JP2006253598A - Method for cleaning cover glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for cleaning cover glass of a solid-state imaging apparatus which is composed of a solid-state image sensing device chip (wafer) and the cover glass with a high cleaning capability and at a low cost. <P>SOLUTION: There is provided a method for cleaning the cover glass for the solid-state imaging apparatus composed of the solid-state image sensing device chip on which solid-state image sensing elements are formed, the cover glass bonded to the solid-state image sensing chip, and a spacer which surrounds the solid-state image sensing elements, has a predetermined thickness, is disposed between the solid-state image sensing device chip and the cover glass, and seals the solid-state image sensing device chip. The method is provided with a first wet cleaning process in which the cover glass having the spacer on its surface is cleaned in pure water, a dry cleaning process in which the cover glass is subjected to ashing by oxygen plasma, and a second wet cleaning process in which the cover glass is cleaned by water vapor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning a cover glass, and more particularly, to a method for cleaning a cover glass when manufacturing a chip size package (CSP) type solid-state imaging device.

  A solid-state imaging device made of a CCD or a CMOS used for a digital camera or a mobile phone is increasingly required to be downsized. For this reason, the conventional large package, in which the entire solid-state image sensor chip is hermetically sealed in a ceramic package or the like, has recently moved to a chip size package (CSP) type, which is approximately the same size as the solid-state image sensor chip. I am doing.

  Under such circumstances, a spacer is formed on the transparent glass plate so as to correspond to the position surrounding the light receiving portion of each solid-state image sensor formed on the wafer (semiconductor substrate). A method has been proposed in which a gap is formed between the wafer and the wafer, and then the transparent glass plate and the wafer are diced along a scribe line and separated into individual solid-state imaging devices ( For example, refer to Patent Documents 1 to 3.)

  As a method for forming a spacer on such a transparent glass plate, photoetching is generally used. FIG. 7 is a cross-sectional view of the step of forming this spacer. In FIG. 7A, a wafer serving as a spacer 13 is bonded to the surface of a cover glass 12 corresponding to a transparent glass plate via an adhesive 13A, and then a pattern of a photoresist R is formed on the surface of the wafer.

  As a wafer to be the spacer 13, for example, a silicon wafer can be used. The pattern of the photoresist R is formed through processes such as resist coating, exposure using a photomask, development, and post baking.

  Next, in FIG. 7B, anisotropic etching is performed on the wafer (silicon wafer) to be the spacer 13 by dry etching to form a pattern of the spacer 13. At this time, the adhesive 13A is not removed because it has etching resistance.

Next, in FIG. 7C, ashing is performed to remove the pattern of the photoresist R and the exposed adhesive 13A. In this way, the pattern of the spacers 13 is formed on the surface of the cover glass 12.
JP-A-7-202152 JP 2002-231921 A JP 2004-6834 A

  However, such a method for forming a spacer has a high probability of causing the following problems (defects 1 to 3).

  Defect 1 is insufficient cleanliness. In the cover glass 12 having the pattern of the spacers 13 formed on the surface, it is necessary to remove all foreign matters having a size of 5 μm or more that affect the image to be captured. However, in the above processing method, dry etching residues, foreign matters due to the environment and the like cannot be sufficiently removed, and the cleanness tends to be insufficient as a cover glass of the solid-state imaging device.

  As a defect 2, an adhesive mark is mentioned. FIG. 8 is a flowchart for explaining a mechanism that causes such a problem. FIG. 8 is a partial cross-sectional view showing an enlarged portion of each solid-state imaging device chip in the cover glass 12 shown in FIG.

  8A is an enlarged view of a portion where the pattern of the spacer 13 in FIG. 7B is not formed. In FIG. 8A, foreign substances 30, 30 such as particles are present on the surface of the layer of the adhesive 13A.

  In FIG. 8B, ashing (oxygen plasma ashing) for removing the pattern of the photoresist R (see FIG. 7B) and the layer of the adhesive 13A is performed. However, as shown in FIG. 8C, if there are foreign substances 30 and 30 such as particles, the foreign substances 30 and 30 act as a mask for ashing, and the removal of the adhesive 13A at this portion is insufficient. It becomes.

