This application claims priority to Korean Patent Application No. 10-2004-0103088, filed on Dec. 8, 2004, which is incorporated herein by reference.
The present invention relates generally to methods for fabricating dual damascene interconnect structures and, in particular, to dual damascene methods in which a sacrificial material containing porogen (a pore forming agent) is used for filling via holes in an interlayer dielectric layer such that the sacrificial material can be transformed to porous material that can be readily removed from the via holes without damaging or removing the interlayer dielectric layer.
Due to continued technological innovations in the field of semiconductor fabrication which allow integrated circuits to be designed according to smaller design rules (DR), semiconductor devices are becoming more highly integrated. Typically, highly integrated circuits are designed using multi-layered metal interconnection structures in which the wires/interconnects are formed from different metals layers of an integrated circuit. Generally, multi-layered metal interconnection lines are formed of a metallic material, such as copper (Cu), having low resistivity and high reliability to yield improved performance. However, copper is difficult to pattern using a conventional photolithography/etching techniques, especially when the copper wires are formed according to relatively small design rules. Accordingly, dual damascene methods have been developed to enable formation of highly integrated copper metal interconnect structures.
In general, dual damascene methods are used to form upper metal lines that are electrically connected to lower metal lines with conductive vias. For example, a conventional dual damascene method generally includes process steps such as forming an interlayer dielectric (ILD) layer over a lower metal line on a semiconductor substrate, etching a via hole in the ILD layer, which is aligned to a predetermined region of the lower metal line, filling the via hole with a sacrificial material and forming a trench region in the ILD layer, which is aligned to the filled via hole. As is known in the art, the use of via-filling sacrificial material allows formation of trench and via contact regions in the ILD layer having excellent etch profiles. Moreover, the sacrificial via filling material protects the lower metal line and sidewall surfaces of the ILD layer in the via contact hole from damage or contamination due to etching atmospheres during trench formation and/or due to subsequent ashing or cleaning steps for removing photoresist material.
After the trench regions are formed in the ILD layer, the sacrificial material remaining in the via hole is etched away using etch chemistries that are selected to provide high etch selectivity of the sacrificial material with respect to the dielectric material of the ILD layer. Thereafter, the upper metal lines and via contacts are formed by filling the via and the trench regions in the ILD layer with conductive material (such as copper).
Although dual damascene methods allow formation of metal interconnect structures that yield improved performance, such methods become more problematic with decreasing design rules. For instance, with decreasing design rules, parasitic resistance and capacitance that exists between adjacent metal wiring layers in a lateral direction or in a vertical direction may affect the performance of the semiconductor devices. Indeed, parasitic capacitance and resistance results in capacitive coupling and cross talk between adjacent metal lines, which decreases the performance. Further, the parasitic resistance and capacitance components result in increased signal leakage and increased power consumption of the semiconductor device.
To reduce parasitic capacitance, dielectric materials having a low dielectric constant, k, are used to form ILD layers. Although the use of low-k dielectric materials provides improved performance, ILD layers formed with such low-k dielectric materials are more susceptible to etching damage. For instance, in the conventional process as described above, an ILD layer formed of a low-k dielectric material can be damaged (contaminated and/or undesirably etched) during removal of the via-filling sacrificial material. Thus, it would be advantageous to provide efficient methods for removing residual sacrificial material without resulting in damage to ILD layers, especially ILD layers formed with low-k dielectric materials.
U.S. Pat. No. 6,833,320 to Meagley et al. discloses a dual damascene process which employs a thermally decomposable sacrificial via-filling material that can be removed from a via hole by thermal decomposition without damaging or removing the ILD layer material. More specifically, Meagley discloses a dual damascene method which generally includes forming a via contact hole in a ILD layer on a semiconductor substrate, depositing a thermally decomposable sacrificial material in the via contact hole, etching the ILD layer and thermally decomposable sacrificial material to form a trench region, and then heating the semiconductor substrate to remove any remaining thermally decomposable sacrificial material within the via contact hole.
