Copper interconnect structures and methods of making same

This application is a Division of U.S. patent application Ser. No. 13/670,711 filed on Nov. 7, 2012.

The present invention relates to the field of integrated circuit technology; more specifically, it relates to copper interconnect structures and methods of making copper interconnect structures.

Copper interconnects are used to interconnect semiconductor devices into circuits. However, current flow in through the interconnect can result in copper migration from the anode end to the cathode end of the interconnect which depletes copper at the anode end of the interconnect resulting in an increase in resistance which will cause the circuit to fail. Accordingly, there exists a need in the art to eliminate the deficiencies and limitations described hereinabove.

A first aspect of the present invention is a structure, comprising: a dielectric layer on a substrate; a first wire formed in a first trench in the dielectric layer, a first liner on sidewalls and a bottom of the first trench and a first copper layer filling all remaining space in the first trench; a second wire formed in a second trench in the dielectric layer, a second liner on sidewalls and a bottom of the second trench and a second copper layer filling all remaining space in the second trench; and an electromigration stop formed in a third trench in the dielectric layer, a third liner on sidewalls and a bottom of the third trench and a third copper layer filling all remaining space in the third trench, the electromigration stop between and abutting respective ends of the first wire and the second wire.

A second aspect of the present invention is a method, comprising: forming a dielectric layer on a substrate; simultaneously forming a first trench and a second trench in the dielectric layer; simultaneously forming a first liner on sidewalls and a bottom of the first trench and a second liner on sidewalls and a bottom of the second trench; simultaneously filling all remaining space in the first trench with a first copper layer to form a first wire in the dielectric layer and filling all remaining space in the second trench with a second copper layer to form a second wire in the dielectric layer; forming a third trench in the dielectric layer; forming a third liner on sidewalls and a bottom of the third trench; and filling all remaining space in the third trench with a third copper layer to form an electromigration stop in the dielectric layer, the electromigration stop between and abutting respective ends of the first wire and the second wire.

These and other aspects of the invention are described below.

The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:

FIGS. 1A , 2 A, 3 A, 4 A, 5 A, 6 A, 7 A, 8 A, 9 A, and 10 A. are top views and FIGS. 1B , 2 B, 3 B, 4 B, 5 B, 6 B, 7 B, 8 B, 9 B and 10 B are corresponding cross-sectional views illustrating fabrication of a copper interconnect structure according to embodiments of the present invention;

FIGS. 10 B 1 and 10 B 2 are alternative cross-sections through line 10 B- 10 B of FIG. 10A ; and

FIGS. 11A , 11 B, 12 , 13 A, 13 B, 14 , 15 A, 15 B and 16 illustrate exemplary copper interconnect structure layouts according to embodiments of the present invention.

Interconnect structures according to embodiments of the present invention are formed of at least two copper damascene wires connected by a copper damascene electromigration stop. The at least two copper damascene wires and the copper damascene electromigration stop are formed in the same interlevel dielectric layer. The at least two copper damascene wires and the copper damascene electromigration stop include respective copper cores and copper diffusion barrier liners. In a preferred embodiment, here are two copper diffusion barrier liners between the copper cores of the two or more damascene wires and the copper core of the copper damascene electromigration stop. The electromigration stops effectively limit the reservoir of copper available for electromigration. The electromigration stops are placed at the intersection of two, three or four wires or formed periodically between short wire segments to make a longer wire comprising the short wire segments and the electromigration stops. The same damascene process is used to form both the copper damascene wires and the copper damascene electromigration stops. The copper diffusion barrier liners are electrically conductive.

A damascene process is one in which wire trenches or via openings are formed in a dielectric layer, an electrical conductor of sufficient thickness to fill the trenches is formed in the trenches and on a top surface of the dielectric. A chemical-mechanical-polish (CMP) process is performed to remove excess conductor and make the surface of the conductor co-planar with the surface of the dielectric layer to form damascene wires (or damascene vias). When only a trench and a wire (or a via opening and a via) is formed the process is called single-damascene.

A via first dual-damascene process is one in which via openings are formed through the entire thickness of a dielectric layer followed by formation of trenches part of the way through the dielectric layer in any given cross-sectional view. A trench first dual-damascene process is one in which trenches are formed part way through the thickness of a dielectric layer followed by formation of vias inside the trenches the rest of the way through the dielectric layer in any given cross-sectional view. All via openings are intersected by integral wire trenches above and by a wire trench below, but not all trenches need intersect a via opening. An electrical conductor of sufficient thickness to fill the trenches and via opening is formed on a top surface of the dielectric and a CMP process is performed to make the surface of the conductor in the trench co-planar with the surface of the dielectric layer to form dual-damascene wires and dual-damascene wires having integral dual-damascene vias.

