flow of step S11.

First, a lower limit value R1 _min of the radius of curvature R1 of the microlens (element 21) is obtained using a pitch P and a value G, which are predetermined values (step S111). In step S111, the value of R1 _min is calculated as R1 _min = P / 2−G.

Subsequently, the focal length f1 and the refraction angle α1 of the microlens (element 21) at R1 _min are obtained by well-known paraxial ray tracing, and there is a thickness D that satisfies the following conditions a) and b). Whether or not (step S112). Note that the thickness D has a limit on the range of values that can be taken by the pixel manufacturing process.
a) f1≈> D
b) α1f1 <≈W / 2

  The condition b) represents the approximate size of the image at the imaging position of the incident light beam 25. In the first determination step S1, as described above, there is no difference in refractive index between the microlens (element 21), the interlayer insulating film (element 15), the protective film (element 19), and the color filter (element) as the condition b). An approximate expression in the case of the above can be adopted.

Further, in step S112, when D satisfying both the conditions a) and b) is not found in the state of R1 = R1 _min , the value of the radius of curvature R1 is gradually increased from R1 _min . When the radius of curvature R1 is increased, the focal length of the microlens (element 21) is increased. Therefore, it is necessary to increase the thickness D for suitably forming an optical image on the photodiode (element 12). There is.

When D satisfying both of the above conditions a) and b) can be obtained by greatly changing the radius of curvature R1, it corresponds to the thickness D _b that satisfies both of the above conditions a) and b) and the thickness D _b . A radius of curvature _Rb is determined. Subsequently, the process proceeds to second process S12 to determine the arrangement of the wiring layer under the condition that the curvature radius _{R b} corresponding has been determined to a thickness _{D b} (elements 16, 17, 18).

  If an appropriate value is not obtained as the thickness D even if the radius of curvature R1 is reduced, NO is selected in step S113. Then, in addition to the microlens (element 21), an intralayer lens (not shown) is further interposed between the in-layer insulating film (element 15) and the protective film (element 19) (step S115). ). In step S115, the radius of curvature R1, R2 is set so as to satisfy the following b ′) where R12 is the combined radius of curvature of the microlens and the intralayer lens when the radius of curvature of the intralayer lens is R2, and f12 is the combined focal length. To decide.

  b ') α1f12 <≈W / 2

  Subsequently, it is examined whether or not D satisfying the following a ′) exists under the condition in which the curvature radii R1 and R2 determined in b ′) are determined (step S116).

  a ′) f12≈> D

  In step S116, when D satisfying the above a ′) can be adjusted in the manufacturing process (YES), the process proceeds to step S114, and the thickness D is determined. When D satisfying a ′) cannot be adjusted (NO), the process proceeds to step S117, and R1 and R2 are determined so as to satisfy b ′) of step S115 with respect to the shortest thickness D that can be adjusted in the manufacturing process. Then, step S11 is completed.

  As described above, in step S11 for determining the power arrangement of the microlens, the dimensions and arrangement of the element 15, the element 19, and the element 21 (and the in-layer lens) among the elements 12 to 21 are determined. Note that if the determination in step S11 is not final but results are inappropriate in the subsequent steps, step S11 may be executed again.

  Subsequent to step S11, step S12 for determining the wiring arrangement is performed. FIG. 8 is a flowchart showing the details of step S12. In step S12, the wiring layer (elements 16, 17, and 18) only considers the function as a field stop. Further, in step S12, the step of determining the arrangement of the element 18 arranged farthest from the photodiode (element 12) among the wiring layers (elements 16, 17, and 18) is first executed. Subsequently, after the arrangement of the elements 18 is determined, step S11 for the elements 17 is performed. In this manner, the arrangement is determined in order from the element 12 with respect to each of the wiring layers. Hereinafter, step S11 for the element 18 will be described as a representative.

  As shown in FIG. 8, first, initial values of the wiring layer intervals E1 and E2 are set (step S121). In the present embodiment, predetermined initial values are used as initial values of E1 and E2, and E1 = E2 = W / 2. Note that other initial values may be adopted as necessary.

  Subsequently, in the range where the opening angle of the incident light beam 25 is 0 ± α0 degrees, several positions including the position where the opening angle = 0 degrees are selected, paraxial marginal ray tracing is performed, and the aperture ratio is measured. (Step S122).

