CA2118743A1 - Optical illumination and inspection system for wafer and solar cell defects - Google Patents
Optical illumination and inspection system for wafer and solar cell defectsInfo
- Publication number
- CA2118743A1 CA2118743A1 CA002118743A CA2118743A CA2118743A1 CA 2118743 A1 CA2118743 A1 CA 2118743A1 CA 002118743 A CA002118743 A CA 002118743A CA 2118743 A CA2118743 A CA 2118743A CA 2118743 A1 CA2118743 A1 CA 2118743A1
- Authority
- CA
- Canada
- Prior art keywords
- inspection system
- article
- manufacture
- light
- optical inspection
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000007689 inspection Methods 0.000 title claims abstract description 24
- 230000003287 optical effect Effects 0.000 title claims abstract description 23
- 230000007547 defect Effects 0.000 title claims description 9
- 238000005286 illumination Methods 0.000 title description 13
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 23
- 239000010703 silicon Substances 0.000 claims abstract description 23
- 239000011521 glass Substances 0.000 claims abstract description 6
- 229910052736 halogen Inorganic materials 0.000 claims abstract description 6
- 230000001427 coherent effect Effects 0.000 claims abstract 5
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 239000000758 substrate Substances 0.000 claims description 10
- 239000006117 anti-reflective coating Substances 0.000 claims description 6
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 claims description 3
- 229910001218 Gallium arsenide Inorganic materials 0.000 claims description 2
- 229910052732 germanium Inorganic materials 0.000 claims description 2
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 2
- 238000002329 infrared spectrum Methods 0.000 claims description 2
- 238000001914 filtration Methods 0.000 claims 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 abstract description 22
- 239000006059 cover glass Substances 0.000 description 20
- 235000012431 wafers Nutrition 0.000 description 7
- 239000000853 adhesive Substances 0.000 description 5
- 230000001070 adhesive effect Effects 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 2
- 241000239290 Araneae Species 0.000 description 1
- 229910000577 Silicon-germanium Inorganic materials 0.000 description 1
- LEVVHYCKPQWKOP-UHFFFAOYSA-N [Si].[Ge] Chemical compound [Si].[Ge] LEVVHYCKPQWKOP-UHFFFAOYSA-N 0.000 description 1
- 230000004956 cell adhesive effect Effects 0.000 description 1
- 238000005352 clarification Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N21/9501—Semiconductor wafers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/8806—Specially adapted optical and illumination features
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
- G01N21/9501—Semiconductor wafers
- G01N21/9505—Wafer internal defects, e.g. microcracks
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S136/00—Batteries: thermoelectric and photoelectric
- Y10S136/29—Testing, calibrating, treating, e.g. aging
Abstract
ABSTRACT OF THE INVENTION
An embodiment of an optical inspection system for detecting cracks in a silicon wafer or in intermediate layers of a solar ceil is disclosed including a laser for providing a coherent light beam. The laser may be a typical HeNe laser. A
video camera sensitive to near infrared frequency light is disposed co-linear with the laser and includes a macro-zoom lens. The solar panel that is to be inspected is located in a test plane and in the field of view of video camera. The laser is used to aid in directing the camera onto the solar panel. A first quartz-halogen collimated light source is projected through and filtered by a long pass filter which passes wavelengths of 1.0 micron.
The filtered collimated light from the light source is projected onto the surface of a white paper panel. The source of the white paper contains irregularities on the same order as the 1.0 micron wavelength of the light through the long pass filter. These irregularities cause the light reflected from the white paper to diffuse. The white paper is positioned such that the diffuse light reflected therefrom falls upon the surface of the solar panel in the test plane. Because the light rays reflected from white paper are diffuse they strike the surface of the solar panel at a plurality of various angles. As the light rays pass through the solar cell layer interfaces will be reflected in the direction of the camera. Those rays which fall in the path of the field of view of the camera, become the object image from which a real image is created and may be viewed on a control monitor. Cracks in the solar cell silicon layer or glass covers can be observed on the control monitor, and printed by a video graphics printer or stored via a VCR for permanent documentation purposes.
An embodiment of an optical inspection system for detecting cracks in a silicon wafer or in intermediate layers of a solar ceil is disclosed including a laser for providing a coherent light beam. The laser may be a typical HeNe laser. A
video camera sensitive to near infrared frequency light is disposed co-linear with the laser and includes a macro-zoom lens. The solar panel that is to be inspected is located in a test plane and in the field of view of video camera. The laser is used to aid in directing the camera onto the solar panel. A first quartz-halogen collimated light source is projected through and filtered by a long pass filter which passes wavelengths of 1.0 micron.