Meagley discloses that the thermally decomposable sacrificial material is a material that may be thermally decomposed and evaporated at an acceptable temperature, preferably less than 450 degrees C., in a reducing atmosphere, so that the thermally decomposable sacrificial material can be removed without damaging dielectric material with a low dielectric constant. The thermally decomposable material may be a combination of inorganic and organic materials such as a combination of silicon-containing and carbonaceous materials (e.g., a hydrocarbon-siloxane polymer hybrid material). Meagley further discloses that a chemical cleaning process may be applied to remove residual/remaining thermally decomposable sacrificial material from the via contact hole after heating the semiconductor substrate to remove thermally decomposable sacrificial material from the via contact hole.
Although the methods disclosed by Meagley may help to minimize damage to an ILD layer formed of low-k dielectric material, the types of thermally decomposable sacrificial materials disclosed by Meagley may actually result in some damage to the ILD layer during removal of the sacrificial material. More specifically, during a thermal process in which the substrate is heated to thermally decompose and evaporate the thermally decomposable sacrificial material, the types of thermally decomposable materials disclosed by Meagley tend to lose structural integrity and shrink when thermally decomposed. The shrinkage of the sacrificial material during thermal decomposition results in significant stresses and strains on the ILD material due to the contact forces applied to the ILD material as the sacrificial material loses structural integrity and shrinks during thermal decomposition.
Moreover, the types of thermally decomposable materials disclosed by Meagley tend to form hard residual materials as a result of thermal processes and thermal decomposition of the sacrificial materials. As noted above, Meagley discloses a method in which a chemical cleaning process can be applied to remove residual/remaining thermally decomposed sacrificial material in a contact via hole. However, the hard residual, thermally decomposed material can be difficult to remove during a subsequent chemical cleaning process, and the type of etch chemistries and/or etching time needed to remove such residual thermally decomposed sacrificial material from the via hole can actually result in damage to the low-k dielectric material forming the ILD layer.
In general, exemplary embodiments of the invention include methods for fabricating dual damascene interconnect structures and, in particular, to dual damascene methods in which a sacrificial material containing porogen (a pore forming agent) is used for filling via holes in an ILD (interlayer dielectric) layer such that the sacrificial material can be transformed to a porous sacrificial material which can be readily removed from the via holes without damaging or removing the interlayer dielectric layer.
More specifically, the sacrificial material is formed with a porogen/matrix material composition that enables the porogen containing sacrificial material to maintain its structure when converted to a porous sacrificial material. In this manner, no stress is applied to surrounding structures due to shrinkage of the sacrificial material when the porogen is removed, thus preventing damage, cracking or breaking of the ILD layer.
Moreover, the formation of pores in the base (matrix) material of the sacrificial material results in an effective increase in the surface area of the sacrificial material that can be contacted by an etch solution/gas, thereby enabling the porous sacrificial material to be more easily and quickly removed and, thus significantly minimizing etch damage to the ILD layer.
In one exemplary embodiment, a method for forming an interconnection structure includes forming an etch stop layer on a semiconductor substrate that has a lower conductive layer formed thereon, forming an ILD (interlayer dielectric) layer on the etch stop layer, forming a via hole through the ILD layer to expose a portion of the etch stop layer, wherein the via hole is aligned with a portion of the lower conductive layer, filling the via hole with a sacrificial material comprising a combination of a base (matrix) material and a porogen material, forming a trench in the ILD layer aligned with the via hole, removing the porogen material from the sacrificial material to convert the sacrificial material to a porous sacrificial material comprising the base (matrix) material with pores formed therein, removing the porous sacrificial material in the via hole to expose a portion of the etch stop layer, removing the exposed portion of the etch stop layer, and forming an interconnection by filling the trench and via hole with a conductive material.
In general, the sacrificial material may be formed of a combination of an organic or inorganic base (matrix) material and a porogen material, wherein the porogen may be removed from the matrix material to create pores or voids in the matrix material while maintaining the structural integrity of the matrix material. In one exemplary embodiment, the base (matrix) material may be an organic SOP (spin-on-polymer) material such as a poly arylene ether-based material, a polymetamethylacrylate-based material, or a vinylethermetacrylate-based material. In another exemplary embodiment, the base (matrix) material may be an inorganic SOG (spin-on-glass) material such as an HSQ (hydrogenSilsesQuioxane)-based material or an MSQ (MethylSilsesQuioxane)-based material.
