CA1194595A - Method for forming video discs - Google Patents
Method for forming video discsInfo
- Publication number
- CA1194595A CA1194595A CA000434535A CA434535A CA1194595A CA 1194595 A CA1194595 A CA 1194595A CA 000434535 A CA000434535 A CA 000434535A CA 434535 A CA434535 A CA 434535A CA 1194595 A CA1194595 A CA 1194595A
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- recording
- intensity
- tracks
- photoresist layer
- light
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Abstract
METHOD FOR FORMING VIDEO DISCS
ABSTRACT OF THE DISCLOSURE
Methods for use in producing a disc-shaped recording master having a thin photoresist recording layer for storing an f.m. information signal with high density. During record-ing, an intensity-modulated writing beam is focused onto the photoresist layer, to form a succession of spaced exposed regions arranged in a plurality of substantially circular and concentric recording tracks. The master further includes a glass substrate having a specially prepared surface r and the photoresist layer is deposited on the surface using a technique that ensures a uniform thickness and a uniform sensitivity to the writing beam. The peak intensity of the writing beam is selectively adjusted such that the succession of spaced exposed regions is formed with an optimum 50/50 duty cycle. After development to remove the spaced exposed regions, the recording master is used to produce a metallic stamper that, in turn, is used to produce disc replicas. Determina-tion of the optimum peak intensity of the recording beam is determined by adjusting the peak intensity of the beam for each of a plurality of adjacent tracks, developing the layer and examining the successive sets of tracks to determine that having the optimum value of duty cycle.
ABSTRACT OF THE DISCLOSURE
Methods for use in producing a disc-shaped recording master having a thin photoresist recording layer for storing an f.m. information signal with high density. During record-ing, an intensity-modulated writing beam is focused onto the photoresist layer, to form a succession of spaced exposed regions arranged in a plurality of substantially circular and concentric recording tracks. The master further includes a glass substrate having a specially prepared surface r and the photoresist layer is deposited on the surface using a technique that ensures a uniform thickness and a uniform sensitivity to the writing beam. The peak intensity of the writing beam is selectively adjusted such that the succession of spaced exposed regions is formed with an optimum 50/50 duty cycle. After development to remove the spaced exposed regions, the recording master is used to produce a metallic stamper that, in turn, is used to produce disc replicas. Determina-tion of the optimum peak intensity of the recording beam is determined by adjusting the peak intensity of the beam for each of a plurality of adjacent tracks, developing the layer and examining the successive sets of tracks to determine that having the optimum value of duty cycle.
Description
METHOD FOR FORMING VIDEO DISCS
This invention xelates generally to methods for forming video discs, and, more particularly, to methods for producing optically-readable video disc masters and stampers for use in forming video disc replicas.
Optically-readable video disc replicas are useful in storing vast quantities of information, usually in the form of a frequency-modulated (f.m.) carrier signal, with a high recording density. The f.m. signal is typically recorded as a sequence of spaced pits or bumps arranged in a succession of substantially circular and concentric recording tracks. Each pit and adjacent space between pits represents one cycle of the f.m.
signal.
Disc replicas are typically formed in injection-molding apparatus using disc-shaped stampers derived from recording masters. A recording master typically includes a glass substrate having a disc shaped, planar surface, with a thin recording layer such as a metal film overlaying it. Information is normally '~,,.
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recorded in the recording layer by focusing an intensiky-modulated writing beam of light onto the layer using a radially-mo~able objective lens, as the master is rotated at a prescribed rate. The intensity of the beam is modulated in accordance with the f.m.
-signal to be alternately greater ~han and less than a predetermined threshold at which the metal film is melted, whereby the succession of spaced pits is formed in the film. The succession of pits and spaces preferably has a nominal duty cycle of 50/50, whereby the signal is recorded with minimum second harmonic distortion.
The present invention resides in methods employed in the manufacture of video disc mastexs of a type having a photoresist recording layer, and in methods for producing stampers from such masters. The master includes a glass substrate with a smooth, planar surface on wh~ch a thin, uniform recording layex of photoresist is deposited. An f.mn information signal is recorded in the photoresist recording layer using an intensity-modulated writing beam of light, producing a succession A of spaced exposed regions arranged in a succession of substantially circular and concentric recording tracks.
In one aspect of the invention, the glass substrate is initially prepared by dispensing an adhesion promoter such as stannous chloride onto the surface of the substrate while the substrate is rotated at a relatively low velocity, e.g., about 75 ~o 100 r~p.m. The surface is then rinsed with water while still being rotated at the relatively slow velocity, thereby removing residual adhesion promoter, after which the rinsed surface is dried by being rotated at a relatively high velocity, e.g., about 750 to 1000 r.p.m.
The method for preparing the substrate can further include preliminary s+eps of polishing the surface -using a polishing compound having a submicron particle size, and then cleaning the polished surface. The cleaning step can include stleps of flushing the surface ~first with a detergent solution and then with water, drying the surface by rotating the substrate at the relatively high velocity, and wiping the surface with acetone to remove traces of dust and oil.
In another aspect of the invention, the photo-resist recording layer is applied to the prepared surface of the glass s~strate by dispensing a photo-resist solution onto the surface as the substrate is being rotated at the relatively low velocity, by then rotating the substrate at the relatively high velocity to partially dry the photoresist solution and form a l;~yer having a substantially uniform thickness, and by finally baking the photoresist-coated substrate in a prescribed fashion to completely dry the photoresist layer. The photoresist solution is preferably Shipley AZ 1350 photoresist having a viscosity of about 1.3 centipoi~e, and in the step of baking, the master is preferably baked at about 80 degrees centigrade, for about 20 minutes.
