Patent Application
20100078329
This application relates to inspection and process control for interconnect substrates, more particularly, ALOX™ substrates.
Microelectronics packaging and interconnection technologies have undergone both evolutionary and revolutionary changes to serve the trend towards miniaturization in electronics equipment, which is now very evident in military, telecommunications, industrial and consumer applications. The trend has been driven by various forces including specialist requirements for size and weight as well as cost and aesthetics, which have led to various innovative developments in packaging of integrated circuits and in connectivity on electronics substrates and circuit boards.
In a broad sense, “microelectronic packaging” can simply be viewed as a way to interface an IC (or a die) with the “real” world of peripherals such as power sources (e.g., power supplies, batteries, and the like), input devices (e.g., keyboards, mouses, and the like), and output devices (e.g., monitors, modems, antennas, and the like). To do this, you need to connect the IC (or die) with the peripheral—basically, to get signals in and out of the IC, as well as to provide operating power to the IC—and this is typically done with wires or conductive traces on a printed wiring board (PWB).
There are many examples (or subsets) of interconnect substrates, one example is the “interposer”. Generally, an interposer provides electrical connections between an IC and a package, may perform a pitch spreading function, typically does not “translate” connection types (rather, has one connection type on both the “in” side and the “out” side), and often must provide a thermal management function.
A fundamental purpose of an interconnect substrate is, simply stated, to electrically connect two electronic components with one another. If, for example, you have a simple two terminal device (such as a simple resistor having two leads) poking through two holes on a PWB to conductors on the underside of the PWB, this is relatively straightforward, even if there is a conductive trace on the PWB which needs to pass under a body portion of the two terminal device (without connecting to it). However, with more complex electronic devices having many terminals (for example, input/output (I/O) connections) it is inevitable that there needs to be many crossovers to effect complex routing of signals (to a lesser extent, power). Solutions to this topological problem is multilayer interconnect technology.
In multilayer interconnect technology, there are typically several metal layers (of conductive traces) separated from one another by layers dielectric material. (Kind of like a layer cake, or lasagna.) Multilayer interconnect substrates with tens of alternating dielectric and conductive layers are not uncommon, and typically many layers are needed to effect complex routing schemes (schematically speaking, many cross-overs).
A key element in every multilayer interconnect technology is the “via”—an electrical connection between conductive traces of two adjacent metal layers separated by a dielectric material.
In conventional multilayer substrate technologies a dielectric sheet is used as base material, in which the vias are formed using drilling (etching or punching) and hole plating process. (A via is kind of like a metal eyelet for shoelaces.)
In multilayer substrate technology one type of via is the “blind” via which extends through a given dielectric layer(s) to a conductive trace on an inner metal layer, rather than completely through the entire substrate. Another blind via may extend through the remaining dielectric layers from a different position on the conductive trace, which could be useful for pitch spreading, or simply for effecting complex interconnections.
Vias provide electrical connectivity between conductive traces on two different (typically adjacent) metal layers, and also can serve a role in conducting heat away from an operating electronic device mounted on the substrate. Typically, with a dielectric-based substrate (such as a ceramic substrate), the vast bulk of the substrate is poor thermal conductivity ceramic material, in which case many vias can be formed and filled to improve the thermal conductivity. ALOX™ substrate technology is described in the following patents and publications: U.S. Pat. No. 5,661,341; U.S. Pat. No. 6,448,510; U.S. Pat. No. 6,670,704; International Patent Publication No. WO 00/31797; and International Patent Publication No. WO 04/049424, the disclosures of which are incorporated herein by reference.
ALOX™ substrate technology is a multilayer substrate technology developed for microelectronics packaging applications. The ALOX™ substrate technology does not require drilling and hole plating—the via is of solid full aluminum and the dielectric is of a high quality ceramic nature. The process is simple and low cost, and contains a low number of process steps. The ALOX™ substrate technology serves as a wide technology platform, and can be implemented in various electronics packaging applications such as for RF, SiP, 3-D memory stacks, MEMS and high power modules and components.
