High-power pulsed magnetically enhanced plasma processing

Magnetically enhanced plasma processing methods and apparatus are described. A magnetically enhanced plasma processing apparatus according to the present invention includes an anode and a cathode that is positioned adjacent to the anode. An ionization source generates a weakly-ionized plasma proximate to the cathode. A magnet is positioned to generate a magnetic field proximate to the weakly-ionized plasma. The magnetic field substantially traps electrons in the weakly-ionized plasma proximate to the cathode. A power supply produces an electric field in a gap between the anode and the cathode. The electric field generates excited atoms in the weakly-ionized plasma and generates secondary electrons from the cathode. The secondary electrons ionize the excited atoms, thereby creating a strongly-ionized plasma. A voltage supply applies a bias voltage to a substrate that is positioned proximate to the cathode that causes ions in the plurality of ions to impact a surface of the substrate in a manner that causes etching of the surface of the substrate.

BACKGROUND OF INVENTION

Plasma processes are widely used in many industries, such as the semiconductor manufacturing industry. For example, plasma etching is widely used in the semiconductor manufacturing industry. There are four basic types of plasma etching processes that are used to remove material from surfaces: sputter etching, pure chemical etching, ion energy driven etching, and ion inhibitor etching.

Sputter etching is the ejection of atoms from the surface of a substrate due to energetic ion bombardment. Pure chemical etching uses a plasma discharge to supply gas-phase etchant atoms or molecules that chemically react with the surface of a substrate to form gas-phase products. Ion-enhanced energy driven etching uses a plasma discharge to supply both etchant and energetic ions to a surface of a substrate. Ion inhibitor etching uses a discharge to provide etchant, energetic ions, and inhibitor precursor molecules that deposit on the substrate to form a protective layer film. It is desirably to increase the uniformity and etch rate of known sputter etching systems.

DETAILED DESCRIPTION

FIG. 1illustrates a cross-sectional view of a known magnetically enhanced etching apparatus100having a radio-frequency (RF) power supply102. The known magnetically enhanced etching apparatus100includes a vacuum chamber104for confining a plasma105. A vacuum pump106is coupled in fluid communication with the vacuum chamber104via a conduit108. The vacuum pump106is adapted to evacuate the vacuum chamber104to high vacuum and to maintain the chamber at a pressure that is suitable for plasma processing. A gas source109, such as an argon gas source, introduces gas into the vacuum chamber104through a gas inlet110. A valve112controls the gas flow to the chamber104.

The magnetically enhanced etching apparatus100also includes a cathode114.

The cathode114is an electrode that is generally in the shape of a circular disk. The cathode114is electrically connected to a first terminal118of a blocking capacitor120with an electrical transmission line122. A second terminal124of the blocking capacitor120is coupled to a first output126of the RF power supply102. The cathode114is isolated from the vacuum chamber104by an insulator128that is used to pass the electrical transmission line122through a wall of the vacuum chamber104.

An anode130is positioned in the vacuum chamber104opposite the cathode114. The anode130is electrically coupled to ground by an electrical transmission line132. A second output134of the RF power supply102is also electrically coupled to ground. An insulator136is used to pass the electrical transmission line132through a wall of the vacuum chamber104in order to isolate the anode130from the vacuum chamber104. The vacuum chamber104can also be electrically coupled to ground.

A pair of magnets140is positioned outside the chamber104to generate a magnetic field142in a direction that is substantially parallel to the top surface of the cathode114. A substrate144is disposed on the cathode114.

In operation, the substrate144to be etched is positioned on the cathode114. The chamber104is sufficiently evacuated to high vacuum by the vacuum pump106. The etching gas from the gas source109is introduced into the chamber104through the gas inlet110. The RF power supply102applies high-frequency radiation at 13.56 MHz through a blocking capacitor120to the cathode114.

The high-frequency radiation applied to the cathode114creates a high-frequency electric field146in a direction that is perpendicular to the top surface of the cathode114. The magnetic field142and the high-frequency electric field146intersect each other in a region148above the substrate144. Electrons are trapped in the region148and collide with neutral atoms from the etching gas. These collisions generate a high-density plasma105. The negatively biased cathode114attracts positively charged ions in the plasma105with sufficient acceleration so that the ions etch a surface of the substrate144.

The RF power applied between the cathode114and the anode130has sufficient amplitude to ionize the etching gas and create the plasma105in the vacuum chamber104. The plasma consists of positive ions and negative electrons. A typical RF driving voltage is between 500 V and 5000 V, and the distance 138 between the, cathode114and the anode130is about 70 mm. Typical pressures are in the range 10 m Torr and 100 m Torr. Typical power densities are in the range of 0.1 W/cm2to 1 W/cm2. Typical plasma densities are 109cm−3−1011cm−3, and the electron temperature is on the order of 3 eV.

The ionization process that generates the plasma105for sputter etching is sometimes referred to as direct ionization or atomic ionization by electron impact and can be described as follows:
Ar+e−→Ar++2e−
where Ar represents a neutral argon atom in the etching gas and e−represents an ionizing electron generated in response to the voltage applied between the cathode114and the anode130. The collision between the neutral argon atom and the ionizing electron results in an argon ion (Ar+) and two electrons.

The plasma discharge is maintained by secondary electron emission from the cathode114. However, typical operating pressures must be relatively high so that the secondary electrons are not lost to the anode130or the walls of the chamber104. These pressures are not optimal for most plasma processes including plasma etching.

The electrons, which cause the ionization, are generally confined by the magnetic fields produced by the magnets140. The magnetic confinement is strongest in a confinement region148where the magnetic field lines are parallel to the surface of the electrode. Generally, a higher concentration of positively charged ions in the plasma is present in the confinement region148than elsewhere in the chamber104. Consequently, the substrate144is etched more rapidly in areas directly adjacent to the higher concentration of positively charged ions. The rapid etching in these areas results in undesirable non-uniform etching of the substrate144.

Dramatically increasing the RF power applied to the plasma alone will not result in the formation of a more uniform and denser plasma that improves the etching uniformity. Improved etching will not occur because the magnetic field will be non-uniform across the electrode and the magnetic field distribution around the electrode will be insufficient to confine the electrons. Furthermore, the amount of applied power that is necessary to achieve a significant increase in uniformity can increase the probability of generating an electrical breakdown condition leading to an undesirable electrical discharge (an electrical arc) in the chamber104.

Pulsing the direct current (DC) power applied to the plasma can be advantageous since the average discharge power can remain low while relatively large power pulses are periodically applied. In addition, the duration of the voltage pulses can be chosen so as to reduce the probability of establishing an electrical breakdown condition. However, very large power pulses can still result in an electrical breakdown condition regardless of their duration. An undesirable electrical discharge will corrupt the etching process, cause contamination in the vacuum chamber104, and can damage the substrate and/or any process layers already fabricated. In addition, using a magnetron-type plasma generator results in a magnetic field that significantly improves confinement. The electrons generated in a magnetron-type plasma generator will have a closed-loop path that generates an E×B drift current that significantly improves confinement.

FIG. 2illustrates a cross-sectional view of an embodiment of a magnetically enhanced plasma processing apparatus200according to the present invention. In one embodiment, the magnetically enhanced plasma processing apparatus200can be configured for magnetically enhanced reactive ion etching. In another embodiment, the magnetically enhanced plasma processing apparatus200can be configured for sputter etching.

