Method and apparatus for removing contaminants on electronic devices

Abstract

The invention provides a unique method and apparatus for removing flash or other contaminants from an electronic package such as encapsulated semiconductor device by exposing the device to plasma gas. In a preferred embodiment, a plasma gas cleaner is provided with a reaction chamber used to house the encapsulated device during a deflashing procedure. Plasma gas is supplied to the reaction chamber for reaction on the surfaces of the device. The reaction of the plasma on these surfaces successfully removes excess encasing material and other contaminants. The plasma gas cleaner may be a plasma gas device used for other process steps (e.g., plasma etching) employed during the fabrication and manufacture of the semi conductor device.

What is claimed as new and desired to be protected by Letters Patent of the United States is:  
     
         1 . A device for removing contaminants from one or more component surfaces of an encapsulated object, the device comprising: 
 an enclosure for housing an encapsulated object; and    a source of plasma gas, coupled to said enclosure, for exposing the encapsulated object in said enclosure to plasma gas;    wherein a reaction of the plasma gas at a component surface of the encapsulated object causes any contaminants thereon to be removed from the component surface of the encapsulated object.    
     
     
         2 . A device as in    claim 1   , wherein the object is an electronic device having conductive component surfaces in the form of metallic leads, and wherein the contaminants are an organic material that interferes with electrical connectivity of the metallic leads of the object.  
     
     
         3 . A device as in    claim 1   , further comprising: 
 a source of heat coupled to said enclosure for providing heat to the encapsulated object in said enclosure simultaneously with the exposure of said object encapsulated to plasma gas.    
     
     
         4 . A device as in    claim 1   , further comprising at least one magazine, said magazine having a plurality of storage units each for holding at least one encapsulated object in said enclosure.  
     
     
         5 . A plasma cleaner comprising: 
 a reaction chamber;    a gas source coupled to said reaction chamber,    an electric field source coupled to said reaction chamber; and    a vacuum pump coupled to said reaction chamber, wherein said vacuum pump maintains vacuum pressure in said reaction chamber and removes by-products produced from reaction on a surface of an encapsulated electronic component of gas, which is supplied to said reaction chamber by said gas source, and an electric field, which is supplied to said reaction chamber by said source of electric field.    
     
     
         6 . A plasma cleaner as in    claim 5   , wherein said gas source supplies Oxygen gas to said reaction chamber.  
     
     
         7 . An apparatus for removing flash from an encapsulated electronic device, the apparatus comprising: 
 a chamber;    a holder for supporting at least one encapsulated electronic device in said chamber, said at least one encapsulated electronic device containing flash on at least one of its surfaces;    a gas inlet for introducing a reactive gas into said chamber; and    a power generator, coupled to said chamber, for converting reactive gas in said chamber into a reactive plasma to induce a plasma reaction on the at least one surface of said at least one encapsulated electronic device.    
     
     
         8 . An apparatus as in    claim 7   , wherein the gas entering said chamber is Argon gas.  
     
     
         9 . An apparatus as in    claim 7   , wherein the encapsulated electronic device is one of a plurality of semiconductor devices housed in said holder which comprises a magazine, wherein the semiconductor devices have flash in the form of resin-bleed appearing on their external leads.  
     
     
         10 . An apparatus as in    claim 7   , wherein said power generator produces radio frequency (RF) energy and introduces the RF energy into said chamber.  
     
     
         11 . A manufacturing device for treating and curing electronic packages, the device comprising: 
 a process unit in which electronic packages are disposed for treatment and curing;    a gas source, coupled to said process unit, for introducing gas into said process unit;    an energy field generator supplying an energy field inside said process unit, to cause within said process unit the gas to produce a plasma which reacts on conductive surfaces of the electronic packages to remove encasing material and contaminants therefrom; and    a heat source providing heat inside said process unit to cure the electronic packages.    
     
     
         12 . A manufacturing device as in    claim 11   , further comprising a vacuum pump, coupled to said process unit, for maintaining a vacuum pressure inside said process unit and evacuating encasing material and contaminants removed from the electronic packages.  
     
     
         13 . A manufacturing device as in    claim 12   , wherein the electronic packages are semiconductor devices having flash appearing on metallic external leads.  
     
