US 20060113675 A1
A semiconductor diffusion barrier layer and its method of manufacture is described. The barrier layer includes of at least one layer of TaN, TiN, WN, TbN, VN, ZrN, CrN, WC, WN, WCN, NbN, AlN, and combinations thereof. The barrier layer may further include a metal rich surface. Embodiments preferably include a glue layer about 10 to 500 Angstroms thick, the glue layer consisting of Ru, Ta, Ti, W, Co, Ni, Al, Nb, AlCu, and a metal-rich nitride, and combinations thereof. The ratio of the glue layer thickness to the barrier layer thickness is preferably about 1 to 50. Other alternative preferred embodiments further include a conductor annealing step. The various layers may be deposited using PVD, CVD, PECVD, PEALD and/or ALD methods including nitridation and silicidation methods.
1. A semiconductor device having enhanced electromigration performance, the device comprising:
a low-k dielectric layer, the low-k dielectric layer having a surface with a recessed feature;
a diffusion barrier layer on the surface of the low-k dielectric layer;
a glue layer on the diffusion barrier layer; and
a conductor on the glue layer, the conductor filling the recessed feature.
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19. A method of reducing electromigration effects in a copper damascene device, the method comprising:
forming a low-k dielectric layer, the low-k dielectric layer having a surface with a recessed feature;
forming a diffusion barrier layer over the surface of the low-k dielectric layer;
forming a glue layer upon the diffusion barrier layer;
filing the recessed feature with a conductor;
annealing the conductor; and
forming a cap layer upon the conductor.
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33. A method for forming a semiconductor device, comprising:
providing a substrate, the substrate including a low-k dielectric layer with an opening;
performing a pore sealing process;
forming a barrier layer within the opening;
forming a glue layer on the barrier layer;
forming a seed layer on the glue layer;
forming a conductor on the seed layer;
and forming a cap layer on the conductor.
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This invention relates generally to semiconductor device fabrication and more particularly to a structure and method for improved resistance to electromigration problems with conductive lines and vias, such as copper, between interconnected layers.
In modern integrated circuits, minimum feature sizes, such as the channel length of field effect transistors, have reached the deep sub-micron range, thereby steadily increasing performance of these circuits in terms of speed and power consumption. As the size of the individual circuit elements is reduced, so is the available real estate for conductive interconnects in integrated circuits. Consequently, these interconnects have to be reduced to compensate for a reduced amount of available real estate and for an increased number of circuit elements provided per chip.
In integrated circuits having minimum dimensions of approximately 0.35 μm and less, a limiting factor of device performance is the signal propagation delay caused by the switching speed of the transistor elements. As the channel length of these transistor elements has now reached 0.18 μm and less, however, capacitance between neighboring conductive structures is increasingly problematic. Parasitic RC time constants therefore require the introduction of a new materials and methods for forming metallization layers.
Traditionally, metallization layers are formed by a dielectric layer stack including, for example, silicon dioxide and/or silicon nitride with aluminum as the typical metal. Since aluminum exhibits significant electromigration at higher current densities, copper is replacing aluminum. Copper has significantly lower electrical resistance and reduced electromigration problems.
The introduction of copper, however, entails a plurality of issues to be dealt with. For example, copper may not be deposited in higher amounts in an efficient manner by well-established deposition methods, such as chemical and physical vapor deposition. Moreover, copper may not be efficiently patterned by well-established anisotropic etch processes and therefore the so-called damascene technique is employed in forming metallization layers including copper lines. Typically, in the damascene technique, the dielectric layer is deposited and then patterned with trenches and vias that are subsequently filled with copper by plating methods, such as electroplating or electroless plating.
A further issue is the ability of copper to readily diffuse in silicon dioxide. Therefore, copper diffusion may negatively affect device performance, or may even lead to a complete failure of the device. It is therefore necessary to provide a diffusion barrier layer between the copper surfaces and the neighboring materials to substantially prevent copper from migrating to sensitive device regions. Silicon nitride is known as an effective copper diffusion barrier, and is thus frequently used as a dielectric barrier material separating a copper surface from an interlayer dielectric, such as silicon dioxide.