In one exemplary embodiment, the porogen can be removed from the sacrificial material by heating the sacrificial material to a temperature above a boiling point of the porogen material to dissolve the porogen material from the base material. The heating may be performed in a vacuum or nitrogen environment. In one exemplary embodiment, the porogen material is selected to have a boiling point in a range of about 150 degrees C. to about less than 400 degrees C.
In another exemplary embodiment, the porogen material can be removed from the sacrificial material by applying UV radiation to the sacrificial material while heating the sacrificial material.
In yet another exemplary embodiment, the porogen material can be removed by applying a plasma treatment to dissolve the porogen material from the base material. The plasma treatment can be performed using a nitrogen-based plasma or hydrogen-based plasma treatment process.
In one exemplary embodiment, the porous sacrificial material can be removed using a wet strip process or an ashing process. For example, when the porous sacrificial material comprises an inorganic base material and the ILD layer is formed of an organic material, the porous sacrificial material can be removed using a wet strip process with an etch chemistry having an etching selectively with respect to the porous material. When the porous sacrificial material is formed of an organic base material and the ILD layer is formed of an inorganic material, the porous sacrificial material can be removed using a plasma ashing or H2 based plasma ashing process or a wet etch process. In all instances, the pores dispersed throughout the porous sacrificial material provides more surface area for etching, enabling quick removal of the porous material from the via contact hole, for instance.
These and other exemplary embodiments, aspects, features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings.
Exemplary embodiments of the invention will now be described more fully with reference to the accompanying drawings in which it is to be understood that the thickness and dimensions of the layers and regions are exaggerated for clarity. It is to be further understood that when a layer is described as being “on” or “over” another layer or substrate, such layer may be directly on the other layer or substrate, or intervening layers may also be present. Moreover, similar reference numerals used throughout the drawings denote elements having the same or similar functions.
Referring to
Referring to
In one exemplary embodiment, the ILD layer (130) is preferably formed of a low-k dielectric material with k less than about 4.2. The ILD layer (130) may be formed of an organic polymer material or an inorganic material. More specifically, the ILD layer (130) may be formed of a silicon oxide layer doped with carbon, fluorine or hydrogen atoms, e.g., a silicon oxycarbide (SiOC) layer, a SiOCH layer, a fluoro-silses-quioxane layer (FSQ) layer, a hydro-silses-quioxane (HSQ) layer or a methyl-silses-quioxane (MSQ) layer. Whatever materials are used for the etch stop layer (120) and ILD layer (130), the ILD layer (130) is preferably formed of a material having a high etching selectivity with respect to the stopper layer (120) and having a low dielectric constant.
The capping layer (140) (or hard mask layer) may be formed to protect the ILD layer (130) from being damaged during plasma processes and to act as a buffer layer for a subsequent CMP process. The capping layer (140) is formed with a material having a high etching selectivity with respect to the ILD layer (130). For example, the hard mask layer (140) may be formed of: (i) an insulating nitride layer, such as a silicon nitride layer (SiN), a silicon carbonitride layer (SiCN) or a boron nitride layer (BN); (ii) an insulating carbide layer, such as a silicon carbide layer (SiC); (iii) a metal nitride layer, such as a tantalum nitride (TaN) layer, a titanium nitride (TiN) layer, a tungsten nitride (WN) layer or an aluminum nitride (AlN) layer; (iv) a metal oxide layer, such as an aluminum oxide (AL2O3) layer, a tantalum oxide (TaO) layer or a titanium oxide (TiO) layer; or (v) a silicon layer such SiO2, or other materials such as SiOF and SiON, for example.
A next step in the exemplary process includes forming a via hole in the ILD layer (130). For example, as further depicted in
In particular, referring to
Referring to
For example, the sacrificial material (162) may be formed of a combination of a porogen material and an organic spin-on-polymer (SOP) base (matrix) material such as a polyaryleneether, polymetamethylacrylate, or a vinylether metacrylate based material. In another exemplary embodiment of the invention, the sacrificial material (162) may be formed of a combination of a porogen material and an inorganic spin-on-glass (SOG) base (matrix) material such as an HSQ (HydrogenSilsesQuioxane) based material or an MSQ (MethylSisesQuioxane) based material.
