Patent Application
20210366866
The inventive concept described herein generally relates to the field of semiconductor device fabrication.
There has been a significant amount of research on connecting rigid integrated circuits to flexible interconnects. Several applications require placement of a device in locations that are hard to reach or benefit from flexible connections due to mechanical damage susceptibility. Examples include biomedical devices such as flexible neural interfaces, read-write magnetic heads, flexible displays, and lab-on-a-chip devices.
Some adopted solutions consist of relatively long flexible connections from the device to the outside environment. This may be achieved by fabrication of metal connections on flexible substrates. A relatively large area is often occupied by the connection structure compared to the device itself. Other solutions concern die attachment to flexible substrates, e.g. Chip-on-flex (COF) technologies. These technologies package individually diced chips in flexible substrates a posteriori.
There is a need for improved flexible connections with respect to at least manufacturing, packaging, and ease of use.
It is an object of the present inventive concept to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in combination.
According to a first aspect of the inventive concept, these and other objects are achieved in full, or at least in part, by a method for manufacturing an unfoldable layered connection on a substrate, the method comprising: providing a substrate with a first layer of sacrificial material; providing a first layer of flexible material over the substrate and the first layer of sacrificial material, thereby at least partially encapsulating the first layer of sacrificial material; providing an opening in the first layer of flexible material, thereby exposing at least a portion of the substrate; providing a first layer of connector material, being an uppermost layer of connector material, over the first layer of flexible material and the substrate, wherein the first layer of connector material is in contact with the substrate, thereby forming a first contact of connector material and a first node of connector material; providing a second layer of flexible material over the first layer of connector material, the second layer of flexible material being in contact with the first layer of flexible material, thereby at least partially encapsulating the first layer of connector material; optionally, exposing at least a portion of the uppermost layer of connector material, thereby forming a second contact of connector material; removing the first layer of sacrificial material, thereby creating a first void interface between the substrate and the first layer of flexible material, thereby forming a first extension across the first void interface being unfoldable along a z-axis being perpendicular to the substrate; wherein the first extension comprises at least part of the first and second layer of flexible material, and the at least partially encapsulated first layer of connector material.
To facilitate the overall description a coordinate system will be used, where the x- and y-axis extend in an extension plane of a major surface of the substrate, whereas the z-axis extends perpendicular to the extension plane of the substrate.
It will be understood, in the context of the present disclosure, that when a component, such as a layer, a film, a region, or a plate, is referred to as being “on” another component, the component may be directly on the other component or intervening components may be present thereon. In particular, it is to be understood that the void interfaces referred to in the present disclosure may serve the purpose of allowing the extensions that are formed to move in relation to the underlying layer(s), regardless of what specific layer(s) the void interface is actually separating. In other words, there may exist a void interface surrounding at least part of the extensions referred to in the present disclosure, thereby forming an extension being un foldable along the z-axis being perpendicular to the substrate.
The term ‘providing’ may in the context of the present disclosure comprise depositing, forming, and/or patterning. For example, in the case of ‘providing a first layer of material’, it is to be understood that the first layer of material may be deposited, formed, and/or patterned. In particular, a material may be formed and/or patterned during the process of depositing the material. The term ‘providing’ may also comprise material already being present when performing the method according to the inventive concept.
The term ‘depositing’ in the context of depositing layers of material should be interpreted broadly as to include any technique of forming a layer of material. In particular, the term ‘depositing’ may encompass spin coating, chemical vapor deposition, physical vapor deposition, sputtering, and similar techniques.
The term ‘patterning’ in the context of depositing material may comprise forming or patterning of the material via various techniques including photolithography, etching, lift-off, masking etc.
The term ‘encapsulated’ may be equivalently exchanged for the term ‘enclosed’ throughout the present disclosure.
Further, it will be understood that some parts of the processes in the present disclosure may be omitted for the sake of brevity. In particular, some steps of masking, patterning, or etching may be omitted since it is believed that the person skilled in the art understands from the present disclosure as a whole how these steps are to be carried out within the present inventive concept.
When materials such as ‘flexible material’, ‘connector material’, or sacrificial material’ are being referred to, it is not necessarily one and the same type of material. The person skilled in the art realizes that it may be possible to use different types of e.g. flexible material in the unfoldable layered connection. In other words, different layers may comprise different types of e.g. flexible material, sacrificial material or connector material.
