Abstract:
Methods and an apparatus for processing a substrate. A first method comprising: reacting a layer formed on the substrate with a plasma to form a reaction product layer; and simultaneously exposing the reaction product layer to resonant radiation to volatilize the reaction product layer. A second method comprising: performing a plasma enhanced chemical vapor deposition to deposit a precursor layer on a substrate; and simultaneously heating the precursor layer by exposure of the precursor layer to resonant radiation to convert the precursor layer to a deposited layer.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the field of plasma processing; more specifically, it relates to a method for plasma etching and plasma enhanced deposition and apparatus for plasma etching and plasma enhanced deposition.  
         BACKGROUND OF THE INVENTION  
         [0002]    In plasma based processing, high-energy electrons are used to convert neutral molecules in the gas phase to charged ions and neutral free radicals. Typically, the gas phase temperature is less than 500° C., whereas the electron cloud has energy equivalent to a temperature in excess of 10,000° C. The ambipolar field resulting from the difference in mobility of the electrons and ions generates an anistropic flux of energetic ions (and neutrals via charge exchange collisions) to the surface of the substrate being processed. This flux, in combination with an isotropic flux of reactive neutral free radicals, either etches material from the surface or deposits material on the surface.  
           [0003]    Simultaneous with the surface chemistry, there is a proportional heating of the surface and heating of the substrate itself, both from plasma radiation and bulk heat applied. If the wafer heating is to high, then damage to structures within the substrate occurs. If the wafer temperature or flux of energetic ions or reactive neutral free radicals is to low, then processing times increase as reaction rates decrease. Increasingly, when plasma processing is applied to advanced materials, no satisfactory compromise between wafer heating, which impacts yield and thus cost, and reaction rates, which impacts, productivity and thus cost, can be found.  
         SUMMARY OF THE INVENTION  
         [0004]    A first aspect of the present invention is a method of processing a substrate comprising: reacting a layer formed on the substrate with a plasma to form a reaction product layer; and simultaneously exposing the reaction product layer to resonant radiation to volatilize the reaction product layer.  
           [0005]    A second aspect of the present invention is a method of processing a substrate comprising: performing a plasma enhanced chemical vapor deposition to deposit a precursor layer on a substrate; and simultaneously heating the precursor layer by exposure of the precursor layer to resonant radiation to convert the precursor layer to a deposited layer.  
           [0006]    A third aspect of the present invention is an apparatus for processing a substrate, the apparatus comprising: a chamber; a process gas distribution system adapted to distribute one or more process gases into the chamber; means for generating a plasma from the one or more process gases, the plasma capable of processing a layer on the substrate; a substrate support within the chamber adapted to hold the substrate to expose a top surface of the substrate to the plasma; a resonant radiation source adapted to expose the layer to resonant radiation; and an exhaust adapted to remove volatilized reaction products from the chamber.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0007]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0008]    [0008]FIG. 1 is a plot of vapor pressure of CuCl 2  versus temperature.  
         [0009]    [0009]FIG. 2 is a schematic diagram illustrating a plasma etch process according to the present invention.  
         [0010]    [0010]FIG. 3 is a schematic diagram illustrating a plasma-enhanced deposition according to the present invention.  
