Abstract:
A method for improving the properties of tunable etch resistant anti-reflective coatings (TERA) is disclosed. The method includes annealing the deposited layer of TERA in an environment containing at least one of hydrogen and deuterium. The annealed layer has an increased concentration of hydrogen and/or deuterium as compared to the deposited film, and may also have an additional concentration of hydrogen or deuterium at the interface between the substrate and the layer of TERA.

Description:
BACKGROUND OF INVENTION  
       [0001]     The present invention is directed to structures and methods useful for fabricating integrated circuits (ICs), in particular structures having a plurality of interconnect layers. More particularly, the present invention is directed to a method for improving the properties of tunable vapor deposited materials which function as antireflective coatings and/or as hardmasks for high resolution lithography.  
         [0002]     The semiconductor industry continues to require devices with an increased device density and a concomitant decrease in device geometry. The continuous size reduction of the critical dimension (CD) of semiconductor devices creates an increasing challenge to balance the need for efficient etch resistance (i.e. resist thickness) with the demands of production-worthy depth-of-focus (DOF). Resist thickness is continuously thinned to accommodate reduced DOF which results from use of tools with higher numerical aperture (NA). As the thickness of the resist is decreased, the resist becomes less effective as a mask for subsequent dry etch image transfer to the underlying substrate, i.e. most if not all of the resist is etched away during the subsequent pattern transfer process. Without significant improvement in the etch selectivity exhibited by current single layer resists (SLR), these systems can not provide the necessary lithographic and etch properties for high resolution lithography.  
         [0003]     Another problem with single layer resist systems is critical dimension (CD) control. Substrate reflections at ultraviolet (UV) and deep ultraviolet (DUV) wavelengths are notorious to produce standing wave effects and resist notching which severely limit CD control of single layer resists. Notching results from substrate topography and non-uniform substrate reflectivity which causes local variations in exposure energy on the resist. Standing waves are thin film interference (TFI) or periodic variations of light intensity through the resist thickness. These light variations are introduced because planarization of the resist presents different thickness through the underlying topography. Thin film interference plays a dominant role in CD control of single layer photoresist processes, causing large changes in the effective exposure dose due to a tiny change in optical phase.  
         [0004]     Various antireflective coating (ARC) and hardmask materials have been developed to alleviate these problems of etch resistance and substrate reflections. Such materials include the tunable vapor deposited materials described in U.S. Pat. No. 6,316,167, the disclosure of which is incorporated herein by reference. These tunable materials have the composition R:C:H:X, wherein R is selected from Si, Ge, B, Sn, Fe, Ti and mixtures of these elements, and X is selected from 0, N, S, F and mixtures of these elements, and X is optionally present. These materials will be referred to as tunable etch resistant ARC, or TERA. Compared to other hardmask materials such as polysilicon, TERA exhibits excellent etch selectivity to resist and to oxide. Selectivity of 1:2.5 to resist and 7:1 to oxide has been demonstrated. TERA is also envisioned as an antireflective layer, so no additional ARC is required for lithography processes using TERA. Thus, the mask open process is simplified, resulting in cost reduction.  
         [0005]     However, lithography processes using TERA have been found to suffer from a large variation of CD post lithography, which limits a successful implementation of TERA as hardmask. The CD variation is attributed to the nonuniformity of as-deposited TERA properties across the wafer. Thus, there is a need in the art for a method to improve TERA uniformity and reduce CD variation across the wafer.  
       SUMMARY OF INVENTION  
       [0006]     The aforementioned deficiencies of the prior art are alleviated through use of the method of the present invention. Specifically, the present invention is directed to a method for improving TERA uniformity by annealing a wafer comprising a TERA film in an environment comprising hydrogen or deuterium, an isotope of hydrogen. Up to 40% CD variation reduction on TERA wafers is demonstrated.  
         [0007]     The present invention is specifically directed to a method comprising: depositing on a surface of a substrate a layer formed of a material; and annealing the layer in an environment comprising at least one of hydrogen and deuterium, thereby forming an annealed layer. The material comprises carbon, at least one of hydrogen and deuterium, and at least one element selected from the group consisting of Si, Ge, B, Sn, Fe and Ti. The material may further comprise at least one element selected from the group consisting of O, N, S and F.  