Further, it may be possible within the scope of the present inventive concept to provide several extensions having layers of flexible material and/or connector material of different thicknesses.
In general, the present inventive concept may reduce the surface footprint of a device having a flexible connection with respect to fabrication and the final device as such. The former may be achieved given the fact that the unfoldable flexible connection is primarily fabricated vertically with respect to the plane of the substrate. The latter may be achieved when manufacturing of several devices having respective unfoldable flexible connections is considered, since the present inventive concept allows for an increase in device density, and less space is required between devices. Some examples of devices benefitting from high density arraying are capacitive micromachined ultrasonic transducers (cMUTs), nanowire transistor arrays, and wide-range chemical and biological array-based screening.
Further, it is to be understood that an unfoldable layered connection according to the inventive concept may comprise several layers of extensions as described in the present disclosure. Additional extensions may be formed by repeating a set of the steps presented in the present disclosure, which will be readily understood by the person skilled in the art. Although some examples only incorporate one or two extensions, it is not to be understood as limiting the scope of the inventive concept.
The first contact of connector material may be in contact with the substrate, thus the unfoldable layered connection may provide routing and/or contact between the substrate and a device in communication with the second contact of connector material.
It is to be understood that the unfoldable layered connection may be arranged on any kind of substrate, and that the unfoldable layered connection may be completely released from the substrate e.g. via a sacrificial material and an etching step.
In the context of the present disclosure, the term ‘meander shaped’ should be understood to comprise bends, turns, windings, curves, annular shapes, right angles, acute angles, and obtuse angles. In particular, a meander shape may refer to a spiral shape. Further, it is to be understood that several extensions together may form a meander shape, although the individual extensions are straight. The meander shape may allow the unfoldable layered connection to go from a substantially two-dimensional extension into a three-dimensional extension during un-folding. An advantage with having a meander shaped first and/or second extension is that a longer unfoldable connection can be achieved without adding additional layers of extensions.
The first node of connector material may be, or comprise, the first contact of connector material.
The step of providing the opening in the first layer of sacrificial material may be performed by etching.
The first extension may be straight or meander shaped. The second extension may be straight or meander shaped. The first and second extension may together form a meander shape. It is to be understood that the first and second extensions may have different shapes.
The method may further comprise exposing the first extension by removing a portion of the first and second layer of flexible material, in order to allow the first extension to unfold along the z-axis. This may be advantageous if several unfoldable layered extensions are being manufactured in parallel on one and the same substrate.
The method may further comprise forming at least one access channel arranged to access the first layer of sacrificial material; wherein the step of providing the opening in the first layer of sacrificial material is performed by etching via the at least one access channel. The at least one access channel may be formed by removing a portion of the first and second layer of flexible material. Hereby, etching may be performed using etchants which must not necessarily be able to permeate through the flexible material. Further, etching speed and/or precision may be improved, even when utilizing etchants which are able to permeate or penetrate through the flexible material.
The method may comprise, after providing the second layer of flexible material, the steps of: providing a second layer of sacrificial material over the second layer of flexible material; providing a third layer of flexible material over the second layer of flexible material and the second layer of sacrificial material, thereby at least partially encapsulating the second layer of sacrificial material; providing a second opening in the second and third layer of flexible material, thereby exposing at least a portion of the first layer of connector material; providing a second layer of connector material thereby being the uppermost layer of connector material over the third layer of flexible material, wherein the second layer of connector material is in contact with the first layer of connector material thereby forming a second node of connector material; providing a fourth layer of flexible material over the second layer of connector material, the fourth layer of flexible material being in contact with the third layer of flexible material, thereby at least partially encapsulating the second layer of connector material; removing the second layer of sacrificial material thereby creating a second void interface between the second and third layer of flexible material, thereby forming a second extension across the second void interface being unfoldable along the z-axis; wherein the second extension comprises at least part of the third and fourth layer of flexible material, and the at least partially encapsulated second layer of connector material.
The removal of the first and second layer of sacrificial material, and any additional layer of sacrificial material, may be performed in a single step.
Hereby, a second extension may be formed over the first extension, the second extension having contact with the first extension via the second node of connector material. Additional extensions may be formed according to the steps above.