The term damascene wire is intended to include single-damascene wires and dual-damascene wires. Interconnects are comprised of damascene wires embedded in interlevel dielectric (ILD) layers. A wiring level is comprised of its ILD layer and damascene wire and there are usually multiple wiring levels stacked one upon the other and interconnected by the via or via bar portions of dual-damascene wires.

FIGS. 1A , 2 A, 3 A, 4 A, 5 A, 6 A, 7 A, 8 A, 9 A, and 10 A. are top views and FIGS. 1B , 2 B, 3 B, 4 B, 5 B, 6 B, 7 B, 8 B, 9 B and 10 B are corresponding cross-sectional views illustrating fabrication of a copper interconnect structure according to embodiments of the present invention. FIG. 1A is a top view and FIG. 1B is a cross-section view through line 1 B- 1 B of FIG. 1A . In FIGS. 1A and 1B an ILD layer 100 is formed on substrate 105 . Dielectric layer 100 may be formed of one or more layers selected from the group consisting of silicon nitride (Si 3 N 4 ), silicon carbide (SiC), and NBLok (SiC(N,H)) and low K (dielectric constant) materials having a relative permittivity of about 4 or less, examples of which include but are not limited to hydrogen silsesquioxane polymer (HSQ), methyl silsesquioxane polymer (MSQ), polyphenylene oligomer, methyl doped silica or SiO x (CH 3 ) y or SiC x O y H y or SiOCH, organosilicate glass (SiCOH), and porous SiCOH. Other examples include porous or nonporous silicon dioxide (SiO 2 ), fluorinated SiO 2 (FSG), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), silicon oxy nitride (SiON), silicon oxy carbide (SiOC) plasma-enhanced silicon nitride (PSiN x ) or NBLock (SiC(N,H)).

FIG. 2A is a top view and FIG. 2B is a cross-section view through line 2 B- 2 B of FIG. 2A . In FIGS. 2A and 2B trenches 110 A and 110 B are etched into but not completely through ILD layer 100 . A full thickness region of ILD layer 100 intervenes between ends 112 A and 112 B of respective trenches 110 A and 110 B. In one example, trenches 110 A and 110 B are formed using a photolithographic process to form a patterned photoresist layer, a reactive ion etch (RIE) of ILD layer 100 , and subsequent removal of the patterned photoresist layer.

FIG. 3A is a top view and FIG. 3B is a cross-section view through line 3 B- 3 B of FIG. 3A . In FIGS. 3A and 3B an electrically conductive layer 115 A is deposited on the bottom 116 A and 116 B and sidewalls 117 A and 117 B of respective trenches 110 A and 110 B and also on the top surface 118 of ILD layer 100 . Because layer 115 A follows (i.e., conforms to) the contours of trenches 110 A and 110 B it is a conformal layer. In one example, layer 115 A is a diffusion barrier to copper. Layer 115 A may comprise one or more layers. In one example, layer 115 A is comprised of a layer of tantalum TaN contacting ILD layer 100 and a layer of Ta on the TaN layer. In one example, layer 115 A is comprised of a layer of titanium TiN contacting ILD layer 100 and a layer of Ti on the TiN layer. In one example, layer 115 A is comprised of a layer of tungsten nitride WN contacting ILD layer 100 and a layer of W on the W layer. Other layer 115 A materials include cobalt tungsten phosphide (CoWP) and cobalt silicide (CoSi). Other layer 115 A materials include dual layers of cobalt silicide (CoSi 2 )/Co, cobalt nitride (CoN)/Co, cobalt phosphide (CoP)/Co, colbalt boride (CoB)/Co, ruthenium nitride (RuN)/Ru, ruthenium phosphide (Ru 3 P 4 )/Ru and ruthenium boride (RuB)/Ru.

FIG. 4A is a top view and FIG. 4B is a cross-section view through line 4 B- 4 B of FIG. 4A . In FIGS. 4A and 4B an electrically conductive copper layer 120 A is formed on the top surface 122 of layer 115 A. In one example, copper layer 120 A is formed by depositing (e.g., evaporating or sputtering) a thin seed copper layer on layer 115 A followed by electroplating a copper layer on the seed layer of sufficient thickness to overfill trenches 110 A and 110 B.

FIG. 5A is a top view and FIG. 5B is a cross-section view through line 5 B- 5 B of FIG. 5A . In FIGS. 5A and 5B a CMP is performed to form damascene wires 125 A and 125 B each comprising a liner 115 and a copper core 120 and having respective top surface 127 A and 127 B. After the CMP, respective top surfaces 127 A and 127 B of wires 125 A and 125 B are coplanar with a top surface 128 of ILD layer 100 .