  Then, the remaining adhesive 13 </ b> A remains as an adhesive trace even after the cleaning that is the next step. Although this adhesive trace greatly deteriorates the quality of the solid-state imaging device, it must be removed, but it is difficult to remove it later by a general cleaning method, which is a serious problem.

Defect 3 includes peeling of the spacer 13. The dry etching residue and the foreign matters resulting from the environment in the above-described defect 1 are organic substances. On the other hand, when the conventional general wet cleaning that acts on the organic substance, for example, cleaning with an SPM liquid (a liquid in which the ratio of H ₂ SO ₄ : H ₂ O ₂ is 4: 1) is performed, the organic substance is caused by the action of the chemical solution. This damages the adhesive of the spacer and causes the spacer 13 to peel off.

  The present invention has been made in view of such circumstances, and is a solid-state imaging device composed of a solid-state imaging device chip (wafer) and a cover glass, such as a chip size package (CSP) type solid-state imaging device. In cleaning the cover glass, an object of the present invention is to provide a method for cleaning the cover glass that eliminates the above-mentioned drawbacks and has high cleaning performance and low cost.

  In order to achieve the above object, the present invention provides a process of forming a large number of solid-state image sensors on the upper surface of a wafer, and individual solid-states at locations corresponding to the solid-state image sensors on the lower surface of a cover glass bonded to the wafer. A step of forming a frame-shaped spacer having a predetermined thickness surrounding the image sensor; a step of aligning the wafer and the cover glass and bonding the spacer through the spacer; and the bonded wafer and the cover In the method for cleaning the cover glass of the solid-state imaging device manufactured by dividing the glass into individual solid-state imaging devices, a first wet cleaning step for cleaning with pure water, and a dry cleaning step for ashing with oxygen plasma And a second wet cleaning step of cleaning with water vapor. A cover glass cleaning method is provided.

  According to the present invention, there are three methods: a first wet cleaning process for cleaning the cover glass on which the spacer is formed with pure water, a dry cleaning process for ashing with oxygen plasma, and a second wet cleaning process for cleaning with water vapor. Therefore, the cover glass on which the spacer is formed by etching can be cleaned with high cleaning performance and at low cost.

  Further, in the present invention according to the above invention, the cleaning method includes a first wet cleaning step of cleaning the cover glass having the spacer formed on the surface with pure water, and the cover glass after the first wet cleaning is subjected to oxygen plasma. The cover glass cleaning method is characterized in that the cleaning is performed by a dry cleaning process in which ashing is performed and a second wet cleaning process in which the cover glass after dry cleaning is cleaned with water vapor.

  According to the present invention, since a cleaning process is provided before and after ashing, high cleaning performance can be obtained. In particular, dry etching residues and environments that have not been removed by ashing by the second wet cleaning process that removes large foreign matters that are the cause of the formation of adhesive marks by the first wet cleaning process before ashing and are cleaned by water vapor after ashing. All foreign matters such as foreign matters can be removed.

  In the present invention, in the second wet cleaning step, the cleaning effect can be further enhanced by using high-pressure water in combination with water vapor.

  Further, in the present invention, in the second wet cleaning step, by using the high pressure water mixed with water vapor, the water vapor penetrates into the interface between the foreign material and the adhesion surface and acts to separate the foreign material. Since it is washed away, the cleaning property is improved and the effect of the present invention can be further exhibited.

  In the present invention, in the second wet cleaning step, after cleaning with steam, cleaning with high-pressure water or high-pressure water mixed with steam can further enhance the effect of steam cleaning.

  Further, in the present invention, by setting the pressure of the high-pressure water to 0.1 MPa or more, it is possible to easily remove the foreign matter that has been easily peeled off due to water vapor penetrating the interface between the foreign matter and the adhesion surface. And the effect of the present invention can be further exhibited.

  As described above, according to the cover glass cleaning method of the present invention, the first wet cleaning step of cleaning the cover glass on which the spacer is formed with pure water, the dry cleaning step of ashing with oxygen plasma, and water vapor Since the cleaning is performed by the three methods including the second wet cleaning step, the cover glass on which the spacer is formed by etching can be cleaned with high cleaning performance and at low cost.

