Interconnect structures with fully aligned vias

A method of forming a fully aligned via connecting two metal lines on different Mx levels by forming a recessed opening above a first metal line in a first ILD; forming a cap on the first ILD and in the recessed openings; forming a second ILD on the cap; forming a metal trench hardmask above the second ILD, forming a metal trench pattern in the metal trench hardmask; forming a via pattern that is self aligned to the metal trench pattern and above a portion of the first metal line; forming a via opening exposing the first metal line by transferring the via pattern and metal trench pattern to lower levels, the via pattern is self-aligned to the recessed opening; and forming a via and a third metal line in the via opening and the transferred metal trench pattern, respectively.

BACKGROUND

The present invention generally relates to semiconductor device manufacturing, and more particularly to fabricating a metal line interconnect (via) fully aligned to both a Mxlevel and a Mx+1level.

The fabrication of Very-Large Scale Integrated (VLSI) or Ultra-Large Scale Integrated circuits (ULSI) requires an interconnect structure including metallic wiring that connects individual devices in a semiconductor chip, to one another. Typically, the wiring interconnect network consists of two types of features that serve as electrical conductors: line features that traverse a distance across the chip, and via features which connect lines in different levels. Typically, the conducting metal lines and vias are comprised of aluminum or copper and are insulated by the interlayer dielectrics (ILD) which are electrical insulators.

In order to improve performance, the semiconductor industry has shrunk the gate length and, as a result, the chip size. As a consequence the interconnect structure that forms the metallic circuitry has also shrunk.

Traditionally, the via levels are one of the most challenging to print with a high process latitude. In order to improve the manufacturability of the lithography step, advanced masks that incorporate phase-shifting and optical proximity correction have been employed. In addition, as the size scale of these interconnects decrease, there is growing concern that overlay error between features in the interconnect structure may lead to reliability issues. Overlay errors result from misalignment during the lithography process as the mask invariably may not be perfectly aligned to the underlying structure. Although overlay errors can be minimized by reworking the lithography, some level of overlay error is unavoidable.

Two key failure modes for interconnects, that may be dependent on overlay error of lithographic patterns, are electromigration (EM) and time dependent dielectric breakdown (TDDB). This is of critical importance, as devices must be fabricated in a manner that enables their function over useful lifetimes and in various environments.

Electromigration failure results when a void forms in the conducting metal feature through metal diffusion leading to a short (or very high resistance) in the circuitry. The mechanism of electromigration is highly dependent upon the current density and the cross section of the metal features. If the wiring is constructed such that the intersection between the via and line is too small, smaller voids formed by electromigration can lead to failure which shortens the electromigration lifetime.

Time dependent dielectric breakdown (TDDB) is a failure mode whereby the insulating materials (or layers) no longer serve as adequate electrical insulators resulting in unintended conductance between two adjacent metal features. This phenomenon is highly dependent upon the electrical field between the metal features as regions with higher electrical fields are more susceptible to TDDB failure. Consequently, it is critical to control the spacing between conducting metal features in order to maintain electrical fields to tolerable levels.

SUMMARY

According to one embodiment of the present invention, a method of forming a fully aligned via to a first metal line and a third metal line is provided. The method may include forming a first metal line and a second metal line in a first inter-level dielectric (ILD); forming a first recessed opening by recessing the first metal line below a top surface of the first ILD; forming a cap on the first ILD and in the first recessed opening; forming a second ILD on the cap; forming a higher level hardmask on the second ILD; forming a metal trench hardmask on the higher level hardmask; forming a metal trench pattern in the metal trench hardmask, wherein a portion of the metal trench pattern is above a portion of the first recessed opening; forming a via pattern material on the metal trench hardmask and in the metal trench pattern; forming a first via pattern in the via pattern material, the first via pattern is located above a portion of the metal trench pattern and above the portion of the first recessed opening, wherein the first via pattern is self aligned to the metal trench pattern; removing the via pattern material; forming a first higher level trench in the higher level hardmask and in the second ILD, wherein the first higher level trench includes a first via opening, wherein the first via opening is the first via pattern transferred to a lower level; and forming a third metal line and a first via in the first higher level trench and in the first via opening, respectively, wherein the via connects the first metal line to the third metal line.

According to another embodiment, a method of forming a fully aligned via to a first metal line and a third metal line is provided. The method may include recessing a first metal line and a second metal line, wherein the first metal line and the second metal line are in a first ILD; forming a cap on the first ILD and on the first and second metal lines; forming a second ILD on the cap; forming a metal trench hardmask above the second ILD and metal trench pattern in the second ILD; forming a via pattern in the second ILD, the via pattern is formed at a vertical intersection of the metal trench pattern and the first metal line, wherein the via pattern is self-aligned to the metal trench pattern; forming a higher level trench in the second ILD, wherein the higher level trench includes a via opening, wherein the via opening is the via pattern transferred to a lower level; and forming a third metal line and a via in the higher level trench and in the via opening, respectively, wherein the via connects the first metal line to the third metal line.

