Abstract:
A method including depositing a material for a gate electrode on a substrate over a dielectric material, the gate electrode material comprising a metal; depositing a capping material over the gate electrode material under processing conditions that will not promote any oxygen species associated with the gate electrode material to travel through the gate electrode material to the substrate; and patterning a gate electrode structure comprising the gate electrode material.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    Integrated circuit devices and processing. 
         [0003]    2. Background 
         [0004]    The scale of a transistor device requires consideration of the desired performance of the device. For example, one goal may be to increase the current flow in the semiconductor material of the transistor. The current flow is proportional to the voltage applied to the gate electrode and the capacitance seen at the gate: 
         [0000]      Q∝C(V−V th ) 
         [0000]    where Q is one measure of the current flow, C is capacitance, V is the voltage applied to the gate electrode, and V th  is the threshold voltage of the device. 
         [0005]    To increase the voltage applied to a device requires an increase in power, P(P∝V 2 ). However, at the same time as increasing the charge in the transistor, subsequent generations also seek to reduce the power required to run the device, since, importantly, a reduction of power reduces the heat generated by the device. Thus, to increase the current flow through the device without increasing the power requires an increase in the capacitance in the gate. 
         [0006]    One way to increase the capacitance is by adjusting the thickness of the gate dielectric. In general, the capacitance is related to the gate dielectric by the following formula: 
         [0000]      C=k ox /t electrical    
         [0000]    where k ox  is the dielectric constant of silicon dioxide (SiO 2 ) and t electrical  is the electrical thickness of the gate dielectric. 
         [0007]    The electrical thickness of the gate dielectric is typically greater than the actual thickness of the dielectric in most semiconductor devices. In general, as carriers flow through the channel of a semiconductor-based transistor device there is a quantum effect experienced in the channel which causes an area directly below the gate to become insulative. The insulative region acts like an extension of the gate dielectric by essentially extending the dielectric into a portion of the channel. The second cause of increase gate dielectric thickness attributable to t electrical  is experienced by a similar phenomenon happening in the gate electrode itself. 
         [0008]    The result of the quantum effect in the channel and a depletion in the gate electrode is an electrical thickness (t electrical ) of the gate dielectric greater than the actual thickness of the gate dielectric. The magnitude of the channel quantum effect and gate electrode depletion may be estimated or determined for a given technology. Accordingly, the electrical thickness (t electrical ) may be calculated and scaled for a given technology. 
         [0009]    To increase the performance of a transistor device, dielectric material having a higher dielectric constant than a dielectric constant of SiO 2  (“high k dielectric material”) have been utilized as have gate electrode of metal materials. A typical formation process is to deposit a metal film over the high k dielectric material and then cap the metal film with polysilicon or other material. The metal film is often exposed to ambient atmospheric conditions prior to capping. Under such conditions, metal films may absorb oxygen from the ambient. When a capping material requiring high temperature deposition conditions, such as a chemical vapor deposition of polycrystalline silicon (“polysilicon”) done at 600° C. or greater, is utilized, the oxygen absorbed in the metal film can travel downward into the semiconductor substrate, and oxidize the semiconductor substrate. A migration of oxygen into the semiconductor substrate tends to increase the electrical thickness (t electrical ) and degrade the capacitance seen at the gate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Features, aspects, and advantages of embodiments will become more thoroughly apparent from the following detailed description, appended claims, and accompanying drawings in which: 
           [0011]      FIG. 1  shows a portion of a semiconductor substrate having an oxide layer formed on a surface thereof and a high k dielectric material formed on the oxide layer. 
           [0012]      FIG. 2  shows the structure of  FIG. 1  following the deposition of a metal film on the high k dielectric. 
           [0013]      FIG. 3  shows the structure of  FIG. 2  following the deposition of a capping layer on the metal film. 
           [0014]      FIG. 4  shows the structure of  FIG. 3  following the patterning of a gate electrode over a gate dielectric. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a portion of a substrate, such as a wafer (e.g., silicon wafer) designated for circuit devices to form, for example, a microprocessor chip. Structure  100  includes substrate  110 , such as a silicon substrate or a silicon on insulator (SOI) substrate. In one embodiment, circuit devices, such as transistor devices, will be formed in and on a surface of substrate  110 . Typically, for a substrate of a silicon wafer, the surface of the wafer is oxidized (e.g., thermal oxidation) to a thickness on the order of 200 angstroms (Å). The oxidized surface is then removed (e.g., etched away) to bare silicon. The surface is then cleaned and oxidized again (e.g., thermal oxidation).  FIG. 1  shows substrate  110  having silicon dioxide (SiO 2 ) film  120  formed thereon. The oxidation may be formed via a wet chemical clean or grown in a furnace. In one embodiment, a suitable thickness for SiO 2  film  120  is on the order of three to 20 angstroms (Å). Representatively, in one embodiment, film  120  formed by a wet chemical clean may be on the order of 3 Å to 10 Å. 
