Patent Application
20090090617
The invention relates to the deposition of films having controlled levels of stress and stress gradients on support substrates. More particularly, the invention relates to methods and apparatus for fabrication of films having controlled levels of uniform and or isotropic stresses and stress gradients on substrates and the application of such films to the fabrication of photolithographically patterned spring contacts.
Thin films are often deposited on substrates by sputtering in glow-discharge plasmas, where ions accelerated out of the plasma knock atoms off of the target (source) material, which are then transported to the substrate. A magnetically confined plasma generator i.e. magnetron, is typically used to increase sputtering efficiency and to reduce the minimum operating pressure. Sputtering is a preferred deposition technique because it can be used for any material, because the energy of the depositing atoms helps film adherence, and because the substrate temperature remains relatively low throughout the deposition process.
Uniformity of film thickness across large substrate areas is usually important in microfabricated devices. One of two approaches is conventionally taken to achieve film thickness uniformity.
One such approach is to position the substrates at a radius far from the target relative to substrate and target diameters. To increase throughput and use targets efficiently, many substrates are positioned at this radius over most of a hemisphere and are kept in a planetary (two-axis) motion so that they occupy a wide range of positions over the hemisphere during the course of the deposition time. This averages out deposition rate variation over the hemisphere.
A second approach uses a rectangular target that is larger than the substrate in the target's long dimension. The substrate is placed close to the target and is passed back and forth across it in linear transport so that the substrate is painted with a uniform swath of film in successive layers much like painting with a roller. Typically 100 nm of film are deposited in each pass. Planetary motion systems have also been used to increase the thickness uniformity of material deposited from rectangular sources by randomizing the path of the substrates relative to the deposition sources, e.g. setting the rotation rate of the substrate about its axis to be much greater than the rotation rate of primary axis of the planetary motion system.
Sputtering is used in the fabrication of various microelectronic structures. For example, D. Smith and S. Alimonda, Photolithographically Patterned Spring Contact, U.S. Pat. No. 5,613,861 (25 Mar. 1997), U.S. Pat. No. 5,848,685 (15 Dec. 1998), and International Patent Application No. PCT/US 96/08018 (Filed 30 May 1996), describe a photolithographically patterned spring contact, which is “formed on a substrate and electrically connects contact pads on two devices.”
Photolithographically patterned spring structures are particularly useful in electrical contactor applications where it is desired to provide high density electrical contacts which may extend over relatively large contact areas and which also may exhibit relatively high mechanical compliance in the normal direction relative to the contact area. Such electrical contactors are useful for applications including integrated circuit device testing (both in wafer and packaged formats), integrated circuit packaging (including singulated device packages, wafer scale packaging, and multiple chip packages) and electrical connectors (including board level, module level, and device level, e.g. sockets.
In addition to providing compliance in the direction normal to the contact plane, photolithographically patterned spring contacts also compensate for thermal and mechanical variations and other environmental factors. An internal stress gradient within the spring contact causes a free portion of the spring to bend up and away from the substrate to a lift height which is determined by the magnitude of the stress gradient. An anchor portion remains fixed to the substrate and is electrically connected to a first contact pad on the substrate. The spring contact is made of an elastic material and the free portion compliantly contacts a second contact pad, thereby contacting the two contact pads. Variations in the internal stress gradient across the substrate surface can cause variations in spring contact lift height.
The ability to produce uniform stress gradients over large substrate areas depends on being able to controllably create a sequence of thin layers of deposited metal, each having controlled levels of mechanical stress. Deposited films having internal stress gradients are characterized by a first layer having a first stress level, a series of intermediate layers having varying stress levels, and a last layer having a last stress. The magnitude of the internal stress gradient is determined by the difference in stress levels between each layer in the film. The curvature of a lifted spring is a function of the magnitude of the internal stress gradient, geometrical factors, e.g. thickness, shape, and material properties, e.g. Young's modulus. After release from the substrate, the free portion of the spring deflects upward until the stored energy is minimized.
For a given curvature, thicker springs require a greater range of stresses than do thinner springs. Thicker springs are preferred when higher forces at a given deflection are required. For example, in certain electrical contactor applications, it is desirable to fabricate spring contacts having a relatively high contact force and a high lift height to provide low electrical resistance and a high mechanical compliance range. The combination of relatively high force and relatively high lift height requires both a relatively high stress gradient and a relatively large range of stress within the deposited film. In other words, springs having relatively large forces and high lift heights typically are relatively thick and have relatively high magnitude internal stress gradients extending over a larger range of stresses.
