CA1057045A - Method for monitoring the surface resistivity of metallized film - Google Patents
Method for monitoring the surface resistivity of metallized filmInfo
- Publication number
- CA1057045A CA1057045A CA240,980A CA240980A CA1057045A CA 1057045 A CA1057045 A CA 1057045A CA 240980 A CA240980 A CA 240980A CA 1057045 A CA1057045 A CA 1057045A
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- CA
- Canada
- Prior art keywords
- resistivity
- deposit
- film
- substrate
- radiation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 31
- 239000011104 metalized film Substances 0.000 title claims abstract description 11
- 238000012544 monitoring process Methods 0.000 title abstract description 5
- 239000000758 substrate Substances 0.000 claims abstract description 39
- 239000010408 film Substances 0.000 claims abstract description 37
- 230000005855 radiation Effects 0.000 claims abstract description 30
- 229910052751 metal Inorganic materials 0.000 claims abstract description 23
- 239000002184 metal Substances 0.000 claims abstract description 23
- 230000008569 process Effects 0.000 claims abstract description 23
- 230000005670 electromagnetic radiation Effects 0.000 claims abstract description 8
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052737 gold Inorganic materials 0.000 claims abstract description 8
- 239000010931 gold Substances 0.000 claims abstract description 8
- 238000001771 vacuum deposition Methods 0.000 claims abstract description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 5
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims abstract description 5
- 229910052802 copper Inorganic materials 0.000 claims abstract description 5
- 239000010949 copper Substances 0.000 claims abstract description 5
- 229910052709 silver Inorganic materials 0.000 claims abstract description 5
- 239000004332 silver Substances 0.000 claims abstract description 5
- 230000005540 biological transmission Effects 0.000 claims description 22
- 238000000151 deposition Methods 0.000 claims description 12
- 230000008021 deposition Effects 0.000 claims description 12
- 229920006267 polyester film Polymers 0.000 claims description 5
- -1 polyethylene Polymers 0.000 claims description 5
- 229920002284 Cellulose triacetate Polymers 0.000 claims description 4
- 239000004812 Fluorinated ethylene propylene Substances 0.000 claims description 4
- NNLVGZFZQQXQNW-ADJNRHBOSA-N [(2r,3r,4s,5r,6s)-4,5-diacetyloxy-3-[(2s,3r,4s,5r,6r)-3,4,5-triacetyloxy-6-(acetyloxymethyl)oxan-2-yl]oxy-6-[(2r,3r,4s,5r,6s)-4,5,6-triacetyloxy-2-(acetyloxymethyl)oxan-3-yl]oxyoxan-2-yl]methyl acetate Chemical compound O([C@@H]1O[C@@H]([C@H]([C@H](OC(C)=O)[C@H]1OC(C)=O)O[C@H]1[C@@H]([C@@H](OC(C)=O)[C@H](OC(C)=O)[C@@H](COC(C)=O)O1)OC(C)=O)COC(=O)C)[C@@H]1[C@@H](COC(C)=O)O[C@@H](OC(C)=O)[C@H](OC(C)=O)[C@H]1OC(C)=O NNLVGZFZQQXQNW-ADJNRHBOSA-N 0.000 claims description 4
- 229920009441 perflouroethylene propylene Polymers 0.000 claims description 4
- 229920002301 cellulose acetate Polymers 0.000 claims description 3
- 229920000139 polyethylene terephthalate Polymers 0.000 claims description 3
- 239000005020 polyethylene terephthalate Substances 0.000 claims description 3
- 230000006872 improvement Effects 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 239000004698 Polyethylene Substances 0.000 claims 2
- 229920000573 polyethylene Polymers 0.000 claims 2
- 230000002596 correlated effect Effects 0.000 claims 1
- 238000009826 distribution Methods 0.000 abstract description 3
- 239000002985 plastic film Substances 0.000 abstract description 2
- 229920006255 plastic film Polymers 0.000 abstract description 2
- 238000004544 sputter deposition Methods 0.000 abstract description 2
- 238000007738 vacuum evaporation Methods 0.000 abstract description 2
- 238000004519 manufacturing process Methods 0.000 abstract 1
- 238000000576 coating method Methods 0.000 description 7
- 239000011248 coating agent Substances 0.000 description 6
- 238000001514 detection method Methods 0.000 description 4
- 238000001704 evaporation Methods 0.000 description 4
- 230000008020 evaporation Effects 0.000 description 4
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- 208000028659 discharge Diseases 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 229920003023 plastic Polymers 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 229910052981 lead sulfide Inorganic materials 0.000 description 2
- 229940056932 lead sulfide Drugs 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000001883 metal evaporation Methods 0.000 description 2
- 238000001465 metallisation Methods 0.000 description 2
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- 239000004926 polymethyl methacrylate Substances 0.000 description 2
- WUPHOULIZUERAE-UHFFFAOYSA-N 3-(oxolan-2-yl)propanoic acid Chemical compound OC(=O)CCC1CCCO1 WUPHOULIZUERAE-UHFFFAOYSA-N 0.000 description 1
- 229910000897 Babbitt (metal) Inorganic materials 0.000 description 1
- DQEFEBPAPFSJLV-UHFFFAOYSA-N Cellulose propionate Chemical compound CCC(=O)OCC1OC(OC(=O)CC)C(OC(=O)CC)C(OC(=O)CC)C1OC1C(OC(=O)CC)C(OC(=O)CC)C(OC(=O)CC)C(COC(=O)CC)O1 DQEFEBPAPFSJLV-UHFFFAOYSA-N 0.000 description 1
- 239000001856 Ethyl cellulose Substances 0.000 description 1
- ZZSNKZQZMQGXPY-UHFFFAOYSA-N Ethyl cellulose Chemical compound CCOCC1OC(OC)C(OCC)C(OCC)C1OC1C(O)C(O)C(OC)C(CO)O1 ZZSNKZQZMQGXPY-UHFFFAOYSA-N 0.000 description 1
