Patent Grant
7780865
1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for semiconductor processing. Specifically, embodiments of the present invention relate to a method and apparatus for depositing a conformal dielectric layer.
2. Description of the Related Art
Forming dielectric layers on a substrate by chemical reaction of gases is one of the primary steps in the fabrication of modern semiconductor devices. These deposition processes include chemical vapor deposition (CVD) as well as plasma enhanced chemical vapor deposition (PECVD), which uses plasma in combination with traditional CVD techniques.
CVD and PECVD dielectric layers can be used as different layers in semiconductor devices. For example, the dielectric layers may be used as intermetal dielectric layers between conductive lines or interconnects in a device. Alternatively, the dielectric layers may be used as barrier layers, etch stops, or spacers, as well as other layers.
Dielectric layers that are used for applications such as barrier layers and spacers are typically deposited over features, e.g., horizontal interconnects for subsequently formed lines, vertical interconnects (vias), gate stacks, etc., in a patterned substrate. Preferably, the deposition provides a conformal layer. However, it is often difficult to achieve conformal deposition.
For example, it is difficult to deposit a barrier layer over a feature with few or no resulting surface defects or feature deformation. During deposition, the barrier layer material may overloaf, that is, deposit excess material on the shoulders of a via and deposit too little material in the base of the via, forming a shape that looks like the side of a loaf of bread. The phenomena is also known as footing because the base of the via has a profile that looks like a foot. In extreme cases, the shoulders of a via may merge to form a joined, sealed surface across the top of the via. The non-uniformity of film thickness across the wafer can negatively impact the drive current improvement from one device to another. Modulating the process parameters alone does not significantly improve the step coverage and pattern loading problems.
Therefore, a need exists for a method of depositing conformal films over formed features in a patterned substrate.
Embodiments of the present invention provide a method of controlling the step coverage and pattern loading of a layer on a substrate. In one embodiment, the method comprises placing a substrate with at least one formed feature across a surface of the substrate into a chamber. A dielectric layer is deposited on the substrate, and the dielectric layer is etched with a plasma from oxygen or a halogen-containing gas selected from the group consisting of fluorine, chlorine, bromine, and combinations thereof to provide a desired profile of the dielectric layer on the at least one formed feature.
In another embodiment, the method comprises placing a substrate with at least one formed feature across a surface of the substrate into a chamber and depositing a dielectric layer on the substrate. The feature comprises a top surface, a sidewall surface, and a bottom surface. The dielectric layer is deposited to a greater thickness on the top surface than on the bottom surface and sidewall surface. The dielectric layer is then etched with a plasma from oxygen or a halogen-containing gas selected from the group consisting of fluorine, chlorine, bromine, and combinations thereof. The dielectric layer is etched at a higher rate on the top surface than on the sidewall surface and bottom surface. The depositing and etching of the dielectric layer is repeated for one or more times to provide a desired profile of the dielectric layer on the at least one formed feature.
In a further embodiment, the method comprises placing a substrate with at least one formed feature across a surface of the substrate into a chamber and depositing a silicon nitride dielectric layer on the substrate. The feature comprises a top surface, a sidewall surface, and a bottom surface. The silicon nitride dielectric layer is deposited to a greater thickness on the top surface than on the bottom surface and sidewall surface. The silicon nitride dielectric layer is then etched with a NF3 plasma at a higher etch rate on the top surface than on the sidewall surface and bottom surface to provide a desired profile of the silicon nitride dielectric layer on the at least one formed feature. The depositing and etching of the silicon nitride dielectric layer may be repeated for one or more times to provide the desired profile.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The present invention provides a method and apparatus for depositing a conformal dielectric layer over a formed feature. Films that can benefit from this process include dielectric materials such as silicon oxide, silicon oxynitride, or silicon nitride films that may be used as spacers or etch stop layers, for example. The films may be carbon doped, hydrogen doped, or contain some other chemical or element to tailor the dielectric properties. The film may be carbon doped or nitrogen doped. For example, the films may be SiCN, SiOC, SiOCN, SiBN, SiBCN, SiC, BN, or BCN films. In one aspect, a combination of thin layers that have been individually deposited and plasma treated provide a more conformal dielectric layer than a single thick dielectric layer. The chambers that may be used for the processes described herein include the PRODUCER® P3 chamber, PRODUCER® APF™ PECVD chamber, PRODUCER® BLACK DIAMOND® PECVD chamber, PRODUCER® BLOK® PECVD chamber, PRODUCER® DARC PECVD chamber, PRODUCER HARP chamber, PRODUCER® PECVD chamber, PRODUCER SACVD chamber, PRODUCER® SE STRESS NITRIDE PECVD chamber, and PRODUCER® TEOS FSG PECVD chamber, each of which are commercially available from Applied Materials, Inc. of Santa Clara, Calif. The chambers may be configured individually, but are most likely part of an integrated tool. The processes may be performed on any substrate, such as a 200 mm or 300 mm substrate or other medium suitable for semiconductor or flat panel display processing. The processing conditions described below are provided with respect to a PRODUCER® SE STRESS NITRIDE PECVD chamber, which has two isolated processing regions. Thus, the flow rates experienced per each substrate processing region are half of the flow rates into the chamber.