In another aspect of the invention, a thin metal layer is formed on the glass substrate prior to the application of the photosensitive recording layer.
Still another aspect of the invention resides in a method for selecting an optimum peak intensity for the intensity-modulated writing beam of light used in recording the f.m. signal on thP photoresist recording layer. In this aspect of the invention, a prc~cribed test signal is initally recorded on ~hc disc in ~
succession of narrow sets of reo~rding tracks, each set bei~g recorded using a wrlting beam havin~ a diferent 9~
peak intensity. Since the photoresist layer i5 exposed whenPver ~he intensity of the beam exceeds a prede-termined threshold, a higher peak intensity results in exposed regions of greater length. Each separate set of recording tracks thus has a different duty cycle.
In o n e method, three vr four sets of tracks are recorded, having peak intensities that vary in steps of about five percent. After deveLopment, in which the exposed regions forming each track are trans-formed into a succession of spaced pits, the developeddisc is examined to determine the particular set of tracks having spaced pits with a duty cycle closest to an optimum value. The peak intensity of the beam is then adjusted in accordance with this determination, whereby the f.m. information signal can thereafter be recorded with the optimum duty cycle on the remaining, unexposed portions of the photoresist layer.
The test signal preferably has a prescribed, constant frequency, and the sets of recording tracks are preferably located near the periphery of the photo-resist layer. Also, each set preferably includes several hundred tracks, and is separated from an adjacent set by a narrow unexposed band of the photo-resist layer. The developed photoresist layer is prefexably examined by scanning each set of tracks with a reading beam of light, to produce a reflected beam that i5 modulated in intensity in accordance with the recorded pattern of spaced pits, and by then detecting the modulated intensity and monitoring it using a spectrum analyzer.
In yet another aspect of the invention, the exposed photoresist layer is developed by dispensing onto the layer, whi:Le it is rotating at the relatively low velocity (e.g., 75 to 100 r~p.m.), first water, to pre-wet the layer, then both water and a developer solution of a prescribed normality, to partially develop the layer, and finally developer solution, alone, to fully develop the layer. The developed photoresist layex is then rinsed with water, to eliminate residual developer solution, and finally rotated at the rela-tively high velocity of preferably 750 to lO00 r.p.m., to dry the developed layer. The photoresist layer is preferably derived from Shipley AZ 1350 photoresist, and the developer solution is preferably either potassium hydroxide or sodium hydroxide, with a normality of about .230 to .240. In another more detailed aspect of the invention, the step of dispensing both water and developer solution has a time duration of about 5 to lO seconds, the step of dispensing developer solution, alone, has a time duration of about 20 seconds, and the step of rinsing has a time duration of about 30 to 60 seconds.
Still another aspect of the invention resides in a technique for producing a stamper from the developed recording master, for use in molding video disc replicas.
In this aspect of the invention, a first thin~ uniform metallic film is vapor deposited onto the developed recording layer, after which a second thin, uniform, metallic film is electroplated onto the first film, the two films together forming an integral metallic layer.
The integral metallic layer is then separated from the underlying master recording, and residual photoresist material is removed from the undersurface of the sepa-rated metallic layer using a suitable solvent, therebyforming the stamper. The first metallic film preferably has a thickness of about 500 to 600 A, and the second metallic film preferably has a thickness of about 15 mils. Both films are preferably formed of nickel.
6~ ¢~
Many other aspects and advantages of the invention will become apparent from ~he following detailed description, taken in conjunction with the accompanying drawings, which disclose, by way of example, the principles of the invention. The accompanying - drawlngs illustrate the invention. In such drawings:
FIG~ 1 is a simplified schematic diagrc~m of apparatus for recording an f.m. information signal on a recording master produced in accordance with the methods of the present invention;
FIG. 2 is an enlarged plan view of a segment of the recording master of FIG. 1, showing a succession of spaced exposed regions arranged in a plurality of substantially circular and concentric recording tracks;
FIG~ 3 is a graph showing the modulated intensity of the writing bec~m in the recording apparatus of FIG. l;
FIG. 4 is a sectional, elevational view of a portion of the recoxding master, taken along a recording track, and showing the photoresist recording layer to be exposed whenever the intensity of the writing beam of FIG~ 3 exceeds a predetermined threshold;
FIG. 5 is a sectional, elevational view of the recording master of E'IG. 4, after development to remove the spaced, exposed regions; and FIGo 6 is a perspective view of a turntc~ble apparatus used in forming the pho-toresist recording layer on the recording master of FIG. 1.
$
Referring now to the drawings, and particularly to FIG. 1, there is shown apparatus for recording a - frequency-modulated (f.m.) information signal on a recording master 11. The master includes a glass substrate 13, with a smooth, planar upper surface on which is deposited a phot3resist layer 15 having a prescrihed, uniform thickness. The photoresist layer is exposed whene~er impinged by a beam of light having an intensity that exceeds a predetermined recording threshold.
The recordlng apparatus includes a writing laser 17 such as an argon ion laser for producing a writing beam of light 19 haviny a prescribed intensity, and an intensity modulator 21 for modulating the intensity of the writing beam in accordance with an f.m. information signal received on line 23. The recording apparatus further includes a spindle motor 25 for rotating the recording master 11 at a prescribed angular velocity, and an objective lens 27 for focusing the intensity-modulated beam onto the photoresist layer 15 of therotating master. The objective lens in mounted on a carriage (not shown) that is radially movable with respect to the master, so that the focused beam traces a spiral pattern on the photoresist layer.
