Patent Publication Number: US-2023151488-A1

Title: Tisin coating method

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/612,853 entitled “TiSiN Coating Method,” filed Jun. 2, 2017, the content of which is incorporated by reference in its entirety. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
    
    
     BACKGROUND 
     Field of the Invention 
     The invention relates to a method for ALD coating of a substrate with a layer containing Ti, Si, N. 
     Description of the Related Art 
     In the ALD method, a layer consisting of a plurality of chemical elements is deposited on a substrate in several successive cycles. Reaction gases containing at least one element that is to be deposited in the layer are used in this process. In these cycles, layers of the same elements or a group of elements are deposited, layer for layer, a reaction gas being introduced into the process chamber in each case and remaining there in the process chamber until the surface of the substrate has become saturated with the reaction gas. In a subsequent Flush or purge step, the residues of the process gas are removed from the process chamber and the same reaction gas or another reaction gas is introduced into the process chamber. The deposition process takes place at elevated temperatures at which a chemical reaction takes place on the substrate surface; in particular a decomposition reaction of the reaction gas may take place on the substrate surface. Volatile reaction products are removed from the process chamber with the flushing gas. 
     The aforementioned document discloses a method for deposition of a diffusion barrier on a layer sequence of an electronic component, for example, a memory component made on silicon substrates, wherein the layer not only serves to limit diffusion but should also be electrically conductive in order to be used as a contact. In a first step a TiN layer is deposited there and then an SiN layer is deposited. The individual cycles are carried out several times one after the other in such a way that a TiSiN layer is formed on the whole. 
     The diffusion resistance of the layer can be increased by increasing the silicon content. When the silicon content is increased in the known process, the electric resistance of the deposited layer increases at the same time, so that the properties of the layer are inferior if it should act as a contact layer. 
     US 2015/0279683 and U.S. Pat. No. 6,911,391 also relate to a method for deposition of TiSiN layers on substrates. 
     Such a method is described in US 2015/0050806 A1. 
     SUMMARY 
     The object of the invention is to provide measures with which a diffusion barrier is increased with regard to its diffusion resistance but at the same time the electric conductivity is not impaired. 
     This object is achieved by the invention defined in the claims, wherein the dependent claims are not just advantageous refinement of the method defined in the independent claim but also constitute independent approaches to solving the problem, wherein individual subfeatures of the independent claims also have independent inventive significance. 
     First and essentially, it is proposed that after an obligatory heating step following transport of the substrate into the process chamber, TiN is deposited on the substrate and/or on a layer already deposited on the substrate, in particular a polysilicon layer. Next an N-free layer or layer sequence of Ti and Si is deposited. Then a TiSiN layer or layer sequence is deposited on the TiS layer. This takes place in three chronologically successive steps, each step being carried out at least once, preferably at least one of these steps or all of these steps being carried out several times in succession. In the first step, a cycle is carried out n times for deposition of TiN, first injecting a reaction gas that contains titanium into the process chamber; then flushing the process chamber with an inert gas; next containing a reaction gas containing nitrogen into the process chamber and finally flushing the process chamber with an inert gas. Nitrogen or argon or some other suitable noble gas or any other suitable gas may be used as the inert gas; n may be 1 but is preferably at least 5. The second step may consist of two substeps, each of which is carried out at least once; but preferably is carried out multiple times. In the first substep a reaction gas containing titanium is injected into the process chamber and then the process chamber is flushed with an inert gas. The first substep may be carried out m times; where m=1, but preferably is at least 5. In the second substep a reaction gas containing silicon is first injected into the process chamber and then the process chamber is flushed with an inert gas. This second substep may be carried out k times; where k=1, but is preferably at least 5. The second step; in which a nitrogen-free area of the coating is essentially preferably deposited; is carried out r times; where r=1, but is preferably at least 10. The third step preferably also consists of two substeps, wherein TiN is deposited in a first substep. To do so, essentially the first step described above is carried out p times. In the first substep of the third step; a reaction gas containing titanium is first injected into the process chamber; then the process chamber is flushed with an inert gas. Next a reaction gas containing nitrogen is injected into the process chamber and then the process chamber is flushed with an inert gas. This first substep of the third step is carried out p times; where p=1, but is preferably at least 2. In the first substep of the third step; a reaction gas containing titanium is first injected into the process chamber. The process chamber is then flushed with an inert gas. Next; a reaction gas containing nitrogen is injected into the process chamber and then the process chamber is flushed with an inert gas. In the first substep of the third step; the