Patent Application
20080029386
1. Sputter Zone—area or “zone” of the material (typically thin film or tape) where its surface becomes the Target surface or Sputtered surface as its existing surface provides material to be sputtered into the deposition zone. In any given moment of the Trans-Zone Sputtering process, the Sputter Zone is located in vicinity of the negative bias electrode of the magnetron assembly, although the relative position of the Sputter Zone is continuously moving with regard to said material.
2. Deposition Zone—area or “zone” of the material (typically thin film or tape) where its surface becomes the Deposition surface as its existing surface provides the area to receive the previously sputtered material. In any given moment of the Trans-Zone Sputtering process, the Deposition Zone is directed to the flux of the sputtered matter ejected from the Sputter Zone, although the relative position of the Deposition Zone is continuously moving with regard to said material.
3. SputtersputterSurface Engineering—as is generally understood in the industry, without limitation; in general, and for clarification only, it refers to a surface of any material that is undergoing any form of restructuring or modification.
4. Target/Sputtered Surface—The surface of any material that in the area of the Sputter Zone where a portion of that material's surface provides material for the flux to be subsequently sputtered onto a Deposition Surface in the Deposition Zone.
5. Deposited Surface—The surface of any material in the area of the Deposition Zone where the material will receive material from the flux generated by previously sputtered material.
6. Simultaneously Engineered—referring to two materials where each is providing material for a flux in the Sputter Zone and at the same time, the flux is deposited on the other respective material in the Deposition Zone.
In the below description and throughout this application, the use of the word “tape” to describe the material that is engineered is not limiting. “Tape” is a general term and also implies any type of thin films or other “tape-like” or “film-like” material which may or may not be processed or delivered in a roll.
In accordance with the present invention, deposition of the sputtered matter, such as metallic, polymeric, or ceramic materials, on the surface of identical material significantly improves various surface properties, including tribological properties, surface hardness, and in some cases fracture toughness. Except for fracture toughness, these surface property enhancements are known in prior art; however, for fracture toughness, if a strong surface layer with strong adhesion is present, there is an increase in the resistance to crack propagation (reference Si reinforcement and glass patent applications here).
In the case of polymers, such as Teflon, such a deposition also decreases or completely closes superficial micro- and nano-pores. Such useful and important improvements are especially effective if a negative bias voltage is applied to the substrate holder with an appropriate design of the magnetron-substrate assembling geometry.
In addition, the doping elements may be introduced together with flux of the sputtered matter to enhance said surface engineering. Doping elements may be introduced as atomic, or molecular, or multi-atomic cluster particles with a complimentary flux from an individual source, such as a complimentary sputtering source, thermal evaporator or external gas supply line. The doping element or combination of different doping elements may be selected from the group of non-metallic elements, such as carbon, silicon, boron, oxygen, and/or the group of metals. More specifically, silicon and oxygen are particularly effective doping elements for improving properties of plastics, while carbon or combination of carbon, silicon and oxygen are particularly effective doping elements for improving properties of metals. According to the present invention, many plastic materials, especially silicones or other silicon-organic polymers may be applied as solid precursors, in particular as the target in RF planar magnetrons in the processes of the surface engineering of metals. On the other hand, metals may be used as doping elements to improve surface thermal resistance, or provide surface electrical conductivity, as well as decorative effects for plastics.
According to the present invention, the surface of the same intact material is subjected to the sputtering and deposition of the flux of sputtered particles in the same process.
Also in accordance with present invention, in every specific moment of the process said sputtering is realized in a limited area, or zone, of the surface of material thereby having undergone surface engineering, while deposition is realized in this specific moment of the process upon the other zone of the surface of material thereby having undergone surface engineering. The sputtered matter is ejected from the material in the sputter zone and deposited upon the surface of the material in the deposition zone. The invented method is named trans-zone sputtering.
The surface engineering by trans-zone sputtering is preferably realized with a DC or an RF planar magnetron.