  Subsequently, the amount of light reaching the photodiode (element 12) is estimated on the basis of the aperture ratio, and the magnitude of the light amount drop at a position where the opening angle is other than 0 degrees is calculated (step S123).

  Subsequently, it is confirmed whether or not the light amount drop calculated in step S123 satisfies the specification of the imaging device 1 (step S124). If the specification is satisfied (YES), step S12 is completed as it is.

When the specification is not satisfied (NO), the values of the wiring layer (element 18) intervals E1 and E2 are gradually enlarged, and the processes from step S122 to step S124 are repeated.
If an appropriate wiring layer interval cannot be found within the limits of the manufacturing process, the process returns to step S11 of the power arrangement of the microlens, the thickness D is shortened, and step S12 is performed again.

  When step S12 is completed, the structure of the peripheral pixels provided in the peripheral portion in the light receiving region 3a is determined based on the variables determined up to step S12. As a method for determining the structure of the peripheral pixels, a method for correcting the structure determined for the central pixel is employed.

  FIG. 9 is a flowchart showing the details of step S13. Hereinafter, a peripheral pixel in which the incident light beam 25 is incident at an inclination of β0 degrees among the peripheral pixels will be described as an example. As shown in FIG. 9, first, in the incident light beam 25 having the inclination angle β0, the light beam passing through the center of the microlens (element 21) is near the surface top of the microlens (element 21) and the photodiode (PD, element). 12) The microlens (element 21) is decentered along the surface of the light receiving region 3a so as to pass through the vicinity of the center of step 12) (step S131). When the above-described interlayer lens is used together with the microlens, both the microlens and the interlayer lens are decentered.

  The amount of eccentricity of the microlens (element 21) is determined by being decomposed into axial components centering on two orthogonal straight lines based on the pixel arrangement direction starting from the center of the light receiving region.

  Subsequently, in the range where the opening angle of the incident light beam 25 is 0 ± α0 degrees, several positions including the position where the opening angle = 0 degrees are selected, paraxial marginal ray tracing is performed, and the aperture ratio is measured. (Step S132).

  Subsequently, the amount of light reaching the photodiode (element 12) is estimated based on the aperture ratio, and the magnitude of the light amount drop at a position where the opening angle is other than 0 degrees is calculated (step S133).

  Subsequently, it is confirmed whether or not the light amount drop calculated in step S123 satisfies the specification of the imaging device 1 (step S134). If the specification is satisfied (YES), step S13 is completed as it is.

  If the specification is not satisfied (NO), the position of the wiring layer (element 18) is decentered along the surface of the light receiving region 3a, and Steps S132 to S134 are repeated.

Thus, by the first determination step S1 including the steps S11 to S13, the first information group I1 indicating the dimensions, relative positional relationship, or physical property information of the elements 12 to 21 is determined by optical analysis.
In the first determination step S1 performed by optical analysis, the first information group I1 for the elements 12 to 21 is determined as a fixed value. However, when determining the structure of a fine pixel having a structure having a length equal to or shorter than the wavelength of light, for example, there is a remarkable difference between the parameter obtained by optical analysis and the actually optimal structure. Deviation may occur.
In order to solve this problem, in the present embodiment, the second determination step S2 is executed subsequent to the first determination step S1.

Below, 2nd determination process S2 of this embodiment is explained in full detail.
The second determination step S2 is a step of determining a second information group indicating the dimensions, relative positional relationship, or physical property information of the elements 12 to 21 by electromagnetic field analysis.

FIG. 10 is a flowchart showing in detail the second determination step S2 for optimizing the pixel structure using electromagnetic field simulation. As shown in FIG. 10, in the second determination step S2, first, the approximate pixel structure determined in the first determination step S1 is input (step S21).
Subsequently, physical property values more detailed than the initial values of the dimensions and arrangement of the elements 12 to 21 used in the first determination step S1 are input as pixel structure initial values in the second determination step S2 (step S22).

  In step S22, detailed shape information (dimensions and arrangement including three-dimensional asymmetry) of the microlens (element 21) and the wiring layer (elements 16, 17, and 18) is added to the substantially pixel structure input in step S21. To do. In addition to the refractive index and its dispersion, an absorption coefficient and its dispersion are added as the physical property values of the components of the pixel. Alternatively, the dielectric constant, magnetic permeability, electrical conductivity, etc. may be used. As a physical property value, a well-known Drude model or a multi-loss induced Lorentz model may be used.