The filtered collimated light from the light source is projected onto the surface of a white paper panel. The source of the white paper contains irregularities on the same order as the 1.0 micron wavelength of the light through the long pass filter. These irregularities cause the light reflected from the white paper to diffuse. The white paper is positioned such that the diffuse light reflected therefrom falls upon the surface of the solar panel in the test plane. Because the light rays reflected from white paper are diffuse they strike the surface of the solar panel at a plurality of various angles. As the light rays pass through the solar cell layer interfaces will be reflected in the direction of the camera. Those rays which fall in the path of the field of view of the camera, become the object image from which a real image is created and may be viewed on a control monitor. Cracks in the solar cell silicon layer or glass covers can be observed on the control monitor, and printed by a video graphics printer or stored via a VCR for permanent documentation purposes.
Description
OPTICAL ILLUMINATION AND INSPECTION SYSTEM
FOR WAFER AND SOLAR CELL DEFECTS
BACKGROUND OF THE INVENTION
The present invention relates to optical systems for inspecting multi-layer silicon devices, and more particularly to an optical system employing near infrared illumination to detect defects in silicon layers.
Inspection systems are available in the art for detecting defects such as cracks in silicon layers, particularly in silicon layers or wafers employed ; 15 in solar cells. Such systems include a source of linearly polarized infrared illumination which is directed entirely onto the solar cell device at a first selected angle. The linearly polarized infrared illumination is reflected from the silicon layer of the solar cell and an infrared video 3 camera is positioned at a second selected angle with respect to the solar cell. The video camera, which includes an infrared linear polarization analyzer, provides a visual image of the silicon layer and cracks in the silicon wafer surface can be observed.
' .:.
.~ A typical infrared solar cell inspection system is .~ described in the publication by J.R. Hodor, H.J.
i 30 Decker, Jr., J. Barney, "Infrared Technology Comes to State-of-the-Art Solar Array Production",` SPIE
Vol. 819, Infrared Technology XIII (1987), pp. 22-29.
.
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The systems previously known in the art employ infrared illumination in the 5 to 15 micron range, and also aim the collimated, linearly polarized infrared illumination directly onto the solar cell.
Such systems result in an image on the video camera screen in which cracks in the silicon layer can be observed.
Available inspection methods, known in the art are extremely complex in design and use, and hindered by large weight constraints. All of the various systems known or proposed to date may no longer be considered practical since the complexity, size and weight constraints of the systems make them too expensive and not portable enough for use in a dynamic aerospace manufacturing and test environment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical inspection system for observing cracks in silicon substrates, but may also be used to detect cracks in gallium arsenide (GaAs) or germanium (Ge) substrates, which requires fewer components than prior art systems.
,~
~ Another object of the present invention is to ; provide an optical inspection system for silicon wafer defects which clearly distinguishes b~tween cover layer cracks and cracks in the silicon wafer.
A further object of the present invention is to `~:
.
FOR WAFER AND SOLAR CELL DEFECTS
BACKGROUND OF THE INVENTION
The present invention relates to optical systems for inspecting multi-layer silicon devices, and more particularly to an optical system employing near infrared illumination to detect defects in silicon layers.
Inspection systems are available in the art for detecting defects such as cracks in silicon layers, particularly in silicon layers or wafers employed ; 15 in solar cells. Such systems include a source of linearly polarized infrared illumination which is directed entirely onto the solar cell device at a first selected angle. The linearly polarized infrared illumination is reflected from the silicon layer of the solar cell and an infrared video 3 camera is positioned at a second selected angle with respect to the solar cell. The video camera, which includes an infrared linear polarization analyzer, provides a visual image of the silicon layer and cracks in the silicon wafer surface can be observed.
' .:.
.~ A typical infrared solar cell inspection system is .~ described in the publication by J.R. Hodor, H.J.
i 30 Decker, Jr., J. Barney, "Infrared Technology Comes to State-of-the-Art Solar Array Production",` SPIE
Vol. 819, Infrared Technology XIII (1987), pp. 22-29.
.
~!
~ .