The stress range is increased when the spring comprises at least one layer of high compressive stress and at least one layer of high tensile stress. There is an upper limit to the compressive and tensile stresses that a thin film can sustain without loosing mechanical integrity.
In addition to controlling film thickness, it is desirable to deposit films having uniform, and controlled stress levels. In DC magnetron sputtering, low plasma pressure increases compression, higher pressure creates tensile stress, and still higher pressure results in porous films that have no mechanical strength in the film plane. There is a lower limit on the practical working pressures that can be achieved in production deposition systems and therefore there is an upper limit to the compressive stress that can be imparted to the film. However, due to its inherent simplicity, magnetron sputter-deposition of films with internal stress gradients formed by increasing plasma pressure during deposition is a presently preferred technique for implementing patterned spring technology. The stress range in a thin film can be maximized by creating compressive stress in a starting layer of a stress gradient within the film and tensile stress in an ending layer of a stress gradient within the film.
In addition to plasma pressure, the angle of incidence at which atoms are deposited on a substrate, i.e. the deposition angle, is also known by those skilled in the art to be an important determinant of film stress, with off-normal or grazing, i.e. shallow, angles of incidence resulting in more tension and, if excessive, in porosity. It is also known that atoms deposited at near normal or normal angles and/or with increased energy result in films with in increased levels of compression.
Side shields have previously been used to reduce the relative amount of deposition from magnetron deposition sources impinging on substrates at shallow angles. For example, McLeod et al., Journal of Vacuum Science Technology, Vol. 14, No. 1, January/February 1977, teach the use of side shields to reduce the amount of “low angle” deposition of Aluminum sputtered from a planar magnetron source to increase the reflectivity of a vapor deposited aluminum films. Side shields have also been used in the prior art for other purposes, such as to reduce the amount of sputter deposited materials on non-targeted surfaces, e.g. on the surfaces of the sputtering apparatus, on the back side of the substrate, on substrate fixtures, and/or on adjacent substrates and sputter targets.
Ion bombardment has previously been used to increase compressive stress in vacuum-deposited films. Increased levels of ion bombardment increase compressive stress and very high levels of ion bombardment result in films with compromised mechanical integrity. Additionally, ion sources operate at pressures up to about 1 milli Torr, while magnetron sputter deposition sources operate from pressures of about 0.5-1 milli Torr and above. Given the limited overlap between the ranges, it is difficult to operate an ion gun and a magnetron sputter source simultaneously in a single vacuum chamber.
It would be advantageous to provide a method and apparatus to create uniform compressive stress across the surface of large substrate areas without the use of ion bombardment from an ion source other than the sputtering target itself, such as to avoid limited overlap between operating pressure ranges ion sources and magnetron sputtering sources.
As well, while sputtering sources are capable of emitting high energy ions capable of creating compressive stress in the deposited film under proper conditions, it is not currently known within the prior art how to produce wide extremes of stress in sputtered films ranging from highly compressive to highly tensile while maintaining high uniformity across large substrate areas without the use of a secondary ion bombardment source, i.e. other than the sputtering target itself.
It would therefore be advantageous to provide a method and apparatus for producing uniform and or isotropic stresses in sputtered films wherein the stress level varies from highly compressive to highly tensile without the use of a secondary ion bombardment source.
Certain applications of photolithographically patterned spring contacts in connectors and IC device probing require that the lift height (in the Z direction) and the tip position (in X and Y direction) are tightly controlled.
It would therefore also be desirable to provide a method and apparatus capable of fabricating photolithographically patterned spring contacts with lift heights and tip positions having predictable and controllable positional errors.
It would also be desirable to provide a method and apparatus capable of fabricating spring contacts having lift heights and tip positions with predictable errors and methods for compensating for the errors to provide spring contacts having lift heights and tip positions with minimized errors.
An enhanced sputtered film processing system and associated method comprises one or more sputter deposition sources each having a sputtering target surface and one or more side shields extending therefrom to increase the relative collimation of the sputtered material, such as about the periphery of the sputtering target surface, toward workpiece substrates. One or more substrates, i.e. workpieces, are provided, wherein the substrates have a front surface and an opposing back surface, and may have one or more previously applied layers, such as to promote adhesion of the sputtered film on the substrate. The substrates and the sputter deposition sources are controllably moved with respect to each other. The increase in relative collimation due to the side shields enables the formation of films with desirable properties including but not limited to high mechanical integrity and controllable internal stress up to the maximum stress that the sputter deposited material can sustain.