Subsequently, the electromagnetic field simulation is performed after setting the light source information and the photodetector in preparation for the electromagnetic field simulation (step S23).
Known methods of electromagnetic field simulation include FEM (Finite Element Method), FDFD method (Finite-Difference Frequency-Domain Method), and FDTD method (Finite-Difference Time-Domain Method, There are several things including finite difference time domain methods.

  In preparation for executing the electromagnetic field simulation, first, a light source that emits a luminous flux incident on a pixel is set. For example, the setting of whether the light source is a continuous light source or a pulse light source, the center wavelength, the amplitude, and the like. As the opening angle and inclination angle of the incident light beam, the opening angle α0 and the inclination angle β0 set in the first determination step S1 can be used. In addition, an electromagnetic field observation area is set as a preparation. For example, a plurality of observation regions may be provided as necessary so as to be set to the photodiode (element 12) of the pixel 31 and the photodiode (element 12) of the adjacent pixel 32. Further, the observation region may be set at a place other than the element 12, for example, may be provided on the surface of the pixel 31.

Subsequently, based on the electromagnetic field information obtained in step S23, values such as optical efficiency, peripheral light loss, and crosstalk are calculated (step S24).
Optical efficiency is the ratio of the spectral irradiance of light incident on the pixel photodiode (element 12) to the spectral irradiance incident on the pixel surface. These irradiances can be calculated by obtaining a pointing vector from electromagnetic field data.

The performance evaluation index of the pixel may be the total received light amount obtained by integrating the pointing vectors in the photodiode region, or the total received light amount may be multiplied by a coefficient such as the sensitivity coefficient of the pixel and the exposure time of the imaging device. You may convert into the total electric charge to generate | occur | produce.
Further, the pixel performance evaluation index may be a ratio (shading) of the light reception amount of the peripheral pixels to the light reception amount of the pixels near the center of the image sensor.

  The pixel performance index may be the amount of crosstalk between adjacent pixels. Note that all of the indexes described above may be used, or indexes other than those described above may be introduced. A program for calculating these evaluation indexes can be created using a commercially available numerical analysis program: MATLAB or the like.

Subsequently, it is determined whether or not the optical efficiency, peripheral light amount drop, crosstalk, and the like have reached a predetermined target (step S25).
In step S25, it is determined whether or not the performance evaluation index calculated in step S24 has reached the target value of the imaging apparatus 1. If the performance evaluation index calculated in step S24 is equal to or greater than the target value, it is determined that the dimensions, arrangement, and material of the pixel components are sufficiently optimized, and the second determination step S2 is completed.
On the other hand, if the performance evaluation index calculated in step S24 does not reach the target value, the process proceeds to step S26.

If the optical efficiency, peripheral light loss, crosstalk, etc. have not reached the target, the dimensions, arrangement, and physical property values of the elements constituting the pixel structure are changed (step S26).
In step S26, the dimensions, arrangement, and materials of the components set in step S22 are changed. Further, a new component, for example, a member that shields light other than the photodiode (element 12) may be added.

  Subsequently, steps S23 to S25 are repeated until (YES) is selected in step S25 based on the dimensions, arrangement, and physical property values of the elements 12 to 21 changed in step S26.

  If YES is selected in step S25, the second determination step S2 is completed. In the second determination step S2, the second information group I2 indicating the dimensions, arrangement, and materials of the elements 12 to 21 is determined. Thereby, the structure of the pixel structure such as the pixel 31 in the image sensor 3 can be determined.

  As described above, according to the structure determination method of the image sensor pixel structure of the present embodiment, the first determination step S1 uses optical analysis to determine the structure based on light transmission and refraction. Furthermore, in the second determination step S2, structure determination is performed by further adding physical property information of the imaging pixel structure by electromagnetic field analysis.

  At this time, the first information group I1 determined as the optimum structure in the first determination step S1 is used as an initial value for the electromagnetic field analysis requiring complicated calculations. Therefore, the number of trials in the electromagnetic field analysis can be reduced.

  In addition, a condition close to the optimal image sensor pixel structure is determined in the first determination step S1. Therefore, it is suppressed that the calculation becomes impossible due to the solution divergence in the second determination step S2, and the possibility that the image sensor pixel structure can be determined increases.

(Modification)
Below, the modification of the structure determination method of the image pick-up element pixel structure of 1st Embodiment is demonstrated with reference to FIG. FIG. 11 is a flowchart showing a second determination step in the structure determination method of the image sensor pixel structure according to this modification.