- 229920001986 Vinylidene chloride-vinyl chloride copolymer Polymers 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 229910052980 cadmium sulfide Inorganic materials 0.000 description 1
- 229920006217 cellulose acetate butyrate Polymers 0.000 description 1
- 229920006218 cellulose propionate Polymers 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 229920001249 ethyl cellulose Polymers 0.000 description 1
- 235000019325 ethyl cellulose Nutrition 0.000 description 1
- 238000009501 film coating Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
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- 238000009434 installation Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000002923 metal particle Substances 0.000 description 1
- 238000009304 pastoral farming Methods 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 229920002620 polyvinyl fluoride Polymers 0.000 description 1
- 238000003908 quality control method Methods 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 239000004627 regenerated cellulose Substances 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/359—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using near infrared light
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Physical Vapour Deposition (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Described herein is a method of monitoring surface resistivity distribution resulting from vacuum deposition of thin, transport metal films on moving plastic film or other transparent substrates. The process comprises applying to the metallized film electromagnetic radiation and detecting and band width of electromagnetic radiation transmitted through or reflected from the metallized film in the near-infrared region, more particularly within the wavelength range of about 1.5 to 3.0 microns. The detected band width permits excellent correlation between transmitted radiation and local conductivity or, reciprocally, resistivity of vacuum deposited gold, silver, and copper. Vacuum deposition can occur, e.g., by vacuum evaporation or sputtering. The metallized films are useful in the production of electrically heated transparent closures such as for automobile windshields.
Described herein is a method of monitoring surface resistivity distribution resulting from vacuum deposition of thin, transport metal films on moving plastic film or other transparent substrates. The process comprises applying to the metallized film electromagnetic radiation and detecting and band width of electromagnetic radiation transmitted through or reflected from the metallized film in the near-infrared region, more particularly within the wavelength range of about 1.5 to 3.0 microns. The detected band width permits excellent correlation between transmitted radiation and local conductivity or, reciprocally, resistivity of vacuum deposited gold, silver, and copper. Vacuum deposition can occur, e.g., by vacuum evaporation or sputtering. The metallized films are useful in the production of electrically heated transparent closures such as for automobile windshields.
Description
~ETHOD FOR MONITORING TH~; SURFACE RESISTIVITY
OF METALLIZED FILM
Field of the Invention . .
This invention relates to a process of monitoring surface resistivity distribution of vacuum deposited metals.
Background of the Invention Vacuum deposited metal thin film coatings have found widespread application as transparent resistance heaters for deicing and demisting transparent enclosures such as windshields.
Typically, such enclosures comprise a thin transparent plastic carrier film or substrate upon which has been deposited a thin conductive metallic film which can be powered by busbar~
normally attached at the edge portions thereof. Ultimately, the metallized substrate is laminated between rigid, transparent plies as of glass in order to form a safety glass-type construction, In order that upon energizing power be dissipated in an optimal manner for the particular deicing function of the ultimate laminated transparency, and to preserve the optical properties required in windshield and like employments, resistivity distribution of the deposited metallic film must be closely controlled. In the past, local resistivity has been determined by measuring the overall ~bus to bus) resistance of the final part and then normalizing the value determined to a ~5 square area configuration. This requires physical contact to a finished part already equipped with busbars. However, it is frequently desirable to determine resistivity of a metallized substrate film prior to the application thereto of busbars or other means of electrical attachment. In United States Patent - 1- ~$ ' ~057C45 3,086,889 to Strong, it is proposed that electrical resistance of a continuously deposited metallic coating be monitored by balancing a bridge circuit against resistance measured between electrical contacts which engage the metallic coated side of a S dielectric sheet material. Unfortunately, where the metallic film whose resistance is to be measured is so thin as is the case where transparency is required, then the fragility of the metallic coating is highly susceptible to disruption by such contact methods of measurement. When the metalli~ed film is subsequently energized, disruptions in the fragile coating give rise to localized regions of high current density which can lead to failure. Accordingly, a need has existed for a means of non-destructively describing the local resistivity of vacuum-deposited thin metal films.
