WO2012108835A1 - Cleaning process for bond surface contamination - Google Patents

Cleaning process for bond surface contamination Download PDF

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Publication number
WO2012108835A1
WO2012108835A1 PCT/SG2011/000061 SG2011000061W WO2012108835A1 WO 2012108835 A1 WO2012108835 A1 WO 2012108835A1 SG 2011000061 W SG2011000061 W SG 2011000061W WO 2012108835 A1 WO2012108835 A1 WO 2012108835A1
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WO
WIPO (PCT)
Prior art keywords
stripping solution
drying
rinsing
ionised
electrical charges
Prior art date
Application number
PCT/SG2011/000061
Other languages
French (fr)
Inventor
Debbie T. ALCALA
Phoi Ching MOK
Original Assignee
Katharos Adhesion Technologies Pte. Ltd.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Katharos Adhesion Technologies Pte. Ltd. filed Critical Katharos Adhesion Technologies Pte. Ltd.
Priority to PCT/SG2011/000061 priority Critical patent/WO2012108835A1/en
Publication of WO2012108835A1 publication Critical patent/WO2012108835A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L24/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
    • C23G5/00—Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
    • C11D2111/00—Cleaning compositions characterised by the objects to be cleaned; Cleaning compositions characterised by non-standard cleaning or washing processes
    • C11D2111/10—Objects to be cleaned
    • C11D2111/14—Hard surfaces
    • C11D2111/22—Electronic devices, e.g. PCBs or semiconductors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L2224/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
    • H01L2224/45001—Core members of the connector
    • H01L2224/45099—Material
    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • H01L2224/85009—Pre-treatment of the connector or the bonding area
    • H01L2224/8501—Cleaning, e.g. oxide removal step, desmearing
    • H01L2224/85019—Combinations of two or more cleaning methods provided for in at least two different groups from H01L2224/8501 - H01L2224/85014
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
    • H01L2224/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • H01L2224/852—Applying energy for connecting
    • H01L2224/85201—Compression bonding
    • H01L2224/85205—Ultrasonic bonding
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L24/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L24/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01013—Aluminum [Al]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01033—Arsenic [As]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01079—Gold [Au]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01082—Lead [Pb]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/013—Alloys
    • H01L2924/0132—Binary Alloys
    • H01L2924/01327—Intermediate phases, i.e. intermetallics compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/013—Alloys
    • H01L2924/014—Solder alloys