At least a first portion of the material sputtered from the sputtering target surface at shallow angles is blocked by the side shields, thereby increasing the relative collimation of the one or more sputter deposition sources, while at least a second portion of the material sputtered from the sputtering target at normal or near normal angles travels beyond the side shields and is deposited on the front surface of the substrates, such that the deposited films preferably comprise high mechanical integrity and/or controllable levels of film stress in the X-Y plane parallel to the substrate.
Desired levels of film stress, ranging from highly compressive to highly tensile, can be achieved by varying sputter deposition conditions such as the deposition gas pressure. If the number of desired passes is determined to be complete, the process is ended. If the process is not done, the relative planar position and angular rotation of any of the substrates and the deposition sources may be controllably changed, and the process is repeated for further controlled deposition.
The enhanced sputtered film processing system and associated method can be used to fabricate a resulting film with substantially uniform thickness and isotropic stress by laminating two or more thin film layers deposited on a substrate. The method comprises moving the sputter deposition sources and the substrates with respect to each other in a predetermined manner during the deposition of each of the two or more thin film layers such that any X-Y anisotropy in stress in each of the two or more thin film layers (in the plane parallel to the substrate), arising from X-Y anisotropy in the deposition angle from the at least one deposition source, is averaged out.
The laminated films having substantially uniform thickness and isotropic stress fabricated using the enhanced sputtered film processing method can be combined to create a stress gradient in a composite film deposited on a substrate. The method comprises fabricating two or more laminated films each having a substantially uniform thickness and predetermined value of isotropic stress, e.g. compressive, neutral, or tensile, in the plane parallel to the substrate such that the resulting composite film comprises a stress gradient in the direction normal to the substrate, e.g. a stress gradient ranging from compressive to neutral to tensile.
The enhanced sputtered film processing system and associated method can be used to fabricate a layer having substantially uniform thickness and isotropic stress functioning as an interface layer to provide adhesion between a substrate and subsequent deposited layers of thin films. The method comprises fabricating a first adhesion layer using a first material, the adhesion layer having a substantially uniform thickness and isotropic stress and subsequently depositing at least one additional layer of at least a second material on the surface of the first adhesion layer.
The enhanced sputtered film processing system and associated method can be used to fabricate one or more springs, e.g. photolithographically patterned, on a substrate. An exemplary method comprises the steps of: forming at least one adhesion layer having a substantially uniform thickness and predetermined value of isotropic stress, subsequently forming a spring film comprising at least one spring material capable of maintaining stress over its fabrication process temperatures and subsequent operating temperatures, the spring film further comprising two or more laminated thin films each having a substantially uniform thickness and predetermined value of isotropic stress thereby forming a stress gradient in the spring film, the spring film stress gradient comprising stresses ranging from compressive to tensile, controllably removing at least a portion of the spring metal layers and the adhesion layer using photolithographic patterning, controllably chemically removing the adhesion layer between at least a portion of the photolithographically patterned one or more springs and the substrate thereby releasing the one or more springs from the substrate such that the resulting one or more spring comprises a fixed portion attached to the substrate and a free portion extending away from the substrate and thereby having a pre-determined lift height and tip position. The above methods are not limited to photolithographically patterned springs and can be used to fabricate springs patterned by other processes, such as but not limited to direct deposition of patterned spring film, micromachining of the spring film using a laser, and/or similar processes.
The enhanced sputtered film processing system and associated method can be used to fabricate spring contacts having properties, e.g. lift heights and tip positions, with predictable errors. An exemplary method for compensating for such errors, such as to provide spring contacts having properties with reduced errors, may comprise the steps of fabricating a first device on a first substrate comprising at least one spring contact, measuring the errors in the properties of the at least one spring contact in the first device, modifying the fabrication processes such as to reduce the errors in spring contact properties of subsequently fabricated devices. The measurable spring contact properties typically comprise any of spring contact length, width, shape, angular orientation, tip height and tip position.
The exemplary enhanced sputtering film processing systems 10a and 10b seen in
In the figures that follow, exemplary substrate motion is shown directly under a sputter deposition source 16 in order to describe the functioning of the side shields 46 and the effect on thin film deposition. Substrate motion can alternately be provided by any means, such as by moving the one or more substrates 14, the deposition source, the area of deposition from the sputter deposition source 16, or combinations thereof, or both. For a given sputtering deposition source 16, side shield 46, substrate to side shield distance, equivalent transport systems suitable for use with the enhanced sputtered film processing system 10 and associated method 150 may comprise any of linear, track, planetary and combinations thereof or other systems equivalent thereto.