In United States Patent 3,397,672 to Dykeman, et al, it is proposed at column 3, lines 2-5, to measure the thickness of vapor-deposited aluminum by detection of radiation emanant from the coating upon application of x-rays. The equipment required for x-ray generation is generally highly expensive and to the economic disadvantages of that proposal must be added the danger to operators and maintenance personnel inevitably inhering in x-ray operation.
In determining what form of radiation will be employed and detected in monitoring resistivity of vacuum-deposited metals, however, more is involved than straight-forward considerations of economy and safety. There is required a wavelength interval which when detected provides a relatively steep and linear curve of transmission or reflectance against resistivity. Moreover, where transmission is to be measured, 3~ a spectral region must be chosen wherein transmission of the bare substrate is high, i.e., a window.
Brief Summary of the Invention In accordance with the present invention there is provided a process for preparation of a transparent metalized substrate having luminous light transmission greater than 20~, by vacuum deposition of a metal selected from the group consisting of silver, gold and copper on a transparent substrate and determining the surface resistivity of the deposit formed on the substrate, the improvement comprising applying electromagnetic radiation within the wave length range of from l.5 to 3.0 microns to the substrate and deposit, detecting a signal comprising electromagnetic radiation within the ~ave length range of from l.5 to 3.0 microns transmitted through the substrate and deposit, and correlating the value of the signal to the surface resistivity of the deposit on the substrate.
Embodiments of the invention will now be described in the description which follows and with reference to the accompanying drawings in which:
Figure 1 schematically represents a vacuum deposition apparatus environment in which the process of the invention can be practiced;
Figure 2 schematically depicts one detection system with which the invention can be practiced; and Figure 3 graphically correlates percent transmission of various band widths of radiation with resistivity of vacuum deposited metal on a particular substrate.
Detailed Descri tson of the Invention P
Turning now to the drawings, with particular reference to Figure 1, there is shown an electron beam gun ~1~)57045 10 positioned below a moving substate 11. The electron beam of the gun is focused onto an evaporant metal 12 located in a crucible 13 recessed into electron gun 10. Evaporant metal 12 is stored in the form of wire on a spool 15. The wire is fed to crucible 13 by feed mechanism 16.
The film substrate 11 is transported from a supply reel 17 over the electron gun 10 to a take-up reel 18 by a friction roller 19 acting on driving roller 20. The friction roller 19 is connected by chains and a gear set to a reversible universal motor (not shown).
Resistivity of the metal deposit applied to sub~
strate 11 is monitored by measuring electromagnetic radiation within the range from about 1.5 to 3.0 microns trànsmitted through the metallized film 21. For purpose of illustration an AC energized radiation source 22 and radiation detector 23 are shown placed on either side of the metallized film 21 at a point downstream from the deposition area for measuring transmission of selected band widths of radiation. The radiation source and detector may be provided with masks to obviate the effect of stray radiation.
The vacuum deposition apparatus is contained in a vacuum chamber 24 and a wall 25 having opening 26 therein for equalization of pressure may be provided to delineate an evaporation chamber from the remainder of the vacuum chamber.
Wall 25 is provided with slit 26a which can be designed to allow insertion of masks that control the size of the slit opening as to both length and width ~not shown). Suitable size of the slit opening is determined by the distance between the substrate and evaporant metal 12. Slit opening length (in the direction of film travel) can be determined by the angle swept out by considering the evaporant beam to originate from a point source in the center of the crucible 13 and defin-ing the limits as the lines tangent to driving roller 20. The width of the slit can be determined in a similar manner using as the limit the edge or width of the plastic film. Glow discharge electrodes 27 and 27' are desirably provided for surface treatment of the substrate 11 in conventional manner.
Preferably, all of the substrate 11 is glow discharged prior to commencement of metal evaporation.
As will be recognized by the art skilled, deposition rate is influenced by the rate of metal evaporation, speed of film travel, nature of glow discharge treatment, source to substrate distance, and system pressure at evaporation. ~n the embodiment shown, glow discharge treatment occurred at 50 microns pressure of argon with power input of 1.4 KV AC and film travel speed of ~ inches per minute. For deposition, film speed was set at approximately 2 feet per minute with evaporator power setting of 0.2 kw. Source to substrate distance was fixed at 8 inches, and evaporations run at a pressure of 2 to 5 times 10 5 torr.
The techniques and apparatus for implementation of the measurement contemplated by this invention are known to those familiar with the art, but in the preferred embodiment employ an AC operated source of radiation such as an incan-descent bulb having a brightness temperature greater than about 800 degrees centigrade with a modulated driver or an optical chopper, optics directing the alternati~ng or chopped radiation through the part to be measured, and a suitable photo detector, rectifier, amplifier, and read-out device. Figure 2 schematically illustrates one suitable system, wherein signal 105~7045 generator 28 supplies a signal amplified by element 29 to radiation source 30. The radiation is directed through the metallized substrate (not shown) and the radiation transmitted by the substrate is received by a sui~ably biased photo detector 31. Preferably a lead sulfide detector is employed for the band widths used in this invention, and radiation transmitted through the metallized film is passed through an optical interference, band-pass filter prior to impingement upon the lead sulfide. The signal generated by detector 31 is applied through element 35 containing a filter and a 2-pole, narrow-pass pre-amplifier to a full wave rectifying power amplifier 32. At 32, the received signal is compared with a reference signal supplied by line 34 and the resulting information displayed by recorder 33.
