Patent Application
20070049043
1. Field of the Invention
Embodiments of the present invention generally relate to the field of semiconductor manufacturing. More particularly, embodiments of the invention relate to a method of forming a nitrided gate dielectric layer.
2. Description of the Related Art
Integrated circuits are composed of many, e.g., millions, of devices that function as basic components such as transistors, capacitors, and resistors. Transistors, such as field effect transistors (FET), typically include a source, a drain, and a gate stack. The gate stack typically includes a substrate, such as a silicon substrate, a gate dielectric, such as silicon dioxide, SiO2, on the substrate, and a gate electrode, such as polycrystalline silicon, on the gate dielectric. The gate dielectric layer generally comprises dielectric materials such as silicon dioxide (SiO2), or a high-K dielectric material having a dielectric constant greater than 4.0, such as silicon oxynitride (SiON), silicon nitride (SiN), hafnium oxide (HfO2), hafnium silicate (HfSiO2), hafnium silicon oxynitride (HfSiON), zirconium oxide (ZrO2), zirconium silicate (ZrSiO2), barium strontium titanate (BaSrTiO3 or BST), lead zirconium titanate (Pb(ZrTi)O3, or PZT), and other suitable materials.
As integrated circuit sizes and the sizes of the transistors thereon decrease, the gate drive current required to increase the speed of the transistor has increased. Because the gate drive current increases as the gate capacitance increases and capacitance is inversely proportional to the gate dielectric thickness, decreasing the dielectric thickness is one method of increasing the drive current.
Attempts have been made to reduce the thickness of SiO2 gate dielectrics below 20 Å. However, it has been found that the use of thin SiO2 gate dielectrics below 20 Å often results in undesirable effects on gate performance and durability. For example, boron from a boron doped gate electrode can penetrate through a thin SiO2 gate dielectric into the underlying silicon substrate. Also, there is typically an increase in gate leakage, i.e., tunneling, with thin dielectrics thus increasing the amount of power consumed by the gate. Further, thin SiO2 gate dielectrics may be susceptible to hot carrier damage, in which high energy carriers traveling across the dielectric can damage or destroy the gate. In addition, thin SiO2 gate dielectrics may also be susceptible to negative bias temperature instability (NBTI), wherein the threshold voltage or drive current drifts with operation of the gate.
One method of forming a dielectric layer suitable for use as the gate dielectric layer in a MOSFET (metal oxide semiconductor field effect transistor) includes nitridizing a thin silicon oxide film in a nitrogen-containing plasma. Increasing the net nitrogen content in the gate oxide to increase the dielectric constant is desirable for several reasons. For example, the bulk of the oxide dielectric may be lightly incorporated with nitrogen during the plasma nitridation process, which reduces the equivalent oxide thickness (EOT) over the starting oxide. The EOT of an alternative dielectric layer in a particular capacitor is the thickness that the alternative dielectric layer would have if its dielectric constant were that of silicon dioxide. This may result in a gate leakage reduction, due to tunneling during the operation of a FET (field effect transistor); at the same time, such increased nitrogen content may also reduce damage induced by tunneling currents during subsequent processing operations. Another benefit of increasing the net nitrogen content of the gate oxide is that the nitridized gate dielectric is more resistant to the problem of gate etch undercut, which in turn reduces defect states and current leakage at the gate edge.
In U.S. Pat. No. 6,610,615 titled “Plasma Nitridation For Reduced Gate Dielectric Layers,” issued on Aug. 26, 2003, McFadden, et al. compared nitrogen profiles in a silicon oxide film for both thermal and plasma nitridation processes (see FIG. 2 of U.S. Pat. No. 6,610,615). The nitrogen profile data for the thermally nitrided oxide shows a first concentration of nitrogen at a top surface of an oxide layer, a generally declining concentration of nitrogen deeper in the oxide, an interfacial accumulation of nitrogen at the oxide-silicon interface, and finally, a nitrogen concentration gradient that is generally declining with distance into the substrate. In contrast, it can be seen that the plasma nitridation process produces a nitrogen profile that is essentially monotonically decreasing from the top surface of the oxide layer through the oxide silicon interface and into the substrate. The undesirable interface accumulation of nitrogen seen with a thermal nitridation process does not occur with the ionic bombardment of the nitrogen plasma. Furthermore, the nitrogen concentration in the substrate is lower, at all depths, than is achieved with the thermal nitridation process.