~' 2 ~ 7 ~ ~
The systems previously known in the art employ infrared illumination in the 5 to 15 micron range, and also aim the collimated, linearly polarized infrared illumination directly onto the solar cell.
Such systems result in an image on the video camera screen in which cracks in the silicon layer can be observed.
Available inspection methods, known in the art are extremely complex in design and use, and hindered by large weight constraints. All of the various systems known or proposed to date may no longer be considered practical since the complexity, size and weight constraints of the systems make them too expensive and not portable enough for use in a dynamic aerospace manufacturing and test environment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical inspection system for observing cracks in silicon substrates, but may also be used to detect cracks in gallium arsenide (GaAs) or germanium (Ge) substrates, which requires fewer components than prior art systems.
,~
~ Another object of the present invention is to ; provide an optical inspection system for silicon wafer defects which clearly distinguishes b~tween cover layer cracks and cracks in the silicon wafer.
A further object of the present invention is to `~:
.
3 2~7-q3 provide an optical inspection system for silicon wafers in solar array panels that gives consistent results for a number of inspections with minimum risk to the solar panels.
In accordance with the present invention therefore, an optical inspection system for solar cells and the like is disclosed wherein the illumination employed is in the near infrared frequencies, and wherein the illumination is diffused and directed onto the solar cell being inspected at a plurality o. separate angles.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic block diagram of the components of an optical inspection system according to the principles of the present invention.
Fig. 2 is a schematic illustration showing typical optical paths for the light sources used in the system of Fig. 1.
Fig. 3 is a schematic illustration showing the interaction of the light rays of the system of Fig.
1 at the various interfaces of a typical solar cell.
Fig. 4 is a more detailed illustration of the`solar cell interfaces and the shadows produced by cracks therein.
.
,.
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In accordance with the present invention therefore, an optical inspection system for solar cells and the like is disclosed wherein the illumination employed is in the near infrared frequencies, and wherein the illumination is diffused and directed onto the solar cell being inspected at a plurality o. separate angles.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic block diagram of the components of an optical inspection system according to the principles of the present invention.
Fig. 2 is a schematic illustration showing typical optical paths for the light sources used in the system of Fig. 1.
Fig. 3 is a schematic illustration showing the interaction of the light rays of the system of Fig.
1 at the various interfaces of a typical solar cell.
Fig. 4 is a more detailed illustration of the`solar cell interfaces and the shadows produced by cracks therein.
.
,.
,, , , ' ' ' '~
4 2 ~
DESCRIPTION OF A PREFERRED EMBODIMENT
OF THE INVENTION
Referring to Fig. 1 an embodiment of an optical inspection system for detecting cracks in a silicon wafer or in intermediate layers of a solar cell is illustrated including a laser 10 for providing a beam of collimated illumination. Laser 10 may be a typical HeNe laser available in the art. A video camera 12 is disposed co-linear with laser 10 and includes a macro-zoom lens 14. The laser 10 is used as a guide for sighting video camera 12 at a selected target location. Camera 12 is sensitive to near infrared frequencies and is also available in the art. The solar panel 16 that is to be inspected is located in a test plane in the path of the illumination from laser 10 and in the field of view of video camera 12.
A first collimated light source 18, for example a quartz halogen lamp, provides illumination 0.9 to 1.2 micron near infrared spectrum is projected through and filtered by a long pass filter ~2 which passes wavelengths of 1.0 micron. The filtered collimated light from light source 18 is projected onto the surface of white paper panel 24. The solar panel 16 may also be illuminated by ; uncollimated unfiltered near infrared light directed at an angle from a second quartz-halogen light source 20. Fig. 1 includes typical dimensions for the placement of the described system components. These dimensions are not critical and are included to show the compactness - ;. . , : ' -. , : : ~ :
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- . . : . - - .
.
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of the system of the present invention.
The surface of the white paper 24 contains irregularities on the order of 1.0 micron which is also on the same order as the wavelength of the near infrared illumination which passes through filter 22. These irregularities cause the light reflected from the surface of white paper 24 to diffuse. The white paper 24 is positioned such that the diffuse light reflected therefrom falls upon the surface of the solar panel 16 positioned in a test plane. Because the light rays reflected from white paper 24 are diffuse they strike the surface of the solar panel 16 at a plurality of various angles.
,' :
Referring to Fig. 2, an illustration is provided showing the light rays from lamp 18 and filter 22 ``~! reflected off white paper 24 at various angles toward solar panel 16 because of the diffuse reflection from the white paper 24 surface.