Substrates employed in this invention are preferably transparent plastic carrier films which most preferably range in thickness from about 0.00025 to about 0.015 inch. Preferred films are cellulose triacetate, cellulose acetate, fluorinated ethylene-propylene copolymers, and polyethylene terephthalate polyester films. Among the wide variety of other suitable candidates for substrate film employment may be mentioned:
cellulose acetate butyrate, cellulose propionate, ethyl cellulose, polymethylmethacrylate, polytrifluorochlorethylene copolymer, polyvinylfluoride, polycarbonate, vinylidene chloride-vinyl chloride copolymer, polyvinylchloride, vinyl chloride-acetate copolymer, and regenerated cellulose films.
Of course, substates other than transparent plastic carrier -films can be employed, e.g., rigid, transparent, substate plies as of glass, stretched polymethylmethacrylate, polycarbon-ate, etc. Preferably such rigid plies,range in thickness from about 0.02 to 0.25 inches. The metals deposited on the substrate films are selected from the group consisting of silver, gold, and copper and are generally deposited in thicknesses within the range from about 100 to 500 angstroms.
The resulting resistivity of the deposited metal generally is within the range from about 10 to about 25 ohms per square.
Both the substrate film and the metal coating deposited thereon are transparent in the sense that visible light is transmitted therethrough without appreciable scatter-ing such that objects beyond are clearly visible. Preferably, the metallized film exhibits luminous light transmission greater than about 20%, and most preferably greater than about 70%.
As has been noted hereinabove, detected wavelengths within the range from about l.S to 3.0 microns have been dis-covered to provide a high level of correlation with resistivity of vacuum-deposited gold, silver, and copper. At wavelengths les~ than about 1.5 micron the requisite slope and relative linearity of the percent transmission-resistivity curve is seldom obtained. Detector response falls off rapidly between 3 and ~ microns, and the metal films at greater wavelengths appear to exhibit uniform reflection regardless of resistivity.
~est results have been obtained when operating at wavelengths between about 1.5 and 2.0 microns, most preferably 1.8 microns.
Figure 3 depicts the relationship of percent transmission of various detected band widths to resistivity of gold vacuum-deposited on a fluorinated ethylene-propylene film. Curve 36 represents percent transmission of white light as detected by a cadmium sulfide detector as a function of resistivity. Curves 37, 38, and 39, respectively, illustrate transmission as a .
~ID57045 ' function of resistivity for detected band widths centered about l.0, 1.5, and 2.0 microns. The latter three curves were drawn from data taken by spectrophotometer readings. Curves 36, 37, 38, and 39, were constructed by (l) measuring the infra red transmission through substrate films bearing metal coatings of various densities and (2) cutting square portions of the coated substrate which include the infra red measured region, attaching busbars thereto, and measuring resistance directly with a DC ohm-meter. The correlative advantage to be gained by practice of the invention in terms of linearity and slope of the transmission-resistivity curve will be apparent from Figure 3. The criticality of the wave-length interval employed in this invention will become apparent when it is considered that curve 37 throughout much of its length exhibits slope no . 15 greater than that for white light, nothwithstanding that the wavelength detected for curve 37 is but 0.5 micron less than j that for curve 38. With gold deposited on a cellulose triacetate substrate, transmission versus resistivity curves have been obtained which are linear between 8 and 20 ohms per square with a slope, in this range, of 0.83 percentage point of transmission per ohm per square, i.e., 12% to 20%
transmission corresponding to from 8 to 20 ohms per square.
With polyethyleneterephthalate polyester film transmission versus resistivity slope of 1.72 percentage point per ohm per square over a range of 9 to 20 ohms per square corresponding to 23 to 42 percent transmission has been obtained by detection of a band width of transmitted radiation at a wave-length interval centered at 1.8 microns. In that wavelength interval, transmission of the bare substrate i~ extremely high, i.e., 92% transmission in vacuum.
l~D57045 In the preferred embodiment, the radiation detected is radiation transmitted through ~he metallized substrate. Of course, the art-skilled will recognize that the invention can also be practiced by detecting reflected radiation, in which instance the included angle of reflection should be as narrow as possible in view of the demonstrated tendency of all wave-lengths of radiation to be reflected at low grazing angles.
Indeed, resort can be had to conventional optical arrangements to provide that the included angle of reflection be zero degree$.
While the invention can be employed to detect reflected radia-tion, preferably the detected radiation is transmitted radia-tion. Slight torsional movement of the film during transport, with resultant deviation of reflected radiation, can displace the signal beam from the view of the detector, falsely simulat-ing variations in the intrinsic reflectivity of the coated film.For this reason, systems operating in the reflective mode require more elaborate detector optics, such as field lens systems, to assure uniform irradiation of the detector during ~ -torsional substrate film movement and attendant signal beam deviation.