         [0008]     The present invention is also directed to a lithographic structure comprising a plurality of layers, at least one layer being formed of a material comprising carbon, deuterium, and at least one element selected from the group consisting of Si, Ge, B, Sn, Fe and Ti. The material may further comprise at least one element selected from the group consisting of O, N, S and F, and also may further comprise hydrogen. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]     The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The drawings are for illustration purposes only and are not drawn to scale. Furthermore, like numbers represent like features in the drawings. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows, taken in conjunction with the accompanying drawings, in which:  
         [0010]     FIGS.  1 ( a )- 1 ( d ) illustrate a preferred embodiment of the method of the present invention;  
         [0011]     FIGS.  2 ( a )- 2 ( b ) illustrate two alternate embodiments for the annealing step of the present invention;  
         [0012]      FIG. 3  illustrates an embodiment of annealed layer of the present invention; and  
         [0013]     FIGS.  4 ( a )- 4 ( b ) illustrate the results of an example of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     The invention will now be described by reference to the accompanying figures. In the figures, various aspects of the structures have been shown and schematically represented in a simplified manner to more clearly describe and illustrate the invention. For example, the figures are not intended to be drawn to scale. In addition, the vertical cross-sections of the various aspects of the structures are illustrated as being rectangular in shape. Those skilled in the art will appreciate, however, that with practical structures these aspects will most likely incorporate more tapered features. Moreover, the invention is not limited to constructions of any particular shape.  
         [0015]     The invention is directed to a method to improve the uniformity of a film such as TERA, thus improving the lithography and etching performance of the film by annealing the deposited film in an environment containing hydrogen or deuterium.  
         [0016]     A preferred embodiment of the method of this invention is illustrated in FIGS.  1 ( a )- 1 ( d ). The method begins in Figure  1 ( a ) with a substrate  10  which may be, for example, a bare silicon wafer, a wafer containing one or more layers of other materials, or a wafer containing various device structures.  
         [0017]     In  FIG. 1 ( b ), a layer  11  of a material such as TERA is deposited on substrate  10 . In general, the layer  11  may be formed of a material such as the tunable vapor deposited materials described in U.S. Pat. No. 6,316,167, the disclosure of which has been incorporated herein by reference. These tunable vapor deposited materials have a structural formula R:C:H:X, wherein R is selected from the group consisting of Si, Ge, B, Sn, Fe, Ti and combinations thereof, and wherein X is not present or is selected from the group consisting of one or more of O, N, S and F. Alternatively, layer  11  may be formed of a material having a structural formula R:C:H:D:X or R:C:D:X, where R and X are as defined above, and D is deuterium.  
         [0018]     Layer  11  may be deposited by any suitable method, including the methods described in U.S. Pat. No. 6,316,167, the disclosure of which has been incorporated herein by reference. For example, layer  11  may be deposited by plasma enhanced chemical vapor deposition (PECVD) techniques. In one type of technique the PECVD process is performed in a parallel plate reactor where the substrate is placed on one of the electrodes. Various exemplary deposition embodiments are disclosed in U.S. Pat. No. 6,316,167.  
         [0019]     When layer  11  is formed of a material having structural formula R:C:H:X, each component is preferably present in the following amounts. The preferred atomic % ranges for R are the following: preferably 0% to 95%, more preferably 0.5% to 95%, most preferably 1 to 60% and most highly preferably 5 to 50%. The preferred atomic % ranges for C are the following: preferably 0% to 95%, more preferably 0.5% to 95%, most preferably 1 to 60% and most highly preferably 5 to 50%. The preferred atomic % ranges for H are the following: preferably 0% to 50%, more preferably 0.5% to 50%, most preferably 1 to 40% and most highly preferably 5 to 30%. The preferred atomic % ranges for X are the following: preferably 0% to 70%, more preferably 0.5% to 70%, most preferably 1 to 40% and most highly preferably 5 to 30%.  
         [0020]     Alternatively, some or all of the hydrogen in the R:C:H:X material may be replaced with deuterium, such that layer  11  is formed of a material having structural formula R:C:H:D:X or R:C:D:X. Layer  11  containing deuterium may be formed by using a precursor material containing deuterium in place of some or all of the hydrogen.  
         [0021]     The method of this invention continues with layer  11  being annealed in an environment containing hydrogen or deuterium. In  FIG. 1 ( c ), the annealing step is shown in an environment containing hydrogen. In an alternative embodiment, the annealing step may be performed in an environment containing deuterium. The annealing environment preferably contains 0.1% to 100% hydrogen and/or deuterium. One or more other gases such as, for example, nitrogen, helium, neon or argon, may be present in the annealing environment.  