The method may further comprise exposing the second extension by removing a portion of the third and fourth layer of flexible material, in order to allow the first extension to unfold along the z-axis.
The at least one access channel may be arranged to access the first and second layer of sacrificial material, and wherein the step of providing the opening in the first and second layer of sacrificial material is performed by etching via the at least one access channel. The at least one access channel may be formed by removing a portion of the third and fourth layer of flexible material, in addition to removing a portion of the first and second layer of flexible material. Hereby, etching may be performed using etchants which must not necessarily be able to permeate through the flexible layers. Further, etching speed and/or precision may be improved.
The first and second nodes may be mutually displaced along the z-axis, and wherein the first and second nodes are connected via connector material. Hereby, a number of extensions of the unfoldable layered connection may be vertically stacked, thus reducing a surface footprint of the unfoldable layered connection.
The first and second nodes may be mutually displaced along an x-axis and/or a y-axis. Hereby, a meander shaped of the first and second extension may be achieved.
The first and second extension may form an angle with respect to each other in a plane being perpendicular to the z-axis. It is to be understood that the angle may be present at least when the unfoldable layered connection is folded, i.e. when the first and second extension are substantially parallel to the substrate.
The etchant may be HF, XeF2, microstrip, acetone, aluminum etchant, titanium etchant, O2 plasma, or EKC. It is to be understood that other etchants may be used, such as any organic or inorganic solvent which may selectively etch the sacrificial material with respect to the flexible material and the connector material. The HF may be in the form of vapor and/or liquid. The XeF2 may be in the form of vapor (gas).
The sacrificial material may be SiO2, amorphous silicon, PMMA, optical photoresist, Al, TiW, or an organic material. It is to be understood that other sacrificial materials may be used for which there exist a solvent or etchant which selectively attacks the sacrificial material with respect to the flexible material and the connector material.
The flexible material may be polyimide, SU-8, parylene-C, PVDF, PDMS, PEDOT:PSS Nafion, or Teflon. It is to be understood that other flexible materials may be used, such other materials are preferably flexible materials which can be deposited and patterned and which are resistant to the solvent or etchants utilized to remove the sacrificial material. An advantage with using the above materials is that cured polyimide is permeable to HF, which may allow etching of SiO2 without the need of access channels or release holes.
The following sections discloses some specific combinations of etchant, sacrificial material, flexible material, and connector material.
One combination of etchant, sacrificial material, flexible material and connector material is HF, photoresist, PMMA and metal respectively.
Yet another combination is HF; SiO2; polyimide; and AlSiCu.
Yet another combination is an aluminum etchant; Al; polyimide; and Cu or TiW.
Yet another combination is XeF2; amorphous silicon; polyimide; and Al.
Yet another combination is XeF2; amorphous silicon; PMMA or SU-8; and Al.
Yet another combination is acetone or microstrip; optical resist; SU-8; and Al.
Yet another combination is EKC; polyimide; SU-8; and Al.
Yet another combination is HF; SiO2; SU-8; and AlSiCu.
Yet another combination is 02 plasma; polyimide; SU-8; and TiW.
As will be understood from the present disclosure, the flexible material may preferably be a flexible material being resistant to the etchant used to remove the sacrificial material. Further, the connector material may preferably be a connector material being resistant to the etchant used to remove the sacrificial material. Preferably, the flexible material is resistant and permeable to the etchant used; the connector material is resistant to the etchant used; and the sacrificial layer is attacked by the etchant. The connector material may be a metal, such as AlSiCu, Cu, TiW, or Al. It should be noted that in case Al is used as sacrificial material, Al should not be used as connector material. In such cases, a different connector material may preferably be selected. In general, the sacrificial material and connector material should not be etched by the same etchant, to allow the sacrificial material to be selectively etched.
The first and second layer of flexible material may have the same thickness. Further, if the unfoldable layered connection comprises a second extension, the third and fourth layer may have the same thickness. In general, the layers of flexible material which at least partially encapsulates the connector material in each respective extension may have the same thickness. Hereby, the connector material may be kept at a neutral axis of the extension, which may reduce stress on the connector material as the extension is flexed, i.e. when the unfoldable layered connection is un-folded. It is to be understood that the term ‘the same thickness’ should be interpreted broadly, and encompasses e.g. ‘substantially the same thickness’.
