JP2006128371A - Solid state image pickup device and its measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of accurately measuring the shape of pixels formed on each layer of a solid state image pickup device and the quantity of positional deviation between the layers to clarify the relation with the optical characteristics. <P>SOLUTION: The solid state image pickup device 10 has a multilayer laminate structure. Laminating marks 14 adjacent to pixels 20 of the peripheral edge of the effective pixel region 11 are formed on each layer outside the effective pixel region. Each time each layer is formed, the laminating marks 14 and the surface shape near them are measured to obtain data of the shape of the pixel constituent element and the quantity of positional deviation between the layers. The optical characteristics of corresponding pixel 20 are measured to the relation of the optical characteristics to nondestructively take hold of the shape of the pixel constituent element and the quantity of positional deviation between the layers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device and a measurement method thereof, and in particular, in a solid-state imaging device having a laminated structure, the shape and the amount of positional deviation of a pixel portion of each layer can be accurately measured, and the relationship between the optical characteristics is clarified. The present invention relates to a solid-state imaging device that can be used and a method for measuring the solid-state imaging device therefor.

  In the solid-state imaging device, the number of pixels is increased and the pixel size is miniaturized. As a result, the sensitivity and the color characteristics are deteriorated, and the SN ratio and the image quality are deteriorated. In order to solve this problem, a structure is used in which an on-chip microlens is formed on the top of the photodiode to increase the light collection rate on the photodiode.

  The on-chip microlens has a large change in the light collection rate on the photodiode depending on its shape and position. In addition, the relative positional relationship of the components of each pixel including the microlens on the upper layer of the photodiode is also important, and a slight positional deviation may be intentionally set in order to obtain the optimum characteristics of the photodiode.

  As described above, it is important in manufacturing a solid-state image pickup device to understand how the shape and the amount of positional deviation of the components of the pixel portion in each layer of the solid-state image pickup device are related to the optical characteristics of the solid-state image pickup device. is there.

  For this reason, the pixel portion of the solid-state imaging device is sliced into a plurality of cross sections with FIB (Focused Ion Beam), and a plurality of SEM images are created by a plurality of SEMs (Scanning Electron Microscope). A method of obtaining a three-dimensional shape has been performed.

  Also proposed is a method of determining the microlens shape defect by forming a ground pattern outside the imaging area and forming an inspection microlens above it, and observing the ground pattern with a microscope through this microlens for inspection. (For example, refer to Patent Document 1).

In addition, in the dummy pixel area outside the effective pixel area, the pattern of some of the pixels is shifted stepwise from the original design value between multiple layers that affect the optical characteristics of the pixel sensor. A method has been proposed in which an error measurement pixel region is provided and the relationship between optical characteristics and pattern deviation is obtained from the output of each pixel sensor in the error measurement pixel region (see, for example, Patent Document 2).
JP-A-11-307750 JP 2003-218334 A

  However, in the method of obtaining the three-dimensional shape of the pixel component from the SEM image of the cross section sliced by the FIB described above, it can be performed only by destructive inspection, and cannot be used for evaluation of the product, and the evaluation takes time. There was a problem.

  Further, in the method described in the above-mentioned Patent Document 1, it can be used for determining the shape defect of the microlens, but the influence of the positional deviation amount cannot be known, and the shape of the pixel constituent elements in the plurality of layers There is a problem that the influence of the positional deviation is not clarified and the structure of a truly optically excellent solid-state imaging device cannot be known.

  Furthermore, in the method described in the above-mentioned Patent Document 2, how the shape factor of the pixel component formed in each layer affects the optical characteristics even if the influence on the optical characteristics due to the pattern deviation is found. There was a problem that it was not possible to grasp whether they were doing.

  The present invention has been made in view of such circumstances, and in a solid-state imaging device having a multi-layer structure, the shape of pixel components formed in each layer and the amount of positional deviation between the layers are in-process. Providing a solid-state imaging device that can be measured accurately and clarifying the relationship with the optical characteristics, and for that purpose, the shape of the pixel component of each layer and the measurement of the amount of misalignment between each layer It aims to provide a method.

  In order to achieve the above object, the present invention provides a solid-state imaging device having a multi-layer structure, wherein at least two of the multi-layers are arranged outside the effective pixel region and are arranged at the periphery of the effective pixel region. A superposition mark adjacent to the pixel portion is formed.

