Tailored electron energy distribution function by new plasma source: hybrid electron beam and RF plasma

Embodiments of hybrid electron beam and RF plasma systems and methods are described. In an embodiment a method of using a hybrid electron beam and RF plasma system may include forming a first plasma of a first type in a first region of a wafer processing structure. Additionally, such a method may include forming a second plasma of a second type in a second region of the wafer processing structure, the second region of the wafer processing structure being coupled to the first region of the wafer processing structure, the second plasma being ignited independently of the first plasma, wherein an electron beam formed by the first plasma is configured to modulate one or more characteristics of the second plasma. This hybrid e-beam and RF plasma system provides a source to control electron energy distribution function.

BACKGROUND OF THE INVENTION

Field of Invention

The present invention relates to systems and methods for substrate processing, and more particularly to a hybrid electron beam and radio frequency (RF) plasma system and method of using the same.

Description of Related Art

Plasma has been used in semiconductor processing to assist etch processes by facilitating the removal of material along fine lines or within vias patterned on a substrate. Etch processes that use plasma include capacitively or inductively coupled plasma, hallow cathode plasma, electron cyclotron resonance plasma, microwave surface wave plasma, and reactive ion etching (RIE). For example, RIE generates plasma via electromagnetic fields with high-energy ions to etch away unwanted materials of the substrate.

High-energy ions generated in RIE are difficult to control within the plasma. Consequently, there are several issues associated with RIE techniques that hinder the overall performance in etching the substrate due to the lack of control of the high-energy ions. Some RIE techniques have broad ion energy distribution (IED) that results in a broad ion beam used to etch the substrate. A broad ion beam decreases the precision required to adequately etch the substrate. Some RIE techniques have charge-induced side effects such as charge damage to the substrate. RIE techniques may also exhibit feature-shape loading effects such as micro loading. Micro loading results when an etching rate of the RIE increases due to a dense area of the substrate. The increased etching rate may result in damage to the substrate.

Some attempts to solve the technical problems described above have been made, such as the systems and methods described in U.S. Pat. No. 9,520,275 to Chen, entitled “Mono-Energetic Neutral Beam Activated Chemical Processing System and Method of Using,” issued on Dec. 13, 2016 and resulting from U.S. patent application Ser. No. 12/053,008 filed on Mar. 21, 2008, and U.S. Patent App. Pub. No. 2014/0360670 of Chen et. al, entitled “Processing System for Non-Ambipolar Electron Plasma (NEP) Treatment of a Substrate With Sheath Potential,” published on Dec. 11, 2014 and resulting from U.S. patent application Ser. No. 14/026,092 filed on Sep. 13, 2013, which are incorporated herein in entirety.

The methods and systems described by Chen in the documents cited above include formation of a first plasma in a first region and formation of a second plasma in a second region. In some systems, the first region and the second region are regions in a single processing chamber. In other systems, the first region and second region are separate chambers coupled by a means of coupling the first plasma and the second plasma. In the described methods, electrons from the first plasma provide energy required to ignite and/or maintain the second plasma. In such systems, the processing chamber that receives the workpiece is grounded. As described below, the methods and systems described herein present a technical improvement on the systems described in Chen and Chen et. al.

SUMMARY OF THE INVENTION

Embodiments of hybrid electron beam and RF plasma systems and methods are described. In an embodiment a method of using a hybrid electron beam and RF plasma system may include forming a first plasma of a first type in a first region of a wafer processing structure. Additionally, such a method may include forming a second plasma of a second type in a second region of the wafer processing structure, the second region of the wafer processing structure being coupled to the first region of the wafer processing structure, the second plasma being ignited independently of the first plasma, wherein an electron beam formed by the first plasma is configured to modulate one or more characteristics of the second plasma.