The substrate may be silicon wafer or a printed circuit board.
The connector material may be an electrically conductive material. However, it may also be possible to manufacture an unfoldable layered connection according to the inventive concept comprising connector material pertaining to other communication techniques, such as light or heat. Consequently, the connector material may be configured to guide light signals, or to conduct heat. A material which conduct light signals should preferably have low optical loss, such as PMMA, EpoCore, or other transparent, flexible and/or ductile polymers. A flexible material in this regard could for example be EpoClad. It is also envisioned that the connector material in a light signaling application may be flexible in itself, and comprise a thin reflective metal coating. The connector material may be AlSiCu or TiW.
The substrate may be a silicon wafer or a printed circuit board. The substrate may be a semiconductor substrate.
The method may further comprise the step of providing a base layer of flexible material over the substrate before the step of providing the first layer of sacrificial material over the substrate. As is readily understood, the first void interface referred to in the present disclosure will thus be created between the base layer of flexible material and the first layer of flexible material.
According to a second aspect of the inventive concept, these and other objects are achieved in full, or at least in part, by an unfoldable layered connection comprising: a substrate; a node of connector material arranged to contact the substrate; a first extension comprising a core of connector material arranged to be in contact with the node, and flexible material arranged to at least partially enclose the core; and a second extension comprising a core of connector material arranged to be in contact with the first extension via a second node of connector material; wherein the first extension is configured to be hingedly connected to the node, thereby allowing un-folding of the first extension along a z-axis being perpendicular to an extension plane of a major surface of the substrate; and wherein the second extension is hingedly connected to the second node, thereby allowing unfolding of the second extension along the z-axis, and wherein the second node is moveable along the z-axis via unfolding of the first extension.
The second node being moveable along the z-axis via unfolding of the first extension may allow the unfoldable layered connection to achieve an increased reach along the z-axis when unfolded.
The first extension may extend along the extension plane of the major surface of the substrate, wherein the first extension comprises a proximal half and a distal half, and wherein the node is arranged in the proximal half and the second node is arranged in the distal half. Further, the node and second node may be separated by at least half the length of the first extension. The length of the first extension may be defined by the length of the core of connector material along the extension plane of the major surface of the substrate. The separation of the node and second node may allow the unfoldable layered connection to achieve an increased reach along the z-axis when unfolded.
The first extension may comprise at least two cores arranged to be in contact with the node, and wherein the flexible material is arranged to at least partially enclose each core. Hereby, an extension comprising two branches is achieved. The two branches may be separated so as to allow them to be moved independently from each other.
An extension may be divided into several separate branches, or sub-extensions, each functioning as a single extension and each having a core of connector material. Hereby, several unfoldable layered sub-connections may be achieved.
As described earlier in the present disclosure, the unfoldable layered connection may comprise at least one extension, such as two extensions or such as a plurality of extensions, wherein the extensions are layered one on top of the other and wherein the extensions are connected to each other via nodes of connector material.
Several unfoldable layered connections according to the inventive concept may be manufactured in parallel on one and the same substrate. The connections are subsequently divided in order to form several separate unfoldable layered connections. An advantage with the present inventive concept in this regard is that a high density of unfoldable layered connections can be achieved owing to the low surface footprint of the unfoldable layered connection according to the inventive concept.
According to a third aspect of the inventive concept, these and other objects are achieved in full, or at least in part, by a use of an unfoldable layered connection according to the second aspect on a silicon wafer or a printed circuit board.
The term ‘hingedly connected’ does not imply a structure resembling a hinge, but rather that the connection may achieve a rotation around a virtual axis. The term ‘hingedly connected’ may be exchanged for ‘flexibly connected’ or ‘movably connected’.
A feature described in relation to one aspect may also be incorporated in other aspects, and the advantage of the feature is applicable to all aspects in which it is incorporated.