The invention has been described hereinabove with particular re~erence to vacuum evaporation techniques of metal deposition. Of course, the art-skilled will recognize that other means of deposition can be employed. As an example of other suitable methods can be mentioned sputtering, wherein residual gases contained in a vacuum chamber are ionized by application of high voltage. The ions are accelerated toward an electrode comprised of the metal to be deposited. When the accelerated ions strike the electrode, their accumulated energy dislodges metal particles from the electrode which are ~L057045 subsequently deposited on the substrate film. In the light of this specification, of course, other means of metal deposition will occur to the art skilled.
Similarly, the art skilled will recognize that DC detection systems can be employed in lieu of the AC system exemplified above. With DC detector systems, expensive signal generators and amplifiers are supplanted by inexpensive batteries and DC
; voltmeters. ~owever, the DC detector system is subject to a temperature drift effect, so that cooling or other suitable means of alleviating this effect should be provided.
From the foregoing, it will be clear to the art skilled that the method of this invention is suitable for diverse employments. For example, the invention can be employed as a quality control or inspection process with discrete coated parts. Alternatively, the method of the invention can be employed to monitor batch coating of individual parts so that deposition is permitted to proceed until a predetermined value of resistivity has been achieved, at which time the deposition apparatus can be switched off automatically and prepared for removal of the coated part and installation of the next part to be coated. Similarly, the invention is applicable to continuous or semi-continuous vacuum metallizing processes wherein the metallic deposit is applied to a moving substrate, such as a film web, which moves continuously or semi-continuously past the point of deposition. In this configura-tion, radiation transmitted through or reflected from the metallized film is monitored at a point immediately following that of deposition and the value of the detected radiation, or monitor signal, can be compred with a predetermined set point or standard value to generate an error signal. The error : ~0~7045 signal c~n be employed to control rate of film transport, power to the electron gun, rate of feed to the electron gun crucible, or otherwise control evaporation or deposition rate in order ~:
to achieve an extended deposit having local resistivity values within specified limits.
Having fully described the invention, it is intended that it be limited only to the legal scope of the cl~ims appended hereto.
OF METALLIZED FILM
Field of the Invention . .
This invention relates to a process of monitoring surface resistivity distribution of vacuum deposited metals.
Background of the Invention Vacuum deposited metal thin film coatings have found widespread application as transparent resistance heaters for deicing and demisting transparent enclosures such as windshields.
Typically, such enclosures comprise a thin transparent plastic carrier film or substrate upon which has been deposited a thin conductive metallic film which can be powered by busbar~
normally attached at the edge portions thereof. Ultimately, the metallized substrate is laminated between rigid, transparent plies as of glass in order to form a safety glass-type construction, In order that upon energizing power be dissipated in an optimal manner for the particular deicing function of the ultimate laminated transparency, and to preserve the optical properties required in windshield and like employments, resistivity distribution of the deposited metallic film must be closely controlled. In the past, local resistivity has been determined by measuring the overall ~bus to bus) resistance of the final part and then normalizing the value determined to a ~5 square area configuration. This requires physical contact to a finished part already equipped with busbars. However, it is frequently desirable to determine resistivity of a metallized substrate film prior to the application thereto of busbars or other means of electrical attachment. In United States Patent - 1- ~$ ' ~057C45 3,086,889 to Strong, it is proposed that electrical resistance of a continuously deposited metallic coating be monitored by balancing a bridge circuit against resistance measured between electrical contacts which engage the metallic coated side of a S dielectric sheet material. Unfortunately, where the metallic film whose resistance is to be measured is so thin as is the case where transparency is required, then the fragility of the metallic coating is highly susceptible to disruption by such contact methods of measurement. When the metalli~ed film is subsequently energized, disruptions in the fragile coating give rise to localized regions of high current density which can lead to failure. Accordingly, a need has existed for a means of non-destructively describing the local resistivity of vacuum-deposited thin metal films.
In United States Patent 3,397,672 to Dykeman, et al, it is proposed at column 3, lines 2-5, to measure the thickness of vapor-deposited aluminum by detection of radiation emanant from the coating upon application of x-rays. The equipment required for x-ray generation is generally highly expensive and to the economic disadvantages of that proposal must be added the danger to operators and maintenance personnel inevitably inhering in x-ray operation.
In determining what form of radiation will be employed and detected in monitoring resistivity of vacuum-deposited metals, however, more is involved than straight-forward considerations of economy and safety. There is required a wavelength interval which when detected provides a relatively steep and linear curve of transmission or reflectance against resistivity. Moreover, where transmission is to be measured, 3~ a spectral region must be chosen wherein transmission of the bare substrate is high, i.e., a window.
Brief Summary of the Invention In accordance with the present invention there is provided a process for preparation of a transparent metalized substrate having luminous light transmission greater than 20~, by vacuum deposition of a metal selected from the group consisting of silver, gold and copper on a transparent substrate and determining the surface resistivity of the deposit formed on the substrate, the improvement comprising applying electromagnetic radiation within the wave length range of from l.5 to 3.0 microns to the substrate and deposit, detecting a signal comprising electromagnetic radiation within the ~ave length range of from l.5 to 3.0 microns transmitted through the substrate and deposit, and correlating the value of the signal to the surface resistivity of the deposit on the substrate.
