JP2003502705A - Numeric aperture increase lens (NAIL) technology for creating high-resolution subsurface images - Google Patents

Abstract

(57) [Abstract] A numerical aperture used in an observation optical system such as a microscope (26) used for viewing inside a substrate such as a semiconductor wafer or a chip or an image forming optical system such as a media recorder, that is, light collection or focusing power. (18-NAIL). As a result, when the n the refractive index of the lens substrate, to increase the resolution of the optical system in the refractive index between n and n ^2.

Description

Detailed Description of the Invention

[0001]     Cross-reference of related applications

The present application is directed to 35 U.S.P. S. C. Under §119 (e), filed June 21, 1999, make a priority claim to conditional application 60 / 140,138. That disclosure is incorporated herein by reference.

[0003]     Receipt of government subsidies

The present invention was implemented with a government grant of grant ECS-9625236 awarded by the National Science Foundation under Contract No. 1210800.

BACKGROUND OF THE INVENTION Standard optical microscopy is due to diffraction limits, also known as Rayleigh or Abbe limits,
There is no ability to obtain lateral resolution with a resolution that is more than half the wavelength of light, and the diffraction-limited spatial resolution is λ / (2 NA), where λ is the wavelength in free space of light collection.
Is. The numerical aperture is defined as NA = n · sin θa, where n is the refractive index of the medium and θa is the focusing angle, that is, the half angle of the focusing region. In order to improve the resolution of diffraction limited microscopy, the NA must be increased. The highest NA value for standard microscope objectives in air environment is less than 1 and the general best value is around 0.6.

One way to increase the NA is to increase the refractive index n of the medium at the location where the focus is formed. Inserting a high refractive index fluid such as oil between the microscope objective and the sample generally increases the NA to a best value of 1.3. Similarly, a microscope design using a high-index hemispherical lens called a solid immersion lens (SIL) with a small distance from the sample can improve the resolution by 1 / n. SIL microscope
There is very little coupling between the focused light and the sample in the high index SIL. Earlier patents on SIL microscopy disclose arrangements where the light is focused on the geometric center of the SIL sphere.

Subsurface imaging of planar samples is usually done by standard microscopy.
The NA remains the same when creating subsurface images of high refractive index samples. This is because the increase in refractive index is completely offset by the decrease in sin θa from refraction at the plane boundary. Standard subsurface imaging also imparts spherical aberration to collection from refraction at coplanar boundaries. The amount of spherical aberration monotonically increases with increasing NA. Subsurface imaging has been done at wavelengths of 1.0 μm or greater through a silicon substrate with best lateral resolution of approximately 1.0 μm.

For the use of SIL microscopy, there have been suggestions for subsurface imaging when the optical phase front is geometrically matched to the SIL surface. However, the disclosed method is limited to an arrangement in which the hemispherical lens collects light from a focal point located at the geometric center of the lens sphere. In this case, the resolution improvement is limited to 1 / n and the area without spherical aberration is limited to points. The image can be formed by scanning the sample and the SIL, but in this case, the scanning accuracy is relaxed by the refractive index n. The image also scans the sample S
The IL can be formed stationary. A feature of the invention described below is the improvement of these standards and SIL microscopy for many subsurface applications.

SUMMARY OF THE INVENTION The present invention provides a lens placed on the substrate surface for observation or imaging of a focal region within a substrate, the numerical aperture of the optical system of which is increased beyond the value in the absence of this lens. give. Enhanced numerical aperture refers to improved resolution in focusing or illumination. The focal point in a specific area within the substrate is formed without any aberration and gives a wide lateral width to the visual field. The substrates and lens media are very close in refractive index n, even if they are not the same.

The present invention provides read / write capabilities for semiconductor devices and circuits, biological / chemical specimens from the underside of the attachment surface, multilayer semiconductors and dielectrics such as silicon substrate on insulator boundaries, and embedded optical media. Find use in observing.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to numerical values of an observation optical system such as a microscope used for observing a structure in a semiconductor wafer or a chip substrate or an image forming optical system used for exposing a substance such as a data medium. A viewing enhancement lens (NAIL) is provided that acts to increase the iris or collection power. The result is to increase the resolution of the optical system by a refractive index between n and n ² , where n is the refractive index of the lens and the substrate. The lens and substrate are generally of the same index of refraction, but similar advantages can be obtained near match.