In the main embodiment of the present invention, the sputter zone and the deposition zone are located on the surface of the same intact material. The sputtered matter is ejected from said sputter zone, and the resulting flux of mono-atomic and/or multi-atomic particles are deposited upon the surface of the material in the deposition zone, while both zones are moving synchronously relatively to the surface of said intact material. This is shown in detail in
1—sputter zone of the tape of the material undergoing to surface engineering.
2—planar magnetron
3—deposition zone of the tape of the material undergoing to surface engineering.
4—substrate holder-electrode.
5—the feed roll of the tape or film of the material undergoing surface engineering.
6—feed section of the surface engineering system.
7,8,10—drive/guide rolls.
9—deposition section of the surface engineering system.
11—take-up roll of the tape of the material having undergone surface engineering.
12—take-up section of the surface engineering system.
In an alternative embodiment of the present invention, both sputtering and deposition processes are realized upon the surfaces of two separate materials simultaneously, each of said separate materials possess said sputter zone and said deposition zone. The sputtered matter ejected from the sputter zone of the first of two said materials is deposited upon the surface of the deposition zone of the second of two said materials; the sputtered matter ejected from said sputter zone of the second of two said materials is deposited upon the surface of deposition zone of the first of two said materials, both the sputter zone and the deposition zone where each of said materials passes through are fixed relative to the chamber, and the two said materials are moving in parallel but in opposite directions, i.e. counter flow. This is shown in detail in
1—first sputter zone of the first side of the tape undergoing to surface engineering.
2—first planar magnetron
3—first deposition zone of the tape/film undergoing surface engineering.
4—first substrate holder-electrode.
5—the feed roll of the tape of the material undergoing surface engineering.
6—feed section of the surface engineering system.
7,8,10,13-17—drive rolls.
11—take-up roll of the tape/film of the material having undergone surface engineering.
12—take-up section of the surface engineering system.
18—second sputter zone of the second side of the tape undergoing to surface engineering.
19—second planar magnetron.
20—second deposition zone of the tape undergoing surface engineering.
21—second substrate holder-electrode.
More specifically, the area of material located at any given moment of the process in the proximity of the negative bias electrode, i.e. in the sputter section of the chamber, becomes a Sputter Zone, and in both embodiments of the invention the location of said Sputter Zone moves relatively to the engineered surface covering, consequently, the entire engineered material. Similar consideration is implied to the Deposition Zone. Any given area of the surface of the surface-engineered material becomes a Sputter Zone first and shortly after a period of time it becomes a Deposition Zone.
According to the main embodiment of the present invention, the positions of said sputter zone and said deposition zone are fixed relative to the chamber, said intact material comprising said sputter zone and said deposition zone is moving relative to the chamber, said moving intact material is preferably but not limited to the shape of a tape.
It is also possible according to the present invention, that an intact material comprising said sputter zone and said deposition zone are fixed relative to the chamber, while said sputter zone and said deposition zone are continuously moving relative to the chamber.
22—the movable semi-closed mini-chamber with magnetron and bias electrode (all designations of internal parts as on
23—flexible contacts.
24—clamps.
A main vacuum chamber encompassing all these parts is not shown in
A disclosed method for surface engineering by trans-zone sputtering according to the present invention, especially with regard to the surface engineering of dielectric materials, in particular surface engineering of polymer materials, may be used in combination with a negative potential applied to the special bias electrode (
Also in accordance with the most preferable embodiment of the present invention, the intact material comprising said sputter zone and said deposition zone has the tape/film moving relative to the chamber. The length of the tape/film is at least ten times greater than the combined length of the said sputter zone length and said deposition zone length. The tape is moving through said sputter zone being in mechanical contact with the magnetron cathode or at a distance from the cathode not exceeding 5 mm, and the tape is moving through said deposition zone being in mechanical contact with the bias electrode or at a distance from said electrode not exceeding 5 mm.