The magnetically enhanced plasma processing apparatus200includes a chamber202, such as a vacuum chamber. The chamber202is coupled in fluid communication to a vacuum pump204through a vacuum valve206. In one embodiment, the chamber202is electrically coupled to ground potential.

The chamber202is coupled to a feed gas source208by one or more gas lines207. In one embodiment, the gas lines207are isolated from the chamber and other components by insulators209. In addition, the gas lines207can be isolated from the feed gas source208using in-line insulating couplers (not shown). A gas flow control system210controls the gas flow to the chamber202. The gas source208can contain any type of feed gas, such as argon. In some embodiments, the feed gas is a mixture of different gases. The different gases can include reactive and non-reactive gases. In one embodiment, the feed gas is a noble gas or a mixture of noble gases.

A substrate211to be processed is supported in the chamber202by a substrate support212. The substrate211can be any type of work piece such as a semiconductor wafer. In one embodiment, the substrate support212is electrically coupled to an output213of a bias voltage source214. An insulator215isolates the bias voltage source214from the chamber202. In one embodiment, the bias voltage source214is an alternating current (AC) power source, such as a radio frequency (RF) power source. In other embodiments (not shown), the substrate support212is coupled to ground potential or is electrically floating.

The magnetically enhanced plasma processing apparatus200also includes a cathode216. In one embodiment, the cathode216is formed of a metal. In one embodiment, the cathode216is formed of a chemically inert material, such as stainless steel. The distance from the cathode216to the substrate211can vary from a few centimeters to about one hundred centimeters.

The cathode216is coupled to an output222of a matching unit224. An insulator226isolates the cathode216from a grounded wall of the chamber202. An input230of the matching unit224is coupled to a first output232of a pulsed power supply234. A second output236of the pulsed power supply234is coupled to an anode238. An insulator240isolates the anode238from a grounded wall of the chamber202. Another insulator242isolates the anode238from the cathode216.

In one embodiment (not shown), the first output232of the pulsed power supply234is directly coupled to the cathode216. In one embodiment (not shown), the second output236of the pulsed power supply234and the anode238are both coupled to ground. In one embodiment (not shown), the first output232of the pulsed power supply234couples a negative voltage impulse to the cathode216. In another embodiment (not shown), the second output236of the pulsed power supply234couples a positive voltage impulse to the anode238.

In one embodiment, the pulsed power supply234generates peak voltage levels that are on the order of 5-10 kV. In one embodiment, operating voltages are between about 50 V and 1000 V. In one embodiment, the pulsed power supply234sustains a discharge current level that is between about 1A and about 5,000A depending on the volume of the plasma. Typical operating currents varying from less than about one hundred amperes to more than about a few thousand amperes depending on the volume of the plasma. In one embodiment, the pulses generated by the pulsed power supply234have a repetition rate that is below 1 kHz. In one embodiment, the pulse width of the pulses generated by the pulsed power supply234is substantially between about one microsecond and several seconds.

The anode238is positioned so as to form a gap244between the anode238and the cathode216that is sufficient to allow current to flow through a region245between the anode238and the cathode216. In one embodiment, the width of the gap244is between approximately 0.3 cm and 10 cm. The surface area of the cathode216and the dimensions of the gap determine the volume of the region245. The dimensions of the gap244and the total volume of the region245are parameters in the ionization process as described herein.

An anode shield248is positioned adjacent to the anode238and functions as an electric shield to electrically isolate the anode238from the plasma. In one embodiment, the anode shield248is coupled to ground potential. An insulator250is positioned to isolate the anode shield248from the anode238.

The magnetically enhanced plasma processing apparatus200also includes a magnet assembly252. In one embodiment, the magnet assembly252is adapted to create a magnetic field254proximate to the cathode216. The magnet assembly252can include permanent magnets256, or alternatively, electromagnets (not shown). The configuration of the magnet assembly252can be varied depending on the desired shape and strength of the magnetic field254. The magnet assembly252can have either a balanced or unbalanced configuration.

In one embodiment, the magnet assembly252includes switching electro-magnets, which generate a pulsed magnetic field proximate to the cathode216. In some embodiments, additional magnet assemblies (not shown) are placed at various locations around and throughout the chamber202depending on the plasma process.

In one embodiment, the magnetically enhanced plasma processing apparatus200is operated by generating the magnetic field254proximate to the cathode216. In the, embodiment shown inFIG. 2, the permanent magnets256continuously generate the magnetic field254. In other embodiments, electro-magnets (not shown) generate the magnetic field254by energizing a current source that is coupled to the electro-magnets. In one embodiment, the strength of the magnetic field254is between about 50 and 2000 gauss. After the magnetic field254is generated, the feed gas from the gas source208is supplied to the chamber202by the gas flow control system210.

In one embodiment, the feed gas is supplied to the chamber202directly between the cathode216and the anode238. Directly injecting the feed gas between the cathode216and the anode238can increase the flow rate of the gas between the cathode216and the anode238. Increasing the flow rate of the gas allows longer duration impulses and thus, can result in the formation higher density plasmas. The flow of the feed gas is discussed further in connection with FIG.3.

In one embodiment, the pulsed power supply234is a component of an ionization source that generates a weakly-ionized plasma. The pulsed power supply234applies a voltage pulse between the cathode216and the anode238. In one embodiment, the pulsed power supply234applies a negative voltage pulse to the cathode216. The amplitude and shape of the voltage pulse are chosen such that a weakly-ionized plasma is generated in the region246between the anode238and the cathode216.

The weakly-ionized plasma is also referred to as a pre-ionized plasma. In one embodiment, the peak plasma density of the pre-ionized plasma is between about 106and 1012cm−3for argon feed gas. In one embodiment, the pressure in the chamber varies from about 10−3to 10 Torr. The peak plasma density of the pre-ionized plasma depends on the properties of the specific plasma processing system.

In one embodiment, the pulsed power supply234generates a low power pulse having an initial voltage of between about 100 V and 5 kV with a discharge current of between about 0.1A and 100A in order to generate the weakly-ionized plasma. In some embodiments the width of the pulse can be in on the order of about 0.1 microseconds to about one hundred seconds. Specific parameters of the pulse are discussed herein in more detail.

In one embodiment, the pulsed power supply234applies a voltage between the cathode216and the anode238before the feed gas is supplied between the cathode216and the anode238. In another embodiment, the pulsed power supply234applies a voltage between the cathode216and the anode238after the feed gas is supplied between the cathode216and the anode238.

In one embodiment, a direct current (DC) power supply (not shown) is used to generate and maintain the weakly-ionized or pre-ionized plasma. In this embodiment, the DC power supply is adapted to generate a voltage that is large enough to ignite the pre-ionized plasma. In one embodiment, the DC power supply generates an initial voltage of several kilovolts between the cathode216and the anode238in order to generate and maintain the pre-ionized plasma. The initial voltage between the cathode216and the anode238creates a plasma discharge voltage that is on the order of 100-1000 V with a discharge current that is on the order of 0.1 A-100 A.