Definitions

  • the present invention relates generally to a process for cleaning, particularly wet cleaning, a surface for wire-bonding.
  • the present invention also relates broadly to a process for bonding wire attachment.
  • Wire-bonding refers to a way of making electrical interconnections to a semiconductor die or a lead frame by forming a bond between a metallic wire and a bonding surface, such as a bond pad on the semiconductor die or the a bond finger on the frame.
  • a bonding surface should ideally be free from contaminations prior to wire-bonding.
  • a process for cleaning a surface for wire-bonding comprising the steps of:
  • the step of removing electrical charges occurs before the step of removing contaminants for avoiding deposits onto the surface.
  • the deposits are caused by reaction between the electrical charges on the surface and the stripping solution.
  • the step of removing electrical charges includes the step of removing the electrical charges with an ionised gas. More preferably the step of removing electrical charges includes the step of directing the ionised gas towards the surface. Even more preferably the step of directing the ionised gas towards the surface includes the step of facilitating reaction of the electrical charges with the ionised gas. Still more preferably the step of facilitating reaction of the electrical charges with the ionised gas particles includes the step of neutralising the electrical charges with the ionised gas.
  • the step of neutralising the electrical charges with the ionised gas particles includes the step of neutralising positive electrical charges with the ionised gas.
  • the step of directing the ionised gas towards the surface includes the step of bombarding the surface with gas particles for dislocating positively charged particles from the surface.
  • the step of removing contaminants with a stripping solution includes the step of immersing the surface in the stripping solution. More preferably the step of immersing the surface in the stripping solution includes the step of maintaining a temperature of the stripping solution between room temperature and approximately 50 degrees Celsius. Even more preferably the step of maintaining a temperature of the stripping solution includes the step of maintaining a temperature of the stripping solution at approximately 40 degrees Celsius.
  • the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 1 to 30 minutes. Even preferably the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 5 minutes
  • the step of immersing the surface in the stripping solution includes the step of exciting the stripping solution at ultrasonic frequencies. More preferably the step of exciting the stripping solution at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation.
  • the step of removing contaminants with a stripping solution includes the step of removing the contaminants with an organic contamination stripper and/or an inorganic contamination stripper.
  • the step of rinsing the surface includes the step of rinsing the surface with a de-ionised agent. More preferably the step of rinsing the surface with a de-ionised agent includes the step of rinsing the surface with de-ionised water.
  • the process further comprises the step of immersing the surface in isopropyl alcohol prior to the step of rinsing the surface with a de-ionised agent.
  • the step of rinsing the surface includes the step of exciting the rinsing agent at ultrasonic frequencies. More preferably the step of exciting the rinsing agent at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation.
  • the step of drying the surface includes the step of drying the surface with a dry gas. More preferably the step of drying the surface for wire-bonding includes the step of drying the surface with a compressed dry gas. Even more preferably the step of drying the surface for wire-bonding includes the step of drying the surface with compressed dry air.
  • the step of drying the surface includes the step of blow drying the surface with the dry gas.
  • the step of drying the surface includes centrifugal drying. Still alternatively the step of drying the surface includes a water displacement method.
  • the surface for wire-bonding includes a surface on a bond pad and/or a surface on a bond finger.
  • the ionised gas includes ionised air.
  • the contaminants include inorganic contaminants, such as oxide or halide species formed on metal or semiconductor surfaces. Additionally or alternatively the contaminants include organic contaminants, such as solder mask debris or residuals, lint, adhesives or foreign materials.