Typically, according to the present invention, said continuously moving tape/film is guided by a driving mechanism of 180 degrees between said sputter section and deposition section, said sputter section is moving in the opposite parallel direction to said deposition section (
In another embodiment of the present invention, said surface engineering is conducted from both sides of said material in one continuous process (
Still in another embodiment of the present invention, said continuously moving tape/film is guided between said source section and said substrate section by a driving mechanism on the angle at least 90 degrees but no greater than 160 degrees, and an additional flux of ions, atoms and/or low-molecular radicals is directed to said substrate section of said moving tape from an additional source, such as second magnetron, or plasmatron, or evaporating source, or ion gun (
Also according with the present invention, the surface engineering by trans-zone sputtering is realized upon the surfaces of two different materials simultaneously and in synch, each of two said materials possess said sputter zone and said deposition zone, the sputtered matter ejected from said sputter zone of the first of two said materials is deposited upon the surface of deposition zone of the second of two said materials, while the sputtered matter ejected from said sputter zone of the second of two said materials is deposited upon the surface of deposition zone of the first of two said materials. In this embodiment, the positions of each sputter zone and deposition zone of each said material are fixed relative to the chamber, said materials are moving synchronously in mutually opposite parallel directions, and the distance between the engineered surfaces of said materials is about or exceeds 5 cm (
When the trans-zone sputtering is applied for engineering of the surfaces of two identical but separate materials simultaneously, said identical materials may be selected from the group of plastics, or from the group of metals.
When the trans-zone sputtering is applied for engineering of the surfaces of two different materials simultaneously, one of said different materials may be selected from the group of plastics, the second of said different materials selected from but not limited to the group of metals.
In another embodiment of the present invention, both said materials are polymer-based materials; one of said materials may be selected from, but not limited to, the group of organic or fluorine-organic polymers, and the second of said materials may be selected from, but not limited to, the group of silicon-organic polymers.
Also according to the present invention, both said materials may be selected from the group of metals.
If metal or metals are subjected to surface engineering by the trans-zone sputtering technique, a special precaution must be undertaken to prevent the high-voltage breakdown between the magnetron cathode and engineered material. The simplest solution is surface insulation of the magnetron cathode with a dielectric, such as an attached thin plate or a deposited dielectric layer while using the RF voltage mode. However, other solutions based on properly designed electrical power supply circuits are also possible.
In an important complimentary embodiment of the present invention, an active gas containing doping elements, including but not limited to carbon, silicon, oxygen, nitrogen, boron and/or one or combination of metallic elements, is supplied into the vacuum chamber during the sputtering/deposition process, preferably directly to the space in proximity of the deposition zone.
Continuous trans-zone sputtering provides greater than 90% utilization rate along the entire length of the tape except its beginning portion and end portion. In the case of very wide tapes, such as 10 to 20-ft wide tapes, a partial loss of sputtered material would occur mostly along the edges in the area with a width of about or less than the distance between the sputter zone and the deposition zone, and it would typically be about or below 1% of the total.
In fact, sputtering would not result with the actual loss of the material because it provides the necessary cleaning in situ (in chamber) prior to deposition. Thus, instead of the usually required special cleaning operation which requires additional operational time and labor, the invented method provides self-cleaning.
Furthermore, because no special target is needed for trans-zone sputtering, the target replacement which usually consumes essential operational time and labor, is completely excluded.
The trans-zone sputtering is a magnetron technology which is completely free from use of an expensive consumable target.
There is no need for water cooling of the magnetron assembly. As a result, the entire magnetron assembly may be located inside the chamber, and it does not experience the force of atmospheric pressure. This brings further advantages: the cathode assembly is thinner, the magnetic design is optimized, and the effectiveness of sputtering, sputtering/power density ratio and energy use all improve. It also reduces the magnetron weight, thus simplifying its installation in the chamber and allowing its movable design.
An additional advantage is an exceptional uniformity of both sputtering and deposition processes and smoothness of the resulted surfaces due to the high speed movement of the consuming and “growing” surfaces relative to the cathode assembly.