The direct current required to generate and maintain the pre-ionized plasma is a function of the volume of the plasma. In addition, the current required to generate and maintain the pre-ionized plasma is a function of the strength of the magnetic field in the region245. For example, in one embodiment, the DC power supply generates a current that is between about 1 mA and 100 A depending on the volume of the plasma and the strength of the magnetic field in the region245. The DC power supply can be adapted to generate and maintain an initial peak voltage between the cathode216and the anode238before the introduction of the feed gas.

In another embodiment, an alternating current (AC) power supply (not shown) is used to generate and maintain the weakly-ionized or pre-ionized plasma. For example, the weakly-ionized or pre-ionized plasma can be generated and maintained using electron cyclotron resonance (ECR), capacitively coupled plasma discharge (CCP), or inductively coupled plasma (ICP) discharge. An AC power supply can require less power to generate and maintain a weakly-ionized plasma than a DC power supply. In addition, the pre-ionized or weakly-ionized plasma can be generated by numerous other techniques, such as UV radiation techniques, X-ray techniques, electron beam techniques, ion beam techniques, or ionizing filament techniques. In some embodiments, the weakly-ionized plasma is formed outside of the region245and then diffuses into the region,245.

Forming a weakly-ionized or pre-ionized plasma substantially eliminates the probability of establishing a breakdown condition in the chamber202when high-power pulses are applied between the cathode216and the anode238. Uniformly distributing the weakly-ionized or pre-ionized plasma over the cathode area results in a more uniform strongly ionized plasma when a high power pulse is applied. The probability of establishing a breakdown condition is substantially eliminated because the weakly-ionized plasma has a low-level of ionization that provides electrical conductivity through the plasma. This conductivity greatly reduces or prevents the possibility of a breakdown condition when high power is applied to the plasma.

Once the weakly-ionized plasma is formed, high-power pulses are then generated between the cathode216and the anode238. In one embodiment, the pulsed power supply234generates the high-power pulses. The desired power level of the high-power pulse depends on several factors including the nature of the etch process, desired etch rate, density of the pre-ionized plasma, and the volume of the plasma. In one embodiment, the power level of the high-power pulse is in the range of about 1 kW to about 10 MW.

Each of the high-power pulses are maintained for a predetermined time that, in one embodiment, is about one microsecond to about ten seconds. In one embodiment, the repetition frequency or repetition rate of the high-power pulses is in the range of between about 0.1 Hz to 1 kHz. In order to minimize undesirable substrate heating, the average power generated by the pulsed power supply234can be less than one megawatt depending on the volume of the plasma. In one embodiment, the thermal energy in at least one of the cathode216, the anode238,and the substrate support212is conducted away or dissipated by liquid or gas cooling such as helium cooling (not shown).

The high-power pulses generate a strong electric field between the cathode216and the anode238. This strong electric field is substantially located in the region245across the gap244between the cathode216and the anode238. In one embodiment, the electric field is a pulsed electric field. In another embodiment, the electric field is a quasi-static electric field. By quasi-static electric field we mean an electric field that has a characteristic time of electric field variation that is much greater than the collision time for electrons with neutral gas particles. Such a time of electric field variation can be on the order of ten seconds. The strength and the position of the strong electric field will be discussed in more detail herein.

The high-power pulses generate a highly-ionized or a strongly-ionized plasma from the weakly-ionized plasma. For example, the discharge current that is formed from this strongly-ionized plasma can be on the order of 5 kA with a discharge voltage that is in the range of 50-500 V for a pressure that is on the order of about 100 m Torr and 10 Torr. In one embodiment, the discharge voltage is chosen to be relatively low so that the probability of sputtering material from the cathode216is low.

In one embodiment, the substrate211is biased more negatively than the cathode216. The positively charged ions in the strongly-ionized plasma accelerate towards the substrate211. The accelerated ions impact a surface of substrate211, causing the surface of the substrate211to be etched. The strongly-ionized plasma of the present invention causes a very uniform and very high etch rate.

In one embodiment of the invention, the ion flux density of the strongly-ionized plasma and the ion energy of the ions in the strongly-ionized plasma are independently controlled. In one embodiment, the ion flux density is controlled by adjusting the power level and the duration of the high-power pulses generated by the pulsed power supply234. In one embodiment, the ion energy of the ions that strike the substrate211and cause the surface of the substrate211to be etched is controlled by adjusting the negative substrate bias voltage generated by the bias voltage source214(FIG.2).

In one embodiment, the strongly-ionized plasma tends to diffuse homogenously in the region246and, therefore tends to create a more homogeneous plasma volume. The homogenous diffusion results in accelerated ions impacting the surface of the substrate211in a more uniform manner than with a conventional plasma etching system. Consequently, the surface of the substrate is etched more uniformly. In one embodiment, this uniformity is achieved without the necessity of rotating the substrate211and/or the magnet assembly252. The physical mechanism responsible for this homogenous diffusion is described with reference to FIG.6A through FIG.6D.

FIG. 3illustrates a cross-sectional view of the cathode216and the anode238of FIG.2. In operation, the feed gas264flows between the cathode216and the anode238. In one embodiment, the flow of the feed gas264is chosen so as to cause a relatively high gas volume exchange in the region245between the cathode216and the anode238.

A pre-ionizing voltage is applied between the cathode216and the anode238across the feed gas264and forms the weakly-ionized plasma. The weakly-ionized plasma is generally formed in the region245and diffuses to a region266as the feed gas264continues to flow. In one embodiment (not shown) the magnet assembly252is adapted to create a magnetic field254in the region245that extends to the center of the cathode. Such a magnetic field assists in diffusing the electrons from area245to area266. In another embodiment, the volume of weakly-ionized plasma in the region245is rapidly exchanged with a fresh volume of feed gas264. The electrons in the weakly-ionized plasma are substantially trapped in the region266by the magnetic field254.

A high-power pulse is then applied between the cathode216and the anode238after the formation of the weakly-ionized plasma in the region245. This high-power pulse generates the strong electric field260in the region245between the cathode216and the anode238. The strong electric field260causes collisions to occur between neutral atoms, electrons, and ions in the weakly ionized plasma. These collisions generate numerous excited argon atoms in the weakly-ionized plasma. In one embodiment, the cathode216and the anode238are adapted for sputter etch materials processing.

The accumulation of excited atoms in the weakly-ionized plasma alters the ionization process. In one embodiment, the strong electric field260facilitates a multi-step ionization process of an atomic feed gas that significantly increases the rate at which the strongly-ionized plasma is formed. The multi-step ionization processes has an efficiency that increases as the density of excited atoms in the weakly-ionized plasma increases. In another embodiment, the strong electric field260enhances the formation of ions of a molecular or atomic feed gas to provide a reactive ion source for reactive ion etching.

In one embodiment, the distance or gap244between the cathode216and the anode238is chosen so as to maximize the rate of excitation of the atoms. The value of the electric field260in the region245depends on the voltage level applied by the pulsed power supply234(FIG. 2) and the dimensions of the gap244between the anode238and the cathode216. In some embodiments, the strength of the electric field260varies between about 5 V/cm and 105V/cm depending on various system parameters and operating conditions of the magnetron system.

