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
  • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
  • H01J37/304—Controlling tubes by information coming from the objects or from the beam, e.g. correction signals
• • 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
  • H01J2237/30—Electron or ion beam tubes for processing objects
  • H01J2237/31—Processing objects on a macro-scale
  • H01J2237/3142—Ion plating
  • H01J2237/3146—Ion beam bombardment sputtering

Definitions

• This invention relates to a novel ion beam vacuum sputtering apparatus for deposition of thin films of sputtered material upon a substrate and to a novel method of effecting ion beam vacuum sputtering. DESCRIPTION OF THE PRIOR ART
• Vacuum sputtering is a well established method for deposition of thin films of sputtered material upon a substrate.
• a beam of ions is fired at a target in a vacuum chamber which is typically maintained at a pressure in the range of from about 10 "5 millibar (about 10 " " Pa) to about 10 "3 millibar (about 10 "2 Pa)
• the resulting impact of the ions against the target causes atoms of the target material to be ejected therefrom and to deposit upon the surface of a substrate, such as a silicon wafer, or a ceramic, metal or glass substrate, positioned in the path of the sputtered atoms.
• Thin film deposition equipment is traditionally controlled by control of time and power. This approach assumes that time dependent variations within the process average out so as to nullify any overall effects. Both for ultra thin films and multilayer complex optical structures this approach is inadequate.
• Shutters are often used to start and stop the deposition of thin films. However, these devices tend to act in a somewhat arbitrary manner and lead to unsatisfactory results. Thus the traverse of the shutter can destroy the film thickness uniformity of ultra thin films, and the repeatability within thicker complex multi-layer structures. In vacuum sputtering it is desirable to control the material deposition flux. This is normally dependent upon the stability of a number of key parameters within the system. While time can normally be accurately monitored and measured, the delivered power stability is limited to typically the order of about 1%. The desired repeatability for thin film applications can be perhaps ten times smaller than the limit dictated by the power supply stability.
• BIBD Broad ion beam deposition
• a range of BIBD systems is commercially available from Nordiko Limited of Hayward Business Centre, New Lane, Havant, Hampshire P09 2NL for the deposition of ultra thin films and for building complex multi-layers.
• These BIBD systems utilise a unique form of r.f. excited broad beam ion source, which is further described in International Patent
• This ion beam source is an efficient device which typically yields about 1 mA of current output for each r.f. watt of input power. However, since a typical current output used lies in the region of from about 200 to about 500 mA, a 1% variation in delivered r.f. power can result in a less than desirable variation in current and ultimately the deposition flux.
• the substrate or substrates is or are loaded and any pre-clean procedure is run.
• the mechanical substrate shutter is closed. 3.
• the deposition ion source will normally be in an idle mode, i.e. the discharge is on but an energetic ion beam is not extracted.
• the invention further seeks to provide a novel sputtering apparatus which enables significantly improved control of the material deposition flux compared with prior art devices .
• a vacuum sputtering apparatus for depositing a thin film of sputtered material on a substrate, the apparatus comprising: a vacuum chamber for containing: a target from which material is to be sputtered; and a substrate upon which material from the target is to be deposited; an ion gun for projecting a beam of ions towards the target, the ion gun including: a plasma generation chamber for generation of a plasma therein; gas admission means for admission to the plasma generation chamber of a gas from which the plasma is to be generated; r.f. coil means for supplying r.f.
• the extraction means including an accelerator grid; r.f. power supply means for supplying r.f. power to the r.f. coil ; d.c. voltage supply means for supplying a d.c. voltage to the accelerator grid to cause extraction of ions from the plasma generation chamber and acceleration thereof in a beam towards the target; and means for deriving from the current flowing from the d.c. voltage supply means to the accelerator grid a control signal for controlling the r.f. power supply means.
