Patent Application
20070048981
The present invention relates generally to semiconductor device manufacturing, and, more particularly, to a method for protecting a semiconductor device from carbon depletion based damage.
In the fabrication of integrated circuit devices, it is often desirable to isolate individual components of the integrated circuits from one another with insulative materials. Such insulative materials may include, for example, silicon dioxide, silicon nitride and silicon carbide. While these materials may have acceptable insulating properties in many applications, they also have relatively high dielectric constants, which can lead to capacitive coupling between proximate conductive elements. This is particularly disadvantageous, given the ever-decreasing distances between conductive circuit elements, and the use of multi-layered structures. An unnecessary capacitive coupling between adjacent wires increases the RC time delay of a signal propagated therethrough, resulting in decreased device performance.
Thus, for specific applications, insulating materials having relatively low dielectric constants (e.g., k<3) are desired. In very large scale integrated circuit (VLSI) technology, silicon dioxide (SiO2) has been traditionally used as an interlevel dielectric (ILD) material in conjunction with aluminum interconnect material. More recently, however, significant advancements have been made to enhance circuit performance by replacing the SiO2 with a “low-k” porous dielectric and by using copper (higher conductivity) interconnect.
One drawback with using porous ILD and IMD (intermetal dielectric) materials in back end of line (BEOL) processing is the damage sustained by the material as a result of various plasma exposure steps (e.g., reactive ion etching (RIE) and stripping). In one respect, this damage is characterized by a gradient in carbon concentration through the depth of the ILD/IMD material wherein the carbon concentration is reduced near the lines and increases down through the bulk of the ILD/IMD material. Historically, upon exposure to plasma processing, denser ILD materials have a carbon depletion layer of less than about 10 nm, and hence are less susceptible to plasma damage. In contrast, the carbon depletion layer for various ultra low-k ILD materials can now extend to depths of up to about 65 nm, which will adversely affect the integrity of the ILD/IMD, thereby increasing leakage current and capacitance.
An existing technique for addressing this problem with regard to porous ILD/IMD materials has been to form thin, dense hardmask films (e.g., about 50 nm in thickness) as a protective layer over the ILD/IMD layers. However, if oxygen is present during the hardmask deposition process, this will have an adverse effect on the overall effective dielectric constant (keff) of the integrated build due to the fact that the dense hardmask film deposition processes can also cause damage to the ILD/IMD layer.
In other words, while attempting to protect the ILD film by first depositing a thin, dense hardmask, it is also possible to create a carbon depletion region at the hardmask/ILD interface in so doing. Thus, to reduce the keff of the device, the hardmask is then reduced to a minimal thickness or subsequently removed during chemical mechanical polishing (CMP). On the other hand, while removing the hardmask lowers the device keff, the original difficulty sought to be prevented (i.e., the susceptibility of exposed porous ILD film to plasma damage during a precleaning process) once again becomes problematic.
Accordingly, it would be desirable to be able to adequately protect a semiconductor device from carbon depletion type damage in a manner that does not adversely affect other beneficial device properties, such as low keff.
The foregoing discussed drawbacks and deficiencies of the prior art are overcome or alleviated by a method for protecting a semiconductor device from carbon depletion type damage. In an exemplary embodiment, the method includes enriching an exposed surface of a porous interlevel dielectric material (ILD) with a carbon based material, and implementing a plasma based operation on the porous ILD material. The enriching of the porous ILD material reduces effects of carbon depletion as a result of the plasma based operation.
In another embodiment, a method for forming a semiconductor device includes forming a porous interlevel dielectric (ILD) layer over a lower capping layer, forming one or more metal structures within the porous ILD layer, and removing one or more hardmask layers used in the formation of the one or more metal structures so as to expose the porous ILD layer. An exposed surface of the porous ILD layer is enriched with a carbon based material, and a cleaning operation is implemented to remove oxide materials from exposed surfaces of the one or more metal structures, wherein the enriching of the porous ILD layer reduces effects of carbon depletion as a result of the cleaning operation.
Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:
FIGS. 1(a) through 1(f) illustrate a conventional cleaning sequence of a semiconductor device, following metal formation within an interlevel dielectric layer, in preparation for capping and formation of subsequent ILD/wiring levels;
FIGS. 2(a) through 2(f) illustrate a method for protecting a semiconductor device from carbon depletion type damage, in accordance with an embodiment of the invention;
FIGS. 3(a) and 3(b) illustrate an alternative embodiment for implementing the carbon enrichment operation and ammonia plasma clean;
FIGS. 4(a) through 4(d) illustrated still an alternative embodiment for implementing the carbon enrichment operation and ammonia plasma clean; and
FIGS. 5(a) through 5(d) illustrate an alternative embodiment of a method for protecting a semiconductor device from carbon depletion type damage, implemented prior to hardmask formation.