As mentioned earlier, a benefit of increasing nitrogen concentration at the gate-electrode-gate oxide interface is that dopant, such as boron, out-diffusion from polysilicon gate electrodes into or through the gate oxide is reduced. This improves device reliability by reducing defect states in the bulk of the gate oxide caused by, for example, in-diffused boron from a boron doped polysilicon gate electrode. Another benefit of reducing nitrogen content at the gate-oxide silicon channel interface is the reduction of fixed charge and interface state density. This improves channel mobility and transconductance. Therefore, plasma nitridation processes has advantages over thermal nitridation processes.
However, as device geometry continues to shrink, there remains a need for a method of depositing gate dielectrics that have thinner Electrical Oxide Thickness (EOT) with improved mobility.
Embodiments of the present invention generally provide a method of forming a nitrided gate dielectric. The method comprises incorporating nitrogen into a dielectric film using a plasma nitridation process to form a nitrided gate dielectric. The first step involves providing a substrate comprising a gate dielectric film. The second step involves inducing a voltage on the substrate. Finally, while maintaining the voltage, the substrate is exposed to a plasma comprising a nitrogen source to form a nitrided gate dielectric on the substrate. In one embodiment, the voltage is induced on the substrate by applying a voltage to an electrostatic chuck supporting the substrate. In another embodiment, the voltage is induced on the substrate by applying a DC bias voltage to an electrode positioned adjacent the substrate.
Embodiments of the invention also provide a method of forming a nitrided gate dielectric in an integrated processing system. A silicon substrate is introduced into a first processing chamber of the integrated processing system where a dielectric film is formed on the substrate. The substrate is transferred to a second processing chamber of the integrated processing system where the substrate is annealed. The substrate is then transferred to a third processing chamber of the integrated processing system where a voltage is induced on the substrate while exposing the substrate to a plasma comprising a nitrogen source to form a nitrided gate dielectric on the substrate. In another embodiment, the substrate is transferred to the second processing chamber of the integrated processing system where the substrate is annealed. In another embodiment, the substrate is transferred to a fourth processing chamber of the integrated processing system where a polysilicon layer is deposited on the substrate. In another embodiment, the voltage induced on the substrate comprises applying a bias voltage of less than about 1200 V at a pressure of 4 Torr of helium.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Embodiments of the present invention relate to the formation of high-k dielectric materials over substrates. The high-K dielectric material may have a variety of compositions that are homogenous, heterogeneous, graded and/or multiple layered stacks or laminates. The high-k dielectric material may include combinations of hafnium, zirconium, titanium, tantalum, lanthanum, aluminum, silicon, oxygen and/or nitrogen. High-K dielectric materials may include hafnium containing materials, such as hafnium oxides (HfOx or HfO2), hafnium silicates (HfSixOy or HfSiO4), hafnium, silicon oxynitrides (HfSixOyNz), hafnium oxynitrides (HfOxNy), hafnium aluminates (HfAlxOy), hafnium aluminum silicates (HfAlxSiyOz), hafnium aluminum silicon oxynitrides (HfAlwSixOyNz), hafnium lanthanum oxides (HfLaxOy), zirconium containing materials, such as zirconium oxides (ZrOx or ZrO2), zirconium silicates (ZrSixOy or ZrSiO4), zirconium silicon oxynitrides (ZrSixOyNz), zirconium oxynitrides (ZrOxNy), zirconium aluminates (ZrAlxOy), zirconium aluminum silicates (ZrAlxSiyOz), zirconium aluminum silicon oxynitrides (ZrAlwSixOyNz), zirconium lanthanum oxides (ZrLaxOy), other aluminum-containing materials or lanthanum-containing materials, such as aluminum oxides (Al2O3 or AlOx), aluminum oxynitrides (AlOxNy), aluminum silicates (AlSixOy), aluminum silicon oxynitrides (AlSixOyNz), lanthanum aluminum oxides (LaAlxOy), lanthanum oxides (LaOx or La2O3), other suitable materials, composites thereof, and combinations thereof. Other high-K dielectric materials useful for dielectric layers may include titanium oxides (TiOx or TiO2), titanium oxynitrides (TiOxNy), tantalum oxides (TaOx or Ta2O5) and tantalum oxynitrides (TaOxNy). Laminate films that are useful dielectric materials for high-K dielectric layers include HfO2/Al2O3, HfO2/SiO2, La2O3/Al2O3 and HfO2/SiO2/Al2O3. The high-K dielectric material preferably comprises hafnium oxide, hafnium silicates, composites thereof, or combinations thereof. Substrates on which embodiments of the invention may be useful include, but are not limited to semiconductor wafers, such as crystalline silicon, silicon oxide, strained silicon, SOI, silicon germanium, doped or undoped polysilicon, doped or undoped silicon wafers, silicon nitride, patterned or non-patterned wafers, and may include materials formed thereover, such as dielectric materials, conductive materials, silicon layers and metal layers.