  As shown in FIG. 11, in the present modification, a step S27 for generating a new structure according to a predetermined algorithm is provided between the step S25 and the step S26.

  In step S27, for example, the nonlinear optimization procedure disclosed in Philip E. Gill, Walter Murray, and Margaret H. Wright, “Practical Optimization”, Academic Press, Inc., San Diego, CA, 1981 is performed in MATLAB or the like. Software is used.

  Further, step S27 may be performed by linking electromagnetic field simulation software to optimization software such as Engineers Japan: iSIGHT.

In addition, a change amount of the performance evaluation index of the pixel with respect to a minute change in the physical property value of the pixel component size, arrangement, and the material may be tabulated, and a new pixel structure may be generated based on the table. good.
By including the step S27 in this manner, new settings for reconfiguring the pixel structure when the pixel performance index does not reach the target are facilitated.

(Second Embodiment)
Hereinafter, a structure determination program for an image sensor pixel structure and a structure determination apparatus for a state image sensor pixel structure according to a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the same parts as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.
FIG. 12 is a block diagram showing a schematic configuration of a structure determining device 50 (hereinafter referred to as “structure determining device 50”) of the image sensor pixel structure according to the present embodiment.

  As illustrated in FIG. 12, the structure determination device 50 according to the present embodiment includes an input unit 51 for inputting information on the dimensions and arrangement positions of the elements 12 to 21, and pixels based on values input in the input unit 51. An HDD (Hard Disk Drive) 52 storing a structure determination program 100 for determining a structure, a RAM (Random Access Memory) 53 storing temporary information based on the structure determination program 100 and the structure determination program 100, and a structure determination A CPU (Central Processing Unit) 54 that performs arithmetic processing based on a command from the program 100 and a display unit 55 that displays a result of arithmetic processing performed by the CPU 54 are provided.

  The structure determination program 100 has a first determination step S1 and a second determination step S2. In the present embodiment, the HDD 52 stores a first determination unit 101 that executes the first determination step S1 and a second determination unit 102 that executes the second determination step S2 that are logically divided.

  In the present embodiment, both the first determination step S1 and the second determination step S2 described in the first embodiment are executed as a simulation by an electronic computer.

  The first determination step S1 can be performed using commercially available optical design software Code-V, Zemax, LightTools, or the like. If the optimization function of these commercially available optical design software is used, the step of determining the power arrangement of the microlens, the step of determining the wiring arrangement, and the step of correcting the structure of the peripheral pixels can be performed simultaneously. That is, optimization is performed using the specifications of the imaging device 1 (the amount of light received by the pixels, the amount of decrease in peripheral light amount, etc.) as target values, and the above-described R1, R2, D, E1, E2, and the amount of eccentricity of the microlens or wiring layer as parameters Should be executed.

  The second determination step S2 can be performed using commercially available optical design software. For example, commercially available products such as Optiwave: OptiFDTD and Lumerical: FDTDSolutions can be used.

  According to the structure determination program 100 of the present embodiment, the determination of the image sensor pixel structure can be performed on an electronic computer, so that it is possible to save the labor of making a prototype of the actual optical element. In addition, since both the first determination step S1 and the second determination step S2 are performed by an electronic computer, iterative calculations for determining the image sensor pixel structure can be quickly performed.

  In addition, according to the structure determination device 50 of the present embodiment, the first determination unit 101 and the second determination unit 102 can determine the imaging element pixel structure. The first determination unit 101 and the second determination unit 102 are provided separately. For this reason, while the 2nd determination part 102 is used, the 1st determination part 101 can be used and subsequent image pick-up element pixel determination can be advanced, and the structure determination of a pixel structure can be performed efficiently. .

  In general, enormous calculation time is required when electromagnetic field analysis is used. For example, when an electromagnetic field analysis is performed on the behavior of light when visible monochromatic light is incident on an image sensor pixel having a pixel pitch of several μm, a general personal computer requires several hours to several tens of hours. In order to optimize the pixel structure, it is necessary to repeat this electromagnetic field analysis, which requires several times to several tens of times of calculation time. Moreover, even if iterative calculation is performed, the optimal solution may not always be obtained because the solution diverges or vibrates.

  In the structure determining apparatus 50 of the present embodiment, a pixel structure close to the optimal solution can be obtained by the first determining step S1. By using the result of the first determination step S1 as the initial value in the second determination step S2, when optimizing the pixel structure in the second determination step S2, the optimization result of the pixel structure with a smaller number of calculations than before. Can be obtained.

