US20030012094A1 - Apparatus and method for focusing light beam and exposure apparatus - Google Patents

Apparatus and method for focusing light beam and exposure apparatus Download PDF

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Publication number
US20030012094A1
US20030012094A1 US10/024,725 US2472501A US2003012094A1 US 20030012094 A1 US20030012094 A1 US 20030012094A1 US 2472501 A US2472501 A US 2472501A US 2003012094 A1 US2003012094 A1 US 2003012094A1
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United States
Prior art keywords
light beam
objective lens
parallel light
detection signal
focusing
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.)
Abandoned
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US10/024,725
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English (en)
Inventor
Masashi Yanagi
Tetsuo Andou
Nobuo Kimura
Hidekazu Nakamoto
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Hitachi Ltd
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Hitachi Ltd
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Filing date
Publication date
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Assigned to HITACHI, LTD. reassignment HITACHI, LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ANDOU, TETSUO, KIMURA, NOBUO, NAKAMOTO, HIDEKAZU, YANAGI, MASASHI
Publication of US20030012094A1 publication Critical patent/US20030012094A1/en
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/26—Apparatus or processes specially adapted for the manufacture of record carriers
    • G11B7/261—Preparing a master, e.g. exposing photoresist, electroforming
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/094—Methods and circuits for servo offset compensation

