Selective deposition of materials for the fabrication of interconnects and contacts on semiconductor devices

One form of the present invention is a method for mask-less selective deposition made up of the steps of contacting a first portion of a substrate with a chemical agent that binds to the substrate to affect the susceptibility of the portion of the substrate to deposition. Following the treatment with the chemical agent, a first layer of a first material is deposited on a second portion of the surface. The first and second portions of the substrate may in fact be the same portion. That is to say, that the chemical agent may enhance or inhibit the deposition of the material of a portion of the substrate.

DETAILED DESCRIPTION OF THE INVENTION While the making and using of various embodiments of the present invention are discussed herein in terms of selective deposition of copper, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and are not meant to limit the scope of the invention in any manner. The present invention modifies the selectivity of a material's surface with respect to the ability of the surface to accept or reject the deposition of a material upon it. Such selectivity is accomplished through an appropriate chemical treatment or modification, altering the properties of the material surface. FIG. 1 depicts a schematic diagram illustrating the processes; In this example, three different materials share the same substrate. Without any treatment, deposition could occur simultaneously on all three materials. Through an appropriate surface treatment, however, deposition takes place on only one of them, such as material 1 , as shown in FIG. 1 . Following another treatment, deposition on material III may be accomplished, and an overall deposition could occur on the entire surface after yet another treatment. It is of note that the source substance for each deposition does not have to be the same. In general, all the materials and the substrate are subjected to the same treatment at the same time. Since different materials have different chemistry, they react differently to the same chemical treatment and, therefore, are differentiated from each other with respect to selective deposition. This is particularly important for certain applications including interconnect and contact formation for microelectronic fabrications. The method of the present invention relies on the variation of chemistry on the material surface and does not require a mask, mold, stamp, templates or the like to be used in patterning or printing a desired structure on a substrate. Therefore, the present method does not suffer from the disadvantages of existing methods, such as lithography. Once the surface chemistry of a given material has been modified, conventional methods including chemical vapor deposition (CVD), plasma vapor deposition (PVD), vacuum deposition (VD), sputtering deposition, and electrochemical plating can be used for the deposition. The chemical treatment of the present invention involves absorption or reaction of certain chemical species on the material's surface to either activate or deactivate the surface toward a deposition. The absorbed species may be removed with a subsequent treatment to restore the original chemical properties of the material's surface. Thus, the surface reactivity of a material may be turned on and off in a controlled manner, making it possible to select one material to be susceptible to deposition initially, and then for another material to be made susceptible subsequently. Materials suitable for such treatment include metals, semiconductors, and insulators. An example of a chemical species for surface treatment are the alkane thiols, which feature variable chain lengths, and are capable of spontaneous absorption on the surface of a given material, such as copper, to modify its properties. The treatment to passivate a material surface involves immersion of the sample, into a solution containing one or more chemical species for a certain period of time (seconds to days depending on the materials and the species). The material is reactivated by a treatment that removes the adsorbed species from the surface by methods including ultraviolet light irradiation, a potential (voltage) pulse application, chemical treatment, ion bombardment, high temperature treatment and the like. 
 EXAMPLE 1 Electrochemical deposition of copper on a copper surface before and after the chemical treatment is shown in FIG. 2 . The deposition was carried out in a solution of 1M CuSO 4 in water with a three-electrode system. Copper rods were used as both counter and reference electrodes. The scan rate was 20 mV/s. It can be seen that the deposition current was at ˜mA level for bare copper surface before chemical treatment and a uniform deposition of copper was seen with or without an optical microscope. However, after the sample was immersed into a solution of ethanol containing 1 mM 1-dodecanethiol (98&plus;%, Aldrich) overnight, the electrochemical deposition current diminished to negligible levels (the baseline) even after the current was amplified by 10,000 times under the same experimental conditions. No trace of copper deposition was observed under the optical microscope, indicating a successful suppression of copper deposition on copper surface by the chemical treatment. 
 EXAMPLE 2 FIG. 3 shows images from a sample with copper structures surrounded by a barrier layer of tantalum. Without any chemical treatment, electrochemical deposition of copper occurred only on copper surface as shown in FIG. 4 . When copper and barrier layers coexist on the same substrate, copper generally will deposit more easily on the copper surface. FIG. 3 depicts images (382 &mgr;m×500 &mgr;m) from a sample that show copper structures surrounded by a barrier layer at two different locations. FIG. 4 depicts an image (382 &mgr;m×500 &mgr;m) of the same sample after copper deposition without pre-chemical treatment. After the sample was immersed into a solution of ethanol containing 1 mM 1-dodecanethiol (98&plus;%, Aldrich) for 4 hours, electrochemical deposition of copper occurred only on the barrier layer as shown in FIG. 5 . In this case, the chemical absorption of the alkanethiol on the copper surface modified its properties and greatly decreased the rate of copper deposition on this surface, making it possible for copper deposition to occur preferentially on the barrier layer. A similar result is seen on the micrometer scale as shown in FIG. 6 . In this case, the less than one micrometer wide copper line clearly separates the two deposited copper zones, which are rough and higher than the copper line. These images demonstrate that the chemical treatment of the present invention for selective deposition functions well even on an extremely small scale. 
 EXAMPLE 3 To demonstrate the reversibility of the chemical application, a negative potential was applied to the test surface. Specifically, after applying a negative potential pulse of 1.3V for 0.2 second, the chemically modified copper surface was restored to its original form. This action removes the adsorbed chemical species and electrochemical deposition of copper on the reactivated copper layer was observed. Both the copper deposition current and the surface appearance were approximately the same as that observed for the original (untreated) copper surface. These results demonstrate the capability of the method of the present invention to reversibly alter the chemistry of a copper surface towards the copper deposition. One particular application of the method of the present invention is to fabricate interconnects and contacts for electronic device as shown in FIG. 7 . The leftmost image in FIG. 7 depicts a barrier layer that covers the surface of an SiO 2 substrate with a desired structure of trenches and vias. A copper layer produced by chemical vapor deposition (CVD) covers all locations except the bottoms and walls in the structure. This is a typical result due to technical limitations in uniform surface coverage into valleys and trenches using CVD. The gaps in the copper deposits will prevent formation of good copper contacts and interconnects in any subsequent electrodeposition step, given the tendency of copper to preferentially electrodeposit on the existing copper. The method of the present invention can be used to fill the gaps in the trenches and vias with copper through a chemical treatment, so that copper may be selectively deposited on the bare barrier surface by electrochemical plating as shown in the center image in FIG. 7 . Another treatment may then reverse the copper surface modification and deposit copper over the entire surface to complete the fabrication of contacts and interconnects. Although this invention has been described and disclosed in relation to certain preferred embodiments, obvious equivalent modifications and alterations thereof will become apparent to one of ordinary skill in this art upon reading and understanding this specification and the claims appended hereto. Accordingly, the presently disclosed invention is intended to cover all such modifications and alterations, and is limited only by the scope of the claims that follow.