         [0016]    Following the oxidation of a surface of substrate  110  (the superior surface as viewed), substrate  110  is transferred to a deposition tool for depositing a dielectric material having a dielectric constant greater than a dielectric constant of SiO 2  (a “high k” dielectric material). Suitable deposition tools include tools capable of depositing a high k dielectric material using atomic layer deposition (ALD) or chemical vapor deposition (CVD) techniques. Suitable high k dielectric materials include, but are not limited to, hafnium oxide (HfO 2 ), zirconium oxide (ZrO 2 ), lanthanum oxide (La 2 O 3 ) and yittrium oxide (Y 2 O 3 ).  FIG. 1  shows high k dielectric material layer  130  deposited as a blanket on SiO 2  layer  120 . A representative thickness of high k dielectric material layer  130  of HfO 2  is on the order of 20 Å. 
         [0017]    Following the deposition of high k dielectric material layer  130 , structure  100  is transferred to a metal deposition tool. Typical transfer of structure  100  from a high k dielectric material layer deposition tool to a metal deposition tool exposes structure  100  to ambient conditions. 
         [0018]      FIG. 2  shows structure  100  following the deposition of metal containing film  140 . A metal containing film, including, but not limited to, titanium nitride (TiN) or tantalum nitride (TaN) may be deposited using physical vapor deposition techniques in a sputter tool. In one embodiment, a deposition process is done under vacuum conditions on the order of 10 −8  torr. 
         [0019]      FIG. 2  shows structure  100  including metal containing film  140  on high k dielectric material layer  130 . In one embodiment, metal containing film  140  has a thickness on the order of 5 Å to 25 Å. In another embodiment, the thickness of metal containing film  140  is on the order of 10 Å to 25 Å. 
         [0020]      FIG. 3  shows the structure of  FIG. 2  following the deposition of capping layer  150  on metal containing film  140 . In one embodiment, capping layer  150  is deposited by sputtering, such as PVD. In an example where capping layer  130  is a silicon material, silicon may be sputter deposited by PVD with substrate  110  at a temperature of −100° C. to 225° C., representatively 100° C. The sputter deposition of silicon will result in capping layer  150  of amorphous silicon. 
         [0021]    By depositing capping layer  150  using a sputter (e.g., PVD) deposition technique, the deposition temperature may be kept at in minimum. This is in contrast to, for example, chemical vapor deposition of, for example, silicon, which requires temperatures of 600° C. or greater. By depositing capping layer  150  at a reduced temperature, the migration of any absorbed oxygen in metal containing film  130  may be minimized. 
         [0022]    In another embodiment, the ability of metal containing layer  140  to absorb oxygen from the ambient is minimized by depositing metal containing film  140  and capping layer  150  in situ. By “in situ” is meant that metal containing film  140  and capping layer  150  may be deposited without exposing structure  100  to ambient conditions between depositions. This may be accomplished, for example, by maintaining the pressure conditions (e.g., vacuum conditions) for both depositions and/or by using one tool for the deposition of metal containing film  140  and capping layer  150 . In the case of sputter deposition of each of metal containing film  140  and capping layer  150 , a suitable tool may be a multi-chamber tool. 
         [0023]      FIG. 4  shows the structure of  FIG. 3  following the patterning of the material layers on a surface of substrate  110  into a gate electrode on a gate dielectric on the substrate.  FIG. 4  shows a composite gate dielectric of SiO 2  layer  120  and high k dielectric material layer  130 .  FIG. 4  shows composite gate electrode of metal containing film  140  and capping layer  150  of, for example, silicon. In one example, capping layer  150  of silicon to be utilized as a portion of gate electrode may have a thickness on the order of 25 Å to 120 Å, the thicker the capping layer the tendency to increase the capacitance at the gate or reduce t electrical . 
         [0024]    One way to pattern the composite gate electrode and composite gate dielectric as shown in  FIG. 4  is through photolithographic techniques wherein, for example, a photoresist material is patterned to expose an area over an area designated for the gate electrode. The blanket-deposited capping layer  150 , metal containing film  140 , high k dielectric material layer  130  are then etched as is SiO 2  layer  120 .  FIG. 4  shows the composite gate electrode and composite gate dielectric in active area  160  of substrate  100  following patterning. Active area  160  is defined, in one embodiment, by shallow trench isolation structure  170 .  FIG. 4  also shows source region  180 A and drain region  180 B formed in substrate  110  as part of the transistor device. 
         [0025]    In the embodiment shown in  FIG. 4 , capping layer  150  of, for example, silicon, is retained as part of a composite gate electrode. In another embodiment, capping layer may be removed in subsequent processing operations and optionally replaced. Accordingly, a material for capping layer  150  is selected, in one embodiment, to act as a seal material to, for example, hermetically seal metal containing film  140  to minimize the absorption of oxygen by metal containing film during subsequent processing operations. Thus, materials other than silicon are as a material for capping layer  150 . A suitable material for a sacrificial layer is, for example, silicon nitride. 
         [0026]    In an embodiment where containing film  140  may be exposed to ambient conditions prior to the deposition of capping layer  150 , a material for capping material  150  should be selected such that it may be deposited under conditions (e.g., a temperature) that will not encourage the migration of any oxygen containing species in metal containing film  140  to migrate toward substrate  110 . 
         [0027]    In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.