         [0022]     The annealing temperature is preferably 350° C. to 500° C., more preferably 380° C. to 450° C., and most preferably 400° C. to 425° C. The annealing duration is preferably 1 min. to 100 min., more preferably 10 min. to 60 min., and most preferably 30 min.  
         [0023]     The annealing process may be performed as a separate step after deposition. Alternatively, the annealing may be performed in situ, i.e., in the same chamber as the deposition process. These two embodiments are illustrated in FIGS.  2 ( a ) and  2 ( b ), which are graphs of the wafer temperature versus time during the method of this invention. A represents the temperature of the substrate prior to deposition of layer  11 , B represents an elevated temperature typically encountered in a deposition chamber during deposition of layer  11 , C represents a lowered temperature of the wafer as the wafer is transferred from the deposition chamber to another chamber or furnace for annealing, D represents an elevated temperature during anneal, and E represents a lowered temperature of the wafer which is ready for further processing. In  FIG. 2 ( a ), the annealing process is performed in a separate chamber or furnace, whereas in  FIG. 2 ( b ), deposition and annealing are performed in an integrated process in the same chamber or tool.  
         [0024]     Following anneal of layer  11 , processing of the wafer may continue. For example, as shown in  FIG. 1 ( d ), photoresist  12  may be deposited on layer  11  and patterned using a conventional lithography process to form openings  13 .  
         [0025]     The method of this invention produces a new film structure containing additional hydrogen and/or deuterium as compared to the deposited film. For example, when deposited layer  11  is formed of a material having structural formula R:C:H:X, and layer  11  is annealed in an environment containing hydrogen, the preferred atomic % ranges for H are the following: preferably 2% to 70%, more preferably 20% to 60%, and most preferably 30 to 50%. Alternatively, when deposited layer  11  is formed of a material having structural formula R:C:H:X, and layer  11  is annealed in an environment containing deuterium, the preferred atomic % ranges for D are the following: preferably 2% to 70%, more preferably 10% to 40%, and most preferably 20 to 30%. In yet another alternative embodiment, when deposited layer  11  is formed of a material having structural formula R:C:D:X, and layer  11  is annealed in an environment containing deuterium, the preferred atomic % ranges for D are the following: preferably 2% to 70%, more preferably 20% to 60%, and most preferably 30 to 50%.  
         [0026]     Moreover, annealed layer  11  may have an additional concentration of hydrogen or deuterium at the interface between substrate  10  and layer  11 .  FIG. 3  illustrates an exemplary profile of H or D concentration across layer  11  and substrate  10 . The solid line represents one possible H or D profile before anneal, and the dotted line represents another possible profile after anneal showing a peak H or D concentration at the interface between layer  11  and substrate  10  due to the accumulation of H or D at the sites of interface defects.  
         [0027]     The following example is provided to illustrate the scope of the invention. Because this example is given for illustrative purposes only, the invention embodied therein should not be limited thereto.  
         [0028]     Example: About 2000 Å of a TERA film was deposited on a set of silicon wafers with 53 Å pad oxide, 1800 Å pad nitride, and 15000 Å borosilicate glass (BSG) oxide. The wafers were then divided into three groups. The first group of the wafers was annealed in a furnace containing 10% hydrogen and 90% nitrogen, and the second group of the wafers was annealed in the same furnace with 100% nitrogen. The annealing temperature was 400° C. and the annealing duration was 30 min. The third group of wafers, which was used as a control group, was not annealed. After the annealing step, all wafers were then subjected to the same lithography process. The photoresist layer had a thickness of approximately 3500 Å after deposition and approximately 3000 Å after exposure. The critical dimensions (CDs) of these three groups were then measured and results are compared in  FIG. 4 .  FIG. 4 ( a ) shows that the mean CD is very close for all wafers regardless of annealing. This indicates that there is no need to change the lithography process when the annealing process is added.  FIG. 4 ( b ) shows that the across-wafer CD variation is reduced from about 25 nm without annealing to about 15 nm with annealing in the environment containing hydrogen. Virtually no change in CD variation was observed with annealing in the environment containing only nitrogen. The reduction of CD variation is attributed to the improved TERA uniformity by annealing in an environment containing hydrogen.  
         [0029]     While the present invention has been particularly described in conjunction with a specific preferred embodiment and other alternative embodiments, it is evident that numerous alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore intended that the appended claims embrace all such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.