• the invention further provides a method of effecting vacuum sputtering of a material from a target onto a substrate in a vacuum chamber so as to deposit a thin film of sputtered material on the substrate, which method comprises: providing an ion gun for projecting a beam of ions towards the target, the ion gun including: a plasma generation chamber for generation of a plasma therein; gas admission means for admission to the plasma generation chamber of a gas from which the plasma is to be generated; r.f. coil means for supplying r.f.
• the extraction means including an accelerator grid; supplying r.f. power to the r.f. co l from an r.f. power supply means; supplying a d.c. voltage from a d.c. voltage supply means to the accelerator grid to cause extraction of ions from the plasma generation chamber and acceleration thereof m a beam towards the target; and deriving from the current flowing from the d.c. voltage supply means to the accelerator grid a control signal for controlling the r.f. power supply means.
• FIG. 1 is a diagram of a vacuum sputtering apparatus embodying the present invention.
• Figures 2 to 6 are circuit diagrams of different forms of control circuit for controlling the operation of the vacuum sputtering apparatus of Figure 1.
• the present invention provides a vacuum sputtering apparatus for depositing a thin film of sputtered material on a substrate.
• This apparatus comprises a vacuum chamber for containing a target from which material is to be sputtered and a substrate upon which material from the target is to be deposited.
• the vacuum chamber also contains an ion gun for projecting a beam of ions towards the target.
• the ion gun includes (i) a plasma generation chamber for generation of a plasma therein, (ii) gas admission means for admission to the plasma generation chamber of a gas from which the plasma is to be generated, (iii) r.f. coil means for supplying r.f.
• the extraction means includes an accelerator grid.
• the apparatus also includes r.f. power supply means for supplying r.f. power to the r.f. coil, and d.c. voltage supply means for supplying a d.c. voltage to the accelerator grid to cause extraction of ions from the plasma generation chamber and acceleration thereof in a beam towards the target. It also comprises means for deriving from the current flowing from the d.c. voltage supply means to the accelerator grid a control signal for controlling the r.f. power supply means.
• the method of the invention involves effecting vacuum sputtering of a material from a target onto a substrate in a vacuum chamber so as to deposit a thin film of sputtered material on the substrate.
• Such a method comprises providing an ion gun of the type described in the preceding paragraph for projecting a beam of ions towards the target.
• r.f. power is supplied to the r.f. coil from an r.f. power supply means
• a d.c. voltage is supplied from a d.c. voltage supply means to the accelerator grid to cause extraction of ions from the plasma generation chamber and acceleration thereof in a beam towards the target.
• control signal generator means comprises resistance means connected in series between the d.c. voltage supply and the accelerator grid and differential amplifier means whose input is connected across the resistance means and whose output provides a control signal which is representative of the current flowing between the d.c. voltage supply and the accelerator grid.
• a control signal may be supplied to a host computer system which is arranged to perform current/time integration and to control the operation of the r.f. power supply means.
• the control signal may be supplied to the r.f. power supply means for direct closed loop accelerator grid current control and stabilisation.
• control signal generator means comprises resistance means connected in series between the d.c. voltage supply and the accelerator grid, differential amplifier means whose input is connected across the resistance means and whose output provides a control signal which is representative of the current flowing between the d.c. voltage supply and the accelerator grid, voltage divider means for providing a voltage signal whose voltage is intermediate between the voltage of the d.c. voltage supply and earth potential, amplifier means for conditioning and amplifying the voltage signal from the voltage divider means whose output provides a signal representative of the accelerator grid voltage, and multiplier integrated circuit means which receives as inputs the outputs from the differential amplifier means and from the amplifier means and whose output provides a control signal which is representative of the power supplied to the accelerator grid.
• control signal can be supplied to a host computer system which is arranged to perform accelerator grid power/time integration and to control the operation of the r.f. power supply means.
• control signal can be supplied to the r.f. power supply means for direct closed loop accelerator grid power control.
• control signal generator means further comprises : second resistance means connected in series between a second d.c. voltage supply and a second accelerator grid of the ion gun; and second differential amplifier means whose input is connected across the second resistance means and whose output provides a control signal which is representative of the current flowing between the second d.c. voltage supply and the second accelerator grid and which is also supplied to the host computer system.