Where it is applicable, especially in the precise surface engineering and super-thin film deposition technologies, the Trans-Zone Sputtering is characterized with exceptionally high productivity; it does not require the expensive consumable targets, and in some instances it avoids the necessity of water cooling of the magnetron cathode assembly; it simplifies the maintenance of equipment, reduces labor requirements and virtually avoids emission.
The invented technology possesses certain innate physical and technical limitations, in particular the limits of achievable thickness of deposited materials due to high power density dissipating in material undergoing surface engineering by sputtering.
The mean depth of the temperature front penetration into the irradiated target is
h=˜{square root[3k(T),t]}cm,
where t is the time of irradiation, seconds; k(T), cm(sup2)/sec is temperature conductivity of irradiated material; k(T)=k/c, where K is its thermal conductivity, and c is the volume heat capacity.
If there is no effective heat sink from the back side of the irradiated material provided, and h>>D, where D is the thickness of the irradiated material, the temperature distribution across the thickness of the irradiated material is rather uniform. If h˜D, the surface temperature is about ˜1.65 of the average temperature across the thickness of the irradiated material. If h<<D, the elaborated energy heats mostly the surface layer ˜L.
The preferable embodiment of the present invention would satisfy the condition h>>D, while the surface temperature in such a condition only slightly exceeds the average temperature, should not be greater than the maximum temperature T* technically feasible for the target material, taking into account its intrinsic physical properties and the entire assembly requirements.
In such a condition the average target temperature is
T≦[(Nt)/(Dc)],
where N is the irradiation power density. In this formula t=d/V, where d is the required thickness of the deposited layer, V—is the deposition rate, e.g.
T˜{[(dN/V)/(Dc)]+T,room>]}
while it is required that T≦T*. Thus, the maximum achievable thickness of deposited layers in the trans-zone sputtering process may be evaluated as:
d≦[T*Dc(v/N)]
Indeed, the surface temperature would be greater but not exceeding ˜1.1 T e.g., the surface temperature may reach but will not exceed about 110% of the average temperature. On the other hand, actual average temperature increase will be a little lower of the above estimate due to a “cooling” effect via irradiation, e.g. transition from solid into non-condensed state of the sputtered flux and ejection energetic sputtered particles out from the irradiated surface, as well back scattering of still slightly energetic argon ions. These mutually compensated effects are of the same order of magnitude and may be neglected in this evaluation.
The inversed value of V/N, e.g. ratio between deposition rate and power density, may be also found in reference publications for different materials. The reference data may be used for an approximate evaluation, while the exact value depends on the specific design of magnetron assembly and should be defined experimentally.
As an example, consider Teflon characterized with the following properties: density ˜2.24 g/cm3, heat capacity c−1 J/g K, and thermal conductivity 2.3-2.5 W/mK in the technically important temperature range of 300 to 600 K. The sputtering rate of Teflon via irradiation by the argon ions with energy ˜1000 eV based on our experience is about or exceeds 6.0 {(nanometer/second)/([W/cm(sup2)]} at ˜300K and strongly increases with the target temperature. The maximum technically feasible temperature for Teflon T*=600 K, and hence the maximum achievable thickness of deposited Teflon films in the trans-zone sputtering process may be evaluated as
(d,nanometers)<(0.4D,micrometers),
while it is assumed that h(t)>>D. Hence, for 100-micrometer thick Teflon tape the maximum achievable thickness of deposited Teflon films in the trans-zone sputtering process is about 40 nm.
At the power density of 10 W/cm(sup2), RF the deposition time of 40-nm thick film would be 0.67 sec, and the mean depth of the temperature front penetration into the irradiated Teflon target would be h(t)=˜0,14 cm, e.g. the condition h(t)>>D is actually satisfied.
Similar although slightly different (small deviations) evaluations of the maximum achievable thickness are justified for other high-temperature plastics, such as polyimides, aromatic polyamides, polyoxybenzoates, silicon-organic polymers, and fluoro-polymers.