  Hereinafter, preferred embodiments of a cover glass cleaning method according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 and FIG. 2 are a perspective view and a cross-sectional view showing a main part of a chip size package (CSP) type solid-state imaging device to which a cover glass cleaning method according to the present invention is applied.

  The solid-state imaging device 21 includes a solid-state imaging device 11A and a rectangular solid-state imaging device chip 11C provided with pads 11B, 11B, which are a plurality of connection terminals for electrical connection with the solid-state imaging device 11A. The frame-shaped spacer 13 is mounted on the solid-state image sensor chip 11C so as to surround the image sensor 11A, and the cover glass 12 is mounted on the spacer 13 and seals the solid-state image sensor 11A.

  The solid-state imaging device chip 11C is obtained by dividing a semiconductor substrate (wafer) described later. Further, the spacer 13 is joined to the cover glass 12 via the adhesive 13A and the solid-state imaging device chip 11C via the adhesive 13B.

  A general semiconductor element manufacturing process is applied to manufacture of the solid-state imaging element 11A. The solid-state imaging device 11A includes a photodiode that is a light-receiving device formed on a wafer (solid-state imaging device chip 11C), a transfer electrode that transfers excitation voltage to the outside, a light-shielding film having an opening, an interlayer insulating film, and an interlayer insulating film. An inner lens formed on the upper part, a color filter provided on the upper part of the inner lens via an intermediate layer, a micro lens provided on an upper part of the color filter via an intermediate layer, and the like.

  Since the solid-state imaging device 11A is configured in this way, light incident from the outside is condensed by the microlens and the inner lens and irradiated to the photodiode, so that the effective aperture ratio is increased.

  The pads 11B, 11B,... Are patterned on the solid-state image sensor chip 11C using, for example, a conductive material. Similarly, wiring is provided between the pad 11B and the solid-state imaging device 11A by pattern formation.

  Further, a through wiring 24 penetrating the solid-state imaging element chip 11C is provided, and conduction between the pad 11B and the external connection terminal 26 is established.

  As a wafer to be divided into a large number of solid-state imaging device chips 11C, a single crystal silicon wafer is generally used.

  The spacer 13 is made of an inorganic material such as silicon. That is, the material of the spacer 13 is preferably a material having physical properties such as a thermal expansion coefficient similar to those of the wafer (the solid-state imaging device chip 11C) and the cover glass 12. For this reason, the material of the spacer 13 is preferably silicon.

  The cover glass 12 is made of a transparent α-ray shielding glass in order to prevent the destruction of the CCD photodiode.

  Next, the cover glass cleaning method according to the present invention will be described. FIG.7 (c) is sectional drawing of the cover glass 12 with a spacer, as already stated. FIG. 3 is a flowchart of the cover glass cleaning method according to the present invention, and a cross-sectional view of the cover glass 12 at that time. Among the cover glasses 12 with spacers in FIG. It is a figure which expands and shows the part corresponding to 11A. FIG. 4 is a table showing conditions for the first wet cleaning, the dry cleaning, and the second wet cleaning.

  In FIG. 3A, dry etching is performed. As shown in FIG. 4, the dry etching apparatus and conditions employ an ICP type ashing method, the oxygen flow rate is adjusted to 99.0 sccm, and the platen power is set to 100 W. The cross section of the cover glass 12 after dry etching is in a state where large foreign matters D, D... And small foreign matters d, d.

  Next, in FIG. 3B, the first wet cleaning is performed. The first wet cleaning is a process of removing large (about several tens of μm) foreign matters D, D... On the adhesive 13A layer, that is, dry etching residues, environmental foreign matters, and the like. And it aims at preventing the production | generation of an adhesive trace demonstrated in FIG.

This first wet cleaning is pure water ultrasonic cleaning. That is, room temperature (room temperature) pure water (ultra pure water) is used as the cleaning liquid. The ultrasonic frequency is 38 kHz, and the ultrasonic density is 0.5 W / cm ² or more. The washing time is 2 minutes. The cross section of the cover glass 12 after the first wet cleaning is in a state in which large foreign matters D, D.