The high-K dielectric layer of step 110 may be deposited on a substrate by conventional deposition techniques such as atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), thermal and plasma techniques and combinations thereof. In a preferred embodiment, the high-k dielectric layer is deposited by an ALD process and apparatus, such as described in co-pending U.S. Provisional Patent Application Ser. No. 60/570,173, filed May 12, 2004, entitled, “Apparatuses And Methods For Atomic Layer Deposition of Hafnium-containing High-K Dielectric Materials,” assigned to Applied Materials, Inc., and herein incorporated by reference. The high-k dielectric layer is generally deposited with a film thickness from about 10 Å to about 1000 Å, preferably from about 20 Å to about 500 Å and more preferably from about 50 Å to about 200 Å, for example, about 100 Å.
During the Decoupled Plasma Nitridation (DPN) process of step 130, the substrate is bombarded with atomic-N formed by co-flowing N2 and a noble gas plasma such as argon. Besides N2, other nitrogen-containing gases may be used to form the nitrogen plasma, such as hydrazines (e.g., N2H4 or MeN2H3), amines (e.g., Me3N, Me2NH or MeNH2), anilines (e.g., C5H5NH2), and azides (e.g., MeN3 or Me3SiN3). Other noble gases that may be used in a DPN process include helium, neon, and xenon. The nitridation process proceeds at a time period from about 10 seconds to about 360 seconds, preferably from about 30 seconds to about 180 seconds, for example, about 120 seconds. Also, the nitridation process is conducted with a plasma power setting at about 300 watts to about 2,700 watts and a pressure at about 10 mTorr to about 100 mTorr. The nitrogen has a flow rate from about 0.1 slm to about 1.0 slm. The individual and total gas flows of the processing gases may vary based upon a number of processing factors, such as the size of the processing chamber, the temperature of the processing chamber, and the size of the substrate being processed. In a preferred embodiment, the nitridation process is a DPN process and includes a plasma formed by co-flowing Ar and N2.
The reactor 200 comprises a process chamber 210 having an electrostatic chuck 216 within a conductive body (wall) 230, and a controller 240. The chamber 210 is supplied with a substantially flat dielectric ceiling 220. Other modifications of the chamber 210 may have other types of ceilings, e.g., a dome-shaped ceiling. Above the ceiling 220 is disposed an antenna comprising at least one inductive coil element 212 (two co-axial elements 212 are shown). The inductive coil element 212 is coupled, through a first matching network 219, to a plasma power source 218. The plasma power source 218 typically is capable of producing up to 3000 W at a tunable frequency in a range from 50 kHz to 13.56 MHz.
The electrostatic chuck 216 includes a first electrode 254 and a second electrode 256 embedded in a dielectric material. The first electrode and second electrode are biased with DC potentials to provide the chucking action that holds the substrate 214. Application of the chucking voltage to the electrostatic chuck 216 and wafer spacing mask produces charge distribution along the underside of the substrate 214 and over the surface of the electrostatic chuck 216. The opposite polarity of these charges produces an attractive electrostatic force between the substrate 214 and the electrostatic chuck 216. This force retains the substrate 214 upon the chuck without relying upon a plasma within the processing chamber to provide a conductive grounding path for the substrate 214. The electrostatic chuck 216 may also be a monopolar chuck.
