JP2006528731A - High peak power plasma pulse power supply by arc handling - Google Patents

Abstract

A magnetron sputtering system is provided that includes a pulsed DC power supply with a peak power density greater than 1 kW / cm ² and the ability to supply peak power from 0.1 MW to several MW. Highly ionized sputtering plasma is generated without first arcing. The power supply includes a pulse circuit, which is connected in series with an energy storage capacitor and an inductor having a switch means for isolating the pulse circuit from the plasma, which means also detects arc conditions And recycle inductor energy into energy storage capacitors. The energy storage capacitor and the inductor connected in series supply an impedance commensurate with the plasma, limit the rising speed of the current and the magnitude of the peak during arcing, and shape the voltage pulse to the plasma.

Description

(Field of Invention)
The present invention relates generally to a magnetron sputtering apparatus and method, and more particularly to a magnetron sputtering apparatus that uses arc handling capabilities to provide high peak power to a sputtering magnetron plasma load.

(Simple explanation of the prior art)
It is desirable to generate metal ions, apply an electrical bias, attract the ions to the workpiece, and coat the substrate. The utility of this approach is the application of surface coatings with irregularities that can impede uniform deposition by normal sputtering (which basically requires a line of sight from the sputtering source to the workpiece form). is there. Filling high aspect ratio trenches with semiconductor devices as well as deposited coatings is possible by biasing the wafer and attracting ions. This is described by Monteiro, JVST B 17 (3), 1999 pg. 1094, and Lu and Kusner, JVST A 19 (5), 2001 pg. 2652.

  Sputter deposition can be facilitated utilizing a plasma in a highly ionized state. A method of operating a conventional sputtering magnetron and generating a highly ionized and dense metal plasma with electrical pulses having high peak power and low load time ratio is described by Kouznetsov et al., Surface and Coatings Technology 122 (1999). ) Pg. 290. Further teachings can be found in Macak et al., JVST A 18 (4), 2000 pg. 1553, Gumdundsson et al., APL, Vol. 78, no. 22, 28 May 2001, pg. 3427 and Ehiasarian et al., Vacuum 65 (2002) p. 147 can also be found.

  US Pat. No. 6,296,742 B1 describes a method for generating a fully ionized plasma for magnetron sputtering. A pulse generator generates pulses up to 10 MW at the sputtering target. As a result, the sputtering gas is completely ionized. In this way, the sputtering gas first takes the form of a glow discharge state, then into an arc discharge state, and finally into a fully ionized state. As shown in FIG. 1 of that patent, the arc discharge state can be described as a breakdown state that occurs when the current density in the abnormal glow discharge region is exceeded, and when the current density becomes higher, the plasma voltage Is characterized by a sudden drop in plasma impedance as shown by the sudden drop. In practical systems, it is usually indicated by a voltage drop in a plasma of no more than a few tens of volts and can be accompanied by a discharge between a portion of the sputtering target and the chamber. The '742 patent points out that, based on the teachings of this patent, the plasma is fully ionized after passing through this arc region.

  Part of the appeal of these technologies is the ability to attract a workpiece by generating a large population of ionic species and applying its bias voltage. The above references on high peak power technology appear to use just a capacitor discharge through an inductor. However, the techniques taught in these references do not disclose any handling performance, and in fact, once a fully ionized state is obtained, arc-free operation can be achieved thereafter. It suggests that. It is inevitable that there will be incomplete points in terms of hardware, but this theory suggests that a completely arc-free region is physically realized during operation (after passing the first arc state). Despite being done, it is basically impossible. It seems impractical to use this technology, that is, to use it commercially without arc handling performance. In addition, since it may take a long time to set the target condition in order to operate in a state close to arc-free at the minimum, it may take a long processing time. Since the target cannot be properly conditioned, operation at the highest power level may be avoided. Thus, with high peak power pulses, a magnetron that produces a dense, highly ionized plasma that minimizes arc energy while still allowing acceptable product and target damage from the arc. Desirably, an apparatus is provided. Considering that the arc state is passed at the start of pulse generation, and that damage can occur, it is highly desirable to avoid the occurrence of the arc state at the beginning of the highly ionized state.

  A typical arc conditioning and diverting device consists of either a circuit that detects the arc and disconnects the power source from the load, or a switch circuit that substantially shorts the power source to extinguish the arc. It was. These types of arc handling methods are very expensive. The reason is that it is necessary to completely turn off the power of the process, waste expensive stock materials, or completely dissipate all the energy stored in the power supply circuit. When used at high power, a short circuit in the power supply can generate very high currents—which may be sufficient to destroy the power supply itself—and to repeatedly dissipate the stored energy, In any case, not only expensive resistive elements for high peak power and high average power, but also a method for cooling them is required.