According to another embodiment, a structure of a fully aligned via is provided. The structure may include a first metal line and a second metal line in a first ILD; a cap covering the first ILD, the second metal line, and a portion of the first metal line; a second ILD on the cap; and a via that electrically connects the first metal line to a third metal line, wherein the third metal line is above the first metal line and runs perpendicular to the first metal line, the via is fully aligned to the first metal line and the third metal line, and the via electrically connects the first metal line to the third metal line.

DETAILED DESCRIPTION

For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the disclosed structures and methods, as oriented in the drawing figures. The terms “overlying”, “atop”, “on top”, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure may be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements. It should be noted, the term “selective to,” such as, for example, “a first element selective to a second element,” means that a first element may be etched and the second element may act as an etch stop.

The present invention generally relates to semiconductor device manufacturing, and more particularly to fabricating a metal line interconnect (via) fully aligned to both a Mxlevel and a Mx+1level. Ideally, it may be desirable to fabricate a via with a specific amount of surface contact and with no overlap. One way to fabricate a fully aligned via is described in detail below by referring to the accompanying drawingsFIGS. 1-11.

FIG. 1is a demonstrative illustration of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method can start with fabricating a first metal line104and a second metal line105in a first interlayer dielectric (hereinafter “first ILD”)102.

The first ILD102may include any materials known in the art, such as, for example, porous silicates, carbon doped oxides, silicon dioxides, silicon nitrides, silicon oxynitrides, or other dielectric materials. The first ILD102may be formed using any method known in the art, such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or physical vapor deposition. The first ILD102may have a thickness ranging from about 25 nm to about 200 nm.

A trench stop hardmask106may include any masking material known in the art, such as, for example, a low-k silicon carbide (SiC) or silicon carbonitride (SiCN). The trench stop hardmask106may be formed on the first ILD102and may be formed using any method known in the art, such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or physical vapor deposition. The trench stop hardmask106may have a thickness ranging from about 1 nm to 50 nm. Metal openings may be formed in the trench stop hardmask106and in the first ILD102using any technique known in the art, such as, for example, wet or dry etching. The trench stop hardmask106may have a trench stop hardmask surface206, and the trench stop hardmask surface206may be a top surface of the trench stop hardmask106.

The first and second metal lines104,105(associated with Mx layer) may be formed in the metal openings. The first and second metal lines104,105may be any conductive materials known in the art, such as, for example, copper (Cu), aluminum (Al), or tungsten (W). The first and second metal lines104,105may be fabricated using any technique known in the art, such as, for example, a single or dual damascene technique. In an embodiment, not illustrated, the first and second metal lines104,105may be copper (Cu) and may include a metal liner, where the metal liner may be metals, such as, for example, tantalum nitride and tantalum (TaN/Ta), titanium, titanium nitride, cobalt, ruthenium, and manganese.

FIG. 2is a demonstrative illustration of a structure100during an intermediate step of a method of fabricating a fully aligned via according to the first embodiment. More specifically, the method may include forming a first recessed opening107aand a second recessed opening107babove the first and second metal lines104,105.

The first and second recessed openings107a,107bmay be formed by etching the first and second metal lines104,105using any etching technique known in the art, such as, for example, a reactive ion etching (RIE) technique and/or wet etches. This may include NF3, Cl2, BCl3, Ar, (may add more here) based plasmas chemistries. Alternatively, wet chemistries may be employed to recess the metal lines104,105. Including acidic chemistries having an oxidizer, e.g., hydrogen peroxide. Furthermore, the metal lines recess can be performed in a manner where the bulk of the conducting line (e.g., Cu or W) may be removed in a separate step from the metal barrier liner which may be comprised of Ti, TiN, Ta, TaN, Co, Ru, Mn, etc. The first recessed opening107amay be formed at the same time as the second recessed opening107b. The first and second recessed openings107a,107bmay be formed by etching the first and second metal lines104,105selective to the trench stop hardmask106, where the first and second metal lines104,105may be etched and the trench stop hardmask106may act as an etch stop. The first and second recessed openings107a,107bmay be formed with a first and second recessed depth (r1, r2), respectively. The first recessed depth (r1) may be the same as the second depth (r2). The first and second depth (r1, r2) may range from about 5 nm to 50 nm. The first and second recessed depth (r1, r2) may be a distance from the trench stop hardmask surface206to a top surface of the first and second metal lines104,105, respectively.

FIGS. 3a-3care demonstrative illustrations of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method may include forming a cap108on the structure100.

In the present embodiment, illustrated asFIG. 3a, the cap108may be deposited directly on top of the trench stop hardmask106and directly on top of the first and second metal lines104,105. The cap108may include any suitable dielectric material, such as, for example, silicon nitride (Si3N4), silicon carbide (SiC), silicon carbonitride (SiCN), hydrogenated silicon carbide (SiCH), or any other material known in the art. The cap108may be formed using any technique known in the art, such as, for example, chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or physical vapor deposition. The cap108may have a thickness ranging from about 10 nm to about 55 nm. The cap108may act as an air or metal diffusion barrier or insulator and may be used to improve interconnect reliability.

In another embodiment, illustrated asFIG. 3b, the cap108may be polished such that the cap108is removed from portions above the trench stop hardmask106but remains above the first and second metal lines104,105. In yet another embodiment, illustrated asFIG. 3c, the trench stop hardmask106may not be used and the cap108may be deposited directly on the first ILD102.

FIG. 4is a demonstrative illustration of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method may include forming a second ILD110, a higher level hardmask112, and a metal trench hardmask114on the structure100. It should be noted that the illustrated embodiments include the cap108covering the trench stop hardmask106and the first and second metal lines104,105as illustrated inFIG. 3a.

The second ILD110may be any material known in the art and may be substantially similar to the first ILD102described above. The second ILD110may be formed using any technique known in the art, such as, for example, plasma enhanced chemical vapor deposition (PECVD). The second ILD110may be formed on the cap108. The second ILD110may be planarized to provide a top surface for subsequent material deposition. The optional planarization process may involve chemical mechanical polishing (CMP).

The higher level hardmask112may be any masking material known in the art and may be substantially similar to the trench stop hardmask106described above. The higher level hardmask112may be formed on the second ILD110.

The metal trench hardmask114may be any masking material known in the art, such as, for example, titanium nitride (TiN). The metal trench hardmask114may be formed on the higher level hardmask112. The metal trench hardmask114may be a different material from the higher level hardmask112to allow for subsequent etching of the metal trench hardmask114selective to the higher level hardmask112, where the metal trench hardmask114can be etched and the higher level hardmask112can act as an etch stop.

FIG. 5is a demonstrative illustration of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method may include etching a metal trench pattern214in the metal trench hardmask114.

The metal trench pattern214may be formed using any etching technique known in the art, such as, for example, reactive ion etch (RIE). In an embodiment, the higher level hardmask112may act as an etch stop for the formation of the metal trench pattern214, and portions of the metal trench hardmask114may be removed selective to the higher level hardmask112to form the metal trench pattern214. In general, the metal trench pattern214may run perpendicular to, and overlap at least a portion of, the first and second metal lines104,105, as illustrated.

FIGS. 6 and 7are a demonstrative illustration of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method may include forming a via pattern material116and etching a first via pattern216aand a second via pattern216b. The structure100illustrated inFIG. 7is a top view of the structure100illustrated inFIG. 6.

The via pattern material116may include any masking materials that are commonly used in lithography known in the art, such as, for example, organic resist coatings or patterning layers. The via pattern material116may be formed on the structure100by spin coating and may be comprised of multiple layers. The via pattern material116may have a thickness ranging from about 5 nm to 500 nm.

Ideally, a via pattern will be aligned to a lower metal line through alignment of lithography techniques, however, some level of misalignment invariably occurs and as device dimensions shrink with technology, this misalignment or overlay errors become more impactful. Consequently, the self-alignment of a via to the lower and higher metal lines may become necessary.

The first and second via patterns216a,216bmay be any shape, such as, for example, a square, a rectangle, or a circle. In general, the first via pattern216amay be defined such that it is placed in a direction that intersects both the metal trench pattern214(illustrated inFIG. 5) and the first metal line104. In general, the second via pattern216bmay be defined to a desired location such that it is etched in a direction that intersects both the metal trench pattern214and the second metal line105. The first and second via patterns216a,216bmay be misaligned relative to the desired location of the higher line but may be self-aligned by the metal trench hardmask114because of the selectivity of the etching technique, where forming the first and second via patterns216a,216bby etching the via pattern material116is selective to the metal trench hardmask114. The first and second via patterns216a,216bmay be formed by any etching technique known in the art, such as, for example, reactive ion etch.