Disclosed herein is a method for protecting a semiconductor device from carbon depletion type damage, such as may be sustained during a plasma based operation such as a hardmask deposition or cleaning (pretreatment) operation for example. Briefly stated, an exposed surface (e.g., low-K ILD post deposition, copper, low-k material) is enriched with carbon prior to a plasma based operation (e.g., hardmask deposition, cleaning operation) of the exposed surface, thereby reducing the degree of carbon depletion in the surface as a result of the plasma based operation. Alternatively, the carbon enriching may be implemented subsequently to, simultaneously with, or in lieu of a more conventional pretreatment operation such as ammonia plasma cleaning, which prepares the device for the deposition of a subsequent capping layer and next interlevel dielectric layer.
Referring initially to FIGS. 1(a) through 1(d), there is shown a series of process flow diagrams illustrating a conventional cleaning sequence of a semiconductor device, following metal formation within an interlevel dielectric layer, in preparation for capping and formation of subsequent ILD/wiring levels. As shown in
Prior to metal formation within the porous ILD 104, a hardmask 106 is patterned such that the porous ILD 104 may be properly etched and the metal fill 108 introduced into the openings formed therein. The hardmask 106 may be a single layer or a dual hardmask (e.g., tetraethoxysilane (TEOS)/octamethyltrisiloxane (OMCTS)), as shown in the figure. As will be appreciated, the metal fill may be implemented in accordance with single damascene processing (i.e., separate via and line formation) or dual damascene processing (i.e., simultaneous via and line formation). As illustrated in
Then, as shown in
Therefore, in accordance with an embodiment of the invention, FIGS. 2(a) through 2(f) illustrate a method for protecting a semiconductor device 200 from carbon depletion type damage. The formation of the metal fill 108 (e.g., copper) within the lower level, ultra low-k porous dielectric layer 104 in FIGS. 2(a) and 2(b) is similar to that depicted in FIGS. 1(a) and 1(b). However, in preparation for a cleaning pretreatment step prior to cap formation,
More specifically, the carbon enrichment operation may include, in one embodiment, silylation of the exposed ILD 104 and metal 108 with silylation agents having —Si—R functionalities (e.g., methyl terminated alkoxy, acetoxy, amino, or chloro silane reagents). Alternatively, the enrichment operation may include exposure to a plasma containing low pressure hydrocarbon species such as CxHy, wherein the species may be an alkane, alkene or alkyne. In order to facilitate breaking of the C—H bond, an alkane species may be used so that carbon is more easily introduced to the plasma ambient. This consumes excess hydrogen (from the NH3 or H2 pre-cleaning gas) that would otherwise chemically alter SiCOH film, thereby providing a path for CO or CO2 and OH or H2O formation (and perhaps additional COH complexes), facilitating the reduction of copper oxide to copper and replacing any carbon depleted from the SiCOH ILD with carbon from the hydrocarbon co-reactant. However, for this process to be efficient, the effective carbon concentration in the plasma must be above a specific threshold to enable complete CuO reduction and still provide sufficient carbon species that can be incorporated into the film. On the other hand, the use of an alkene or alkyne would provide a higher carbon to hydrogen ratio in order to maximize the replenishment of carbon lost from the SiCOH.
Regardless of the specific type of carbon enrichment operation implemented,
As indicated above, the carbon enrichment operation need not necessarily be performed prior to the plasma clean operation. For example, the carbon enrichment operation and plasma clean may be implemented in a single step by introduction of a hydrocarbon species into the ammonia (or hydrogen) plasma as depicted in FIGS. 3(a) and 3(b). In this embodiment, the free carbon reacts with hydrogen from the ammonia to avoid carbon depletion of the SiCOH ILD 106 or to provide a source of carbon that can replenish the carbon removed from the SiCOH. In still another embodiment depicted in FIGS. 4(a) through 4(d), the ammonia plasma clean step can be followed by the carbon enrichment operation to replenish the carbon removed from the SiCOH during the ammonia treatment. It is still further contemplated that the plasma treatment may be eliminated entirely by implementing a hydrocarbon enrichment step to both reduce the copper oxide and maintain a source of carbon for the SiCOH, ultra low-k ILD layer.
Finally, FIGS. 5(a) though 5(d) illustrate an alternative embodiment of a method for protecting a semiconductor device from carbon depletion type damage, implemented prior to hardmask formation. As stated previously, in addition to ammonia (or hydrogen) plasma, certain hardmask formation processes can also subject a porous ILD layer 104 to carbon depletion. Thus, as shown in
The resulting enriched carbon portion 204 of the porous ILD layer 104 is shown in
While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