coating thus includes an area containing nitrogen. A second substep and in particular the last substep, in which only silicon is deposited by injecting a reaction gas that contains silicon into the process chamber is carried out following the first substep, wherein; here again; a cycle consisting of injecting the reaction gas containing silicon into the process chamber and then flushing the process chamber with the inert gas is carried out q times, where q=1 or preferably is at least S. The third step, in which TiSiN is deposited on the whole, can be carried out r times, where r=1 but preferably is at least 10. It is provided in particular that in carrying out the third step, the reaction gas of the last substep does not contain any nitrogen. As a result of the method according to the invention, an area containing TiN, i.e., having Ti—N bonds, is deposited on the layer of the substrate containing silicon in the first step due to the method according to the invention. A second area, which is a core area in which essentially Si—Si bonds or Si—Ti bonds are formed, is deposited on this first area which is a borderline report [sic; area]. These bonds have a much lower bond energy (approximately 100 eV) than the Ti—N bond in which the bond energy is approximately 450 eV. This method is carried out in particular in such a way that TiSi 2  is formed in different phases and has a lower electrical resistance than TiSiN, for example. To this extent, it is advantageous if an N-free component is deposited in the last substep of the third step, wherein the reaction gas does not contain any nitrogen component for this purpose which does not take part in the chemical reaction although N 2  can. In the last step a third area of the coating is deposited, this being a borderline region containing nitrogen. The individual layer thicknesses of the three layers are preferably 2 Å to 200 A with the sum total of the three layers being 5 A to 500 A. All three layers could be repeated insitu and in sequence to yield film thicknesses of 5 A to 500 A. The gaseous compounds of titanium, silicon and nitrogen known from the prior art, for example, TiCl 4 , TDMAT or TDEAT are used as the reaction gases. Dichlorosilane (SiH2Cl 2 ) or SiHCl 3 , SiCl 4 , SiH 4  or Si 2 H 6  may be used for the reaction gas containing silicon. NH 3  or MMH may be used as the reaction gas containing nitrogen. This method begins with heating of the substrate to a temperature of 400° C. to 700° C. at a total pressure in the range between 5 millibar and 0.6 millibar (Equivalent to 0.5 mtorr to 7.5 mTorr). Next the three steps described above are carried out. After cooling the substrate, it is removed from the process chamber. The term substrate as used here in particular is understood to refer to a prestructured and precoated wafer on which a structured silicon-containing layer sequence has already been deposited, for example, a layer sequence of a memory module. The TiSiN coating deposited according to the invention can then be connected by means of wires made of copper or the like. 
     The coating is preferably deposited in a reactor that can be evacuated using a vacuum system. Inside the reactor there is a gas inlet element for introducing the reaction gases and/or the inert gas. The gas inlet element may be in the form of a shower head. It may have a plurality of sectors or segments, wherein the segments or sectors form separate chambers into which the reaction gas containing Ti, the reaction gas containing Si or the reaction gas containing N can be injected separately from one another. The gas inlet element may extend over the total area extent of the substrate which sits on a heated susceptor. The gas inlet element may be cooled but it may also be heated. The substrate is preferably sitting on a susceptor which may be heated by a plurality of heating element so that the susceptor has a plurality of heating zones which may be heated independently of one another. A uniform temperature profile can be adjusted on the substrate surface in this way. In particular, a temperature profile with a minimal lateral temperature gradient can be adjusted on the substrate surface. 
     In addition, the invention relates to a coating applied to a substrate and having a first borderline region with which the coating is adjacent to the substrate or to a layer applied to the substrate. The coating also has a second borderline region which is opposite the first borderline region and to which a metallic or metal ceramic contact is applied. The second borderline region has a surface area, which comes in contact with the contact material. Between the first borderline region and the second borderline region there is a core region. The inventive coating has the following properties: the first borderline region has a higher nitrogen concentration than the core region. The second borderline region has a higher nitrogen concentration than the core region. The core region is preferably free of nitrogen. The surface area of the second borderline region is preferably free of nitrogen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail below on the basis of exemplary embodiments, in which: 
         FIG.  1    shows the process steps in chronological succession as a block diagram, 
         FIG.  2    shows schematically the structure of a reactor for carrying out the process in a type of cross section and 
         FIG.  3    shows the cross section through a gas inlet element of a device illustrated in  FIG.  2   , 
         FIG.  4    shows schematically and on an enlarged scale a layer deposited by the method according to the invention on a substrate  17 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  2    shows schematically the structure of a coating device arranged inside a reactor housing  11  that is sealed airtight. A plurality of inlet lines is provided, such that it is possible to feed a gas stream into a gas inlet element  12  through each of these feeder lines. The gas inlet element  12  has a plurality of gas outlet openings  13  through which the gas fed into the gas inlet element  12  can enter a process chamber  10 . The bottom of the process chamber  10  is formed by the top side of a susceptor  16  on which the substrate  17  to be coated sits. The susceptor  16  can be heated to a process temperature by means of a heater  15 . 