         [0011]    [0011]FIG. 4 is a schematic diagram of a first plasma etch/deposition system according to the present invention;  
         [0012]    [0012]FIG. 5 is a schematic diagram of a second plasma etch/deposition system tool according to the present invention;  
         [0013]    [0013]FIG. 6A is a schematic diagram of a prismatic infrared radiation source;  
         [0014]    [0014]FIG. 6B is a schematic diagram of a grating based infrared radiation source; and  
         [0015]    [0015]FIG. 6C is a schematic diagram of a tunable laser infrared radiation source. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    [0016]FIG. 1 is a plot of vapor pressure of CuCl 2  versus temperature. In a plasma etch process, gas phase reactant species (free radicals and ions) are formed in the plasma. The reactant species then strike on a surface of a substrate and chemically react with the surface. The reaction rate is directly related to the volatility (partial pressure) of the product of the reaction (if the product is not removed then the surface becomes coated with reaction product, effectively blocking fresh reactants from reaching un-reacted material). An example of such a process is the etching of copper in chlorine. In the plasma, chlorine free radicals and chlorine ions are created (plasma activation), the chlorine free radicals and ions strike on a copper surface and form copper chloride (ion surface activation) which is a solid. Then the copper chloride is converted to a gas (volatilization) due to heat generated from the reaction, radiant heat from the plasma or bulk heating of the substrate. This set of reactions may be written:  
         Plasma Activation: Cl 2 →2Cl + +2e   (1)  
         Ion Surface Activation: Cu+Cl+Cl + →CuCl 2 (s)   (2)  
         Volatilization (&gt;600° C.): CuCl 2 (s)+Δ→CuCl 2 ↑  (3)  
         [0017]    In FIG. 1, it can be seen that a temperature of about 750° C. is required to produce a partial vapor pressure of CUCl 2  of about 1 Torr. As the temperature decreases the partial pressure of CuCl 2  decreases. At less than 600° C., the partial pressure of CuCl 2  is so low (only a couple of hundredths of a Torr) that the surface is effectively passivated and no further reaction can occur. Therefore, there is a temperature P T , which is the optimum temperature for plasma etching copper in chlorine. However, there may be a maximum temperature W T , which the substrate can be allowed to reach. In FIG. 1 W T  is indicated as being a temperature of about 300-400° C. At 300-400° C., the vapor pressure of CuCl 2  is essentially zero and no volatilization of CuCl 2  will occur so the reaction rate will be essentially zero. For example, in etching copper films on silicon wafers containing sensitive MRAM devices(magnetic random access memory devices) the wafer temperature cannot exceed 250° C. For CMOS (complimentary metal oxide silicon) devices, the wafer temperature cannot exceed 300 to 350° C. due to thermal budgets required to protect diffusion portions of the transistors.  
         [0018]    In the present invention, an additional process step (resonant heating) is added that locally heats the CuCl 2  formed, but not a significant portion of the surrounding copper film. The reactions for this process may be written:  
         Plasma Activation: Cl 2 →2Cl + +2e   (1)  
         Ion Surface Activation: Cu+Cl+Cl + →CuCl 2 (s)   (2)  
         Resonant Heating: CuCl 2 (s)+hv→[CuCl 2 (s)] E    (4)  
         Volatilization (&gt;600° C.): [CUCl 2 (s)] E +δΔ→CuCl 2 ↑  (5)  
         [0019]    The resonant heating is accomplished by supplying electromagnetic energy (radiation) at a wavelength (or frequency) that will couple to and thus excite of one of the vibrational states of CuCl 2 . In equation (4), “h” is Planck&#39;s constant and “v” is frequency. Therefore, resonant radiation is defined as radiation having a wavelength that will couple with a vibrational state of the material exposed to the resonant radiation. Resonant heating is discussed more fully infra. Thus, in reaction (4) the CuCl 2  (s) is resonant heated so that the heat (δΔ) required in reaction (5) for volatilization of the excited CuCl 2  is only a fraction of the heat required (Δ) in reaction (3) for volatilization of the CuCl 2 .  
         [0020]    This allows for either a lower temperature plasma process to be used or aggressive cooling of the wafer to be performed. Sufficient electromagnetic energy may be supplied so that the resonant heating is all that is required and the CuCl 2  volatilizes as reaction (4) occurs.  
         [0021]    Examples of other metals that may be plasma etched according to the present invention are platinum and iron. The reactions for Pt may be written:  
         Plasma Activation: Cl 2 →2Cl + +2e   (6)  
         Ion Surface Activation: Pt+Cl + →PtCl (s)   (7)  
         Resonant Heating: PtCl (s)+hv→[PtCl (S)] E    (8)  
         Volatilization (&gt;600° C.): [PtCl (S)] E +δΔ→PtCl (s)↑  (9)  
         [0022]    The reactions for iron are similar, except the minimum volatilization temperature for iron chloride is greater than 900° C. Other metals and non-metallic films may also be etched according to the present invention  
         [0023]    [0023]FIG. 2 is a schematic diagram illustrating a plasma etch process according to the present invention. In FIG. 2, formed on a substrate  100  is an insulator layer  105 . Formed on insulator  105  is a copper layer  110 . Formed on etchable layer  110  is a masking layer  115 . Trenches  120  are being etched in etchable layer  110 . A reaction product layer  125  is continuously formed and removed at the bottom of each trench  120  so each trench becomes increasingly deeper. Reactant species X as well as electromagnetic energy hv strike on masking layer  115  and etchable layer  110 . The material of masking layer  115  is chosen to not react with reactant species X or vibrationally couple with electromagnetic energy hv. However, reactant species X is chosen to react with etchable layer  110  to form reaction product layer  125  and the wavelength of electromagnetic energy hv is chosen to vibrationally couple with the reaction product layer and hence heat the reaction product layer to sufficiently high enough temperature to volatilize the reaction product layer into vaporized reaction product Z. The amount and wavelengths of electro-magnetic energy hv is discussed infra.  