  • FIG. 1 A flow diagram illustrating the steps of an embodiment of the cleaning process in accordance with the present invention.
  • the present invention relates generally to a process for cleaning a surface, such as a bond pad on a semiconductor die or a bond finger on a lead frame, for wire-bonding.
  • this cleaning process is conducted after semiconductor wafer fabrication and before wire-bonding.
  • the cleaning process comprises the steps of (i) removing electrical charges from the surface, (ii) removing contaminants from the surface with a stripping solution, (iii) rinsing the surface with a rinsing agent, and (iv) drying the surface.
  • a bonding surface cleaned by this cleaning process may then be suitable for subsequent attachment of a bonding wire by way of bonding methods such as gold ball bonding or aluminium wedge bonding.
  • Fig. 1 illustrates an embodiment of the cleaning process 10 in accordance with this invention.
  • a stream of ionised gas or air may be blown or otherwise directed towards the bonding surface for removing any electrical charges,, particularly any positive electrical charges, such as positive ions built up on the surface resulting from the oven curing procedure of the wafer fabrication.
  • the ionised gas or air being negatively charged, may react with and neutralise the positive electrical charges on the surface.
  • the ionised gas or air when blown or otherwise directed towards the bonding surface may also assist in the removal of contaminants on the surface by the bombardment of gas particles to dislocate any loosely-held contaminants or positive ions from the surface.
  • the surface may be immersed in a stripping solution to remove any contaminants from the surface.
  • the stripping solution may be contained in a stripping bath, where the temperature of the solution is maintained at between room temperature and 50 degrees Celsius, with the optimum cleaning efficiency expected to be obtained at approximately 40 degrees Celsius. It is envisaged that an immersion time of approximately 1 to 30 minutes (with a recommended immersion time of approximately 5 minutes) may be required for the stripping solution to be effective in removing contaminants.
  • the stripping solution may include an organic contamination stripper and/or an inorganic contamination stripper to assist removal of organic and/or inorganic contamination from the surface. For example, any amine or fluoride based chemicals or strippers may be suitable.
  • an ultrasonic generator may be immersed in the stripping solution to excite the stripping solution at ultrasonic frequencies.
  • the acoustic waves generated in the stripping solution under appropriate circumstances causes cavitation, which may agitate any particles at the ultrasonic frequencies on the surface and may therefore remove contaminants from the surface.
  • step 12 should occur before step 14 to avoid unwanted deposits onto the bonding surface due to, for example, any chemical reaction between the electrically charged surface and the stripping solution.
  • the surface is rinsed by de-ionised water or any suitable de-ionised agent.
  • the surface prior to the rinsing step, the surface may be immersed in isopropyl alcohol to improve the effectiveness of the de-ibnised water in the rinsing step.
  • an ultrasonic generator may be used at step 16 to excite the de-ionised water at ultrasonic frequencies to further assist cleaning of the surface.
  • the acoustic waves generated in the de-ionised water under appropriate circumstances causes cavitation, which may agitate any particles at the ultrasonic frequencies on the surface and may therefore remove contaminants from the surface.
  • the surface is dried by blowing a dry gas, such as dry compressed air, on towards the surface.
  • a dry gas such as dry compressed air
  • the surface may be dried by centrifugal drying or a water displacement method. It should be noted that drying methods, such as nitrogen blow dry or Marangoni drying, used in wafer fabrication with more stringent dryness requirement may also be used but are not strictly necessary.
  • NSTEOL Non-stick on lead
  • short tail stoppages may be significantly reduced.
  • More uniform intermetallic growth and intermetallic coverage of approximately 80 to 90% may be achieved.
  • the step of removing electrical charges by, for example, an ionised gas may prevent unwanted deposits introduced on the bonding surface when immersed in the stripping solution.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Cleaning By Liquid Or Steam (AREA)