• a vacuum sputtering apparatus preferably further comprises shutter means in the vacuum chamber between the target and the substrate and movable between a first position in which the shutter means shields the substrate from material sputtered from the target and a second position in which it permits material sputtered from the target to reach the substrate, whereby with the shutter means in its first position the parameters for the ion beam can be established and verified, whereafter the d.c. power supply to the accelerator grid can be turned off, and whereby with the shutter means in its second position the d.c. power supply to the accelerator grid can be turned back on again to effect extraction of ions from the plasma generation chamber to form an ion beam and to cause material to be sputtered from the target and to be deposited upon the substrate.
• a surface of the target is so positioned in the vacuum chamber of the apparatus of the invention that the ion beam impinges upon it at an oblique angle whereby material ejected from the target travels along a path which is directed away from that of the ion beam.
• the ion beam strikes the target at an angle to its surface of from about 30° to about 60°, for example about 45°.
• the substrate is preferably so positioned that material ejected from the target strikes it an angle which is normal to the surface of the substrate or at an angle which is oblique to the surface of the substrate.
• Such an oblique angle can correspond to an angle to the direction normal to the surface of the substrate of up to about 50°, for example an angle of from about 30° to about 45° to the direction normal to the surface of the substrate.
• the orientation of the substrate relative to the path of material sputtered from the target can be selected so as to optimise the uniformity of deposited material or to optimise the directionality of deposition.
• the substrate is mounted upon a substrate table, which is typically arranged so as to be rotatable.
• the table is preferably rotatable at up to many hundred rpm, e.g. up to about 1000 rpm or higher. In many cases, however, it will suffice for the table to be rotatable at a speed of up to about 30 rpm, eg from about 5 rpm up to about 20 rpm.
• ion current integration In broad beam ion deposition (BIBD) there is a glow discharge generation system that produces an abundance of positive ions within a semi-closed volume. On one side of this volume is a perforated structure comprising a number of apertures within an ion accelerator.
• BIBD broad beam ion deposition
• the current output of the source is dependent upon the concentration of ions generated in the glow discharge and the voltages applied to the extraction system.
• the voltage applied from the extraction bias supplies from the switched mode d.c. power supplies is very stable.
• the power delivered from the solid state r.f. power supplies is less stable and it is the resulting variation in power input that caused problems in the prior art systems.
• the current output from the ion source, and hence the ion flux also varies; this in turn leads to variability in the sputtered material flux.
• the required current and the predicted deposition time are determined and then the current is integrated during the deposition enabling the total number of delivered coulombs of ions to be tracked.
• the deposition can be terminated upon completion of the next integral revolution of the substrate table.
• the ion current integration can be monitored and an algorithm continuously used to adjust the current to ensure that the correct current dose is delivered at the completion of the desired number of integral table revolutions.
• the accelerator grid current is preferably differentially measured in the ground line (i.e. in the coaxial cable screen) , thereby eliminating the need for high side measuring equipment. This also has the advantage of lower superimposed r.f. ripple levels, and substantially reduced cost. Differential measurement ensures that "common mode" noise effects are rejected, ensuring high signal integrity.
• a vacuum sputtering apparatus 1 comprises a vacuum chamber which is indicated generally in broken lines by reference numeral 2.
• Vacuum chamber 2 is provided with a conventional high vacuum pump (not shown) by means of which vacuum chamber 2 can be evacuated to a low pressure suitable for effecting vacuum sputtering.
• the pressure within vacuum chamber 2 in use is in the range of from about 10 ⁇ 5 millibar (about 10 "4 Pa) to about 10 "3 millibar (about 10 "2 Pa) .
• Ion gun 3 mounted in vacuum chamber 2 is an ion gun 3, which is of the general type disclosed in International Patent Publication No. WO 98/18150, the entire contents of which are incorporated herein by reference.