  Furthermore, it is also desirable to provide a magnetron sputtering apparatus and method that can generate peak power of 1 MW or more, can achieve high yield in commercial use, and has excellent arc handling capability. One of the objects of the present invention is to provide a magnetron sputtering plasma system that has the ability to both detect an arc and perform an action that limits the energy supplied to the arc. It is a further object of the present invention to avoid transient arcing of individual pulses without first being in an arced state, and thus not potentially damaging the chamber, substrate or target. It is to provide a system that generates a magnetron sputtering plasma that is highly ionized without such a situation.

(Outline of the present invention)
The present invention provides an apparatus and method for generating a high current pulse suitable for applying high peak power to a high-density magnetron plasma having excellent arc handling capability. In one embodiment of the present invention, a pulse circuit comprising an energy storage capacitor is repeatedly charged and discharged through an inductor in series with the plasma. The combination of inductor and capacitor contributes to pulse shaping, which has three functions. First, it has been found that initial arc conditions can be avoided by appropriately shaping the pulse. This is done by adjusting the beginning of the voltage pulse. In one embodiment, a network is added to control the voltage rise rate, control the unclamped peak amplitude of the pulse voltage if the plasma does not ignite, and the frequency at which the voltage waveform rings, Control is performed particularly when plasma does not ignite. This circuit according to this embodiment corresponds to a resistor in series with a capacitor short-circuited on the output side of the pulsar, or equivalent to that realized as a distributed circuit consisting of many discrete capacitors and resistors. To do. Parasitic capacitors and resistors can also be used in devices and circuit conductors. In addition, the circuit clamps or limits the voltage pulse to the maximum level and works with a diode, which is normally reverse biased in series with a capacitor held at the clamp voltage and is connected to the output of the pulsar. Connected. This circuit is activated when the amplitude of the voltage pulse exceeds an adjustable set value and serves to prevent the voltage from exceeding the set value. This is advantageous in that it can prevent unwanted arcing inside and outside the vacuum chamber. All this makes it possible to achieve a highly ionized plasma state without first being in an arc state.

  Second, the pulse network or mesh is responsible for providing an impedance commensurate with the plasma. Thirdly, this network plays a role in suppressing the rising speed and peak amplitude of the current when a subsequent arc occurs. An arc can be detected during a pulse when the discharge voltage drops and falls below the set voltage threshold, or when the discharge current increases and rises above the set current threshold. Note that the arc condition represents a reduction in the impedance of the plasma and is also expressed by the ratio of voltage and current, ie, a method of detecting one or both is useful. When an arc is detected, the energy storage capacitor disconnects the inductor in series to stop the increase in current. The pulse circuit is disconnected from the plasma load and the inductor energy is recycled to the energy storage capacitor.

  In a typical sputtering plasma, in the glow or abnormal glow state, the ratio of ionic species is relatively low, at most on the order of a few percent. If the present invention is used, the sputtering plasma in a highly ionized state can achieve an ionization ratio of 10% or more. Even in sputtering systems where the ionization ratio is usually very low, such as a carbon sputtering system, a highly ionized plasma uses the present invention to increase the proportion of ionic species in the plasma by more than five times. That can be achieved.

  By using the apparatus and method of the present invention, a highly ionized sputtering plasma can be generated without first taking an arc discharge state. The arc handling features of the present invention help to mitigate and extinguish arcs that occur while the sputtering plasma is present.

(Detailed explanation)
FIG. 1 illustrates one embodiment of a magnetron plasma processing system 10. The DC power source 12 is connected to the magnetron plasma processing chamber 14 via the pulse circuit 16. The magnetron plasma processing chamber may be a conventional magnetron chamber having a magnetron cathode 18 and an anode 20 well known to those skilled in the art. When performing sputtering, the material target serves as the cathode 18. Pulsed DC power supply 16 is available from Advanced Energy Industries, Inc. A type such as the MegaPulser ^TM model made by the manufacturer may be used, and a high voltage pulse is applied between the cathode 18 and the anode 20 to ignite the plasma 22 between the electrodes. The plasma acts on the material of the cathode 18 so that the substrate 26 in the chamber is coated. This is done by making ions from the plasma 22 collide with the material target, ie, the cathode 18. As a result, the atoms sputtered from the target are deposited on the surface of the substrate 26. The embodiment of FIG. 1 also includes a smaller optional dc power supply 28. This is a power source for keeping the plasma ignited and maintaining the magnetron at the lowest voltage even during the high voltage pulse from the pulse circuit 16. This power supply can also be used to ignite the plasma from the beginning before starting operation with high pulses.

