US20080047584A1 - Method for cleaning diffraction gratings - Google Patents
Method for cleaning diffraction gratings Download PDFInfo
- Publication number
- US20080047584A1 US20080047584A1 US11/895,392 US89539207A US2008047584A1 US 20080047584 A1 US20080047584 A1 US 20080047584A1 US 89539207 A US89539207 A US 89539207A US 2008047584 A1 US2008047584 A1 US 2008047584A1
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- United States
- Prior art keywords
- grating surface
- acid solution
- oxidizing
- grating
- exposing
- 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.)
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/0006—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 with means to keep optical surfaces clean, e.g. by preventing or removing dirt, stains, contamination, condensation
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
Definitions
- the present invention relates to methods of cleaning diffraction gratings, and more particularly to a method of cleaning diffraction gratings by exposure to a number of cleaning steps including exposure to aqueous base solutions, aqueous acid solutions, and an oxygen plasma, for the purpose of maximizing the laser damage resistance of the gratings.
- Diffraction gratings are an essential component of high-energy short-pulse laser systems. They act to expand the time-duration of seed pulses to enable propagation of these pulses through gain media for purposes of amplification, and then to re-compress the time duration of these pulses following amplification. As discussed in the article entitled, “Manufacture and Development of Multilayer Diffraction Gratings,” Proc. of SPIE Vol. 5991, September 2005, incorporated by reference herein, multilayer dielectric (MLD) diffraction gratings are often preferred for such applications due to the high intrinsic laser damage thresholds of the materials comprising the MLD grating.
- MLD multilayer dielectric
- the grating surface be completely clean and free from any contamination that can possibly absorb any small fraction of the incident light, as this absorption leads to multi-photon ionization, electronic avalanche breakdown and physical damage to the grating surface due to high laser intensities and the electric field enhancement effects of the grating surface inherent during the recompression process.
- the process of manufacturing gratings can introduce a wide variety of surface contaminants, including, for example, organic photoresist material from the mask generation process, metals and fluoro-hydrocarbon deposits from the ion-beam etching process, and airborne organic and particulate contamination from all types of sources. It is the deposits from the ion beam etching steps that are typically the most troublesome to remove.
- One known method for cleaning diffraction gratings involves exposing the grating to an oxygen plasma in a vacuum process. While this is effective in oxidizing and desorbing organic contamination, it does little to remove trace metallic contamination, for instance.
- Other cleaning methods are also known for cleaning mirrors, lenses, and other substantially planar optics subjected to high laser intensities, which employ mechanical means, such as ultrasonic, megasonic, or manual contact of the surface, even by polishing compounds, to mechanically remove contaminants.
- mechanical means such as ultrasonic, megasonic, or manual contact of the surface, even by polishing compounds
- One aspect of the present invention includes a method of cleaning a diffraction grating comprising: exposing the grating surface to an oxidizing acid solution to remove metallic contaminants and residue organic compounds; rinsing the grating surface with de-ionized water; exposing the grating surface to an oxygen plasma ashing process using reactive oxygen species to oxidize and remove fluorinated hydrocarbon residue; exposing the grating surface again to an oxidizing acid solution to remove metallic contaminants and residue organic compounds; and rinsing the grating surface with de-ionized water.
- MLD gratings consisting of alternating layers of, for example, HfO 2 /SiO 2 with a grating etched into the top SiO 2 layer:
- a grating surface Exposure of a grating surface to aqueous base (5% NaOH solution or commercial RS6 solution available from Cyantek Corporation of Fremont, Calif.), at room temperature in a gentle agitation, e.g. by flowing the aqueous base thereon. Preferably, this is performed for approximately 5 minutes. This removes the bulk of the organic photoresist mask. This step is immediately followed by extensive rinsing with de-ionized (DI) water, and preferably ultrapure DI water.
- DI de-ionized
- aqueous oxidizing acid solution preferably aqueous oxidizing sulfuric acid solution such as for example NanostripTM or NanostripTM 2X solution, commercially available from Cyantek Corporation, self-heated by periodic addition of water to 50-70 C., or at room temperature, in a gentle agitation (e.g. flow) process. This is preferably performed for approximately 60 minutes. This removes metallic contaminants and residue organic compounds.
- a point-of-use oxidizing acid solution such as for example ‘Piranha’ solution, can be used to similar effect, although not at room temperature. This step is immediately followed by extensive rinsing with ultrapure DI water.
- Piranha solution is a mixture of a strong acid (e.g. sulfuric acid, H 2 SO 4 ) and a strong oxidizing agent (e.g. hydrogen peroxide, H 2 O 2 ) which produces an extremely energetic solution.