Another embodiment of a method may include forming a first plasma of a first type in a first region of a wafer processing structure. Additionally, such a method may include forming a second plasma of a second type in a second region of the wafer processing structure, the second region of the wafer processing structure being coupled to the first region of the wafer processing structure, the second plasma being maintained by a combination of energy received from a radio frequency (RF) energy source and from an electron beam introduced from the first plasma to the second plasma, wherein a ratio of energy from the electron beam formed by the first plasma and the energy received from the RF energy source is selectable to modulate one or more characteristics of the second plasma.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Methods and systems for controlling plasma performance are presented. However, one skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention.

Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. In referencing the figures, like numerals refer to like parts throughout.

Additionally, it is to be understood that “a” or “an” may mean “one or more” unless explicitly stated otherwise.

As used herein, the term “substrate” means and includes a base material or construction upon which materials are formed. It will be appreciated that the substrate may include a single material, a plurality of layers of different materials, a layer or layers having regions of different materials or different structures in them, etc. These materials may include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate may be a semiconductor substrate, a base semiconductor layer on a supporting structure, a metal electrode or a semiconductor substrate having one or more layers, structures or regions formed thereon. The substrate may be a conventional silicon substrate or other bulk substrate comprising a layer of semi-conductive material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, and other semiconductor or optoelectronic materials, such as silicon-germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped.

Referring now to the drawings, where like reference numerals designate identical or corresponding parts throughout the several views.

FIG.1illustrates one embodiment of a system100for generating a hybrid plasma formed from energy from an electron beam energy source and an RF energy source. In an embodiment, the system100may include a first energy source102and a second energy source104. The first energy source102may be coupled to a first region106of a wafer processing structure and the second energy source104may be coupled to a second region108of the wafer processing structure. In an embodiment, the wafer processing structure may include a single plasma processing chamber having two distinct regions corresponding to the first region106and the second region108. Alternatively, the wafer processing structure may include a plurality of separate processing chambers defining the first region106and the second region108respectively.

In such embodiments, the first region106and the second region108may be communicatively coupled together via one or more channels114. A channel114may be a conduit through or an aperture in one or more sidewalls defining the first region106and the second region108. In one embodiment, a single channel114is defined. In another embodiment a plurality of channels114are defined. In an embodiment, the size of the channel114may be variable. In another embodiment, a number of channels114may be variable. In still a further embodiment, the channel structure is static, but one or more electric characteristics of the first plasma110is variable, via control of the first energy source102.

As illustrated, the first energy source102may ignite and maintain a first plasma110. The first plasma110may be an electron rich plasma. In one embodiment, the first energy source102may be an inductively coupled plasma (ICP) energy source. The ICP energy source may include a power generator and an antenna configured for ICP plasma generation. Alternatively, the first energy source is a transformer coupled plasma (TCP) energy source. In another embodiment, the first energy source102may be a hollow cathode plasma source. In further embodiments, the electrons for forming the electron beam116may be generated by a filament or any other suitable electron source that may be known or become known to one of ordinary skill in the art.

In an embodiment, the second energy source104may ignite the second plasma112and the electron beam116may be configured to modulate one or more characteristics of the second plasma112. In an alternative embodiment, the second plasma112may be ignited by energy from the electron beam116, and the second energy source104may provide energy for maintaining the second plasma112, where the ratio of the energy from the electron beam116and the energy from the second energy source104may be controlled, via a controller120, to modulate one or more characteristics of the second plasma112. In still another embodiment, the second plasma112may be both ignited and maintained by the electron beam116, and the second energy source104may provide energy for modulating one or more characteristics of the second plasma112. The second energy source104may include one or more types of RF or microwave plasma sources, including a surface wave energy source, an ICP source, an electron cyclotron resonance (ECR) source, or a capacitively coupled plasma (CCP) source.

In an embodiment, electrons from the first plasma110may be directed to the second plasma112via a channel114. In an embodiment, the channel114may form an electron beam116that is directed into the second plasma112. In an embodiment, the electron beam116may modulate one or more characteristics of the second plasma112. Specifically, the electron beam116may modulate the electron energy distribution function in the second plasma112. In another embodiment, the electron beam116may ignite the second plasma112, and the second energy source104may modulate one or more characteristics of the second plasma112.

