CHLORINE-FREE REMOVAL OF MOLYBDENUM OXIDES FROM SUBSTRATES

Methods of removing molybdenum oxide from a surface of a substrate comprise exposing the substrate having a molybdenum oxide layer on the substrate to a halide etchant having the formula RmSiX4-m, wherein m is an integer from 1 to 3, X is selected from iodine (I) and bromine (Br) and R is selected from the group consisting of a methyl group, ethyl group, propyl group, butyl group, cyclohexyl group and cyclopentyl group. The methods may be performed in a back-end-of-the line (BEOL) process, and the substrate contains a low-k dielectric material.

TECHNICAL FIELD

Embodiments of the disclosure generally relate to electronic devices and methods of forming electronic devices. In particular, embodiments of the disclosure relate to etching of molybdenum oxides with non-chlorine etchants.

BACKGROUND

When molybdenum (Mo) surfaces are exposed to oxygen, the surfaces form a layer of molybdenum oxide (MoOx). Removal of the MoOx requires harsh processes that are not compatible with back-end-of-the-line (BEOL) packaging processes. During BEOL processes, the MoOx may form in areas of low-k dielectric materials that are highly susceptible to damage caused by traditional precleaning processes. Traditional hydrogen-based plasma processes can be used to remove MoOx, however, these traditional hydrogen-based plasma processes cannot fully reduce MoOx due to the high stability of Mo(OH) y and difficulty of de-hydration. Another common way is to remove MoOx use MoClx (x=4-6) to etch MoOx, but this approach is limited by temperature, and non-selectivity over Mo and CI residue, which restricted use of MoClx etching in BEOL. Accordingly, new methods for removal of MoOx are needed that are compatible with BEOL packaging processes.

SUMMARY

One or more embodiments of the disclosure are directed to methods of processing a substrate. In one or more embodiments, a processing method comprises exposing the substrate having a molybdenum oxide layer on the substrate to a halide etchant having the formula RmSiX4-m, wherein m is an integer from 1 to 3, X is selected from iodine (I) and bromine (Br) and R is selected from the group consisting of a methyl group, ethyl group, propyl group, butyl group, cyclohexyl group and cyclopentyl group. The halide etchant in one or more embodiments is in gas form and is an etchant gas.

One or more embodiments may further comprise exposing the substrate having the molybdenum oxide layer on the substrate to a purge gas, and wherein exposing the substrate having the molybdenum oxide layer on the substrate to the etchant gas and the purge gas comprises an atomic layer etching cycle.

Embodiments may further comprise non-transitory, computer readable medium having instructions stored thereon that, when executed, causes a processing chamber to perform a method comprising exposing the substrate having a molybdenum oxide layer on the substrate to a halide etchant having the formula RmSiX4-m, wherein m is an integer from 1 to 3, X is selected from iodine (I) and bromine (Br) and R is selected from the group consisting of a methyl group, ethyl group, propyl group, butyl group, cyclohexyl group and cyclopentyl group and comprise exposing the substrate having the molybdenum oxide layer on the substrate to a purge gas, and wherein exposing the substrate having the molybdenum oxide layer on the substrate to the etchant gas and the purge gas comprises an atomic layer etching cycle.

DETAILED DESCRIPTION

The methods provided herein according to one or more embodiments provide an improved process for removing molybdenum oxide (MoOx) in back-end-of-the-line (BEOL) processes. Current BEOL preclean processes are challenged to reduce or remove molybdenum oxide without damage to low-k materials. The methods have the advantage over traditional BEOL preclean processes in that the methods can achieve full removal of MoOx with no chlorine residue in the low-k material and no significant carbon loss or damage to the low-k material. The methods are also compatible with current BEOL hydrogen gas (H2) preclean approaches and integration flows. The methods also have the advantage of being able to more fully reduce MoOx compared to traditional hydrogen-based plasma processes and to avoid problems with de-hydration.