     
         14 . A semiconductor processing subsystem for cleaning and heat treating semiconductor devices, the subsystem comprising: 
 a reaction section in which semiconductor packages are disposed for cleaning and baking;    a source of gas, coupled to said reaction section, for exposing the semiconductor packages disposed in said reaction section to reactive gas;    a radio frequency (RF) power supply connected to said reaction section to selectively supply an RF field to said reaction section and causing said reactive gas to form a plasma;    a vacuum, attached to a vacuum port in said reaction section, for evacuating any by-products resulting from a reaction of the reactive gas on surfaces of the semiconductor packages when the RF field is supplied to said reaction section; and    a heat source providing heat inside said reaction section to bake the semiconductor packages inside said reaction section;    wherein said reaction section further comprises:    at least one powered shelf, coupled to said energy field generator through a power bus;    at least one grounded shelf, coupled to a grounded bus; and    at least one magazine having a plurality of storage units, each storage unit housing one or more encapsulated semiconductor packages.    
     
     
         15 . A semiconductor processing subsystem as in    claim 14   , wherein said vacuum maintains the pressure inside said reaction section at less than one atmosphere.  
     
     
         16 . In a manufacturing system for manufacturing a semiconductor device, wherein the manufacturing system includes subsystems for (1) fabricating a plurality of integrated circuit (IC) dies on a wafer, (2) selecting one of the IC dies from the wafer, (3) attaching the selected IC die to a lead frame, (4) wire bonding the selected IC die to inner leads of the lead frame, (5) encapsulating the bonded IC die and inner leads of the lead frame in encasing material to produce a semiconductor device package having only outer leads of the lead frame exposed, (6) deflashing residual encasing material and contaminants from the semiconductor device package, and (7) curing the semiconductor device package, a deflashing apparatus comprising: 
 a reaction chamber housing a plurality of semiconductor device packages during a deflashing procedure;    a source of gas supplying deflashing gas to said reaction chamber;    a gas inlet, wherein said source of gas is in communication with said reaction chamber through said gas inlet;    a voltage source, wherein an electric field is created in said reaction chamber through coupling of said reaction chamber with said voltage source; and    a vacuum pump, coupled to said reaction chamber, wherein said reaction chamber is placed under a vacuum pressure by said vacuum pump;    wherein the deflashing gas from said source of gas reacts in response to the electric field created in said reaction chamber by said voltage source on surfaces of the semiconductor device package housed in said reaction chamber, and wherein removed encasing material is evacuated from said reaction chamber by said vacuum pump.    
     
     
         17 . A deflashing apparatus as in    claim 16   , wherein organic bonds between the encasing material and such surfaces are broken by said reaction to remove the encasing material from the outer leads of the semiconductor device package.  
     
     
         18 . A deflashing apparatus as in    claim 16   , further comprising a heat source, coupled to said reaction chamber, for supplying heat to said reaction chamber before and during the deflashing procedure so as to effectuate curing of the encasing material of the semiconductor device package at least before the deflashing procedure.  
     
     
         19 . A deflashing apparatus as in    claim 16   , further comprising a heat source, coupled to said reaction chamber, for supplying heat to said reaction chamber during the deflashing procedure so as to effectuate curing of the encasing material of the semiconductor device package at least during the deflashing procedure.  
     
     
         20 . A deflashing apparatus as in    claim 16   , further comprising a heat source, coupled to said reaction chamber, for supplying heat to said reaction chamber during and after the deflashing procedure so as to effectuate curing of the encasing material of the semiconductor device package at least after the deflashing procedure.  
     
     
         21 . A system for manufacturing an encased electronic device, the system comprising: 
 a fabricator, operative to fabricate an electronic device;    an encapsulator, receiving a fabricated electronic device after said fabricator, for encasing the fabricated electronic device, the encasing producing encased electronic device having external lead members; and    a plasma cleaner, receiving the encased electronic device after said encapsulator, wherein said plasma cleaner is operative to clean the external lead members of the encased electronic device using plasma gas.    
     
     
         22 . A system as in    claim 21   , wherein said plasma cleaner comprises: 
 a plurality of shelves for supporting a plurality of encased electronic devices, each shelf being electrically biased;    a field generator, coupled to at least one biased shelf of said plurality of shelves, for generating an electric field which propagates from the at least one biased shelf;    a source of gas operative to expose the plurality of electronic devices supported by said plurality of shelves to a plasma forming gas, wherein the generated field causes the gas to form a plasma.    
     