FIG. 1 shows such an observation system, in which a computer controlled XYZ motion support 12 holds a specimen 14 in a holder 16. Numerical aperture increase lens (NAIL
18) is placed over the specimen. Generally, the NAIL and the specimen are precision ground to eliminate as much voids as possible, and are small enough to avoid the effects of refraction at the NAIL-substrate boundary, and are in intimate contact, at least within a fraction of the wavelength. Light from objects within the substrate 14, typically from back illumination provided by holder 16 or from surface illumination from above, passes through NAIL 18 and then objective lens 20 and exit lens 24 of microscope system 24. Through the video camera 3
0 or other, observation, recording or imaging element. The signal from the camera 30 is sent to a computer 32 or other processing, storage and / or viewing system for display and recording. This makes it possible to record a series of images over a long period of time, which allows time-resolved measurements. A computer may also be programmed to manually or automatically operate the stage 12 to scan in the X, Y, and / or Z directions to capture an image in a two-dimensional or three-dimensional area.

FIG. 2a shows an enlarged view of NAIL 18 'and substrate 14'. NAI
Since L18 'is generally smaller than a full hemisphere and has a vertical height D, its center away from the outer surface by radius of curvature R is located at point 40 in substrate 14'. While NAIL increases the numerical aperture of the observing objective as described above, it is also desirable to have stigmatic viewing. Within the substrate, there is a spherical surface that is focused and obtains aberration-free observation depending on the depth. This is deeper than point 40, as explained below. The fields of view on either side of this sphere also have an aplanatic or nearly aplanatic distance, providing a planar area in which the objective lens can see with increased resolution and no aberration. If the distance of the field of view into the substrate is X, then D = R (1 + 1 / n) -X. N
The radial phase front, which passes through the ALL in both directions, is geometrically distinct from the convex surface of the NAIL, which allows the observation of substrate depths well beyond the NAIL.

FIG. 2 b shows an observation through the NAIL 18 ″ in the substrate 14 ″ by the objective lens 42 regarding the field of view 44 at the bottom of the substrate 14 ″. The field of view includes, for example, the underside of the processing area of the semiconductor wafer, which contains information about the quality of the finished semiconductor chip or other element. In general, as shown in FIG. 2c, NAIL 18 ″ ″ and substrate 14 ″ ″ may be any element where it is desirable to observe the field of view within the substrate using enhanced resolution. Examples include a microscope slide with a NAIL overlay and a cover glass and thermal imaging of a heat-dissipating semiconductor in operation.

FIG. 3 relates to a single solid object 50 whose upper part 52 represents the NAIL of the present invention and the rest is the substrate to be looked into for aberration-free viewing of the field of view on the spherical surface 54. Virtual plane 58 shows the dividing line between the NAIL and the substrate. Surface 5
4 is defined by R / n as the depth below the center of curvature 60 of NAIL 52.

Due to the optimum resolution, the optics of the microscope are best matched to those of NAIL.
This is reached when the following relations are met:

[0017] ^{_{s = (f 1 - 2)}} / R (n + 1 / n);

[0018]   Where f₁Is the focal length of the objective lens, f_TwoAs the exit lens focal length
Inner lens principal point distance (from objective lens to exit lens principal point) = s + f₁+ F _Two Is.

Advantages of the aplanatic focus include that the regions on either side of the spherical surface 54, as shown in FIG. 3, can also cause the plane 64, which typically contains the region of interest, to be substantially aplanatic. .

An additional advantage of NAIL is that the aplanatic region has a relatively wide lateral width, thus requiring fewer steps for image construction. Thus, it is possible to accept a wide range of off-axis observations. Since various NAILs are generally used to adapt to various substrate depths, NAIL sets and arrays of NAILs will be used. NAIL also coats to minimize reflections on background or foreground illumination. NAILs are also processed as compound lenses and / or with modified objective lens designs to correct chromatic aberrations.

FIG. 4A illustrates an additional use of the present invention in testing for changes or states of optical properties of biological or chemical specimens. The substrate 100 is an NA that covers it as above
It has an IL lens 102. The substrate has an insulating or other layer 104 to which the specimen 106 can be attached. The specimen surface is generally placed in a focal area, which corresponds to the focal area 54 in which any light characteristic in the atmosphere, i.e. illuminated, transmitted or reflected light, can be seen through NAIL 102 at enhanced resolution. The substrate may have a translucent metal thereon for purposes such as strengthening the specimen bond.