Other objectives, features and advantages of the present inventive concept will appear from the following detailed disclosure, from the attached claims as well as from the drawings.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. Further, the use of terms “first”, “second”, and “third”, and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. All references to “a/an/the [element, device, component, means, step, etc]” are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description of different embodiments of the present inventive concept, with reference to the appended drawings, wherein:
It may be repeated that some parts of the processes in the present disclosure may be omitted for the sake of brevity. In particular, some steps of masking, patterning, or etching may be omitted since it is believed that the person skilled in the art understands from the present disclosure as a whole how these steps are to be carried out within the present inventive concept. Some possible techniques which may be incorporated into the method described below include chemical vapor deposition (CVD), plasma etching, ashing, reactive ion etching (RIE), dry etching, inductively coupled plasma etching, lithography, and sputtering.
Further, it should be noted that the illustrated figures are not necessarily drawn to scale.
For the sake of clarity, it should also be noted that the disclosures made below in conjunction with
In the disclosures following below, the base layer of flexible material will be referred to as a first layer of flexible material. Subsequent layers of flexible material are numbered accordingly. In general, the terminology used, e.g. referring to a ‘first’, ‘second’, or ‘third’ layer, should not be interpreted as limiting the scope of the inventive concept, but merely as means for providing clarity in the following disclosure.
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The substrate 702 and the sacrificial material 710 may be provided in one step as illustrated, e.g. the substrate 702 and the sacrificial material 710 may be provided as a pre-fabricated piece in the method according to the inventive concept. It is further envisioned that additional steps of the method according to the inventive concept may be performed in a single step, e.g. may be provided as a pre-fabricated piece. On the contrary, it is also envisioned that the substrate 702 may first be provided, and that the first layer of sacrificial material 710 may subsequently be provided over the substrate 702.
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Further, an opening 768 has been provided in the first layer of flexible material 712, thereby exposing at least a portion of the substrate 702. As is readily understood by the person skilled in the art, the opening 768 may be provided by e.g. removing part of the first layer of flexible material 712, and/or via masking when providing the first layer of flexible material 712.
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Further, a second opening 770 has been provided in the second and third layer of flexible material 718, 722, thereby exposing at least a portion of the first layer of connector material 714. As is readily understood by the person skilled in the art, the second opening 770 may be provided by e.g. removing part of the second and third layer of flexible material 718, 722, and/or via masking when providing the second and third layer of flexible material 718, 722.
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Further, at least a portion of the uppermost layer of connector material, in this case the second layer of connector material 724, has been exposed, thereby forming a second contact of connector material 724. This may be achieved by e.g. removing part of the fourth layer of flexible material 728, and/or via masking when providing the fourth layer of flexible material 728.
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The first extension comprises at least part of the first and second layer of flexible material 712, 718, and the at least partially encapsulated first layer of connector material 714. The second extension comprises at least part of the third and fourth layer of flexible material 722, 728, and the at least partially encapsulated second layer of connector material 724. The resulting device is an unfoldable layered connection 700 comprising a first and a second extension 740, 742.
A method for manufacturing an unfoldable layered connection on a substrate according to one aspect of the inventive concept, wherein the method does not comprise forming the optional base layer of flexible material, will now be described. The advantages and technical features discussed above are equally applicable to this specific aspect.
Such a method may be specified by the steps of:
providing a first layer of connector material over a substrate;
forming the first layer of connector material into a first contact of connector material;
providing a first layer of sacrificial material over the substrate;
providing a first layer of flexible material over the substrate and the first layer of sacrificial material, thereby at least partially encapsulating the first layer of sacrificial material;
removing at least a portion of the first layer of flexible material;
providing a second layer of connector material being an uppermost layer of connector material onto the first layer of flexible material, wherein the second layer of connector material is in contact with the first layer of connector material thereby forming a first node of connector material;
providing a second layer of flexible material onto the second layer of connector material, the second layer of flexible material being in contact with the first layer of flexible material, thereby at least partially encapsulating the second layer of connector material;
exposing at least a portion of the uppermost layer of connector material, thereby forming a second contact of connector material;
removing the first layer of sacrificial material, thereby creating a first void interface between the substrate and the first layer of flexible material, thereby forming a first extension across the first void interface being unfoldable along a z-axis being perpendicular to the substrate;
wherein the first extension comprises at least part of the first and second layer of flexible material, and the at least partially encapsulated second layer of connector material.
The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18180798.3 | Jun 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/067376 | 6/28/2019 | WO | 00 |