         [0024]    Regions  130  in etchable layer  110  near the bottom  135  of each trench  120  define the extent of local radiant heating caused by the coupling of electromagnetic energy hv with reaction product layer  125 . The temperature of regions  130  is less than the volatilization temperature of reaction product layer  125 . If the temperature of reaction product layer  125  is T1, the temperature of region  130  is T2 and the temperature of substrate  100  is T3, then the following relationship holds: T1&gt;T2&gt;T3.  
         [0025]    In one example, masking layer  115  is plasma enhanced chemical vapor deposition (PECVD) oxide, etchable layer  110  is Cu, Pt or Fe and the reactant species X is Cl free radicals/ions.  
         [0026]    Turning to how much energy most be supplied by electromagnetic energy hv, a relatively straightforward approximation may be made. A 300 mm diameter wafer with 50% exposed etchable layer (Cu in a Cl 2  system in the present example) is assumed and the heat of vaporization of the reaction product, heat of formation of the reaction product and general plasma induced heating is assumed to be provided by the reactive plasma flux. The reactive area is 0.5π(150×10 −1  m) 2  and given an etch rate of 2E10 −9  m/s, the volume rate of CuCl 2  removal is 0.07 mm 3 /s. This translates into a mole removal rate of CuCl 2  of (8.92 g/cm 3 )×(1 mole/98.9 g)×(0.07 mm 3 /s)=6.2×10 −6  mole/s. Given that ΔH=CpΔT×mole, where ΔH is enthalpy, Cp=48.7 J/K mole is the heat capacity of copper and ΔT=500° K. (the assumed difference between CuCl 2  volatilization temperature and the wafer temperature), then ΔH=0.15 Joules/s=150 mW. Given half the source energy is directed away from the wafer (as in the etch system illustrated in FIG. 4 and described infra) a 300 mW source for a 300 mm diameter wafer=0.42 mW/cm 2  is required.  
         [0027]    Turning to how the wavelength of electromagnetic energy hv is determined, and continuing the CUCl 2  example, it can be seen from Table I that 5 possible wavelengths, corresponding to five transition energies of CuCl 2  could be used.  
                                                 TABLE I                                   CuCl 2  Vibrational   Coupling               Transition Energy   Wavelength           cm −1     μm   Designation                                        9567.5   1.04   Near IR           6877   1.45   Near IR           1910.9   5.2   Mid IR           364.5   27.4   Mid IR           98.6   101.4   Far IR                      
 
         [0028]    Turning to sources of infrared (IR) energy, and continuing the CuCl 2  example, it can be seen from Table II that at least four possible IR sources could be used that give the requisite 0.42 mW/cm 2  of spectral radiance using a 5 nm bandpass filter. The bandpass filter is required to filter wavelengths that would couple with materials other than CuCl 2 .  
                                             TABLE II                                   Spectral radiance       Source   Radiating   Wavelength   (mW cm-2, with 5 nm       Type   material   range   band pass filter)                                Nerst   Zirconia, yittria or    0.4-20 μm   1       Glower   thoria at           1200-2000° K       Globar   SiC at      1-40 μm   1           1300-1500° K       Tungsten   Tungsten   0.3-2.5 μm   100           2000-3000° K       Xeon Arc   High Pressure     0.2-1 μm   1000           (&gt;10 Torr Xe)                  
 
         [0029]    All the sources in Table II belong to the class of sources known as broadband sources.  