Definitions

  • the present invention generally relates to a focus control method and an apparatus therefor. More particularly, the present invention is concerned with a focus control method and an apparatus therefor which can advantageously be employed in an optical recording system (which may also be referred to as the exposure system) for optically recording data on a medium such as an optical disk or the like. Further, the preset invention is concerned with the optical recording system itself as well.
  • an optical recording system which may also be referred to as the exposure system
  • the preset invention is concerned with the optical recording system itself as well.
  • a focus control apparatus is employed for maintaining constant the distance which intervenes between a disk (i.e., object, hereinafter also referred to as the raw disk) and an objective lens.
  • a focusing light beam having a wavelength differing from that of a recording or writing light beam is employed for protecting the raw disk against the influence exerted by the focusing light beam.
  • a so-called achromatic lens whose focal position or focal length remains the sane for different wavelengths has been used as the objective lens for the purpose of focusing the recording light beam.
  • both the focusing light beam and the recording light beam can impinge onto the objective lens in the form of parallel light beams without incurring any appreciable degradation in the focusing precision or accuracy even when the optical path length changes due to upward/downward movement or displacement of the objective lens following the change in the position of the raw disk.
  • the achromatic lens is not available as the objective lens yet.
  • it is required to cause the focusing light beam to be incident on the objective lens in a non-parallel state in consideration of refraction ascribable to the difference in the wavelength.
  • the raw disk 4 moves downwardly or descend by 1 ⁇ m, being accompanied with downward movement of the objective lens 3 by 1 ⁇ m in following the displacement of the raw disk, i.e., when the optical path length increases by 1 ⁇ m, the position of the focal point of the focusing light beam will deviate from that of the recording light beam by ca. 40 nm.
  • Another object of the present invention is to provide a focus control apparatus for carrying out the method mentioned above.
  • change in the optical path length of the focusing light beam is detected by detecting upward/downward movement(s) of the objective lens to thereby control the movement of the objective lens so that the change in the optical path length of the focusing light beam can correctively be compensated for.
  • a focus control method in which the change in the optical path length of the focusing light beam is detected by detecting upward/downward movement(s) of the objective lens for thereby driving the objective lens in such a manner that the focused state of the focusing light beam can be sustained or maintained.
  • a focus control apparatus in which a focusing light beam is used and which includes a unit for detecting change of the optical path length of the focusing light beam and a unit for correcting the position of an objective lens on the basis of the change as detected.
  • an optical recording system equipped with the focus control apparatus which includes a unit for detecting change of the optical path length precision of the focusing light beam and a unit for correcting the position of an objective lens on the basis of the change as detected.
  • FIG. 1 is a view showing generally and schematically a structure of a focus control apparatus according to an embodiment of the present invention
  • FIG. 2 is a block diagram showing, by way of example, circuit arrangements of a control arithmetic unit and an auto-focus correcting unit, respectively, in the focus control apparatus shown in FIG. 1;
  • FIG. 3 is a waveform diagram showing a difference signal processed by a control arithmetic unit shown in FIG. 1;
  • FIGS. 4A, 4B and 4 C are views for illustrating change behaviors of a focal length (imaging distance) for a non-parallel focusing light beam in dependence on distance between an objective lens and a convex lens used in the apparatus shown in FIG. 1;
  • FIG. 5 is a view showing a relation between focal length for a parallel light beam (recording light beam) and that for a non-parallel light beam (focusing light beam) as a function of the distance between the objective lens and the convex lens.
  • FIG. 1 is a view showing generally and schematically a structural configuration of the focus control apparatus according to an embodiment of the invention.
  • the focus control apparatus is generally comprised of two major portions, i.e., an optical system and a control system.
  • the optical system includes a light source 1 for generating a focusing light beam 2 , an objective lens 3 for focusing the light beam 2 onto the raw disk 4 , and a dual type light receiving element 6 for receiving and detecting a reflection light beam 5 resulting from reflection of the focusing light beam 2 at the raw disk 4 to thereby output a pair of output signals A and B designated by 6 a and 6 b , respectively.
  • the writing or recording light beam 16 is inputted from a system differing from the focusing system to be subsequently reflected at a half-mirror 17 disposed intermediate between the convex lens 12 and the objective lens 3 in the direction toward the raw disk or object 4 to thereby irradiate a resist layer of the raw disk 4 .
  • control system is composed of a control arithmetic unit 7 designed for arithmetically determining difference between the output signals A and B ( 6 a and 6 b ) of the dual type light receiving element 6 to thereby output an objective-lens control signal 8 and an objective-lens drive unit 9 for driving the objective lens 3 in response to the objective-lens control signal 8 .
  • the objective lens 3 is disposed above the raw disk 4 and so arranged as to be moved or driven in the vertical direction Z orthogonal to the raw disk 4 by means of the objective-lens drive unit 9 .
  • the focusing light beam 2 emitted from the light source 1 impinges onto the objective lens 3 to undergo refraction in the objective lens to be subsequently focused onto the raw disk 4 .
  • the focusing light beam reflected at the raw disk (object) 4 again undergoes refraction in the objective lens 3 to exit as the reflection light beam 5 which then impinges onto the dual type light receiving element 6 .
  • the paired outputs A and B ( 6 a ; 6 b ) of the dual type light receiving element 6 change in dependence on the distance intervening between the objective lens 3 and the raw disk 4 .
  • the output signals A and B of the dual type light receiving element 6 are inputted to the control arithmetic unit 7 for arithmetically determining displacement or movement of the objective lens 3 relative to the raw disk 4 .
  • the objective-lens control signal 8 outputted from the control arithmetic unit 7 is then fed to the objective-lens drive unit 9 to thereby maintain the focused state of the objective lens 3 relative to the raw disk 4 .
  • a skew type auto-focus scheme may be adopted in which a difference signal (A ⁇ B) outputted from the dual type light receiving element 6 is made use of.
  • the difference signal (A ⁇ B) outputted from the dual type light receiving element 6 exhibits a characteristic referred to as the S-curve characteristic, as is illustrated in FIG. 3. So long as the distance between the objective lens 3 and the raw disk 4 coincides with the focal length of the objective lens 3 , the difference signal (A ⁇ B) mentioned above assumes a value zero. On the other hand, when the distance between the objective lens and the raw disk is shorter than the focal length of the objective lens, the difference signal (A ⁇ B) assumes minus polarity (negative value) while the polarity of the difference signal becomes plus (positive) in case the distance is longer than the focal length of the objective lens 3 .
  • the objective lens 3 can be maintained in the state focused relative to the raw disk or object 4 .
  • control system performs a negative feedback control so that the difference between the paired outputs A and B of the dual type light receiving element 6 constantly assumes the value zero, whereby pull-in operation is effectuated in conformance with the S-curve characteristic illustrated in FIG. 3, as a result of which the operating point of the control system is pulled-in to the center point of the S-curve so long as no disturbance affects the control system, whereby the operation thereof is stabilized.
  • the focusing light beam 2 emitted from the light source 1 is regulated to a non-parallel beam state through cooperation of a concave lens 11 and a convex lens 12 before being incident onto the objective lens 3 in consideration of the precondition that the objective lens 3 is not an achromatic lens. More specifically, when the objective lens 3 is not achromatic, the objective lens exhibits noncoincident focal points, respectively, for a recording light beam of different waveform (described later on) and the focusing light beam 2 incident on the objective lens 3 as the parallel beams, respectively.