     
         23 . A semiconductor processing plant comprising: 
 a fabrication station for fabricating a plurality of integrated circuits (ICs) on a semiconductor medium;    a selective separator station for selectively separating the semiconductor medium fabricated in said fabrication station into a plurality of individual ICs;    a packaging station which receives a selected one of the plurality of individual ICs separated by said selective separator station, wherein said packaging station mounts the individual IC on a lead structure and surrounds the selected individual IC with encasing material to form a semiconductor package having extending leads;    a cleaning station which receives the semiconductor package from said packaging station, said cleaning station including: a reaction chamber, a supply of reactive gas, and a vacuum, said cleaning station producing a plasma for deflashing encasing residue from the semiconductor package which is temporarily housed in said reaction chamber; and    a baking station containing a heat source for exposing said semiconductor package to heat so as to cure the encasing material of the semiconductor package.    
     
     
         24 . A semiconductor device manufacturing system comprising: 
 a fabrication section for producing a plurality of fabricated integrated circuit (IC) dies;    a die selection and separation section for selecting is an IC die from the plurality of IC dies fabricated in said fabrication section;    a die attachment section for attaching the selected IC die to a lead frame;    a pre-mold cleaning section which removes any contaminants from the die and lead frame attached in said die attachment section;    a wire bonding section which bonds respective bonding pads on the selected die with respective inner leads of the lead frame attached to the selected die;    a molding section which encapsulates the selected die and inner leads of the lead frame attached to the selected die to form an encapsulated package leaving only outer leads of the lead frame exposed;    a deflash section which includes a plasma cleaner, the plasma cleaner comprising: a reaction chamber, a gas supply, a radio frequency energy source, and a disposal mechanism, said deflash section exposing the encapsulated package to plasma produced in said reaction chamber to substantially remove any flash appearing on the outer leads of the encapsulated package, said disposal mechanism taking removed flash out of said chamber;    a final cure section which heats the encapsulated package; and    a lead plating section which coats the outer leads of the encapsulated package with a layer of conductive material.    
     
     
         25 . A semiconductor device manufacturing system as in    claim 24   , wherein said final cure section is incorporated in the plasma cleaner.  
     
     
         26 . A semiconductor device manufacturing system as in    claim 24   , wherein said plasma cleaner in said deflash section is used in said pre-mold cleaning section.  
     
     
         27 . A method of processing an encapsulated object comprising the steps of: 
 encapsulating an object to form an individual package of the object, the individual package having conductive members which are external to the individual package; and    plasma cleaning the individual package to remove interfering encapsulating material appearing on or between the conductive members.    
     
     
         28 . A method as in    claim 27   , further comprising the step of heating the formed individual package to cure the encapsulation.  
     
     
         29 . A method as in    claim 28   , wherein said step of plasma cleaning and said step of heating the formed individual package are performed at least in some part simultaneously.  
     
     
         30 . A method in    claim 27   , wherein the object is an encapsulated semiconductor device, and said step of plasma cleaning includes removing flash from external leads of the semiconductor device.  
     
     
         31 . A method of removing encapsulation flash from a semiconductor package having leads external to the package, the method comprising the steps of: 
 placing a semiconductor package in a chamber;    introducing gas into the chamber;    converting the gas into a reactive plasma; and    reacting the plasma on a surface of at least one external lead of the semiconductor package so as to remove flash therefrom.    
     
     
         32 . A method as in    claim 31   , wherein the gas in said introducing step is composed of Argon and air.  
     
     
         33 . A method of removing foreign material from external leads of a semiconductor package, the method comprising the steps of: 
 transferring a plurality of semiconductor packages to a reaction chamber;    introducing gas into the reaction chamber;    causing dissociation in the gas in the reaction chamber; and,    exposing foreign material on the leads of the semiconductor packages to free radicals derived from the dissociation of the gas in the reaction chamber;    
     
     
         34 . A method as in    claim 33   , wherein said step of heating the semiconductor packages commences prior to and extends during the performance of said step of exposing foreign material on the leads of the semiconductor packages; and wherein said step of transferring a plurality of semiconductor packages commences before said step of causing dissociation in the gas.  
     
     
         35 . A process for producing an encapsulated electronic device, the process comprising the steps of: 
 fabricating at least one electronic device;    encapsulating the at least one electronic device;    plasma cleaning the at least one electronic device after said encapsulating step; and    curing the encapsulation of said at least one electronic device.    
     