Returning to step 206, the dielectric layer may be etched in the same chamber in which the dielectric layer is deposited or in a different chamber that is part of the same integrated tool as the deposition chamber and is connected to the deposition chamber by a transfer chamber of the integrated tool. The oxygen or halogen-containing gas may be introduced into the chamber individually or in combination with an inert gas, such as argon or helium. The etch step 206 is performed using a plasma that is generated remotely or in situ. The length of the etch step 206 may be at least 0.1 seconds, such as between about 0.1 seconds and about 45 seconds, e.g., between about 15 seconds and about 45 seconds. The etch profile can be configured to match the deposition profile by adjusting the halogen-containing gas flow rate and length of exposure. For example, the etch rate may be higher on the top surface of the feature than on the sidewall surface or bottom surface of the feature. Typically, the etch rate on the top surface is about 10% higher than the etch rate on the sidewall surface or the bottom surface. In some instances, an etch rate of about 50 percent may be desirable. As defined herein, an etch rate of about 50 percent corresponds to an etch process that removes about 50 percent of the thickness of the dielectric layer that is deposited. Also, deposition step 204 may alternatively be a two part deposition process, such as two seconds of plasma at a first power and precursor partial pressure and two additional seconds at a second power and second precursor partial pressure.
In embodiments in which the etch step 206 is performed using a plasma that is remotely generated, the plasma may be produced by exposing oxygen or a halogen-containing gas selected from the group consisting of fluorine, chlorine, bromine, and combinations thereof to microwave energy in a remote plasma source that is connected to the chamber in which the dielectric layer is deposited. For example, the plasma may be generated from NF3, which provides reactive fluorine species. The NF3 may be introduced into the chamber at a flow rate between about 10 sccm and about 20 slm. The NF3 may be introduced into the chamber with argon or helium as a dilution gas. The argon and helium may also help sustain the plasma in the chamber. The argon or helium may be introduced into the chamber at a flow rate between about 100 sccm and about 20 slm. The pressure in the chamber during the etch may be between about 10 mTorr and about 760 Torr, and the temperature of a substrate support in the chamber may be set to between about 100° C. and about 650° C.
In embodiments in which the etch step 206 is performed using a plasma that is generated in situ, i.e., in the chamber, the plasma may be generated by RF power. The RF power may be provided at a high frequency, such as between about 1 MHz and about 13.56 MHz, e.g., about 2 MHz to about 13.56 MHz, a low frequency between about 100 kHz and about 1 MHz, e.g., between about 100 kHz and about 400 kHz, or a mixed frequency comprising a frequency between about 1 MHz and about 13.56 MHz, e.g., about 2 MHz to about 13.56 MHz, a low frequency between about 100 kHz and about 1 MHz, e.g., between about 100 kHz and about 400 kHz. The halogen-containing gas that is selected from the group consisting of fluorine, chlorine, bromine, and combinations thereof and is used as an etching gas may be NF3, or a carbon and fluorine-containing gas, such as CF4 or C4F8. The oxygen or halogen-containing gas may be introduced into the chamber at a flow rate between about 10 sccm and about 20 slm. The oxygen or halogen-containing gas may be introduced into the chamber with argon or helium as a dilution gas. The argon and helium may also help sustain the plasma in the chamber. The argon or helium may be introduced into the chamber at a flow rate between about 100 sccm and about 20 slm. The pressure in the chamber during the etch may be between about 10 mTorr and about 760 Torr, and the temperature of a substrate support in the chamber may be set to between about 100° C. and about 650° C. The spacing between a showerhead electrode and a substrate support electrode in the chamber may be between about 100 mils and about 3000 mils. The spacing may be adjusted to control the stability of the plasma.
Embodiments of the invention include process sequences in which a single deposition step 204 and a single etching step 206 are performed and process sequences that include a repeat step 210 with multiple deposition and etching steps. A process sequence comprising a single deposition step and a single etching step may be performed for a dielectric layer that has a high etch rate on a sidewall surface of a feature of the dielectric layer relative to the etch rate on a top surface of a feature of the dielectric layer. For example, the etch rate on the sidewall surface may be at least about 10% of the rate at which the dielectric layer is etched from the top surface. Dielectric deposition processes that provide a lower ion bombardment on the sidewalls of features than on the top or bottom of features can result in higher etch rates of the dielectric on the sidewall rather than on the bottom or top of features.
By keeping the thickness of the etched material constant for different thickness of deposited dielectric layers and thus varying the percent of the dielectric layers that was etched, it was found that the bottom pattern loading effect for process sequences comprising a single deposition step and a single etching step was independent of the thickness of the deposited dielectric layer for dielectric layers having a thickness of up to 1000 Å.
