JP2004296738A - Method for manufacturing solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid state imaging device in which the need for cleaning work is eliminated after residual organic matters are removed. <P>SOLUTION: A wafer for a spacer is pasted with an adhesive to a glass substrate, i.e. the substrate of cover glass for protecting the upper part of a solid state image sensor. The wafer for a spacer is applied with a resist mask and then etched to form a spacer for protecting the circumference of the solid state image sensor on the glass substrate. Organic matters, e.g. the adhesive and the resist mask remaining on the glass substrate after etching are removed by ashing which causes neither contamination nor damage to the glass substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a solid-state imaging device using a wafer level chip size package structure.
[0002]
[Prior art]
Digital cameras using a solid-state imaging device and a semiconductor memory instead of a silver salt film have become widespread. In addition, portable telephones that can be taken easily by incorporating a solid-state imaging device and a semiconductor memory, and small electronic devices such as electronic notebooks are also widespread. Therefore, downsizing of the solid-state imaging device is desired.
[0003]
One mounting method for reducing the size of a solid-state imaging device is a wafer level chip size package structure (hereinafter abbreviated as wafer level CSP) that completes mounting of the solid-state imaging device at a wafer level without using a package (hereinafter referred to as wafer level CSP). For example, see Patent Document 1). In this solid-state imaging device using the wafer level CSP, a spacer is arranged on the upper surface of the solid-state imaging device chip so as to surround the solid-state imaging device, and a cover glass for sealing the solid-state imaging device is attached on the spacer. Thus, a solid-state imaging device is formed.
[0004]
The post-process of the solid-state imaging device is performed as follows. First, an inorganic material substrate, such as a silicon wafer (hereinafter referred to as a spacer wafer), which serves as a spacer substrate, is bonded to a transparent glass substrate which serves as a cover glass substrate with an adhesive or the like. A resist mask having a spacer shape is formed on the spacer wafer using photolithography, and a portion not covered with the resist mask is etched. Thereby, a large number of spacers are formed on the glass substrate. An adhesive is applied to the end face of each spacer, and a glass substrate is bonded to a chip wafer on which a large number of solid-state imaging elements are formed. Thereafter, by dicing the glass substrate and the wafer, a large number of solid-state imaging devices having a wafer level CSP structure are completed.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-231921
[Problems to be solved by the invention]
The resist mask and the adhesive remain on the glass substrate and the back surface of the spacer after the spacer is formed by etching. These residual organic substances must be removed before the glass substrate and the chip wafer are bonded together. The cover glass is required to be clean so as not to prevent light reception by the solid-state imaging device. Therefore, depending on the method for removing the residual organic matter, the glass substrate may be scratched or soiled, and it is necessary to devise a cleaning process for the glass substrate. This cleaning process increases the number of manufacturing steps and costs of the solid-state imaging device. Patent Document 1 does not disclose a method for removing the resist mask and the adhesive from the glass substrate, and the development of a method capable of maintaining the glass substrate in a clean state after the removal of the adhesive and the resist mask is desired. It was rare.
[0007]
An object of the present invention is to provide a method for manufacturing a solid-state imaging device that eliminates the need for a cleaning operation after removal of residual organic matter.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, the method for manufacturing a solid-state imaging device according to the present invention uses ashing or wet processing when removing the adhesive and the mask from the transparent substrate on which a large number of spacers are formed. It is what. According to this, since the residual organic matter is efficiently removed and the cleaning operation after the removal is not required, the number of manufacturing steps and the cost can be reduced. In addition, when removing residual organic substances by ashing, an adhesive having high ashing suitability is used.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 and FIG. 2 are a perspective view and a cross-sectional view showing a main part of a solid-state imaging device having a wafer level CSP structure manufactured by the manufacturing method of the present invention. The solid-state imaging device 2 includes a rectangular solid-state imaging element chip 4 provided with the solid-state imaging element 3, a frame-shaped spacer 5 attached on the chip 4 so as to surround the solid-state imaging element 3, and the spacer 5 And a cover glass 6 which is attached on top and seals the solid-state imaging device 3.