- a strong acid e.g. sulfuric acid, H 2 SO 4
- a strong oxidizing agent e.g. hydrogen peroxide, H 2 O 2
- Piranha solution must be prepared immediately before use, has a very limited shelf life, and cannot be stored in normal closed containers due to an explosive pressure buildup caused by the gradual loss of hydrogen peroxide gas, ergo “point of use.”
- grating surface again to aqueous oxidizing acid solution, (preferably NanostripTM or NanostripTM 2X solution), self heated by periodic addition of water to 50-70 C., or at room temperature, in a gentle agitation (e.g. flow) process for approximately 60 minutes. This removes metallic contaminants possibly introduced by the ashing process. This step is immediately followed by extensive rinsing with ultrapure DI water.
- aqueous oxidizing acid solution preferably NanostripTM or NanostripTM 2X solution
- the above process can be modified as necessary due to the incompatibility of certain MLD coating materials to certain chemistries. For example, if an Al 2 O 3 etch-stop layer is incorporated into the MLD stack, treatment with aqueous base or hot acid is not possible due to dissolution of this layer.
- the cleaning process is modified by removing the first step (i.e. exposure to aqueous base) and changing steps (2) and (5) to room-temperature NanostripTM solution for a longer period of time greater than 60 minutes.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Cleaning Or Drying Semiconductors (AREA)
- Detergent Compositions (AREA)
- Cleaning By Liquid Or Steam (AREA)
Abstract
Description
- This application claims priority in provisional application filed on Aug. 23, 2006, entitled “Method for Cleaning Diffraction Gratings” Ser. No. 60/839,753, by Jerald A. Britten et al, and incorporated by reference herein.
- The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
- A. TECHNICAL FIELD
- The present invention relates to methods of cleaning diffraction gratings, and more particularly to a method of cleaning diffraction gratings by exposure to a number of cleaning steps including exposure to aqueous base solutions, aqueous acid solutions, and an oxygen plasma, for the purpose of maximizing the laser damage resistance of the gratings.
- B. DESCRIPTION OF THE RELATED ART
- Diffraction gratings are an essential component of high-energy short-pulse laser systems. They act to expand the time-duration of seed pulses to enable propagation of these pulses through gain media for purposes of amplification, and then to re-compress the time duration of these pulses following amplification. As discussed in the article entitled, “Manufacture and Development of Multilayer Diffraction Gratings,” Proc. of SPIE Vol. 5991, September 2005, incorporated by reference herein, multilayer dielectric (MLD) diffraction gratings are often preferred for such applications due to the high intrinsic laser damage thresholds of the materials comprising the MLD grating.
- In order for such gratings to operate properly and optimally, however, it is important that the grating surface be completely clean and free from any contamination that can possibly absorb any small fraction of the incident light, as this absorption leads to multi-photon ionization, electronic avalanche breakdown and physical damage to the grating surface due to high laser intensities and the electric field enhancement effects of the grating surface inherent during the recompression process. The process of manufacturing gratings, however, can introduce a wide variety of surface contaminants, including, for example, organic photoresist material from the mask generation process, metals and fluoro-hydrocarbon deposits from the ion-beam etching process, and airborne organic and particulate contamination from all types of sources. It is the deposits from the ion beam etching steps that are typically the most troublesome to remove.
- One known method for cleaning diffraction gratings involves exposing the grating to an oxygen plasma in a vacuum process. While this is effective in oxidizing and desorbing organic contamination, it does little to remove trace metallic contamination, for instance. Other cleaning methods are also known for cleaning mirrors, lenses, and other substantially planar optics subjected to high laser intensities, which employ mechanical means, such as ultrasonic, megasonic, or manual contact of the surface, even by polishing compounds, to mechanically remove contaminants. However, the submicron surface relief structures of diffraction gratings are extremely fragile and cannot survive such mechanical cleaning methods.
- Therefore, it would be advantageous to provide a method for cleaning diffraction gratings involving a number of cleaning operations to remove all contamination from the surface of an MLD diffraction grating that are not all removable by a single cleaning process or chemistry.
- One aspect of the present invention includes a method of cleaning a diffraction grating comprising: exposing the grating surface to an oxidizing acid solution to remove metallic contaminants and residue organic compounds; rinsing the grating surface with de-ionized water; exposing the grating surface to an oxygen plasma ashing process using reactive oxygen species to oxidize and remove fluorinated hydrocarbon residue; exposing the grating surface again to an oxidizing acid solution to remove metallic contaminants and residue organic compounds; and rinsing the grating surface with de-ionized water.