  Subsequently, in FIG.3 (c), it draws up with warm water (warm pure water) and performs drying. As another known drying method, there is a solvent vapor drying method, which is not preferable because the adhesive 13A is easily dissolved by the solvent.

  Next, in FIG. 3D, dry cleaning (ashing) using oxygen plasma is performed. This ashing is a process of removing the photoresist R on the spacer 13 and the adhesive 13A on the cover glass 12. Since it is difficult to remove the adhesive 13A on the cover glass 12 in a subsequent process (second wet cleaning process), it is necessary to completely remove the adhesive 13A in the dry cleaning (ashing).

  As the ashing apparatus and conditions, various known apparatuses and conditions applicable to semiconductor manufacturing and the like can be adopted. Thereby, the pattern of the photoresist R and the exposed layer of the adhesive 13A are removed, and the cross section of the cover glass 12 is in the state shown in FIG.

  Next, in FIG. 3E, the second wet cleaning is performed. This second wet cleaning is a mixture of cleaning with water vapor and cleaning with high-pressure pure water, and is a process in which dry etching residues and environmental foreign matter that cannot be removed by removal treatment with oxygen plasma are lifted and removed from the cover glass 12. is there.

  FIG. 5 shows a water vapor cleaning apparatus used in the second wet cleaning process. The water vapor cleaning apparatus 50 includes a work table 51 that rotates by placing a cover glass 12 having a spacer formed on the surface, and a two-fluid mixing injection nozzle that mixes water vapor and high-pressure pure water and injects the liquid onto the surface of the cover glass 12. 52, a high-pressure pure water supply device 53 that supplies pure water to the two-fluid mixing injection nozzle 52 via the flow control valve 55, the regulator 56, and the stop valve 57, and water vapor to the two-fluid mixing injection nozzle 52 via the stop valve 58. It consists of water vapor generating means 54 to be supplied. The water vapor generating means 54 has a pure water tank and a heater, and heats pure water with the heater to generate water vapor.

  The two-fluid mixing injection nozzle 52 has a structure as shown in FIG. 6, for example. That is, the inner nozzle 52A to which pure water is supplied and the outer nozzle 52B to which water vapor is supplied have a double structure, and water vapor and high-pressure pure water are injected from the outer nozzle 52B in a mixed state.

  In addition, although the high pressure pure water was supplied to the inner nozzle 52A and the water vapor was supplied to the outer nozzle 52B, the water vapor may be supplied to the inner nozzle 52A and the high pressure pure water may be supplied to the outer nozzle 52B. Various deformation structures are used as the fluid mixing / injecting nozzle 52.

  As shown in FIG. 4, the cleaning conditions of the second wet cleaning step are such that the water vapor pressure is 0.1 MPa to 0.5 MPa, and the temperature is 100 ° C. to 150 ° C. The high-pressure pure water has a pressure of 0.2 MPa to 0.5 MPa and a water amount of 0 to 1.0 (l / min).

  The distance between the two-fluid mixing jet nozzle 52 and the surface of the cover glass 12 is 10 mm, and the cleaning time is 5 minutes. When the pressure of the high-pressure pure water is lower than 0.1 MPa, foreign matters cannot be completely removed, so that 0.1 MPa or more is necessary, and the above-described 0.2 MPa to 0.5 MPa is more preferable.

  In the second wet cleaning step, water vapor that has permeated the foreign matter changes to water at the interface between the cover glass 12 and the foreign matter, thereby reducing the adhesion of the foreign matter to the glass. Moreover, the physical removal capability is given by spraying high-pressure pure water simultaneously with water vapor. Since this steam cleaning does not use chemicals and does not etch glass or Si, the adhesive is not damaged, and the adhesive strength is not lowered. Therefore, it is possible to improve the cleaning performance without worrying about the work damage.

  Next, the work table 51 of the water vapor cleaning device 50 is rotated at high speed, and the placed cover glass 12 is spin-dried. For this reason, the drying process by another apparatus is omissible. The above is the steam cleaning shown in FIG. In this state, various foreign substances D, D..., D, d.