  According to the present invention, by measuring the overlay mark and the surface shape in the vicinity thereof each time each layer is formed, it is possible to obtain data of the pixel component shape of each layer and the amount of positional deviation between the layers. For this reason, by measuring the optical characteristics of the corresponding pixels, the relationship between the optical characteristics, the shape of the pixel component of each layer, and the amount of misalignment between layers can be grasped nondestructively.

  In addition, since the overlay mark is formed adjacent to the peripheral pixel portion of the effective pixel region portion, the overlay mark and the measurement pixel portion can be measured within the same measurement range, and measurement with respect to the overlay mark is possible. It is easy to specify the pixel portion. In addition, since the overlay mark is arranged outside the effective pixel area, the number of effective pixels is not reduced.

  Further, according to the present invention, the overlay mark formed in the upper layer is formed directly on the overlay mark formed in the lower layer, and is formed in a slightly smaller size than the overlay mark formed in the lower layer. The

  According to this, since the overlay marks of each layer can be formed by being stacked in multiple layers in a pyramid upward, it is possible to easily calculate the amount of displacement with respect to the lower layer of each layer.

  Furthermore, in the present invention, a plurality of the overlay marks are formed in each layer. According to this, since a plurality of overlay marks are formed in each layer, it is possible to accurately measure the amount of interlayer displacement. Further, it is possible to estimate the shape and displacement of an arbitrary pixel portion in the effective pixel region portion.

  In order to achieve the above object, the present invention provides a method for measuring a solid-state image pickup device for obtaining a relationship between structure data and optical characteristics of a solid-state image pickup device having a laminated structure. Forming an overlay mark adjacent to the pixel portion at the periphery of the effective pixel region portion outside the effective pixel region portion, and a position of the overlay mark and a surface shape of the effective pixel region portion in the vicinity thereof. A step of measuring, and forming a pattern of each pixel portion above the predetermined layer, and forming an overlay mark adjacent to the peripheral pixel portion of the upper effective pixel region portion outside the effective pixel region portion A step of measuring a surface shape of an effective pixel region portion in the vicinity of the position of the overlay mark on the upper layer, and an optical characteristic of the pixel portion of the effective pixel region portion measuring the surface shape Measuring the shape data of the pixel portion of each layer, the positional displacement data between the layers, and the optical property data of the corresponding pixel portion by each step, and obtaining the structure data and the optical property of the solid-state image sensor It is characterized by seeking association.

  According to the measurement method of the solid-state imaging device of the present invention, the pattern of the pixel portion is formed in a predetermined plurality of layers, and the overlay mark adjacent to the pixel portion at the periphery of the effective pixel region portion is formed, and the layers are overlapped for each layer. Since the position of the alignment mark and the surface shape of the effective pixel area in the vicinity thereof are measured, the shape data of the pixel portion of each layer and the positional deviation data between layers can be obtained nondestructively, and the optical characteristics of the corresponding pixel portion can be obtained. By measuring, it is possible to obtain matching between the structure data of the solid-state imaging device and the optical characteristics.

  In the present invention, the measurement of the position of the overlay mark and the measurement of the surface shape of the effective pixel area near the overlay mark are measured by the same measuring machine. According to this, the measurement of the position of the overlay mark and the measurement of the surface shape of the effective pixel area near the overlay mark are simultaneously measured by the same measuring machine, and the positional relationship of the measurement pixel portion is easily specified. be able to.

  As described above, according to the solid-state imaging device and the measuring method thereof according to the present invention, the shape of the components of the pixel portion formed in each layer of the solid-state imaging device and the amount of positional deviation between the respective layers are accurately measured nondestructively. And the relationship with optical characteristics can be clarified. Also, by feeding back the information to design and simulation, the sensitivity and color characteristics of the solid-state imaging device can be improved efficiently.

  Hereinafter, preferred embodiments of a solid-state imaging device and a measuring method thereof according to the present invention will be described in detail with reference to the accompanying drawings. In each figure, the same number or symbol is attached to the same member.

  FIG. 1 is a plan view of a solid-state imaging device. The solid-state imaging device 10 includes an effective pixel region portion 11, an invalid pixel region portion 12 disposed so as to surround the effective pixel region portion 11, and a light-shielding region (OB; Optical Black) disposed so as to surround the invalid pixel region portion 12. .. And a plurality of overlay marks 14, 14,... Formed in the invalid pixel region 12 or over both the invalid pixel region 12 and the OB region.

  The effective pixel area 11 is a part that uses the output of each pixel part therein as the output of the solid-state image sensor 10, and the invalid pixel area part 12 uses the output of each pixel part inside thereof as the output of the solid-state image sensor 10. This is the part that is not used. Further, the OB portion is a portion where the opening to the photodiode PD described later is closed, and the output of the photodiode PD hardly occurs.

