Patent Application
20080057701
The present invention benefits from the discovery that a poison-blocking-layer can be placed underneath a photoresist layer being used to fabricate a dual damascene interconnect structure. The term poison-blocking-layer as used herein refers to a layer that blocks the entry of base-containing molecules that can deteriorate (“poisons”) the photosensitivity of a photoresist. Example base-containing molecules include ammonia, ethylamine, and dimethylamine borane. E.g., in many cases, the poison-blocking-layer is an amine-blocking-layer.
The poison-blocking-layer prevents the diffusion of poisons (e.g., amines) from underlying structures of the integrated circuit (IC) into the photoresist. In some cases, the poison-blocking-layer is removed from the IC at some stage in the manufacturing process after patterning the photoresist. In other cases, the poison-blocking-layer is retained in the final IC structure. Sometimes the poison-blocking-layer can serve additional functions, e.g., as a bottom anti-reflective coating (BARC), a hard mask (HM) or a chemical mechanical polishing (CMP) stop layer.
To limit excessive etching of the target ILD layer 212, or to limit the damage to the ILD 212 during a resist patterning rework, it is desirable to deposit a HM 215 on the surface 210. As an example, the HM 215 can comprise silicon carbide deposited by plasma-enhanced chemical vapor deposition (PECVD), or other materials and procedures well know to those skilled in the art. Because the HM 215 does not cover the via opening 205, however, it does not block the diffusion of poisons into a subsequently deposited photoresist layer.
To limit the etching of the target ILD layer 212 to just that needed to form the via opening 205, it is also desirable to deposit an etch stop layer 220 on the underlying ILD layer 125 and metal interconnect 130. The etch stop layer 220 is deposited using conventional procedures such as PECVD or other procedures well know to those skilled in the art. Some preferred etch stop materials comprise silicon carbide (SiC), silicon nitride (SiN), silicon carbon nitride (SiCN), silicon oxycarbon (SiCO), or combined layers thereof.
In some cases, to adhere the etch stop layer 220 to the metal (e.g., copper) interconnect 130, the surface 210 is pretreated with an ammonium-containing plasma. It is believed that such ammonium plasma pretreatments can provide a source of poisons (e.g., amines) that can contaminate a subsequently deposited photoresist layer.
Some preferred sacrificial fill material 305 comprise a BARC. As well known to those skilled in the art, a BARC layer helps to eliminate photolithographic artifacts and thereby improve the uniformity of feature definitions across the substrate 110. However, in the present case, a BARC serving as the sacrificial fill material 305 is used for its structural role of filling the via opening 205 and its etch selectivity (being similar to the ILD layer 212), rather than its optical properties. Examples of suitable sacrificial fill material 305 include an organic BARC material (e.g., a 193 nm anti-reflective coating such as ACR29A from Brewer Science, Inc., Rolla Mo.). In other cases, however, the sacrificial fill material 305 can comprise an inorganic material such a silicon oxide based BARC materials, such as DUO™ (Honeywell Electronic Materials, Tempe Ariz.).
It is believed that such sacrificial fill materials 305, however, do not prevent poisons from diffusing through the filled via opening 205 and into a subsequently deposited photoresist layer.
It is important for the poison-blocking-layer 510 to not line the entire via opening 205 because the poison-blocking-layer 510 will then become part of the dual damascene interconnect 200. If the dielectric constant of the poison-blocking layer is higher than the dielectric constant of the ILD, then it is less desirable for the poison-blocking-layer 510 to be retained as part of a liner in the dual damascene interconnect 200. Such may be the case when e.g., the poison-blocking-layer 510 is composed of a high dielectric constant material (e.g., a dielectric constant greater than 4). The presence of such a high dielectric constant material in the ILD 125 can disadvantageously increase the effective dielectric constant of the ILD 125 and thereby increase the RC-delay time of the IC 100.
The selection of suitable materials, deposition conditions, and the thickness of the poison-blocking-layer 510 have not been previously recognized as result-effective-variables that are important to the fabrication of dual damascene interconnects.
In some cases the poison-blocking-layer 510 comprises a dense material (e.g., a density of about 2 gm/cm3 or greater) that can impede the diffusion of poisons through it. Examples include metal nitrides like titanium silicon nitride or tantalum nitride, or metals like titanium or tantalum. Such conducting materials, however, must be removed from the completed IC 100 because they would otherwise create electrical shorts in the IC 100.
In addition, some materials, such as tantalum, can present challenges when etching to from the trench of the dual damascene interconnect 200. E.g., aggressive etch conditions must be used to remove the tantalum poison-blocking-layer 510 before switching to milder conditions used to etch the ILD 125. In such instances, there is a risk of over-etching the ILD 125.
In other cases, the poison-blocking-layer 510 comprises a non-conducting material. The use of a non-conducting material has an advantage compared to a conducting poison-blocking-layer 510 in that it can be left on the surface 210 in the final IC 100. This eliminates the need to perform additional processing steps (e.g. CMP) to remove the poison-blocking-layer 510. Example non-conducting materials for the poison-blocking-layer 510 include silicon carbide (SiC) or boron-carbonitride (BCxNy).
In some cases, however, it is still desirable to remove the non-conducting poison-blocking-layer 510 from the completed IC 100. An important benefit of removing the poison-blocking 510 is that it cannot affect the effective dielectric constant of the ILD 125.