Abstract

In one aspect, the present invention relates generally to a process for cleaning, particularly wet cleaning, a surface for wire-bonding. The process comprises the steps of (i) removing electrical charges from the surface, (ii) removing contaminants from the surface with a stripping solution, (iii) rinsing the surface with a rinsing agent, and (iv) drying the surface. In another aspect, the present invention relates broadly to a process for bonding wire attachment comprising the above steps of the cleaning process and a subsequent step of attaching of a bonding wire to the cleaned surface.

Description

CLEANING PROCESS FOR BOND SURFACE CONTAMINATION
FIELD OF THE INVENTION
The present invention relates generally to a process for cleaning, particularly wet cleaning, a surface for wire-bonding. The present invention also relates broadly to a process for bonding wire attachment.
BACKGROUND OF THE INVENTION
Wire-bonding refers to a way of making electrical interconnections to a semiconductor die or a lead frame by forming a bond between a metallic wire and a bonding surface, such as a bond pad on the semiconductor die or the a bond finger on the frame. To improve bonding characteristics such as intermetallic coverage, intermetallic growth and lead frame oxidation a bonding surface should ideally be free from contaminations prior to wire-bonding.
Existing pre-wire-bonding cleaning methods such as plasma cleaning and strip blowing have limited cleaning capabilities. For example, these existing methods may not ensure proper intermetallic diffusion or may not be effective in removing organic contaminants.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a process for cleaning a surface for wire-bonding, the process comprising the steps of:
removing electrical charges from a surface for wire-bonding;
removing contaminants from the surface with a stripping solution;
rinsing the surface with a rinsing agent; and
drying the surface.
Preferably the step of removing electrical charges occurs before the step of removing contaminants for avoiding deposits onto the surface. In particular, the deposits are caused by reaction between the electrical charges on the surface and the stripping solution. Preferably the step of removing electrical charges includes the step of removing the electrical charges with an ionised gas. More preferably the step of removing electrical charges includes the step of directing the ionised gas towards the surface. Even more preferably the step of directing the ionised gas towards the surface includes the step of facilitating reaction of the electrical charges with the ionised gas. Still more preferably the step of facilitating reaction of the electrical charges with the ionised gas particles includes the step of neutralising the electrical charges with the ionised gas. Still more preferably the step of neutralising the electrical charges with the ionised gas particles includes the step of neutralising positive electrical charges with the ionised gas. Alternatively or additionally the step of directing the ionised gas towards the surface includes the step of bombarding the surface with gas particles for dislocating positively charged particles from the surface.
Preferably the step of removing contaminants with a stripping solution includes the step of immersing the surface in the stripping solution. More preferably the step of immersing the surface in the stripping solution includes the step of maintaining a temperature of the stripping solution between room temperature and approximately 50 degrees Celsius. Even more preferably the step of maintaining a temperature of the stripping solution includes the step of maintaining a temperature of the stripping solution at approximately 40 degrees Celsius.
Preferably the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 1 to 30 minutes. Even preferably the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 5 minutes
Preferably the step of immersing the surface in the stripping solution includes the step of exciting the stripping solution at ultrasonic frequencies. More preferably the step of exciting the stripping solution at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation.
Preferably the step of removing contaminants with a stripping solution includes the step of removing the contaminants with an organic contamination stripper and/or an inorganic contamination stripper. Preferably the step of rinsing the surface includes the step of rinsing the surface with a de-ionised agent. More preferably the step of rinsing the surface with a de-ionised agent includes the step of rinsing the surface with de-ionised water.
Preferably the process further comprises the step of immersing the surface in isopropyl alcohol prior to the step of rinsing the surface with a de-ionised agent.
Preferably the step of rinsing the surface includes the step of exciting the rinsing agent at ultrasonic frequencies. More preferably the step of exciting the rinsing agent at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation. Preferably the step of drying the surface includes the step of drying the surface with a dry gas. More preferably the step of drying the surface for wire-bonding includes the step of drying the surface with a compressed dry gas. Even more preferably the step of drying the surface for wire-bonding includes the step of drying the surface with compressed dry air. Preferably the step of drying the surface includes the step of blow drying the surface with the dry gas. Alternatively the step of drying the surface includes centrifugal drying. Still alternatively the step of drying the surface includes a water displacement method.
Preferably the surface for wire-bonding includes a surface on a bond pad and/or a surface on a bond finger.
Preferably the ionised gas includes ionised air.
Typically the contaminants include inorganic contaminants, such as oxide or halide species formed on metal or semiconductor surfaces. Additionally or alternatively the contaminants include organic contaminants, such as solder mask debris or residuals, lint, adhesives or foreign materials.
According to a second aspect of the invention there is provided a process for bonding wire attachment, the process comprising the steps of:
removing electrical charges from a surface for wire-bonding;
