Patent Application
20120301706
1. Technical Field
The disclosure generally relates to a method for depositing liner materials on porous low temperature substrates by plasma enhanced atomic layer deposition (PE-ALD). In particular, a SiNxCy liner is formed on a porous low dielectric constant (low-k) substrate by PE-ALD, without any penetration of the pores of the surface of the substrate. The method provides the deposition of a liner that prevents pore penetration of a low-k material.
2. Discussion of the Background
Materials have been developed and studied for reducing the dielectric constant of dielectrics for back end of the line (BEOL) processes and similar processes. One of the promising candidates of materials for this purpose is porous low dielectric constant (low-k) materials. These dielectrics may include porous low-k materials, such as SiCO, and spin-on dielectrics, including porous SiLK™, a low-k dielectric resin (a trademark of Dow Chemical Company, and JSR LKD 5109™, a low-k dielectric material containing Si, C, O, and H (a trademark of JSR Micro, Inc.). However, there are several issues to be solved in implementing these materials.
A major concern in industry is the penetration of liner materials, such as tantalum nitride (TaN), into the pores of such dielectric low-k materials, when the liners are deposited by various methods including chemical vapor deposition (CVD) and atomic layer deposition (ALD). In particular, ALD has become a more promising technique than CVD to deposit liners for various technologies, due to its ability to produce highly conformal films. However, the extremely good conformality of the technique causes easier penetration to the inside pores of porous low-k materials. Further, surface treatment, including plasma treatment, only produces partial success by sealing these surface pores.
Another concern is that the performance in advanced microelectronic chips has become more and more limited by the signal propagation delay in interconnect wiring on these chips. This delay is a function of the electrical resistance of the wires and the effective capacitance resulting from the dielectric medium surrounding the wires. It has been found that the replacement of aluminum (Al) wires with lower resistivity copper (Cu) wires enables the reduction of the interconnect resistance, and the reduction of effective interconnect capacitance may be achieved through the use of lower dielectric constant (k) insulators between interconnect wires. In particular, one efficient way to lower the k value of insulators has been to use porous dielectrics. In particular, k values as low as 1.4 have been achieved by starting with a fully dense insulator with a k value of about 2.7, for example spin-on glass films of the silsesquioxane type, and introducing up to about 55%-60% porosity. However, current ALD of metal liners results in severe penetration into nano pores of porous low-k materials.
Strategies to prevent this penetration has been studied and developed. One strategy has been the use of thin protective layer, preferably low-k materials. However, the use of spin-on techniques does not provide conformal coating to high aspect ratio dual damascene structures. Therefore, in view of the foregoing, there remains a need for a technique to deposit a liner that prevents pore penetration of a low-k material.
This disclosure provides a plasma-enhanced ALD (PE ALD) of SiNxCy, as a protective layer for consecutive deposition of metal liners without penetration.
Accordingly, the following aspects provide a method for employing plasma enhanced atomic layer deposition (PE-ALD) to deposit a SiNxCy liner on various porous low-k materials. In particular, during PE-ALD, the surface of porous low-k materials is exposed to plasma for the several initial cycles. Since the plasma effectively seals the surface of the pores, real time pore sealing occurs through the deposition.
In one aspect, the method of depositing the SiNxCy liner by PE-ALD comprises:
forming a SiNxCy liner on a surface of a low-k substrate having pores on a surface thereon,
wherein x+y ranges from about 0.8 to 1.2,
wherein the low-k substrate is repeatedly exposed to a aminosilane-based precursor and a nitrogen or hydrogen plasma until a thickness of the liner is obtained, and
wherein the liner is prevented from penetrating inside the pores of a surface of the substrate.
In another aspect, the disclosure provides a method in which a protective layer is first formed on the low-k material substrate by PE-ALD from the aminosilane-based precursor and a nitrogen plasma, and then a substantially stoichiometric SiNxCy layer is formed by PE-ALD from the aminosilane-based precursor and a plasma consisting of hydrogen and nitrogen.
In a further aspect, the disclosure provides a porous low-k substrate having a SiNxCy liner formed thereon according to above method, without penetration of pores on a surface of the substrate.
Still other objects and advantages of the present disclosure will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only in the preferred embodiments, simply by way of illustration of the best mode. As will be realized, the disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the intent of this disclosure. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
A more complete appreciation of the disclosure and many of the attendant advantages will be readily obtained, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying figures.
In the method of the disclosure, a number of cycles may be repeated in accordance with the PE-ALD technique. In one embodiment, the method is carried out in a noncommercial ALD chamber capable of handling sample sizes as large as 200 mm diameter. The chamber may include a reactive-gas grade turbo molecular pump with a working base pressure of 10−7 Torr. Sample heating may be conducted using a ceramic resistive heating plate, which provides growth temperatures up to 450° C. The heating, in one embodiment, runs at approximately 300° C. The temperature may be controlled by varying current to the heater, which may be calibrated against a thermocouple attached to the sample.