The starting material in the ALOX™ process is a conductive aluminum sheet. A first step in the process is masking the top and bottom of the sheet using conventional masking techniques and materials (for example, lithography and/or photoresist). Via structures are formed using anodization of the sheet through the whole thickness of the sheet. The exposed areas are converted into aluminum oxide, which is ceramic in nature and a highly insulating dielectric material. The protected unexposed areas remain as aluminum elements—the connecting vias.
In its simplest form, an ALOX™ interconnect substrate is formed by electrochemical anodic oxidation of selected portions of an initially conductive valve metal (for example, aluminum, titanium, or tantalum) substrate resulting in areas (regions) of conductive (starting) material which are geometrically defined and isolated from one another by areas (regions) of anodized (non-conductive, such as aluminum oxide, or alumina) isolation structures. “Vertical” isolation structures extend into the substrate, including completely through the substrate. “Horizontal” isolation structures extend laterally across the substrate, generally just within a surface thereof. Anodizing from one or both sides of the substrate can be performed to arrive at complex interconnect structures.
In a more complex form, such as disclosed in U.S. Pat. No. 6,670,704, using this innovative process, a multilayer low cost ceramic board is formed. A complete “three metal layer” core contains an internal aluminum layer, top and bottom patterned copper layers with though vias and blind vias incorporated in the structure. The ALOX™ technology offers a very simple and low cost production process; excellent thermal performance product, superior mechanical and electrical properties. The ALOX™ technology is illustrated in the following figures.
Notice in step (d) that the anodizing proceeds partially anisotropically, extending slightly under the photoresist and also tapering in width from thickest at the top and bottom surfaces of the substrate to thinner within the body of the substrate. In step (d), anodization proceeds from both sides of the substrate. (In a situation involving a layer rather than a substrate, anodization would proceed from only an exposed side of the layer.) The resulting aluminum oxide is porous.
The photoresist islands 105 are stripped (e), and pore filling material, such as a resin is diffused into the porous oxide regions of the layer/substrate. For a substrate, resin for example can be diffused from both sides. (Theoretically, the substrate could be impregnated with resin before photoresist strip.) The result is an aluminum via 108 extending completely through the substrate from one surface thereof to the opposite surface thereof, and the via is isolated from other such vias (not shown) by the insulating (and impregnated) aluminum oxide material 106. This is referred to by the assignee as the “core of cores”.
Next, metal interconnect layers 110 of conductive traces (such as copper) are applied (f), using conventional technology to achieve what the assignee refers to as a “core”, which is a 3 metal layer structure. The process illustrated generally in
Unless otherwise noted, or as may be evident from the context of their usage, any terms, abbreviations, acronyms or scientific symbols and notations used herein are to be given their ordinary meaning in the technical discipline to which the disclosure most nearly pertains. The following terms, abbreviations and acronyms may be used throughout the descriptions presented herein and should generally be given the following meaning unless contradicted or elaborated upon by other descriptions set forth herein. Some of the terms set forth below may be registered Trademarks®.
Generally, the disclosure is described in the context of ALOX™ substrate technology. The ALOX™ substrate technology employs area selective anodization of aluminum substrates for forming patterned anodized (oxidized) areas defining corresponding patterned electrically-isolated aluminum conductive areas, such as vias extending through the substrate. Typically, a vertical isolation structure surrounding a via will be ring-shaped.
As used herein, aluminum is exemplary of any number of “valve metal” starting materials that is initially a good electrical conductor, and which can be selectively converted to a non-conductive (insulating) material (such as, but not limited to aluminum oxide) by a process such as (but not limited to) electrochemical anodic oxidation resulting in conductive areas (regions) which are defined and isolated from one another by the insulting areas (regions).
The inventors have noted that aluminum oxide (Al2O3) is relatively transparent to light and that therefore, a fully oxidized zone (such as vertical isolation structure) can be visually observed and inspected using light transmission. The inspection process may be automated.
