JP4024001B2 - Method and apparatus for optical inspection of multilayer electronic components - Google Patents

Abstract

A novel optical inspection technique for multi-layer wafers and the like in which conductor patterns of a top layer only are to be inspected, such layer being upon an intermediate transparent or translucent insulation layer in tu rn upon a base layer(s) thereunder, wherein the intermediate layer only is fluoresced, displaying the top layer conductors as dark in the field of fluorescent light, and causing reflections from layers below the intermediat e layer effectively to disappear to obviate confusion with the top layer conductors to be inspected.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to optical inspection of electronic components and the like, and more particularly to optical inspection of wafers, flat display panels, multichip modules, movable circuit patches, decals and the like from which integrated circuit chips are formed. These consist of an upper layer of various patterns of conductors, an intermediate layer of transparent or translucent insulators (often with the conductor layer on the outer top), ceramic, glass, metal, etc. And a lower layer having conductors of various patterns.
[0002]
[Prior art]
Conventionally, fluorescent radiation has been used to inspect electronic circuit boards consisting of an epoxy layer containing conductors that form the circuit to be deposited. This conductor is typically a metal that can have a very rough surface, such as copper, copper oxide, tin-plated copper, and the like. Here, the rough surface means that the defect cannot be inspected by using an optical image processing technique because it is too troublesome. As a result, inspection device manufacturers use lasers with wavelengths that are particularly suitable for fluorescing epoxy layers having conductors that make up electronic circuits. In doing this, the epoxy background fluoresces at various wavelengths (colors), but the conductor does not emit light and appears dark. Therefore, when the conductor has a defect such as a broken conductor, such a defect appears as a non-dark area and can be detected. Furthermore, since the short circuit appears as a shadow in a place that should be a bright region, it is detected as a defect. What is important in the use of this fluorescence is, in particular, to overcome the effects of optical fluctuations or to image defects in the uneven conductor itself.
[0003]
Mat. Resi. Soc. Symp Proc. Vol 381, 1995, pp. 165-173, RADeVries et al., Entitled “Digital Optical Imaging Of Benzo-Cyclobritene (BCB) Thin Films On Silicon Wafers” It is described that a thin film is fluorescently emitted to detect variations or particles.
[0004]
Fluorescence is also used to detect various cracks and defects in mechanical parts, etc., and the fluorescent material is applied on the part so that the fluorescent material remains only in the cracks or defects where the fluorescent material enters. Wiped off.
[0005]
[Problems to be solved by the invention]
On the other hand, in connection with the high-density multilayer integrated circuit component, which is regarded as a problem related to the present invention, several layers or coatings including conductive wires are sequentially stacked on the lower base substrate layer, and transparent or translucent layers are formed thereon. An intermediate insulator layer is overlaid. When inspecting upper layer defects including conductor patterns, a very unique problem arises when inspecting such defects and the like of such multilayer parts. This problem is due to the combination of reflections from any superimposed layers, and incident light is reflected not only from the top layer, but also from lower layers, and all these reflections overlap, causing the top conductor This is because even if it is necessary to distinguish only the inspection of the pattern layer, this cannot be performed.
[0006]
Attempts to identify upper conductive pattern images using dark locations, shallow angle illumination, color identification, and cross-polarization illumination were unsuccessful.
[0007]
[Means for Solving the Problems]
However, the basis of the present invention is that the conductor of the upper conductor pattern is through the use of intermediate light that propagates in a preferably translucent or transparent insulator layer that fluoresces at different wavelengths depending on the predetermined wavelength of incident light. Since the incident light is reflected at its original wavelength and does not fluoresce, it can be distinguished immediately, and only the desired inspection of the upper layer conductor can be performed in a discriminative and selective manner, below the intermediate phosphor layer. The discovery is that any reflection of incident light from a layer can be successfully solved by rejecting, masking, or erasing.
[0008]
Such approaches have been carefully done in the prior art on pre-machined flat level surfaces, but these techniques are used for irregularly uneven boards, mass-produced circuit board angles. It is not suitable for conductors and wafers with a mark, and is solved by the present invention.
[0009]
SUMMARY OF THE INVENTION Accordingly, a primary object of the present invention is to provide a new and improved method and apparatus for enabling differential and selective inspection of defects such as upper layers of multilayer electronic components including intermediate and lower layers. Is to provide. The upper layer contains a pattern of conductors such as lines that should be individually inspected for such defects, and the intermediate layer consists of a transparent or somewhat translucent insulator that fluoresces depending on the predetermined incident wavelength of incident light. The upper conductor is selectively displayed as a dark image on the fluorescent intermediate layer image to provide a fluorescent image masked by reflection from the lower layer.