The sample 106, as shown in FIG. 4b, can be placed in an environment in which an excitation or fixed or varying environment with microwave energy can be applied to the sample 106, such as delimited by a housing 108.

FIG. 5 illustrates an application of the present invention used to view a specimen 106, such as a microscope slide with a coverslip 118 covering the specimen 106, on a substrate 116. The NAIL lens 120 is placed on the coverslip and the material is sized to create an aplanatic focus area on the specimen 106 as described above. The NAIL lens can be placed on the substrate with the same focal area as described above.

FIG. 6 illustrates a NAIL of the present invention used for making and reading media. In this case, the substrate 130 includes read or write or read / write media such as CDs, DVDs, minidisc players and recorders. Optics 132 are shown to represent the well known device for writing and / or reading to such media. NAIL 134 creates a focal region in the plane occupied by layer 136. This layer is responsive to input laser light from one type of optics 132 (with or without other influences, such as a magnetic field), either permanent or erasable for later reading by another type of optics 132. Make possible records in layers.

7a-7d show actual NAIL usage results where a back-illumination system 150 was used to image the layers of the semiconductor structure as illustrated in FIG. 2b. Figure 7a shows a structural image obtained using a conventional 5.4X microscope without NAIL. 7b and c
Shows an observation using NAIL over a semiconductor substrate. The N-type diffusions machined at locations 140 and 142 in the polycrystalline silicon test line and semiconductor respectively are clearly shown. Figure 7d shows a linear scan across the image of Figure 7c, showing sharp resolution at an enhancement factor of about 96X.

The present invention also provides a semiconductor device formed between silicon and an insulator in silicon-on-insulator (SOI) processing by placing the junction in the focus and aberration-free region of observation, as shown in FIG. It is also useful for testing inside joints. Here, layer 160 represents the boundary between semiconductor material 162 and insulator 164. NAIL 166 allows for a strengthening inspection of this boundary. In the case of a semiconductor material as NAIL and / or substrate, Si, Ge, SiGe, GaAs, GaSb, GaP
, InP, GaN, or combinations of materials containing combinations of basic atoms of triple or higher structure are particularly useful.

The present invention is also useful for detecting Raman scattering from within a substrate in Raman spectral analysis. 9a-9b show an array 170 of NAIL 172 of the present invention mounted on a substrate 174. At this time, the single objective lens 176 can be used with a plurality of NAILs 172. This has the advantage of having a wide field of view. In addition, by using NAIL172 having different dimensions,
Various depths within the substrate 174 can be observed with a focus without aberrations. Figure 1
0 is NAIL 180, generally of the same or similar diameter, useful in the practice of the invention.
182, ... 184 sets are shown.

To carry out the invention as illustrated in FIG. 1 using an external lens optics,
The overall characteristics of chromatic aberration can be corrected by the combined characteristics of NAIL and other system optical components. The present invention with chromatic aberration correction also enables broad spectrum analysis in thermal imaging at infrared wavelengths and near infrared wavelength visual inspection of semiconductor circuits and devices.

[Brief description of drawings]

FIG. 1 illustrates an imaging system having a numerical aperture increasing lens (NAIL) according to the present invention.

FIG. 2a is a cross-sectional view of NAIL and substrate in a typical viewing relationship.

FIG. 2b is a cross-sectional view of NAIL and an observation objective lens for observing the inside of the substrate.

FIG. 2c is a cross-sectional view of a generalized NAIL and substrate relationship showing the scope of application for the present invention.

FIG. 3 is a cross-sectional view of a medium showing a geometrical and mathematical relationship between a NAIL surface and an aplanatic focal plane.

4a-4b NA of the present invention in specimen inspection on substrate bottom.
The additional use of IL is shown.

FIG. 5 shows an application of the invention used to observe a specimen under a coverslip.

FIG. 6 illustrates the use of the invention in the read / write area.

7a-7d show actual images from the use of the invention in observing semiconductor structures.

FIG. 8 illustrates the present invention for boundary inspection in SOI devices.