., Referring to Fig. 3, an illustration is provided ~3 showing the component layers of a solar cell of panel 16 which include the solar cell material 16A
having a metallized back surface 16B, which supports a layer 16A of silicon germanium or a GaAs ~ material. A layer of coverglass 16D is disposed on `~j solar cell 16A by cell adhesive 16C and a coverglass 16E with an anti-reflective coating 16F
is located on coverglass 16D. The structure 16A, ;` 16B, 16C, 16D, 16E, and 16F in Fig. 3 depicts one `' solar cell of the solar panel 16. Since light ,~
~c ~:' $-: . ' .
6 ~ 7~,~
bends at the interface between two transparent substances with different indices of refraction, each near infrared light ray reflected from the diffuse surface of white paper 24 will strike the coverglass layer 16E and be partially transmitted through the glass at various angles according to Snell's Law For Refraction (Ml sin 01 = M2 sin 02 where Ml is the index of refraction for the first transparent substance.
M2 is the index of refraction for the second transparent subs$ance.
01 is the angle of the light ray with respect to the interface as it enters from the first substance.
02 is the angle of the light ray with respect to the interface as it exits into the second substance.
The near infrared light reflected from the white paper 24 will also strike the coverglass 16E and be partially reflected according to the Law of Reflection which states that the incident angle 0;
is equal to the angle of reflection 0r (0i = 0r).
~:
Thus, each individual ray of light reflected from the white paper 24 and falling on coverglas's 16E
will consist of two subsequent rays; a transmitted ; (refracted) ray and a reflected ray. While both reflection ~nd refraction o~ the light r~ys will ~ , ~ . . . .
.
,~: . ' , . ' ' ~ :. . ,,. : ~ .
21~7~3 occur at the interface between the coverglass 16D
- and the adhesive 16C, no total internal reflections will occur because the light rays are travelling into a more optically dense substance.
All of the light rays have four transitions, or angle changes, they must undergo as they pass through, or are reflected from, the other various interfaces within the layers of the solar cell.
Initially each light ray must cross the interface between the anti-reflective coating 16F and the coverglass 16E, the interface between the coverglass 16D and the adhesive 16C, the interface between the adhesive 16C and the silicon wafer 16A, and lastly the interface between the silicon 16A
and the metallized back surface 16B. All interfaces allow for the light rays to either be reflected or transmitted through to the next media.
Total internal reflection will only occur for ~` 20 certain light rays at the interface between air and the anti-reflective coating 16F. As the light rays pass through the solar cell interfaces some will be l reflected back toward the white-paper 24, while -~ others, as shown in Fig. 3, will be reflected in the direction of the field of view of the camera 12 and its zoom lens 14. Those rays which fall in the path of the field of view of the Camera 12, become the object image from which a real image is created and may be viewed on a control monitor (not shown) ~ 30 which is associated with the video camera 10 One `` skilled in the art will appreciate that camera 12 may also include provision for video tape recording, and a video graphics printer for .
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8 21~ 8 7l~
permanent documentation of the defe~t.
The image which is seen on the control monitor - arises solely from the contribution of the first collimated quartz-halogen light source 18 with its attached Iong pass filter 22. The second light source 20, an unfiltered uncollimated quartz-halogen light is only used to illuminate the solar panel 16 when it is necessary to verify whether a detected crack is a crack in the coverglass or a crack in the bare silicon of the cell. All interfaces of the layers of the solar cell will result in shadows appearing on the surface of the silicon layer 16A, but the only two surfaces of concern are those of the coverglass and bare solar cell.
In Fig. 3, the dark line within the solar cell perpendicular to the surface 16A designated by reference number 26 indicates a crack in the bare ;
silicon and reference number 28 indicates shadows of the actual crack 26 created by illuminating the cracks 26 at the various interfaces.
: 25 Fig. 4 is an illustration of the various shadows which are created in the layers of the solar cell at the separate interfaces. Shadow 28A is at the anti-reflective coating/coverglass interface, shadow 28B is at the coverglass/adhesive interface, shadow 28C is at the adhesive/silicon interfa~e and shadow 28D is at the silicon, metallization interface.
`I ' '.