     The susceptor  16  may be rotated about an axis of rotation D in its plane of extent. The rotation takes place relative to the gas inlet element  12 . A gas outlet  14  to which a vacuum pump is connected is provided. 
     An inert gas can be fed into a chamber  18  of the gas inlet element  12  through a feeder line by means of a first mass flow controller  22 . A gas containing nitrogen can be fed by means of a mass flow controller  23  into a chamber  19  separated from the former by an airtight seal. A gas containing titanium can be fed into a chamber  20  separated from the former with an airtight seal, by means of a mass flow controller  24 . A gas containing silicon can be fed into a chamber  21  of the gas inlet element  12  by means of a mass flow controller  25 . 
       FIG.  3    shows as an example the spatial arrangement of the individual chambers  18 ,  19 ,  20 ,  21  in the gas inlet element  12 . The chambers may be arranged like spokes. When the substrate  17  is rotated relative to the gas inlet element  12 , the reaction gas or inert gas fed into the process chamber  10  comes in contact with all regions of the surface of the substrate  17 . 
     Semiconductor components for memory element or the like have electrically active layers containing silicon. These layers must be electrically contactable in order to connect the layers to bond wires, for example. A TiSiN coating is applied between the contact and the layer, the process of application of this layer being designed so that the layer has the lowest possible electrical resistance while at the same time forming a high diffusion barrier which prevents the contact metal applied to the TiSiN coating from diffusing into the silicon layer. For deposition of this layer, an ALD method (atomic layer deposition) is used according to the invention. In this method, a reaction gas is fed into the process chamber  10  in alternation with an insert gas for flushing the process chamber  10 . This takes place by introducing the respective gas into the cavity in the gas inlet element  12  and discharge the gas from the plurality of gas outlet openings  13  arranged like a sieve into the process chamber  10 . The reaction gas is fed into the process chamber  10  in such a concentration and over such a period of time until the surface of the substrate  17  applied to the susceptor  16  has become saturated with the reaction gas and/or a reaction product of the reaction gas, for example, a decomposition product. Then the gas residues are flushed out of the process chamber  10 . This is accomplished by introducing an inert gas into the process chamber  10 , wherein the inert gas may be nitrogen or a noble gas. 
     According to the invention the coating is applied in a number of successive coating steps, each of which may in turn comprise substeps and is preferably repeated several times. The process is carried out in such a way that essentially Si—Si bonds or Si—Ti bonds are formed in the core area of the coating so that the coating consists mostly of TiSi 2  which has a lower electrical resistance than TiSiN. On the other hand, however, the process is carried out in such a way that the interface facing underneath layer and the interface of the coating having the subsequent layer have a higher nitrogen content than the core region of the coating. The coating consists essentially of three regions, a lower interface connected to the substrate surface and/or the layer containing the silicon there, said interface consisting essentially of TiN, the core region of the coating consisting essentially of Ti and Si and an upper interface consisting essentially of TiSiN. 
     The conduct of the process is explained in greater detail below with reference to the accompanying  FIG.  1   . First, in a substrate transport step (wafer transport)  4 , the substrate  17  is introduced into the process chamber  10  where the substrate  17  rests on the susceptor  16 . By heating the susceptor  16  with a heater  15  having a plurality of heating zones, the substrate is heated to a process temperature. This takes place by passing an electric current through a wire resistor of the heater  15 . 
     In a first process step 1, TiN is deposited. To do so, a reaction gas containing Ti is first introduced into the process chamber  10  until the surface of the substrate  17  is saturated with the process gas (Ti). Then residues of the reaction gas containing Ti or its reaction products which do not remain on the surface of the substrate  17  are flushed out of the process chamber  10  by means of an inert gas (P). Next a reaction gas containing nitrogen is fed into the process chamber until the surface of the substrate  17  has been saturated with it (N). Next by introducing the inert gas, the reaction gas containing nitrogen is flushed out of the process chamber  10  (P). These four successive sequences form a first step 1 that is repeater n times resulting in a layer preferably 10 A thick but up to 50 nm thick. 
     In a second following step 2 the TiSi core material is deposited. This second step 2 consists of two substeps 2.1,2.2, wherein Ti is deposited in the first substep and Si is deposited in the second substep. In the first substep 2.1, a reaction gas containing Ti is first introduced into the process chamber  10  a total of m times and then gas residues are flushed out of the process chamber  10  by introducing an inert gas (P). Following this first substep 2.1 of the second step 2 which is carried out at least once but preferably several times, the second substep 2.2 is performed. In this second substep 2.2, a reaction gas containing silicon is first fed into the process chamber  10  (Si) and then the process chamber  10  is flushed by introducing an inert gas (P). The second substep 2.2 is carried out a total of k times, where k is preferably greater than 1. 
