Abstract:
A method of forming a dielectric layer on a semiconductor substrate, comprised with multiple dielectric constants and multiple equivalent oxide thicknesses (EOT), has been developed. After formation of a high dielectric constant (high k), layer, on a semiconductor substrate, a first region of the high k layer is subjected to a process directed at incorporating elements into a top portion of the high k layer, while a second region of the high k layer remains protected during this procedure. An anneal treatment results in the processed high k layer now exhibiting a different dielectric constant, as well as a different EOT, than the unprocessed, second region of the high k layer, not exposed to the above procedures.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a gate insulator layer comprised with multiple dielectric constants, and with multiple thicknesses, on the same semiconductor chip.  
           [0003]    (2) Description of Prior Art  
           [0004]    Micro-miniaturization, or the ability to fabricate semiconductor devices with sub-micron features, has allowed device integration to progress to where an entire system on chip (SoC), can now be realized. The concept of SoC however requires multiple gate insulator layer thicknesses, as well as gate insulator layers offering multiple dielectric constants, to satisfy specific functions of the SoC design. The attainment of different gate insulator thicknesses on specific regions of a semiconductor substrate has been achieved via implantation into the semiconductor substrate prior to the thermal oxidation procedure used for growth of a silicon dioxide gate insulator layer, with the implanted species either enhancing or reducing the oxidation rate of the semiconductor substrate thus allowing various silicon dioxide gate insulator thicknesses to be obtained. Implantation of such ions as fluorine, argon, and nitrogen, have been used to adjust the differential oxidation rates. However for enhanced device performance the thickness of gate insulator layers are being scaled down to thicknesses below 20 Angstroms, making the procedure of implantation into semiconductor prior to oxidation difficult to implement.  
           [0005]    This invention will describe procedures in which specific regions of a gate insulator layer are formed with a specific dielectric constant and a specific thickness, while other regions of the same gate insulator layer are formed with a different dielectric constant and at a different thickness, accomplished via incorporation of various elements into specific regions of a gate insulator layer. Prior art such as Gilmer, in U.S. Pat. No. 6,348,386 B1, Ma et al, in U.S. Pat. No. 6,297,539 B1, Ma et al, in U.S. Pat. No. 6,207,589 B1, and Kaushik et al, in U.S. Pat. No. 6,184,072 B1, describe methods of forming metal oxide gate insulator layers. None of the above prior arts however describe the novel procedures illustrated in this present invention wherein incorporation of specific elements into specific regions of a gate insulator layer allow a different dielectric constant and different equivalent oxide thickness (EOT), than that of the non-processed regions of gate insulator, to be realized.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of this invention to form a gate insulators layer on a semiconductor substrate, comprised with various dielectric constants and various equivalent oxide thicknesses.  
           [0007]    It is another object of this invention to initially form a high dielectric constant (high k), layer on a semiconductor substrate, followed by placement of elements into specific regions of the high k layer to change the dielectric constant and to change the EOT of the region of high k layer exposed to this procedure.  
           [0008]    It is still another object of the invention where a first embodiment places a first type of element into a high k layer to decrease the dielectric constant while increasing the EOT of the high k layer, while a second embodiment of the invention places a second type of element into a high k layer to increase the dielectric constant while decreasing the EOT of the processed high k layer.  
           [0009]    In accordance with the present invention a method of forming a gate insulator layer comprised with various dielectric constants, and various equivalent oxide thicknesses (EOT), on the same semiconductor substrate, via incorporation of elements into a high k, gate insulator layer, to change the dielectric constant as well as the equivalent oxide thickness (EOT), of the gate insulator layer, is described. A first embodiment of this invention features the formation of a first high k dielectric layer on a semiconductor substrate followed by immersion or implantation of first type elements into a region of the first high k dielectric layer not covered by a block-out shape. An anneal procedure results in the first portion of the first high k layer, the portion exposed to the immersion of implantation procedure, now comprised with a lower dielectric constant, and an increased EOT, when compared to a second portion of the first high k layer not exposed to the immersion or implantation procedure. A second embodiment of this invention features the formation of a second high k dielectric layer on a semiconductor substrate followed by immersion or implantation of second type elements into a region of the second high k dielectric layer not covered by a block -out shape. An anneal procedure results in a first portion of the second high k layer, the region exposed to the immersion of implantation procedure, now comprised with a higher dielectric constant, and a decreased EOT, when compared to a second portion of the second high k layer not exposed to the immersion or implantation procedure. Formation of gate structures on underlying gate insulator layers, comprised with various EOT and various dielectric constants, is then performed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The object and other advantages of this invention are best described in the preferred embodiment with reference to the attached drawings that include:  
         [0011]    FIGS.  1 - 3 , which schematically, in cross-sectional style, describe a first embodiment of this invention in which immersion or implantation of a first group of elements into a first region of a first high k gate insulator layer, results in the exposed gate insulator region now comprised with a lower dielectric constant and a thicker equivalent oxide thicknesses (EOT), than a second region of the first high k layer not exposed to the immersion or implantation procedure.  