As shown in FIGS. 2, 3 and 4, the intensity of the intensity-modulated beam 19 is alternately greater than and less than the predetermined recording threshold of the photoresist layer 15, whereby a succession of spaced exposed regions 29, arranged in a plurality of substantially circular and concentric recording tracks 31, is formed in the layer. Each exposed region and adjacent space correspond to one cycle of the f.mO
8 ;~
signal. FIG. S depicts the recording master 11 after de~elopment to remo~e the exposed regions, the master then being in suitable condition for use in producing a stamper.
The recording master 11 is initially prepared for use with the recording apparatus of FIG. 1 using a special process in which the upper surface of the glass substrate 13 is first ground and polished, and then cleaned. The photore.sist layer 15 is then formed by dispensing a photoresist solution onto the surface, after which it is dried and baked in a prescribed fashion. After baking, the recording master i5 in suitable condition for recording. In another aspect of the invention, a thin metal layer is formed on the substrate prior to forming the photosensitive layer.
More particularly, the planar surface of the glass substrate 13 is initially prepared by first grinding it in a conventional manner, using an aluminum oxide compound having about a nine-micron grit. The surface is then polished using a zirconium oxide or cerium oxi~e polishing compound of sub-micron particle size.
Cerium oxide has been found to polish the surface more quickly, but is generally more difficult to clean.
The polished surface of the glass substrate 13 is cleaned in a special three-step process. First, the surface is flushed with high-purity, de~ionized water and brushed with a fine brush to remove most of the polishing compound. The de-ionized water preferably has a resistivity of 18 mega-ohms centimeter. The cleaned surface of the glass substrate 13 is thereafter inspected ~y examining it with the naked eye under a high-intensity light. Under this light, defects such as scratches and microscopic pits appear as point 9 ~ ~4~9~:1 sources of scattered light. When a defect is detected, a microscope is used to measure its size. If any defects larger ~han 25 microns are detected, or if the numher of defects under 10 microns exceed one per square millimeter, the substrate is rejected and the polishing and cleaning sequences are repeated. The surface is then wiped with acetone to remove any traces of dust and oil introduced cluring handling.
Second, the surface is flushed with a detergent 501ution, and third, the surface is again flushed with de-ionized water for a period of about ten to twenty minutes.
After cleaning/ the substrate 13 is placed on a turntable, as shown in FIG. 5, and rotated at an angular velocity of about 750-1000 r.p.m., to dry the surface.
~IG. 6 depicts apparatus for use in forming the photo-resist layer 15 on the cleaned substrate 13. The apparatus includes a variable speed motor 33 for rotating the substrate in a prescribed fashion, and a pivot arm 35 on which are mounted three dispensing tubes 37, 39, and 41 for dispensing de-ionized water, a stannous chloride solution, and a photoresist solution, respectively, in a prescribed sequence.
The substrate 13 is first rotated at an angular velocity of about 75 to 100 r.p.m., while stannous chloride is dispensed onto the cleaned upper surface through the dispensing tube 39. The pivot arm 35 is pivoted manually so that stannous chloride is applied to the entire surface. It is believed that the stannous chloride molecules adhere to the cleaned surface of the substrate, and thereby promote a subsequent adhesion of the photoresist solution.
10 ~ 3~;
Water is then dispensed onto the surface through the dispensing tube 37, to rinse off residual stannous chloride solution, and the angular velocity of the motor 33 i9 then increased to about 750-1000 r.p.m., to dry the rinsed surface. The surface is nGw in propex condition for dispensing of the photoresist solution.
The photoresist solution is prepared by diluting Shipley AZ 1350 photoresist with Shipley AZ thinner, which is believed to include cellosolve acetate, in a ratio of about 3 to 1. This provides a solution having a viscosity of about 1.3 centipoise, which is then filtered to remove particle~ larger than about one half micron. visc09ity can be measured by standard techniques, such as, for example, using a Canon-Finske viscometer.
The diluted photor~sist solution is then dispensed through the tube 41 onto the prepared surface of the substrate 13, as the substrate is being rotated by the variable ~peed motor 33 at an angular velocity of about 75-100 r.p.m. Again, the pivot arm 35 is pivoted manually so that the solution is dispensed across the entire radius of the substrate. At the speeds below about 75 r.p.m., a film of substantially uniform thickness can be achieved only if a relatively lengthy spread time is allowed but this increases the likelihood of contamination of the layer. At speeds above about 100 r.p.m., on the other hand, radial streaks and flow marks can result, affecting the quality of the subsequent recording of information. About 35 ml of photoresist solution are required to fully coat a substrate having a diameter of about 35.56 cmn After the photoresist solution has been coated onto the surface of the substrate 13, the angular velocity of the motor 33 is increased to about 750-lO00 r.p.m., until dry. This provides a prescribed, uniform thickness for the photoresist layer 15.
-Recognizing the fact that the ~hickness of thephotoresist layer 15 is inversely proportional to both rOp.m. and temperature, the specific angular velocity at which the substrate is rotated to partially dry the photoresist solution can be conveniently adjusted to provide the prescribed thickness. The appropriate angular velocity can be determlned in a conventional manner using, for example, a Tolansky interferometer.
This technique provides an indication of the relative thickness of the layer and, using an iterative process, in which the angular velocity is successively adjusted, the optimum velocity can be determined. If the viscosity and temperature of the photoresist solution can be maintained substantially uniform, this angular velocity calibration need be perfoxmed only infre quently. It is presently preferred that the layer have a thickness of about I150 A to 1350 A, and replica discs subsequently produced will have information-bearing bumps or pits of corxesponding heightO
If it i5 determined that the dried photoresist layer 15 is defective in any way (e.g., containing radial streaks or foreign particles), the layer can be removed using a suitable solvent such as Shipley AZ
thinnerO A new layer can then be applied in the manner described above.