     The second step 2 consisting of the two substeps 2.1 and 2.2 is preferably carried out a total of r times until the required layer thickness of a core layer, which consists of TiSi and is essentially free of nitrogen is deposited, this layer thickness may also be preferably 10 A thick but up to 50 nm. 
     The second step 2 is followed by a third step 3 in which TiSiN is deposited. The third step consists of two substeps 3.1,3.2 which follow one another and can be carried out a total of 1 times where 1 is 1 or preferably greater than 1. 
     The first substep 3.1 of the third step 3 corresponds essentially to the first step 1. TiN is deposited; so a reaction gas containing titanium is first fed into the process chamber  10  (Ti)f which is then flushed by introducing an inert gas (P). Following that a reaction gas containing nitrogen is introduced into the process chamber  10  (N) whereupon the process chamber  10  is again flushed by introducing an inert gas (P). The substep 3.1 can be carried out a total of p times where p=1 or is preferably greater than 1. 
     The second substep 3.2 of the third step 3 is carried out without the use of a reaction gas containing N. First the reaction gas containing silicon is fed into the process chamber  10  (Si). Then the process chamber  10  is flushed by introducing the inert gas (P)f whereupon the second substep 3.2 of the third step 3 can be carried out a total of q times where q=1 or is preferably greater than 1. 
     After cooling the process chamber  10 , the substrate  17  is removed from the process chamber  10  in a transport step (wafer transport)  4 . 
     The gases mentioned in the introduction are used as the reaction gases, for example; the reaction gas containing Ti may be TiCl 4 , TDMAT or TDEAT and the reaction gas containing Si may be SiH 2 Cl 2 , SiHCl 3 , SiCl 4 , SiH 4  or Si 2 H 6 . The reaction gas containing N may be NH 3  or MMH. The inert gas may be N 2  or a noble gas. 
     Due to the use of a gas inlet element  12  having chambers  18 ,  19 ,  20 ,  21  arranged like sectors around a center; a uniform flow pattern can be achieved within the process chamber. The gas inlet element  12  which is in the form of a shower head can be cooled or heated. A thermal equilibrium can be established. The susceptor  16  may also be heated or cooled. The heater  15  is in particular a multizone heater, preferably two heaters being at different distances radially from the center are arranged around the center. The chambers  19  to  21  may each be flushed with the inert gas in the respective gas change so that no reaction gas remains there. 
     By means of SiN measurements or XPS measurements, it has been shown that the bonding energy between the individual atoms is much lower in the core region of the layer than in the two interfaces, thus indicating that TiSiN is formed only in the boundary regions and essentially Si—Si and/or Si—Ti is formed in the core region. 
       FIG.  4    shows schematically a section through a coating  30  deposited on a substrate  17 . The substrate  17  is shown only symbolically and includes a silicon wafer with a layer structure deposited on it, wherein the interface of the substrate  17  facing the coating  30  may be a surface of a layer containing silicon. 
     The coating  30  consists of a first boundary region  31 , which is deposited directly on the surface of the substrate  17 , a core region  33 , which is connected to the first boundary region  31  and a second boundary region  32 , which has a surface  34  to which a contact wire can be connected. 
     The layer  30  deposited with the method described previously has a first interface  31 , which has an elevated nitrogen concentration, wherein the nitrogen concentration in the first boundary region  31  is greater than that in the core region  33 . The core region  33  is preferably essentially free of nitrogen. The second boundary region  32  has a higher nitrogen concentration than the core region  33 . The surface  34  is preferably free of nitrogen. 
     In the first boundary region  31  and in the second boundary region  32 , TiSiN compounds with a high bond energy are formed (TiN 455.6 eV). In the core region  33  essentially Si—Si bonds with a bond energy of 99.6 eV and Ti—Si bonds are formed. The coating  30  deposited by the method according to the invention has a high electrical conductivity and forms a high diffusion barrier. It has an essentially crystalline property and a layer thickness of approximately 0.65 nm to 650 nm. 
     The preceding discussion serves to illustrate the inventions covered by the patent application as a whole, each also independently improving upon the prior art at least through the following combinations of features, wherein two, more or all of these combinations of features may also be combined further, namely: 
     A method for ALD coating of a substrate  17  with a layer containing Ti, Si, N, wherein a reaction gas is fed into a process chamber  10  containing the substrate  17  in a plurality of successive steps 1, 2, 3 in one or more n, m, k, l, p, q, r cycles and then a flushing gas is fed into the same process chamber,
         wherein TiN is deposited in a first step 1 with a reaction gas containing TI and with a reaction gas containing N,   in a second step 2 which follows the former step, TiSi is deposited with a reaction gas containing Ti and a reaction gas containing Si,   and in a third step 3 following the second step 2, TiSiN is deposited with a reaction gas containing Ti, with a reaction gas containing N and with a reaction gas containing Si is deposited.       