In an embodiment, the system100includes one or more components for supply electric energy to portions of the system100and for electrically grounding one or more components. In such an embodiment, the system100includes a connection to electrical ground122and an electric potential source124. In one embodiment, the first region106may be electrically floated with respect to ground122. In an embodiment, the electric potential source124may be coupled to the first region106and apply a negative electric potential to one or more components of the first region106. In one embodiment, the electric potential source124may apply a negative electric potential to a surface of a plasma chamber defining the first region106. In addition, at least a portion of the second region108may be electrically grounded by the electrical ground122. In an embodiment, a surface of a plasma chamber defining the second region108may be coupled to the electrical ground122.

In such embodiments, the negative electric potential applied to the first region106and the ground applied to the second region108may facilitate directing the electron beam116through the channel114and into the second plasma112. In a further embodiment, such an arrangement may enhance one or more performance parameters of the second plasma112in a region proximate to the workpiece118. The workpiece118may be, in an embodiment, a semiconductor wafer to be processed in the system100. In one embodiment, the negative-to-ground arrangement described inFIG.1may be used to enhance bombardment of a surface of the workpiece118with electrons from the second plasma112.

FIG.2illustrates an embodiment of a method200of using a hybrid electron beam and RF plasma system100. In one embodiment, the method200may include forming a first plasma of a first type in a first region of a wafer processing structure, as shown at block202. Additionally, such a method200may include forming a second plasma of a second type in a second region of the wafer processing structure, the second region of the wafer processing structure being coupled to the first region of the wafer processing structure, the second plasma being ignited independently of the first plasma as shown at block204. In an embodiment, an electron beam formed by the first plasma is configured to modulate one or more characteristics of the second plasma as shown at block206.

FIG.3illustrates another embodiment of a method300of using a hybrid electron beam and RF plasma system100. In an embodiment, the method300may include forming a first plasma of a first type in a first region of a wafer processing structure, as shown at block302. Additionally, such a method300may include forming a second plasma of a second type in a second region of the wafer processing structure, the second region of the wafer processing structure being coupled to the first region of the wafer processing structure, the second plasma being maintained by a combination of energy received from a radio frequency (RF) energy source and from an electron beam introduced from the first plasma to the second plasma as shown at block304. In such an embodiment, a ratio of energy from the electron beam formed by the first plasma and the energy received from the RF energy source is selectable to modulate one or more characteristics of the second plasma as shown at block306.

FIG.4is a graphical representation of the electron energy probability function (EEPF), a representation of electron density, with respect to electron energy measured in electron Volts (eV). Curve402represents the EEPF with respect to electron energy for the second plasma112, where the second plasma112is formed solely from energy received from the electron beam116. Curve404represents EEPF with respect to electron energy for the second plasma112, where the second plasma is formed solely from energy received from the second energy source104. Curve406represents a function of EEPF with respect to electron energy for a hybrid plasma formed from a combination of energy from the second energy source104and from the electron beam116. In one embodiment, the electron energy curve may be measured off the electron beam line, and parallel to the electron beam116. The electron energy of the hybrid plasma represented by curve406may be variable between bounds set by curves402and404respectively, in response to variations in the current and energy of the electron beam116, the energy and the pressure from the second energy source104. For example, the size or number of channels114may be varied to modify the electron beam116. Alternatively, the first energy source102may be tuned to modify the electron beam116.

There are several benefits of creating a tunable hybrid plasma, including an ability to perform an etch process that is more isotropic or more anisotropic depending upon the settings. Increasing the electron density may increase etch rates, and lowering the electron density may decrease etch rates. One of ordinary skill may recognize further benefits of a tunable system as described herein. For example, modification of the EEPF curve may modify the ionization rate in the second plasma112, the chemical reaction on the wafer to precisely control etching profile and etching rate.

FIG.5is a graphical representation of the electron density (EEPF) with respect to electron energy, where the measurement is taken directly in the path of the electron beam116and perpendicular to the electron beam116.FIG.5shows that the EEPF may be adjusted over a relatively wide range of electron energies, which can be beneficial for high aspect ratio etch processes.

Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.