[0010]
A further object is to provide a novel optical inspection technique in which an inspection of an upper layer including a conductor etc. can be imaged while effectively completely erasing reflections from the layer including the underlying conductor. That is.
[0011]
Other and further objects will now be described, and more particularly will be outlined in the appended claims.
[0012]
SUMMARY However, as an overview, perhaps from one of its broadest aspects, the present invention includes a method for optically inspecting an upper layer of a multilayer electronic component having an intermediate layer and a lower layer. The upper layer includes a pattern of conductors to be inspected, and the intermediate layer is made of a transparent or translucent insulator, and this method selects a predetermined wavelength of light incident on the intermediate insulator layer to select the conductor or other Reacting the layers at different wavelengths so that they do not fluoresce, irradiating incident light onto the upper layer of the component, reflecting incident light from the layers and returning reflected light to the inspection camera, and Returning fluorescence from the middle layer to the camera and selectively imaging only the returned fluorescence to suppress all other incident light reflected from the top and bottom layers of the middle layer to the camera, thereby The non-fluorescent pattern of the conductor is expressed as a dark color in contrast to the background of the fluorescent interlayer image, and the reflection from below the intermediate layer is effectively removed. Preferred design techniques and optimal modes of operation are described in detail below. The present invention will be described with reference to the accompanying drawings.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Preferred Embodiment of the Invention A typical multi-layer chip having the features described above is shown in FIGS. These include, for example a ceramic base or substrate layer L _4, having a layer L ₃ of the metal conductor C as shown in Figure the top. Then, in order, typically transparent or translucent is desirable and is covered with an intermediate layer L ₂ made of, for example, organic polyimide, and the intermediate layer L _{2 further} includes a lower conductor C on the intermediate insulator layer L _2. insulated from the conductor C ¹ on the upper layer L ₁ to be overlaid.
[0014]
Illustrated is a state in which the incident light L from the light source is directed onto the upper layer L _{1 of the} chip by the half mirror M and reflected from the upper layer pattern of the conductor C ¹ . Thick vertical arrows indicate incident light L and reflected light R returning to the inspection camera. The intermediate insulator layer L ₂ that covers the lower conductor C of the layer L ₃ does not become flat, but has an irregular shape with depressions formed by the settling of the layers, as shown in the figure. Conductor C ¹ of the top, as shown in FIG, by irregularities or depressions projecting layer L _2, may be tilted somewhat, some of the reflection from the conductor C ^1, deposited conductors C ¹ Although the angle of the layer may not reach the camera, the planar area of the conductor C ¹ returns reflected upward inspection camera direction R. Referring to the light transfer characteristics of the semi-transparent or transparent intermediate insulator layer L ₂ , in FIG. 1B, light is also reflected back from the underlying conductor C and substrate layer L ₄ to the camera CAM. This results in the synthesis of overlapping reflections from the various layers, which will be fully explained later, but in many cases this confusion makes the inspection of upper conductors extremely difficult if not impossible.
[0015]
The camera and imaging circuit are, for example, my U.S. Pat. Nos. 1, pp. 119, for the purpose of image inspection as the camera passes through or scans over chips or other parts made of multilayer structures. It may be of the kind described in .5,119,434 and 4,697,088. As a further illustration, other optical inspection devices are described in US Pat. Nos. 5,058,982 and 5,333,052.
[0016]
In the present invention, the confusion, the special use of the incident light wavelength L to fluorescence light of greater wavelength than the incident light only in the intermediate insulating layer L _2, is dramatically avoided. This fluorescence, in FIG. 1C, causes some trend rays to be directed to the camera CAM by the lens L ¹ , as shown schematically by the dotted line as reflected light F returning in all directions from the rough surface of the layer L ₂ . By aligning the direction, it also includes rays indicated by dotted lines that radiate out of the vertical direction from the exposed lower slope / indentation region of the intermediate layer not covered by the tilted conductor. By filtering all the rays other than the above-mentioned large wavelength fluorescence with the FIL, the reflection R of the incident wavelength in FIGS. 1A and 1B is removed by the filter FIL, and only the fluorescence F from the intermediate layer L ₂ is imaged by the camera CAM. Will be converted. By making the thickness of the fluorescent intermediate layer L ₂ sufficiently thick so as not to transmit light almost completely, the pattern of the upper conductor C ¹ is displayed as a shadow on the fluorescent image of the layer L _2. The And since the reflection R of the incident light wavelength from the layer below the intermediate layer L ₂ is masked or removed, they are effectively removed (FIGS. 1A and 1B show that they do not pass through the filter FIL). have), it is possible to test only a clear and selective pattern of the upper layer of conductor C ^1.