  • a recording light beam of 257 nm in wavelength is projected onto a commercially available objective lens rated for 257 nm in a parallel beam.
  • the focal point of the objective lens for the recording light beam of 257 nm be coincident with that for the focusing light beam of 650 nm, it is required to set an angle of incidence of 5.5 degrees for the focusing light beam on the assumption that the incident beam diameter of the focusing light beam is 3.3 mm.
  • the focusing light beam 2 is caused to be incident on the objective lens 3 in the non-parallel state.
  • the optical path length of the focusing light beam 2 and the reflection light beam 5 will change correspondingly, which in turn results in that the position of the reflection light beam 5 changes in dependence on the change of the optical path length, ultimately giving rise to change of the output of the dual type light receiving element 6 .
  • the objective-lens control signal 8 outputted from the control arithmetic unit 7 is affected correspondingly, incurring such unwanted situation that the objective lens 3 is driven in response to the change of the optical path length in addition to the driving quantity required for maintaining the focused state by the objective-lens drive unit 9 .
  • the achievable focusing accuracy suffers degradation.
  • the inter-lens distance between the convex lens 12 and the objective lens 3 will change when the objective lens 3 moves in following the upward/downward movement of the raw disk or object 4 , which naturally involves corresponding change in the position of the focal point of the focusing light beam.
  • FIGS. 4A, 4B and 4 C As can be seen in these figures, as the inter-lens distance between the convex lens 12 and the objective lens 3 changes, the incidence distance changes correspondingly, as indicated by a, a′ and a′′, whereby the imaging distance is caused to change, as indicated by b, b′ and b′′.
  • the imaging distance of the focusing light beam coincides with that of the recording light beam.
  • the imaging distance b′ of the focusing light beam is longer than the imaging distance b of the recording light beam.
  • the imaging distance b′ of the focusing light beam is shorter than the imaging distance b of the recording light beam.
  • the driving quantity for the objective lens is detected from the objective-lens control signal 8
  • the change in the optical path length of the focusing light beam 2 is detected by an auto-focus correcting unit 13 a quantity of influence which the objective-lens control signal 8 undergoes due to the change of the optical path length is arithmetically determined and that a correcting signal 14 is supplied to the control arithmetic unit 7 to thereby compensate for the objective-lens control signal 8 outputted from the control arithmetic unit 7 so that the focused state can be sustained, for thereby enhancing the focusing accuracy.
  • the objective-lens drive unit 9 is ordinarily implemented in the form of a voice coil. Accordingly, a current flowing through the voice coil may serve as the objective-lens control signal 8 .
  • the relation between the voice coil current and the quantity or magnitude of movement of the voice coil (and hence the objective lens) as driven by the voice coil current can be measured or established in advance. Accordingly, on the basis of the results of the measurement performed in advance, the concerned quantity or magnitude with which the voice coil is driven (i.e., the position of the objective lens) can be determined.
  • FIG. 2 is a block diagram showing generally and schematically circuit arrangements of the control arithmetic unit 7 and the auto-focus correcting unit 13 , respectively.
  • the control arithmetic unit 7 includes a subtracter 23 to which the outputs A and B ( 6 a and 6 b ) of the dual type light receiving element are inputted, whereby a difference signal (A ⁇ B) 24 is generated as the output signal of the subtracter 23 .
  • the difference signal 24 is inputted to an offset adder/subtracter unit 26 to undergo addition/subtraction processing with the output of an offset setting unit 21 and a correcting signal 14 outputted from the auto-focus correcting unit 13 .
  • the output signal of the offset adder/subtracter unit 26 is then amplified by an amplifier 27 whose amplification factor can be set by a gain setting unit 22 .
  • the output signal of the amplifier 27 serves as the objective-lens control signal 8 .
  • a feedback loop including the optical system shown in FIG. 1 is inserted between the output of the amplifier 27 (i.e., the objective-lens control signal 8 ) and the output A; B ( 6 a ; 6 b ) of the dual type light receiving element 6 , wherein the gain setting unit 22 serves to set the loop gain of the feedback loop.
  • the offset setting unit 21 serves to shift the operating point on the difference signal 24 to thereby shift the positions of the focal points of the recording light beam and the focusing light beam 2 relative to each other.
  • the output of the offset setting unit 21 is a direct current having a constant level.
  • the auto-focus correcting unit 13 includes a low-pass filter 31 for eliminating high-frequency components, from the objective-lens control signal, the output signal of which is inputted to a DC-component subtracter 32 for elimination of DC component, whereby low-frequency component (0 to 200 Hz) of the objective-lens control signal 8 is extracted.
  • a low-pass filter 31 for eliminating high-frequency components, from the objective-lens control signal, the output signal of which is inputted to a DC-component subtracter 32 for elimination of DC component, whereby low-frequency component (0 to 200 Hz) of the objective-lens control signal 8 is extracted.
  • the objective-lens control signal 8 bears a proportional relation to the upward/downward movement of the objective lens around the position of the focal point thereof.
  • the correcting signal 14 Since the displacement of the objective lens is equal to the change in the optical path length of the focusing light beam (i.e., distance between the convex lens 12 and the objective lens 3 ), it is possible to generate the correcting signal 14 by amplifying the low frequency component signal to an appropriate level by means of an amplifier 33 .
  • the correcting signal 14 is then inputted to the offset adder/subtracter unit 26 of the control arithmetic unit 7 , whereby the feedback loop mentioned previously is implemented.
  • the correcting quantity can be obtained by employing an amplifier having a proper gain as the amplifier 33 .
  • the low frequency component is added, so to say, as disturbance through the feedback loop, whereby the operating point can be sifted to a position deviated from the origin on the S-curve shown in FIG. 3, as a result of which the position of the objective lens 3 is offset such that in the case shown in FIG. 4A, the objective lens 3 is moved downwardly (descended), whereas in the case shown in FIG. 4C, the objective lens 3 is moved upwardly (ascended), whereby the distance between the raw disk or object 4 and the objective lens 3 is maintained at b.
  • the objective lens is driven by the objective-lens drive unit so as to maintain the focused state while taking into account the change in the optical path length for protecting the focusing accuracy from degradation.
  • changes in the optical path lengths of the focusing light beam 2 and the reflection light beam 5 are detected by the auto-focus correcting unit 13 , whereon the quantity with which the change of the optical path lengths effects the objective-lens control signal 8 is arithmetically determined to thereby generate the correcting signal 14 which is then inputted to the control arithmetic unit 7 .
  • the quantity mentioned above is subtracted from the objective-lens control signal 8 for thereby generating the proper signal required for maintaining the focused state by driving or displacing the objective lens correspondingly.
  • the focusing accuracy can be enhanced.
  • the present invention is not restricted to the skew-type auto-focus system.
  • the invention can equally find application to the auto-focus system of astigmatism and knife-edge type.
  • the focus control for the exposure system can be realized without need for using the achromatic lens as the objective lens.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Automatic Focus Adjustment (AREA)
  • Manufacturing Optical Record Carriers (AREA)
US10/024,725 2001-07-13 2001-12-21 Apparatus and method for focusing light beam and exposure apparatus Abandoned US20030012094A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2001-213006 2001-07-13
JP2001213006A JP2003030867A (ja) 2001-07-13 2001-07-13 フォーカス制御方法及び装置とそれを用いた原盤露光装置