While molybdenum materials/doping have been used in front-end-of-the-line (FEOL) structure manufacturing processes, molybdenum materials/doping have not been used in BEOL processes due to the inability to remove MoOx in areas containing low-k materials. Molybdenum materials/doping provides for the formation of enhanced performance contacts formed during middle-of-the-line (MOL) processes such as in logic applications. Providing improved processes for the removal of the exposed molybdenum materials during BEOL packaging processes, such MOL contacts become possible. Current processes lack any feasible approaches to reduce or remove the MoOx for BEOL without dealing significant damage to the low-k dielectric materials.

For example, strong plasma treatments may be able to fully reduce MoOx, but would inevitably cause unacceptable damage to the low-k dielectric material. Therefore, such an approach cannot be applied to BEOL applications. However, according to one or more embodiments of the present disclosure, methods are provided to remove MoOx with negligible damage to the low-k dielectric materials. In some embodiments, a chlorine-free process is used to remove the MoOx at a process temperature of approximately below 400° C., for example in a range of from 150° C. to 400° C., 200° C. to 400° C., 250° C. to 400° C., 300° C. to 400° C., 150° C. to 350° C., 200° C. to 350° C., 250° C. to 350° C., 300° C. to 350° C., 150° C. to 300° C., 200° C. to 300° C., and 250° C. to 300° C. The chlorine-free methods according to one or more embodiments are configured to remove MoOx with no negative chlorine impacts to BEOL applications such methods involving a barrier, a liner and Cu layers. The methods according to some embodiments utilizes an atomic layer etching (ALE) process.

As semiconductor devices continue to increase in design and material component complexity, the selective removal of materials has become critical for continued scaling and improvement of semiconductor devices. Selective atomic layer etching (ALE) has emerged as a precise etching method that employs self-limiting surface reactions. Selective ALE of metal oxides (MOx) is particularly important for a number of semiconductor technologies but can be difficult to accomplish due to the inherent stability of these oxide materials.

Atomic layer etching involves the exposure of a substrate to an etchant gas for a first period of time and then exposure to a purge gas for a second period of time. The exposure to the etchant gas and a purge gas comprises an atomic layer etching cycle, and the atomic layer etching cycle may be repeated multiple times to achieve the desired level of removal of the molybdenum oxide layer from the surface of the substrate.

Referring now to FIG. 1, a schematic view of an atomic layer etching process is shown. A substrate 100 having a molybdenum oxide layer 110 on the substrate is exposed to an etchant for a first period of time. The molybdenum oxide layer has a thickness (t1) prior to exposure to the etchant. After exposure to the etchant, the molybdenum oxide layer 110 has a thickness (t2) that is less than the thickness (t1). Thereafter, the substrate 100 having the molybdenum oxide layer 110 on the substrate 100 may be exposed again to the etchant to further reduce the thickness (t2) of the molybdenum oxide layer 110. In one or more embodiments, prior to a second exposure to the etchant gas, the substrate 100 having the molybdenum oxide layer 110 thereon is exposed to a purge gas. Each exposure of the substrate 100 having the molybdenum oxide layer thereon comprises a cycle. The cycle may be repeated from 1 to 1000 time to reduce the thickness of the molybdenum oxide layer 110. In some embodiments, the cycle is repeated until the molybdenum oxide layer 110 is removed from the substrate.

The purge gas is configured to remove etchant gas and any etching by-products away from the substrate. In one or more embodiments, the purge gas is selected from an inert gas, such as nitrogen, argon and helium.

In some embodiments, exposure of the substrate 100 having the molybdenum oxide layer 110 thereon may be exposed the etchant gas and the purge gas by a gas distribution plate 130 that is part of an atomic layer etching chamber (not shown). Referring now to FIG. 2, the gas distribution plate comprises alternating channels which are configured to direct alternating streams of an etchant gas and a purge gas. In some embodiments, the gas distribution plate 130 includes an optional pump channel disposed between etchant gas channel and purge channel. The gas distribution plate 130 can be any suitable distribution plate known to those skilled in the art, and specific gas distribution plates described should not be taken as limiting the scope of the invention. The output face of the gas distribution plate 130 faces the molybdenum oxide layer 110 on the substrate.