removing contaminants from the surface with a stripping solution; rinsing the surface with a rinsing agent;
drying the surface; and
attaching a bonding wire to the surface.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1 A flow diagram illustrating the steps of an embodiment of the cleaning process in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED E BODIMENT(S)
The present invention relates generally to a process for cleaning a surface, such as a bond pad on a semiconductor die or a bond finger on a lead frame, for wire-bonding. Typically this cleaning process is conducted after semiconductor wafer fabrication and before wire-bonding. The cleaning process comprises the steps of (i) removing electrical charges from the surface, (ii) removing contaminants from the surface with a stripping solution, (iii) rinsing the surface with a rinsing agent, and (iv) drying the surface. A bonding surface cleaned by this cleaning process may then be suitable for subsequent attachment of a bonding wire by way of bonding methods such as gold ball bonding or aluminium wedge bonding.
Fig. 1 illustrates an embodiment of the cleaning process 10 in accordance with this invention. At step 12, a stream of ionised gas or air may be blown or otherwise directed towards the bonding surface for removing any electrical charges,, particularly any positive electrical charges, such as positive ions built up on the surface resulting from the oven curing procedure of the wafer fabrication. The ionised gas or air, being negatively charged, may react with and neutralise the positive electrical charges on the surface. Furthermore the ionised gas or air when blown or otherwise directed towards the bonding surface may also assist in the removal of contaminants on the surface by the bombardment of gas particles to dislocate any loosely-held contaminants or positive ions from the surface.
At step 14, the surface may be immersed in a stripping solution to remove any contaminants from the surface. The stripping solution may be contained in a stripping bath, where the temperature of the solution is maintained at between room temperature and 50 degrees Celsius, with the optimum cleaning efficiency expected to be obtained at approximately 40 degrees Celsius. It is envisaged that an immersion time of approximately 1 to 30 minutes (with a recommended immersion time of approximately 5 minutes) may be required for the stripping solution to be effective in removing contaminants. The stripping solution may include an organic contamination stripper and/or an inorganic contamination stripper to assist removal of organic and/or inorganic contamination from the surface. For example, any amine or fluoride based chemicals or strippers may be suitable. To further assist cleaning of the surface, an ultrasonic generator may be immersed in the stripping solution to excite the stripping solution at ultrasonic frequencies. The acoustic waves generated in the stripping solution under appropriate circumstances causes cavitation, which may agitate any particles at the ultrasonic frequencies on the surface and may therefore remove contaminants from the surface.
Ideally step 12 should occur before step 14 to avoid unwanted deposits onto the bonding surface due to, for example, any chemical reaction between the electrically charged surface and the stripping solution.
At step 16, the surface is rinsed by de-ionised water or any suitable de-ionised agent. In some embodiments, prior to the rinsing step, the surface may be immersed in isopropyl alcohol to improve the effectiveness of the de-ibnised water in the rinsing step. Similar to step 14, an ultrasonic generator may be used at step 16 to excite the de-ionised water at ultrasonic frequencies to further assist cleaning of the surface. The acoustic waves generated in the de-ionised water under appropriate circumstances causes cavitation, which may agitate any particles at the ultrasonic frequencies on the surface and may therefore remove contaminants from the surface.
At step 8, the surface is dried by blowing a dry gas, such as dry compressed air, on towards the surface. Alternatively, the surface may be dried by centrifugal drying or a water displacement method. It should be noted that drying methods, such as nitrogen blow dry or Marangoni drying, used in wafer fabrication with more stringent dryness requirement may also be used but are not strictly necessary.
It has been observed that a wire-bonding surface cleaned by this embodiment of the cleaning process provides significantly better bonding characteristics. For examples: • Lead frame oxidation is reduced such that stitch pull may be improved from 1 to 4 gr/min.
• Non-stick on lead (NSOL) and short tail stoppages may be significantly reduced. · More uniform intermetallic growth and intermetallic coverage of approximately 80 to 90% may be achieved.
• There is a reduction of foreign material embedded in the bonding surface,
• There is a reduction of cratering.
Having described an embodiment of the cleaning method, it should be apparent that the invention also has the following advantages:
• The use of a stripping solution assists to remove both organic contaminants, such as solder mask debris or residuals, lint, adhesives from a wafer back- grinding tape and foreign materials from the production or fabrication environment, and inorganic contaminants such as oxide and halide species on the metal surfaces.
• The step of removing electrical charges by, for example, an ionised gas may prevent unwanted deposits introduced on the bonding surface when immersed in the stripping solution.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment(s) are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A process for cleaning a surface for wire-bonding, the process comprising the steps of:
removing electrical charges from a surface for wire-bonding; removing contaminants from the surface with a stripping solution;
rinsing the surface with a rinsing agent; and
drying the surface.
2. A process as claimed in claim 1 wherein the step of removing electrical charges occurs before the step of removing contaminants for avoiding deposits onto the surface.
3. A process as claimed in claim 2 wherein the deposits are caused by reaction between the electrical charges on the surface and the stripping solution.