[0010]
The solid-state imaging device chip 4 includes a plurality of connection terminals 8 used for connecting a rectangular silicon substrate 4a, a solid-state imaging device 3 formed on the silicon substrate 4a, and an electronic device in which the solid-state imaging device 2 is incorporated. It consists of. The solid-state image sensor chip 4 is formed by forming a large number of solid-state image sensors 3 and connection terminals 8 on a chip wafer and dicing the wafer for each solid-state image sensor 3. The thickness of the silicon substrate 4a is, for example, about 300 μm.
[0011]
The solid-state image sensor 3 is composed of a CCD, for example. A color filter and a microlens are stacked on the CCD. The connection terminal 8 is formed by printing on the silicon substrate 4a using, for example, a conductive material. The connection terminal 8 and the solid-state imaging device 3 are connected by a wiring layer formed on the silicon substrate 4a. The spacer 5 is made of an inorganic material such as silicon, and has a width dimension of, for example, about 200 μm and a thickness of about 10 to 200 μm. The cover glass 6 is made of transparent α-ray shielding or glass that does not generate α-rays from itself in order to prevent destruction of the photodiode of the CCD. The cover glass 6 also has a function of reinforcing the solid-state imaging device 2 and has a thickness of about 500 μm, for example.
[0012]
FIG. 3 is a flowchart showing a post-process of the solid-state imaging device, “formation of spacer on glass substrate (first process)”, “bonding of glass substrate and chip wafer (second process)”. , “Dicing (third step)”. FIG. 4 is a flowchart showing the first to fifth steps of the first step. As shown in FIG. 5A, in the first step, a wafer-shaped glass substrate 10 that is a base material of the cover glass 6 and a spacer wafer 11 that is a base material of the spacer 5 are bonded together by an adhesive 12. The
[0013]
A thicker glass substrate 10 and spacer wafer 11 (for example, in the case of the spacer wafer 11, a standard wafer of t625 μm in the case of a φ6 inch size silicon wafer) is used. And after bonding together, the glass substrate 10 and the wafer 11 for spacers of required thickness can be obtained by grinding and grind | polishing in a 2nd step. Thereby, material cost can be suppressed and handling property can be improved.
[0014]
Since the adhesive 12 needs to be applied thinly (for example, t10 μm or less) and uniformly to the glass substrate 10 using a spin coating method or the like, a low viscosity of 500 cps or less is preferable. As the type of the adhesive 12, a thermosetting type (room temperature type), a UV curable type, or the like is popular. However, since the glass substrate 10 having the α-ray shielding function has a different thermal expansion coefficient from the spacer wafer 11 made of silicon, the glass substrate 10 and the spacer wafer 11 are warped or damaged when the adhesive 12 is heated and cured. There is. Therefore, in the present embodiment, a UV curable adhesive is used as the adhesive 12. Since this UV curable adhesive can be cured by irradiating ultraviolet rays from the glass substrate 10 side, the glass substrate 10 and the spacer wafer 11 can be bonded together in a short time.
[0015]
In addition, as a selection criterion for the adhesive 12 used for bonding the glass substrate 10 and the spacer wafer 11, removal suitability can be given. Although details will be described in the fifth step, in this embodiment, the unnecessary adhesive 12 remaining on the glass substrate 10 is removed by ashing. Therefore, selecting a low molecular weight adhesive as an adhesive that can be easily removed by ashing is also effective for improving the manufacturing efficiency of the solid-state imaging device 2.
[0016]
As an adhesive having a high removal efficiency by ashing other than a low molecular weight adhesive, an adhesive that does not contain a C═C bond or has a low bonding ratio can be selected. This is because the binding force of C = C is not easy to break even with decomposition energy by oxygen plasma.