A process sequence comprising multiple deposition and etching steps may be performed for a dielectric layer that has a low etch rate on a sidewall surface of a feature of the dielectric layer relative to the etch rate on a top surface of a feature of the dielectric layer. For example, the etch rate on the sidewall surface may be less than about 10% of the rate at which the dielectric layer is etched from the top surface. The etch rates may be determined by measuring the thickness of the dielectric layer at the bottom, sidewall, and top of a feature using SEM or TEM cross-sections before and after the dielectric layer is etched and calculating the thickness etched per the time period of the etch. Increasing the number of deposition and etching cycles may improve the pattern loading effect.
In an exemplary embodiment, a process sequence comprising two or three deposition and etching cycles may be performed for dielectric layers for use as etch stop liners for features sites of 90 nm and below. The dielectric layer may be deposited to a thickness of between about 300 Å and about 400 Å in each cycle, and a thickness of between about 100 Å and about 200 Å of the dielectric layer may be etched in each cycle.
Experimental testing of embodiments of the invention shows that the etch profile can be controlled to match the deposition profile, that is, to provide a higher etch rate across the top surface of formed features than at the bottom or along the sidewalls of the formed feature.
Scanning electron microscopy photographs of a cross section of formed features also show that an NF3 plasma etch for 45 seconds comprising 50 sccm of NF3, 3 L of argon, 100 W of low frequency RF power at 350 kHz, a chamber pressure of 1.5 Torr, and a spacing of 1000 mils can reduce the bottom pattern loading effect (PLE) of a silicon nitride dielectric layer by about 30 percent (from a PLE of 67% to 41%) and that such etch processes can be used to modulate the step coverage for other dielectric film deposition processes. The film stress was not affected by the etch process. The sidewall loading was reduced from 46% to 33%, and the top loading was reduced from 10% to 3%. As the pattern loading effect is measured as the percentage of film thickness difference between a film thickness on portion, such as the bottom, top, or sidewall, of a feature in a substrate region with a few features (an isolated area) and a film thickness on a corresponding portion of a feature in a substrate region with high density of features (a dense area), a lower pattern loading effect percentage reflects a higher film thickness uniformity across a substrate.
A comparison of pattern loading and bottom thickness as a function of the type of etch was performed using NF3 as the fluorine-containing etching gas on a silicon nitride dielectric layer. No etch, a low frequency RF plasma etch at 100 W, a high frequency RF plasma etch at 50 W, and a remote plasma source etch were compared for a process sequence comprising depositing 400 Å of a silicon nitride dielectric layer, etching 200 Å of the silicon nitride dielectric layer, and then depositing 450 Å of the silicon nitride dielectric layer. The low frequency RF plasma etch and the high frequency RF plasma etch provided similar pattern loading effect results, while the remote plasma source etch resulted in a greater pattern loading effect and an etch rate uniformity of more than 20 percent. It is believed that the RF plasma in situ etching methods are more efficient in providing an etch profile that is similar to the deposition profile, i.e., higher etch rates on the top surface of features and slower etch rates on the sidewall surface of features, than remote plasma etching methods as the etching species are accelerated toward the substrate surface directionally by the sheath voltage in in situ RF methods while the etching profile is more isotropic in remote plasma etching methods.
While the embodiment of
The plasma and precursor and optional additional gases introduced during step 620 are followed by the introduction of oxygen gas to the chamber during oxygen purge step 630. The oxygen purge step 630 is performed by introducing oxygen or nitrous oxide into the chamber at a time period and partial pressure that is selected to purge the residual silicon containing precursor and optional additional gases. Next, during oxygen plasma treatment step 640, an oxygen-containing gas such as oxygen or nitrous oxide is introduced into the chamber. The plasma is provided at about 50 W to about 400 W for about 0.1 seconds to about 20 seconds.
Experimental tests of a process similar to
Several combinations of helium and OMCTS were tested to determine the best ratio for developing a dielectric layer. A ratio of about twice as much helium to OMCTS as the silicon containing precursor and additional gas yielded a film with the greatest film thickness. Also, scanning electron micrographs of a film deposited with OMCTS, a film deposited with OMCTS and oxygen plasma at 90 mTorr, and a film deposited with OMCTS and oxygen plasma at 2 Torr indicate that the film deposited with OMCTS and oxygen plasma at 2 Torr provides the best pattern loading effect and step coverage of the three films.
Nitrous oxide and oxygen were compared for use in the oxygen plasma treatment step 640. Scanning electron micrographs of a film deposited using nitrous oxide and a film deposited using oxygen indicate that the film deposited using oxygen had the better pattern loading effect and step coverage of the two films.
The advantage of the processes described above is that they result in films with improved step coverage and pattern loading. The process cycles that can be performed in the same chamber require less processing time than processes requiring multiple chambers. The overall thermal budget and individual substrate process temperatures are lower than in processes that do not use plasma.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 60/788,279, filed Mar. 31, 2006, which is herein incorporated by reference. Further, this application is related to co-pending U.S. patent application Ser. No. 11/694,856, filed Mar. 30, 2007, and co-pending U.S. patent application Ser. No. 11/668,911, filed Jan. 30, 2007.
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