Sidewall treatment for low dielectric constant (low K) materials by ion implantation

[0002] 1. Field of the Invention

[0003] This invention relates generally to semiconductor fabrication technology, and, more particularly, to techniques for filling contact openings and vias with copper and creating copper interconnections and lines.

[0004] 2. Description of the Related Art

[0005] There is a constant drive within the semiconductor industry to increase the operating speed of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate dielectric thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the FET, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors. Additionally, reducing the size, or scale, of the components of a typical transistor also increases the density, and number, of the transistors that can be produced on a given amount of wafer real estate, lowering the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.

[0006] However, reducing the size, or scale, of the components of a typical transistor also requires reducing the size and cross-sectional dimensions of electrical interconnects to contacts to active areas, such as N⁺ (P⁺) source/drain regions and a doped-polycrystalline silicon (doped-polysilicon or doped-poly) gate conductor, and the like. As the size and cross-sectional dimensions of electrical interconnects get smaller, resistance increases and electromigration increases. Increased resistance and electromigration are undesirable for a number of reasons. For example, increased resistance may reduce device drive current, and source/drain current through the device, and may also adversely affect the overall speed and operation of the transistor. Additionally, electromigration effects in aluminum (Al) interconnects, where electrical currents actually carry Al atoms along with the current, causing them to electromigrate, may lead to degradation of the Al interconnects, further increased resistance, and even disconnection and/or delamination of the Al interconnects.

[0007] The ideal interconnect conductor for semiconductor circuitry will be inexpensive, easily patterned, have low resistivity, and high resistance to corrosion, electromigration, and stress migration. Aluminum (Al) is most often used for interconnects in contemporary semiconductor fabrication processes primarily because Al is inexpensive and easier to etch than, for example, copper (Cu). However, because Al has poor electromigration characteristics and high susceptibility to stress migration, it is typical to alloy Al with other metals.

[0008] As discussed above, as semiconductor device geometries shrink and clock speeds increase, it becomes increasingly desirable to reduce the resistance of the circuit metallization. The one criterion that is most seriously compromised by the use of Al for interconnects is that of conductivity. This is because the three metals with lower resistivities (Al has a resistivity of 2.824+10⁻⁶ohms-cm at 20° C.), namely, silver (Ag) with a resistivity of 1.59×10⁻⁶ohms-cm (at 20° C.), copper (Cu) with a resistivity of 1.73×10⁻⁶ohms-cm (at 20° C.), and gold (Au) with a resistivity of 2.44×10⁻⁶ohms-cm (at 20° C.), fall short in other significant criteria. Silver, for example, is relatively expensive and corrodes easily, and gold is very costly and difficult to etch. Copper, with a resistivity nearly on par with silver, immunity from electromigration, high ductility (which provides high immunity to mechanical stresses generated by differential expansion rates of dissimilar materials in a semiconductor chip) and high melting point (1083° C. for Cu vs. 659° C. for Al), fills most criteria admirably. However, Cu is difficult to etch in a semiconductor environment. As a result of the difficulty in etching Cu, an alternative approach to forming vias and metal lines must be used. The damascene approach, consisting of etching openings such as trenches in the dielectric for lines and vias and creating in-laid metal patterns, is the leading contender for fabrication of sub-0.25 micron (sub-0.25 μ) design rule Cu-metallized circuits.

[0009] However, the lower resistance and higher conductivity of the Cu interconnects, coupled with higher device density and, hence, decreased distance between the Cu interconnects, may lead to increased capacitance between the Cu interconnects. Increased capacitance between the Cu interconnects, in turn, results in increased RC time delays and longer transient decay times in the semiconductor device circuitry, causing decreased overall operating speeds of the semiconductor devices.

[0010] One conventional solution to the problem of increased capacitance between the Cu interconnects is to use “low dielectric constant” or “low K” dielectric materials, where K is less than or equal to about 4, for the interlayer dielectric layers (ILD's) in which the Cu interconnects are formed using the damascene techniques. However, low K dielectric materials are difficult materials to use in conjunction with the damascene techniques. For example, low K dielectric materials are susceptible to being damaged and weakened during the etching and subsequent processing steps used in the damascene techniques. In particular, the sidewalls of openings such as trenches and/or vias formed in low K dielectric materials are especially vulnerable.

[0011] The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.

[0012] In one aspect of the present invention, a method is provided, the method comprising forming a first conductive structure, and forming a first dielectric layer above the first conductive structure. The method also comprises densifying a portion of the first dielectric layer above at least a portion of the first conductive structure, and forming a first opening in the densified portion of the first dielectric layer.

[0013] In another aspect of the present invention, a device is provided, the device comprising a first conductive structure, and a first dielectric layer above the first conductive structure. The device also comprises a first opening in the first dielectric layer above at least a portion of the first conductive structure, the first opening formed in a densified portion of the first dielectric layer.