[0017]
An alignment sticking device is used for bonding the glass substrate 10 and the spacer wafer 11 together. The alignment sticking apparatus applies the adhesive 12 to the upper surface of the glass substrate 10 by using a spin coat method, and the spacer wafer 11 whose position is adjusted in the XY direction and the rotational direction by the orientation flat on the glass substrate 10. After the superposition, the adhesive 12 is cured by irradiating ultraviolet rays from the glass substrate 10.
[0018]
In addition, when the glass substrate 10 and the spacer wafer 11 are bonded together, no bubbles or voids should be generated between them. This is because the layer of the adhesive 12 not only bonds the glass substrate 10 and the spacer wafer 11 but also functions to securely seal the solid-state imaging device 3. For this reason, the alignment sticking apparatus performs the bonding of the glass substrate 10 and the spacer wafer 11 in a chamber capable of forming a working environment in a reduced pressure to vacuum state (for example, 10 Torr or less). Further, for bonding the glass substrate 10 and the spacer wafer 11, anodic bonding, fusion bonding, direct bonding, room temperature bonding, or the like that does not use any adhesive or inclusions may be used.
[0019]
As shown in FIG. 5B, in the second step, grinding and polishing are performed to reduce the thickness of the bonded glass substrate 10 and spacer wafer 11. It is also possible to use the glass substrate 10 and the spacer wafer 11 having a thickness after completion, and in this case, the second step for the purpose of grinding and polishing can be omitted.
[0020]
As shown in FIG. 5C, in the third step, a resist mask 15 is formed on the upper surface of the spacer wafer 11. The resist mask 15 is created using a known photolithography technique. First, an unexposed resist is applied on the spacer wafer 11. Next, the resist is exposed through an exposure mask in which the pattern of the spacer 5 is formed, and development processing is performed. Thereby, a large number of resist masks 15 having the shape of the spacers 5 are formed on the spacer wafer 11.
[0021]
It should be noted that the resist mask 15 needs to have a thickness that prevents the resist mask 15 itself from being consumed by the etching gas when the spacer wafer 11 is through-etched by dry etching in the fourth step. When the resist mask 15 is formed, not only the pattern of the spacer 5 but also an alignment mark and a resist pattern of an outer ring provided on the outer periphery of the wafer are formed.
[0022]
As shown in FIG. 5D, in the fourth step, a large number of spacers 5 are formed on the glass substrate 10 by etching. As an etching method that can be used for creating the spacer 5, for example, there is anisotropic dry etching, and a chlorine-based or fluorine-based etching gas can be used. A parallel plate RIE (reactive ion etching) is generally used as an anisotropic dry etching apparatus, but the dimensional accuracy is maintained when the height of the spacer 5 exceeds 100 μm. In order to secure high productivity, it is preferable to use an ICP (inductively coupled plasma) type dry etcher.
[0023]
Furthermore, when it is necessary to suppress the squareness of the side surface of the spacer 5 to ± 5 ° or less, it is preferable to use a Bosch process that can proceed with vertical processing while preventing side etching of the side surface. The Bosch process refers to a process in which etching and deposition, which coats the entire workpiece with a polymer that is not eroded by the etching, are alternately repeated. When the Bosch process is used for manufacturing the spacer 5, the polymer coated in the deposition step remains on the surface of the glass substrate 10 (hereinafter referred to as a polymer residue) and the transparency of the glass substrate 10 is impaired. Therefore, in order to eliminate this polymer residue, it is preferable to lower the polymer coating level in the deposition process just before the spacer 5 is processed. Also, the etching rate may be lowered in accordance with the decrease in the coating rate.
[0024]
Moreover, in order to reduce the polymer residue by the Bosch process, the following method can also be taken. That is, the Bosch process is terminated just before the etching through the spacer wafer 11 is completed, and the formation of the spacer 5 is completed by normal etching without performing deposition.
