Abstract:
A dielectric material layer is formed on a carrier material. A gas mixture containing at least one precursor comprising a metallic element is alternately circulated with an oxidant gas in contact with the carrier material under first oxidizing conditions so as to form a first sub-layer having dielectric qualities. A gas mixture containing the same precursor then is circulated in contact with the first sub-layer under second oxidizing conditions being more strongly oxidizing than the first oxidizing conditions so as to form a second sub-layer having dielectric qualities.

Description:
PRIORITY CLAIM  
       [0001]     The present application claims priority from French Application for Patent No. 05 09642 filed Sep. 21, 2005, the disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field of the Invention  
         [0003]     The present invention relates to integrated circuits, and more particularly to the production of a layer including at least one dielectric material used, for example, for a capacitor.  
         [0004]     2. Description of Related Art  
         [0005]     It is known to produce planar or three-dimensional capacitors using a technology based on aluminum (Reactive Ion Etching, RIE) or based on copper (Damascene type integration).  
         [0006]     The capacitors are conventionally obtained from a metal-insulator-metal (MIM) stack in which the lower electrode is a conductive material, for example TiN, the insulator is preferably a dielectric material with high permittivity (high-K material) and the upper electrode is a conductive material, for example TiN.  
         [0007]     Such capacitors can be produced at the interconnections of an integrated circuit and, for example, after the fourth metallization level in the interconnections. The production of such capacitors actually within an integrated circuit thus still represents a difficulty, given that this production must not entail deterioration of the other components already produced.  
         [0008]     Furthermore, the formation of a dielectric layer on a lower electrode also presents a certain number of problems.  
         [0009]     Specifically, the steps for forming a dielectric layer are generally carried out under an oxidizing atmosphere in the high temperature range, preferably at temperatures above 350° C., in order to obtain a dielectric layer with good quality in terms of stoichiometry.  
         [0010]     These formation steps generally entail oxidation of the lower electrode, however, causing its deterioration as well as the formation of an interface layer between the lower electrode and the dielectric layer. This interface layer may have a density greater than that of the dielectric layer and a thickness which may amount to 25 angstroms. When the dielectric material is an oxide, furthermore, oxidation of the lower electrode is accelerated owing to diffusion of oxygen from the oxide to the lower electrode, thereby increasing the thickness of the interface layer being formed.  
         [0011]     These problems result in the appearance of leakage currents which, in particular, entail degradation of the electrical performance of the capacitor.  
         [0012]     FR 2847593 thus describes the formation of a tantalum pentoxide layer on a carrier material in an oxidizing atmosphere at a temperature of between 300 and 350° C. from a gas mixture containing a tantalum precursor, the partial pressure of the precursor in the gas mixture being greater than or equal to 25 mTorr.  
         [0013]     In view of the preceding, there is a need in the art to produce a dielectric layer having good quality in stoichiometric terms while minimizing the appearance of leakage currents.  
       SUMMARY OF THE INVENTION  
       [0014]     One embodiment provides a method for forming a layer having at least one dielectric material on a carrier material, in which:  
         [0015]     a gas mixture, containing at least one precursor comprising a metallic element, then an oxidant gas are circulated in contact with the carrier material under first oxidizing conditions so as to form a first layer having at least one dielectric material, and  
         [0016]     a gas mixture containing the precursor is circulated in contact with the first layer under second oxidizing conditions, the second oxidizing conditions being more strongly oxidizing than the first oxidizing conditions.  
         [0017]     A dielectric layer with good quality in stoichiometric terms is then obtained while reducing to a minimum the thickness of the interface layer between the lower electrode and the dielectric layer.  
         [0018]     The term first oxidizing conditions is intended to mean conditions which make it possible to minimize the oxidation of the lower electrode during the formation of the first layer consisting of at least one dielectric material.  
         [0019]     These oxidizing conditions make it possible in particular to obtain an interface layer, arranged between the lower electrode and the first dielectric layer, which has a thickness of less than 5 angstroms.  
         [0020]     In other words, the formation of the first layer having at least one dielectric material takes place under first oxidizing conditions which make it possible to minimize the oxidation of the lower electrode and, consequently, to reduce the thickness of the interface layer arranged between the lower electrode and the first layer having at least one dielectric material.  
         [0021]     In this way, both an interface of good quality which limits the leakage currents of the dielectric layer and also satisfactory bulk properties are obtained.  
         [0022]     Furthermore, the two steps of the method which were described above allow the electrical performance to be controlled better by controlling the interface between the lower electrode and the dielectric layer.  