         [0012]    FIGS.  4 - 6 , which schematically, in cross-sectional style, describe a second embodiment of this invention in which immersion or implantation of a second group of elements into a first region of a second high k gate insulator layer, results in the exposed gate insulator region now comprised with a higher dielectric constant and a thinner equivalent oxide thickness (EOT), when compared to the second region of the second high k layer not exposed to the immersion or implantation procedure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    The method of forming a gate insulator layer on a semiconductor substrate, wherein a first region of the gate insulator layer features a dielectric constant and a equivalent oxide thickness (EOT), different the dielectric constant and EOT of a second region of the gate insulator layer, will now be described in detail. Semiconductor substrate  1 , comprised of single crystalline material featuring a &lt;100&gt;crystallographic orientation, is used and schematically shown in FIG. 1. Shallow trench isolation (STI) region  2 , comprised of an insulator filled shallow trench shape, is next formed via definition of a shallow trench shape in a top portion of semiconductor substrate  1 , followed by insulator filling of the shallow trench shape and removal of unwanted regions of insulator layer from the top surface of semiconductor substrate  1 . The shallow trench shape can be defined via photolithographic and dry etching procedures, using Cl 2  as an etchant for silicon, while the insulator layer used for filling of the shallow trench shape can be a silicon oxide layer obtained via low pressure chemical vapor deposition (LPCVD), or via plasma enhanced chemical vapor deposition (PECVD), procedures. Removal of unwanted portions of insulator is either accomplished via a chemical mechanical polishing (CMP) procedure, or via a selective dry etching procedure using CHF 3  as an etchant for the insulator layer. Dielectric layer  3   a , comprised of either hafnium oxide (HfO 2 ), zirconium oxide (ZrO 2 ), or cerium oxide (CeO 2 ), is next grown on semiconductor substrate  1 , to a physical thickness between about 40 to 80 Angstroms, featuring a high dielectric constant (high k), between about 20 to 28. The equivalent oxide thickness (EOT), of dielectric layer  3   a , is between about 7 to 13 Angstroms. Dielectric layer  3   a , schematically shown in FIG. 1, is obtained via atomic layer deposition (ALD), or metal organic chemical vapor deposition (MOCVD), procedures, performed at a temperature between about 200 to 500° C. A first embodiment of this invention allowing a first region of the gate insulator layer to be formed on a first portion of the semiconductor substrate, featuring a specific dielectric constant and a specific insulator thickness, while a second region of the gate insulator layer, located on a second portion of the same semiconductor substrate, is processed to exhibit a lower dielectric constant and thicker insulator layer than the first region of the gate insulator layer, is next described. Photoresist shape  4 , is formed on a first region of dielectric layer  3   a , allowing the exposed portion of dielectric layer  3   a , to experience immersion or implantation of specific elements, such as silicon, germanium, or aluminum. Incorporation of an element such as silicon into a HfO 2  dielectric layer is accomplished via either plasma immersion procedures, performed at a power between about 50 to 1000 watts, at a pressure between about 10 to 500 mtorr, or performed via implantation of the specific element such as silicon, at an implant energy between about 0.1 to 1.0 KeV, and at an implant dose between about 1E13 to 1E15 atoms/cm 2 , resulting in the creation of dielectric layer  3   b . This is schematically shown in FIG. 2.  