An aspect of some embodiments of the invention relates to providing a method for process control in ALOX™ substrate fabrication. A step in ALOX™ substrate fabrication is anodizing an aluminum panel, area selectively, to form pre-designed zones (vertical isolation structures) in the panel, which are fully oxidized through the whole thickness of the panel. Methods are disclosed for monitoring this process step and determining when it is complete using visual inspection of transmitted light through the oxidized zones. The inspection process may be automated.
According to an embodiment of the disclosure, a method of making an interconnect substrate comprises: providing a valve metal substrate; selectively anodizing the substrate to form vertical isolation areas that extend completely through the substrate; and determining whether the vertical isolation areas have been fully formed by shining light through the substrate. The valve metal substrate may be aluminum.
Light may be observed shining through the substrate, and a determination may be made that a given vertical isolation area is defined as fully formed if it appears as a continuous area of light. The vertical isolation areas may extend through the substrate, surround and define valve metal vias which extend through the substrate and which are electrically isolated from other valve metal vias and from the body of the substrate, in which case a given vertical isolation area is determined to be fully formed if it appears as a continuous ring of light surrounding a corresponding one of the valve metal vias.
Observing whether the vertical isolation areas are fully formed may be performed during anodizing the substrate, and the process of forming the vertical isolation areas may be continued if they are determined to not be fully formed, until they are fully formed.
According to an embodiment of the disclosure, apparatus for inspecting an interconnect substrate comprising a valve metal substrate having a plurality of vertical isolation areas extending completely through the substrate and defining a plurality of valve metal vias electrically isolated from the body of the substrate, comprises: a light source for shining light through the substrate; and detectors for observing whether the vertical isolation areas are fully formed.
The substrate may be held (supported) by a scanning mechanism, such as an X-Y mechanism under computer control, or by a light table. Inspection may be performed using a microscope, and determining whether the vertical isolation areas are fully formed (analyzing images) may be performed with the computer.
The apparatus may be capable of functioning while the substrate is in an anodizing bath. A first mirror may be provided for reflecting light from a light source external the bath, through the substrate, to a second mirror for reflecting light passing through the substrate to external the bath. Means for moving the mirrors to scan the substrate may be provided, and means for moving the substrate in the bath may be provided, to effect scanning.
There is therefore provided in accordance with an embodiment of the invention, a method of forming an insulator that passes through a metal substrate comprising: anodizing a region of the substrate to form the insulator; illuminating the region with light; and determining if the light passes through the substrate at the region to determine if the insulator passes completely through the substrate.
Optionally, the method comprises determining a pattern for the light that passes through the substrate. Optionally, the method comprises determining whether the pattern is satisfactory. Optionally, the method comprises determining deeming that the insulator is satisfactorily formed when the pattern is satisfactory. Additionally or alternatively, the method comprises stopping anodization when the pattern is satisfactory.
In some embodiments of the invention, determining if the light passes through the region comprises determining during anodization. In some embodiments of the invention, determining if the light passes through the region comprises determining when anodization has stopped.
There is further provided in accordance with an embodiment of the invention, a method of forming an insulator that passes through a metal substrate comprising: anodizing a region of the substrate to form the insulator; illuminating the region with light; and stopping anodization when a sufficient amount of light passes through the substrate at the region. There is further provided in accordance with an embodiment of the invention, a method of making an interconnect substrate comprising an insulated via that passes through the substrate, comprising forming an insulator in accordance with an embodiment of the invention that completely surrounds a region of non-anodized metal.
In some embodiments of the invention, the metal is a valve metal.
There is further provided in accordance with an embodiment of the invention apparatus for forming an insulator that passes through a metal substrate comprising: apparatus for anodizing a region of the substrate to form the insulator; a light source configured to illuminate the region with light; and at least one detector positioned to receive light that passes through the substrate at the region.
Optionally the apparatus comprises a scanning mechanism that moves the substrate relative to the detector so that light passing through the region is incident on the at least one detector.