[0014] The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, and in which:

[0015] FIGS. 1-8 schematically illustrate a single-damascene copper interconnect process flow according to various embodiments of the present invention;

[0016] FIG. 9 schematically illustrates multiple layers of copper interconnects according to various embodiments of the present invention;

[0017] FIG. 10 schematically illustrates copper interconnects according to various embodiments of the present invention connecting source/drain regions of an MOS transistor;

[0018] FIGS. 11-18 schematically illustrate a dual-damascene copper interconnect process flow according to various embodiments of the present invention;

[0019] FIG. 19 schematically illustrates multiple layers of copper interconnects according to various embodiments of the present invention; and

[0020] FIG. 20 schematically illustrates copper interconnects according to various embodiments of the present invention connecting source/drain regions of an MOS transistor.

[0021] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0022] Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0023] Illustrative embodiments of a method for semiconductor device fabrication according to the present invention are shown in FIGS. 1-20. Although the various regions and structures of a semiconductor device are depicted in the drawings as having very precise, sharp configurations and profiles, those skilled in the art recognize that, in reality, these regions and structures are not as precise as indicated in the drawings. Nevertheless, the attached drawings are included to provide illustrative examples of the present invention.

[0024] In general, the present invention is directed towards the manufacture of a semiconductor device. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the present method is applicable to a variety of technologies, for example, NMOS, PMOS, CMOS, and the like, and is readily applicable to a variety of devices, including, but not limited to, logic devices, memory devices, and the like.

[0025] As shown in FIG. 1, a first dielectric layer 120 and a first conductive structure 140 (such as a copper intermetal via connection) may be formed above a structure 100 such as a semiconducting substrate. However, the present invention is not limited to the formation of a Cu-based interconnect above the surface of a semiconducting substrate such as a silicon wafer, for example. Rather, as will be apparent to one skilled in the art upon a complete reading of the present disclosure, a Cu-based interconnect formed in accordance with the present invention may be formed above previously formed semiconductor devices and/or process layer, e.g., transistors, or other similar structure. In effect, the present invention may be used to form process layers on top of previously formed process layers. The structure 100 may be an underlayer of semiconducting material, such as a silicon substrate or wafer, or, alternatively, may be an underlayer of semiconductor devices (see FIG. 10, for example), such as a layer of metal oxide semiconductor field effect transistors (MOSFETs), and the like, and/or a metal interconnection layer or layers (see FIG. 9, for example) and/or an interlayer dielectric (ILD) layer or layers, and the like.

[0026] In a single-damascene copper process flow, according to various embodiments of the present invention, as shown in FIGS. 1-8, the first dielectric layer 120 is formed above the structure 100, adjacent the first conductive structure 140. A second dielectric layer 130 is formed above the first dielectric layer 120 and above the first conductive structure 140. A patterned photomask 150 is formed above the second dielectric layer 130, using photolithography, for example. The first dielectric layer 120 has the first conductive structure 140 disposed therein. The first dielectric layer 120 has an etch stop layer (ESL) 110 (typically silicon nitride, Si₃N₄, or SiN, for short) formed and patterned thereon, between the first dielectric layer 120 and the second dielectric layer 130 and adjacent the first conductive structure 140. If necessary, the second dielectric layer 130 may have been planarized using chemical-mechanical planarization (CMP). The second dielectric layer 130 has a hard mask layer 160 (typically also SiN) formed and patterned thereon, using the patterned photomask 150, the hard mask layer 160 being disposed between the second dielectric layer 130 and the patterned photomask 150.

[0027] The first and second dielectric layers 120 and 130 may be formed from a variety of “low dielectric constant” or “low K” (K is less than or equal to about 4) dielectric materials. The low K first and second dielectric layers 120 and 130 may be formed by a variety of known techniques for forming such layers, e.g., a chemical vapor deposition (CVD) process, a low-pressure CVD (LPCVD) process, a plasma-enhanced CVD (PECVD) process, a sputtering process, a physical vapor deposition (PVD) process, a spin-on coating process (such as a spin-on glass process), and the like, and each may have a thickness ranging from approximately 1000 Å-5000 Å, for example.

[0028] The low K first and second dielectric layers 120 and 130 may be formed from a variety of low K dielectric materials, where K is less than or equal to about 4. Examples include Applied Material's Black Diamond®, Novellus' Coral®, Allied Signal's Nanoglass®, JSR's LKD5104, and the like. In one illustrative embodiment, the low K first and second dielectric layers 120 and 130 are each comprised of Applied Material's Black Diamond®, each having a thickness of approximately 5000 Å, each being formed by being blanket-deposited by a PECVD.