         [0030]    [0030]FIG. 3 is a schematic diagram illustrating a plasma-enhanced deposition according to the present invention. The principles of the present invention described supra in relation to plasma etching are applicable to PECVD processing as well. The example of silicon oxide deposition will be used. In FIG. 3, being formed on a substrate  140  is SiO 2  layer  145 . Being formed on SiO 2  layer  145  is a precursor (SiH 3 ) 2 O layer  150  formed from (SiH 3 ) 2 O precipitate formed in the gas phase plasma. The chemical name of (SiH 3 ) 2 O is silicyl oxide. (SiH 3 ) 2 O layer  150  is continuously be transformed into SiO 2  layer  145  as the deposition continues by resonant heating caused by electro-magnetic energy hv impinging on the newly formed (SiH 3 ) 2 O layer  150  and subsequent release of H 2 O and H 2 . The reactions for SiO 2  deposition according to the present invention may be written:  
         Plasma Activation: SiH 4 +e→SiH 3 +H   (10A)  
         N 2 O+e→&gt;NO+O   (10B)  
         Surface Precipitate: 2 SiH 3 +O→(SiH 3 ) 2 O (s)   (11)  
         Precursor Resonant Heating: (SiH 3 ) 2 O (s)+hv→(SiH 3 ) 2 O (s)   (12)  
         Volatilization (&gt;600° C.): (SiH 3 ) 2 O (s)+5 O→2 SiO 2 +H 2 ↑+2 H 2 O↑  (13)  
         [0031]    While precursor (SiH 3 ) 2 O layer  150  is resonantly heated to at least 600° C., under laying SiO 2  layer  145  does not absorb a significant amount of this resonant radiation. Since (SiH 3 ) 2 O layer  150  can be heated to very high temperatures the resultant PECVD SiO 2  has properties similar to low pressure high temperature chemical vapor deposition (LPCVD) SiO 2 . Other materials, for example silicon nitride, may be deposited according to the present invention.  
         [0032]    [0032]FIG. 4 is a schematic diagram of a first plasma etch/deposition system according to the present invention. In FIG. 4, plasma etch/deposition system  200  includes a chamber  205 , a wafer chuck  210 , solenoidal coils  215 , a transmissive window  220  in a top  225  of chamber  205 , an optional bandpass filter  230  and IR sources  235 . A wafer  240  is located on a top surface  245  of wafer chuck  210 . Chamber  205  is fitted with a reactant gas supply  250  and an exhaust  255 . A radio frequency (RF) power supply  260 A is coupled between solenoidal coils  215  and ground in order to strike and maintain a plasma  265  and an RF bias power supply  260 B is coupled between wafer chuck  210  and ground in order to control forward bias (etch) power. IR source  235  generates infrared radiation  270 , which passes through optional bandpass filter  230  and window  220  to strike a top surface  275  of wafer  240  wherein the infrared radiation couples with the reaction products of either the plasma etch or PECVD process being performed in chamber  205  as described in reference to FIGS. 2 and 3 and described supra.  
         [0033]    IR source  235  may be one selected from Table II or another source, for example, a tunable IR laser. Bandpass filter  230  is not required in the cases of monochromatic IR sources (i.e. tunable IR laser) but only when broadband sources (i.e. those listed in table II) are used. Alternative radiation/wavelength selection sub-systems are illustrated in FIGS. 6A, 6B and  6 C and described infra. Table III lists some suitable window materials.  
                           TABLE III                                   Window Material   Wavelength                           Sapphire (Al 2 O 3 )   0.17-5.5 μm           Germanium    1.8-23 μm           Silicon    1.2-15 μm           Quartz    0.4-3 μm           Silver Bromide   0.45-35 μm           Rubidium Bromide   0.45-35 μm                      
 
         [0034]    The choice of window material is a function of the resonant IR wavelength selected and the plasma reaction selected. E.g. the window must pass the required frequency and not be attacked by the plasma process.  
         [0035]    Process parameters for a typical non-volatile metal etch process (i.e. Cu, Pt, Fe, etc.) that may be run in plasma etch/deposition system  200  include (for 8 inch wafers and scalable for 12 inch wafers) a Cl 2  flow rate of 160 sccm, an Ar flow rate of 40 sccm, a BCL 3  flow rate of 13 sccm, chamber pressure of 36 mT, a wafer temperature of 375° C., RF power of 900-1200 watts and bias power of 450 watts.  