Although copper exhibits superior characteristics with respect to resistance to electromigration compared to aluminum, the ongoing shrinkage of feature sizes, however, leads to increased current densities, thereby causing a non-acceptable degree of electromigration. Electromigration is a diffusion phenomenon occurring under the influence of an electric field, which leads to copper diffusion in the direction of the moving charge carriers. This can produce voids in the copper lines that may cause device failure. It has been confirmed that these voids typically originate at the copper silicon nitride interface and represent one of the most dominant diffusion paths in copper metallization structures. It is therefore of great importance to produce high quality interfaces between the copper and the diffusion barrier layer to reduce the electromigration to an acceptable degree.
As previously noted, the device performance of extremely scaled integrated circuits is substantially limited by the parasitic capacitances of adjacent interconnect lines, which may be reduced by decreasing the resistivity thereof and by decreasing the capacitive coupling in that the overall dielectric constant of the dielectric layer is maintained as low as possible. Since silicon nitride has a relatively high dielectric constant k of approximately 7 compared to silicon dioxide (k≈4) or other silicon dioxide based low-k dielectric layers (k<4), it is generally preferable to form the silicon nitride layer with a minimum thickness. It turns out, however, that the barrier characteristics of the silicon nitride layer depend on the thickness thereof so that thinning the silicon nitride layer, as would be desirable for a reduced overall dielectric constant, may not be practical to an extent as required for further scaling semiconductor devices including copper metallization layers without compromising device performance.
In light of the above-specified problems, a need exists for diffusion barrier layers exhibiting an improvement with respect to diffusion barrier efficiency, resistance to electromigration, lower parasitic capacitance, and other problems.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention, in which improved structures and methods relating to copper diffusion barriers yield devices having enhanced electromigration performance.
In a preferred embodiment, a semiconductor device comprises a substrate and a dielectric layer on the substrate. The dielectric layer has at least one opening. The dielectric layer, if porous, may optionally undergo a pore-sealing process thereby improving its dielectric characteristics. A diffusion barrier layer is deposited on the dielectric layer. A conductor, preferably copper, is deposited over the barrier. An optional glue layer is deposited between the barrier layer and the conductor.
In an alternative preferred embodiment, the thickness ratio of the glue layer to the barrier layer is about 1 to 50. Another alternative embodiment comprises treating the barrier with an electron beam or an RTP process to improve properties such as adhesion and conductivity.
In other preferred embodiments, the barrier layer comprises a layer about 10 to 30 Angstroms thick. The barrier layer includes of at least one layer of TaN, TiN, WN, TbN, VN, ZrN, CrN, WC, WN, WCN, NbN, AlN, and combinations thereof. The barrier layer may be applied using physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or plasma enhanced atomic layer deposition (PEALD).
In other preferred embodiments, the glue layer comprises a metal-rich nitride about 10 to 500 Angstroms thick. It is applied using PVD, CVD, PECVD, PEALD, or preferably ALD. Alternative preferred embodiments may include a glue layer comprising at least one layer of Ru, Ta, Ti, W, Co, Ni, Al, Nb, AlCu, and combinations thereof.
Still other preferred embodiments may further include a cap layer deposited at least upon the conductor. It may be deposited by ALD, PVD, PECVD, PEALD, and/or CVD methods, including nitridation and silicidation methods. The cap layer preferably includes at least one layer of Co, W, Al, Ta, Ti, Ni, or Ru, and combinations thereof.
Other alternative preferred embodiments further include a conductor annealing step. Preferably, the annealing step is performed at about 150 to 450° C., for about 0.5 to 5 minutes, in N2/H2 forming gas.
Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the specific embodiments disclosed might be readily utilized as a basis for modifying or designing other structures or processes for carrying out the purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions and variations on the example embodiments described do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.
The operation and fabrication of the presently preferred embodiments are discussed in detail below. However, the embodiments and examples described herein are not the only applications or uses contemplated for the invention. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention or the appended claims.