Additional embodiments of the invention are directed to methods of processing a substrate. The substrate 100 having a molybdenum oxide layer 110 thereon is moved laterally adjacent to the gas distribution plate 130 comprising a plurality of elongate gas channels connected to supplies of a purge gas and an etchant gas. The elongate gas channels include a first gas port to deliver an etchant gas and a second gas port to deliver a purge gas. The first gas is delivered to the substrate surface and the second gas is delivered to the substrate surface. The process or exposure time for each of the etchant gas and the purge gas can be in the range of about 0.001 second to about 60 seconds. In an exemplary embodiment, exposure to the etchant gas occurs for a period of from about 0.5 seconds to 1.5 seconds and exposure to the purge gas occurs from about 2 to 30 seconds, for example 5 seconds.

This type of ALE process may be referred to as a spatial ALE, where the etchant gas and the purge gas are flowed into separate regions of a processing chamber and the substrate is moved between and among the regions. The different regions are separated by vacuum stream or pump to prevent mixing of etchant gas and the purge gas. The ALE process can also be performed by a time-domain process where the processing chamber is filled with the etchant gas and then purged to remove the excess etchant gas and etchant by-products. In the time-domain process, the substrate can remain stationary.

Thus, according to one or more embodiments methods are provided that are useful in back-end-of-the line (BEOL) processes, for example, where the substrate contains a low-k dielectric material.

Thus, an exemplary embodiment is directed to a method of removing molybdenum oxide from a surface of a substrate, the method comprising exposing the substrate having a molybdenum oxide layer on the substrate to a halide etchant having the formula RmSiX4-m, wherein m is an integer from 1 to 3, X is selected from iodine (I) and bromine (Br) and R is selected from the group consisting of a methyl group, ethyl group, propyl group, butyl group, cyclohexyl group and cyclopentyl group. The method can be performed in a substrate processing chamber including a gas distribution plate or in any type of substrate processing chamber capable of performing an atomic layer etching (ALE) process. In some embodiments, the X is any halide.

In some embodiments, the halide is bromine (Br). In other embodiments, the halide is iodine (I). Exposing the substrate occurs at temperature in a range of from a range of from 150° C. to 400° C. according to some embodiments, more particularly in a range of from 200° C. to 400° C. or in a range of from 250° C. to 400° C.

In some specific embodiments, the method comprises exposing the substrate having the molybdenum oxide layer on the substrate to a purge gas, and wherein exposing the substrate having the molybdenum oxide layer on the substrate to the etchant gas and the purge gas comprises an atomic layer etching cycle. In some embodiments, the purge gas is an inert gas. Exposing the substrate and the molybdenum oxide layer reduces the thickness of the molybdenum oxide layer. The cycle can be repeated multiple times to reduce the thickness of the molybdenum oxide layer to a desired thickness or target thickness. In some embodiments, the method comprises completely removing the molybdenum oxide layer from the substrate.

One or more method embodiments according to the present disclosure may be implemented in hardware, firmware, software, or any combination thereof.

Embodiments may also be implemented as instructions stored using one or more computer readable media, which may be read and executed by one or more processors. A computer readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing platform or a “virtual machine” running on one or more computing platforms). For example, a computer readable medium may include any suitable form of volatile or non-volatile memory. In some embodiments, the computer readable media may include a non-transitory computer readable medium.

For example, embodiments may further comprise non-transitory, computer readable medium having instructions stored thereon that, when executed, causes a processing chamber to perform a method comprising exposing the substrate having a molybdenum oxide layer on the substrate to a halide etchant having the formula RmSiX4-m, wherein m is an integer from 1 to 3, X is selected from iodine (I) and bromine (Br) and R is selected from the group consisting of a methyl group, ethyl group, propyl group, butyl group, cyclohexyl group and cyclopentyl group and comprise exposing the substrate having the molybdenum oxide layer on the substrate to a purge gas, and wherein exposing the substrate having the molybdenum oxide layer on the substrate to the etchant gas and the purge gas comprises an atomic layer etching cycle.