In some embodiments, the gap244can be between about 0.30 cm and about 10 cm depending on various parameters of the process. In one embodiment, the electric field260in the region245is rapidly applied to the pre-ionized or weakly-ionized plasma. In some embodiments, the rapidly applied electric field260is generated by a voltage pulse having a rise time that is between about 0.1 microsecond and ten seconds.

In one embodiment, the dimensions of the gap244and the parameters of the applied electric field260are chosen to determine the optimum condition for a maximum rate of excitation of the atoms in the region245. For example, an argon atom requires an energy of about 11.55 eV to become excited. Thus, as the feed gas264flows through the region245, the weakly-ionized plasma is formed and the atoms in the weakly-ionized plasma undergo a stepwise ionization process.

The excited atoms in the weakly-ionized plasma then encounter the electrons that are trapped in the region266by the magnetic field254. Excited atoms only require about 4 eV of energy to ionize while neutral atoms require about 15.76 eV of energy to ionize. Therefore, the excited atoms will ionize at a much higher rate than neutral atoms. In one embodiment, ions in the strongly-ionized plasma strike the cathode216causing secondary electron emission from the cathode216. These secondary electrons are substantially trapped by the magnetic field254and interact with any neutral or excited atoms in the strongly-ionized plasma. This process further increases the density of ions in the strongly-ionized plasma as the feed gas264is replenished.

The multi-step ionization process corresponding to the rapid application of the electric field260can be described as follows:
Ar+e−→Ar*+e−
Ar*+e−→Ar++2e−
where Ar represents a neutral argon atom in the feed gas and e−represents an ionizing electron generated in response to a pre-ionized plasma, when sufficient voltage is applied between the cathode216and the anode238. Additionally, Ar* represents an excited argon atom in the weakly-ionized plasma. The collision between the excited argon atom and the ionizing electron results in an argon ion (Ar+) and two electrons.

The excited argon atoms generally require less energy to become ionized than neutral argon atoms. Thus, the excited atoms tend to more rapidly ionize near the surface of the cathode216than the neutral argon atoms. As the density of the excited atoms in the plasma increases, the efficiency of the ionization process rapidly increases. This increased efficiency eventually results in an avalanche-like increase in the density of the strongly-ionized plasma. Under appropriate excitation conditions, the portion of the energy applied to the weakly-ionized plasma that is transformed to the excited atoms is very high for a pulsed discharge in the feed gas.

Thus, in one aspect of the invention, high-power pulses are applied to a weakly-ionized plasma across the gap244to generate a strong electric field260between the anode238and the cathode216. This strong electric field260generates excited atoms in the weakly-ionized plasma. The excited atoms diffuse to the center of the cathode and are rapidly ionized by secondary electrons emitted by the cathode216. The rapid ionization results in a strongly-ionized plasma having a large ion density that is formed in an area proximate to the cathode216.

In one embodiment of the invention, a higher density plasma is generated by controlling the flow of the feed gas264in the region245. In this embodiment, a first volume of feed gas264is supplied to the region245. The first volume of feed gas264is then ionized to form a weakly-ionized plasma in the region245. Next, the pulsed power supply234(FIG. 2) applies a high power electrical pulse across the weakly-ionized plasma. The high power electrical pulse generates a strongly-ionized plasma from the weakly-ionized plasma.

The level and duration of the high power electrical pulse is limited by the level and duration of the power that the strongly-ionized plasma can absorb before the high power discharge contracts and terminates. In one embodiment, the flow rate of the feed gas264is increased so that the strength and the duration of the high-power electrical pulse can be increased in order to increase the density of the strongly-ionized plasma.

In one embodiment, the strongly-ionized plasma is transported through the region245by a rapid volume exchange of feed gas264. As the feed gas264moves through the region245, it interacts with the moving strongly-ionized plasma and also becomes strongly-ionized from the applied high-power electrical pulse. The ionization process can be a combination of direct ionization and/or stepwise ionization as described herein. Transporting the strongly-ionized plasma through the region245by a rapid volume exchange of the feed gas264increases the level and the duration of the power that can be applied to the strongly-ionized plasma and, thus, generates a higher density strongly-ionized plasma in the region246.

FIG. 4illustrates a graphical representation300of the applied power of a pulse as a function of time for periodic pulses applied to the plasma in the magnetically enhanced plasma processing apparatus200of FIG.2. At time t0, the feed gas from the gas source208flows into the chamber202before the pulsed power supply234is activated. The time required for a sufficient quantity of gas to flow from the gas source208into the chamber202depends on several factors including the flow rate of the gas and the desired pressure in the chamber202.

In one embodiment (not shown), the pulsed power supply234is activated before the feed gas flows into the chamber202. In this embodiment, the feed gas is injected between the anode238and the cathode216where it is ignited by the pulsed power supply234to generate the weakly-ionized plasma.

In one embodiment, the feed gas flows between the anode238and the cathode216between time t0and time t1. At time t1the pulsed power supply234generates a pulse302between the cathode216and the anode238that has a power which is between about 0.01 kW and 100 kW depending on the volume of the plasma. The pulse302is sufficient to ignite the feed gas to generate the weakly-ionized plasma.

In one embodiment (not shown), the pulsed power supply234applies a potential between the cathode216and the anode238before the feed gas264(FIG. 3) from the gas source208is delivered into the chamber202. In this embodiment, the feed gas264is ignited as it flows between the cathode216and the anode238. In other embodiments, the pulsed power supply234generates the pulse302between the cathode216and the anode238during or after the feed gas264from the gas source208is delivered into the chamber202.

The power generated by the pulsed power supply234partially ionizes the gas that is located in the region245between the cathode216and the anode238. The partially ionized gas is also referred to as a weakly-ionized plasma or a pre-ionized plasma. As described herein, the formation of the weakly-ionized plasma substantially eliminates the possibility of creating a breakdown condition when high-power pulses are applied to the weakly-ionized plasma.

In one embodiment, the power is continuously applied for between about one microsecond and one hundred seconds to allow the pre-ionized plasma to form and be maintained at a sufficient plasma density. In one embodiment, the power from the pulsed power supply234is continuously applied after the weakly-ionized plasma is ignited to maintain the weakly-ionized plasma. The pulsed power supply234can be designed so as to output a continuous nominal power in order to generate and sustain the weakly-ionized plasma until a high-power pulse is delivered by the pulsed power supply234.

Between time t2and time t3, the pulsed power supply234delivers a high-power pulse304across the weakly-ionized plasma. In some embodiments, the high-power pulse304has a power that is in the range of between about 1 kW and 10 MW depending on parameters of the magnetically enhanced plasma processing apparatus200. The high-power pulse has a leading edge306having a rise time of between about 0.1 microseconds and ten seconds.

The high-power pulse304has a power and a pulse width that is sufficient to transform the weakly-ionized plasma to a strongly-ionized plasma. In one embodiment, the high-power pulse304is applied for a time that is in the range of between about ten microseconds and ten seconds. At time t4, the high-power pulse304is terminated.

The power supply224maintains the weakly-ionized plasma after the delivery of the high-power pulse304by applying background power that, in one embodiment, is between about 0.01 kW and 100 kW. The background power can be a pulsed or continuously applied power that maintains the pre-ionization condition in the plasma, while the pulsed power supply234prepares to deliver another high-power pulse308.