     A method which is characterized in that a cycle consisting of introducing the reaction gas containing Ti, flushing the process chamber  10  with an inert gas, feeding the reaction gas containing N and flushing the process chamber  10  with a reaction gas is carried n times in the first step 1, where n&gt;1. 
     A method which is characterized in that in the second step 2 a first substep 2.1 consisting of introducing the reaction gas containing Ti and then flushing the process chamber  10  with an inert gas is carried out m times, where m&gt;1 and in which a second substep 2.2 in which the reaction gas containing Si is introduced into the process chamber  10  and then the process chamber  10  is flushed with the inert gas, is carried out k times where k&gt;1. 
     A method which is characterized in that the two substeps 2.1,2.2 are carried out 1 times in succession where 1&gt;1. 
     A method which is characterized in that in the third step 3 a first substep 3.1, in which the reaction gas containing Ti is introduced into the process chamber  10  and then the process chamber  10  is flushed with an inert gas, next the reaction gas containing N is introduced into the process chamber  10  and then the process chamber  10  is flushed with an inert gas is carried out p times where p&gt;1, and in a second substep 3.2 the process gas containing Si is fed into the process chamber  10  and next the process chamber  10  is flushed with an inert gas wherein the second substep 3.2 is carried out q times in succession, where q&gt;1. 
     A method which is characterized in that the third step 3 is carried out r times in succession where r&gt;1. 
     A method which is characterized in that the reaction gas containing Ti is introduced at a partial pressure of less than 12×10 −3  millibar; the reaction gas containing Si and having a partial pressure between 1×10 −3  and 4×10 −3  millibar is introduced and/or the reaction gas containing N is introduced at a partial pressure between 9×10 −3  and 8×10 −1  millibar. 
     A method that is characterized in that the total pressure inside the process chamber  10  is in the range between 0.6 and 6 millibar and the steps 1, 2, 3 are carried out at temperatures in the range between 400 and 700° C., wherein the times for feeding the reaction gases are in the range between 0.4 and 60 seconds. 
     A method which is characterized in that the reaction gas containing Ti is TiCl 4 , TDMAT or TDEAT and/or the reaction gas containing Si is SiH 2 Cl 2 , SiHCl 3 , SiCl 4 , SiH 4  or Si 2 H 6  and/or the reaction gas containing N is NH 3  or MMH. 
     A coating which is characterized in that the nitrogen content in the first and second boundary ranges  31 ,  32  is greater than that in the core region  33 . 
     A coating which is characterized in that the core region  33  is essentially free of nitrogen. 
     A coating which is characterized in that the surface  34  of the second boundary region facing away from the substrate  17  is free of nitrogen. 
     All the features disclosed here are essential to the invention (either alone or in combination with one another). Thus, the full disclosure content of the respective/attached priority documents (photocopy of the previous patent application) has also been included for the purpose of incorporating features of these documents into the claims in the present patent application). The dependent claims characterized with their features independent inventive refinements of the prior art even without the features of a claim that has been included by way of reference, in particular to compile divisional applications on the basis of these claims. The invention defined in each claim may additionally have one or more of the features defined in the preceding description, in particular features provided with reference numerals and/or cited in the list of reference numerals. The invention also relates to design forms in which individual features of those cited in the preceding description are not implemented, in particular inasmuch as they are recognizably not essential for the respective intended purpose or can be replaced by other means having the same technical effect. 
     
