Abstract:
A method of reducing impurities in a high-k dielectric layer comprising the following steps. A substrate is provided. A high-k dielectric layer having impurities is formed over the substrate. The high-k dielectric layer being formed by an MOCVD or an ALCVD process. The high-k dielectric layer is annealed to reduce the impurities within the high-k dielectric layer.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to semiconductor fabrication and more specifically to processes of fabricating high-k dielectric layers.  
       BACKGROUND OF THE INVENTION  
       [0002]     Current high-k gate dielectric processes developed to meet the future transistor performance requirements in the 0.10 μm generation and beyond consist of generally two types: atomic layer chemical vapor deposition (ALCVD) and metal organic chemical vapor deposition (MOCVD). These processes permit formation of the necessary high-k film thickness and thickness uniformity.  
         [0003]     However, MOCVD processes introduce undesired carbon (C)-containing impurities and the more mature ALCVD processes which use chlorine (Cl)-containing precursors create a sufficiently high chlorine content in the high-k films that degrades the electric performance of the devices using those high-k films.  
         [0004]     For example, while an MOCVD process may use Zr(OC 2 H 5 ) 4  to form an ZrO 2  film, carbon impurities (and hydrogen impurities) are formed in the high-k ZrO 2  dielectric layer.  
         [0005]     In another example, in an ALCVD process H 2 O is pulsed, then purged and then an HfCl 4  precursor is pulsed then purged to form an HfO 2  film. However, chlorine (Cl) impurities are formed in the high-k HfO 2  film, especially proximate the interface between the HfO film and the substrate over which it is formed. ALCVD processes generally have a low process temperature of from about 250 to 350° C.  
         [0006]     U.S. Pat. No. 6,271,094 B1 to Boyd et al. describes a method of making MOSFET with a high dielectric constant (k) gate insulator and minimum overlap capacitance.  
         [0007]     U.S. Pat. No. 6,153,477 to Gardner et al. describes a process of forming an ultra-short transistor channel length using a gate dielectric having a relatively high dielectric constant.  
         [0008]     U.S. Pat. No. 6,114,228 to Gardner et al. describes a method of making a semiconductor device with a composite gate dielectric layer and gate barrier layer.  
         [0009]     U.S. Pat. No. 6,090,723 to Thakur et al. describes conditioning processes including annealing or high-k dielectrics.  
         [0010]     U.S. Pat. No. 6,008,095 to Gardner et al. describes a process for the formation of isolation trenches with high-k gate dielectrics.  
       SUMMARY OF THE INVENTION  
       [0011]     Accordingly, it is an object of one or more embodiments of the present invention to provide a improved process of forming high-k dielectric layers.  
         [0012]     It is another object of one or more embodiments of the present invention to provide an improved annealing process for repairing defects at silicon/high-k dielectric layer interfaces.  
         [0013]     Other objects will appear hereinafter.  
         [0014]     It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate is provided. A high-k dielectric layer having impurities is formed over the substrate. The high-k dielectric layer being formed by an MOCVD or an ALCVD process. The high-k dielectric layer is annealed to reduce the impurities within the high-k dielectric layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:  
         [0016]     FIGS.  1  to  4  schematically illustrate a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Unless otherwise specified, all structures, layers, steps, methods, etc. may be formed or accomplished by conventional steps or methods known in the prior art.  
         [0000]     Initial Structure  
         [0018]     As shown in  FIG. 1 , structure  10  includes shallow trench isolation (STI) structures  12  formed therein. Structure  10  is preferably a silicon substrate and is understood to possibly include a semiconductor wafer or substrate. STIs  12  are comprised of thermal oxide, SACVD oxide or HDP-CVD oxide and are more preferably HDP-CVD oxide.  
         [0019]     A high-k dielectric layer  14  is formed over silicon substrate  10  generally between STIs  12  to a thickness of preferably from about 5 to 200 Å and more preferably from about 20 to 100 Å. High-k dielectric layer  14  is preferably comprised of a metal oxide or a metal silicate formed by either an MOCVD process which introduces carbon (and hydrogen) impurities or an ALCVD process which introduces chlorine impurities, and does not decompose under the annealing  16  conditions of the present invention.  
         [0020]     High-k dielectric layer  14  is preferably: (1)a metal oxide such as HfO 2 , ZrO 2 , La 2 O 3 , Y 2 O 3 , Al 2 O 3  or TiO 2  and more preferably HfO 2 , ZrO 2  or Al 2 O 3 , or (2) a metal silicate such as HfSi x O y , ZrSi x O y , LaSi x O y , YSi x O y , AlSi x O y  or TiSi x O y  and more preferably HfSi x O y  or ZrSi x O y .  
         [0000]     Anneal of Deposited High-k Dielectric Layer  14 —One Key Step of the Invention  
         [0021]     In one key step of the invention and as illustrated in  FIG. 2 , the deposited high-k dielectric layer  14  is annealed  16  at a temperature of preferably from about 280 to 820° C., more preferably from about 300 to 800° C. and most preferably from about 300 to 700° C. for preferably from about 0.5 to 300 seconds, more preferably from about 2 to 100 seconds for rapid thermal anneal (RTA) process and from about 5 to 300 minutes for furnace annealing processes to drive out the chlorine; and carbon and hydrogen impurities to form an impurity-free high-k dielectric layer  14 ′. That is the chlorine, carbon and/or hydrogen impurities are reduced to preferably less than about 20% to 2 times which improves the electrical performance of the subsequently formed transistors/devices incorporating impurity-free high-k dielectric layer  14 ′.  
         [0022]     The anneal  16  is preferably by rapid thermal processing (RTP) or by a furnace anneal and is conducted so as to minimize recrystallization of the high-k dielectric layerl 4 . The anneal  16  is carried out in the presence of ambients that are preferably H 2 , N 2 , H 2 /N 2 , H 2 /O 2 , O 2 /N 2 , He or Ar and are more preferably H 2 /N 2  or O 2 /N 2 . The presence of oxygen (O 2 ) is kept low to avoid additional oxidation of the high-k dielectric layer  14 .  
         [0000]     Formation of Gate Layer  18   
         [0023]     As shown in  FIG. 3 , a gate layer  18  is formed over impurity-free high-k dielectric layer  14 ′ to a thickness of preferably from about 100 to 3000 Å and more preferably from about 500 to 2000 Å. Gate layer  18  is preferably comprised of polysilicon (poly) or a metal (metal gate) such as TaN/W, TiN/W, TaN/Al or TiN/Al and is more preferably polysilicon.  
         [0000]     Further Processing  
         [0024]     Further processing may then proceed. For example, as shown in  FIG. 4 , gate layer  18  and impurity-free high-k dielectric layer  14 ′ are patterned to form gate electrode  20  comprised of patterned gate layer  18 ′ and impurity-free high-k dielectric layer  14 ″.  
         [0025]     Additional processing may continue thereafter. For example, silicide formation, LDD implants, gate sidewall spacer formation, HDD implants, etc. to complete formation of a transistor or device incorporating gate electrode  20 .  
       ADVANTAGES OF THE PRESENT INVENTION  
       [0026]     The advantages of one or more embodiments of the present invention include:  
         [0027]     1. improved transistor/device electrical performance; and  
         [0028]     2. improved process for high-k film quality.  
         [0029]     While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.