At time t5, the pulsed power supply234delivers another high-power pulse308. In one embodiment, the repetition rate between the high-power pulses304,308is between about 0.1 Hz and 1 kHz. The particular size, shape, width, and frequency of the high-power pulses304,308depend on various factors including process parameters, the design of the pulsed power supply234, and the design of the magnetically enhanced plasma processing apparatus. The shape and duration of the leading edge308and the trailing edge310of the high-power pulse304is chosen to sustain the weakly-ionized plasma while controlling the rate of ionization of the strongly-ionized plasma. In one embodiment, the particular size, shape, width, and frequency of the high-power pulse304is chosen to control the etch rate of the substrate211(FIG.2).

FIG. 5illustrates graphical representations320,322, and324of the absolute value of applied voltage, current, and power, respectively, as a function of time for periodic pulses applied to the plasma in the magnetically enhanced plasma processing apparatus200of FIG.2. In one embodiment, at time t0(not shown), the feed gas264(FIG. 3) from the gas source208flows into the chamber202before the pulsed power supply234is activated. The time required for a sufficient quantity of feed gas264to flow from the gas source208into the chamber202depends on several factors including the flow rate of the feed gas264and the desired pressure in the chamber202.

In the embodiment shown inFIG. 5, the power supply234generates a constant power at time t1. At time t1, the pulsed power supply234generates a voltage326across the anode238and the cathode216. In one embodiment, the voltage326is approximately between 100 V and 5 kV. The period between time t0and time t1(not shown) can be on the order of several microseconds up to several milliseconds. At time t1, the current328and the power330have constant value.

Between time t1and time t2, the voltage326, the current328, and the power330remain constant as the weakly-ionized plasma is generated. The voltage332at time t2is between about 100 V and 5 kV. The current334at time t2is between about 0.1A and 100A. The power336delivered at time t2is between about 0.01 kW and 100 kW.

The power336generated by the pulsed power supply234partially ionizes the gas that is located between the cathode216and the anode238. The partially ionized gas is also referred to as a weakly-ionized plasma or a pre-ionized plasma. As described herein, the formation of the weakly-ionized plasma substantially eliminates the possibility of creating a breakdown condition when high-power pulses are applied to the weakly-ionized plasma. The suppression of this breakdown condition substantially eliminates the occurrence of undesirable arcing in the chamber202.

In one embodiment, the period between time t1and time t2is between about one microsecond and one hundred seconds to allow the pre-ionized plasma to form and be maintained at a sufficient plasma density. In one embodiment, the power336from the pulsed power supply234is continuously applied to maintain the weakly-ionized plasma. The pulsed power supply234can be designed so as to output a continuous nominal power in order to sustain the weakly-ionized plasma.

Between time t2and time t3, the pulsed power supply234delivers a large voltage pulse338across the weakly-ionized plasma. In some embodiments, the large voltage pulse338has a voltage that is in the range of 200V to 30 kV. In some embodiments, the period between time t2and time t3is between about 0.1 microseconds and ten seconds. The large voltage pulse338is applied between time t t3and time t4, before the current across the plasma begins to increase. In one embodiment, the period between time t3and time t4can be between about 10 nanoseconds and one microsecond.

Between time t4and time t5, the voltage340drops as the current342increases. The power344also increases between time t4and time t5, until a quasi-stationary state exists between the voltage346and the current348. The period between time t4and time t5can be on the order of several hundreds of nanoseconds.

In one embodiment, at time t5, the voltage346is between about 50V and 1000V, the current348is between about 10 A and 5 kA and the power350is between about 1 kW and 10 MW. The power350is continuously applied to the plasma until time t6. In one embodiment, the period between time t5and time t6is approximately between one microsecond and ten seconds.

In one embodiment, the magnetically enhanced plasma processing apparatus is configured for plasma etching. In this embodiment, to substantially prevent sputtering from the cathode216, the voltage346is between about 50 V and 1000 V and the current348is between about 1000A and 10,000A at time t5.

The pulsed power supply234delivers a high-power pulse having a maximum power350and a pulse width that is sufficient to transform the weakly-ionized plasma to a strongly-ionized plasma. At time t6, the maximum power350is terminated. In one embodiment, the pulsed power supply234continues to supply a background power that is sufficient maintain the plasma after time t6.

In one embodiment, the power supply224maintains the plasma after the delivery of the high-power pulse by continuing to apply a power352that can be between about 0.01 kW and 100 kW to the plasma. The continuously generated power maintains the pre-ionization condition in the plasma, while the pulsed power supply234prepares to deliver the next high-power pulse.

At time t7, the pulsed power supply234delivers the next high-power pulse (not shown). In one embodiment, the repetition rate between the high-power pulses is between about 0.1 Hz and 10 kHz. The particular size, shape, width, and frequency of the high-power pulses depend on various factors including process parameters, the design of the pulsed power supply234, and the design of the magnetically enhanced plasma processing system.

In another embodiment (not shown), the power supply234generates a constant voltage. In this embodiment, the voltage320is continuously applied from time t2until time t6. The current322and the power324rise until time t6and then remain at a relatively constant level until the voltage320is terminated. The increased current and power generate excited atoms.

FIG.6A throughFIG. 6Dillustrate various simulated magnetic field distributions400,402,404, and406proximate to the cathode216for various electron E×B drift currents in the magnetically enhanced plasma processing apparatus200of FIG.2. Plasmas generated by a magnetron have strong diamagnetic properties so the magnetron discharge tends to exclude external magnetic fields from the plasma volume. The simulated magnetic fields distributions400,402,404, and406indicate that high-power plasmas having high current density tend to diffuse homogeneously in the area246of the magnetically enhanced plasma processing apparatus200of FIG.2.

The high-power pulses between the cathode216and the anode238generate secondary electrons from the cathode216that move in a substantially circular motion proximate to the cathode216according to crossed electric and magnetic fields. The substantially circular motion of the electrons generates an electron E×B drift current. The magnitude of the electron E×B drift current is proportional to the magnitude of the discharge current in the plasma and, in one embodiment, is approximately in the range of between about three and ten times the magnitude of the discharge current.

In one embodiment, the substantially circular electron E×B drift current generates a magnetic field that interacts with the magnetic field generated by the magnet assembly252. In one embodiment, the magnetic field generated by the electron E×B drift current has a direction that is substantially opposite to the magnetic field generated by the magnet assembly252. The magnitude of the magnetic field generated by the electron E×B drift current increases with increased electron E×B drift current. The homogeneous diffusion of the strongly-ionized plasma in the region246is caused, at least in part, by the interaction of the magnetic field generated by the magnet assembly252and the magnetic field generated by the electron E×B drift current.

In one embodiment, the electron E×B drift current defines a substantially circular shape for low current density plasma. However, as the current density of the plasma increases, the substantially circular electron E×B drift current tends to describe a more complex shape as the interaction of the magnetic field generated by the magnet assembly252, the electric field generated by the high-power pulse, and the magnetic field generated by the electron E×B drift current becomes more acute. For example, in one embodiment, the electron E×B drift current has a substantially cycloidal shape. Thus, the exact shape of the electron E×B drift current can be quite elaborate and depends on various factors.