The porogen material may be any suitable material (a solid, liquid, or gaseous material) that is removable from the base matrix material to create pores or voids in the cured base matrix material. Many types of materials, such as polymeric materials, may be used as a porogen, and the type of porogen used will depend on the compatibility of the porogen with the matrix material. For example, the porogen and base material are preferably selected such that the porogen material can thermally degrade at temperatures below the thermal stability temperature of the matrix material. In addition, the porogen and base materials are preferably selected such that while the sacrificial material is cured, the phase separation between the porogen and matrix material is such that the porogen aggregates and forms masses of porogen material, which are substantially equally dispersed throughout the matrix material.
In addition to exemplary properties discussed above, the sacrificial material (162) is formed of materials that provide uniform gap filling characteristics to minimize formation of voids in the sacrificial material (162). Moreover, the sacrificial material (162) is preferably selected to have dry etch properties that are similar to the dry etch properties of the dielectric material that forms the ILD layer (130). For example, the sacrificial material (162) preferably has a dry etch rate that is slightly faster than the dry etch rate of the ILD layer (130) for a given dry etch chemistry. As explained below, this ensures that a sufficient amount of sacrificial material remains in the via hole (150) during formation of the trench region. Moreover, as will be explained below, the base (matrix) material of the sacrificial material (162) is selected such that after removal of the porogen material from the sacrificial material, the remaining base (porous matrix) material has a wet etch rate that is significantly faster than the wet etch rate of the ILD layer (130). As explained below, this enables removal of the remaining porous sacrificial material in the via hole (150) after the trench regions is formed. Whether an SOP or SOG sacrificial material is used will depend on the material that forms the ILD layer (130) and the desired etch selectivity between the ILD layer (130) and sacrificial material (162) for the given etch chemistries.
In general, the layer of sacrificial material (162) may be formed by forming a solution of matrix material, porogen and a solvent, and applying the sacrificial material solution to the substrate by a method such as spin coating. To cure the sacrificial material, the solvent can be removed by evaporation and/or heating, resulting in a sacrificial material (162) having the porogen material dispersed in the matrix material. Further thermal processing may be applied to separate the porogen from the matrix material and form masses of porogen material dispersed throughout the matrix material and fully cure the matrix material. As discussed below, further heat treatment is applied to remove the porogen material from the matrix material to form a porous matrix material.
When forming the sacrificial material solution, the amount of matrix material relative to the amount of porogen may be adjusted to obtain a desired porosity. For example, in one exemplary embodiment, the sacrificial material (162) comprises porogen material in an amount of about 1 wt % to about 70 wt % of a total weight of the sacrificial material (162).
A next step in the exemplary process is forming a trench region in the ILD layer (130). Referring to
Referring to
Referring to
In one exemplary embodiment of the invention, the porogen material can be removed from the sacrificial material by heating the sacrificial material to a temperature above a boiling point of the porogen material to dissolve the porogen material from the base material. The heating is performed for about 1 minute to about 2 hours. The heating is performed in a vacuum, nitrogen or another inert ambient environment. In one exemplary embodiment, the boiling point of the porogen material is in a range of about 150 degrees C. to about less than 400 degrees C. In another embodiment, UV radiation can be applied to the sacrificial material while heating the sacrificial material to assist in removal of the porogen material. In another exemplary embodiment of the invention, removing the porogen material may be performed using a plasma treatment process to dissolve the porogen material from the base material. The plasma treatment is performed using a nitrogen-based plasma or hydrogen-based plasma.
Advantageously, the porous sacrificial material (162′, 162a′) is formed such that the matrix material maintains its structural integrity (the matrix base material maintains its structure), but is porous. Therefore, when the porogen containing sacrificial material (162) is converted to porous sacrificial material (162′), no stress is applied to the ILD layer (e.g., stress due to shrinkage as in the conventional process), thus preventing damage, cracking or breaking of the ILD layer. Moreover, the porosity of the remaining matrix material results in an effective increase in the surface area of the sacrificial material, thereby enabling the porous sacrificial material (160, 162a) in the via hole (150) and on the hard mask layer (140) to be more easily and quickly removed and, thus significantly minimizing damage to the ILD layer when removing such porous material.