Some preferred non-conducting materials for the poison-blocking-layer 510 include metal oxides such as aluminum oxide (Al2O3) or tantalum oxide (Ta2O5). Metal oxides having a high density are preferred, e.g., the density of Al2O3 and Ta2O5 are about 4 and 8 gm/cm3, respectively.
In some cases, it is beneficial to choose a poison-blocking-layer 510 that can be deposited as a thin layer and yet still prevent diffusion of poisons through it. E.g., sometimes the thickness 520 of a SiC poison-blocking-layer 510 required to prevent the diffusion of poisons (e.g. more than about 40 nm) is greater than desired in the case where the poison-blocking-layer 510 is retained in the completed IC 100. E.g., a 40 nm thick poison-blocking-layer 510 made of a material with a high dielectric constant (e.g., a silicon nitride having a dielectric constant of about 7) could significantly contribute to an increase in the effective dielectric constant of the ILD layer 125.
The use of a dense non-conducting metal oxide, such as Al2O3 is preferred because this permits a thinner poison-blocking-layer 510 to be used (e.g., a thickness 520 of about 50 nm, more preferably 20 nm or less, and more preferably 5 to 2.5 nm). It is desirable to use a thin poison-blocking-layer 510 because a thin poison-blocker-layer will have less effect on the effective dielectric constant of the ILD layer 125 as compared to a thicker layer.
In some cases, material used to form the poison-blocking-layer 510 is selected because it can be deposited at low temperatures. E.g., the temperatures (e.g., 350 to 400° C.) at which Al2O3, SiC or BCxNy containing poison-blocking-layers 510 are deposited may be incompatible with certain sacrificial fill materials 305. E.g., organic sacrificial fill materials 305, comprising organic polymers such as ACCUFLO® (Honeywell Electronic Materials, Tempe Ariz.) become unstable at temperatures above 250° C.
Certain non-conducting metal oxides, such as Al2O3, desirable because they can be deposited at temperatures that are compatible with certain types of sacrificial fill materials 305 (e.g., about 200 to 250° C.). E.g., in some preferred embodiments depositing the poison-blocking-layer 510 comprises using an atomic-layer deposition (ALD) process, at less than 250° C., to deposit an Al2O3 layer to a thickness 520 of about 5 nm. However, CVD or PVD methods at these temperatures could also be used to deposit the Al2O3 layer, or other metal oxide layer, to form the poison-blocking-layers 510.
In some cases, the material of the poison-blocking-layer 510 can be selected for its ability to perform other functions that facilitate the manufacture of the IC 100. For instance, in some embodiments, the poison-blocking-layer 510 serves as a HM for the ILD layer 212. E.g., an Al2O3 poison-blocking-layer 510 can also functions as a HM, thus eliminating the need to deposit a separate HM layer 215.
Preferably, the photoresist is an ultraviolet photoresist, and more preferably a 193 nm resist. As well known to those skilled in the art, there are discrete ultraviolet exposure technologies corresponding to particular wavelengths of light emitted by e.g., lasers. For instance, conventional lasers used in photolithography typically emit ultraviolet light at wavelengths of 248 nm, 193 nm, or 157 nm. Photoresists that are exposed to these wavelengths of light are termed 248 nm resists, 193 nm resists and 157 nm resists, respectively. The photoresist, however, could be any type of resist material whose photosensitivity, on exposure to ultraviolet light or other wavelengths of radiation, is affected by the presence of poisons.
In some embodiments a BARC layer 630 is deposited (e.g., via a spin-on process) on the poison-blocking-layer 510 before depositing the photoresist layer 620. The BARC can comprise any organic or inorganic material capable of reducing light reflectance during photolithography to define the trench pattern 610. In some cases the BARC comprises the same material as the sacrificial fill material 305. In other embodiments however, the poison-blocking-layer 510 can serve as the BARC for trench patterning. E.g., an Al2O3 poison-blocking-layer 510 can also function as the BARC, thus eliminating the need to deposit a separate BARC layer 630.
Consider as an example the case where the ILD 125 comprises organo-silicate glass (OSG) and the poison-blocking-layer 510 comprises tantalum. A suitable etch process for removing the poison-blocking-layer 510 comprises a conventional plasma etch for etching metals using e.g., Cl-based plasma chemistry. For poison-blocking-layers 510 having a thickness 520 of less than about 50 nm, it is more desirable to use a plasma etch relying on ion bombardment and using inert chemistry (e.g., Ar-based plasma chemistry). A suitable etch process for removing the ILD 125 (having a thickness of about 200 nm) comprises a conventional plasma etch for etching dielectrics using e.g., a CxFy-based plasma chemistry.
There is an advantage in leaving the poison-blocking-layer 510 on the underlying ILD 212 when forming the next ILD 910. When ammonium plasma pre-treatment is performed to improve the adhesion of an etch stop layer 950 for the metal structure of the next ILD 910 (analogous to the metal structure 730 depicted in
The dual damascene interconnect 200 can be formed by any of the embodiments of the process described above in the context of
In some cases the poison-blocking-layer is retained e.g., as part of a CMP stop for removing one or more metal layer 740, 745, 750 (
In other cases, such as illustrated in
Those skilled in the art to which the invention relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described example embodiments, without departing from the invention.