[0025]
In addition, wet etching can be used for etching for forming the spacer. Although wet etching has some difficulty in processing time and dimensional accuracy, it can perform batch processing and continuous processing of several tens of wafers at a time, so overall throughput is much more efficient than dry etching. is there. In addition, there is an advantage that the cost of the apparatus can be kept lower than that of the dry etching apparatus.
[0026]
As an etchant used for wet etching, potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) is suitable. Further, since the resist mask is affected by the chemical solution, it is necessary to form the mask with a Si oxide film or a metal thin film. Furthermore, normal wet etching is isotropic etching, but a spacer wafer having a crystal plane orientation of “110” is employed, and a spacer mask is formed by rotating 45 ° from the orientation flat surface. Thus, anisotropic etching along the crystal plane can be performed, and the side surface of the spacer 5 can be finished at a right angle.
[0027]
As shown in FIG. 5E, in the fifth step, the adhesive 12 and the resist mask 15 remaining on the glass substrate 10 are removed. For the removal process of the residual organic substance, an ashing process in which the organic substance is decomposed and removed by oxygen plasma is used. In this ashing process, since the glass substrate 10 is not contaminated, there is no need to clean the glass substrate 10 after the residual organic substances are removed. The ashing process may be performed on the dry etcher immediately after the etching of the spacer 5 or may be performed by a dedicated asher. Further, in order to realize the composition (ashing characteristics) of the adhesive 12 and the target processing speed, a fluorine-based, hydrogen-based, or argon-based gas may be used or added to oxygen.
[0028]
Thus, the etching formation of the spacer 5 and the removal of the adhesive 12 and the resist mask 15 are processed in a dry consistent process, so that the processing can be finished in a clean state of the glass substrate 10, and the cleaning process is performed. Without being bonded to the chip wafer on which the solid-state imaging device 3 is formed.
[0029]
Note that a wet process can be used to remove the adhesive 12 and the resist mask 15. In this wet treatment, the residual organic matter is decomposed (dissolved) by immersing the glass substrate 10 in a chemical solution such as a solvent, a strong acid, or a strong alkali solution. As an advantage of the wet processing, the entire glass substrate 10 can be cleaned by the chemical cleaning process in addition to the reduction of the apparatus cost and the improvement of the throughput.
[0030]
As described above, as described in the first to fifth steps of the first process, the glass substrate 10 and the spacer wafer 11 are first integrated, and then the spacer 5 is processed and residual organic substances are removed. Therefore, the process can be simplified as compared with the case where the thin and fragile spacer wafer 11 is handled alone.
[0031]
In the second step, as shown in FIGS. 6 and 7B, a glass substrate 10 on which a large number of spacers 5 are formed and a chip wafer 17 on which a large number of solid-state imaging elements 3 are formed are bonded together. . First, as shown in FIG. 7A, the adhesive 18 is thinly and uniformly applied on the spacer 5, alignment mark, and outer ring of the glass substrate 10. For applying the adhesive 18 to the spacer 5, the adhesive is thinly and evenly applied on a plate such as another sheet or wafer, and this is transferred to the spacer 5, alignment mark, and outer ring of the glass substrate 10. The method is used. According to this method, a thin layer of the adhesive 18 having a uniform thickness can be formed on the spacer 5 without being influenced by the handleability of the adhesive 18 represented by viscosity.
[0032]
Further, as another application method of the adhesive 18, a method using a dispenser according to the handleability of the adhesive 18 or a method of spray coating in a lump by covering only the region to be opposed to the solid-state imaging device 3. A method using screen printing technology can be selected.
[0033]
As described above, in the method in which a large number of spacers 5 are bonded to the chip wafer 17 in a lump, the positional accuracy and the bonding process are more important than the case where the spacers 5 separated one by one are arranged on the chip wafer 17. Is also realistic. Further, the glass substrate 10 and the chip wafer 17 are bonded to each other and the solid-state imaging device 3 is sealed before the dicing process, so that the concern about dust can be completely canceled.