For example,FIG. 6Aillustrates the magnetic field lines408produced from the interaction of the magnetic field generated by the magnet assembly252and the magnetic field generated by an electron E×B drift current410illustrated by a substantially circularly shaped ring. The electron E×B drift current410is generated proximate to the cathode216.

In the example shown inFIG. 6A, the electron E×B drift current410is approximately one hundred amperes (100A). In one embodiment of the invention, the electron E×B drift current410is between approximately three and ten times as great as the discharge current. Thus, in the example shown inFIG. 6A, the discharge current is approximately between 10A and 30A. The magnetic field lines408shown inFIG. 6Aindicate that the magnetic field generated by the magnet assembly252is substantially undisturbed by the relatively small magnetic field that is generated by the relatively small electron E×B drift current410.

FIG. 6Billustrates the magnetic field lines412produced from the interaction of the magnetic field generated by the magnet assembly252and the magnetic field generated by an electron E×B drift current414. The electron E×B drift current414is generated proximate to the cathode216. In the example shown inFIG. 6B, the electron E×B drift current414is approximately 300A. Since the electron E×B drift current414is typically between about three and ten times as great as the discharge current, the discharge current in this example is approximately between 30A and 100A.

The magnetic field lines412that are generated by the magnet assembly252are substantially undisturbed by the relatively small magnetic field generated by the relatively small electron E×B drift current414. However, the magnetic field lines416that are closest to the electron E×B drift current414are somewhat distorted by the magnetic field generated by the electron E×B drift current414. The distortion suggests that a larger electron E×B drift current should generate a stronger magnetic field that will interact more strongly with the magnetic field generated by the magnet assembly252.

FIG. 6Cillustrates the magnetic field lines418that are produced from the interaction of the magnetic field generated by the magnet assembly252and by the magnetic field generated by an electron E×B drift current420. The electron E×B drift current420is generated proximate to the cathode216. In the example shown in FIG.6C, the electron E×B drift current420is approximately 1,000 A. Since the electron E×B drift current420is typically between about three and ten times as great as the discharge current, the discharge current in this example is approximately between 100 A and 300 A.

The magnetic field lines418that are generated by the magnet assembly252exhibit substantial distortion that is caused by the relatively strong magnetic field generated by the relatively large electron E×B drift current420. Thus, the larger electron E×B drift current420generates a stronger magnetic field that strongly interacts with and can begin to dominate the magnetic field generated by the magnet assembly252.

The interaction of the magnetic field generated by the magnet assembly252and the magnetic field generated by the electron E×B drift current420substantially generates magnetic field lines422that are somewhat more parallel to the surface of the cathode216than the magnetic field lines408,412, and416in FIG.6A and FIG.6B. The magnetic field lines422cause the strongly-ionized plasma to more uniformly distribute in the area246.

Thus, the strongly-ionized plasma is substantially uniformly diffused in the area246. The cathode216is, therefore, bombarded more uniformly by positive ions as compared with conventional magnetically enhanced etching systems. This uniform bombardment generates secondary electrons that are uniformly distributed in the area246. The secondary electrons uniformly interact with the substantially uniform strongly-ionized plasma. Consequently, the substrate211(FIG. 2) is more uniformly etched in a magnetically enhanced plasma etching process according to the invention.

FIG. 6Dillustrates the magnetic field lines424produced from the interaction of the magnetic field generated by the magnet assembly252and the magnetic field generated by an electron E×B drift current426. The electron E×B drift current426is generated proximate to the cathode216. In the example shown inFIG. 6D, the electron E×B drift current426is approximately 5 kA. The discharge current in this example is approximately between 500A and 1,700A.

The magnetic field lines424generated by the magnet assembly252are relatively distorted due to their interaction with the relatively strong magnetic field generated by the relatively large electron E×B drift current426. Thus, in this embodiment, the relatively large electron E×B drift current426generates a very strong magnetic field that is substantially stronger than the magnetic field generated by the magnet assembly252.

FIG. 7illustrates a cross-sectional view of another embodiment of a magnetically enhanced plasma processing apparatus450according to the present invention. The magnetically enhanced plasma processing apparatus450includes an electrode452that generates a weakly-ionized or pre-ionized plasma. The electrode452is also referred to as a pre-ionizing filament electrode and is a component in an ionization source that generates the weakly-ionized plasma.

In one embodiment, the electrode452is coupled to an output454of a power supply456. The power supply456can be a DC power supply or an AC power supply. An insulator458isolates the electrode452from the grounded wall of the chamber202. In one embodiment, the electrode452is substantially shaped in the form of a ring electrode. In other embodiments, the electrode452is substantially shaped in a linear form or any other shape that is suitable for pre-ionizing the plasma.

In one embodiment, a second output460of the power supply456is coupled to the cathode216. The insulator226isolates the cathode216from the grounded wall of the chamber202. In one embodiment, the power supply456generates an average output power that is in the range of between about 0.01 kW and 100 kW. Such an output power is sufficient to generate a suitable current between the electrode452and the cathode216to pre-ionize the feed gas that is located proximate to the electrode452.

In operation, the magnetically enhanced plasma processing apparatus450functions in a similar manner to the magnetically enhanced plasma processing apparatus200of FIG.2. The magnetic field254is generated proximate to the cathode216. In one embodiment, the strength of the magnetic field254is between about fifty and two thousand gauss. The feed gas is supplied from the gas source208to the chamber202by the gas flow control system210.

The power supply456applies a suitable current between the cathode216and the electrode452. The parameters of the current are chosen to establish a weakly-ionized plasma in the area246proximate to the electrode452. In one embodiment, the power supply456generates a voltage that is between about 100 V and 5 kV with a discharge current that is between about 0.1 A and 100A depending on the volume of the plasma. An example of specific parameters of the voltage will be discussed herein in more detail in connection with FIG.8.

In one embodiment, the resulting pre-ionized plasma density is in the range of between approximately 106and 1012cm−3for argon sputtering gas. In one embodiment, the pressure in the chamber202is in the range of approximately 10−3to 10 Torr. As previously discussed, the weakly-ionized or pre-ionized plasma substantially eliminates the possibility of establishing a breakdown condition in the chamber202when high-power pulses are applied to the plasma.

The pulsed power supply234then generates a high-power pulse between the cathode216and the anode238. The high-power pulse generates a strongly-ionized plasma from the weakly-ionized plasma. The parameters of the high-power pulse depend on various parameters including the volume of the plasma, the desired deposition rate, and the concentration of the pre-ionized plasma necessary for etching the substrate211.

In one embodiment, the high-power pulse between the cathode216and the anode238is in the range of about 1 kW to about 10 MW. In one embodiment, the discharge current density that can be generated from the strongly-ionized plasma is greater than about 1 A/cm2for a pressure of approximately 10 m Torr. In one embodiment, the high-power pulse has a pulse width that is in the range of approximately one microsecond to several seconds. In one embodiment, the repetition rate of the high-power discharge is in the range of between about 0.1 Hz to about 10 kHz.

The average power generated by the pulsed power supply can be chosen to minimize undesirable substrate heating. For example, the average power generated by the pulsed power supply can be chosen to be less than one megawatt depending on the volume of the plasma. In one embodiment, the thermal energy in at least one of the cathode216, the anode238, and the substrate support212can be conducted away or dissipated by liquid or gas cooling (not shown).