- Generally, single-step cleaning for MLD diffraction gratings for high laser damage resistance is not possible due to the several types of contamination present on the surface that are not removed by any one process. A number of cleaning operations are necessary to remove all contamination from the surface of an MLD diffraction grating. The exact details of the cleaning steps can be influenced by the materials comprising the diffraction grating, and also be influenced by the manner in which these materials have been deposited during the multilayer coating process.
- Applicants have demonstrated the following process to be effective for the cleaning of MLD gratings consisting of alternating layers of, for example, HfO2/SiO2 with a grating etched into the top SiO2 layer:
- (1) Exposure of a grating surface to aqueous base (5% NaOH solution or commercial RS6 solution available from Cyantek Corporation of Fremont, Calif.), at room temperature in a gentle agitation, e.g. by flowing the aqueous base thereon. Preferably, this is performed for approximately 5 minutes. This removes the bulk of the organic photoresist mask. This step is immediately followed by extensive rinsing with de-ionized (DI) water, and preferably ultrapure DI water.
- (2) Exposure of grating surface to aqueous oxidizing acid solution, preferably aqueous oxidizing sulfuric acid solution such as for example Nanostrip™ or Nanostrip™ 2X solution, commercially available from Cyantek Corporation, self-heated by periodic addition of water to 50-70 C., or at room temperature, in a gentle agitation (e.g. flow) process. This is preferably performed for approximately 60 minutes. This removes metallic contaminants and residue organic compounds. Alternatively, a point-of-use oxidizing acid solution, such as for example ‘Piranha’ solution, can be used to similar effect, although not at room temperature. This step is immediately followed by extensive rinsing with ultrapure DI water. It is appreciated that Piranha solution is a mixture of a strong acid (e.g. sulfuric acid, H2SO4) and a strong oxidizing agent (e.g. hydrogen peroxide, H2O2) which produces an extremely energetic solution. However, Piranha solution must be prepared immediately before use, has a very limited shelf life, and cannot be stored in normal closed containers due to an explosive pressure buildup caused by the gradual loss of hydrogen peroxide gas, ergo “point of use.”
- (3) Optionally, exposure of grating surface to a weak tetrymethyl ammonium hydroxide solution to neutralize any remaining acidic residue on the surface, flowed by extensive rinsing with ultrapure DI water. This is performed prior to the next step.
- (4) Exposure of grating surface to an oxygen plasma “ashing” process using reactive oxygen species generated by RF excitation of an oxygen flow in a vacuum chamber for a period of several hours. This process oxidizes and removes fluorinated hydrocarbon residue.
- (5) Exposure of grating surface again to aqueous oxidizing acid solution, (preferably Nanostrip™ or Nanostrip™ 2X solution), self heated by periodic addition of water to 50-70 C., or at room temperature, in a gentle agitation (e.g. flow) process for approximately 60 minutes. This removes metallic contaminants possibly introduced by the ashing process. This step is immediately followed by extensive rinsing with ultrapure DI water.
- The above process can be modified as necessary due to the incompatibility of certain MLD coating materials to certain chemistries. For example, if an Al2O3 etch-stop layer is incorporated into the MLD stack, treatment with aqueous base or hot acid is not possible due to dissolution of this layer. The cleaning process is modified by removing the first step (i.e. exposure to aqueous base) and changing steps (2) and (5) to room-temperature Nanostrip™ solution for a longer period of time greater than 60 minutes.
- While particular operational sequences, materials, temperatures, parameters, and particular embodiments have been described and or illustrated, such are not intended to be limiting. Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.