Optionally, the scanning mechanism moves the substrate relative to the light source so that light passing through the region is incident on the at least one detector. Additionally or alternatively, the scanning mechanism moves the substrate. In some embodiments of the invention, the scanning mechanism moves the light source. In some embodiments of the invention, the scanning mechanism moves the at least one detector. In some embodiments of the invention, the at least one detector comprises a microscope. In some embodiments of the invention, the light source is configured to illuminate the substrate during anodizing.
Reference will be made in detail to preferred embodiments, examples of which may be illustrated in the accompanying drawing figures. The figures are intended to be illustrative, not limiting. Although the disclosure is generally described in the context of these preferred embodiments, it should be understood that it is not intended to limit the claims to these particular embodiments.
Certain elements in selected ones of the figures may be illustrated not-to-scale, for illustrative clarity. The cross-sectional views, if any, presented herein may be in the form of “slices”, or “near-sighted” cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity.
Cross-hatching may or may not be used in cross-sectional views. If it is, close-spaced diagonal line cross-hatching is used to indicate insulator and wide-spaced cross hatching is used to indicate conductor.
Elements of the figures are typically numbered as follows. The most significant digits (hundreds) of the reference number correspond to the figure number. For example, elements of
The disclosure relates to inspection techniques for interconnect substrates, such as ALOX™ substrates.
When aluminum is anodized, it becomes converted to aluminum oxide. Whereas aluminum is a good electrical conductor, aluminum oxide is an electrically-insulting material, thus enabling a substrate of aluminum (valve metal) to be made into an interconnect substrate having electrically-isolated aluminum structures such as vias extending through the substrate by anodizing (converting to aluminum oxide) selected areas of the substrate.
The inventors have noted that for such a substrate (referred to herein as an “ALOX™ substrate”) the anodized (aluminum oxide) areas are relatively transparent to light. Thus, when an ALOX™ substrate is held up to light, one can see evidence of the structures “buried” within the substrate. The aluminum portions of the substrate block light, and aluminum oxide portions extending completely through the substrate transmit light. Therefore, a vertical isolation ring (of aluminum oxide) surrounding a via (of aluminum) is readily observed as a ring of light. This phenomenon of having two materials in the substrate (aluminum, aluminum oxide) having different transparency, is used, in accordance with some embodiments of the invention, for inspecting ALOX™ substrates, both during and after processing, as described herein below.
In a first step 202, masking processes are performed. This includes photolithography, dense anodizing and second masking. Generally, a pattern of masking material, such as dense oxide mask, photoresist mask, is disposed on the surface(s) of the substrate, using conventional photolithography techniques, to prevent the areas covered by masking material from being anodized and, conversely, to allow the areas not covered by masking material to be anodized, as is known. This step is performed to mask the substrate, prior to anodization, using known processes.
In a next step 204, the substrate is anodized, using known processes.
In a next step 206, the substrate is inspected, as described greater detail hereinbelow. (Generally, the purpose of inspection is to determine whether the anodization is complete, and is based on transmitted light inspection.) Good inspection is generally advantageous at this stage, because the following processes are expensive (pore filling, sputtering, lapping).
In a next step 208, post-anodization processes, such as copper metallization (refer to
Generally, the technique(s) disclosed herein are directed at monitoring the results of the anodizing step (204). Generally, a desired result is full anodization completely through selected areas of the aluminum substrate, to form regions of electrical insulation surrounding and isolating conducting regions. The conducting and insulating regions may have any of various desired shapes. Optionally, the insulating regions are ring-shaped aluminum oxide vertical isolation areas enclosing and electrically isolating aluminum via structures extending through the substrate.
Note that the internal aluminum layer 304 is horizontally spaced apart from the aluminum via 306, the aluminum via 306 is horizontally spaced apart from the composite aluminum structure 308, and the composite structure 308 is horizontally spaced apart form the internal aluminum layer 310.