         [0014]    After removal of photoresist shape  4 , via plasma oxygen ashing procedures, an anneal procedure is used to activate the incorporated ions in dielectric layer  3   b , resulting in a dielectric layer  3   b , such as HfSi x O y , featuring a dielectric constant between about 8 to 16, lower than the dielectric constant of non-treated dielectric layer  3   a . In addition although the physical thickness of dielectric layer  3   b , remains between about 40 to 80 Angstroms, the change in dielectric constant results in an EOT for dielectric layer  3   b , of between about 13 to 27 Angstroms. Therefore the desired result of providing multiple thicknesses within a gate insulator layer, on the same semiconductor substrate, is accomplished. The anneal procedure, which can be an optional step since the immersed or implanted species can provide a portion of the changes in dielectric constant and EOT without annealing, is performed at a temperature between about 400 to 700° C., in an inert, or in an oxidizing ambient. A conductive layer such as doped polysilicon, titanium nitride, tantalum nitride, or molybdenum is next formed on the underlying dielectric layers, at a thickness between about 1000 to 2000 Angstroms, via chemical vapor deposition (CVD), or via plasma vapor deposition (PVD), procedures. A photoresist shape, not shown in the drawings, is then employed as a mask to allow an anisotropic reactive ion etching (RIE) procedure, using Cl 2  or SF 6  as an etchant, to define conductive gate structures  5 , on thinner EOT, underlying dielectric or gate insulator layer  3   a , and on thicker EOT, underlying dielectric or gate insulator layer  3   b . This is schematically shown in FIG. 3.  
         [0015]    A second embodiment of this invention directed at obtaining a first region of a gate insulator layer on a semiconductor substrate, featuring a specific dielectric constant and a specific insulator thickness, while a second region of the same gate insulator layer located on the same semiconductor substrate, is formed with a higher dielectric constant and thinner equivalent oxide thickness than the first region of the gate insulator layer, is next described. Dielectric layer  6   a , comprised of aluminum oxide (Al 2 O 3 ), is formed on semiconductor substrate  1 , with a physical thickness between about 80 to 100 Angstroms, and with a dielectric constant between about 10 to 14, translating to a EOT between about 27 to 33 Angstroms. Aluminum oxide, dielectric layer  6   a , is obtained via CVD procedures. This is schematically shown in FIG. 4.  
         [0016]    Photoresist shape  7 , is next formed on a first region of dielectric layer  6   a , allowing the exposed portion of dielectric layer  6   a , to experience immersion or implantation of specific elements, such as hafnium, zirconium, or silicon. Incorporation of an element such as hafnium into the Al 2 O 3  layer is accomplished via either plasma immersion procedures, performed at a power between about 50 to 1000 watts, at a pressure between about 10 to 50 mtorr, or performed via implantation of the specific element such as hafnium, at an implant energy between about 0.1 to 1.0 KeV, and at an implant dose between about 1E13 to 1E15 atoms/cm 2 , resulting in the creation of dielectric layer  6   b . This is schematically shown in FIG. 5.  
         [0017]    After removal of photoresist shape  7 , via plasma oxygen ashing procedures, an optional anneal procedure can be used to activate the incorporated hafnium element in the Al 2 O 3  layer resulting in an HfAl x O y  dielectric layer  6   b . Dielectric layer  6   b , HfAl x O y , features a dielectric constant between about 12 to 20, higher than the dielectric constant of non-treated dielectric layer  6   a . In addition, although the physical thickness of dielectric layer remains between about 80 to 100 Angstroms, the change in dielectric constant results in an EOT for dielectric layer  6   b , of between about 20 to 25 Angstroms, less than the EOT of non-treated Al 2 O 3  counterparts. Therefore the desired result of providing multiple thicknesses for specific regions of a gate insulator layer, is again accomplished. The anneal procedure, which again can be an optional step since the immersed or implanted species can provide a portion of the desired changes in dielectric constant and EOT without annealing, is performed at a temperature between about 400 to 700° C., in an inert, or in an oxidizing ambient. A conductive layer such as doped polysilicon, titanium nitride, tantalum nitride, or molybdenum is next formed on the underlying dielectric layers, at a thickness between about 1000 to 2000 Angstroms, via chemical vapor deposition (CVD), or via plasma vapor deposition (PVD), procedures. A photoresist shape, not shown in the drawings, is then employed as a mask to allow an anisotropic reactive ion etching (RIE) procedure, using Cl 2  or SF 6  as an etchant, to define conductive gate structures  5 , on thicker EOT, underlying dielectric or gate insulator layer  6   a , and on thinner EOT, underlying dielectric or gate insulator layer  6   b . This is schematically shown in FIG. 6.  
         [0018]    While this invention has been particularly shown and described with reference to, the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of this invention.