Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/321—Radio frequency generated discharge the radio frequency energy being inductively coupled to the plasma
  • H01J37/3211—Antennas, e.g. particular shapes of coils
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/321—Radio frequency generated discharge the radio frequency energy being inductively coupled to the plasma
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32431—Constructional details of the reactor
  • H01J37/32623—Mechanical discharge control means
  • H01J37/32651—Shields, e.g. dark space shields, Faraday shields
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/32—Processing objects by plasma generation
  • H01J2237/33—Processing objects by plasma generation characterised by the type of processing
  • H01J2237/334—Etching

Definitions

• This invention relates to plasma processing and particularly to plasma etching with an inductively coupled plasma.
• ICPs inductively coupled plasmas
• RF energy is applied to a coil that surrounds a vacuum chamber outside of a chamber wall made of quartz.
• the coil generates a magnetic field within the chamber which excites electrons and forms a plasma. While the field is iargely inductively coupled, the development of a high peak to peak voltage across the coil causes some degree of capacitive coupling of energy into the chamber.
• Such voltage has, in situations, developed a sheath of 900 to 1000 volts, for example, which imparts substantial energy to ions in the plasma. Such energy is enough to cause an undesirable degree of sputtering of the inside of the chamber wall and the sheath reduces the useful volume of the plasma.
• An objective of the present invention is to provide shielding of a chamber from capacitive coupling.
• a particular objective of the invention is to provide efficient shielding from an RF coil that is provided around the chamber to inductively couple RF energy into plasma within the chamber. It is a further objective of the present invention to provide shielding that prevents capacitive coupling between a chamber and an exterior coil while facilitating plasma ignition.
• a plasma processing chamber particularly an etching chamber, is provided having an external loop-shaped RF inductor.
• the inductor is preferably a helical coil for inductively coupling RF energy into the chamber to form a plasma within the chamber.
• a Faraday shield is provided outside of the chamber wall between the wall and the inductor. The shield is grounded so as to provide effective shielding of capacitive coupling of voltage from the coil to the plasma within the chamber and is slitted to allow inductive coupling of the RF energy into the chamber.
• the ground connection is localized to a limited section of the inductor so as to allow a peak-to-peak voltage to develop across the gap when the RF current is initially induced into the shield from the inductor.
• a cylindrical shield is positioned against the outside of a quartz chamber wall between the wall and a helical coil that encircles the wall and is spaced slightly from the wall.
• the shield preferably has a plurality of closely spaced internal slits extending axially almost the height of the shield, but less than the entire height of the shield, leaving at least one edge of the shield uninterrupted by the slits, thereby leaving at least one circumferential path of uninterrupted metal conductor around almost the entire circumference of the chamber.
• a full height slit or gap interrupts the entire height of the shield, thereby avoiding a continuous 360° circumferential conductive path formed by the shield around the chamber.
• the coil which surrounds the chamber outside of the shield, inductively couples RF energy into the chamber to energize a plasma.
• the shield is preferably grounded at only one point on its circumference, for example, at a point directly opposite or 180° from the full height gap.
• the gap, as well as the internal slits are approximately 1/8 inch wide, with strips of the metallic portion of the shield being about 1/8 inch wide between the slits and gap.
• a peak-to-peak voltage develops across the coil.
• the energization of the coil couples an RF voltage onto the shield which results in a peak-to-peak voltage developing across the narrow full height gap.
• the shield is grounded diametrically opposite the gap, the voltages on the opposite edges of the shield bordering the gap are equal and opposite relative to ground potential.
• This peak-to-peak voltage may be several thousand volts, for example, 5000 volts RF, peak-to-peak.
• This voltage produces a strong RF electric field that extends through the quartz chamber wall and into the chamber where, within a time interval in the order of one or a few milli-seconds, it ignites a plasma opposite the gap inside the chamber.
• the plasma once ignited, propagates, also in a time interval in the order of a milli-second, around the perimeter of the chamber inside of and close to the chamber wall, where the plasma forms a belt of conductive ionized gas around the circumference of the chamber inside of the chamber.
• this plasma belt forms the voltage across the gap of the shield quickly drops to a nominal voltage in the order of 10 to 20 volts, for example, 14 volts, peak-to-peak.
• a plasma is formed that fills the chamber with very low capacitive coupling of voltage from the coil to the plasma, resulting in a low plasma potential and small plasma sheath between the plasma and the circumferential quartz side wall of the chamber.
• the shield couples energy form the coil to quickly ignite a plasma upon the initial energization of the coil.
• Fig. 1 is a side view of a sputter etching apparatus, partially broken away, embodying principles of the present invention.
• Fig. 2 is a top view, partially in cross-section, of the apparatus of Fig. 1.