The exemplary systems 10, such as 10a as seen in
As seen in
In some preferred embodiments of the enhanced sputtering film processing system 10, e.g. system 10b, side shields 46 are added to the linear magnetron sputter deposition sources 16, such as to improve the properties of deposited materials 74, and/or to enable the fabrication of film layers, e.g. 174, having high levels of compressive stress. As is described in detail below, systems 10 having side shields 46 have been seen to provide high quality multilayer substrates 178 (
In some embodiments of the enhanced sputtering film processing system 10, the side shields 46 comprise any of an electrically conductive material and an electrically insulating material. In some embodiments of the enhanced sputtering film processing system 10, the side shields 46 are electrically connected to a source of electrical potential selected from the group consisting of positive, negative, neutral, and ac potential. As well, in some embodiments of the enhanced sputtering film processing system 10, the side shields 46 may contain internal subdivisions having shapes selected from the group consisting of rectangles, squares, circles, polygons and combinations thereof.
As seen in
As seen in
In linear transport 72, such as seen in
In the exemplary systems 10a, 10b seen in
As seen in
Some preferred embodiments of the enhanced sputtered film processing system 10 use two sputter deposition sources 16, e.g. 16a and 16b, oriented at approximately at right angles to each other, so that each of the substrates 14 executes two target passes 88 during each plate 12 rotation, with each pass 88 having the substrate's 14 X and Y directions reversed relative to the pass direction. This laminates the material 74, to average out the X-Y anisotropy that is inherent to conventional linear transport 72.
The substrates 14 are preferably rotated 17 at substantially the same angular velocity but opposite sign, relative to the plate 12, as substrates 14 are rotated about a fixed point, such as to provide a uniform film thickness, whereby a point on the inner edge of each substrate 14, i.e. towards the center of the plate 12, traverses the sputter deposition source 16 at the same linear velocity as an outer point, i.e. opposite the inner point, and thus accumulates deposit for the same length of time per pass 88.
As seen in
While the exemplary systems 10a and 10b seen in
In some system embodiments 10, an ion source 20 may be located at a point around the plate 12, to bombard the film with ions 33 and thereby impart compressive stress when desired or perform a sputter etching or cleaning process.
Over the course of a single rotation of plate 12, each substrate 14 experiences periodic variation in several process parameters that affect stress, e.g. deposition angle of incidence and azimuthal orientation to the target's longitudinal axis 47 (
The relative increase in deposition in the near normal angle range also results in an increase the average energy of the depositing atoms. Experimental data provided below indicate that such effects may combine to produce layers having a crystallographic structure that is consistent with inherent compressive stress when the sputter sources are operated at low deposition pressures.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the adhesion layer 172 may comprise one or more layers having an inherent level of stress fabricated from a chemically dissolvable material, such as comprising a material selected from the group consisting of titanium, chromium, nitride and combinations thereof.
At exemplary step 151, a counter P may be initialized in association with a number of deposited layers. At step 156, the substrates 14 and the sputter deposition sources 16 are controllably moved with respect to each other, such that at least a portion of the material sputtered from the sputtering target surface 62a travels beyond the side shields 46 and is deposited on the front surface 94a of the substrates 14.
As seen at step 153, the counter P is incremented to reflect the deposited layer from step 156. A decision step 155 may be made to determine if two or more layers, e.g. 174, have been deposited. If not 159, the process typically returns 164 to step 156 for further controlled deposition. If two or more layers, e.g. 174, have 157 been deposited, and if the number of desired passes 88 is determined 158 to be completed, e.g. two or more layers as desired for the fabrication of any of layers having isotropic internal stress, stress gradients in the direction normal to the substrate, and the construction of at least one photolithographically patterned spring 246 (
As seen at exemplary step 162 in
In some embodiments of the enhanced sputtered film processing process 150, such as seen in the exemplary method 150 of
The enhanced sputtered film processing system 10 and method 150 provides sputtered films that are controllably uniform and/or isotropic. In an embodiment of the enhanced sputtered film processing system 10, the sputtering source configuration geometry allows the fabrication of films with uniform thickness having inherent internal stresses ranging from compressive to neutral to tensile while minimizing X-Y stress anisotropy, i.e. stress non-uniformity across the substrate, where the X-Y refers to two orthogonal dimensions, e.g. 25,27 (
Desired levels of film stress, ranging from highly compressive to highly tensile, can be achieved by varying sputter deposition conditions such as the deposition gas pressure. In some embodiments of the enhanced sputtered film processing system 10 and method 150, one or more sputter deposition conditions are controlled such that the one or more layer 174 is formed with a controllable internal stress in a plane parallel to the substrates 14 up to the maximum internal stress that the spring material can sustain.