• Ion gun 3 includes a plasma generation chamber 4, a composite grid structure 5, a substantially flat r.f. induction coil 6, and a plurality of primary bar magnets 7 arranged around the periphery of plasma generation chamber 4 for trapping electrons adjacent the wall of plasma generation chamber .
• Composite grid structure 5 has at least two grids. Thus it may include, as described in International Patent Publication No. WO 98/18150, first, second and third multi-apertured grids positioned in close proximity to one another.
• the first grid is in this case connected to a first positive potential source and contacts the plasma in the plasma generation chamber 2 in use of the vacuum sputtering apparatus 1. Its potential is less than that of the plasma and accordingly acts as an accelerator grid to cause extraction of ions from the plasma generation chamber and acceleration thereof in a beam towards the target.
• the second grid which is next to the first grid, is connected in use of the vacuum sputtering apparatus 1 to a second potential source of lower potential than the first positive potential source. Its function is to produce a first acceleration field for further accelerating ions from the plasma in the plasma generation chamber 4 through the first grid towards and through the second grid.
• the third grid is mounted next to the second grid, on the opposite side thereof from the first grid, and is connected, in use of the apparatus 1, to ground so as to produce a second retarding field forming an electrostatic beamlet collimation system and also preventing electrons from streaming back into plasma generation chamber 2.
• the apertures in the three grids of composite grid structure 5 are aligned one with another so that ions emerging from an aperture in the first grid can be accelerated through a corresponding aperture in the second grid and then pass through a corresponding aperture in the third grid to form a beamlet.
• the resulting plurality of beamlets from the third grid form an ion beam downstream from the third grid.
• This ion beam is represented diagrammatically in Figure 1 by arrow 8 and is arranged to impinge, in use of apparatus 1, on a target 9.
• the first grid typically has a positive potential in the range of from about +500 V to about +2000 V, for example about +1000 V, applied to it, while the second grid has a negative potential in the range of from about -150 V to about -1000 V, for example about -850 V, applied to it, and the third grid is at ground potential .
• the impact of ions in ion beam 8 upon target 9 causes atoms to be ejected from target 9 as indicated by arrow 10.
• a mechanical shutter 11 of conventional type is disposed in the path of atoms sputtered from target 9. When shutter 11 is open the sputtered atoms are deposited as a sputtered layer upon substrate 12.
• Substrate 12 is mounted on substrate table 13 which is arranged so as to be rotatable about axis 14 as indicated by arrow 15.
• substrate table 13 can be rotated at a speed of up to about 30 rpm or more, for example up to many hundred rpm, e.g. 200 rpm.
• Gas for generation of the plasma in plasma generation chamber 4 can be bled in via a suitable inlet, as described in International Patent Publication No. WO 98/18150, as indicated by arrows 16.
• gases for this purpose include Ar, Kr, Xe, 0 2 , C0 2 , N 2 , CH « , C 2 H 6 , C 3 H 8 , Cl 2 , SF 6 , C 2 F 6 , or a C 2 F 6 /CHF 3 mixture.
• a volatile hydrocarbon can be bled in via the inlet.
• a plasma neutraliser (not shown) similar to plasma neutraliser 7 of Figure 1 of International Patent Publication No. WO 98/18150 should be mounted in vacuum chamber 2 to prevent a charge building up on substrate 12.
• FIG 2 is a circuit diagram of the control circuit used for controlling the sputtering apparatus 1 of Figure 1. This circuit is designed to measure differentially the current levels in the ion source accelerator grid. The ion source has two additional grids beyond the accelerator grid.
• a voltage supply 21 provides a constant positive d.c. potential for applying a bias potential to the accelerator grid 22 of the ion gun 3 of the sputtering apparatus 1 of
• FIG. 1 that is to say the grid in contact with the plasma in the plasma generation chamber 4.
• a high precision/high stability resistor 23 is placed in series with the screen of the coaxial d.c. accelerator grid cable 24.
• a second d.c. voltage supply 25 is connected by a coaxial cable 26 to a second accelerator grid 27.
• the third grid 28 is connected by a cable 29 to earth.