  A large number of such solid-state imaging elements 10 are formed on a wafer, and in the manufacturing process, each process is performed in the form of a wafer and finally divided into chips of individual solid-state imaging elements 10.

  FIG. 2 is an enlarged view of a portion A in FIG. As shown in FIG. 2, the effective pixel region portion 11 and the invalid pixel region portion 12 are formed with a large number of pixel portions 20, 20,. The pixel portions 20, 20,... Are arranged adjacent to the R, G, and B pixels by the color filter 26 described later. Further, the overlay mark 14 is formed in the invalid pixel region portion 12 adjacent to the peripheral pixel portion 20 of the effective pixel region portion 11.

  Q in FIG. 2 represents a range in which the shape of the constituent elements of the pixel unit 20 and measurement of the positional deviation between the layers described later and the optical characteristics of the pixel unit 20 are measured. This range Q is the overlay mark 14. And a plurality of pixel units 20 can be measured simultaneously.

  The size of the range Q is about 20 μm square to 50 μm square. The size of the pixel unit 20 is about 1 μm to 3 μm, and the overlay mark 14 is a rectangle having one side of 1 μm to 50 μm or less, and becomes smaller from the lower layer to the upper layer.

  3 is an enlarged view of the B and C portions in FIG. 2. FIG. 3A is a cross-sectional view of the pixel portion 20 in the B portion, and FIG. 3B is a cross-sectional view of the overlay mark 14 in the C portion. is there.

  As shown in FIG. 3A, the pixel unit 20 includes a silicon substrate Si, a photodiode PD that is a light receiving element formed on the silicon substrate Si, a transfer electrode 21 that transfers excitation voltage to the outside, and an opening 22A. The light shielding film 22, the interlayer insulating film 23, the inner lens 24 formed on the interlayer insulating film 23, the color filter 26 provided on the inner lens 24 via the planarizing layer 25, and the flat on the color filter 26. And a microlens 28 provided through a conversion layer 27.

  Since the pixel unit 20 is configured in this way, light incident from the outside is condensed by the microlens 28 and the inner lens 24 and irradiated to the photodiode PD, so that the effective aperture ratio is increased.

  As shown in FIG. 3B, the overlay mark 14 includes a light shielding film overlay mark 14A, an interlayer insulation film overlay mark 14B, an inner lens overlay mark 14C, a color filter overlay mark 14D, and The microlens overlay mark 14E is divided and provided corresponding to each layer. In the present invention, these are collectively referred to as an overlay mark 14.

  Each overlay mark 14 is formed with a slightly smaller size than the overlay mark 14 in the lower layer, and is stacked in a pyramid shape above. Further, the distance from each pixel portion 20 of each layer to the center of the overlay mark 14 of that layer is designed to be the same distance between the layers. Each overlay mark 14 is formed simultaneously with the formation of each corresponding layer.

  Next, a measurement method of the solid-state imaging device 10 according to the embodiment of the present invention will be described using the flowchart of FIG. 4 and FIGS. 5 and 6. This measurement is the measurement of the shape of the component of the pixel unit 20 and the amount of interlayer displacement in each layer, and the measurement of the optical characteristics of the pixel unit 20.

  First, the base structure of the solid-state imaging device 10 is formed, and the opening shape of the photodiode PD is formed. That is, a process is performed until the photodiode PD, the transfer electrode 21, the light shielding film 22, the light shielding film overlay mark 14A, and the opening 22A of the light shielding film 22 are formed on the silicon substrate Si.

  At this time, a plurality of light shielding film overlay marks 14A are formed around the effective pixel area 11, and each light shielding film overlay mark 14A is in the vicinity of the effective pixel area 20 and has no effect on the product characteristics. It is formed in the pixel region portion 12 or the OB portion 13 (step S11).

  Next, the wafer on which the solid-state imaging device 10 that has been subjected to the above-described steps is formed is set in an AFM (Atomic Force Microscope), and the solid to be measured by alignment means (mark recognition means) attached to the AFM. The light-shielding film overlay mark 14A of the image sensor 10 is recognized (step S12).