An exemplary method for controlling gas pressure comprises controllably admitting an inert gas, e.g. Argon, into the vacuum chamber 15 (
Those skilled in the art will recognize that the function of the present system and method embodiments 10, 150 are not limited to the specific example presented above for controlling gas pressure within a vacuum chamber 15. Other equivalent means for controlling deposition may be substituted for use with the enhanced sputtered film processing system 10 and associated method 150 described herein.
If the number of desired passes is determined to be complete, the process 150 is ended 168. If the process 150 is not done, the relative planar position and angular rotation of any of the substrates and the deposition sources may be controllably changed 162, and the process 156 is repeated for further controlled deposition.
The enhanced sputtered film processing system 10 and associated method 150 can be used to fabricate a resulting film with substantially uniform thickness and isotropic stress by laminating two or more thin film layers deposited on a substrate 14. The method comprises moving the sputter deposition sources and the substrates with respect to each other in a predetermined manner during the deposition of each of the two or more thin film layers such that any X-Y anisotropy in stress in each of the two or more thin film layers (in the plane parallel to the substrate), arising from X-Y anisotropy in the deposition angle from the at least one deposition source, is averaged out.
An exemplary enhanced sputtered film processing system 10 and associated method 150 provides at least two rectangular sputter deposition sources 16, one or more substrates 14, a drive mechanism 13 (
The laminated films having substantially uniform thickness and isotropic stress fabricated using the enhanced sputtered film processing method can be combined to create a stress gradient in a composite film deposited on a substrate. The method comprises fabricating two or more laminated films each having a substantially uniform thickness and predetermined value of isotropic stress, e.g. compressive, neutral, or tensile, in the plane parallel to the substrate such that the resulting composite film comprises a stress gradient in the direction normal to the substrate, e.g. a stress gradient ranging from compressive to neutral to tensile. In some embodiments, the stresses in the plurality of layers range from compressive to tensile. In other embodiments, the stresses in the plurality of layers range from tensile to compressive. As well, in some embodiments, stresses in the plurality of layers may include any combination of controlled transitions between any of compressive, neutral, or tensile isotropic stress.
For embodiments of the process 150 which are used to produce composite multilayer springs 264, the layers 174 may preferably be fabricated from an elastic material such as a metal comprising any of MoCr, Tungsten, Tantalum and/or any combination thereof.
In reference to the
The enhanced sputtered film processing system 10 and method 150 may preferably provide a substantially identical amount of deposition from each different deposition angle as for each other deposition angle, wherein the overall deposited film behaves substantially isotropically in properties, e.g. such as mechanical, electrical, and optical properties, in all directions parallel to the substrate 14 and at different angles of rotation about the normal axis 18 (
Some embodiments of the enhanced sputtered film processing system 10 and method 150 preferably comprise moving each substrate 14 past a same one or more sputter deposition sources 16 of depositing material in a planetary manner, wherein each time the substrate 14 passes by one of the sputter deposition sources 16 of depositing material as the substrate 14 executes a planetary orbit, the substrate 14 has been rotated about the substrate's normal axis 18 with respect to the sputter deposition source 16 by which the substrate 14 is passing.
In one embodiment, one or more substrates 14 are preferably rotated about 360/n degrees each time the substrates 14 passes by one of n the sputter deposition sources 16, wherein n is an integer larger than 2, or preferably by about 90 degrees if n is 2.
Some embodiments of the enhanced sputtered film processing system 10 and method 150 preferably comprise providing two or more sputter deposition sources 16 arranged about a circle 24, as seen in
In one system embodiment 10, the source 16 of depositing material exhibits two-fold symmetry in a relevant anisotropic property of the depositing material source. In one system embodiment 10, a substrate rotation of about 270 degrees is equivalent to a substrate rotation of about 90 degree with respect to the anisotropy in the relevant property of the film layer when the source 16 exhibits two-fold symmetry.
Some embodiments of the enhanced sputtered film processing system 10 and method 150 preferably comprise providing two or more sputter deposition sources 16, wherein each sputter deposition source 16 has two-fold symmetry, wherein the sputter deposition sources 16 are disposed relative to one another such that a relevant anisotropic property of a sputter deposition source 16 is rotated by a pre-set angle with respect to a previous sputter deposition source 16, wherein each substrate 16 maintains a fixed rotational orientation about its normal axis 18 as it orbits, as measured from a stationary point; and wherein the film is deposited in layers 174, e.g. 174a,174b, having an anisotropy rotated by the preset angle for each successive layer 174.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the pre-set angle ranges from about 45 to about 135 degrees. In alternate embodiments of the enhanced sputtered film processing system 10 and method 150, the pre-set angle ranges from about 80 to about 100 degrees. In another embodiment, the pre set angle is about 90 degrees. In another embodiment, the pre set angle is 90 degrees. In another embodiment, the pre set angle is determined by experiment to optimize the properties of the material 74 and one or more layers 174, e.g. to minimize stress variations or spring lift height 262 (
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the sputter deposition sources 16 of depositing material comprise linear magnetron sputter deposition sources 16 from which the depositing material emanates in a pattern that approximates a rectangle having rounded corners. Each such sputter deposition source 16 is preferably equipped with a side shield 46 that extends 48 along at least a portion of each of the long sides of each sputter deposition source 16, and may also extend along at least a portion 50 of the ends of each sputter deposition source 16.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the distance from the sputtering target surface 62a to the edge of the side shield 46 is greater than the distance from the substrate 14 to the edge of the side shield 46. In a second embodiment, the distance from the sputtering target surface 62a to the edge of the side shield 46 is about three times the distance from the substrate 14 to the edge of the side shield 46.