A magnetron treatment chamber, when providing a high voltage pulse, the pulse circuit 16, the inductor L _1, consisting of the energy storage capacitor C ₁ connected in series through a switch S _1. Inductor L ₁ is via the switch S _2, is connected to the cathode of the magnetron.

FIG. 2 shows waveforms when the circuit is normally operated. During the entire sequence, _{S 2} is closed, _{S 3} is open. Capacitor C ₁ is charged to its initial voltage by dc power supply 12. Discharging starts with S ₁ and capacitor C ₁ is discharged to the plasma load through inductor L ₁ . The control circuit starts the timing of the switch for controlling the charge time of the capacitor C _1, the pulse is discharged to the load. The waveforms of V _c , I _inductor , V _LOAD , and I _load are determined only by the initial value of V _c , the C ₁ value and the L ₁ value, and the characteristics of the plasma load and the output cable.

FIG. 3 is a typical waveform of an arc generated during one pulse from the pulse circuit 16. The sequence is shown in FIG. 2 and starts as described above, but when an arc occurs, the current value increases and the voltage decreases until the arc is detected. The arc is detected in one or two ways. The specific circuit techniques necessary to implement the arc detection method are well known to those skilled in the art. One method can detect an arc when the load current exceeds a set threshold. This threshold can be updated to suit the actual situation by predicting the output current for each pulse. The output current is predicted based on the plasma load characteristics and the initial values of V _c , the C ₁ value, and the L ₁ value, and a margin for preventing erroneous detection is added. The prediction of output current based on these parameters is well known to those skilled in the art. Alternatively, the current threshold may be based on the average peak current plus a margin to prevent false arc detection. At this time, it is desirable to exclude pulses with a high arc current from the average value calculation. Another method is detected when the load voltage falls below a set threshold. That is when the load current exceeds a second current threshold, which is used only in this second method. If an arc is detected, S ₁ opens immediately, S ₃ is closed with a slight delay, S ₂ opens then a slight delay. This blocks the load from the pulse circuit 16, starts the energy of resonant transfer from the inductor _{L 1} to the capacitor _{C 1} (resonant transfer). As a result, during the arc generation, the energy in the inductor L ₁ is recycled in the capacitor C _1. This arc handling sequence minimizes the energy delivered to the load during the arc. If the arc handling Preparation (Provisions) is, and energy stored in C _1, the energy stored in L ₁ to flow in the arc, the target and the workpiece, it would be damaging almost certainly. Preparing for arc handling makes it possible to use this method commercially.

The present embodiment shown in FIG. 1 also has a circuit configuration for shaping a voltage pulse supplied to the magnetron plasma. The ring-up circuit 30 is prepared for the purpose of adjusting the voltage rising speed of the pulse, the magnitude of the voltage pulse, and the frequency with which the voltage waveform rings. Ring-up circuit 30 includes a capacitor C ₂ in series with resistor R ₁ which is short-circuited to the power source output. A ring-up circuit can be applied as a discrete capacitor or distributed network of resistors, and can be used as a parasitic capacitance or resistance found in other circuit elements and configurations of the device. By shaping the voltage pulse supplied to the plasma using the ring-up circuit, the arc generation accompanying the start of the pulse can be eliminated, and the arc state is not entered during the start of the pulse.

The voltage pulses generated from the embodiment of FIG. 1 are also shaped and adjusted by the clamp circuit 32. The clamp circuit includes a reverse-biased diode D ₃ in series with a combination of a capacitor C ₃ in parallel with a clamp power supply 34. The clamp circuit 32 works so that the voltage level of the pulse does not reach a predetermined maximum value level. By limiting the pulse voltage, the clamp circuit prevents the arc condition from becoming large when the voltage runaway occurs, for example, when the pulse voltage increases due to parasitic capacitance at the power supply output. Thus, the clamp voltage can be set to a value high enough that the plasma can reach a highly ionized state, but not to an arc condition due to overvoltage.