Details of the monopolar electrostatic chuck are described in U.S. Pat. No. 5,982,607, entitled “Monopolar Electrostatic Chuck Having An Electrode In Contact With A Workpiece,” assigned to Applied Materials, Inc., issued Nov. 9, 1999, and herein incorporated by reference to the extent not inconsistent with the invention. Another example of an electrostatic chuck is described in U.S. Pat. No. 5,315,473, entitled “Technique For Improving Chucking Reproducibility,” assigned to Applied Materials, Inc., issued May 24, 1994 and herein incorporated by reference to the extent not inconsistent with the invention.
The electrostatic chuck 216 is coupled, through a second matching network 224, to a biasing power source 222. The biasing power source 222 is generally capable of producing a RF signal having a tunable frequency of 50 kHz to 13.56 MHz and a power of between 0 and 5000 watts. Optionally, the biasing power source 222 may be a DC or pulsed DC source. A controller 240 comprising a central processing unit (CPU) 244, a memory 242, and support circuits 246 for the CPU 244 and facilitates control of the components of the chamber 210 and, as such, of the nitridation process as discussed.
In another embodiment, the voltage for operating the electrostatic chuck 216 can be supplied by a separate “chuck” power supply (not shown). One output terminal of the chucking power supply is connected to the chuck electrode. The other output terminal typically is connected to electrical ground, but alternatively may be connected to a metal body portion of the electrostatic chuck 216. In operation, the substrate is placed in contact with the dielectric material, and a direct current voltage is placed on the electrode to create the electrostatic attractive force or bias to adhere the substrate on the upper surface of the electrostatic chuck 216.
In operation, a semiconductor wafer 214 is placed on the electrostatic chuck 216 and process gases are supplied from a gas panel 238 through entry ports 226 to form a gaseous mixture 250. The gaseous mixture 250 is ignited to form a plasma 255 in the chamber 210 by applying power from the plasma source 218. The pressure within the interior of the chamber 210 is controlled using a throttle valve 227 and a vacuum pump 236. Typically, the chamber wall 230 is coupled to an electrical ground 234. The temperature of the wall 230 is controlled using liquid-containing conduits (not shown) that run through the wall 230.
The temperature of the substrate 214 is controlled by stabilizing a temperature of the electrostatic chuck 216. In one embodiment, helium gas from a gas source 248 is provided via a gas conduit 249 to channels (not shown) formed in the surface of the electrostatic chuck 216 to a fine space (not shown) formed between the reverse surface of the substrate 214 and the upper surface of the electrostatic chuck 216. During processing, the electrostatic chuck 216 may be heated by a resistive heater (not shown) within the pedestal of the electrostatic chuck 216 to a steady state temperature and then the helium gas facilitates uniform heating of the substrate 214. Using such thermal control, the substrate 214 is maintained at a temperature between about 200° C. to 350° C.
To facilitate control of the process chamber 210 as described above, the controller 240 may be one of any form of general-purpose, computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory 242, or computer-readable medium, of the CPU 244 may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits 246 are coupled to the CPU 244 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. The inventive method is generally stored in the memory 242 as a software routine. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU 244.
Other details of the Decoupled Plasma Nitridation process reactor 400 are described in U.S. Patent Application Publication No. 2004/0242021, entitled “Method And Apparatus For Plasma Nitridation Of Gate Dielectrics Using Amplitude Modulated Radio Frequency Energy,” assigned to Applied Materials, Inc., published Dec. 2, 2004 and herein incorporated by reference to the extent not inconsistent with the invention. Examples of suitable DPN chambers include the DPN Centura™, which is commercially available from Applied Materials, Inc., Santa Clara, Calif.
Integrated Processing Sequence
In step 335, the substrate is transferred to an anneal chamber, such as the CENTURA™ RADIANCE™ rapid thermal processing (RTP) chamber available from Applied Materials, Inc., located in Santa Clara, Calif., for a post deposition annealing of the HfSiOx film. In step 340, a post deposition anneal is performed where the substrate is annealed at a temperature from about 500° C. to about 1200° C., preferably from about 550-700° C. for a time period from about 1 second to about 240 seconds, preferably from about 30 seconds to about 90 seconds, for example, at about 650° C. for about 60 seconds. Generally, the anneal chamber atmosphere contains at least one anneal gas, such as O2, N2, NH3, N2H4, NO, N2O, or combinations thereof. The anneal chamber is maintained at a pressure from about 5 Torr to about 100 Torr, for example, at about 50 Torr.