Claims (15)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/895,392 US20080047584A1 (en) | 2006-08-23 | 2007-08-23 | Method for cleaning diffraction gratings |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US83975306P | 2006-08-23 | 2006-08-23 | |
US11/895,392 US20080047584A1 (en) | 2006-08-23 | 2007-08-23 | Method for cleaning diffraction gratings |
Publications (1)
Publication Number | Publication Date |
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US20080047584A1 true US20080047584A1 (en) | 2008-02-28 |
Family
ID=39107441
Family Applications (1)
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US11/895,392 Abandoned US20080047584A1 (en) | 2006-08-23 | 2007-08-23 | Method for cleaning diffraction gratings |
Country Status (2)
Country | Link |
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US (1) | US20080047584A1 (en) |
WO (1) | WO2008024480A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20090281016A1 (en) * | 2008-05-01 | 2009-11-12 | Advanced Technology Materials, Inc. | LOW pH MIXTURES FOR THE REMOVAL OF HIGH DENSITY IMPLANTED RESIST |
Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4740410A (en) * | 1987-05-28 | 1988-04-26 | The Regents Of The University Of California | Micromechanical elements and methods for their fabrication |
US4885106A (en) * | 1987-01-27 | 1989-12-05 | Micro-Image Technology Limited | Storable semiconductor cleaning solution containing permonosulphuric acid |
US5464480A (en) * | 1993-07-16 | 1995-11-07 | Legacy Systems, Inc. | Process and apparatus for the treatment of semiconductor wafers in a fluid |
US5814157A (en) * | 1995-05-15 | 1998-09-29 | Nec Corporation | Method for cleaning a semiconductor wafer with an improved cleaning solution |
US5989354A (en) * | 1997-12-22 | 1999-11-23 | Lucent Technologies, Inc. | Method for removing thin, organic materials from semiconductor dies and micro-lenses |
US6348100B1 (en) * | 1999-07-01 | 2002-02-19 | International Business Machines Corporation | Resist bowl cleaning |
US20020066717A1 (en) * | 1999-12-02 | 2002-06-06 | Steven Verhaverbeke | Apparatus for providing ozonated process fluid and methods for using same |
US20040244423A1 (en) * | 2003-03-28 | 2004-12-09 | Hoya Corporation | Method of manufacturing an optical glass element |
US20050039948A1 (en) * | 1999-06-02 | 2005-02-24 | Motoo Asai | Multi-layer printed circuit board and method of manufacturing multi-layer printed circuit board |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20040055621A1 (en) * | 2002-09-24 | 2004-03-25 | Air Products And Chemicals, Inc. | Processing of semiconductor components with dense processing fluids and ultrasonic energy |
-
2007
- 2007-08-23 WO PCT/US2007/018763 patent/WO2008024480A2/en active Application Filing
- 2007-08-23 US US11/895,392 patent/US20080047584A1/en not_active Abandoned
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4885106A (en) * | 1987-01-27 | 1989-12-05 | Micro-Image Technology Limited | Storable semiconductor cleaning solution containing permonosulphuric acid |
US4740410A (en) * | 1987-05-28 | 1988-04-26 | The Regents Of The University Of California | Micromechanical elements and methods for their fabrication |
US5464480A (en) * | 1993-07-16 | 1995-11-07 | Legacy Systems, Inc. | Process and apparatus for the treatment of semiconductor wafers in a fluid |
US5814157A (en) * | 1995-05-15 | 1998-09-29 | Nec Corporation | Method for cleaning a semiconductor wafer with an improved cleaning solution |
US5989354A (en) * | 1997-12-22 | 1999-11-23 | Lucent Technologies, Inc. | Method for removing thin, organic materials from semiconductor dies and micro-lenses |
US20050039948A1 (en) * | 1999-06-02 | 2005-02-24 | Motoo Asai | Multi-layer printed circuit board and method of manufacturing multi-layer printed circuit board |
US6348100B1 (en) * | 1999-07-01 | 2002-02-19 | International Business Machines Corporation | Resist bowl cleaning |
US20020066717A1 (en) * | 1999-12-02 | 2002-06-06 | Steven Verhaverbeke | Apparatus for providing ozonated process fluid and methods for using same |
US20040244423A1 (en) * | 2003-03-28 | 2004-12-09 | Hoya Corporation | Method of manufacturing an optical glass element |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20090281016A1 (en) * | 2008-05-01 | 2009-11-12 | Advanced Technology Materials, Inc. | LOW pH MIXTURES FOR THE REMOVAL OF HIGH DENSITY IMPLANTED RESIST |
US8026200B2 (en) * | 2008-05-01 | 2011-09-27 | Advanced Technology Materials, Inc. | Low pH mixtures for the removal of high density implanted resist |
Also Published As
Publication number | Publication date |
---|---|
WO2008024480A3 (en) | 2008-06-19 |
WO2008024480A2 (en) | 2008-02-28 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: ENERGY, U.S. DEPARTMENT OF, DISTRICT OF COLUMBIA Free format text: CONFIRMATORY LICENSE;ASSIGNOR:CALIFORNIA, THE REGENTS OF THE UNIVERSITY OF;REEL/FRAME:020106/0970 Effective date: 20070920 |
|
AS | Assignment |
Owner name: REGENTS OF THE UNIVERSITY OF CALIFORNIA, THE, CALI Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BRITTEN, JERALD A.;NGUYEN, HOANG T.;REEL/FRAME:020115/0779 Effective date: 20070822 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |