Patent Application
20070048980
The present invention relates generally to semiconductor device processing techniques, and, more particularly, to a method for post-RIE (reactive ion etch) passivation of semiconductor surfaces in preparation for epitaxial growth thereon.
In the realm of semiconductor manufacturing, reactive ion etching (RIE) and epitaxial layer growth are common processes used in forming various types of semiconductor devices. For example, in CMOS device manufacturing, there has recently been introduced certain performance enhancing techniques such as “hybrid orientation technology” (HOT), in which n-type devices are manufactured on silicon of a first crystalline orientation and p-type devices are manufactured on silicon of a second crystalline orientation in order to maximize the carrier mobility of both the n-type and p-type devices. In addition, strained silicon (e.g., devices with a SiGe replacement source/drain region) is another technique that has been used to enhance carrier mobility and increase the switching speed of high-performance CMOS circuits.
Prior to the epitaxial growth step, a pre-clean sequence is typically used, which concludes with an etch (e.g., aqueous hydrofluoric acid (HF)) to remove the oxide layer on the portion of the substrate targeted for the epitaxial growth. This etch step is necessary since epitaxial growth can only occur on a bare crystal surface. While a certain amount of residual interfacial oxygen is acceptable for epitaxial growth, this value is typically much less than one monolayer (ML). If the surface oxygen content is high enough, it will detrimentally affect the growth of the epitaxial layer by nucleating defects or completely blocking the growth.
However, one side effect associated with the conventional HF pre-clean results from the fact that the HF etch rate of a deposited oxide is much higher than that of the native oxide. Thus, where deposited oxide structures are present (e.g., shallow trench isolations, sidewall spacers), such structures may suffer significant erosion from the HF pre-clean. Moreover, even after the HF pre-clean, there is typically some queue time in which a native oxide begins to re-grow on the surface. In order to remove such additional native oxide, a subsequent clean step such as a hydrogen pre-bake step may also be used. Unfortunately, this additional step is also disadvantageous in that a hydrogen bake can significantly increase the thermal budget of the epitaxial process.
Accordingly, in such types of applications where an epitaxial growth layer (e.g., Si or SiGe) is formed subsequent to an RIE step, it would be desirable to be able to prepare a semiconductor surface for epitaxial growth following RIE in a manner that overcomes the disadvantages associated with HF etching and hydrogen baking.
The above discussed drawbacks and deficiencies of the prior art are overcome or alleviated by a method for preparing a substrate for epitaxial crystal growth thereon. In an exemplary embodiment, the method includes performing a reactive ion etch (RIE) on a selected area of the substrate to be prepared for epitaxial crystal growth, discontinuing the introduction of an etchant species associated with the RIE, and introducing a monolayer forming species into a chamber containing the substrate. The monolayer forming species is selected so as to form a passivating monolayer on the selected area of the substrate, wherein the monolayer is resistant to the formation of native oxide thereon.
In another embodiment, a method for forming a semiconductor device layer includes performing a reactive ion etch (RIE) on a selected area of a semiconductor substrate, discontinuing the introduction of an etchant species associated with the RIE, and introducing a monolayer forming species into a chamber containing the substrate. The monolayer forming species is selected so as to form a passivating monolayer on the selected area of the substrate, said monolayer being resistant to the formation of native oxide thereon. An epitaxially grown layer is then formed on the monolayer.
Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:
Disclosed herein is a method for post-RIE passivation of semiconductor surfaces in preparation for epitaxial growth thereon. Briefly stated, a passivating monolayer (such as fluorine, for example) is formed on a semiconductor surface post-RIE and in preparation for epitaxial layer growth thereon. In particular, by altering a conventional RIE process to introduce (for example) neutral molecular fluorine into the processing chamber once the plasma source is turned off, a self-limiting fluorine monolayer may be formed that is stable and controls the native oxide formation thereon. This in turn eliminates the need for a separate pre-clean step altogether, and the queue time window may be correspondingly increased or even eliminated.
Referring initially to
Although the above described apparatus illustrates an inductively coupled RIE reactor, it will be appreciated that a capacitively coupled RIE could also be used. Moreover, a pure chemical etch apparatus (i.e., no sputtering component) could be used wherein a single RF source is provided for plasma creation only.
Referring now to
In block 204, the wafer is subjected to a reactive ion etching in order to remove material (e.g., oxides, nitrides, silicon) and expose a substrate surface for selective epitaxial growth thereon. The RIE may be carried out, for example, using the general type of apparatus 100 shown in
Thus, as illustrated in block 206, a preclean sequence is used to prepare the newly etched substrate surfaces for epitaxial growth. The preclean sequence may begin, for example, with wet cleaning the substrate surface using an RCA clean (as is known to one skilled in the art) containing hydrogen peroxide (H2O2). In addition, to remove native oxide from the substrate (e.g., silicon) surface, an immersion in HF solution or treatment by an HF vapor is used. The HF cleaned surface is then rinsed in de-ionized water and dried to initially result in a substantially hydrophobic oxide free surface by passivating the surface with Si—H bonds.
However, due to practical queue-related time constraints, the clean surface will begin to re-oxidize and, as such, an optional hydrogen pre-bake operation is implemented as shown in block 208. This may be implemented, for example, in the same chamber used for the epitaxy deposition or, alternatively, in a separate baking chamber. The hydrogen pre-bake process is intended to remove residual oxide from the substrate surface prior to the epitaxy deposition. Finally, as shown in block 210, the selected substrate areas (having undergone an HF etch and optional hydrogen pre-bake), have the desired epitaxial layer formed thereon.
In contrast,
More specifically, as illustrated in block 306, the source of the reactive plasma (etchant) species is removed once the RIE endpoint is reached. For example, this may be implemented by deactivating the plasma source of the reactive species (i.e., the second RF excitation source 114 in contact with the induction coils of the RIE apparatus 100 of
In an exemplary embodiment, the neutral species is halogen based and, more particularly, is fluorine based. The neutral species may be introduced using molecular fluorine (F2) for example, or through a fluorine compound such as (but not limited to) CF4, C2F6, SF6, NF3, and C3F8. Where a fluorine based species is used as the RIE etchant itself, the same may also be used as the neutral species after the RIE is completed. Alternatively, a different source for the neutral species (with respect to the reactive species) may be introduced into the RIE chamber. Finally, once the passivating monolayer is formed, the desired epitaxial growth is formed on the passivated surfaces of the substrate, as shown in block 310.
While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