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US10/024,725 Abandoned US20030012094A1 (en) 2001-07-13 2001-12-21 Apparatus and method for focusing light beam and exposure apparatus
US10/083,542 Expired - Fee Related US6728171B2 (en) 2001-07-13 2002-02-27 Arrangements for correction of focusing light beam, and system using the same

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US10/083,542 Expired - Fee Related US6728171B2 (en) 2001-07-13 2002-02-27 Arrangements for correction of focusing light beam, and system using the same

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US (2) US20030012094A1 (de)
EP (1) EP1276102A3 (de)
JP (1) JP2003030867A (de)
KR (1) KR20030006925A (de)
CN (1) CN1397939A (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100302920A1 (en) * 2009-05-29 2010-12-02 Hitachi-Lg Data Storage, Inc. Optical Disk Drive and Program Therefor

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JP2006184303A (ja) * 2004-12-24 2006-07-13 Olympus Corp 画像検査装置
JP5289768B2 (ja) * 2005-09-29 2013-09-11 オリンパス株式会社 焦点位置決定方法、焦点位置決定装置、微弱光検出装置及び微弱光検出方法
EP1804100B1 (de) * 2005-12-30 2018-02-21 Datalogic IP TECH S.r.l. Verfahren und Vorrichtung zur Fokussierung eines Laserstrahls
KR100984766B1 (ko) * 2009-09-02 2010-10-01 (주)엠디 도교의 결합장치

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US20030012091A1 (en) 2003-01-16
JP2003030867A (ja) 2003-01-31
CN1397939A (zh) 2003-02-19
US6728171B2 (en) 2004-04-27
EP1276102A3 (de) 2004-10-06
KR20030006925A (ko) 2003-01-23
EP1276102A2 (de) 2003-01-15

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