     
         36 . A process as in    claim 35   , wherein said step of plasma cleaning comprises the steps of: 
 introducing a plasma gas into a chamber;    reacting the plasma gas with a surface of the encapsulated electronic device; and    removing by-products resulting from said step of reacting with the surface of the encapsulated electronic device.    
     
     
         37 . A process of manufacturing a package for a semiconductor integrated circuit (IC) device, the process comprising the steps of: 
 attaching an IC die to a center pad of a lead frame using a bonding agent;    plasma cleaning the IC die to remove any excess bonding agent appearing on the IC die;    wire bonding the IC die to inner leads of the lead frame;    placing the IC die and the lead frame in a mold;    injecting encasing material into the mold around the die and the lead frame to form an individual package completely encapsulating the IC die and the inner leads of the lead frame while leaving outer leads of the lead frame exposed;    plasma cleaning the outer leads of the lead frame to remove any residue encasing material appearing on or between the outer leads of the lead frame as a result of performing said step of injecting encasing material; and    heating the formed individual package for final curing to produce a package for the semiconductor IC.    
     
     
         38 . A process as in    claim 37   , wherein said step of plasma cleaning the outer leads of the lead frame and said step of heating the formed individual package are performed simultaneously.  
     
     
         39 . A process as in    claim 37   , further comprising the step of plating the outer leads of the lead frame after said step of plasma cleaning and before said step of heating the formed individual package.  
     
     
         40 . A process as in    claim 37   , wherein said step of plasma cleaning the IC die and said step of plasma cleaning the outer leads of the lead frame are conducted using the same plasma cleaning device.  
     
     
         41 . A method of making a memory device, the method comprising the steps of: 
 fabricating a plurality of memory integrated circuits as (IC) dies on a wafer of silicon;    separating a selected IC die from the plurality of IC dies on the wafer;    attaching the selected IC die to a center pad of a lead frame using a bonding agent;    inspecting the IC die and lead frame to ensure the die is attached correctly;    performing a first cleaning step on both the IC die and the lead frame using a plasma cleaner to remove any excess bonding agent IC;    wire bonding the IC die to inner leads of the lead frame;    placing the wire bonded IC die and lead frame in an injection encasement mold;    injecting plastic encasing material into the mold around the wire bonded IC die and lead frame to form an individual package which encapsulates the IC die and the inner leads of the lead frame while leaving outer leads of the lead frame exposed to the external environment;    performing a second cleaning step on the outer leads of the lead frame using the plasma cleaning chamber used in said first cleaning step to remove any residue encasing material appearing on and between the outer leads of the lead frame; and    simultaneously, with said second cleaning step, heating the formed individual package for final curing using the plasma cleaning chamber used in both said first cleaning step to produce a memory circuit housed in an encased package.    
     
     
         42 . A method of making a memory device, the method comprising the steps of: 
 fabricating a plurality of memory integrated circuits in the form of a plurality of integrated circuit (IC) dies on a wafer of silicon;    selecting one memory IC die from the plurality of IC dies on the wafer;    after the selection, separating the selected one IC die from the plurality of IC dies on the wafer;    then, attaching the selected IC die to a center pad of a lead frame using a bonding agent of epoxy;    next, performing a first cleaning step on both the IC die and also the lead frame using a plasma cleaner chamber to remove any excess bonding agent resulting from said step of attaching the selected IC die;    next, wire bonding the IC die to inner leads of the lead frame upon plasma cleaning the IC die and lead frame;    then, placing the wire bonded IC die and lead frame in an injection encasement mold;    after said step of placing, injecting plastic encasing material into the mold around the wire bonded IC die and lead frame to form an individual package encapsulating the IC die and the inner leads of the lead frame while leaving outer leads of the lead frame exposed to the environment external to the encased IC die and inner leads of the lead frame;    after said injecting plastic step, performing a second cleaning step on the outer leads of the lead frame using the plasma cleaning chamber used in said first cleaning step now to remove any residue encasing material appearing on and between the outer leads of the lead frame as a result of performing said step of injecting plastic encasing material; and    simultaneously with said second cleaning step, heating the formed individual package for final curing using the plasma cleaning chamber used in both said first cleaning step and said second cleaning step to result in a memory device housed in a plastic package.