12 ~ $
After removal from the turntable apparatus of FIG. 6, the recording master ll is baked, to fully dry the photoresist layer 15 and thereby maximize its exposure tolerance. The master is preferably baked at about 80 centigrade for about 20 minutes~ These -parameters must be maintained to a ~ight tolerance, to minimize variations in exposure tolerances when succes-sively recording information on a number of recording masters.
Since the exposure sensitivities of each of a number of recording masters is likely to be slightly different from the others, it is desirable to optimize the peak intensity for the intensity modulated beam of light l9 (FIG. l) for each master, so that the f.m.
information signal can be recorded with an optimum 50/50 duty cycle. In accordance with another aspect of the invention, a prescribed test signal is recorded on each master 11 in a plurality of sets of adjacent recording tracks, each set recorded with a different peak intensity. Ater the test signal tracks have been developed, using a developing technique described in detail below, the recording master is examined to determine the particular set of tracks having a duty cycle closest to the desired 50/50 value. The optimum peak intensity thereby can be determined and the f.m.
information signal thereafter can be recorded with the optimum duty cycle on the remaining, unexposed portions of the recording master.
The test signal preferably has a constant fre~uency of about 7 to 8 MHæ, and the signal is preferably recorded on three or four sets of tracks each set recorded with a peak beam in-tensity that varies by about five percent. Each set is recorded for about lO
seconds, correspondiny to several hundred recording tracks. Also the sets are pre:Eerably separated from each other by narrow bands of unexposed portions of the photoresist layer 15, and are located in a narrow region-adjacent the inner periphery of the layer.
The successive sets of developed recording tracks can be conveniently examined using a reading beam of light (not shown) for scanning each set to produce a reflected bQam having an intensity that is modulated in accordance with the recorded test signal. The reflected beam is modula-ted in intensity because the reflectance of unaltered portions of photoresist layer 15 is about 4 percent, whereas the reflectance of altered portions of the layer is essentially zero. The modulated beam is suitably detected and monitored in a conventional spectrum analyzer, to determine the presence of second harmonic distortion. This distortion is a minimum when the test signal is recorded with the optimum 50/50 duty cycle It is not necessary that the reading beam follow any individual recording track in each set of tracks, since the same test signal i5 recorded on adjacent tracks. Care must be taken, however, to ensure that eccentricities in the recordiny master 11 do not cause the reading beam to scan more than a single set of tracks at a time. The reading beam is preferably produced by a helium-neon laser so that its wavelength will not expose the photoresist layer 15.
Using the recording apparatus of FIG. 1, with the - peak intensity of the writing beam 19 adjusted to the prescribed, optimum value, the f.m. information signal is then recorded on the remaining, unexposed portion of the photoresist recording layer 15. The recorded master 11 ls then developed to convert each recording track into a succession of spaced pits of uniform depth and width and of continuously-variable length.
In yet another novel aspect of the invention, the exposed recording master 11 is developed in a special process in which a succession of fluids are ~ispensed onto the master as it is being rotated by a turntable of the type depicted in FIG. 6, at a velocity of about 75 to 100 r.p.m. In the process, water is first dispensed to pre-wet the layer, then both water and a developer solution of prescribed normality are dispensed, to partially develop the layer, and finally developer solution, alone is dispensed, to fully develop the layer. The developed photoresist layer is then rinsed with water, to remove residual developer solution, after which the angular velocity of the rotating master is increased to about 750-1000 r.p.m., to dry the developed layer.
The preferred developer solution is selected from a group including potassium hydroxide and sodium hydroxide, and has a normality of about 0.230 to 0.240.
Preferably t the step of dispensing both water and developer solution has a duration of about 5 to 10 seconds, the step of dispensing developer solution, alone, about 20 seconds, and the step of rinsing about 30 to 60 seconds.
A stamper, suitable for use in molding video disc replicas, is produced from the developed recording master 11. In another aspect of the invention, the stamper is produced by first vapor depositing a uniform metallic film of about 500-600 A thickness onto the photoresist recording layer 15, and then electroplating a second uniform metallic film of about 15 mils thick-ness onto the first film. The undersurface of the first film conforms exactly to the pattern of spaced ~ 5 pits formed in the photoresist layer, and the two films together form an integral metallic layer. This integral metallic layer can be separated from the underlying recording master and residual photoreslst material removed using a suitable photoresist thinner, thereby forming the stamper. In one embodiment, both metallic films are formed of nickel.
It will thus be appreciated from the foregoing description that the present invention provides a number of novel techniques for use in efficiently producing recording masters. The masters include photoresist recording layers in which fOm. information signals can be recorded with high signal~to-noise ratios and high density. In other aspects of the invention, metallic stampers are produced rom these recording masters, for use in molding replicas of the master .
Although the invention has been described in detail, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and scope of the invention.
Accordingly, it is not intended that the invention be limited, except as by the appended claims.
This invention xelates generally to methods for forming video discs, and, more particularly, to methods for producing optically-readable video disc masters and stampers for use in forming video disc replicas.
Optically-readable video disc replicas are useful in storing vast quantities of information, usually in the form of a frequency-modulated (f.m.) carrier signal, with a high recording density. The f.m. signal is typically recorded as a sequence of spaced pits or bumps arranged in a succession of substantially circular and concentric recording tracks. Each pit and adjacent space between pits represents one cycle of the f.m.
signal.
Disc replicas are typically formed in injection-molding apparatus using disc-shaped stampers derived from recording masters. A recording master typically includes a glass substrate having a disc shaped, planar surface, with a thin recording layer such as a metal film overlaying it. Information is normally '~,,.