The gas flow control system210provides a feed gas flow rate that is high enough to maintain the strongly-ionized plasma. Additionally, the vacuum valve206controls the pressure so as to maintain the pressure inside the chamber202in a range that maintains the strongly-ionized plasma.

The ions in the strongly-ionized plasma accelerate towards the substrate211and impact the surface of the substrate211. The strongly ionized plasma results in a very high etch rate of the substrate material. Furthermore, as described herein in connection withFIG. 6AthoughFIG. 6D, the strongly-ionized plasma generated by the plasma processing systems according to the present invention tends to diffuse homogenously in the area246due to the interaction of generated magnetic fields. The homogenous diffusion results in a more uniform distribution of ions impacting the surface of the substrate211compared with conventional plasma etching systems, thereby resulting in relatively uniform etching of the substrate211.

FIG. 8illustrates a graphical representation500of pulse power as a function of time for periodic pulses applied to the plasma in the magnetically enhanced plasma processing system450of FIG.7. In one embodiment, the feed gas from the gas source208flows into the chamber202at time t0, before either the power supply456or the pulsed power supply234are activated.

In another embodiment, prior to the formation of the weakly-ionized plasma, the power supply456and/or the pulsed power supply234are activated at time t0before the feed gas enters the chamber202. In this embodiment, the feed gas is injected between the electrode452and the cathode216where it is ignited by the power supply456to generate the weakly-ionized plasma.

The time required for a sufficient quantity of feed gas to flow into the chamber202depends on several factors including the flow rate of the feed gas and the desired operating pressure in the chamber202. At time t1the power supply456generates a power502that is in the range of between about 0.01 kW to about 100 kW between the electrode452and the cathode216. The power502causes the feed gas proximate to the electrode452to become partially ionized, thereby generating a weakly-ionized plasma or a pre-ionized plasma.

At time t2, the pulsed power supply234delivers a high-power pulse504to the weakly-ionized plasma that is on the order of less than 1 kW to about 10 MW depending on the volume of the plasma. The high-power pulse504is sufficient to transform the weakly-ionized plasma to a strongly-ionized plasma. The high-power pulse has a leading edge506having a rise time of between about 0.1 microseconds and ten seconds.

In one embodiment, the pulse width of the high-power pulse504is in the range of between about one microsecond and ten seconds. The high-power pulse504is terminated at time t4. Even after the delivery of the high-power pulse504, the power502from the power supply456is continuously applied to sustain the pre-ionized plasma, while the pulsed power supply234prepares to deliver another high-power pulse508. In another embodiment (not shown), the power supply456is an AC power supply and delivers suitable power pulses to ignite and sustain the weakly-ionized plasma.

At time t5, the pulsed power supply234delivers another high-power pulse508. In one embodiment, the repetition rate of the high-power pulses is between about 0.1 Hz and 10 kHz. The particular size, shape, width, and frequency of the high-power pulse depend on the process parameters and on the design of the pulsed power supply234and the plasma processing system. The shape and duration of the leading edge506and the trailing edge510of the high-power pulse504is chosen to control the rate of ionization of the strongly-ionized plasma. In one embodiment, the particular size, shape, width, and frequency of the high-power pulse504is chosen to control the etch rate of the substrate material.

FIG.9A throughFIG. 9Care cross-sectional views of various embodiments of cathodes216′,216″, and216′″ according to the present invention. FIG.9A throughFIG. 9Cillustrate one side (the right side with reference toFIG. 7) of each cathode216′,216″, and216′″. The left side of each cathode216′,216″, and216′″ is generally symmetrical to the illustrated right side. FIG.9A throughFIG. 9Cillustrate various configurations of the electrode452and the cathodes216′,216″, and216′″. These various configurations can affect the parameters of the electric field generated between the electrode452and each of the cathodes216′,216″, and216′″.

The parameters of the electric field can influence the ignition of the pre-ionized plasma as well as the pre-ionization process generally. In one embodiment, these various embodiments create the necessary conditions for breakdown of the feed gas and ignition of the weakly-ionized plasma in the region between the anode238and each respective cathode216′,216″, and216′″.

FIG. 9Aillustrates one side of the cathode216′. The surface518of the cathode216′ is substantially parallel to the ring-shaped electrode452and extends past the bend520of the ring-shaped electrode452. In this embodiment, the electric field lines (not shown) from the electric field generated between the cathode216′ and the ring-shaped electrode452are substantially perpendicular to the cathode216′ along the circumference of the ring-shaped electrode452. This embodiment can increase the efficiency of the pre-ionization process.

FIG. 9Billustrates one side of the cathode216″. In this embodiment, the electric field lines (not shown) generated between the cathode216″ and the electrode452are substantially perpendicular to the cathode216″ at the point528on the cathode216″. The electric field in the gap530between the electrode452and the cathode216″ is adapted to ignite the plasma from the feed gas flowing through the gap530. Depending on various parameters, such as where the magnetic field is generated relative to the point528and the pressure in the area proximate to the cathode216″, this embodiment can increase the efficiency of the pre-ionization process.

FIG. 9Cillustrates one side of the cathode216′″. In this embodiment, the electric field lines (not shown) generated between the cathode216′″ and the electrode452are substantially perpendicular to the cathode216′″ at the point538. The electric field in the gap540between the electrode452and the cathode216′″ is adapted to ignite the plasma from the feed gas flowing through the gap540. This embodiment can increase the efficiency of the pre-ionization process depending on various parameters, such as where the magnetic field is generated relative to the point538and the pressure in the area proximate to the cathode216′″.

FIG. 10is a cross-sectional view of another embodiment of a magnetically enhanced plasma processing apparatus450′ according to the present invention. This embodiment is similar to the magnetically enhanced plasma processing apparatus450of FIG.7. However, in this embodiment, the electrode452′, which is a component of the ionization source, substantially surrounds the cathode216.

The position of the electrode452′ relative to the cathode216is chosen to achieve particular electrical conditions in the gap244between the anode238and the cathode216. For example, in this embodiment, since the pre-ionizing electrode452′ is not physically located in the region245′ between the anode238and the cathode216, it does not interfere with the strong electric field that results when a high-power pulse is applied between the anode238and the cathode216. Additionally, the location of the pre-ionizing electrode452′ results in a more uniformly distributed weakly-ionized plasma in the region246′.

The power supply456applies a substantially constant voltage between the cathode216and the electrode452′. The substantially constant voltage generates a weakly-ionized or pre-ionized plasma proximate to the electrode452′ and the cathode216. The pre-ionized plasma substantially eliminates the possibility of establishing a breakdown condition in the chamber202when high-power pulses are applied to the plasma.

In one embodiment, the power supply456is a DC power supply that generates a DC voltage that is in the range of between about 100 V and 5kV with a discharge current that is in the range of between about 0.1 A and 100 A. In another embodiment, the power supply456is an AC power supply that generates voltage pulses between the cathode216and the electrode452′.

Since the electrode452′ substantially surrounds the cathode216, a distance462between the electrode452′ and the cathode216can be varied by changing the diameter of the electrode452′. For example, the distance462can be varied from about 0.3 cm to about 10 cm. The distance462is chosen to maintain the weakly-ionized plasma in the region246′. The vertical position of the electrode452′ relative to the cathode216can also be varied.