• the current flow to the accelerator grid 22 develops a voltage drop across resistor 23.
• the voltage generated across resistor 23 is differentially amplified by amplifier 30.
• the scaled voltage output of amplifier 30, which represents accelerator grid current, i.e. the current flowing between voltage supply 21 and accelerator grid 22, is fed into a host computer control system 31 for accelerator grid current control.
• Host computer control system 31 controls an r.f. power supply unit 32 and also controls the accelerator grid current at a set point value, for which purpose it is provided with an accelerator grid current control set point as indicated by reference numeral
• Host computer control system 31 is connected via an r.f. matching unit 34 to r.f. power coil 6 of ion gun 3.
• r.f. power supply unit 34 is arranged to produce a commercially acceptable high radio frequency, such as 13.65 MHZ or a multiple thereof.
• Host computer control system 31 is also arranged to perform fast current/time integration and thus determine the number of coulombs that have passed from voltage supply 21 to accelerator grid 22.
• the circuit diagram of Figure 3 is similar to that of Figure 2 except that the scaled voltage output of amplifier 30 is fed directly into r.f. power supply unit 32 for direct closed loop accelerator grid current control.
• Reference numeral 35 indicates an accelerator grid current control set point .
• Figure 4 shows a third possible circuit diagram in which like reference numerals indicate like parts to those of Figures 2 and 3.
• a further high precision/high stability resistor 36 is placed in series with the screen of the coaxial cable 26 for the second accelerator grid 27.
• the voltage generated across resistor 36 is differentially amplified by amplifier 37.
• the outputs of amplifiers 30 and 37 are fed into the host computer system 31 which is arranged to perform a calculation of a function of the current i flowing in line 24, of the current i 2 flowing in line 26, and to integrate this with respect to time t:
• this function may be:
• the factor c which is typically an experimentally determined value in the range 0 to 3, is chosen to allow for loss of beam ions to the second grid 27 and the third grid 28 and to allow for a proportion of current i ⁇ being generated by electron attraction.
• the factor c generally varies from one ion gun to another and can be determined for a particular ion gun, for example, by choosing a value for c and a given set of sputtering conditions and measuring the deposited thickness ⁇ x of material for a given number of coulombs as determined by function F above. Then slightly different sputtering conditions are chosen and the thickness ⁇ 2 of material deposited under those conditions for the same number of coulombs is also measured.
• FIG. 5 shows a fourth possible circuit diagram in which like reference numerals have been used to indicate like parts to those of Figures 2 to 4.
• a potential divider including resistors 38 and 39 taps off a portion of the accelerator grid voltage and the resulting signal is conditioned and amplified by amplifier 40.
• the outputs from amplifiers 30 and 40 are fed into a multiplier integrated circuit 41 whose output is a scaled proportion of the accelerator beam power.
• the output from multiplier integrated circuit 41 is then fed to host computer control system 31 which detects the total power transmitted from voltage source 21 to accelerator grid 22 and is arranged to perform accelerator grid power/time integration.
• Figure 6 shows a fifth circuit diagram for controlling the vacuum sputtering apparatus of Figure 1. Again, like reference numerals are used to designate like parts in the circuit diagrams of Figures 2 to 5.
• the output signal from multiplier integrated circuit 41 is fed into the r.f. power supply unit 32 for direct closed loop accelerator grid power control .
• the composite grid structure 5 has been described as having three grids. It is, however, alternatively possible to utilise a composite grid structure that has two grids only or a composite grid structure with four grids.
• the first or accelerator grid which is bathed by the plasma within the plasma generation chamber 2 is typically positively biased in use.
• the positive potential to which the first grid is biased determines the beam voltage and is typically in the range of from about +500 V to about +2000 V.
• the second grid which is on the outer side from the plasma generation chamber 2 from the first grid, is negatively biased, typically to a negative voltage of from about -150 V to about -1000 V.