In
Furthermore, due to the existence of the pores in the base material, the wet etch process results in removing the sacrificial material 2-4 times faster than removal of the same, non-porous base material because the wet etch solution can readily penetrate into the porous base material. In other words, the existence of the pores in the base material effectively increases the surface area of the sacrificial material to which the etch solution can be applied. The increased etch rate of the porous sacrificial material allows fast and efficient removal of the porous sacrificial material to minimize or otherwise prevent damage to the ILD layer (130).
When the porous sacrificial material (162′, 162a′) is formed of an organic base material and the ILD layer (130) is formed of an inorganic material, the porous sacrificial material (162′, 162a′) can be removed using a plasma ashing or H2 based plasma ashing process or a wet etch process. When the sacrificial material is formed of an organic material, the sacrificial material does not have be preserved during ashing. In such instance, the sacrificial material and photoresist can be removed simultaneously, but more effectively by generating pores in the sacrificial layer. In one exemplary embodiment, the porogen material in sacrificial layer can be removed as follows. First, an anneal process and/or UV process is performed prior to ashing. Next, an ashing process is performed, which comprises a plasma treatment process as well as thermal process.
After removing the porous sacrificial material (162′, 162a′), the next step of the exemplary method includes removing the portion of the etch stop layer (120) that is exposed on the bottom of the via hole (150) to expose the lower conductive layer (110). This etch process may be performed using known techniques to selectively etch the material forming the etch stop layer (120) without etching the ILD layer (130). The resulting structure is depicted in the exemplary diagram of
Thereafter, referring to
The exemplary methods described above with reference to
Referring to
Comparing the exemplary diagram of
Referring to
Referring to
Referring to
Referring to
Referring to
In one exemplary method, the etching (327) is performed using an etch chemistry that is highly selective to hard mask layer (282), the capping layer (140) and ILD layer (130) with respect to the sacrificial material (262). In this manner, the capping layer (140) and ILD layer (130) are etched at a significantly greater rate than the sacrificial material (262) such that the sacrificial material (262) above capping layer (140) acts as an etch mask after the hard mask layer (282) is etched away, and such that the sacrificial material (262a) in the bottom of the via hole (150) is not over etched, thereby protecting the etch stop layer (120) and lower interconnection line (110) from exposure to the etching atmosphere. For example, as depicted in
Referring to
As noted above, the porogen material can be removed from the sacrificial material by heating the sacrificial material to a temperature above a boiling point of the porogen material to dissolve the porogen material from the base material. The heating is performed for about 1 minute to about 2 hours. The heating is performed in a vacuum or nitrogen environment. In one exemplary embodiment, the boiling point of the porogen material is in a range of about 150 degrees C. to about less than 400 degrees C. In another embodiment, UV radiation can be applied to the sacrificial material while heating the sacrificial material to assist in removal of the porogen material. In another exemplary embodiment of the invention, removing the porogen material may be performed using a plasma treatment process to dissolve the porogen material from the base material. The plasma treatment is performed using a nitrogen-based plasma or hydrogen-based plasma.
Advantageously, the porous sacrificial material (262a′) in the via hole maintains its structural integrity (the matrix base material maintains its structure) but is porous. Therefore, the porous material (262a′) in the via hole (150) does not add stress to sidewall surfaces of the ILD layer in the via hole (150) (e.g., stress due to shrinkage as in the conventional process). Moreover, the porous structure effectively increases the surface area of the sacrificial material enabling the porous material (262′, 262a′) to be more easily removed, thus significantly minimizing damage to the ILD layer when removing the porous material (262a′) in the via hole (150).
Next, referring to
After removing the remaining porous sacrificial material (262′, 262a′), the next step of the exemplary method includes removing the portion of the etch stop layer (120) that is exposed on the bottom of the via hole (150) to expose the lower conductive layer (110). This etch process may be performed using known techniques to selectively etch the material forming the etch stop layer (120) without etching the ILD layer (130). The resulting structure is depicted in the exemplary diagram of
Thereafter, referring to
Although exemplary embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to the exemplary embodiments described herein, and that various other changes and modifications may be readily envisioned by one of ordinary skill in the art without departing form the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
10-2004-0103088 | Dec 2004 | KR | national |