[0017]
FIG. 2 shows a fluorescence intensity spectrum of a preferable argon layer light source X for a preferable polyimide material having a transparent or translucent characteristic that functions as the insulating film layer L ₂ as described above.
[0018]
Comparison between FIG. 3 and FIG. 4 shows the effect of the present invention when this is used. FIG. 3 is a normal white light image generated from such a multilayer wafer circuit, showing all layers below the upper conductor layer. Changes in the surface of the conductor are also clearly visible. By using this technique, the upper layer is inspected without causing interference or overlap due to any reflection of light from the lower layer.
[0019]
In this multi-layer wafer structure, the top layer appears white with a plurality of dark lines across it caused by the phase change, and all the layers below are also visible. This means that it is not only extremely difficult to determine the upper layer, but that it is virtually impossible to find a broken or shorted or defective upper conductor of interest. In contrast, FIG. 4 is a photograph of the fluorescent image obtained in accordance with the present invention of FIG. 1C, clearly showing the top conductor. With this technique, the upper layer is inspected without interference or overlap due to reflection of any light from the underlying layer.
[0020]
FIG. 5 shows another multichip module having three layers. In this example, it is difficult to determine the upper layer, and many lines and bands cross the image due to phase changes. However, in FIG. 6, using the present invention (FIG. 1C), the fluorescent image clearly distinguishes the upper conductor, excluding the other underlying layers.
[0021]
Thus, while the present invention has been described generally with respect to a fluorescent insulator layer, the preferred layer is a polyimide organic that fluoresces in response to an incident argon light wavelength of 488 (or 514) [nm]. This fluorescence spectrum is in the range of about 500 to 7000 [nm] in FIG. 2, and as shown in FIGS. 4 and 6, the selective filter (FIL) is effective for any reflection that occurs from non-fluorescent materials upon incidence. It is this range that can be separated. Other wavelength light sources and similar fluorescent materials as described in the above articles can also be used in accordance with the principles of the present invention. A preferred lower layer or base substrate L ₄ is selected from ceramic, glass, epoxy and metal. In addition, the present invention can be applied to any similar multilayer electronic component or other component that requires selectivity for inspection of the upper layer without causing confusion due to reflections from the lower layer. These include flat display panels, multichip modules, movable circuit patches and decals and other applications as well as the wafer from which the integrated circuit chips are formed.
[0022]
Further modifications will be apparent to those skilled in the art, all of which are considered to be within the scope defined by the spirit of the invention and the appended claims.
[Brief description of the drawings]
FIGS. 1A and 1B are partial cross-sectional views illustrating reflection of light from a multilayer chip or the like to a camera according to the technique of the present invention. FIG. 1B is a diagram illustrating a position scanned from the position of FIG. 1A to the front of the camera, that is, to the left.
FIG. 1C is a similar view at the next scanning position, showing that fluorescent scattered light returns from only the intermediate layer to the camera.
FIG. 2 is a graph showing a range of a preferable fluorescence spectrum emitted from a preferable interlayer insulating material in response to argon incident light having an emission line wavelength of 488 [nm].
FIG. 3 is a diagram showing the overlap of synthesized and indistinguishable reflections arising from various layers of a conventional multilayer wafer, indicating that it is almost impossible to detect defects only in the upper layer.
FIG. 4 is a selection diagram of a fluorescent intermediate insulator layer according to the present invention, the overall solution of the problem by selectively identifying the upper layer pattern of the conductor and removing all reflections from below the intermediate layer. Shows how.
FIGS. 5 and 6 are views showing the same contents as in FIGS. 3 and 4 for another wafer, respectively, and again show the effect of the present invention.