In some alternate embodiments of the enhanced sputtered film processing system 10 and method 150, the distance from the sputtering target surface 62a to the edge of the side shield 46 is optimized by experiment. For example, at a given distance 35 between the substrate surface 94a and the edge of the side shield 46 which is preferably minimized and determined, such as subject to geometrical system constraints, the distance from the sputtering target surface 62a to the edge of the side shield 46 may be experimentally optimized to yield films with desired properties and high mechanical integrity, such as but not limited to any of:
Sputter deposition sources 16 equipped with side shields 46 have been demonstrated to be capable of depositing layers of materials such as MoCr films with ranges of inherent compressive stress without the use of a secondary ion gun 20. Stress levels have been achieved ranging from in excess of about −1.5 GPa compressive to in excess of about +1.5 GPa tensile without an ion gun as the pressure of the working gas in the deposition chamber is varied from about 1 milli Torr to about 15 milli Torr.
Sputter deposition sources 16 equipped with side shields 46 have also been demonstrated to be capable of depositing layers of materials such as titanium with inherent compressive stress without the use of a secondary ion gun 120. Stress levels have been achieved ranging from in excess of about −0.5 GPa compressive to in excess of about +0.2 GPa tensile as the pressure of the working gas in the deposition chamber is varied from about 2 milli Torr to about 10 milli Torr.
Dual magnetron sputter deposition sources 16 equipped with side shields 46 have been demonstrated to be capable of depositing materials such as MoCr films 174 and titanium films 172 with improved uniformity and isotropy over larger substrate areas compared to single magnetron sputter deposition sources 16 or dual magnetron sputter deposition sources 16 not equipped with side shields 46.
The adhesion layer 172 may itself comprise one or more layers 172 having an inherent level of stress. An adhesion layer 172 provides adhesion between the substrate 14 and subsequently deposited film layers 174. In some embodiments, the fabricated adhesion layer 172 comprises any of titanium, chromium, nitride and/or any combination thereof.
The exemplary monolithic micro-fabricated spring contacts 246 comprise stress metal springs that are photolithographically patterned and fabricated on a substrate 14 using batch mode semiconductor manufacturing processes. As a result, the spring contacts 264 are fabricated en masse, and can be fabricated with spacings equal to or less than that of semiconductor bonding pads or with spacings equal to or greater than those of printed circuit boards, i.e. functioning as an electrical signal space transformer.
Monolithic micro-fabricated spring contacts 264, such as seen in
Additionally, optical signals can be transmitted through the resultant substrate 14 by fabricating openings of sufficient size through the substrate 14 through which the optical signals can be transmitted. The holes may be unfilled or filled with optically conducting materials including but not limited to polymers, glasses, air, vacuum, etc. Lenses, diffraction gratings and other optical elements can be integrated to improve the coupling efficiency or provide frequency discrimination when desired.
In some embodiments, the stress metal springs 264 may preferably be fabricated by sputter depositing a titanium adhesion/release layer 172 having a thickness of 1,000 to 5,000 angstrom on a ceramic or silicon substrate 14 (approximately 10-40 mils thick) having a diameter ranging from about 1 millimeter to about 1 meter, which may further comprise electrically conductive vias pre-fabricated in the substrate 14 having diameters of 1-10 mils. Electrically conductive traces fabricated with conventional photolithographic processes connect the spring contacts to such conductive vias and to the circuits to which they may ultimately connect. A common material used to fabricate stress metal springs is MoCr, however other metals with similar characteristics, e.g. elements or alloys, may be used. An exemplary stress metal spring contact is formed by depositing a MoCr film in the range of 1-5 μm thick with a built-in internal stress gradient of about 1-5 GPa/μm. An exemplary MoCr film is fabricated by depositing 2-10 layers 174 of MoCr, each layer 174 about 0.2-1.0 μm thick. Each layer 174 is deposited with varying levels of internal stress ranging from up to 1.5 GPa compressive to up to 2 GPa tensile.