¢~
recorded in the recording layer by focusing an intensiky-modulated writing beam of light onto the layer using a radially-mo~able objective lens, as the master is rotated at a prescribed rate. The intensity of the beam is modulated in accordance with the f.m.
-signal to be alternately greater ~han and less than a predetermined threshold at which the metal film is melted, whereby the succession of spaced pits is formed in the film. The succession of pits and spaces preferably has a nominal duty cycle of 50/50, whereby the signal is recorded with minimum second harmonic distortion.
The present invention resides in methods employed in the manufacture of video disc mastexs of a type having a photoresist recording layer, and in methods for producing stampers from such masters. The master includes a glass substrate with a smooth, planar surface on wh~ch a thin, uniform recording layex of photoresist is deposited. An f.mn information signal is recorded in the photoresist recording layer using an intensity-modulated writing beam of light, producing a succession A of spaced exposed regions arranged in a succession of substantially circular and concentric recording tracks.
In one aspect of the invention, the glass substrate is initially prepared by dispensing an adhesion promoter such as stannous chloride onto the surface of the substrate while the substrate is rotated at a relatively low velocity, e.g., about 75 ~o 100 r~p.m. The surface is then rinsed with water while still being rotated at the relatively slow velocity, thereby removing residual adhesion promoter, after which the rinsed surface is dried by being rotated at a relatively high velocity, e.g., about 750 to 1000 r.p.m.
The method for preparing the substrate can further include preliminary s+eps of polishing the surface -using a polishing compound having a submicron particle size, and then cleaning the polished surface. The cleaning step can include stleps of flushing the surface ~first with a detergent solution and then with water, drying the surface by rotating the substrate at the relatively high velocity, and wiping the surface with acetone to remove traces of dust and oil.
In another aspect of the invention, the photo-resist recording layer is applied to the prepared surface of the glass s~strate by dispensing a photo-resist solution onto the surface as the substrate is being rotated at the relatively low velocity, by then rotating the substrate at the relatively high velocity to partially dry the photoresist solution and form a l;~yer having a substantially uniform thickness, and by finally baking the photoresist-coated substrate in a prescribed fashion to completely dry the photoresist layer. The photoresist solution is preferably Shipley AZ 1350 photoresist having a viscosity of about 1.3 centipoi~e, and in the step of baking, the master is preferably baked at about 80 degrees centigrade, for about 20 minutes.
In another aspect of the invention, a thin metal layer is formed on the glass substrate prior to the application of the photosensitive recording layer.
Still another aspect of the invention resides in a method for selecting an optimum peak intensity for the intensity-modulated writing beam of light used in recording the f.m. signal on thP photoresist recording layer. In this aspect of the invention, a prc~cribed test signal is initally recorded on ~hc disc in ~
succession of narrow sets of reo~rding tracks, each set bei~g recorded using a wrlting beam havin~ a diferent 9~
peak intensity. Since the photoresist layer i5 exposed whenPver ~he intensity of the beam exceeds a prede-termined threshold, a higher peak intensity results in exposed regions of greater length. Each separate set of recording tracks thus has a different duty cycle.
In o n e method, three vr four sets of tracks are recorded, having peak intensities that vary in steps of about five percent. After deveLopment, in which the exposed regions forming each track are trans-formed into a succession of spaced pits, the developeddisc is examined to determine the particular set of tracks having spaced pits with a duty cycle closest to an optimum value. The peak intensity of the beam is then adjusted in accordance with this determination, whereby the f.m. information signal can thereafter be recorded with the optimum duty cycle on the remaining, unexposed portions of the photoresist layer.
The test signal preferably has a prescribed, constant frequency, and the sets of recording tracks are preferably located near the periphery of the photo-resist layer. Also, each set preferably includes several hundred tracks, and is separated from an adjacent set by a narrow unexposed band of the photo-resist layer. The developed photoresist layer is prefexably examined by scanning each set of tracks with a reading beam of light, to produce a reflected beam that i5 modulated in intensity in accordance with the recorded pattern of spaced pits, and by then detecting the modulated intensity and monitoring it using a spectrum analyzer.
In yet another aspect of the invention, the exposed photoresist layer is developed by dispensing onto the layer, whi:Le it is rotating at the relatively low velocity (e.g., 75 to 100 r~p.m.), first water, to pre-wet the layer, then both water and a developer solution of a prescribed normality, to partially develop the layer, and finally developer solution, alone, to fully develop the layer. The developed photoresist layex is then rinsed with water, to eliminate residual developer solution, and finally rotated at the rela-tively high velocity of preferably 750 to lO00 r.p.m., to dry the developed layer. The photoresist layer is preferably derived from Shipley AZ 1350 photoresist, and the developer solution is preferably either potassium hydroxide or sodium hydroxide, with a normality of about .230 to .240. In another more detailed aspect of the invention, the step of dispensing both water and developer solution has a time duration of about 5 to lO seconds, the step of dispensing developer solution, alone, has a time duration of about 20 seconds, and the step of rinsing has a time duration of about 30 to 60 seconds.
Still another aspect of the invention resides in a technique for producing a stamper from the developed recording master, for use in molding video disc replicas.
In this aspect of the invention, a first thin~ uniform metallic film is vapor deposited onto the developed recording layer, after which a second thin, uniform, metallic film is electroplated onto the first film, the two films together forming an integral metallic layer.
The integral metallic layer is then separated from the underlying master recording, and residual photoresist material is removed from the undersurface of the sepa-rated metallic layer using a suitable solvent, therebyforming the stamper. The first metallic film preferably has a thickness of about 500 to 600 A, and the second metallic film preferably has a thickness of about 15 mils. Both films are preferably formed of nickel.