Claims (8)

An imaging system inspection camera (CAM) for optical inspection of an upper layer (L1) of a multilayer electronic component (C) having incident light (L) of a predetermined wavelength and an intermediate layer (L2) and a lower layer (L4); Optically inspect using
The upper layer (L1) is tested to cover only a portion of the intermediate layer made of a transparent or translucent insulation of material that fluoresces at a different wavelength (L2) from the predetermined wavelength in response to the incident light Having a conductor pattern (C ′) to be
The conductor pattern (C ′) exposes a plurality of fluorescent regions of the intermediate layer (L2) to the camera (CAM);
Wherein only the fluorescence wavelength by the camera (CAM) A method which is required to be received, while effectively removing the light reflected from the layer below the intermediate layer (L2), the intermediate and selectively transmitting only the wavelength of the incident light having a predetermined fluorescence wavelength of the layer (L2) (FIL), said intermediate layer being the fluorescent image background as opposed to the dark the conductor of the (L2) In a method configured to generate an image of a pattern in the camera,
The intermediate layer (L2) is a layer with irregular irregularities having a relatively flat region between a plurality of recesses, and the pattern of the conductor has an angle with respect to the axis of the incident light (L) Inspecting a multilayer part having a conductor (C ′ ) on the intermediate layer (L2) ,
In order to collect fluorescent light not only from fluorescent light emitted parallel to the optical axis of the incident light from the intermediate layer (L2) but also from light emitted along a direction not parallel to the axis the alignment with respect to the camera the said wavelength selectively transmitting fluorescent light in front of the (CAM) by a collimator lens (L ') camera (CAM), the aligning process is not covered by said conductor said An image generated by the camera that also allows the reception of fluorescent light emitted off the vertical direction from the area of the exposed recess, thereby operating the fluorescent light to be received and imaged by the camera. Providing the fluorescent image with enhanced contrast of the dark conductor pattern in the method.   The method of claim 1, wherein the intermediate layer comprises vias or connecting holes that appear dark in the fluorescent image that appears to be reflected through these holes from a non-fluorescent layer below the intermediate layer.   The method according to claim 1 or 2, wherein the lower layer (L4) is a base substrate selected from the group consisting of ceramic, glass and metal.   The method according to any one of claims 1 to 3, wherein the intermediate layer (L2) is an organic layer capable of emitting fluorescence in response to the incident light wavelength.   The method of claim 4, wherein the organic layer comprises polyimide.   The incident light (L) is generated by an argon light source having a predetermined radiation of 488 [nm] or 514 [nm], and the different wavelength of the fluorescent insulator is a spectrum in the range of 500 to 700 [nm]. The method according to claim 1, wherein   The multilayer electronic component (C) is selected from the group consisting of a wafer for forming an integrated circuit chip, a flat display panel, a multichip module, a movable circuit patch and a decal. the method of. An apparatus for optically inspecting an upper layer (L1) of a multilayer electronic component (C) having an intermediate layer (L2) and a lower layer (L4), wherein the upper layer (L1) is a transparent or translucent insulator Including a pattern (C ′) of a conductor to be inspected that is disposed on and covers a portion of the intermediate layer (L2) of
The device
An incident light source of a predetermined wavelength that responds by fluorescence of the intermediate layer (L2) rather than the conductor and other layers at different wavelengths ;
An optical path that directs the incident light (L) to the upper layer and returns a reflection (R) of the incident light to an inspection camera (CAM) for imaging the upper layer (L1);
Means for filtering the reflected light of the predetermined wavelength and preventing the camera from receiving the light of the predetermined wavelength, and effectively removing reflection from below the intermediate layer (L2). while, in the apparatus in which the image of the non-fluorescently conductor pattern as opposed dark image in the background of the image of the middle tier that fluorescence (L2) is adapted to form the camera (CAM),
The intermediate layer (L2) has irregularities formed at irregular intervals, and the conductor pattern (C ′ ) forms an angle with respect to the axis of the incident light (L). A conductor overlying (L2) , and the device is not only for the fluorescent light emitted parallel to the optical axis of the incident light from the intermediate layer (L2) , but also for the optical axis. A collimating lens (L ′) in front of the camera (CAM) for condensing fluorescent light even for light emitted along a non-parallel direction;
The fluorescent light selectively transmitted in front of the camera (CAM) is aligned with the camera (CAM) by the collimating lens (L ′), whereby the collimating lens (L ′) becomes the conductor. Also enables the reception of fluorescent light emitted off the vertical direction from the exposed recessed area not covered by the light, so that the fluorescence is received and imaged by the camera ( CAM) And providing the fluorescent image with enhanced contrast of the dark conductor pattern (C ′ ) in the image generated by the camera ( CAM) .

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