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! . : .,, - ' 2ll87~3 ~- The near infrared light which is used to detec~
: bare solar cell cracks and coverglass cracks comes ~- originally from the light source 18. .Both coverglass cracks and solar cell cracks may be viewed simultaneously at the camera. That is to say from the view of the camera they appear to be superimposed on top of one another, when in reality they are on two different planes. To a trained ~ observer looking at a control monitor screen with a : 10 picture of a cracked solar cell it would be simple ,.
to tell the difference between a coverglass crack or a solar cell crack. Coverglass tends to shatter or crack in a curved manner, similar to the strands ~: of a spider web. Bare solar cell will crack in 45 ~ 15 or 30 straight lines depending on the crystal; orientation of the bare solar cell material. To an untrained eye it might not be so easy to make the clarification. Viewing is more difficult if the ~ coverglass breaks over the cell so that you have `~ 20 both surfaces cracked but with your eye you can not be sure if both surfaces are cracked or if it is really just one surface. This is why the secondary light source 20 is used; as a way to support the determination. If the light source 20 is turned on and you see a series of bright dots reflected back at you on the control monitor then you know the coverglass is definitely cracked. More particularly, the secondary light source 20 is turned on to verify whether or not there is any total internal reflection of the light rays. If in fact the light beams from the secondary source 20 e~hibit the characteristic of total internal reflection then it determines that the ccverglass ., ~-2 ~ ~ 8 ~ ~
is effectively cracked. This phenomenon occurs when a single light ray strikes the crack in the glass ~t such an angle that is either equal to or greater than the critical angle for the interface from the air to the anti-reflective coating on the coverglass.
What has been described is a simple, compact and portable test system to easily identify and document solar cell and coverglass cracks for accurately characterizing the reliability and quality of the solar cells contained on a solar panel. The present invention offers the capability to easily verify the reliability of hardware on site before it is launched into the space environment. Its flexibility of use and implementation into any sort of test station make it not only feasible, but cost effective as well, and thus a particularly essential asset to any space oriented application.
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DESCRIPTION OF A PREFERRED EMBODIMENT
OF THE INVENTION
Referring to Fig. 1 an embodiment of an optical inspection system for detecting cracks in a silicon wafer or in intermediate layers of a solar cell is illustrated including a laser 10 for providing a beam of collimated illumination. Laser 10 may be a typical HeNe laser available in the art. A video camera 12 is disposed co-linear with laser 10 and includes a macro-zoom lens 14. The laser 10 is used as a guide for sighting video camera 12 at a selected target location. Camera 12 is sensitive to near infrared frequencies and is also available in the art. The solar panel 16 that is to be inspected is located in a test plane in the path of the illumination from laser 10 and in the field of view of video camera 12.
A first collimated light source 18, for example a quartz halogen lamp, provides illumination 0.9 to 1.2 micron near infrared spectrum is projected through and filtered by a long pass filter ~2 which passes wavelengths of 1.0 micron. The filtered collimated light from light source 18 is projected onto the surface of white paper panel 24. The solar panel 16 may also be illuminated by ; uncollimated unfiltered near infrared light directed at an angle from a second quartz-halogen light source 20. Fig. 1 includes typical dimensions for the placement of the described system components. These dimensions are not critical and are included to show the compactness - ;. . , : ' -. , : : ~ :
: . : , , ~
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.
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of the system of the present invention.
The surface of the white paper 24 contains irregularities on the order of 1.0 micron which is also on the same order as the wavelength of the near infrared illumination which passes through filter 22. These irregularities cause the light reflected from the surface of white paper 24 to diffuse. The white paper 24 is positioned such that the diffuse light reflected therefrom falls upon the surface of the solar panel 16 positioned in a test plane. Because the light rays reflected from white paper 24 are diffuse they strike the surface of the solar panel 16 at a plurality of various angles.
,' :
Referring to Fig. 2, an illustration is provided showing the light rays from lamp 18 and filter 22 ``~! reflected off white paper 24 at various angles toward solar panel 16 because of the diffuse reflection from the white paper 24 surface.
., Referring to Fig. 3, an illustration is provided ~3 showing the component layers of a solar cell of panel 16 which include the solar cell material 16A
having a metallized back surface 16B, which supports a layer 16A of silicon germanium or a GaAs ~ material. A layer of coverglass 16D is disposed on `~j solar cell 16A by cell adhesive 16C and a coverglass 16E with an anti-reflective coating 16F
is located on coverglass 16D. The structure 16A, ;` 16B, 16C, 16D, 16E, and 16F in Fig. 3 depicts one `' solar cell of the solar panel 16. Since light ,~
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6 ~ 7~,~
bends at the interface between two transparent substances with different indices of refraction, each near infrared light ray reflected from the diffuse surface of white paper 24 will strike the coverglass layer 16E and be partially transmitted through the glass at various angles according to Snell's Law For Refraction (Ml sin 01 = M2 sin 02 where Ml is the index of refraction for the first transparent substance.