  In the embodiment described above, the steam and the high-pressure pure water are mixed and sprayed onto the cover glass 12 in the second wet cleaning step, but first, the stop valve 57 is closed and the supply of the high-pressure pure water is cut off. It is also possible to inject only water vapor, and after a predetermined time, the stop valve 58 is closed to cut off the water vapor and the stop valve 57 is opened to spray high-pressure pure water.

  First, the stop valve 57 is closed and the supply of high-pressure pure water is cut off to inject only water vapor. After a predetermined time, the stop valve 57 is opened to spray a mixed fluid of water vapor and high-pressure pure water. May be.

  As described above, according to the cover glass cleaning method of the present invention, the first wet cleaning process using the pure water ultrasonic cleaning is provided before the dry cleaning process using the oxygen plasma ashing, and the spacer 13 is formed on the surface. Since the cover glass 12 is washed with pure water to which ultrasonic waves are applied, the foreign matters D, D... On the surface of the adhesive 13A can be removed.

  In addition, since the second wet cleaning process using water vapor and high-pressure pure water is provided after the dry cleaning process using oxygen plasma ashing, the foreign matter d that cannot be removed by oxygen plasma ashing is completely removed from the surface of the cover glass 12 (lift-off). Thus, the spacer-free cover glass 12 that can be used as the cover glass 12 of the solid-state imaging device 21 and has no spacer peeling can be obtained.

The perspective view of the solid-state imaging device to which the cleaning method of the cover glass concerning the present invention is applied Sectional drawing of the principal part of the solid-state imaging device to which the cleaning method of the cover glass which concerns on this invention is applied FIG. 2 is a flowchart of a cover glass cleaning method according to the present invention, and a cross-sectional view of the cover glass at that time. Table showing conditions of first wet cleaning, dry cleaning, and second wet cleaning Conceptual diagram showing a steam cleaning device Partial sectional view showing a two-fluid mixing nozzle of a steam cleaning device Cross-sectional view of the process of forming the spacer Flow diagram explaining the mechanism that causes defects in the formation of spacers

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Wafer (substrate), 11A ... Solid-state image sensor, 11B ... Pad, 11C ... Solid-state image sensor chip, 12 ... Cover glass, 13 ... Spacer, 13A ... Adhesive, 21 ... Solid-state image sensor, 30, D, d ... Foreign matter, 50 ... water vapor cleaning device, 52 ... two-fluid mixing nozzle, R ... photoresist

Claims (6)

Forming a large number of solid-state image sensors on the upper surface of the wafer;
Forming a frame-shaped spacer of a predetermined thickness in a shape surrounding each solid-state image sensor at a position corresponding to the solid-state image sensor on the lower surface of the cover glass bonded to the wafer;
Aligning the wafer and the cover glass and bonding via the spacer;
Dividing the bonded wafer and the cover glass into individual solid-state imaging devices;
In the method for cleaning the cover glass of the solid-state imaging device manufactured by:
A first wet cleaning step of cleaning with pure water;
A dry cleaning process for ashing with oxygen plasma;
And a second wet cleaning step of cleaning with water vapor. The cleaning method includes:
A first wet cleaning step of cleaning the cover glass having the spacer formed thereon with pure water;
A dry cleaning step of ashing the cover glass after the first wet cleaning with oxygen plasma;
A second wet cleaning step of cleaning the cover glass after dry cleaning with water vapor;
The method for cleaning a cover glass according to claim 1, wherein   The method for cleaning a cover glass according to claim 1 or 2, wherein the second wet cleaning step uses high-pressure water in addition to water vapor.   The cover glass cleaning method according to claim 3, wherein the second wet cleaning step uses high-pressure water mixed with water vapor.   The method for cleaning a cover glass according to claim 3, wherein the second wet cleaning step is performed by cleaning with high pressure water or high pressure water mixed with water vapor after cleaning with water vapor.   The method for cleaning a cover glass according to any one of claims 3, 4, and 5, wherein the pressure of the high-pressure water is 0.1 MPa or more.

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