Individual micro-fabricated stress metal spring contact fingers 264 are photolithographically patterned and released from the substrate 14, using an etchant to dissolve the release layer 162. The sheet resistance of the finger 264 can be reduced by electroplating with a conductive metal layer (such as copper or gold). The force generated by the spring contact 264 can be increased by electrodepositing a layer of a material, such as nickel, on the finger 264 to increase the spring constant of the finger 264. In interposer applications, the quality of the electrical contact 264 can be improved by electrodepositing depositing a material, such as rhodium, onto the tip 264 through a photomask, prior to releasing 244 the finger 264 from the substrate 14.
The lift height 262 (
Some embodiments of the method 150 and system 10 comprise processes for fabricating spring contacts having properties with predictable errors and methods for compensation and reduction of errors in subsequently fabricated spring contact properties, e.g. lift heights and tip positions.
An exemplary method for compensation and reduction of the errors in spring contact properties comprises the steps of: fabricating a first device on a first substrate comprising at least one spring contact, measuring the errors in the properties of the at least at least one spring contact in the first device, modifying the fabrication processes such as to reduce the errors in the properties of subsequently fabricated devices. The measurable properties comprise any of spring contact length, width, shape, angular orientation, tip height and tip position.
An exemplary process for fabricating spring contacts comprises the steps of fabricating a first calibration spring array of photolithographically patterned springs on a substrate, each member of the calibration spring array being positionally distributed over a designated area of the substrate, at least one photomask used in fabricating the calibration spring array such as to define any of the length, width, shape, angular orientation, and position of each spring in the calibration spring array; measuring the errors in any of the length, width, shape, angular orientation, position, spring lift height, and tip position of each member of the fabricated calibration spring array and determining an error correction matrix for each member or the calibration spring array; and compensating a second device spring array for any errors in any of the length, width, shape, angular orientation, position, spring lift height, and tip position in the vicinity of each member of the fabricated calibration spring array using the correction matrix to adjust the photolithographic pattern on at least one photomask used to fabricate the device spring array such as by changing any of the length, width, shape, angular orientation, and position of the each member of the device spring array relative to the substrate to reduce any errors in spring lift height and tip position of any of the one or more photolithographically patterned springs in the device.
It has been determined experimentally that photolithographically patterned MoCr springs 246 exhibit higher lift heights 262 when fabricated on titanium release films 162 deposited at lower pressures using dual magnetron sputter deposition sources 16 equipped with side shields 46.
Differences have been observed in resultant lift height 262 and twist 272, e.g. 272a,272b of photolithographically patterned MoCr springs 246 that are fabricated on top of titanium release films 162. For example, MoCr springs 246 have been observed to exhibit increased lift height 262 when fabricated on top of titanium release films 162 that are fabricated at lower deposition pressures. Films comprised of materials such as titanium deposited at low pressures may have crystallographic structures, grain sizes and/or orientations that may differ from such films deposited at higher pressures.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, a distance along a substrate normal axis 18 and between a substrate surface 94a and a target surface 62a from which depositing material 74 emanates is sufficiently smaller than a distance between material as it emanates from an end of the rectangular emanation pattern and a nearest edge of the substrate 14, such that a relevant property of the sputtered material 74 is sufficiently uniform along the substrate 14 from a center of the substrate 14 to the substrate's edge.
Some embodiments of the enhanced sputtered film processing system 10 and method 150 comprise a symmetrical disposition at least one sputter deposition source 16 having a side shield 46 at any of successive different deposition angles of rotation of the substrate 14 and/or of the sputter deposition source 16 about a normal axis 18 of the substrate 14, and deposition of successive layers 174, e.g. 174a, 174b on the substrate 14, such as to achieve high levels of stress in the film layers 174, wherein the stress is both isotropic in a film plane and uniform over large areas of a substrate surface 94a.
Some embodiments of the enhanced sputtered film processing system 10 and method 150 preferably provide a single or a multi-atomic-layer-scale deposition thickness 182 (
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the substrates 14 are rotated by about 90 degrees relative to the sputter deposition source 16 over which it is passing between successive passes 88 to laminate the film 174, such as to minimize X-Y anisotropy in a film plane.
Some embodiments of the enhanced sputtered film processing system 10 and method 150 comprise using magnetron sputter deposition sources 14 that are longer, when compared to a substrate diameter, than is needed for uniform film thickness; wherein film stress non-uniformity along a longitudinal axis 47 of the source 16 is minimized.