4. A process as claimed in any one of the preceding claims wherein the step of removing electrical charges includes the step of removing the electrical charges with an ionised gas.
5. A process as claimed in claim 4 wherein the step of removing electrical charges includes the step of directing the ionised gas towards the surface.
6. A process as claimed in claim 5 wherein the step of directing the ionised gas towards the surface includes the step of facilitating reaction of the electrical charges with the ionised gas.
7. A process as claimed in claim 6 wherein the step of facilitating reaction of the electrical charges with the ionised gas particles includes the step of neutralising the electrical charges with the ionised gas.
8. A process as claimed in claim 7 wherein the step of neutralising the electrical charges with the ionised gas particles includes the step of neutralising positive electrical charges with the ionised gas.
9. A process as claimed in any one of claims 5 to 8 wherein the step of directing the ionised gas towards the surface includes the step of bombarding the surface with gas particles for dislocating positively charged particles from the surface.
10. A process as claimed in any one of the preceding claims wherein the step of removing contaminants with a stripping solution includes the step of immersing the surface in the stripping solution.
11. A process as claimed in claim 10 wherein the step of immersing the surface in the stripping solution includes the step of maintaining a temperature of the stripping solution at between room temperature and approximately 50 degrees Celsius.
12. A process as claimed in claim 11 wherein the step of maintaining a temperature of the stripping solution includes the step of maintaining a temperature of the stripping solution at approximately 40 degrees Celsius.
13. A process as claimed in any one of claims 10 to 12 wherein the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 1 to 30 minutes.
14. A process as claimed in daim 3 wherein the step of immersing the surface in the stripping solution includes the step of immersing the surface in the stripping solution for approximately 5 minutes.
15. A process as claimed in any one of claims 10 to 14 wherein the step of immersing the surface in the stripping solution includes the step of exciting the stripping solution at ultrasonic frequencies.
16. A process as claimed in claim 15 wherein the step of exciting the stripping solution at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation.
17. A process as claimed in any one of the preceding claims wherein the step of removing contaminants with a stripping solution includes the step of removing the contaminants with an organic contamination stripper and/or an inorganic contamination stripper.
18. A process as claimed in any one of the preceding claims wherein the step of rinsing the surface includes the step of rinsing the surface with a de-ionised agent.
19. A process as claimed in claim 18 wherein the step of rinsing the surface with a de-ionised agent includes the step of rinsing the surface with de-ionised water.
20. A process as claimed in either of claims 18 or 19 further comprising the step of immersing the surface in isopropyl alcohol prior to the step of rinsing the surface with a de-ionised agent.
21. A process as claimed in any one of the preceding claims wherein the step of rinsing the surface includes the step of exciting the rinsing agent at ultrasonic frequencies.
22. A process as claimed in claim 21 wherein the step of exciting the rinsing agent at ultrasonic frequencies includes the step of removing from the surface contaminants agitated by cavitation caused by ultrasonic excitation.
23. A process as claimed in any one of the preceding claims wherein the step of drying the surface includes the step of drying the surface with a dry gas.
24. A process as claimed in claim 23 wherein the step of drying the surface for wire-bonding includes the step of drying the surface with a compressed dry gas.
25. A process as claimed in claim 24 wherein the step of drying the surface for wire-bonding includes the step of drying the surface with compressed dry air.
26. A process as claimed in any one of the preceding claims wherein the step of drying the surface includes the step of blow drying the surface with the dry gas.
27. A process as claimed in any one of claims 1 to 25 wherein the step of drying the surface includes centrifugal drying.
28. A process as claimed in any one of claims 1 to 25 wherein the step of drying the surface includes a water displacement method.
29. A process as claimed in any one of the preceding claims wherein the surface for wire-bonding includes a surface on a bond pad and/or a surface on a bond finger.
30. A process as claimed in any one of claims 4 to 29 wherein the ionised gas includes ionised air.
31. A process as claimed in any one of the preceding claims wherein the contaminants include an inorganic contaminant.
32. A process as claimed in claim 31 wherein the inorganic contaminant includes oxide or halide species formed on metal or semiconductor surfaces.
33. A process as claimed in any one of the preceding claims wherein the contaminants include an organic contaminant.
34. A process as claimed in claim 33 wherein the organic contaminant includes solder mask debris or residuals, lint, adhesives or foreign materials.
35. A process for bonding wire attachment, the process comprising the steps of: removing electrical charges from a surface for wire-bonding;
removing contaminants from the surface with a stripping solution;
rinsing the surface with a rinsing agent;
drying the surface; and
attaching a bonding wire to the surface.
PCT/SG2011/000061 2011-02-10 2011-02-10 Cleaning process for bond surface contamination WO2012108835A1 (en)

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WO2020152120A1 (en) 2019-01-23 2020-07-30 Basf Se Oxime ester photoinitiators having a special aroyl chromophore
WO2021175855A1 (en) 2020-03-04 2021-09-10 Basf Se Oxime ester photoinitiators

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WO2015036910A1 (en) 2013-09-10 2015-03-19 Basf Se Oxime ester photoinitiators
WO2020152120A1 (en) 2019-01-23 2020-07-30 Basf Se Oxime ester photoinitiators having a special aroyl chromophore
WO2021175855A1 (en) 2020-03-04 2021-09-10 Basf Se Oxime ester photoinitiators

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