Typically, most polymers possess innate nanopores causing the eventual penetration of chemical agents through polymeric films, walls of the vessels, etc. It is understood from a general knowledge and from the practices of the prior art, that vapor deposition, especially from a relatively high energy flux generated by sputtering, produces a more uniform, dense and pore free layer. In many cases, such as chemically ultra-resistant materials as Teflon, a deposition of a dense surface layer of the same material would be especially desirable. The Trans-Zone Sputtering technique would be most effective for such applications.
In the case of metals, the condition h(t)>>D is almost always satisfied due to their high thermal conductivity, but the power consumption during the sputtering is one order, or even two orders of magnitude higher, and the maximum achievable thickness is correspondingly lower:
Aluminum characterized with heat capacity 25.1 J/Mol K=0.93 J/g K, density 2.7 g/cm(sup3), thermal conductivity 218 W/m K, sputtering rate/power density ratio in the above defined conditions ˜0,7{(nanometer/second)/([W/cm(sup2)]} at 300K. Hence, for 100-micrometer thick aluminum tape the maximum achievable thickness of deposited films in the trans-zone sputtering process is about 5 nm.
This thin surface layer will effectively improve surface of many materials.
Besides a higher density and uniformity, the Trans-Zone Sputtering would also cure the shallow surface mechanical defects and will close the grain boundaries commonly causing the crack nucleation, as well as corrosion in metals. In high-melting materials, like many transition metals and ceramics, the nanostructured or even amorphous surface layer would be formed as the result of the surface engineering by Trans-Zone Sputtering technique.
Similar evaluations of the maximum achievable thickness of deposited films in the trans-zone sputtering process for some other metals are:
NOTE: all the above estimates of the maximum achievable thickness of deposited films in the trans-zone sputtering process are based on a regular magnetron design without special optimization available based on thin water-free assembly located inside of vacuum chamber. This additional optimization would increase V/N ratio between deposition rate and power density, and thus increase achievable film thickness.
The invention is illustrated further by the following examples.
In the below example a 200-micrometer thick Teflon tape underwent surface engineering with the purpose to close superficial nano-pores in the typical diameter range of 1 nm to 4 nm. The engineering was conducted using a rectangular magnetron; the width of the sputter zone is 8″, and the sputtered and deposited layers are 10-nm thick. The power density is 10 W/cm (sup2), RF.
The distance between the tape and magnetron cathode is 2 mm.
Note: this 2-mm gap is designated for decreasing the heat exchange between the tape and magnetron cathode; the exact width of the gap is not critical, and even occasional touching between tape and cathode will not result in damage.
The deposition time of 10 nm thick film is 0.5 second, the tape speed is 24 m/min. The step-wise procedure is as follows:
Observations: the tapes are hot (˜100 degree C.).
The copper tapes and polyimide tape are installed in geometry shown on
Final thickness of the copper layer upon polyimide is 8 nm. The copper layer is deposited instantly after cleaning of the polyimide substrate by ion sputtering and possesses high adhesion to polyimide and uniformity. Typically in the case of fast moving tape, the variation in uniformity will be less than 0.1% within 1 inch. Uniformity of composition and thickness is much better than plus/minus 1% within 1 m of length.
With foil, 20-40 microns, and you have a couple of centimeters it's about 10-50 m long), but in industry 1 m diameter and 40 microns thick, the average length will be 1.5 m; it may be used as the ground layer for copper plating.
Final thickness of polyimide layer upon copper tape is 32 nm. Polyimide layer provides anti-corrosion protection for the coated cooper surface.
1.5 m×(0.5 m/40 microns)=1.5 m×(500000 microns/40 microns)=18750 m=18.75 km.
It is therefore apparent that the invention accomplishes its intended objectives. While embodiments of the invention have been described in detail, that is done for the purpose of illustration, not limitation.