  Therefore, in the structure determination apparatus 50 of this embodiment, the calculation time required for optimization can be reduced by about several tens of percent compared to the conventional method. This corresponds to a reduction of several tens of hours to several hundreds of hours in an electronic computer having a processing capability of the above-described personal computer. As a result, there is an effect that the pixel structure can be determined even with an electronic computer having an arithmetic processing capability similar to that of a personal computer that is generally popular.

As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.
For example, in the first embodiment, the two-dimensional approximate size and the approximate arrangement along the surface of the light receiving region 3a are determined in the first determination step S1, but the present invention is not limited to this, and the three-dimensional structure of the pixel in the first determination step. Can also be determined by optical analysis.

  In the first embodiment, an example is shown in which the dimensions and arrangement of elements determined in advance by the specifications of the imaging device or the manufacturing process are not variables. However, the present invention is not limited to this, and the dimensions and arrangement of the elements can be determined as variables within the adjustable range in the first determination step.

  In the first embodiment, the first determination step S1 has been described as being calculated by the paraxial ray tracing method. However, the present invention is not limited to this, and the first determination step is also performed by the geometric optical ray tracing method. Can do. In this case, since the size and arrangement of the image sensor pixel structure can be determined with higher accuracy than that performed by the paraxial ray tracing method, the number of calculations in the second determination step, that is, accuracy can be reduced with a short calculation time. A high pixel structure optimization result can be obtained.

  Furthermore, the first determination step can also be performed by wave optical analysis. In this case, the size and arrangement of the image sensor pixel structure can be determined with higher accuracy than the geometric optical ray tracing method. Therefore, it is possible to obtain a highly accurate optimization result of the pixel structure with a smaller number of calculations, that is, with a shorter calculation time in the second determination step.

  In the first embodiment, the example in which the structure is determined for the center and the peripheral two regions in order to determine the structure of the pixel has been described. However, the present invention is not limited to this. It is also possible to determine the structure for a plurality of pixels (for example, at predetermined intervals). In this case, it is possible to individually design the pixel structure at multiple points, which was impossible to execute because the time required for structure determination in the conventional method is enormous, and the degree of light loss between the center and the periphery of the light receiving area It is possible to adjust to a suitable structure in response to the change of.

12, 13, 14, 15, 16, 17, 18, 19, 20, 21 Element 31, 32, 33 Pixel (image sensor pixel structure)
I1 1st information group I2 2nd information group S1 1st determination process S2 2nd determination process 101 1st determination part 102 2nd determination part

Claims (6)

First determination to determine, by optical analysis, a first information group indicating the size, relative positional relationship, or physical property information of the element disposed in the imaging element pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. Process,
Subsequent to the first determination step, the physical property information of the element and the first information group more detailed than the initial condition of the element used in the first determination step, the dimensions of the element, relative A second determination step for determining a second information group indicating positional relationship or physical property information by electromagnetic field analysis;
A method for determining a structure of an image sensor pixel structure.   The structure determination method for an image sensor pixel structure according to claim 1, wherein the optical analysis is an optical analysis based on a paraxial theory.   The structure determination method for an image sensor pixel structure according to claim 1, wherein the optical analysis is an optical analysis based on geometric optics.   The structure determination method for an image sensor pixel structure according to claim 1, wherein the optical analysis is an optical analysis based on wave optics. First determination to determine, by optical analysis, a first information group indicating the size, relative positional relationship, or physical property information of the element disposed in the imaging element pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. Process,
Subsequent to the first determination step, the physical property information of the element and the first information group more detailed than the initial condition of the element used in the first determination step, the dimensions of the element, relative A second determination step for determining a second information group indicating positional relationship or physical property information by electromagnetic field analysis;
For determining the structure of an image sensor pixel structure that causes a computer to process the image. First determination to determine, by optical analysis, a first information group indicating the size, relative positional relationship, or physical property information of the element disposed in the imaging element pixel structure having at least a light receiving element, a wiring circuit, and an optical system as elements. And
Second indicating the dimension, relative positional relationship, or physical property information of the element using the physical property information of the element and the first information group more detailed than the initial condition of the element used in the first determination unit as an initial condition . A second determination unit for determining an information group by electromagnetic field analysis;
An apparatus for determining a structure of an image sensor pixel structure.

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