         [0023]     In particular, leakage currents can be obtained which are less than 3.10 −5  amperes per cm 2  of dielectric at 125° C. under the application of a relative voltage equal to about 5 volts to the terminals of the electrodes, for a dielectric layer which has a thickness of 400 angstroms. These leakage currents are in particular about 100 times to 1000 times less than those generally measured for dielectric layers produced according to the conventional formation steps.  
         [0024]     The oxidant gas advantageously contains water vapor in order to minimize the oxidation of the carrier material during the formation of the first layer.  
         [0025]     As a variant, the carrier material is heated to a temperature of between 250 and 350° C. during the formation of the first layer and/or the first layer is formed with a plasma having a power of less than 150 watts, in order to work under less oxidizing conditions than during the formation of the second dielectric layer.  
         [0026]     According to one embodiment, the gas mixture is circulated in a chamber in which the carrier material is placed, and in which the chamber is purged between the circulation of the gas mixture and the circulation of the oxidant gas during the formation of the first layer. Such a purging step makes it possible to reduce the concentration of the precursors which have not become attached on the surface of the carrier material. Furthermore, this purging step can make it possible to avoid oxidation reactions between the precursors which are not attached to the surface of the carrier material and the oxidant gas.  
         [0027]     Preferably, the gas mixture is circulated in an oxidizing atmosphere after having formed a thickness between 5 and 1000 angstroms of the first layer.  
         [0028]     According to one embodiment, a gas mixture, containing the precursor in an oxidizing atmosphere, and a plasma are circulated alternately in contact with the first layer, in order to obtain a dielectric layer of good quality in terms of stoichiometry.  
         [0029]     Advantageously, the gas mixture contains tertbutylimido-tris-diethylamino tantalum (t-BuN=Ta(NEt 2 ) 3 ) or tantalum pentaethoxide (Ta(OEt) 5 ).  
         [0030]     According to one characteristic, the carrier material is a semiconductor material or material comprising a metal.  
         [0031]     Advantageously, the carrier material is selected from titanium nitride (TiN), tantalum nitride (TaN), copper, aluminum, tungsten, ruthenium, tungsten nitride (WN), tungsten carbonitride (WCN).  
         [0032]     Advantageously, the dielectric material is selected from Ta 2 O 5 , Al 2 O 3 , TiO 2 , ZrO 2  and/or HfO 2 .  
         [0033]     According to another aspect, the invention also relates to a layer consisting of at least one dielectric material, which can be obtained by the method described above.  
         [0034]     According to another aspect, the invention also relates to an integrated circuit comprising at least one capacitor comprising a layer having at least one dielectric material arranged between two electrodes and obtained by the method described above.  
         [0035]     According to one characteristic, an interface layer arranged between the electrode and the layer having at least one dielectric material has a thickness of less than 5 angstroms.  
         [0036]     According to one characteristic, the layer consisting of at least one dielectric material has a thickness of between 20 and 2000 angstroms and, for a dielectric layer with a thickness equal to 400 angstroms, has a leakage current of less than 3.10 −5  A/cm 2  at 125° C. under a relative voltage difference of about 5 volts applied between the two electrodes.  
         [0037]     In an embodiment, a method for forming a dielectric material layer on a carrier material comprises circulating a gas mixture containing at least one precursor having a metallic element followed by an oxidant gas in contact with the carrier material under first oxidizing conditions so as to form a first dielectric material layer, and then circulating a gas mixture containing the same precursor in contact with the first layer under second oxidizing conditions so as to form a second dielectric material layer, the second oxidizing conditions being more strongly oxidizing than the first oxidizing conditions.  
         [0038]     In an embodiment, a dielectric material layer comprises a first dielectric material sub-layer formed on a carrier material by alternately circulating a gas mixture containing at least one precursor having a metallic element and an oxidant gas under first oxidizing conditions, and a second dielectric material sub-layer formed on the first dielectric material sub-layer by circulating a gas mixture containing the same precursor under second oxidizing conditions being more strongly oxidizing than the first oxidizing conditions.  