Due to the recombination and/or deactivation of reactive species for PE-ALD on porous surfaces of low-k substrates, including the inside surface of pores, the conformality of liners by PE-ALD generally includes nano scale pores, though the conformality of liner is sufficient for depositing desired liners inside the trenches and vias. Thus, the penetration of liners during PE-ALD is further minimized. In addition, the in situ surface treatment by plasma inside the deposition chamber can further minimize the penetration for certain low-k materials. Since the deposition chamber has built-in plasma comparability, no extra surface treatment chamber is required.
Generally, a SiNxCy liner may be formed on a porous low-k material substrate, which may be a patterned porous low-k substrate, by PE-ALD from a aminosilane-based precursor and a plasma. In the formula of SiNxCy, x+y is within the range of about 0.8 to 1.2, preferably approaching 1, in which x may equal about from 0.01 to 0.99 and y may equal about from=0.99 to 0.01.
The low-k substrate is exposed to an aminosilane-based precursor. A precursor which has been investigated for the silylation of low-k materials is bis(dimethylamino)dimethylsilane (BDMA-DMS). The chemical structure of the precursors is very similar to that of pentakis(dimethylamino)tantalum, which is a metal organic precursor used for ALD of tantalum nitride (TaN) liners. However, this disclosure is not limited to BDMA-IBM DMS precursor or other aminosilanes, and may include other silylation (silylating) agents with a similar structure as ALD precursors for the process. For instance, silylation agents that may be used include, but are not limited to, mono-, di-, or tri-alkoxy(alkyl)silanes, chloro(alkyl)silanes, bromo (alkyl) silanes, thiocyanate(alkyl) silanes, phosphonates or combinations thereof.
In a preferred embodiment, the PE-ALD method, in accordance with this disclosure, has been developed from the reaction of BDMA-DMS and atomic hydrogen.
The glass tube may be maintained at 65 ° C. to develop adequate vapor pressure and all the delivery lines were heated to 80 ° C. to prohibit condensation of the precursor. To improve the delivery of the aminosilane-based precursor, a carrier gas including, e.g., argon (Ar), may be used, the flow of which may be controlled by a mass flow controller upstream from the source tube. In one embodiment, the substrate is exposed to >1000 Langmuirs (L) of aminosilane carried by Ar gas. It should be understood that a Langmuir equals exposure for is at 10−6 Torr. The chamber may be evacuated, e.g., using an evacuation pump.
In one embodiment, no purging gas is used between metal precursor and plasma exposure. However, it should be understood that a purging gas may be used, which should not change the result of the method.
Substrates upon which the method may be implemented include any low-k material, which may include but is not limited to, silicon dioxide (SiO2), hydro-fluoric (HF) dipped silicon (Si), JSR LKD 5109™ or a similar material, nanoglass, SiCO, and SiLK™.
A hydrogen (atomic hydrogen), oxygen, nitrogen, helium, or combination thereof plasma may be used to treat the above-mentioned porous low-k materials before ALD.
In another embodiment, the low-k substrate is exposed to nitrogen plasma. In this embodiment, a gate valve for nitrogen is opened for a radio frequency (RF) source. The RF plasma source may be any conventional plasma source including, for example, a quartz tube wrapped with copper (Cu) coil for producing the plasma. PE-ALD from the aminosilane-based precursor in the hydrogen results in the formation of the SiNxCy liner or a protective layer.
For JSR LKD 5109™, nanoglass, and SiCO porous low k materials, BDMA-DMS and atomic hydrogen produced by plasma may be used to deposit SiNxCy by PE-ALD. For porous SiLK™, since the atomic hydrogen etches the SiLK™ substrates, nitrogen plasma has been used instead. After 10 to 50 cycles of nitrogen plasma based process, the plasma gas may be switched to hydrogen and deposition to desired thickness has been done. In a separate embodiment, the chamber may be evacuated again and one cycle of PE-ALD to form the SiNxCy liner is completed. A number of cycles may be repeated, which determines the thickness of the liner or protective layer.
Next, a subsequent substantially stoichiometric SiNxCy diffusion barrier layer may be formed by PE-ALD from the aminosilane-based precursor and a plasma of hydrogen and nitrogen. This step may be repeated for a number of cycles, which determines the thickness of the substantially stoichiometric SiNxCy diffusion barrier layer. For instance, the number of cycles employed may be 100 cycles for the protective layer and 800 cycles for substantially stoichiometric SiNxCy diffusion barrier layer.
In another embodiment, the initial or protective layer(s) may be TaN deposited by PE-ALD, in which a subsequent substantially stoichiometric SiNxCy diffusion barrier layer by PE-ALD may be formed on the TaN, and an additional TaN layer deposited on the diffusion barrier layer. In other words, the SiNC layer may be deposited between PE-ALD of TaN, such that TaN/SiNxCy/TaN may be formed.
Turning to the non-limiting illustrations of the disclosure, film layers were prepared according to the method and analyzed by Rutherford Backscattering Spectrometry (RBS). As shown in
Obviously, numerous modifications and variations of the disclosure are possible in light of the above disclosure. It is therefore understood that within the scope of the appended claims, the disclosure may be practiced otherwise than as specifically described herein.
This application is a divisional of co-pending Application No. 12/203,338, filed on Sep. 3, 2008, and for which priority is claimed under 35 U.S.C. §120, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12203338 | Sep 2008 | US |
| Child | 13568808 | US |