With further reference toFIGS. 6 and 7, the first and second via patterns216a,216bmay each overlap a portion of the metal trench pattern214. The first and second via patterns216a,216bmay overlap the metal trench hardmask114on two sides of each of the first and second via patterns216a,216b. The overlap of the first and second via patterns216a,216bto the metal trench hardmask114may cause the first and second via patterns216a,216bto self-align to the metal trench pattern214, as illustrated. The self-alignment of the first and second via patterns216a,216bmay be formed because of the selectivity of the etching technique, where forming the first and second via patterns216a,216bby etching the via pattern material116is selective to the metal trench hardmask114.

In the exemplary embodiment, the first and second via patterns216a,216bmay be formed through the higher level hardmask112and partially through the second ILD110. In an alternative embodiment, the first and second via patterns216a,216bmay be formed through both the higher level hardmask112and the second ILD110. In yet another embodiment, the first and second via patterns216a,216bmay be formed partially through the higher level hardmask112and not reach the second ILD110. A depth of the first and second via patterns216a,216bmay be a function of etch selectivity of the materials used or a first or second desired via depth, respectively.

FIGS. 8 and 9are demonstrative illustrations of a structure100during an intermediate step of a method of fabricating a fully aligned via according to an exemplary embodiment. More specifically, the method may include removing the via pattern material116and etching a first higher level trench317aand a second higher level trench317b. The structure100illustrated inFIG. 9is a top view of the structure100illustrated inFIG. 8.

The via pattern material116may be removed using any method known in the art, such as, for example, reactive ion etch or strip. The first and second higher level trenches317a,317bare formed from the metal trench pattern214(illustrated inFIG. 5). The relative depths of the first and second via patterns216a,216bmay be carried into the first and second via openings417a,417b, respectively. The first and second higher level trenches317a,317bmay be etched using any etching technique known in the art, such as, for example, reactive ion etch. The etching technique of the first and second higher level trenches317a,317bmay be etch selective to the metal trench hardmask114and the trench stop hardmask106, where the second ILD110may be etched and the metal trench hardmask114and the trench stop hardmask106may act as an etch stop. The etch selectivity of the second ILD110to the trench stop hardmask106may allow for self-alignment of a first via opening417aand a second via opening417bto the trench stop hardmask106. The first and second via openings417a,417bmay be formed during formation of the first and second higher level trenches317aand317b. The first and second via openings417a,417bmay be formed in a portion of the first and second recessed openings107a,107b(illustrated inFIG. 2). In the exemplary embodiment the first via opening417arepresents a portion of the first recessed opening107aabove the first metal line104. In the exemplary embodiment the second via opening417brepresents a portion of the second recessed opening107babove the second metal line105. The first and second via openings417a,417bmay be self-aligned to both the metal trench hardmask114and the trench stop hardmask106.

FIGS. 10 and 11are demonstrative illustrations of a structure100during an intermediate step of a method of fabricating fully aligned via according to an exemplary embodiment. More specifically, the method may include depositing a third metal line118and a forth metal line120in the first and second higher level trenches317a,317b, respectively.

The first and second metal lines104,105, may be different or substantially similar materials compared to the third and forth metal lines118,120, or any variation therein. The first and second metal lines104,105and the third and fourth metal lines118,120may be any conductive materials, such as, for example, copper (Cu), aluminum (Al), or tungsten (W). In an embodiment, the third and fourth metal lines118,120may be copper (Cu) and may include a metal liner, where the metal liner may be a tantalum nitride/tantalum (TaN/Ta) combination. The first and second, metal lines104,105may be fabricated using any technique known in the art, such as, for example, a single or dual damascene techniques. The third and fourth metal lines118,120may be fabricated using a dual damascene technique. In the exemplary embodiment, the third metal line118may be formed in the first higher level trench317aand in the first via opening417a, and may reach the first metal line104. In the exemplary embodiment, the fourth metal line120may be formed in the second higher level trench317band in the second via opening417b, and may reach the second metal line105. The structure may be polished to a top surface of the metal trench hardmask114(illustrated inFIG. 10), polished to a top surface of the higher level hardmask112(illustrated inFIG. 11), or any other surface.

A first via (interconnect)119aand second via (not shown in the illustration) may be formed at the same time and of the same material as the third and fourth metal line118,120. The first via119amay connect the first metal line104to the third metal line118. The second via may connect the second metal line105to the fourth metal line120. The self-alignment of the first and second via patterns216a,216bto the metal trench pattern214and the self-alignment of the first and second higher level trenches317a,317bto the trench stop hardmask106may produce a first via119aand second via that are fully aligned, where the first via119ais fully aligned to the first and third metal lines104,118and the second via is fully aligned to the second and fourth metal line105,120.