The pulsed power supply234generates a high-power pulse between the cathode216and the anode238as described herein. The high-power pulse generates a strongly-ionized plasma from the weakly-ionized plasma.

FIG. 11illustrates a cross-sectional view of another illustrative embodiment of a magnetically enhanced plasma processing apparatus450″ according to the present invention. The magnetically enhanced plasma processing apparatus450″ is similar to the magnetically enhanced plasma processing apparatus450of FIG.7. For example, the electrode452″ is a component of an ionization source. However, the electrode452″ is coupled to a first power supply464and also to an additional second power supply466. The position of the electrode452″ relative to the cathode216is chosen to achieve particular plasma processing characteristics.

A first output468of the first power supply464is coupled through the insulator458to a first side470of the electrode452″. A second output472of the first power supply464is coupled to a second side474of the electrode452″ through an insulator.476. The first power supply464is adapted to generate a current through the electrode452″. The current essentially generates heat in the electrode452″ and the heated electrode452″ emits electrons into the area245″. In one embodiment, the first power supply464is a DC power supply and applies a substantially constant current through the electrode452″. In another embodiment, the first power supply464is an AC power supply.

A first output478of the second power supply466is coupled to the anode238through an insulator480. A second output482of the second power supply466is coupled to the second side474of the electrode452″. The second power supply466is adapted to apply a voltage between the electrode452″ and the anode238. The second power supply466can be an AC power supply or a DC power supply. In one embodiment, the second power supply466generates a voltage in the range of about between 100V and 5 kV with a discharge current that is in the range of between about 0.1A and 100A.

In one embodiment, the second power supply466applies a substantially constant voltage that generates a weakly-ionized or pre-ionized plasma proximate to the electrode452″ and the cathode216. The pre-ionized plasma substantially eliminates the possibility of establishing a breakdown condition in the chamber202when high-power pulses are applied to the plasma.

The high-power pulsed power supply234then generates a high-power pulse between the cathode216and the anode238. The high-power pulse generates a strongly-ionized plasma from the weakly-ionized plasma. The parameters of the high-power pulse depend on various parameters including the volume of the plasma, the desired etch rate, and the desired concentration of the pre-ionized plasma as described.

FIG. 12is a flowchart600of an illustrative process for magnetically enhanced plasma etching according to the present invention. The process is initiated (step602) by activating various systems in the magnetically enhanced plasma processing apparatus200of FIG.2. For example, the chamber202is initially pumped down to a specific pressure (step604). Next, the pressure in the chamber202is evaluated (step606). In one embodiment, feed gas is then pumped into the chamber (step608).

The gas pressure is then evaluated (step610). If the gas pressure is correct, the pressure in the chamber202is again evaluated (step612). If the pressure in the chamber202is correct, an appropriate magnetic field is generated proximate to the feed gas (step614). In one embodiment, the magnet assembly252ofFIG. 2includes at least one permanent magnet, and consequently, the magnetic field is generated constantly, even before the process is initiated. In another embodiment, a magnetic assembly (not shown) includes at least one electromagnet, and consequently, the magnetic field is generated only when the electromagnet is operating.

When the magnetic field is appropriate (step616), the feed gas is ionized to generate a weakly-ionized plasma (step618). In one embodiment, the weakly-ionized plasma is generated by creating a relatively low current discharge in the gap244between the cathode216and the anode238of FIG.2. In another embodiment, the weakly-ionized plasma can be generated by creating a relatively low current discharge between the electrode452and the cathode216of FIG.7. In yet another embodiment, the electrode452″ is heated to emit electrons proximate to the cathode216of FIG.11. In the embodiment ofFIG. 11, a relatively low current discharge is created between the anode238and the electrode452″.

In the embodiment shown inFIG. 2, the weakly-ionized plasma is generated by applying a potential across the gap244between the cathode216and the anode238before the introduction of the feed gas. In the embodiment shown inFIG. 7, the weakly-ionized plasma is generated by applying a potential difference between the electrode452and the cathode216ofFIG. 7before the introduction of the feed gas to generate the weakly-ionized plasma.

If the gas is weakly-ionized (step620), a negative bias is applied to the substrate (step621). A strongly-ionized plasma is then generated from the weakly-ionized plasma (step622). In one embodiment, the strongly-ionized plasma is generated by applying a high-power pulse between the cathode216and the anode238. As previously discussed, the high-power pulse results in the generation of a strong electric field in the gap244between the anode238and the cathode216. The strong electric field results in a stepwise ionization process for atomic feed gases and enhanced formation of ions in molecular feed gases that result in a strongly ionized plasma. In one embodiment, the strongly-ionized plasma is substantially homogeneous in the area246of FIG.2. This homogeneity results in substantially uniform etching of the substrate211.

The substrate211attracts ions from the strongly-ionized substantially uniform plasma because the substrate211is negatively biased relative to the cathode216. This causes the ions to bombard the substrate211causing etching of the substrate material. In one embodiment, once the strongly-ionized plasma is formed (step624), the plasma etching is monitored (step628) by known monitoring techniques. Once the plasma etching is completed (step630), the plasma etch process is ended (step632).

FIG. 13is a flowchart650of an illustrative process for controlling the etch rate according to the present invention. The process is initiated (step602) by activating various systems in the magnetically enhanced plasma processing apparatus200of FIG.2. For example, the chamber202is initially pumped down to a specific pressure (step604). Next, the pressure in the chamber202is evaluated (step606). In one embodiment, feed gas is then pumped into the chamber (step608). The gas pressure is evaluated (step610). If the gas pressure is correct, the pressure in the chamber202is again evaluated (step612). If the pressure in the chamber202is correct, an appropriate magnetic field is generated proximate to the feed gas (step614).

Assuming that the magnetic field is appropriate (step616), the feed gas is ionized to generate a weakly-ionized plasma (step618). In one embodiment, the weakly-ionized plasma is generated by creating a relatively low current discharge between the cathode216and the anode238of FIG.2.

After the weakly-ionized plasma is generated (step620), a negative bias is applied to the substrate (step621). A strongly-ionized plasma is then generated from the weakly-ionized plasma (step622). In one embodiment, the strongly-ionized plasma is generated by applying a high-power pulse in the gap244between the cathode216and the anode238. In one embodiment, the strongly-ionized plasma is substantially homogeneous in the area246of FIG.2. This homogeneity results in more uniform etching of the substrate211. The substrate211attracts ions from the strongly-ionized plasma and the ions bombard the substrate211causing etching of the substrate material.

In one embodiment, once the strongly-ionized plasma is formed (step624), the etch rate is monitored (step652) by known monitoring techniques. If the etch rate is not sufficient (step654), the power delivered to the plasma is increased (step656). In one embodiment, increasing the magnitude of the high-power pulse applied in the gap244between the cathode216and the anode238increases the power delivered to the plasma. In one embodiment (not shown), to control the ion energy of the ions bombarding the substrate, the negative bias applied to the substrate (step621) is varied. The etch rate is again evaluated (step652). This process continues until the etch rate is sufficient (step654), and etching continues (step658). Once the plasma etch is completed (step660), the etch process is ended (step662).

Equivalents