• the first accelerator grid which is bathed by the plasma within the plasma generation chamber 2 is also typically positively biased and the voltage of this grid defines the beam voltage. Typically this grid is biased to a positive potential of from about +500 V to about +2000 V.
• a second (or first intermediate) grid which is the next grid outward from the plasma generation chamber 2 after the first grid, is biased negatively, typically to a voltage of from about -150 V to about -1000 V.
• a third (or second intermediate) grid which is the next grid outward from the first intermediate grid, is normally also negatively biased, typically at a voltage of from about -50 V to about -500 V.
• the fourth grid is the furthest away from the plasma generation chamber and is typically held at ground potential.
• the second (or first intermediate) grid is tuned to provide the desired beam extraction and minimise the grid current to the second grid.
• the third (or second intermediate) grid is used to tune the beam quality.
• an additional signal can be generated which represents the current flowing in the cable connected to the third grid, in a similar manner to that in which a signal is generated for grid 27 in the circuit of Figure 4.
• This additional signal can also be used as part of a grid power control function or a coulomb integration function in the host computer system 31.
• a substrate 12 is mounted on rotatable substrate table 13, or a plurality of substrates 12 are mounted on respective rotatable substrate tables 13, and placed within vacuum chamber 2. If the substrate or substrates 12 is or are nonconducting, then a plasma neutraliser is also provided within vacuum chamber 2. Vacuum chamber 2 is then evacuated to an appropriate sputtering pressure and any necessary pre- cleaning procedure is run. Next the substrate shutter 11 is closed. The ion gun 3 is powered up in idle mode so that a plasma is generated in plasma generation chamber 4 but with the extraction grids, including accelerator grid 22, turned off so that an energetic ion beam is not extracted from the plasma generation chamber 4.
• the extraction grids including accelerator grid 22, are then turned on and the required parameters for the ion beam 8 are established and verified.
• the extraction voltages, including that supplied by voltage source 21 to accelerator grid 22, are then turned off.
• the shutter 11 is then opened.
• the extraction voltages, including the voltage supplied to accelerator grid 22, are then turned on and the deposition period is started, this being synchronised with the rotation of substrate table 13.
• substrate table 13 is rotated at a speed of from about 10 to about 20 rpm.
• the apparatus of the invention is preferably arranged to operate under the control of software which permits automatic rotational speed adjustment.
• software is adapted so that the operative can enter via a conventional computer keyboard details of the desired deposition time and a proposed rotational speed for the substrate table 13.
• the software then calculates an adjusted rotational speed which will provide an integral number of complete revolutions of the substrate table 13.
• the adjusted rotational rate is calculated according to the algorithm:
• INT(x) returns an integral value of a floating point number.
• the adjusted rotational speed will be: j TM* honored 60 x INT(15 x 30/60)
• the computer software could be programmed so as to permit a search for adjusted rotational speeds for the substrate table 13 to be made within a range of about 25% from the value entered by the operative which will allow an integral number of substrate table revolutions to be made within the desired deposition parameters.
• a search would have found, for example, that a rotational speed of 12 rpm (rather than 14 rpm) would give an integral number of revolutions for the substrate table 13 for a deposition time of 4 minutes 15 seconds.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Physical Vapour Deposition (AREA)
• Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
• Electron Sources, Ion Sources (AREA)

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• 1999
  • 1999-09-17 GB GBGB9922110.3A patent/GB9922110D0/en not_active Ceased
• 2000
  • 2000-09-18 WO PCT/GB2000/003577 patent/WO2001022470A1/en not_active Ceased
  • 2000-09-18 DE DE60035054T patent/DE60035054T2/de not_active Expired - Lifetime
  • 2000-09-18 AU AU74338/00A patent/AU7433800A/en not_active Abandoned
  • 2000-09-18 EP EP00962690A patent/EP1212777B1/en not_active Expired - Lifetime
  • 2000-09-18 AT AT00962690T patent/ATE363726T1/de not_active IP Right Cessation
  • 2000-09-18 JP JP2001525747A patent/JP2003522296A/ja active Pending

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