FIG. 6A is a top view and FIG. 6B is a cross-section view through line 6 B- 6 B of FIG. 6A . In FIGS. 6A and 6B a cap layer 130 is selectively deposited on the copper cores 120 of wires 125 A and 125 B. While cap layer 130 may overlap liners 115 of wires 125 A and 125 B, it is not deposited on liners 115 . Cap layer 130 is not deposited on ILD layer 100 . Exemplary materials for cap layer 130 include, but are not limited to Co, Ru, W rhodium (Rh) and platinum (Pt).

FIG. 7A is a plan view and FIG. 7B is a cross-section view through line 7 B- 7 B of FIG. 7A . In FIGS. 7A and 7B a patterned block mask 135 is formed over capping layer 130 , any exposed edges of liner 115 and top surfaces of ILD layer 100 . Patterned block mask 135 has an opening 140 . Opposing ends 142 A and 142 B of respective wires of wires 125 A and 125 B are exposed in opening 140 . A region of top surface 128 of ILD layer 100 between ends 142 A and 142 B is also exposed in opening. In one example, patterned block mask is photoresist and opening 140 is formed photolithographically.

FIG. 8A is a plan view and FIG. 8B is a cross-section view through line 8 B- 8 B of FIG. 8A . In FIGS. 8A and 8B a trench 145 is formed in ILD layer 100 where the ILD layer is not protected by block mask 135 or wires 125 A and 125 B. Capping layer 130 protects wires 125 A and 125 B during the etching process used to form trench 145 . In one example, trench 145 is formed by a RIE process. In FIG. 8B , a bottom surface 147 of trench 145 is coplanar with respective bottom surfaces 148 A and 148 B of wires 125 A and 125 B. In other words, trench 145 extends into ILD layer 100 the same distance as wires 125 A and 125 B. Alternatively, trench 145 may extend into ILD layer 100 a lesser or greater distance as wires 125 A and 125 B.

FIG. 9A is a plan view and FIG. 9B is a cross-section view through line 9 B- 9 B of FIG. 9A . In FIGS. 9A and 9B an electrically conductive layer 150 A is deposited on the exposed surfaces of capping layer 130 , wires 125 A and 125 B and ILD layer 100 . Because layer 150 A follows (i.e., conforms to) the contours of trench 145 it is a conformal layer. Next, an electrically conductive copper layer 155 A is formed on the top surface 157 of layer 150 A. In one example, copper layer 155 A is formed by depositing a thin seed copper layer on layer 150 A followed by electroplating a copper layer on the seed layer of sufficient thickness to overfill trench 145 . In one example, layer 150 A is a diffusion barrier to copper. Layer 150 A may comprise one or more layers. Exemplary materials for layer 150 A are the same as for layer 115 A described supra.

FIG. 10A is a top view and FIG. 10B is a cross-section view through line 10 B- 10 B of FIG. 10A . In FIGS. 10A and 10B a CMP is performed to form electromigration stop 160 comprising a liner 150 and a copper core 155 and having a top surface 162 . After the CMP, top surface 162 of electromigration stop 160 is coplanar with respective top surfaces 127 A and 127 B of wires 125 A and 125 B (as well as the top surface of ILD layer 100 ). Electromigration stop 160 is in direct physical and electrical contact with ends 142 A and 142 B of respective wires 125 A and 125 B. Electromigration stop 160 stops copper migration from wire 125 A to wire 125 B and from wire 125 B to wire 125 A. In FIG. 10B , a bottom surface 163 of electromigration stop 160 is coplanar with respective bottom surfaces 148 A and 148 B of wires 125 A and 125 B. In other words, electromigration stop 160 extends into ILD layer 100 the same distance as wires 125 A and 125 B. Alternatively, electromigration stop 160 may extend into ILD layer 100 a lesser or greater distance than wires 125 A and 125 B extend into ILD layer 100 as illustrated in FIGS. 10 B 1 and 10 B 2 .

FIGS. 10 B 1 and 10 B 2 are alternative cross-sections through line 10 B- 10 B of FIG. 10A . In FIG. 10 B 1 , bottom surface 163 of electromigration stop 160 extends into ILD layer 100 a lesser distance than wires 125 A and 125 B extend into ILD layer 100 . In FIG. 10 B 2 , bottom surface 163 of electromigration stop 160 extends into ILD layer 100 a greater distance than wires 125 A and 125 B extend into ILD layer 100 .