In some embodiments of the enhanced sputtered film processing system 10, e.g. 10a (
The substrates 14 can be either round, e.g. less than or equal to 100 mm diameter or greater that 100 mm, or square, e.g. less than or equal to 100 mm on a side, or greater than 100 mm on a side. Other embodiments could utilize substrates of other shapes and sizes as well.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, the substrates 14 may comprise any of ceramic, silicon, glass, glass ceramic, diamond, FR4 or other printed circuit board, a polymer, e.g. polyimide, and/or any combination thereof.
Functional Embodiment. An exemplary embodiment of the system 10 was installed in a conventional 10-7 Torr stainless-steel or aluminum high-vacuum chamber with elastomer seals and cryopumping, such as manufactured by Leybold and other vendors.
The exemplary system 10b comprised at least two rectangular magnetron sputter sources 16, such as those manufactured by Leybold, and an ion gun 20 with a 6-inch diameter beam, such as a Kaufman-style gun, as manufactured by Commonwealth, and arranged as seen in
The planetary linkage for wafer motion is connected so that the wafers 14 remain in the same rotational orientation about their own normal axes 18 relative to a fixed point as they orbit about the central axis 28 of the chamber.
The exemplary plate 12 rotating about the central axis 28 carries 6″ wafers on a 10-inch orbiting radius from the center of the plate 12, and the 14-inch long magnetron sputter deposition sources 16 and the ion gun are centered on the wafers 14. Fixturing is arranged so that the wafers 14 are exposed to an even angular distribution and flux of depositing material across their surface 94a.
Calibration Process. As discussed above, the enhanced sputter deposition system 10 may preferably be optimized based upon experimental calibration of operating parameters.
Calibration step 1. Film stress vs. pressure of an Ar sputtering gas is measured by sputter deposition at various fixed pressures onto thin wafers. The stress is then calculated in a conventional manner by means of the change in curvature of the wafer caused by the deposition.
Calibration step 2. Deposition of a multilayer structure is carried out using a progression from compressive to tensile stress along the positive-slope portion of the stress-pressure curve. Springs are patterned and lifted, and spring curvature radius is calculated from lift height.
Typical Parameters. Typical operating parameters used for deposition in some current embodiments of the system 10 are as follows (ranges are shown in brackets):
MoCr alloy target, typ. 0-20 at. % Cr: power 2400 W (500-10,000), gas flow: Ar 80 sccm (10-500), pressure: 0.6 to 15 mT (0.2-50), plate rotation rate: 30 rpm (1-240).
Ion Gun: beam current from 50 to 500 mA, ion energy from 200 to 1000 eV.
System Performance. System performance was tested and measured over a variety of operating parameters for different embodiments of the enhanced sputtering system 10.
It is typically preferred to deposit material 74 at as high a rate as possible, both to increase production throughput and to minimize the deleterious effect of co-depositing impurities from the background gasses in the vacuum chamber. Whereas the best quality films are formed at relatively high rates of rotation, both wear on the mechanical bearings and particulate generation can be minimized by reducing the rotation rate. In a production deposition system, the rotation rate may preferably be chosen so as to optimize the number of monolayers deposited per pass, i.e. to reduce the rotation rate by an amount that increases the number of monolayers deposited, without significantly degrading the desired film properties such as the uniformity of stress in the X, Y, and Z directions.
For example, at a typically time-averaged deposition rate of 0.5 nm/sec (1.8 um/hr or about 1.5 monolayers/sec), the plate 12 may rotate at 1 to 240 rpm. This rotation rate may be as much as about 10 times faster than is needed or desired in conventional planetary deposition, and about 100 times faster than the pass time in linear transport.
In some embodiments of the enhanced sputtered film processing system 10 and method 150, measurement and/or compensation are provided for any of the lift height 262 and the X-Y position of photolithographically patterned spring contacts 246. For example, any of the spring length and angle may preferably be measured and/or adjusted on the photolithographic mask to compensate for any errors measured in produced spring substrate assemblies.
While some embodiments of the enhanced sputtered film processing system 10 and method 150 are implemented for the fabrication of photolithographically patterned springs 246 with lift heights and tip positions having predictable positional errors, the system 10 and method 150 may alternately be used for a wide variety of sputter deposition environments, such as to provide mechanical compliance and/or electrical connections between any of contacts, connectors, and/or devices or assemblies.
Accordingly, although the invention has been described in detail with reference to a particular preferred embodiment, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US06/27423 | 7/14/2006 | WO | 00 | 12/5/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60699647 | Jul 2005 | US |