9a-9b illustrate the use of the invention in an array.

FIG. 10 shows a set of NAILs according to the present invention.

─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Goldberg, Bennett, Bee.             United States 02160 Massachusetts             Newton Berkshire Road, Tutu               26 F term (reference) 2H087 KA09 NA14 QA01 QA07

Claims (31)

[Claims] 1. A lens having an extended numerical aperture for use in observing or imaging light emitted from or into a substance passing through the surface of the substrate, the lens being aligned with the surface of the substrate. A lens having a first surface and a second surface having a convex shape; a lens having a focal region in the substrate when the first surface of the lens contacts the substrate surface; A viewing light or imaging light that passes through the convex mold surface with a phase front that is geometrically distinct from the mold surface shape. 2. The lens of claim 1, wherein the viewing light or imaging light comprises the infrared, visible, or ultraviolet spectrum. 3. The lens according to claim 1, wherein the lens is a chromatic aberration correcting compound lens. 4. The lens of claim 1, wherein the refractive index of the lens and the substrate are matched. 5. The lens of claim 1, wherein the lens and the substrate are integrally formed from substantially the same material. 6. The lens of claim 1, wherein one or both of the lens and the substrate are processed from a semiconductor material. 7. The semiconductor material is essentially Si, Ge, SiGe, G
7. The lens of claim 6, selected from the group comprising aAs, GaSb, GaP, InP, GaN, or a combination thereof. 8. The lens of claim 1, wherein the substrate comprises a fabrication structure including devices and circuitry located at or near the focal region. 9. The lens of claim 1 wherein the substrate includes a textured structure in or near the focal region that emits blackbody radiation to enable thermal imaging. 10. The lens of claim 1, wherein the substrate is a silicon wafer on insulator having a boundary in the focal region. 11. The lens of claim 1, wherein the substrate comprises a translucent metal on its surface in the focal region. 12. The lens according to claim 1, wherein the convex surface shape is a spherical surface, 13. The lens has a radius of curvature R, the medium has a refractive index n, and the focal region originates at a radius R / n from the geometric center of the convex spherical surface. Lens. 14. The focal region is aberration-corrected and extends over the entire radius region such that the surface cutting the region orthogonal to the radius has an aberration-corrected focal region. lens. 15. The lens of claim 14, wherein the focal region has the cutting surface parallel to the substrate surface. 16. An optical system comprising one or more lenses in combination with one or more lenses according to claim 1 and having chromatic aberration correction. 17. An optical system comprising one or more of the lenses of claim 1, which is responsive to light from said lenses to produce its image using the enhanced resolution of the objective lens in said focal region. 18. The optical system of claim 17, further comprising an array of said lenses. 19. The optical system of claim 17, further comprising an objective lens or set of lenses for adjusting the depth of the focal region in the substrate. 20. The imaging system has an objective lens and an exit lens,
Its main point is, the R and lens diameter, when n is a refractive index about said lens and the _substrate, the distance according to the relationship of ^{_{d = f 1 + f 2 -f}} 1 2 / R (n + 1 / n) d 18. The optical system of claim 17, which is separated by. 21. The optical system of claim 17, wherein said optical system comprises broad spectral chromatic aberration correction at infrared wavelengths for thermal imaging. 22. The optical system of claim 17, wherein said optical system is prepared for operation at near infrared wavelengths for substrate passage visual inspection of semiconductor circuits and devices. 23. The optical system of claim 17, including a system for Raman scattering measurement. 24. The optical system of claim 17 including a time resolved measurement system. 25. The lens of claim 1, further comprising a second surface suitable for placing a specimen on the substrate, the focal region being at or near the second surface. 26. The lens of claim 25, further comprising a system for testing the specimen in a predetermined environment. 27. The lens of claim 25, further comprising a source of excitation of the specimen. 28. The lens of claim 1, wherein the substrate includes a specimen holder having an upper surface in the focal region and a coverslip over it. 29. The lens of claim 1 further comprising a substrate responsive to illumination of a predetermined characteristic in the focal plane to create a readable record of the presence of the illumination. 30. The lens of claim 29, further comprising a read / write system having the substrate as a recordable and readable medium. 31. The lens of claim 1, further comprising a recording / playback system for reading data in the focal area, wherein the substrate is a data medium.