         [0036]    Examples of commercial plasma systems that may be modified to practice the present invention (i.e. addition of window  220 , optional filter  230 , and IR source  235 ) include, but are not limited to, the AMAT DPS etch system and the AMAT HDP deposition system both manufactured by Applied Materials Corporation, Santa Clara, Calif.  
         [0037]    [0037]FIG. 5 is a schematic diagram of a second plasma etch/deposition system according to the present invention. In FIG. 5, plasma etch/deposition system includes a chamber  305 , a wafer chuck  310 , plate  315 , a transmissive window  320  in a sidewall  325  of chamber  305 , an optional bandpass filter  330  and IR sources  335 . A wafer  340  is located on a top surface  345  of wafer chuck  310 . Chamber  305  is fitted with a reactant gas supply  350  and an exhaust  355 . An RF power supply  360 A is coupled between plate  315  and ground in order to strike and maintain a plasma  365  and an RF bias power supply  360 B is coupled between wafer chuck  310  and ground in order to control forward bias (etch) power. IR source  335  generates infrared radiation  370 , which passes through optional bandpass filter  330  and window  320  to strike a top surface  375  of wafer  340  wherein the infrared radiation couples with the reaction products of either the plasma etch or PECVD process being performed in chamber  305  as described in reference to FIGS. 2 and 3 and described supra.  
         [0038]    IR source  335  may be one selected from Table II or another source, for example, a tunable IR laser. Bandpass filter  330  is not required in the cases of monochromatic IR sources (i.e. tunable IR laser) but only when broadband sources (i.e. those listed in table II) are used. Alternative radiation/wavelength selection sub-systems are illustrated in FIGS. 6A, 6B and  6 C and described infra. Table III supra lists some suitable window materials.  
         [0039]    Process parameters for a typical silane based oxide deposition process (i.e. Cu, Pt, Fe, etc.) that may be run in plasma etch/deposition system  300  include (for 8 inch wafers and scalable for 12 inch wafers) a SiH 4  flow rate of 300 sccm, a N 2  flow rate of 1500 sccm, a N 2 O flow rate of 9500 sccm, chamber pressure of 2400 mT, a wafer temperature of 400° C., a plate power of 1100 watts and wafer chuck power of 0 watts (no wafer chuck power).  
         [0040]    Examples of commercial plasma systems that may be modified to practice the present invention (i.e. addition of window  320 , optional filter  330 , and IR source  335 ) include, but are not limited to, the LAM research 2300 etch system manufactured by Lam Research, Fremont, Calif., and the Novellus PECVD system manufactured by Novellus Corporation, San Jose, Calif.  
         [0041]    [0041]FIG. 6A is a schematic diagram of a prismatic infrared radiation source. In FIG. 6A, an IR source  400  generates polychromatic IR radiation  405 , which is dispersed into its component wavelengths  410  by a prism  415 . A resonant wavelength (actually range of wavelengths)  420  is selected by tunable wavelength selection window  425 . IR source  400  may be selected from Table II supra. Suitable prism material and their wavelength ranges are listed in Table IV.  
                                             TABLE IV                                   Prism Material   Wavelength                                        SiO 2     0.25-2   μm           LiF   0.2-5   μm           CaF   0.2-9   μm           BaF2   0.2-13   μm           NaCl   2-16   μm           KBr   10-25   μm           CsI   15-50                      
 
         [0042]    [0042]FIG. 6B is a schematic diagram of a grating based infrared radiation source. In FIG. 6B, an IR source  430  generates polychromatic IR radiation  435 , which is dispersed into its component wavelengths  440  by a grating  445 . A resonant wavelength  450  (actually range of wavelengths) is selected by tunable wavelength selection window  455 . IR source  430  may be selected from Table II supra. Suitable prism material and their wavelength ranges are listed in Table V.  
                                             TABLE IV                                   Grating Density               Grooves/mm   Wavelength                                        300-600   0.8-2.5   μm           100-300   2.5-50   μm            30-100   50-1000   μm                      
 
         [0043]    [0043]FIG. 6C is a schematic diagram of a tunable laser infrared radiation source. In FIG. 6B, an tunable laser IR source  460  generates narrow beam monochromatic IR radiation  465 , which is dispersed into a wide beam monochromatic IR radiation  470  by a dispersing reflector  475 .  
         [0044]    The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.