The remainder of the substrate 302 (those areas which are not aluminum) have been converted to aluminum oxide (to define the aluminum structures described hereinabove), as follows:
For purposes of this example, the substrate 302 is being inspected, after anodizing (step 202). Methods for making the exemplary substrate 302, and the substrate itself, are known.
An observer, looking at the opposite side, in this example, a bottom surface 334 of the substrate 302 will see patterns of dark and light, corresponding to areas where there is aluminum (such as 304, 306, 308, 310), and areas where there is aluminum oxide, respectively. This is reminiscent of looking at an X-ray, except that instead of seeing bones, the observer can see aluminum structures (and, the observer can view the structures directly, rather than through the intermediary of film).
Notice in
Aluminum oxide (ceramic) is relatively transparent, as compared with aluminum (metal). A typical via structure, such as 306, has a shape that is round (looking at it from either surface 332 or 334 of the substrate), surrounded by a ring of anodization (such as the areas 314 and 318, which are contiguous with one another).
In ALOX™ technology, vias are typically round, and tend to have a tapered shape, as illustrated in
Regarding the via 306, the observer will be able to see the aluminum via structure 306 as a substantially opaque (non-light transmissive, non-transparent, non-translucent) “dark” circle 346 surrounded by a relatively transparent “light” ring-shaped area 348. The dark circle corresponds to the larger diameter of the via 306 within the substrate 302. The observer may also be able to distinguish a smaller circle 350, which is the smaller diameter of the via 306 at the surface of the substrate 302.
The observer will also be able to see the inner edge of the internal aluminum layer 304 (which may be in the form of a ring 352 surrounding the via 306).
The ability to observe light areas 348 corresponding to regions such as 314 and 318 (
Again, the examples set forth herein are generally in the context of round-shaped vias surrounded by rings of vertical isolation. Hence, full anodization will be indicated by bright, continuous ring of light surrounding a dark circle.
Recalling that it is the areas which are not covered by masking material (step 202) that become anodized (step 204), hence relatively transparent, it is evident that the inspection of the substrate for rings of light can be performed either before stripping the masking material, such as during the anodizing process (as described hereinbelow), or after stripping the masking material, such as after the anodizing process (as described hereinbelow.
Generally, as is known, the purpose of a via in an interconnect substrate is to effect an electrical connection between an isolated area on the top surface of the substrate and a corresponding isolated area on the bottom surface of the substrate, and an ALOX™ substrate is no different in this regard. In this regard, the purpose of the aluminum via structure 306 is realized if the surrounding aluminum oxide vertical isolation area (the ceramic ring formed around the aluminum via 306) is completely formed—in this example, the areas 314 and 318 being fully oxidized.
In
Typically, for making vias (406, compare 306), the top and bottom masking patterns are identical. Areas, which are not intended to be anodized are masked (covered) by material 424 and 428. Areas covered by mask material 424 and 428 will become the aluminum vias 406 (not formed yet, shown with dashed lines). Masking material 424 and 426 determines the main bodies of vias 406 and remains throughout the anodizing process. In areas between the masking material 404, anodization will proceed, to form the vertical isolation structures 414 (not formed yet) which electrically isolate the vias 414 from the other vias 414 and from the body of the substrate 402. Masking material 428 and 430 is provided so that that during anodizing, rate of growth of anodized material into substrate 402 proceeds at a relatively same rate for most regions between vias 406. Masking material 428 and 430 does not remain throughout the anodizing process. The material is configured to dissolve and/or amalgamate with material anodized during the anodizing process and disappear, or to be removed, at about a time when anodizing has penetrated for example from surface 403 or 404 to a depth of about 15% or 25% of the total thickness of substrate 402. Use of masking material to control rate of growth of anodized material is described in U.S. Pat. No. 6,670,704 the disclosure of which is incorporated herein by reference.
Once masked, anodization can proceed using any of various suitable anodizing methods known in the art.
The anodization process is largely anisotropic, and will proceed not only through the substrate 402, but also under the masking material 424, 426, 428 and 430. The size (such as diameter) of a masking element 424, 426 is generally approximately the same size as the resulting via 406 (that is, the diameter of the via 406 within the substrate 402).