FIGS. 11A and 11B illustrate exemplary copper interconnect structure layouts according to embodiments of the present invention. In FIG. 11A , a series of wires 200 A, 200 B, 200 C and 200 D (comprised of copper cores 205 and copper diffusion barrier liners 210 ) are interconnected electrically and physically by electromigration stops 215 A, 215 B and 215 C (comprised of copper cores 220 and copper diffusion barrier liners 225 ). The materials of liners 210 and 225 may be the same or different. Wire 200 B has a length L 1 measured between electromigration stops 215 A and 125 B and wire 200 C has a length L 2 measured between electromigration stops 215 B and 125 C. In one example, L 1 and L 2 are less than the Blech length. A wire having a length below the Blech length will not fail by electromigration because mechanical stress buildup causes an atom back flow which reduces or compensates for the electromigration atom flow towards the anode. FIG. 11B illustrates that electromigration stops can be used in place of a corner region of a single contiguous wire. In one example, copper diffusion barrier liners 210 and 225 are electrically conductive. Liners 210 and 225 may comprise one or more layers. Exemplary materials for liners 210 and 225 are the same as for layer 115 A described supra.

FIG. 12 illustrates an exemplary copper interconnect structure layout according to embodiments of the present invention. In FIG. 12 , three wires 200 E, 200 F and 200 G (comprised of copper cores 205 and copper diffusion barrier liners 210 ) are interconnected electrically and physically by an electromigration stop 215 D (comprised of copper core 220 and copper diffusion barrier liner 225 ). Wire 200 E is on the opposite side of electromigration stop 215 D from wires 200 F and 200 G. The materials of liners 210 and 225 may be the same or different. The number of wires (three) should be considered exemplary and there can be few as three wires or more than three wires as long as there is at least one wire on a first side of the electromigration stop and are least two wires on a different side (in one example on an opposite side) of the electromigration stop.

FIGS. 13A and 13B illustrate an exemplary copper interconnect structure layout according to embodiments of the present invention. FIG. 13A illustrates four mutually orthogonal wires 125 H, 125 I, 125 J and 125 K that are to be interconnected by an electromigration stop. Dashed line 255 indicates the opening in the patterned photoresist layer that defines the topological extents of the electromigration stop (see, for example, FIG. 7A ) of FIG. 13B (and also FIG. 14 ). In FIG. 13B , the four wires 125 H, 125 I, 125 J and 125 K (comprised of copper cores 120 and copper diffusion barrier liners 115 ) are interconnected by electromigration stop 235 (comprised of copper core 155 and copper diffusion barrier liner 150 ). Liner 115 and 150 may be the same or different. Wires 125 H and 125 J have a common first longitudinal axis 227 and wires 125 I and 125 K have a common second longitudinal axis 228 . First axis 227 is perpendicular to second axis 228 . Electromigration stop 235 is thus formed at the cardinal intersection of the axes of wires 125 H, 125 I, 125 J and 125 K.

FIG. 14 is similar to FIG. 13B except only three wires 125 H, 125 I and 125 J are interconnected by an electromigration stop 240 (comprised of copper core 155 and copper diffusion barrier liner 150 ).

FIGS. 15A and 15B illustrate an exemplary copper interconnect structure layout according to embodiments of the present invention. FIG. 15A illustrates the same four mutually orthogonal wires 125 H, 125 I, 125 J and 125 K of FIG. 13A that are to be interconnected by an electromigration stop except that they are spaced further apart. Dashed line 260 indicates the opening in the patterned photoresist layer that defines the topological extents of the electromigration stop (see, for example, FIG. 7A ) of FIG. 15B . In FIG. 15B , the four wires 125 H, 125 I, 125 J and 125 K (comprised of copper cores 120 and copper diffusion barrier liners 115 ) are interconnected by electromigration stop 250 . Electromigration stop 250 is thus formed at the cardinal intersection of the axes of wires 125 H, 125 I, 125 J and 125 K. Electromigration stop 250 differs from electromigration stop 235 of FIG. 13 in that electromigration stop 250 includes a body 255 (comprised of copper core 150 and copper diffusion barrier liner 155 ) and corner projections 265 A, 265 B, 265 C and 265 D comprised of copper cores 150 and copper diffusion barrier liners 155 . The liners ( 115 ) of corner projections 265 A, 265 B, 265 C and 265 D are simultaneously formed with and contiguous with the liner ( 115 ) of electromigration stop 250 , but the copper cores ( 120 ) of corner projections 265 A, 265 B, 265 C and 265 D though simultaneously formed with the copper core ( 120 ) of electromigration stop 250 are not contiguous with the copper core ( 120 ) of electromigration stop 250 . Also, only the three wires 125 H, 125 I and 125 J may be formed as in FIG. 14 in which case corner regions 265 A and 265 D would merge.

FIG. 16 is similar to FIG. 15 except the copper cores ( 120 ) of corner projections 265 A, 265 B, 265 C and 265 D are contiguous with the copper core ( 120 ) of body 255 .

Thus, the embodiments of the present invention provide copper interconnect structures that are resistant to and can prevent electromigration fails dependent upon the geometry of the interconnect structures.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.