This invention relates generally to semiconductor device fabrication and more particularly to a structure and method for improved resistance to electromigration problems with conductive lines and vias, such as copper, between interconnected layers. The present invention will now be described with respect to preferred embodiments in a specific context, namely the creation of copper conductive lines and vias in the damascene process. It is believed that embodiments of this invention are particularly advantageous when used in this process. It is further believed that embodiments of this invention are advantageous when used in other semiconductor fabrication applications wherein diffusion barriers and electromigration, for example, are a concern. It is further believed that embodiments described herein will benefit other integrated circuit interconnection applications not specifically mentioned. Therefore, the specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Referring now to
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For example, the IMD layer 112 is a low-k (i.e. k less than about 4) dielectric, for example a carbon doped silicon dioxide, also referred to as organo silicate glass (OSG) and C-oxide. In alternative embodiments, low-k materials may include borophosphosilicate glass (BPSG), borosilicate glass (BSG), phosphosilicate glass (PSG), deposited over the surface of the semiconductor structures to a thickness of between about 5000 to 9000 Angstroms and preferably planarized. Exemplary organic low-k materials include polyarylene ether, hydrogen silesquioxane (HSQ), methyl silsesquioxane (MSQ), polysilsequioxane, polyimide, benzocyclbbutene, and amorphous Teflon. Other types of low-k materials suitably used with the method of the present invention include fluorinated silicate glass (FSG) and porous oxides. In preferred embodiments, the dielectric layer is preferably a low-k material containing C, O, Si, and F, such as fluorine-doped —(O—Si(CH3)2—O)—.
Open pores in low-k materials, e.g. IMD layer 112, are known to degrade performance. Therefore embodiments include a pore-sealing method comprising plasma pore sealing using Ar and NH3, e-beam pore sealing, metal organic pore sealing, or preferably vapor pore sealing. In preferred embodiments, a low-k surface is subjected to treatment with 4MS (tetramethylsilane) at a temperature of about 400° C. The 4MS used in the treatment of the present invention can be replaced by trimethylsilane, dimethylsilane or methylsilane. The vapor can be composed of organic or metal-organic molecules, preferably having a size larger than 10 Å. The temperature ranges from about 350-450° C. for about 5-30 seconds.
The e-beam pore sealing employs an electron beam with a typical condition of 2000˜5000 keV, 1˜6 mA, and 75˜100 μC/cm2. Plasma pore sealing uses an Ar plasma to bombard the low-k surface to block the pores of the sidewall of the dual damascene.
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The dual damascene structure 100 is formed by first sequentially photolithographically patterning and anisotropically etching the via opening 104 through the etch stop layer 114, the IMD layer 112, and at least partially through the first etch stop layer 103. This is followed by a similar process to photolithographically pattern and anisotropically etch a trench opening 106 through the etch stop layer 114 and a portion of the IMD layer 112. These steps form a trench opening 106 overlying and encompassing the via opening 104. It will be appreciated that the trench opening 106 may encompass one or more via openings 104 and that the trench opening 106 and via opening 104 may be formed in separate stacked IMD layers 112 including another etch stop layer 114 formed between the respective IMD layers.
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In alternative preferred embodiments, the barrier layer includes a first barrier layer on the surface of the low-k dielectric layer and a second barrier layer on the first barrier layer. The first barrier layer includes an atomic layer deposited (ALD) material selected from the group consisting essentially of Ta, W, and combinations thereof. The second barrier layer is selected from the group consisting essentially of Ni, Co, Al, AlCu alloy, W, Ti, Ta, Ra, Ru, and combinations thereof. An optional Cu seed layer may be deposited on the second barrier layer.
The barrier layer 116 may be applied using physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or plasma enhanced atomic layer deposition (PEALD). In preferred embodiments, the barrier layer 116 comprises TaN, and it is deposited using atomic layer deposition (ALD).