6~ ¢~
Many other aspects and advantages of the invention will become apparent from ~he following detailed description, taken in conjunction with the accompanying drawings, which disclose, by way of example, the principles of the invention. The accompanying - drawlngs illustrate the invention. In such drawings:
FIG~ 1 is a simplified schematic diagrc~m of apparatus for recording an f.m. information signal on a recording master produced in accordance with the methods of the present invention;
FIG. 2 is an enlarged plan view of a segment of the recording master of FIG. 1, showing a succession of spaced exposed regions arranged in a plurality of substantially circular and concentric recording tracks;
FIG~ 3 is a graph showing the modulated intensity of the writing bec~m in the recording apparatus of FIG. l;
FIG. 4 is a sectional, elevational view of a portion of the recoxding master, taken along a recording track, and showing the photoresist recording layer to be exposed whenever the intensity of the writing beam of FIG~ 3 exceeds a predetermined threshold;
FIG. 5 is a sectional, elevational view of the recording master of E'IG. 4, after development to remove the spaced, exposed regions; and FIGo 6 is a perspective view of a turntc~ble apparatus used in forming the pho-toresist recording layer on the recording master of FIG. 1.
$
Referring now to the drawings, and particularly to FIG. 1, there is shown apparatus for recording a - frequency-modulated (f.m.) information signal on a recording master 11. The master includes a glass substrate 13, with a smooth, planar upper surface on which is deposited a phot3resist layer 15 having a prescrihed, uniform thickness. The photoresist layer is exposed whene~er impinged by a beam of light having an intensity that exceeds a predetermined recording threshold.
The recordlng apparatus includes a writing laser 17 such as an argon ion laser for producing a writing beam of light 19 haviny a prescribed intensity, and an intensity modulator 21 for modulating the intensity of the writing beam in accordance with an f.m. information signal received on line 23. The recording apparatus further includes a spindle motor 25 for rotating the recording master 11 at a prescribed angular velocity, and an objective lens 27 for focusing the intensity-modulated beam onto the photoresist layer 15 of therotating master. The objective lens in mounted on a carriage (not shown) that is radially movable with respect to the master, so that the focused beam traces a spiral pattern on the photoresist layer.
As shown in FIGS. 2, 3 and 4, the intensity of the intensity-modulated beam 19 is alternately greater than and less than the predetermined recording threshold of the photoresist layer 15, whereby a succession of spaced exposed regions 29, arranged in a plurality of substantially circular and concentric recording tracks 31, is formed in the layer. Each exposed region and adjacent space correspond to one cycle of the f.mO
8 ;~
signal. FIG. S depicts the recording master 11 after de~elopment to remo~e the exposed regions, the master then being in suitable condition for use in producing a stamper.
The recording master 11 is initially prepared for use with the recording apparatus of FIG. 1 using a special process in which the upper surface of the glass substrate 13 is first ground and polished, and then cleaned. The photore.sist layer 15 is then formed by dispensing a photoresist solution onto the surface, after which it is dried and baked in a prescribed fashion. After baking, the recording master i5 in suitable condition for recording. In another aspect of the invention, a thin metal layer is formed on the substrate prior to forming the photosensitive layer.
More particularly, the planar surface of the glass substrate 13 is initially prepared by first grinding it in a conventional manner, using an aluminum oxide compound having about a nine-micron grit. The surface is then polished using a zirconium oxide or cerium oxi~e polishing compound of sub-micron particle size.
Cerium oxide has been found to polish the surface more quickly, but is generally more difficult to clean.
The polished surface of the glass substrate 13 is cleaned in a special three-step process. First, the surface is flushed with high-purity, de~ionized water and brushed with a fine brush to remove most of the polishing compound. The de-ionized water preferably has a resistivity of 18 mega-ohms centimeter. The cleaned surface of the glass substrate 13 is thereafter inspected ~y examining it with the naked eye under a high-intensity light. Under this light, defects such as scratches and microscopic pits appear as point 9 ~ ~4~9~:1 sources of scattered light. When a defect is detected, a microscope is used to measure its size. If any defects larger ~han 25 microns are detected, or if the numher of defects under 10 microns exceed one per square millimeter, the substrate is rejected and the polishing and cleaning sequences are repeated. The surface is then wiped with acetone to remove any traces of dust and oil introduced cluring handling.
Second, the surface is flushed with a detergent 501ution, and third, the surface is again flushed with de-ionized water for a period of about ten to twenty minutes.
After cleaning/ the substrate 13 is placed on a turntable, as shown in FIG. 5, and rotated at an angular velocity of about 750-1000 r.p.m., to dry the surface.
~IG. 6 depicts apparatus for use in forming the photo-resist layer 15 on the cleaned substrate 13. The apparatus includes a variable speed motor 33 for rotating the substrate in a prescribed fashion, and a pivot arm 35 on which are mounted three dispensing tubes 37, 39, and 41 for dispensing de-ionized water, a stannous chloride solution, and a photoresist solution, respectively, in a prescribed sequence.
The substrate 13 is first rotated at an angular velocity of about 75 to 100 r.p.m., while stannous chloride is dispensed onto the cleaned upper surface through the dispensing tube 39. The pivot arm 35 is pivoted manually so that stannous chloride is applied to the entire surface. It is believed that the stannous chloride molecules adhere to the cleaned surface of the substrate, and thereby promote a subsequent adhesion of the photoresist solution.
10 ~ 3~;
Water is then dispensed onto the surface through the dispensing tube 37, to rinse off residual stannous chloride solution, and the angular velocity of the motor 33 i9 then increased to about 750-1000 r.p.m., to dry the rinsed surface. The surface is nGw in propex condition for dispensing of the photoresist solution.