  Next, the surface shape of the light-shielding film overlay mark 14A and its periphery (range Q in FIG. 2) is simultaneously measured by AFM. The measurement is scanned over the entire area Q of FIG. FIG. 5 shows this measurement part, FIG. 5 (a) is a cross-sectional view of the effective pixel portion 20, and FIG. 5 (b) is a cross-sectional view of the light-shielding film overlay mark 14A portion. Since the scanning range of the AFM is sufficiently larger than the pixel portion 20 and the overlay mark 14, the surface shape data of the pixel portion 20 and the overlay mark 14 can be captured simultaneously.

  As shown in FIG. 5A, when the surface of the light shielding film 22 is scanned with the short needle 51 attached to the AFM cantilever 52, the cantilever 52 is bent by the atomic force between the atom of the short needle 51 and the atom of the light shielding film 22A. The amount of deflection is detected with a laser to detect surface irregularities, and the surface shape of the light shielding film 22 is measured including the opening 22A. The shape of the light-shielding film overlay mark 14A is also measured in the same manner (step S13). Next, the measured surface shape data is stored in a memory in the computer (step S14).

  Next, an upper layer is formed, and a pixel part component and an overlay mark 14 for the layer are formed. For example, as shown in FIG. 6A, an interlayer insulating film 23 and an interlayer insulating film overlay mark 14B shown in FIG. 6B are formed (step S15).

  Next, it is determined whether or not to measure the shape of the pixel part constituent element (for example, the interlayer insulating film 23) of the layer and the overlay mark 14 (for example, the overlay mark 14B for the interlayer insulating film) of the layer (step S16).

  If it is determined in step S16 that the measurement is not performed (No), the process returns to step S15 to further form an upper layer. If it is determined in step S16 that measurement is to be performed (Yes), the wafer is set on the AFM, and the overlay mark 14 of the layer is recognized by the alignment means attached to the AFM (step S17).

  Next, the shape of the pixel part component and the overlay mark 14 of the layer is measured by AFM (step S18), and the measured surface shape data is stored in the memory in the computer (step S19).

  Next, it is determined whether or not the measurement of the uppermost pixel unit component and the overlay mark 14 has been completed (step S20). If the measurement has not been completed (NO), the process returns to step S15, and this processing is performed. Repeat until the upper layer measurement is complete.

  In parallel with this process, the amount of misalignment between the layers (the amount of misalignment between the upper layer and the lower layer) is calculated by a computer from the data of the lower layer overlay mark 14 and the upper layer overlay mark 14 and stored in the memory. Remember. Since the overlay mark 14 has a box-in-box shape as shown in FIGS. 2 and 3B, for example, the amount of misalignment between layers is measured by detecting the edge of the stepped portion. (Step S21).

  If it is determined in step S20 that the measurement of the uppermost layer has been completed (Yes), the optical characteristics of the effective pixel portion 20 in the range Q in which the surface shape is measured next are measured. The detection of the optical characteristics is performed by a probe test apparatus composed of a prober and a tester having a fixed illumination system.

  First, the pixel unit 20 that measures optical characteristics is recognized from the position of the overlay mark 14. Since the probe test apparatus can obtain the charge of the pixel portion at an arbitrary position, if the position of the overlay mark 14 is located on which pixel portion on the solid-state imaging device 10 is determined, It is possible to determine which pixel unit 20 is the pixel unit 20 that has measured the positional deviation, and to measure the optical characteristics thereof.

  By the way, since the photodiode PD formed under the overlay mark 14 is shielded from light by the overlay mark 14, the position of the pixel portion 20 in which the sensitivity is remarkably lowered in the invalid pixel area portion 12 is superimposed. It becomes the position of the mark 14, and the position of the overlay mark 14 can be accurately specified. For this reason, the low-sensitivity pixel portion 20 in the invalid pixel region portion 12 is detected by the probe test device, the position of the overlay mark 14 is recognized, and the pixel portion 20 for measuring the optical characteristics is recognized therefrom (step S22). ).

  Next, the optical characteristics of the pixel units 20, 20,.

  Next, with respect to the plurality of pixel portions 20, 20,... Obtained in this way, the relationship between the optical characteristics in the same pixel portion 20, the shape of the constituent elements of each layer, and the amount of displacement is analyzed by a computer. Matching is performed to improve efficiency (step S24). The above is the measurement method of the solid-state imaging device according to the embodiment of the present invention.

  The plurality of pixel portions 20, 20,... Are distributed to the three types of R, G, and B by the color filter 26, so that at least three pixel portions 20, 20, and 20 of R, G, and B are measured. It is necessary to do.