         [0039]     In another embodiment, a method for forming a dielectric material layer on a carrier material comprises: (a) circulating a gas mixture containing at least one precursor having a metallic element to form a monolayer on the carrier material; (b) applying an oxidant gas under first oxidizing conditions so as to oxidize the monolayer and form a first dielectric material sub-layer; and (c) circulating a gas mixture containing the same precursor in contact with the oxidized monolayer under second oxidizing conditions so as to form a second dielectric material sub-layer over the first dielectric material sub-layer, the second oxidizing conditions being more strongly oxidizing than the first oxidizing conditions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]     A more complete understanding of the method and apparatus of the present invention may be acquired by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:  
         [0041]      FIG. 1  schematically illustrates an integrated circuit comprising a capacitor obtained according to one embodiment; and  
         [0042]     FIGS.  2  to  4  schematically illustrate the steps of an embodiment of a layer consisting of at least one dielectric material. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]     As illustrated in  FIG. 1 , an integrated circuit  1  comprises active components  2 , for example transistors, in a substrate  3 . The integrated circuit  1  also comprises stacked metallization levels  5   a ,  6   a ,  7   a ,  8   a  and  9   a  separated by dielectric layers  5   b ,  6   b ,  7   b  and  8   b  formed above the substrate  3 . Arranged between the substrate  3  and the metallization level  5   a , there is a dielectric layer  4  in which there are vias  10  providing the electrical connection of the active components  2 .  
         [0044]     A capacitor  30  has furthermore been produced between the metallization levels  8   a  and  9   a  of the integrated circuit  1 . In other words, the capacitor  30  is situated in the dielectric layer  8   b.    
         [0045]     The capacitor  30  comprises a dielectric layer  32 , for example a layer of tantalum pentoxide (Ta 2 O 5 ), sandwiched between a lower electrode  31  resting on the upper surface of the metallization level  8   a  and an upper electrode  33  resting under the lower surface of the metallization level  9   a . The electrodes  31  and  33  may consist of titanium nitride (TiN) or tungsten. A via  11  is arranged between the upper electrode  33  and the metallization level  9   a , thus providing the electrical connection.  
         [0046]     Under a relative voltage difference of about 5 volts applied between the two electrodes  31  and  33 , a leakage current is measured which may be less than 3.10 −5  A/cm 2  at a temperature of 125° C. for a dielectric layer which has a thickness of 400 angstroms. Furthermore, an X-ray analysis of the interface situated between the lower electrode  31  and the dielectric layer  32  can show that an interface layer is obtained whose thickness is in particular less than 5 angstroms.  
         [0047]     FIGS.  2  to  4  represent the principal steps of an embodiment making it possible to obtain a capacitor  30  having a dielectric layer  32  as described above and as illustrated in  FIG. 1 .  
         [0048]     The fabrication is carried out by means of a chamber  12  in which a plate  13  is placed, the upper surface of which has a layer on top comprising a carrier material  31 , for example of titanium nitride or tungsten, as represented in  FIG. 2 . Injection means  14  and  15 , arranged in the walls of the chamber  12  and extending to above the plate  13 , make it possible for a gas mixture  16  containing for example tertbutylimido-tris-diethylamino tantalum (t-BuN=Ta(NEt 2 ) 3 ) or tantalum pentaethoxide (Ta(OEt) 5 ) to be brought alternately into contact with the carrier material  31  in the chamber  12 .  
         [0049]     Purging means  18  and  19  are also arranged in the walls of the chamber  12 .  
         [0050]     The chamber  12  also comprises injection means  21  and  22 , which will be used during a second step of the formation of the dielectric layer  32 .  
         [0051]     Thus, during a first step, the gas mixture  16  is injected into the chamber  12  through the injection means  14  so as to saturate the upper surface of the carrier material  31  in order to form a tantalum monolayer  40 . After the formation of the tantalum monolayer  40 , the interior of the chamber  12  is purged using the purging means  18  and  19 . The purging may be carried out by circulating a gas  20  in the chamber  12 , for example argon or nitrogen.  
         [0052]     This purging makes it possible to minimize the concentration of free precursors which remain in the chamber  12  and which have not become attached on the surface of the carrier material  31  in order to form the tantalum monolayer  40 . This purging can also make it possible to avoid a parasitic oxidation reaction between the free precursors and the oxidant gas  17 .  
         [0053]     Once the purging has been carried out, the oxidant gas  17  is circulated in contact with the carrier material  31  in order to oxidize the tantalum monolayer  40 . A tantalum pentoxide (Ta 2 O 5 ) monolayer  32   a  as represented in  FIG. 3  is thereby formed. The oxidant gas  17  is preferably water vapor, so as to minimize the oxidation of the carrier layer  31 .  
         [0054]     Thus, the gas mixture  16  containing for example tertbutylimido-tris-diethylamino tantalum (t-BuN=Ta(NEt 2 ) 3 ) and the oxidant gas  17  are alternately circulated in contact with the carrier material  31  several times, each time with a purging step in between, in order to form a first tantalum pentoxide layer  32   a  with a thickness which may lie between 5 and 1000 angstroms.  