M2 is the index of refraction for the second transparent subs$ance.
01 is the angle of the light ray with respect to the interface as it enters from the first substance.
02 is the angle of the light ray with respect to the interface as it exits into the second substance.
The near infrared light reflected from the white paper 24 will also strike the coverglass 16E and be partially reflected according to the Law of Reflection which states that the incident angle 0;
is equal to the angle of reflection 0r (0i = 0r).
~:
Thus, each individual ray of light reflected from the white paper 24 and falling on coverglas's 16E
will consist of two subsequent rays; a transmitted ; (refracted) ray and a reflected ray. While both reflection ~nd refraction o~ the light r~ys will ~ , ~ . . . .
.
,~: . ' , . ' ' ~ :. . ,,. : ~ .
21~7~3 occur at the interface between the coverglass 16D
- and the adhesive 16C, no total internal reflections will occur because the light rays are travelling into a more optically dense substance.
All of the light rays have four transitions, or angle changes, they must undergo as they pass through, or are reflected from, the other various interfaces within the layers of the solar cell.
Initially each light ray must cross the interface between the anti-reflective coating 16F and the coverglass 16E, the interface between the coverglass 16D and the adhesive 16C, the interface between the adhesive 16C and the silicon wafer 16A, and lastly the interface between the silicon 16A
and the metallized back surface 16B. All interfaces allow for the light rays to either be reflected or transmitted through to the next media.
Total internal reflection will only occur for ~` 20 certain light rays at the interface between air and the anti-reflective coating 16F. As the light rays pass through the solar cell interfaces some will be l reflected back toward the white-paper 24, while -~ others, as shown in Fig. 3, will be reflected in the direction of the field of view of the camera 12 and its zoom lens 14. Those rays which fall in the path of the field of view of the Camera 12, become the object image from which a real image is created and may be viewed on a control monitor (not shown) ~ 30 which is associated with the video camera 10 One `` skilled in the art will appreciate that camera 12 may also include provision for video tape recording, and a video graphics printer for .
..
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.. . . .
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8 21~ 8 7l~
permanent documentation of the defe~t.
The image which is seen on the control monitor - arises solely from the contribution of the first collimated quartz-halogen light source 18 with its attached Iong pass filter 22. The second light source 20, an unfiltered uncollimated quartz-halogen light is only used to illuminate the solar panel 16 when it is necessary to verify whether a detected crack is a crack in the coverglass or a crack in the bare silicon of the cell. All interfaces of the layers of the solar cell will result in shadows appearing on the surface of the silicon layer 16A, but the only two surfaces of concern are those of the coverglass and bare solar cell.
In Fig. 3, the dark line within the solar cell perpendicular to the surface 16A designated by reference number 26 indicates a crack in the bare ;
silicon and reference number 28 indicates shadows of the actual crack 26 created by illuminating the cracks 26 at the various interfaces.
: 25 Fig. 4 is an illustration of the various shadows which are created in the layers of the solar cell at the separate interfaces. Shadow 28A is at the anti-reflective coating/coverglass interface, shadow 28B is at the coverglass/adhesive interface, shadow 28C is at the adhesive/silicon interfa~e and shadow 28D is at the silicon, metallization interface.
`I ' '.
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! . : .,, - ' 2ll87~3 ~- The near infrared light which is used to detec~
: bare solar cell cracks and coverglass cracks comes ~- originally from the light source 18. .Both coverglass cracks and solar cell cracks may be viewed simultaneously at the camera. That is to say from the view of the camera they appear to be superimposed on top of one another, when in reality they are on two different planes. To a trained ~ observer looking at a control monitor screen with a : 10 picture of a cracked solar cell it would be simple ,.