An ALD deposited, TaN barrier layer 116 is particularly advantageous in forming a damascene structure with reduced capacitance and reduced electromigration effects. As semiconductor dimensions continue to shrink, capacitance between conductive structures is increasingly problematic. Applicants have found that ALD barrier 116 deposition is more preferred than, for example, PVD. In the preferred embodiment comprising a TaN barrier 116, for example, applicants found that ALD significantly reduces the parasitic capacitance between neighboring conductive structures by as much as 11.5%, as compared to PVD. An ALD deposited barrier, therefore, enables thinner metal lines because the metal line with ALD barrier has a lower effective resisitvity.
In still other embodiments, the barrier layer 116 includes a Ta/TaN bi-layer structure. Ta/TaN bilayer embodiments include: PEALD TaN and ALD Ta, ALD TaN and PEALD Ta, or PEALD TaN and PEALD Ta.
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In alternative embodiments, the glue layer 118 preferably comprises two layers (not specifically shown). The first layer is preferably a metal-rich thin layer from about 130 to 170 Angstroms, preferably about 150 Angstroms. The second layer is stoichiometric metal nitride layer about 500 to 600 Angstroms, preferably about 550 Angstroms. The glue layer 118 may be applied using PVD, CVD, PECVD, PEALD, and, preferably, ALD at a deposition rate less than about lA/sec at about 100-300° C.
Alternative embodiments include a glue layer 118 consisting of Ru, Ta, Ti, W, Co, Ni, Al, Nb, AlCu alloy, and combinations thereof. In preferred embodiments, the ratio of the glue layer 118 thickness to the barrier layer 116 thickness is about 1 to 50.
Prior to deposition of a conductor, a seed layer 119 is optionally deposited over the glue layer 118 by, for example, PVD and/or CVD. Seed layer 119, preferably copper, is PVD deposited to form a continuous layer about 400 to 700 Å thick over the wafer process surface, thereby providing a continuously conductive surface for forming the bulk of the copper during the ECD process.
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In other embodiments of the present invention, there is an alternative method to improve adhesion between the barrier layer and adjacent layers. The deposition of the barrier layer, as described above, may further include a thermal treatment such as electron beam annealing or rapid thermal processing, RTP. Preferred treatments advantageously enhance wetability and/or adhesion between the barrier layer and the copper layer.
The thermal adhesion process is preferably performed at an intermediate stage during the ALD deposition of the barrier. Typically, barrier formation such as ALD TaN includes multiple steps. First, a Ta precursor is used to form a saturated surface layer. Next, the saturated surface layer is reduced and nitrided using NH3 to form a TaxNy monolayer. The thermal adhesion treatment occurs between these two steps. In the case of a WCN barrier, which is a three-step deposition process, the thermal adhesion is performed prior to the reduction step. The RTP may be incorporated into the ALD chamber. A typical RTP temperature is about 200 to 400° C.
A chemical mechanical polishing (CMP) may be used to polish the conductor fill to the level of the feature. In another alternative, electropolishing or overburden reduction may be used in place of CMP or serially with CMP. In the alternative, a simultaneous CMP and plating process may be performed. As shown in
Referring still to
Following CMP planarization, alternative preferred embodiments include a seed layer (not shown) and conductor 120 anneal. Preferably, the annealing step is performed at about 150 to 450° C., for about 0.5 to 5 minutes, in N2/H2 forming gas. The anneal causes metals in the seed layer to migrate or diffuse throughout the copper fill layer (120), thereby forming a copper-metal fill layer (120). Preferably, the Cu seed layer includes titanium. Annealing advantageously causes the Ti to distribute approximately uniformly within conductor layer 120 and form a uniform copper-titanium fill layer (120). The anneal also causes granularity of the surface of the conductor layer 120 and results in improved adhesion between the conductor layer 120 and a cap layer (as shown in
Still other embodiments may include a cap layer comprising at least one layer of a carbon-containing dielectric (such as SiC, SiOC, SiCN), a nitrogen-containing dielectric, a nitrogen-containing conductive layer, or a silicon-containing layer.
Referring now to
The embodiments of the invention described above are exemplary and not limiting, and variations that are apparent to those skilled in the art that include the features of the invention are within the scope of the invention and the appended claims. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
For example, it will be readily understood by those skilled in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present invention. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.