       
         
           
               
             
               
                   
               
               
                 List of Reference Numerals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Process step 
               
               
                 2 
                 Process step 
               
               
                 2.1 
                 Substep 
               
               
                 2.2 
                 Substep 
               
               
                 3 
                 Process step 
               
               
                 3.1 
                 Substep 
               
               
                 3.2 
                 Substep 
               
               
                 4 
                 Transport step 
               
               
                 5 
                 Heating step 
               
               
                 6 
                 Transport step 
               
               
                 10 
                 Process chamber 
               
               
                 11 
                 Reactor housing 
               
               
                 12 
                 Gas inlet element 
               
               
                 13 
                 Gas outlet opening 
               
               
                 14 
                 Gas outlet 
               
               
                 15 
                 Heater 
               
               
                 16 
                 Susceptor 
               
               
                 17 
                 Substrate 
               
               
                 18 
                 Chamber 
               
               
                 19 
                 Chamber 
               
               
                 20 
                 Chamber 
               
               
                 21 
                 Chamber 
               
               
                 22 
                 Mass flow controller 
               
               
                 23 
                 Mass flow controller 
               
               
                 24 
                 Mass flow controller 
               
               
                 25 
                 Mass flow controller 
               
               
                 30 
                 Coating 
               
               
                 31 
                 Boundary region 
               
               
                 32 
                 Boundary region 
               
               
                 33 
                 Core region 
               
               
                 34 
                 Surface 
               
               
                 D 
                 Axis of rotation 
               
               
                 k 
                 Cycle number 
               
               
                 l 
                 Cycle number 
               
               
                 m 
                 Cycle number 
               
               
                 n 
                 Cycle number 
               
               
                 p 
                 Cycle number 
               
               
                 q 
                 Cycle number 
               
               
                 r 
                 Cycle number