• Fig. 1 illustrates a plasma etching apparatus 10 having a base 11 to which is sealed a quartz bell jar 12 having a circumferential side wall 13 and an integral top 14.
• the sidewall 13 is typically approximately 15 to 16 inches in diameter and about 3/8 inches thick.
• the bell jar 12 has a lip 13a which is sealed to the base 11 to provide a vacuum tight chamber 15 in which is processed a substrate, such as a wafer 16, supported on a substrate support 17.
• the bell jar 12 and support 17 are centered on an axis of symmetry 19 of the chamber 145 and sidewall 13.
• a helical coil 20 Surrounding the cylindrical side wall 13 of the bell jar 12, spaced a close distance of 1/16 to 1/4 inches, preferably about 1/8 inches, from the outside of the wall 13, is a helical coil 20.
• the coil 20 is connected across an RF generator 21 which operates to energize the coil with RF energy preferably at a medium frequency of, for example, 460 KHz.
• the coil 20 in the illustrated embodiment is grounded at its center 22.
• the coil 20 when energized, couples RF energy into the chamber 15 to support a plasma for etching the substrate 16 on the support 17.
• a Faraday shield 30 Also surrounding the cylindrical side wall 13 of the bell jar 12 and preferably in close proximity to or in contact with the outer surface of the wall 13 is a Faraday shield 30.
• the shield 30 is formed of a conductive sheet metal material and forms a loop that surrounds the wall 13 inside of the coil 20 which is spaced by a cylindrical space 29 from the shield 30.
• the shield 30 substantially surrounds the wall 13 but for a narrow gap 31 along one side of the wall 13 about 1/8 inches wide.
• the gap 31 is disposed parallel to the axis 19 of the cylindrical sidewall 13 of the bell jar 12.
• the gap 31 completely interrupts current paths around the circumference of the shield except for a small amount of capacitive conductivity of the RF energy across the gap 31.
• the shield 30 is also provided with a plurality of slits 32 that are separated by conductive strips 33, each about 120 in number and of approximately equal width.
• the slits 32 are disposed parallel to the gap 31 and parallel to the axis 19 of the chamber 15.
• the slits 32 each have a length which is approximately 1/4 inch less than the height of the shield 30, which in turn is preferably greater than the height of the coil 20.
• the conductive strips 33 each connect at their upper end to a horizontal band 33a and at their lower end to a horizontal band 33b, which bands each completely encircle the bell jar except where they are interrupted by the upper and lower ends of the gap 31.
• the shield 30 is grounded at a single angular position 34 on its circumference, preferably diametrically opposite the gap 31.
• a circumferential RF current is induced in the shield 30 which is accompanied by a voltage that is neutral at the ground point 34 but is in the order of magnitude of 1000 peak-to-peak volts across the gap 31.
• This peak-to- peak voltage is further accompanied by an RF electrical field 35 at the gap 31 which extends through the wall 13 in the vicinity of the gap 31 into the chamber 12.
• the electrical field 35 across the gap 31 on the inside of the chamber wall 12 ignites a plasma in the vicinity of the gap 31 within a millisecond or so after the coil 20 is first energized.
• This plasma results in the production, within a millisecond or so after plasma ignition, of a sheath of electrons about 2 centimeters in width encircling the chamber 12 and oscillating at the frequency of the RF energy, immediately inside of the cylindrical side wall 13, whereupon the voltage across the gap 31 drops to a voltage in the range of from 10 to 20 volts.
• a plasma quickly fills the chamber 12.
• the shield 30 effectively reduces or substantially eliminates capacitive coupling of energy from the coil 20 to the plasma in the chamber 12 that would impart a high potential and a correspondingly large surrounding plasma sheath to the plasma in the chamber 12. As a result, plasma etching of the quartz bell jar 12 is minimized.
• the shield 30 does so without interfering with the ignition of the plasma, and rather, functions to quickly and efficiently ignite a plasma in the chamber 12 upon the energization of the coil 20.
• An apparatus for plasma processing a substrate comprising: a vacuum chamber having a dielectric wall; an inductor positioned outside of the chamber in proximity to the wall; an RF energy source connected to the inductor; a Faraday shield positioned between the inductor and the wall, the shield being in the shape of a loop having opposite ends and a circumference interrupted by at least one gap bordered by the opposite ends of the shield, whereby the opposite ends of the shield are in close proximity to each other across the gap; the shield having a localized ground connection that allows RF current induced around the loop to develop a peak-to-peak voltage across the opposite ends of the loop and the gap that is sufficiently high, when no RF plasma is present in the chamber, to produce a plasma igniting electric field adjacent the gap inside of the wall of the chamber.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Power Engineering (AREA)
• Plasma Technology (AREA)
• Drying Of Semiconductors (AREA)

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Applications Claiming Priority (2)

Publications (1)

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Cited By (4)

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Citations (4)

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• 1999
  • 1999-02-19 US US09/255,613 patent/US6248251B1/en not_active Expired - Lifetime
• 2000
  • 2000-01-27 JP JP2000600289A patent/JP5123446B2/ja not_active Expired - Fee Related
  • 2000-01-27 KR KR1020017010541A patent/KR100794423B1/ko not_active Expired - Fee Related
  • 2000-01-27 WO PCT/US2000/002032 patent/WO2000049638A1/en not_active Ceased

Patent Citations (4)

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