to tell the difference between a coverglass crack or a solar cell crack. Coverglass tends to shatter or crack in a curved manner, similar to the strands ~: of a spider web. Bare solar cell will crack in 45 ~ 15 or 30 straight lines depending on the crystal; orientation of the bare solar cell material. To an untrained eye it might not be so easy to make the clarification. Viewing is more difficult if the ~ coverglass breaks over the cell so that you have `~ 20 both surfaces cracked but with your eye you can not be sure if both surfaces are cracked or if it is really just one surface. This is why the secondary light source 20 is used; as a way to support the determination. If the light source 20 is turned on and you see a series of bright dots reflected back at you on the control monitor then you know the coverglass is definitely cracked. More particularly, the secondary light source 20 is turned on to verify whether or not there is any total internal reflection of the light rays. If in fact the light beams from the secondary source 20 e~hibit the characteristic of total internal reflection then it determines that the ccverglass ., ~-2 ~ ~ 8 ~ ~
is effectively cracked. This phenomenon occurs when a single light ray strikes the crack in the glass ~t such an angle that is either equal to or greater than the critical angle for the interface from the air to the anti-reflective coating on the coverglass.
What has been described is a simple, compact and portable test system to easily identify and document solar cell and coverglass cracks for accurately characterizing the reliability and quality of the solar cells contained on a solar panel. The present invention offers the capability to easily verify the reliability of hardware on site before it is launched into the space environment. Its flexibility of use and implementation into any sort of test station make it not only feasible, but cost effective as well, and thus a particularly essential asset to any space oriented application.
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Claims (10)
1. An optical inspection system for observing physical defects in an article of manufacture comprising:
a source of a collimated light beam, means disposed in the path of said collimated light beam for filtering said collimated light beam to pass specific wavelengths of said collimated light beam, means disposed in the path of said collimated light beam for diffusing said collimated light beam at said specific wavelengths and directing said diffused light onto and illuminating said article of manufacture, and observation means directed onto said article of manufacture responsive to said coherent light and said diffused light for providing an image of said article of manufacture wherein physical defects in said article of manufacture wherein physical defects in said article of manufacture are apparent in said image.
a source of a collimated light beam, means disposed in the path of said collimated light beam for filtering said collimated light beam to pass specific wavelengths of said collimated light beam, means disposed in the path of said collimated light beam for diffusing said collimated light beam at said specific wavelengths and directing said diffused light onto and illuminating said article of manufacture, and observation means directed onto said article of manufacture responsive to said coherent light and said diffused light for providing an image of said article of manufacture wherein physical defects in said article of manufacture wherein physical defects in said article of manufacture are apparent in said image.
2. An optical inspection system according to claim 1 where said article of manufacture is a structure including a crystalline substrate, wherein said physical defects in said article of manufacture are cracks in said crystalline layer, wherein said source of collimated light produces light in the near infrared spectrum, and wherein said diffused light illuminates said crystalline layer to produce shadows representative of said cracks which are apparent in said image of said observation means and wherein said optical inspection system further includes a source of narrow coherent light beam directed onto said layer for aligning said observation means onto said crystalline layer.
3. An optical inspection system according to claim 2 wherein said source of coherent light is a laser that produces a coherent light beam, that functions as a guide to aid in determination of position of said physical defects in said article of manufacture.
4. An optical inspection system according to claim 3 wherein said source of near infrared collimated light is a quartz-halogen lamp, said filtering means is a long pass filter, and said diffusing means is a sheet of white paper disposed in the path of said filtered collimated light for reflecting the filtered collimated light rays onto said crystalline layer structure at a plurality of separate angles.
5. An optical inspection system according to claim 4 wherein said article of manufacture is a multi-layered device including a crystalline substrate, a transparent layer bonded onto said crystalline layer and an anti-reflective coating disposed on said transparent layer.
6. An optical inspection system according to claim 5 wherein said article of manufacture is a solar cell, said crystalline substrate is a substrate of silicon, and said transparent layer is composed of a plurality of separate layers of transparent glass.
7. An optical inspection system according to claim 5 wherein said article of manufacture is a solar cell, said crystalline substrate is a substrate of gallium arsenide, and said transparent layer is composed of a plurality of separate layers of transparent glass.
8. An optical inspection system according to claim 5 wherein said article of manufacture is a solar cell, said crystalline substrate is a substrate of germanium, and said transparent layer is composed of a plurality of separate layers of transparent glass.
9. An optical inspection system according to claim 5 wherein said system further includes a source of a uncollimated light directed onto said solar cell for producing shadows representative of cracks in said transparent layer wherein said shadows representative of said cracks in ; said crystalline layer and said shadows representative of cracks in said transparent layer are apparent and distinguishable in said image of said observation means.