         [0055]     This step of forming a first tantalum pentoxide layer  32   a  is carried out under weakly oxidizing conditions in order to reduce the risks of oxidizing the carrier material  31 , and in order to minimize the formation of an interface layer between the carrier material  31  and the first tantalum pentoxide layer  32   a . In other words, this first step makes it possible to control the quality of the interface between the carrier material  31  and the first tantalum pentoxide layer  32   a  and can make it possible to avoid oxidizing the carrier material  31 .  
         [0056]     Furthermore, the alternate circulation of the gas mixture  16  and the oxidant gas  17  also makes it possible to reduce the risks of oxidizing the carrier material.  
         [0057]     As a variant, in order to engage weakly oxidizing conditions, the carrier material  31  may be heated to a heating temperature of between 250 and 350° C. by heating means (not shown in  FIG. 2 ) which may be situated level with the plate  13 .  
         [0058]     As an alternative or in addition, oxygen assisted by a plasma with a power of less than 150 watts may also be circulated using an injection means (not shown in  FIG. 2 ) during the formation of the first tantalum pentoxide layer  32   a  in order to engage weakly oxidizing conditions.  
         [0059]     As another alternative or in addition, water vapor assisted by plasma or N 2 O assisted by plasma with a power of less than 150 watts or a mixture of these plasma assisted gases may also be circulated, or even a mixture of these gases which is not plasma assisted.  
         [0060]     The gas mixture  16  is subsequently circulated in contact with the tantalum pentoxide layer  32   a  under conditions more strongly oxidizing than the conditions for forming the first tantalum pentoxide layer  32   a.    
         [0061]     In this way, the gas mixture  16  is circulated in contact with the first tantalum pentoxide layer  32   a  in the chamber  12  by using an injection means  14 , then an oxidant gas  23  is circulated there by using an injection means  22  as represented in  FIG. 4 . With a pausing time of a few milliseconds, preferably between 10 ms and 1000 ms, a plasma  24  is subsequently circulated by using an injection means  21 . A tantalum pentoxide monolayer  32   b  is thereby formed.  
         [0062]     The operation is repeated several times until a second tantalum pentoxide layer  32   b  is obtained with a sufficient thickness.  
         [0063]     Oxygen is preferably used as the oxidant gas  23  in order to work under an oxidizing atmosphere during the formation of the second tantalum pentoxide layer  32   b.    
         [0064]     A plasma  24  which has a power of more than 150 watts is preferably used.  
         [0065]     The tantalum pentoxide layer  32   b  may also be obtained by MOCVD deposition (metal organic chemical vapor deposition).  
         [0066]     During this second step, a second tantalum pentoxide layer  32   b  is thereby formed which is positioned on the first tantalum pentoxide layer  32   a.    
         [0067]     This second step therefore takes place under conditions more strongly oxidizing than the conditions for forming the first tantalum pentoxide layer  32   a.    
         [0068]     This second step makes it possible to obtain a second tantalum pentoxide layer  32   b  which has a good quality in terms of stoichiometry. The second tantalum pentoxide layer  32   b  may, in particular, not have any oxygen vacancies.  
         [0069]     Following the combination of these two steps, a tantalum pentoxide layer  32  with satisfactory bulk properties as well as a good interface is thereby obtained in contact with the carrier material  31 . The tantalum pentoxide layer  32  has in particular a thickness of between 20 and 2000 angstroms and a quantity of impurities in particular less than 20%. The interface layer between the carrier material  31  and the dielectric layer  32  may have a thickness of less than 5 angstroms.  
         [0070]     The leakage currents of the tantalum pentoxide layer  32  may in particular be 100 times less than the leakage currents measured for a tantalum pentoxide layer produced according to a MOCVD (metal organic chemical vapor deposition) method.  
         [0071]     The capacitor  30  as represented in  FIG. 1  is subsequently produced according to the conventional steps for obtaining a capacitor known to the person skilled in the art.  
         [0072]     Such an embodiment may be employed in particular for semiconductor/dielectric/metal capacitor structures (MIS structures) or metal/dielectric/metal capacitor structures (MIM structures) for dynamic random-access memory applications.  
         [0073]     Such an embodiment may also be employed in order to fabricate the gate oxide of an MOS transistor.  
         [0074]     Although preferred embodiments of the method and apparatus of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.