[0034]
As shown in FIGS. 7C and 7D, in the third step, after the adhesive 18 that bonds the glass substrate 10 and the chip wafer 17 is sufficiently cured, the glass substrate 10 and the chip wafer 17 are then cured. And dicing. A dicing tape 20 is attached to the back surface of the chip wafer 17 so that the solid-state imaging devices 2 do not fall apart after dicing. Further, in order to prevent contamination by grinding scraps or grinding liquid, a protective tape 21 for preventing contamination may be attached to the surface of the glass substrate 10. Instead of the dicing tape 20 and the protective tape 21, a surface protective coating that can be easily applied and removed can be applied.
[0035]
For dicing the glass substrate 10, a grindstone formed of diamond or CBN abrasive grains of about # 400 to # 1500 is used. Since the glass substrate 10 is a hard and brittle material, chipping of the cutting edge and wear of the grinding wheel become problems during cutting, and the cutting speed cannot be increased. Therefore, instead of processing with a single grindstone, it is advisable to adopt a multi-blade configuration in which several grindstones are assembled on a shaft and multiple pieces are cut at once. As a result, the processing efficiency of about 0.1 to 10 mm / s can be doubled by the number of blades assembled.
[0036]
After the dicing of the glass substrate 10 is completed, the chip wafer 17 is diced in the same manner. Thereafter, the dicing tape 20 and the protective tape 21 are peeled off to complete the solid-state imaging device 2.
[0037]
【The invention's effect】
As described above, according to the method for manufacturing a solid-state imaging device of the present invention, residual organic substances such as an adhesive and a mask remaining on the transparent substrate after etching of the spacer can be efficiently removed, and after the removal of the residual organic substances Since the transparent substrate is not required to be cleaned, manufacturing man-hours and costs can be reduced.
[Brief description of the drawings]
FIG. 1 is an external perspective view showing a configuration of a solid-state imaging device manufactured using the present invention.
FIG. 2 is a cross-sectional view of a main part showing a configuration of a solid-state imaging device.
FIG. 3 is a flowchart illustrating a procedure of a post-process of the solid-state imaging device.
FIG. 4 is a flowchart showing a procedure of a first step.
FIG. 5 is a cross-sectional view of the main part showing the state of the glass substrate and spacer wafer in the first step.
FIG. 6 is a perspective view showing a bonded state of a glass substrate and a chip wafer.
FIG. 7 is a cross-sectional view of the main part showing the state of the glass substrate and spacer wafer in the second and third steps.
[Explanation of symbols]
2 Solid-state imaging device 3 Solid-state imaging device 4 Solid-state imaging device chip 5 Spacer 6 Cover glass 10 Glass substrate 11 Spacer wafer 12 Adhesive 15 Resist mask 17 Chip wafer

Claims (2)

Forming a number of spacers surrounding the solid-state image sensor on a transparent substrate;
Bonding a wafer for a chip on which a large number of solid-state image sensors are formed and a spacer on a transparent substrate, surrounding each solid-state image sensor with a spacer, and sealing the top of each solid-state image sensor with a transparent substrate;
In a manufacturing method of a solid-state imaging device comprising a step of dividing a chip wafer and a transparent substrate for each solid-state imaging device and forming a large number of solid-state imaging devices,
The step of forming the spacer on the transparent substrate includes:
Bonding the transparent substrate and the spacer substrate to be a base material of the spacer with an adhesive;
Forming a spacer-shaped mask on the surface of the spacer substrate;
Etching the spacer substrate to form a number of spacers on the transparent substrate;
And a step of removing the adhesive and the mask from the transparent substrate using ashing or wet processing. 2. The method of manufacturing a solid-state imaging device according to claim 1, wherein when the ashing is used, an adhesive having high ashing suitability is used as an adhesive used for bonding the transparent substrate and the spacer substrate.

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