  As described above, according to the solid-state imaging device and the measuring method of the present invention, the relationship between the formation state of the internal structure of each pixel unit 20 constituting the solid-state imaging device 10 and the optical characteristics can be obtained without destroying the product. Since the information can be accurately grasped, the sensitivity and color characteristics of the solid-state imaging device 10 can be efficiently improved by feeding back the information to the design and manufacturing process.

  Further, it is possible to analogize the shape and position variation of an arbitrary pixel portion in the chip from the shape information of the plurality of effective pixel portions 20, 20,.

  Furthermore, by accumulating these data, it is possible to infer how much the optical characteristics will ultimately be during the measurement of the structure of the multiple layers, so that the middle of the manufacturing process Thus, it is possible to construct a yield prediction system for determining whether a product is a non-defective product or a defective product.

  In the above-described embodiment, the overlay mark 14 is rectangular. However, the present invention is not limited to this, and various shapes other than the rectangle can be used as long as the position can be recognized. Further, although the overlay mark 14 is provided for every layer except the intermediate layer, it may be formed only on a predetermined layer such as only the light shielding film layer and the microlens layer.

  Further, in the above-described embodiment, the shape of the pixel portion 20 and the interlayer positional deviation of each layer are measured using the same measuring device (AFM). However, the overlay mark 14 is measured to obtain the interlayer positional deviation amount. Can also be measured using an optical method such as an overlay measuring instrument.

  However, considering the detection error of the edge due to the optical method and considering the efficiency of being able to perform measurement simultaneously with the shape measurement of the pixel unit 20, the SPM (Scanning Probe Microscope) is more effective than the optical method. ) Is preferred.

  In addition, since it is necessary to measure an insulating material in SPM, it is preferable to use AFM rather than STM (Scanning Tunneling Microscope).

  Further, the present invention is not limited to the AFM, but can be measured after the CMP (Chemical Mechanical Polishing) process, which is a planarization process in the semiconductor field, so that it can be measured in a wafer shape and measured over the entire surface of the wafer. A wide area AFM used for wafer flatness, step measurement and the like is suitable. Further, a wide area AFM with a wafer autoloader is more preferable because a plurality of wafers can be processed automatically.

The top view showing the solid-state image sensing device concerning an embodiment of the invention Detailed view of part A in FIG. Sectional drawing showing a pixel part and an overlay mark part 7 is a flowchart showing a method for measuring a solid-state imaging device according to an embodiment of the present invention. Sectional drawing showing the light-shielding film part and the overlay mark for light-shielding films Sectional drawing showing interlayer insulating film and overlay mark for interlayer insulating film

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Solid-state imaging device, 11 ... Effective pixel area part, 12 ... Invalid pixel area part, 13 ... Light-shielding area (OB) part, 14 ... Overlay mark, 20 ... Pixel part, PD ... Photodiode, Si ... Silicon substrate, Q ... Range

Claims (5)

A solid-state imaging device having a multilayer structure,
A solid-state imaging device, wherein at least two layers of the multilayer are formed with overlay marks that are arranged outside the effective pixel region portion and adjacent to a pixel portion at the periphery of the effective pixel region portion.   The overlay mark formed in the upper layer is formed directly on the overlay mark formed in the lower layer, and is formed in a slightly smaller size than the overlay mark formed in the lower layer. The solid-state imaging device according to claim 1.   The solid-state imaging device according to claim 1, wherein a plurality of the overlay marks are formed in each layer. In a measurement method of a solid-state imaging device for obtaining a relationship between structure data and optical characteristics of a solid-state imaging device having a laminated structure,
Forming a pattern of each pixel portion in a predetermined layer, and forming an overlay mark adjacent to the peripheral pixel portion of the effective pixel region portion outside the effective pixel region portion;
Measuring the position of the overlay mark and the surface shape of the effective pixel region in the vicinity thereof;
Forming a pattern of each pixel portion above the predetermined layer, and forming an overlay mark adjacent to the peripheral pixel portion of the upper effective pixel region portion outside the effective pixel region portion;
Measuring the position of the overlay mark on the upper layer and the surface shape of the effective pixel region in the vicinity thereof,
Measuring the optical characteristics of the pixel portion of the effective pixel region portion where the surface shape is measured, and the shape data of the pixel portion of each layer, the misalignment data between the layers, and the corresponding pixel portion optical A method for measuring a solid-state imaging device, characterized by obtaining characteristic data and obtaining a relationship between the structure data of the solid-state imaging device and optical characteristics.   5. The solid-state imaging device according to claim 4, wherein the measurement of the position of the overlay mark and the measurement of the surface shape of the effective pixel region near the overlay mark are measured by the same measuring device. Measuring method.

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