  FIG. 4 illustrates the operation of a magnetron plasma processing system to generate a sputtering plasma in a highly ionized state without first being in an arc discharge state. Shown in FIG. 4 is the change of the sputtering plasma voltage, current, and impedance characteristics with respect to time during the passage of one pulse wave during device operation. The pulse DC power supply first applies a large negative voltage exceeding minus 1800 V to the material target (cathode) of the sputtering system. When the plasma is generated, the current increases through the plasma and reaches a level close to minus 400A. At this point, the plasma is in a highly ionized state. When a pulse lasting about 150 microseconds passes, the voltage does not drop suddenly to a level of tens of volts. This may be a characteristic of the arcing condition. The plasma state can also be understood by referring to the plasma impedance. When plasma is generated, the plasma impedance is initially high, but then settles to a nearly constant value of about 3.5Ω. At the end of the pulse, the impedance rises again abruptly as the current drops back to zero. The plasma impedance never drops sharply to an arc level, i.e. well below the steady state level of about 3.5Ω.

  The present invention thus provides a new high peak power plasma pulsed power supply for magnetron sputtering with arc handling that minimizes arc damage. The present invention can do this by preventing the arcing state before entering the highly ionized state, adjusting the initial pulse, further cutting off the pulse circuit from the plasma load, and the arc conditions. This is because when the current is detected, it returns to the energy storage capacitor to recycle the inductor energy stored for the high peak power pulse. This arc condition occurs once a highly ionized state occurs.

  While this application illustrates and describes specific construction and details of operation, these descriptions are exemplary and alternative embodiments and equivalents are within the spirit and scope of the invention. It should be understood that things can also be easily made by those skilled in the art. Accordingly, the present invention is intended to embrace all such alternative embodiments and equivalents that are within the spirit and scope of the appended claims.

FIG. 1 shows a schematic diagram of a magnetron plasma processing system incorporating the principles of the present invention. FIG. 2 shows waveforms during normal operation of the magnetron plasma processing system shown in FIG. FIG. 3 shows waveforms during arc handling operation. FIG. 4 shows the current, voltage, and impedance characteristics of the sputtering plasma during operation of the magnetron plasma processing system.

Claims (12)

A sputter deposition method comprising:
a) providing a plasma chamber having a sputtering gas disposed therein;
b) providing a material target disposed in the plasma chamber;
c) providing a pulsed DC power supply that periodically applies voltage pulses to the material target, the voltage pulses ionizing the sputtering gas for plasma generation, and the plasma is first arced It becomes a highly ionized state without becoming a discharged state,
d) Sputtering atoms from the target by bombarding the material target with ions from the plasma, wherein the atoms are deposited on the substrate surface proximate to the plasma. And a method comprising. The method of claim 1, wherein the pulsed DC power source applies power greater than 0.1 MW with a peak power density greater than 1 kW / cm ² .   The method of claim 1, wherein by controlling the voltage rise rate of the voltage pulse applied to the material target, the plasma is in the highly ionized state without first being in an arc discharge state.   4. The method of claim 3, wherein the voltage rise rate of the voltage pulse is controlled using a circuit with a resistor connected in series with a capacitor.   The method of claim 1, wherein by limiting an amplitude of the voltage pulse to a maximum level, the plasma is in the highly ionized state without first being in an arcing state.   6. The method of claim 5, wherein the amplitude of the voltage pulse is limited using a circuit with a resistor connected in series with a capacitor.   6. The method of claim 5, wherein the amplitude of the voltage pulse is limited using a circuit comprising a reverse bias diode, a capacitor, and a clamp voltage power supply. A sputter deposition system,
a) a plasma chamber having a sputtering gas therein;
b) a material target placed in the plasma chamber;
c) a pulsed DC power supply that periodically applies a voltage pulse to the material target, the voltage pulse ionizing the sputtering gas for highly ionized plasma generation;
d) A sputter deposition system comprising: a pulse shaping circuit that shapes a voltage pulse so that the plasma can be in a highly ionized state without first being in an arced state.   The sputter deposition system of claim 8, wherein the pulse shaping circuit controls the voltage rise rate of the voltage pulse.   The sputter deposition system of claim 9, wherein the pulse shaping circuit comprises a resistor connected in series with a capacitor.   The sputter deposition system of claim 8, wherein the pulse shaping circuit limits an amplitude of the voltage pulse to a maximum level.   The sputter deposition system of claim 11, wherein the pulse shaping circuit comprises a reverse biased diode, a capacitor, and a clamp voltage power source.

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