In step 345, the substrate is then transferred into a plasma chamber containing at least a nitrogen-containing gas where a voltage is induced on the wafer followed by plasma nitridation in step 350. The voltage is between about 300 V and about 5000 V, for example at about 1200 V. The plasma nitridation process continues for about 2 seconds to about 20 minutes to control the nitridation dose in HfSiOxNy formation in step 350. In step 355, the substrate is transferred back to the RTP processing chamber where a post nitridation anneal, step 360, is performed. During the post nitridation anneal, the substrate is annealed at a temperature from about 600° C. to about 1200° C., preferably from about 700-1100° C. for a time period from about 1 second to about 120 seconds, preferably from about 30 seconds to about 90 seconds, for example, at about 1000° C. for about 60 seconds. Generally, the anneal chamber atmosphere contains at least one anneal gas, such as O2, N2, NH3, N2H4, NO, N2O, or combinations thereof. The anneal chamber is maintained at a pressure from about 5 Torr to about 100 Torr, for example, at about 15 Torr. Alternatively, the post nitridation anneal comprises a two-step process in which an inert or reducing step is followed by an oxidizing step.
After forming the gate dielectric, a gate electrode, such as polysilicon may be deposited by low pressure chemical vapor deposition (LPCVD), atomic layer epitaxy (ALE), thermal decomposition methods, or other methods known in the art. The polysilicon layer generally contains dopants such as boron, phosphorous or arsenic. The gate electrode can also be a metal layer.
The cleaning module 410 generally includes one or more substrate cassettes 412, one or more transfer robots 414 disposed in a substrate transfer region, and one or more single-substrate clean chambers 416. Other aspects and embodiments of a single-substrate clean system are disclosed in U.S. patent application Ser. No. 09/891,849, entitled “Method and Apparatus for Wafer Cleaning, filed Jun. 25, 2001 and in U.S. patent application Ser. No. 09/891,791, entitled “Wafer Spray Configurations for a Single Wafer Processing Apparatus,” filed Jun. 25, 2001, both of which are herein incorporated by reference in their entirety to the extent not inconsistent with the present disclosure.
The thermal processing/deposition mainframe system 430 generally includes load lock chambers 432, a transfer chamber 434, and processing chambers 436A, 436B, 436C, and 436D. The transfer chamber 434 is preferably between 1 mTorr to about 100 Torr and preferably comprises a non-reactive gas ambient, such as a N2 ambient. The load lock chambers 432 allow for the transfer of substrates into and out from the thermal processing/deposition mainframe system 430 while the transfer chamber 434 remains under a low pressure non-reactive environment. The transfer chamber includes a robot 440 having one or more blades which transfers the substrates between the load lock chambers 432 and processing chambers 436A, 436B, 436C, and 436D. Any of the processing chambers 436A, 436B, 436C, or 436D may be removed from the thermal processing/deposition mainframe system 430 if not necessary for the particular process to be performed by the system 430.
It is believed that it is advantageous to perform the pre-treatment step 320 (
One embodiment of the integrated processing system 400 configured to form a high-K dielectric layer comprises processing chamber 436A adapted to perform the Decoupled Plasma Nitridation process as described above, processing chamber 436B adapted to perform a process such as a chemical vapor deposition chamber or an atomic layer deposition chamber, adapted to deposit a high dielectric constant material, such as a hafnium containing layer. In another embodiment, processing chamber 436C comprises a rapid thermal processing (RTP) chamber where the structure may be annealed. The RTP chamber may be a XE, XE Plus or Radiance chamber available from Applied Materials, Inc. In another embodiment, processing chamber 436D comprises a low pressure chemical vapor deposition chamber (LPCVD), such as a POLYgen chamber, available from Applied Materials, Inc, adapted to deposit a gate dielectric layer. Other embodiments of the system 400 are within the scope of the present invention. For example, the position of a particular processing chamber on the system may be altered or the number of processing chamber may be altered.
While the above embodiments are described with respect to
Performance of the Chucked DPN Process for Gate Dielectrics
In
In
A comparison of the chuckless process in
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