Embodiments of the invention will now be described in the description which follows and with reference to the accompanying drawings in which:
Figure 1 schematically represents a vacuum deposition apparatus environment in which the process of the invention can be practiced;
Figure 2 schematically depicts one detection system with which the invention can be practiced; and Figure 3 graphically correlates percent transmission of various band widths of radiation with resistivity of vacuum deposited metal on a particular substrate.
Detailed Descri tson of the Invention P
Turning now to the drawings, with particular reference to Figure 1, there is shown an electron beam gun ~1~)57045 10 positioned below a moving substate 11. The electron beam of the gun is focused onto an evaporant metal 12 located in a crucible 13 recessed into electron gun 10. Evaporant metal 12 is stored in the form of wire on a spool 15. The wire is fed to crucible 13 by feed mechanism 16.
The film substrate 11 is transported from a supply reel 17 over the electron gun 10 to a take-up reel 18 by a friction roller 19 acting on driving roller 20. The friction roller 19 is connected by chains and a gear set to a reversible universal motor (not shown).
Resistivity of the metal deposit applied to sub~
strate 11 is monitored by measuring electromagnetic radiation within the range from about 1.5 to 3.0 microns trànsmitted through the metallized film 21. For purpose of illustration an AC energized radiation source 22 and radiation detector 23 are shown placed on either side of the metallized film 21 at a point downstream from the deposition area for measuring transmission of selected band widths of radiation. The radiation source and detector may be provided with masks to obviate the effect of stray radiation.
The vacuum deposition apparatus is contained in a vacuum chamber 24 and a wall 25 having opening 26 therein for equalization of pressure may be provided to delineate an evaporation chamber from the remainder of the vacuum chamber.
Wall 25 is provided with slit 26a which can be designed to allow insertion of masks that control the size of the slit opening as to both length and width ~not shown). Suitable size of the slit opening is determined by the distance between the substrate and evaporant metal 12. Slit opening length (in the direction of film travel) can be determined by the angle swept out by considering the evaporant beam to originate from a point source in the center of the crucible 13 and defin-ing the limits as the lines tangent to driving roller 20. The width of the slit can be determined in a similar manner using as the limit the edge or width of the plastic film. Glow discharge electrodes 27 and 27' are desirably provided for surface treatment of the substrate 11 in conventional manner.
Preferably, all of the substrate 11 is glow discharged prior to commencement of metal evaporation.
As will be recognized by the art skilled, deposition rate is influenced by the rate of metal evaporation, speed of film travel, nature of glow discharge treatment, source to substrate distance, and system pressure at evaporation. ~n the embodiment shown, glow discharge treatment occurred at 50 microns pressure of argon with power input of 1.4 KV AC and film travel speed of ~ inches per minute. For deposition, film speed was set at approximately 2 feet per minute with evaporator power setting of 0.2 kw. Source to substrate distance was fixed at 8 inches, and evaporations run at a pressure of 2 to 5 times 10 5 torr.
The techniques and apparatus for implementation of the measurement contemplated by this invention are known to those familiar with the art, but in the preferred embodiment employ an AC operated source of radiation such as an incan-descent bulb having a brightness temperature greater than about 800 degrees centigrade with a modulated driver or an optical chopper, optics directing the alternati~ng or chopped radiation through the part to be measured, and a suitable photo detector, rectifier, amplifier, and read-out device. Figure 2 schematically illustrates one suitable system, wherein signal 105~7045 generator 28 supplies a signal amplified by element 29 to radiation source 30. The radiation is directed through the metallized substrate (not shown) and the radiation transmitted by the substrate is received by a sui~ably biased photo detector 31. Preferably a lead sulfide detector is employed for the band widths used in this invention, and radiation transmitted through the metallized film is passed through an optical interference, band-pass filter prior to impingement upon the lead sulfide. The signal generated by detector 31 is applied through element 35 containing a filter and a 2-pole, narrow-pass pre-amplifier to a full wave rectifying power amplifier 32. At 32, the received signal is compared with a reference signal supplied by line 34 and the resulting information displayed by recorder 33.
Substrates employed in this invention are preferably transparent plastic carrier films which most preferably range in thickness from about 0.00025 to about 0.015 inch. Preferred films are cellulose triacetate, cellulose acetate, fluorinated ethylene-propylene copolymers, and polyethylene terephthalate polyester films. Among the wide variety of other suitable candidates for substrate film employment may be mentioned:
cellulose acetate butyrate, cellulose propionate, ethyl cellulose, polymethylmethacrylate, polytrifluorochlorethylene copolymer, polyvinylfluoride, polycarbonate, vinylidene chloride-vinyl chloride copolymer, polyvinylchloride, vinyl chloride-acetate copolymer, and regenerated cellulose films.