10. An optical inspection system according to claim 5 wherein said collimated, filtered light has a wavelength of approximately 1.0 micron and wherein said sheet of white paper has a surface with irregularities in the order on 1.0 micron.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/042,890 US5334844A (en) | 1993-04-05 | 1993-04-05 | Optical illumination and inspection system for wafer and solar cell defects |
| US042,890 | 1993-04-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2118743A1 true CA2118743A1 (en) | 1994-10-06 |
Family
ID=21924285
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002118743A Abandoned CA2118743A1 (en) | 1993-04-05 | 1994-03-10 | Optical illumination and inspection system for wafer and solar cell defects |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5334844A (en) |
| EP (1) | EP0619484B1 (en) |
| JP (1) | JPH06308042A (en) |
| CA (1) | CA2118743A1 (en) |
| DE (1) | DE69414630T2 (en) |
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| US8768040B2 (en) * | 2011-01-14 | 2014-07-01 | Varian Semiconductor Equipment Associates, Inc. | Substrate identification and tracking through surface reflectance |
| US9234843B2 (en) | 2011-08-25 | 2016-01-12 | Alliance For Sustainable Energy, Llc | On-line, continuous monitoring in solar cell and fuel cell manufacturing using spectral reflectance imaging |
| TWI454689B (en) * | 2011-12-29 | 2014-10-01 | Chroma Ate Inc | Optical inspecting system |
| DE202013009329U1 (en) | 2013-10-18 | 2014-03-14 | Institut für innovative Technologien, Technologietransfer, Ausbildung und berufsbegleitende Weiterbildung (ITW) e.V. | High-performance surface light source |
| DE102013017501A1 (en) | 2013-10-18 | 2015-04-23 | Institut für innovative Technologien, Technologietransfer, Ausbildung und berufsbegleitende Weiterbildung (ITW) e. V. | Method and device for testing silicon components |
| US10480935B2 (en) | 2016-12-02 | 2019-11-19 | Alliance For Sustainable Energy, Llc | Thickness mapping using multispectral imaging |
| JP6797481B2 (en) * | 2017-03-01 | 2020-12-09 | 株式会社ディスコ | Semiconductor ingot inspection method, inspection equipment and laser processing equipment |
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| DE102018201723B4 (en) * | 2018-02-05 | 2022-11-03 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Methods for inspecting buried structures in solar cells and solar cell precursors |
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| US20230119076A1 (en) * | 2021-09-01 | 2023-04-20 | Arizona Board Of Regents On Behalf Of Arizona State University | Autonomous polarimetric imaging for photovoltaic module inspection and methods thereof |
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| US4026656A (en) * | 1975-09-02 | 1977-05-31 | Owens-Illinois, Inc. | Stone detector |
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| JPH0641910B2 (en) * | 1988-03-04 | 1994-06-01 | 三井金属鉱業株式会社 | Method of measuring the dispersion of resistivity |
| JPH0711494B2 (en) * | 1988-06-16 | 1995-02-08 | 松下電工株式会社 | Inspection method for translucent containers |
| FR2641866B1 (en) * | 1988-12-26 | 1993-03-05 | Aerospatiale | METHOD AND INSTALLATION FOR MONITORING PROTECTIVE WINDOWS OF SOLAR CELLS |
| FR2686697B1 (en) * | 1992-01-27 | 1994-04-29 | Aerospatiale | DEVICE FOR DETECTING DEFECTS IN TWO - LAYERED PARTS, PARTICULARLY IN SOLAR CELLS. |
-
1993
- 1993-04-05 US US08/042,890 patent/US5334844A/en not_active Expired - Lifetime
-
1994
- 1994-03-10 CA CA002118743A patent/CA2118743A1/en not_active Abandoned
- 1994-04-05 DE DE69414630T patent/DE69414630T2/en not_active Expired - Fee Related
- 1994-04-05 JP JP6067193A patent/JPH06308042A/en active Pending
- 1994-04-05 EP EP94302398A patent/EP0619484B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0619484A1 (en) | 1994-10-12 |
| DE69414630D1 (en) | 1998-12-24 |
| EP0619484B1 (en) | 1998-11-18 |
| DE69414630T2 (en) | 1999-06-17 |
| JPH06308042A (en) | 1994-11-04 |
| US5334844A (en) | 1994-08-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |