Abstract:
An atomic layer deposition process that reduces defective bonds formed when depositing atomic layers on a substrate or atomic layer when forming an integrated circuit device. As the layers are formed, a substrate or previous layer is exposed to a first reactant. After the substrate or layer has reacted with the first reactant, the substrate or layer is exposed to a second reactant. During or after exposure to the second reactant, electromagnetic radiation is applied to the substrate or layer. The electromagnetic radiation excites any defective bonds that may form in the deposition process to an energy level high enough to cause the elements forming the defective bonds to react with other elements contained in the second reactant. The reaction forms desirable bonds which attach to the substrate or previous layer to form an additional new layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of co-pending U.S. patent application Ser. No. 10/749,347, filed Dec. 30, 2003. 
     
    
     FIELD  
       [0002]     Atomic layer deposition.  
       BACKGROUND  
       [0003]     Atomic layer deposition (ALD) is a deposition technique used to coat various features in the manufacturing process of circuit devices. To coat features, a film is grown layer by layer by exposing the surface to alternating pulses of reactants, each of which undergoes a self-limiting reaction, generally resulting in controlled film thickness. Each reactant exposure provides an additional atomic layer to previously deposited layers.  
         [0004]     A film growth cycle generally consists of two pulses, each pulse being separated by purges. For oxide films, the substrate is first exposed to an oxidizing agent which results in oxygen bonding with the surface of the substrate or previous layer.  
         [0005]     In the ideal case, the exposed surface fully reacts with the oxidizing agent, but not with itself. Next, a reactant is exposed to the surface. The reactant reacts with the previous layer to form a single atomic layer directly bonded to the underlying surface. Finally, an oxygen containing species is exposed to the substrate, which reacts with the reactant to form a finished layer.  
         [0006]     The film growth cycle may be repeated as many times as necessary to achieve a desired film thickness. In theory, each deposited layer formed by this process is defect free. However, the practical aspects of ALD do not necessarily lead to such defect-free films in which all of the bonds are fully formed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Various embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements.  
         [0008]      FIG. 1  shows a substrate, in one embodiment, being exposed to a first reactant.  
         [0009]      FIG. 2  shows the substrate of  FIG. 1  in a hydroxyl-saturated state on a first surface.  
         [0010]      FIG. 3  shows the substrate of  FIG. 2  purged of the first reactant.  
         [0011]      FIG. 4  shows the substrate of  FIG. 3  being exposed to a second reactant and electromagnetic radiation.  
         [0012]      FIG. 5  shows a rastering configuration.  
         [0013]      FIG. 6  shows the substrate of  FIG. 4  in a reactant-saturated state.  
         [0014]      FIG. 7  shows the substrate of  FIG. 6  purged of the reactant.  
         [0015]      FIG. 8  shows the substrate of  FIG. 7  exposed to a third reactant and electromagnetic radiation.  
         [0016]      FIG. 9  shows the substrate of  FIG. 8  in a hydroxyl-saturated state on a second surface.  
         [0017]      FIG. 10  shows the substrate of  FIG. 9  purged of the reactant and forming an atomic layer.  
         [0018]      FIG. 11  shows an atomic layer, in one embodiment, being exposed to a fourth reactant.  
         [0019]      FIG. 12  shows the atomic layer of  FIG. 11  in a reactant-saturated state.  
         [0020]      FIG. 13  shows the atomic layer of  FIG. 12  purged of the reactant.  
         [0021]      FIG. 14  shows the atomic layer of  FIG. 13  being exposed to a fifth reactant.  
         [0022]      FIG. 15  shows the atomic layer of  FIG. 14  in a hydroxyl-saturated state.  
         [0023]      FIG. 16  shows the atomic layer of  FIG. 15  purged of the reactant and forming a second atomic layer. 
     
    
     DETAILED DESCRIPTION  
       [0024]      FIG. 1  shows a semiconductor substrate such as a portion of a semiconductor wafer (e.g., silicon wafer). Substrate  100  may also be formed of gallium arsenide or any other material suitable for use as a semiconductor substrate (e.g., semiconductor on insulator structure). Reference to a silicon substrate will be made herein.  
         [0025]      FIG. 1  shows substrate  100  being exposed to a first reactant in the formation of a binary metal oxide dielectric layer on surface  102  of substrate  100 . First reactant  150 , in one embodiment, is an oxygen source. In the embodiment shown in  FIG. 1 , first reactant  150  is water (H 2 O). Other suitable oxygen sources include, but are not limited to, oxygen gas, ozone, peroxide and ammonium hydroxide (NH 4 OH).  
         [0026]     In  FIG. 1 , as substrate  100  is exposed to first reactant  150 , substrate  100  reacts with first reactant  150  to form hydroxyl moieties (OH)  155  on surface  102  of substrate  100 . In another embodiment, first reactant  150  is ammonia (NH 3 ). In embodiments where first reactant  150  is ammonia, NH 2  molecules form on surface  102  of substrate  100 .  
         [0027]      FIG. 2  shows substrate  100  in a hydroxyl-saturated state. Hydroxyl saturation occurs when the surface of substrate  100  becomes saturated with hydroxyl moieties  155 . Representatively, to achieve a hydroxyl-saturated state on a silicon substrate, substrate  100  is exposed to first reactant  150  for about 0.1 to about 300 seconds and may be exposed by way of submersing substrate  100  into a bath, spraying first reactant  150  over the surface of substrate  100 , or any other method that substantially exposes substrate  100  to first reactant  150 . As described, the reaction between substrate  100  and first reactant  150  is self-limiting in that there is limited available silicon with which first reactant  150  may react. Therefore, increasing the exposure of substrate  100  to first reactant  150  beyond a time period of complete saturation is acceptable.  
         [0028]      FIG. 3  shows substrate  100  in a hydroxyl-saturated state after purging the reactant. Once hydroxyl saturation is achieved, substrate  100  is removed from the reactant-containing environment and may be dried.  
         [0029]      FIG. 4  shows hydroxyl-saturated substrate  100  being exposed to a second reactant and electromagnetic radiation. In one embodiment, second reactant  165  is a metal-containing substance or compound (e.g., a salt). In the embodiment shown in  FIG. 4 , second reactant  165  is zirconium tetrachloride (ZrCl 4 ). Other suitable reactant substances include, but are not limited to, salts (e.g., chloride salts, fluoride salts, bromide salts, iodide salts, etc.) of titanium, aluminum, gallium, cesium, indium, hafnium, tantalum, praseodymium, niobium, scandium, lutetium, cerium and lanthanum. Second reactant  165 , in general, is a metal chloride or any other suitable metal-containing substance or compound.  
         [0030]     Hydroxyl-saturated substrate  100  is exposed to second reactant  165  by immersing substrate  100  into a bath containing second reactant  165 , spraying second reactant  165  over the surface of substrate  100 , or any other method that substantially exposes substrate  100  to second reactant  165 . As hydroxyl-saturated substrate  100  is exposed to second reactant  165 , hydroxyl moieties  155  on surface  102  of substrate  100  begin to react with second reactant  165  to form, in one embodiment, SiOZrCl 3  molecules  160  on surface  102  of substrate  100  and free hydrochloric acid (HCl)  175 . It is also possible for second reactant  165  to react with two hydroxyl moieties  155  to form O 2 ZrCl 2  molecule  180  while releasing two equivalents of HCl  175 .  
         [0031]     Hydrochloric acid  175  is either in a liquid or gaseous state and is dispersed away from substrate  100  by a purge gas or vacuum in a chamber. Representatively, in a typical process to predominately or completely react hydroxyl moieties  155  with second reactant  165 , substrate  100  is, for example, placed in an immersion bath for about 0.1 to about 300 seconds. As described, the reaction between hydroxyl moieties  155  and second reactant  165  is self-limiting in that there is limited available hydroxyls with which second reactant  165  may react. Therefore, increasing the exposure of substrate  100  to second reactant  165  beyond a time period of complete saturation is acceptable.  
         [0032]     During the reaction of hydroxyl moieties  155  and second reactant  165 , dangling bonds and reactant bonds can form. Dangling bonds occur when a reactant element, Zr in this example, bonds with another reactant element, Zr, instead of, in one case, an oxygen atom when forming an atomic layer film on a surface. Reactant bonds occur when a reactant compound, ZrCl 4  in this example, does not fully react with a reactant but instead bonds with desired bonds, Zr-O, to form Zr-Cl bonds in an ALD film layer.  
         [0033]     During the early stages of film nucleation, dangling bonds and reactant bonds can alter the atomic configuration of the film and result in islanding and poor film growth. In addition, dangling bonds and reactant bonds inhibit the formation of subsequently deposited atomic layers.  
         [0034]     To reduce or minimize the number of these defective bonds, substrate  100  is exposed to electromagnetic radiation  145  after hydroxyl/reactant bond formation. Substrate  100  may be exposed to electromagnetic radiation either while being exposed to second reactant  165 , after removal of substrate  100  from a second reactant  165 —containing environment, or both during exposure to second reactant  165  and after removal from a second reactant  165 —containing environment. As defective bonds are exposed to electromagnetic radiation  145 , the defective bonds become excited and rise to a greater energy level.  
         [0035]     When the bonds reach an activation energy level, the bonds are in a state where they tend to seek out other elements with which to form new bonds. Thus, the electromagnetic radiation at the proper wavelength modifies the reaction kinetics to encourage the destruction of defective bonds and the formation of desirable bonds. For example, since the activation energy for the conversion of surface —ZrCl x  to surface —ZrCl x-1 (OH) is approximately +1.6 kcal/mole, a photon-emitting device may be used to expose the target area to a wavelength that will cause energy levels to gain at least +1.6 kcal/mole. In one embodiment, the energy required to activate a reactant and/or dangling bond is insufficient to activate a desired bond (e.g., a Zr-O bond).  
         [0036]     In one embodiment, electromagnetic radiation is supplied by a tunable laser. The tunable laser, in one embodiment, is a dye laser. In an embodiment where substrate  100  is a wafer, one technique for exposing substrate  100  to an electromagnetic radiation source is by revolving the wafer in the presence of a dye laser. The dye laser emits pulses of radiation onto the wafer along circular revolutions or rasters becoming subsequently larger or smaller as the laser is advanced from either a center or edge of the wafer, respectively. In one embodiment, a rastering speed is selected such that one or more pulses of a dye laser, for example, deliver sufficient energy to substrate  100  to activate undesired bonds (e.g., to deliver an energy to an undesired bond equal to or greater than an activation energy for the bond).  
         [0037]     The selection of the wavelength of light depends on the type of defect encountered. In one embodiment, electromagnetic radiation  145  is targeted to an area of the electromagnetic spectrum wherein the defective bonds will become strongly excited, but the desired chemical bonds will remain unaffected. In one example, undesirable bonds such as Zr-Cl or Zr-Zr bonds in an ALD process for ZrO 2  formation would be targeted for a process using an oxygen source or a reactant such as H 2 O and ZrCl 4 , respectively. In this example, the desired bonds in the matrix would include Si-O bonds near the substrate surface and Zr-O bonds in subsequent layers.  
         [0038]      FIG. 5  shows a rastering configuration for exposing defect bonds to electromagnetic radiation. In this configuration, wafer  510  is on a pedestal or similar stag that can be rotated. Laser  500  scans across the surface of wafer  510  to remove any defective bonds. Laser  500  is adjustable such that laser  500  can emit wavelengths of light at pre-determined frequencies. Thus, wafer  510 , and any defective bonds that may exist on wafer  510  in the dielectric layer, are exposed to enough electromagnetic radiation to excite the defective bonds as laser  500  scans across wafer  510 .  
         [0039]      FIG. 6  shows substrate  100  in a reactant-saturated state. In this state, the surface of substrate  100  containing SiOH bonds has reacted with the reactant to form SiOZrCl 3  molecules  160  on the surface of substrate  100 .  
         [0040]      FIG. 7  shows the surface of substrate  100  saturated with SiOZrCl 3  molecules  160  after removal of the reactant and HCR. After surface  102  of substrate  100  is saturated with SiOZrCl 3  molecules  160 , substrate  100  is removed from the reactant-containing environment and possibly dried. After substrate  100  is dried, SiOZrCl 3  molecule-saturated substrate  100  is exposed to another reactant.  
         [0041]      FIG. 8  shows SiOZrCl 3  molecule-saturated substrate  100  being exposed to a third reactant and electromagnetic . In one embodiment, third reactant  250  is an oxygen source. In another embodiment, third reactant  250  is ammonia. In the embodiment shown in  FIG. 8 , the oxygen source is H 2 O. Other suitable oxygen sources include, but are not limited to, oxygen gas, ozone, peroxide and ammonium hydroxide.  
         [0042]     In the embodiment shown in  FIG. 8 , when SiOZrCl 3  molecules  160  on surface  102  of substrate  100  are exposed to third reactant  250 , a reaction occurs forming SiOZr(OH)Cl 2  molecules  255  on surface  102  of substrate  100  and free HCl molecules  275 . In embodiments where third reactant  250  is ammonia, a reaction occurs forming SiNZrCl 2 NH 2  molecules on surface  102  of substrate  100  and free HCl molecules  275 .  
         [0043]     Hydrochloric acid  275  is either in a liquid or gaseous state and is dispersed away from substrate  100  by a purge gas or vacuum in a chamber. Representatively, in a typical process to predominately or completely react SiOZr(OH)Cl 2  molecules  255  with third reactant  250 , substrate  100  is, for example, placed in an immersion bath or sprayed for about 0.1 to about 300 seconds. As described, the reaction between SiOZrCl 3  molecules  160  and third reactant  250  is self-limiting in that there is limited available SiOZrCl 3  molecules  160  with which third reactant  250  may react. Therefore, increasing the exposure of substrate  100  to third reactant  250  beyond a time period of complete saturation is acceptable.  
         [0044]     To reduce or minimize the number of defective bonds, substrate  100  is exposed to electromagnetic radiation  245  after hydroxyl bond formation. Electromagnetic radiation  245  may be any of the embodiments similar to electromagnetic radiation  145  discussed above.  
         [0045]     Substrate  100  may be exposed to electromagnetic radiation  245  either while being exposed to third reactant  250 , after removal of substrate  100  from a third-reactant  250 -containing environment, or both during exposure to third reactant  250  and after removal from a third reactant  250 -containing environment. As defective bonds are exposed to electromagnetic radiation  245 , the defective bonds become excited and rise to a greater energy level.  
         [0046]     When the bonds reach an activation energy level, the bonds are in a state where they tend to seek out other elements with which to form new bonds. Thus, the electromagnetic radiation at the proper wavelength modifies the reaction kinetics to encourage the destruction of defective bonds and the formation of desirable bonds. For example, since the activation energy for the conversion of surface —ZrCl x  to surface  ZrCl   x-1 (OH) is approximately +1.6 kcal/mole, a photon-emitting device may be used to expose the target area to a wavelength that will cause energy levels to gain at least +1.6 kcal/mole. In one embodiment, the energy required to activate a reactant and/or dangling bond is insufficient to activate a desired bond (e.g., a Zr-O bond).  
         [0047]      FIG. 9  shows the surface of substrate  100  after third reactant  250  has fully reacted with the SiOZrCl 3  molecules. After the SiOZrCl 3  molecules have fully reacted with third reactant  250 , the surface of substrate  100  becomes saturated with SiOZr(OH) 3  molecules  260  while forming additional free HCl molecules in a reaction represented by the equations: 
 SiOZr(OH)Cl 2 +2 H 2 O →SiOZr(OH) 3 +2HCl  SiOZr(OH) 2 Cl+SiOZr(OH) 3 →SiOZr(OH) 2   31  O—(OH) 2 ZrOSi+HCl  
         [0048]      FIG. 10  shows a finished first atomic layer formed by an ALD process after substrate  100  has been removed from the reactant-containing environment. In this example, atomic layer  105  is formed of zirconium oxide (ZrO 2 ) molecules  270  having hydroxyl moieties  255  bonded to ZrO 2  molecules  270 . Atomic layer  105  is now prepared and capable of having an atomic layer formed upon it.  
         [0049]      FIG. 11  shows atomic layer  105  being exposed to a fourth reactant. In one embodiment, fourth reactant  265  is a metal-containing substance or compound (e.g., a salt). In the embodiment shown in  FIG. 11 , fourth reactant  265  is zirconium chloride. Other suitable reactant substances and compounds include, but are not limited to, salts (e.g., chloride salts, fluoride salts, bromide salts, iodide salts, etc.) of titanium, aluminum, gallium, cesium, indium, haffiium, tantalum, praseodymium, niobium, scandium, cerium, lutetium and lanthanum. Fourth reactant  265 , in general, is a metal chloride or any other suitable metal-containing substance.  
         [0050]     Layer  105  is exposed to fourth reactant  265  by immersing layer  105  into a bath containing fourth reactant  265 , spraying fourth reactant  265  over surface  107  of layer  105 , or any other method that substantially exposes layer  105  to fourth reactant  265 . The exposure time should be long enough to maximize the reaction between layer  105  and fourth reactant  265 . In one embodiment, layer  105  is exposed to fourth reactant  265  for about 0.1 to about 300 seconds, but because the reaction is self-limiting, a longer exposure time will not adversely affect dielectric layer formation.  
         [0051]     As layer  105  is exposed to fourth reactant  265 , the hydroxyl moieties  255  on surface  107  of layer  105  begin to react with fourth reactant  265  to form, in this embodiment, ZrOZrCl 3  molecules  260  on surface  107  of layer  105  and free hydrochloric acid  275 . Hydrochloric acid  275  is either in a liquid or gaseous state and is dispersed away from layer  105  by a purge gas or vacuum in a chamber. Representatively, in a typical process to predominately or completely react hydroxyls  255  with fourth reactant  265 , layer  105  is, for example, placed in an immersion bath or sprayed for about 0.1 to about 300 seconds. As described, the reaction between hydroxyl moieties  255  and fourth reactant  265  is self-limiting in that there is limited available hydroxyls with which fourth reactant  265  may react. Therefore, increasing the exposure of layer  105  to fourth reactant  265  beyond a time period of complete saturation is acceptable.  
         [0052]     During the reaction of hydroxyl moieties  255  and fourth reactant  265  dangling and reactant bonds can form. To reduce or minimize the number of these defective bonds, layer  105  is exposed to electromagnetic radiation  245 . Layer  105  may be exposed to electromagnetic radiation either while being exposed to fourth reactant  265 , after removal of layer  105  from a fourth reactant  265  - containing environment, or both during exposure to fourth reactant  265  and after removal from a fourth reactant  265 -containing environment. In one embodiment, layer  105  is exposed to electromagnetic radiation  245  for about 0.1 to about 180 seconds. As the defective bonds are exposed to electromagnetic radiation  245 , the defective bonds become excited and rise to a greater energy level.  
         [0053]     Sufficient exposure to electromagnetic radiation  245  during, after or both during and after exposure to fourth reactant  265  allows layer  105  to become substantially defect-free. Layer  105  is substantially defect free because defective bonds that may have formed are excited by the electromagnetic radiation to a higher energy level causing the defect bonds to be more likely to react with a precursor to form non-defective sites, in this case, Zr-O bonds on the substrate. Thus, defect bonds are reduced or minimized since the reaction essentially replaces the undesired bonds on the layer with desirable bonds.  
         [0054]      FIG. 12  shows layer  105  in a reactant-saturated state. In this state, surface  107  of layer  105  containing ZrO(OH) bonds has reacted with the reactant to form ZrOZrCl 3    260  molecules on surface  107  of layer  105   
         [0055]      FIG. 13  shows surface  107  of layer  105  saturated with ZrOZrCl 3  molecules  260  after purging the reactant. After surface  107  of layer  105  is saturated with ZrOZrCl 3  molecules  260 , layer  105  is removed from the reactant-containing environment and possibly dried. After layer  105  is dried, ZrOZrCl 3  molecule-saturated layer  105  is exposed to another reactant.  
         [0056]      FIG. 14  shows ZrOZrCl 3  molecule-saturated layer  105  being exposed to a fifth reactant. In one embodiment, fifth reactant  350  is an oxygen source. In another embodiment, fifth reactant  350  is ammonia. In the embodiment shown in  FIG. 14 , the oxygen source is H 2 O. Other suitable oxygen sources include, but are not limited to, oxygen gas, ozone, peroxide and ammonium hydroxide.  
         [0057]     In this embodiment, when ZrOZrCl 3  molecules on surface  107  of layer  105  are exposed to fifth reactant  350 , a reaction occurs forming ZrOZr(OH)Cl 2  molecules  355  on surface  107  of layer  105  and free HCl molecules  375 . In embodiments where third reactant  250  is ammonia, a reaction occurs forming ZrNZrCl 2 NH 2  molecules on surface  107  of layer  105  and free HCl molecules  375 .  
         [0058]     Hydrochloric acid  375  is either in a liquid or gaseous state and is dispersed away from layer  105  by a purge gas or vacuum in a chamber. Representatively, in a typical process to predominately or completely react ZrOZrCl 3  molecules with fifth reactant  350 , layer  105  is, for example, placed in an immersion bath or sprayed for about 0.1 to about 300 seconds. As described, the reaction between ZrOZrCl 3  molecules and fifth reactant  350  is self-limiting in that there is limited available ZrOZrCl 3  molecules with which fifth reactant  350  may react. Therefore, increasing the exposure of layer  105  to fifth reactant  350  beyond a time period of complete saturation is acceptable.  
         [0059]      FIG. 15  shows the surface of layer  105  after fifth reactant  350  has fully reacted with the ZrOZrCl 3  molecules. After the ZrOZrCl 3  molecules have fully reacted with fifth reactant  350 , surface  107  of layer  105  has become saturated with ZrOZr(OH) 3  molecules  355  while forming additional free HCl molecules in a reaction represented by the equations: 
 ZrOZr(OH)Cl 2 +2 H 2 O →ZrOZr(OH) 3 +2HCl  ZrOZr(OH) 2 Cl+ZrOZr(OH) 3 →ZrOZr(OH) 2 -μO—(OH) 2 ZrOZr+HCl  
         [0060]      FIG. 16  shows a finished second atomic layer formed by an ALD process after layer  105  has been removed from the reactant-containing environment. Second layer  110  is formed of ZrO molecules  370  having OH molecules  355  bonded to ZrO molecules  370 . Layer  110  is now prepared and capable of having an atomic layer formed upon it.  
         [0061]     The process of forming individual layers upon previous layers may be repeated until the number of desired layers and/or film thickness is reached. As each layer is deposited without defects, overall device integrity and manufacturing yield increases.  
         [0062]     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of embodiments of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.