Of course, substates other than transparent plastic carrier -films can be employed, e.g., rigid, transparent, substate plies as of glass, stretched polymethylmethacrylate, polycarbon-ate, etc. Preferably such rigid plies,range in thickness from about 0.02 to 0.25 inches. The metals deposited on the substrate films are selected from the group consisting of silver, gold, and copper and are generally deposited in thicknesses within the range from about 100 to 500 angstroms.
The resulting resistivity of the deposited metal generally is within the range from about 10 to about 25 ohms per square.
Both the substrate film and the metal coating deposited thereon are transparent in the sense that visible light is transmitted therethrough without appreciable scatter-ing such that objects beyond are clearly visible. Preferably, the metallized film exhibits luminous light transmission greater than about 20%, and most preferably greater than about 70%.
As has been noted hereinabove, detected wavelengths within the range from about l.S to 3.0 microns have been dis-covered to provide a high level of correlation with resistivity of vacuum-deposited gold, silver, and copper. At wavelengths les~ than about 1.5 micron the requisite slope and relative linearity of the percent transmission-resistivity curve is seldom obtained. Detector response falls off rapidly between 3 and ~ microns, and the metal films at greater wavelengths appear to exhibit uniform reflection regardless of resistivity.
~est results have been obtained when operating at wavelengths between about 1.5 and 2.0 microns, most preferably 1.8 microns.
Figure 3 depicts the relationship of percent transmission of various detected band widths to resistivity of gold vacuum-deposited on a fluorinated ethylene-propylene film. Curve 36 represents percent transmission of white light as detected by a cadmium sulfide detector as a function of resistivity. Curves 37, 38, and 39, respectively, illustrate transmission as a .
~ID57045 ' function of resistivity for detected band widths centered about l.0, 1.5, and 2.0 microns. The latter three curves were drawn from data taken by spectrophotometer readings. Curves 36, 37, 38, and 39, were constructed by (l) measuring the infra red transmission through substrate films bearing metal coatings of various densities and (2) cutting square portions of the coated substrate which include the infra red measured region, attaching busbars thereto, and measuring resistance directly with a DC ohm-meter. The correlative advantage to be gained by practice of the invention in terms of linearity and slope of the transmission-resistivity curve will be apparent from Figure 3. The criticality of the wave-length interval employed in this invention will become apparent when it is considered that curve 37 throughout much of its length exhibits slope no . 15 greater than that for white light, nothwithstanding that the wavelength detected for curve 37 is but 0.5 micron less than j that for curve 38. With gold deposited on a cellulose triacetate substrate, transmission versus resistivity curves have been obtained which are linear between 8 and 20 ohms per square with a slope, in this range, of 0.83 percentage point of transmission per ohm per square, i.e., 12% to 20%
transmission corresponding to from 8 to 20 ohms per square.
With polyethyleneterephthalate polyester film transmission versus resistivity slope of 1.72 percentage point per ohm per square over a range of 9 to 20 ohms per square corresponding to 23 to 42 percent transmission has been obtained by detection of a band width of transmitted radiation at a wave-length interval centered at 1.8 microns. In that wavelength interval, transmission of the bare substrate i~ extremely high, i.e., 92% transmission in vacuum.
l~D57045 In the preferred embodiment, the radiation detected is radiation transmitted through ~he metallized substrate. Of course, the art-skilled will recognize that the invention can also be practiced by detecting reflected radiation, in which instance the included angle of reflection should be as narrow as possible in view of the demonstrated tendency of all wave-lengths of radiation to be reflected at low grazing angles.
Indeed, resort can be had to conventional optical arrangements to provide that the included angle of reflection be zero degree$.
While the invention can be employed to detect reflected radia-tion, preferably the detected radiation is transmitted radia-tion. Slight torsional movement of the film during transport, with resultant deviation of reflected radiation, can displace the signal beam from the view of the detector, falsely simulat-ing variations in the intrinsic reflectivity of the coated film.For this reason, systems operating in the reflective mode require more elaborate detector optics, such as field lens systems, to assure uniform irradiation of the detector during ~ -torsional substrate film movement and attendant signal beam deviation.
The invention has been described hereinabove with particular re~erence to vacuum evaporation techniques of metal deposition. Of course, the art-skilled will recognize that other means of deposition can be employed. As an example of other suitable methods can be mentioned sputtering, wherein residual gases contained in a vacuum chamber are ionized by application of high voltage. The ions are accelerated toward an electrode comprised of the metal to be deposited. When the accelerated ions strike the electrode, their accumulated energy dislodges metal particles from the electrode which are ~L057045 subsequently deposited on the substrate film. In the light of this specification, of course, other means of metal deposition will occur to the art skilled.
Similarly, the art skilled will recognize that DC detection systems can be employed in lieu of the AC system exemplified above. With DC detector systems, expensive signal generators and amplifiers are supplanted by inexpensive batteries and DC
; voltmeters. ~owever, the DC detector system is subject to a temperature drift effect, so that cooling or other suitable means of alleviating this effect should be provided.