The mask elements 424, 426 must be properly sized and the anodization process controlled so that the anodization does not proceed laterally completely across the intended via 406 at the surface(s) of the substrate 402. Else, that would result in a “buried via” (resembling an internal aluminum layer, such as 304) which does not emerge at the surface of the substrate 402.
In
An unsuccessful, or “partial” anodization may look something like the partially complete anodization illustrated in
To give the reader an idea of scale, the area being shown in
To give the reader an idea of scale, the area being shown in
All three vias schematically shown being inspected in
Generally, a substrate 602 under test is placed in an X-Y scanning mechanism, schematically represented by a rectangle 604, such as in a frame holding (supporting) the edges of the substrate, rather than on a table, so that light from a light source 606 can be directed at a surface (bottom, as viewed in the figure) of the substrate, and light passing through the substrate can be detected/observed by an optical apparatus such as a microscope 608. With an optical apparatus such as a microscope 608, X-Y scanning (in this example, moving the substrate) is needed so that the entire substrate can be brought into the field of view (FOV) of the microscope.
Alternatively, the substrate may be placed on (and supported by) a light table, such as of the type used to view photographic negatives, and the light table may be stationary. If the light table is stationary, the microscope (or other optical apparatus) can be fitted for X-Y motion so that the entire surface of the substrate can be scanned—in this example, by moving the field of view across a stationary substrate.
In either case, an X-Y mechanism for moving the substrate or the microscope while it is being inspected would be under the control of a computer for controlling movement of the X-Y mechanism. The computer is also capable of analyzing images of the substrate being inspected, using any suitable matching algorithm, such as by comparing images to templates stored in computer memory, for example, or more detailed analysis of the rings of light, their intensity, their uniformity, their dimensions, and any other similar criteria.
The X-Y “scanning” would generally be required if the light source emits a beam of light, rather than a diffuse field of light, which illuminates only a portion of the substrate, so that the entire substrate may be scanned and inspected.
Light is directed from a light source 706 external to the tank, down (as viewed) into tank 704, to a first mirror 708 within the tank, which reflects the light, optionally at 90 degrees, onto a surface 703 (left, as viewed in the figure) of the substrate. Light passing through the substrate is reflected by a second mirror 710 to an optical apparatus such as a microscope 712. Supports, indicated by small circles behind the mirrors may be provided for moving the mirrors to facilitate scanning the substrate, such as by pivoting.
As in the previous (off line) example, some form of scanning may be required. In this case, the mirrors can be scanning mirrors, capable of rotating about appropriate axes so that the entire substrate may be scanned by a beam of light. Supports, indicated by small circles behind the mirrors may be provided for rotating the mirrors to facilitate scanning the substrate, such as by pivoting. Alternatively and/or additionally, the substrate itself can be moved to effect or augment “scanning”, such as being withdrawn from the bath (as illustrated). For example, the mirrors could control scanning left and right, while the substrate is moved to effect scanning up and down. To this end, means (such as a robotic device which clamps the substrate and inserts it into the bath) may be provided for moving the substrate in the bath, to effect at least one axis of scanning.
As in the previous (off line) example, the scanning mechanism would be under the control of a computer, which also analyzes images of the substrate under inspection such as by comparing images to templates stored in computer memory, for example.
The process disclosed herein may be conducted on large panels of aluminum typically having thousands of isolated aluminum vias and oxidized zones distributed over the substrate area.
The inspection technique disclosed herein can be used in different modes to achieve various objectives, such as:
1) for end point detection for the process step (204) of anodizing:
It will be apparent to those skilled in the art that various modifications and variation can be made to the techniques described in the present disclosure. Thus, it is intended that the present disclosure covers the modifications and variations of the techniques, provided that they come within the scope of the appended claims and their equivalents.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IL2007/000246 | 2/25/2007 | WO | 00 | 8/25/2009 |