The photoresist solution is prepared by diluting Shipley AZ 1350 photoresist with Shipley AZ thinner, which is believed to include cellosolve acetate, in a ratio of about 3 to 1. This provides a solution having a viscosity of about 1.3 centipoise, which is then filtered to remove particle~ larger than about one half micron. visc09ity can be measured by standard techniques, such as, for example, using a Canon-Finske viscometer.
The diluted photor~sist solution is then dispensed through the tube 41 onto the prepared surface of the substrate 13, as the substrate is being rotated by the variable ~peed motor 33 at an angular velocity of about 75-100 r.p.m. Again, the pivot arm 35 is pivoted manually so that the solution is dispensed across the entire radius of the substrate. At the speeds below about 75 r.p.m., a film of substantially uniform thickness can be achieved only if a relatively lengthy spread time is allowed but this increases the likelihood of contamination of the layer. At speeds above about 100 r.p.m., on the other hand, radial streaks and flow marks can result, affecting the quality of the subsequent recording of information. About 35 ml of photoresist solution are required to fully coat a substrate having a diameter of about 35.56 cmn After the photoresist solution has been coated onto the surface of the substrate 13, the angular velocity of the motor 33 is increased to about 750-lO00 r.p.m., until dry. This provides a prescribed, uniform thickness for the photoresist layer 15.
-Recognizing the fact that the ~hickness of thephotoresist layer 15 is inversely proportional to both rOp.m. and temperature, the specific angular velocity at which the substrate is rotated to partially dry the photoresist solution can be conveniently adjusted to provide the prescribed thickness. The appropriate angular velocity can be determlned in a conventional manner using, for example, a Tolansky interferometer.
This technique provides an indication of the relative thickness of the layer and, using an iterative process, in which the angular velocity is successively adjusted, the optimum velocity can be determined. If the viscosity and temperature of the photoresist solution can be maintained substantially uniform, this angular velocity calibration need be perfoxmed only infre quently. It is presently preferred that the layer have a thickness of about I150 A to 1350 A, and replica discs subsequently produced will have information-bearing bumps or pits of corxesponding heightO
If it i5 determined that the dried photoresist layer 15 is defective in any way (e.g., containing radial streaks or foreign particles), the layer can be removed using a suitable solvent such as Shipley AZ
thinnerO A new layer can then be applied in the manner described above.
12 ~ $
After removal from the turntable apparatus of FIG. 6, the recording master ll is baked, to fully dry the photoresist layer 15 and thereby maximize its exposure tolerance. The master is preferably baked at about 80 centigrade for about 20 minutes~ These -parameters must be maintained to a ~ight tolerance, to minimize variations in exposure tolerances when succes-sively recording information on a number of recording masters.
Since the exposure sensitivities of each of a number of recording masters is likely to be slightly different from the others, it is desirable to optimize the peak intensity for the intensity modulated beam of light l9 (FIG. l) for each master, so that the f.m.
information signal can be recorded with an optimum 50/50 duty cycle. In accordance with another aspect of the invention, a prescribed test signal is recorded on each master 11 in a plurality of sets of adjacent recording tracks, each set recorded with a different peak intensity. Ater the test signal tracks have been developed, using a developing technique described in detail below, the recording master is examined to determine the particular set of tracks having a duty cycle closest to the desired 50/50 value. The optimum peak intensity thereby can be determined and the f.m.
information signal thereafter can be recorded with the optimum duty cycle on the remaining, unexposed portions of the recording master.
The test signal preferably has a constant fre~uency of about 7 to 8 MHæ, and the signal is preferably recorded on three or four sets of tracks each set recorded with a peak beam in-tensity that varies by about five percent. Each set is recorded for about lO
seconds, correspondiny to several hundred recording tracks. Also the sets are pre:Eerably separated from each other by narrow bands of unexposed portions of the photoresist layer 15, and are located in a narrow region-adjacent the inner periphery of the layer.
The successive sets of developed recording tracks can be conveniently examined using a reading beam of light (not shown) for scanning each set to produce a reflected bQam having an intensity that is modulated in accordance with the recorded test signal. The reflected beam is modula-ted in intensity because the reflectance of unaltered portions of photoresist layer 15 is about 4 percent, whereas the reflectance of altered portions of the layer is essentially zero. The modulated beam is suitably detected and monitored in a conventional spectrum analyzer, to determine the presence of second harmonic distortion. This distortion is a minimum when the test signal is recorded with the optimum 50/50 duty cycle It is not necessary that the reading beam follow any individual recording track in each set of tracks, since the same test signal i5 recorded on adjacent tracks. Care must be taken, however, to ensure that eccentricities in the recordiny master 11 do not cause the reading beam to scan more than a single set of tracks at a time. The reading beam is preferably produced by a helium-neon laser so that its wavelength will not expose the photoresist layer 15.
Using the recording apparatus of FIG. 1, with the - peak intensity of the writing beam 19 adjusted to the prescribed, optimum value, the f.m. information signal is then recorded on the remaining, unexposed portion of the photoresist recording layer 15. The recorded master 11 ls then developed to convert each recording track into a succession of spaced pits of uniform depth and width and of continuously-variable length.
In yet another novel aspect of the invention, the exposed recording master 11 is developed in a special process in which a succession of fluids are ~ispensed onto the master as it is being rotated by a turntable of the type depicted in FIG. 6, at a velocity of about 75 to 100 r.p.m. In the process, water is first dispensed to pre-wet the layer, then both water and a developer solution of prescribed normality are dispensed, to partially develop the layer, and finally developer solution, alone is dispensed, to fully develop the layer. The developed photoresist layer is then rinsed with water, to remove residual developer solution, after which the angular velocity of the rotating master is increased to about 750-1000 r.p.m., to dry the developed layer.