From the foregoing, it will be clear to the art skilled that the method of this invention is suitable for diverse employments. For example, the invention can be employed as a quality control or inspection process with discrete coated parts. Alternatively, the method of the invention can be employed to monitor batch coating of individual parts so that deposition is permitted to proceed until a predetermined value of resistivity has been achieved, at which time the deposition apparatus can be switched off automatically and prepared for removal of the coated part and installation of the next part to be coated. Similarly, the invention is applicable to continuous or semi-continuous vacuum metallizing processes wherein the metallic deposit is applied to a moving substrate, such as a film web, which moves continuously or semi-continuously past the point of deposition. In this configura-tion, radiation transmitted through or reflected from the metallized film is monitored at a point immediately following that of deposition and the value of the detected radiation, or monitor signal, can be compred with a predetermined set point or standard value to generate an error signal. The error : ~0~7045 signal c~n be employed to control rate of film transport, power to the electron gun, rate of feed to the electron gun crucible, or otherwise control evaporation or deposition rate in order ~:
to achieve an extended deposit having local resistivity values within specified limits.
Having fully described the invention, it is intended that it be limited only to the legal scope of the cl~ims appended hereto.
Claims (17)
1. In a process for preparation of a transparent metalized substrate having luminous light transmission greater than 20%, by vacuum deposition of a metal selected from the group consisting of silver, gold, and copper on a transparent substate and determining the surface resistivity of the deposit formed on the substrate, the improvement comprising applying electromagnetic radiation within the wave-length range of from 1.5 to 3.0 microns to the substrate and deposit, detecting a signal comprising electromagnetic radiation within the wavelength range of from 1.5 to 3.0 microns transmitted through the substrate and deposit, and correlating the value of the signal to the surface resistivity of the deposit on the substrate .
2. A process according to claim 1 wherein the deposition of the metal on the substrate proceeds until a predetermined value of resistivity has been achieved.
3. The process according to claim 1 wherein the metal is deposited on a moving transparent film and the electro-magnetic radiation is applied at a point immediately following that of deposition of the metal.
4. The process according to any one of claims 1 to 3 wherein the value of the detected signal is compared with a predetermined value to generate an error signal.
5. The process according to any one of claims 1 to 3 wherein the value of the detected signal is compared with a predetermined value to generate an error signal and wherein the error signal is employed to control the amount of metal deposited on the film so as to achieve resistivity value from about 10 to 25 ohms per square.
6. The process according to any one of claims 1 to 3 wherein the value of the detected signal is compared with a predetermined value to generate an error signal and wherein the error signal is employed to control the rate of deposition of metal on the film in order to achieve an extended deposit having local resistivity values within specified limits.
7. The process according to any one of claims 1 to 3 wherein the value of the detected signal is compared with a predetermined value to generate an error signal and wherein the detected signal is compared with a reference signal and the resulting information displayed on a recorder.
8. The process of any one of claims 1 to 3 wherein the carrier film has a thickness within the range of about 0.00025 to 0.015 inch and wherein the said deposit exhibits resistivity in the range from about 5 to 50 ohms per square.
9. The process of any one of claims 1 to 3 wherein the carrier film has a thickness within the range of about 0.00025 to 0.015 inch and wherein the said deposit exhibits resistivity in the range from about 10 to 25 ohms per square.
10. The process of any one of claims 1 to 3 wherein the carrier film is selected from the group consisting of cellulose acetate, cellulose triacetate, fluorinated ethylene-propylene copolymer, and polyethylene terephthalate-polyester films.
11. The process of any one of claims 1 to 3 wherein the carrier film is selected from the group consisting of cellulose acetate, cellulose triacetate, fluorinated ethylene-propylene copolymer, and polyethylene terephthalate-polyester films and wherein the vacuum deposited metal is gold.
12. The process of any one of claims 1 to 3 wherein the carrier film is a polyethylene terephthalate polyester film.
13. The process of any one of claims 1 to 3 wherein the metalized film has integrated visible light transmission greater than about 70%.
14. The process of any one of claims 1 to 3 wherein the source of applied radiation is an incandescent source having a brightness temperature greater than about 800°C.
15. The process of any one of claims 1 to 3 wherein the detected radiation is radiation having a wavelength of about 1.8 microns.
16. A process according to any one of claims 1 to 3 wherein the percent transmission of the applied radiation through the substrate and deposit is determined from the value of the detected signal and the percent transmission correlated to the surface resistivity of the deposit.
17. The process of any one of claims 1 to 3 wherein the said deposit exhibits resistivity in the range from about 10 to 25 ohms per square.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA240,980A CA1057045A (en) | 1975-12-03 | 1975-12-03 | Method for monitoring the surface resistivity of metallized film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA240,980A CA1057045A (en) | 1975-12-03 | 1975-12-03 | Method for monitoring the surface resistivity of metallized film |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057045A true CA1057045A (en) | 1979-06-26 |
Family
ID=4104652
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA240,980A Expired CA1057045A (en) | 1975-12-03 | 1975-12-03 | Method for monitoring the surface resistivity of metallized film |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1057045A (en) |
-
1975
- 1975-12-03 CA CA240,980A patent/CA1057045A/en not_active Expired
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