The preferred developer solution is selected from a group including potassium hydroxide and sodium hydroxide, and has a normality of about 0.230 to 0.240.
Preferably t the step of dispensing both water and developer solution has a duration of about 5 to 10 seconds, the step of dispensing developer solution, alone, about 20 seconds, and the step of rinsing about 30 to 60 seconds.
A stamper, suitable for use in molding video disc replicas, is produced from the developed recording master 11. In another aspect of the invention, the stamper is produced by first vapor depositing a uniform metallic film of about 500-600 A thickness onto the photoresist recording layer 15, and then electroplating a second uniform metallic film of about 15 mils thick-ness onto the first film. The undersurface of the first film conforms exactly to the pattern of spaced ~ 5 pits formed in the photoresist layer, and the two films together form an integral metallic layer. This integral metallic layer can be separated from the underlying recording master and residual photoreslst material removed using a suitable photoresist thinner, thereby forming the stamper. In one embodiment, both metallic films are formed of nickel.
It will thus be appreciated from the foregoing description that the present invention provides a number of novel techniques for use in efficiently producing recording masters. The masters include photoresist recording layers in which fOm. information signals can be recorded with high signal~to-noise ratios and high density. In other aspects of the invention, metallic stampers are produced rom these recording masters, for use in molding replicas of the master .
Although the invention has been described in detail, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and scope of the invention.
Accordingly, it is not intended that the invention be limited, except as by the appended claims.
Claims (6)
1. A method for selecting an optimum peak intensity for a beam of light used in recording on a disc-shaped recording medium a cyclically modulated information signal extending between upper and lower limits, wherein the recording medium includes a photoresist layer that is exposed whenever impinged by a beam of light having an intensity greater than a predetermined threshold, the method including steps of:
modulating the intensity of the beam of light in accordance with a prescribed test signal, the intensity being alter-nately greater than and less than the predetermined recording threshold of the photoresist layer; directing the intensity-modulated beam of light onto the photoresist layer as the medium is rotated in a prescribed fashion, to form a sequence of spaced, exposed regions arranged in a succession of substantially circular and concentric recording tracks;
adjusting the peak intensity of the intensity-modulated beam of light for each of a plurality of adjacent tracks, whereby each set is recorded using a different peak intensity and the spaced, exposed regions in each set have a different duty cycle; developing the exposed photoresist layer, to remove the exposed regions and thereby change each recording track into a succession of spaced pits; examining the successive sets of recording tracks to determine the partic-ular set having spaced pits with a duty cycle closest to an optimum value; and adjusting the peak intensity of the beam of light in accordance with the determination made in the step of examining, whereby a cyclically modulated information signal extending between upper and lower limits can there-after he recorded with the optimum duty cycle on unexposed portions of the photoresist layer.
modulating the intensity of the beam of light in accordance with a prescribed test signal, the intensity being alter-nately greater than and less than the predetermined recording threshold of the photoresist layer; directing the intensity-modulated beam of light onto the photoresist layer as the medium is rotated in a prescribed fashion, to form a sequence of spaced, exposed regions arranged in a succession of substantially circular and concentric recording tracks;
adjusting the peak intensity of the intensity-modulated beam of light for each of a plurality of adjacent tracks, whereby each set is recorded using a different peak intensity and the spaced, exposed regions in each set have a different duty cycle; developing the exposed photoresist layer, to remove the exposed regions and thereby change each recording track into a succession of spaced pits; examining the successive sets of recording tracks to determine the partic-ular set having spaced pits with a duty cycle closest to an optimum value; and adjusting the peak intensity of the beam of light in accordance with the determination made in the step of examining, whereby a cyclically modulated information signal extending between upper and lower limits can there-after he recorded with the optimum duty cycle on unexposed portions of the photoresist layer.
2. A method as defined in Claim 1, wherein the recording tracks formed in the step of directing form a narrow band located near the periphery of the photoresist layer.
3. A method as defined in Claim 1, wherein each set of recording tracks is separated from an adjacent set by a narrow, unexposed band of the photoresist layer.
4. A method as defined in Claim 1, wherein each set of recording tracks includes several hundred tracks.
5. A method as defined in Claim 1, wherein the test signal has a prescribed, constant frequency.
6. A method as defined in Claim 4, wherein the step of examining includes steps of: scanning each set of recording tracks with a reading beam of light, to produce a modulated reading beam of light having an intensity that varies in accordance with the recorded pattern of spaced pits; detecting the intensity of the modulated reading beam of light and producing a cor-responding electrical signal; and monitoring the electrical signal using a spectrum analyzer.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US17674380A | 1980-08-11 | 1980-08-11 | |
| US176,743 | 1980-08-11 | ||
| CA000377670A CA1186570A (en) | 1980-08-11 | 1981-05-15 | Method for forming video discs |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000377670A Division CA1186570A (en) | 1980-08-11 | 1981-05-15 | Method for forming video discs |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1194595A true CA1194595A (en) | 1985-10-01 |
Family
ID=25669325
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000434537A Expired CA1191597A (en) | 1980-08-11 | 1983-08-12 | Method for forming video discs |
| CA000434535A Expired CA1194595A (en) | 1980-08-11 | 1983-08-12 | Method for forming video discs |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000434537A Expired CA1191597A (en) | 1980-08-11 | 1983-08-12 | Method for forming video discs |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1191597A (en) |
-
1983
- 1983-08-12 CA CA000434537A patent/CA1191597A/en not_active Expired
- 1983-08-12 CA CA000434535A patent/CA1194595A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1191597A (en) | 1985-08-06 |
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