[0029] As shown in FIG. 2, the patterned photomask 150 is trimmed, using a controlled photoresist trim, for example, forming a trimmed photomask 250. The patterned photomask 150 may be trimmed by ashing, using a molecular oxygen (O₂) ashing, for example. Approximately 100-500 Å of the patterned photomask 150 may be trimmed by the ashing.

[0030] As shown in FIG. 3, a densification implant 300 (indicated by the arrows) may be implanted into the low K second dielectric layer 130 to form a densified region 330 in the low K second dielectric layer 130 above at least a portion of the first conductive structure 140. The densification implant 300 increases the density of the low K second dielectric layer 130 in the densified region 330 by about 5-50%, and, hence, reinforces and strengthens the low K second dielectric layer 130 in the densified region 330 prior to etching. In various illustrative embodiments, the densified region 330 may be formed by being implanted with a densification dose of silicon (Si), silicon dioxide (SiO₂), germanium (Ge), and the like. The densification dose of the densification implant 300 may range from about 5.0×10¹³−2.0×10¹⁵ions/cm²at an implant energy ranging from about 5-50 keV. The densified region 330 may be subjected to a rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 400-1000° C. for a time ranging from approximately 5-60 seconds. The RTA process may activate the densification implant 300 and reinforce the densification process.

[0031] As shown in FIG. 4, a metallization pattern is then formed by using the etch stop layer 110 and the hard mask layer 160 (FIGS. 3-4). For example, openings (such as an opening or trench 420 formed above at least a portion of the first conductive structure 140) for conductive metal lines, contact holes, via holes, and the like, are etched into densified regions (such as the densified region 330 in FIG. 3) of the second dielectric layer 130. Densified sidewalls 430, portions of the densified region 330 (FIG. 3), remain adjacent sides 440 of the opening 420. The densification implant 300 increases the density of the densified sidewalls 430 of the opening 420, and, hence, reinforces and strengthens the densified sidewalls 430 of the opening 420. The opening 420 may be formed by using a variety of known anisotropic etching techniques, such as a reactive ion etching (RIE) process using hydrogen bromide (HBr) and argon (Ar) as the etchant gases, for example. Alternatively, an RIE process with CHF₃and Ar as the etchant gases may be used, for example. Dry etching may also be used in various illustrative embodiments. The etching may stop at the etch stop layer 110.

[0032] As shown in FIG. 5, the trimmed photomask 250 and the hard mask layer 160 are then stripped, the etch stop layer 10 is removed above the first conductive structure 140, and a thin barrier metal layer of tantalum (Ta) 525A and a copper seed layer 525B are applied to the entire surface using vapor-phase deposition (FIG. 5). The barrier metal layer 525A and the Cu seed layer 525B blanket-deposit an entire upper surface 530 of the second dielectric layer 130 as well as surfaces of the sides 440 and bottom areas 450 of the opening 420, forming a conductive surface 535, as shown in FIG. 5.

[0033] The barrier metal layer 525A may be formed of at least one layer of a barrier metal material, such as tantalum or tantalum nitride, and the like. For example, the barrier metal layer 525A may also be formed of titanium nitride, titanium-tungsten, nitrided titanium-tungsten, or another suitable barrier material. The copper seed layer 525B may be formed on top of the one or more barrier metal layers 525A by physical vapor deposition (PVD) or chemical vapor deposition (CVD), for example.

[0034] The bulk of the copper trench-fill is frequently done using an electroplating technique, where the conductive surface 535 is mechanically clamped to an electrode (not shown) to establish an electrical contact, and the structure 101) is then immersed in an electrolyte solution containing Cu ions. An electrical current is then passed through the wafer-electrolyte system to cause reduction and deposition of Cu on the conductive surface 535. In addition, an alternating-current bias of the wafer-electrolyte system has been considered as a method of self-planarizing the deposited Cu film, similar to the deposit-etch cycling used in high-density plasma (HDP) tetraethyl orthosilicate (TEOS) dielectric depositions. In various alternative embodiments, a metal seed layer (other than a Cu seed layer) may be electroplated to form a metal structure in the opening or trench 420 formed above at least a portion of the first conductive structure 140.

[0035] As shown in FIG. 6, this process typically produces a conformal coating of Cu 640 of substantially constant thickness across the entire conductive surface 535. As shown in FIG. 7, once a sufficiently thick layer of Cu 640 has been deposited, the layer of Cu 640 is planarized using chemical mechanical polishing (CMP) techniques. The planarization using CMP clears all Cu and barrier metal from the entire upper surface 530 of the second dielectric layer 130, leaving the Cu 640 only in a metal structure such as a Cu-filled trench, forming a Cu-interconnect 745, adjacent remaining portions 725A and 725B of the one or more barrier metal layers 525A and copper seed layer 525B (FIGS. 5 and 6), respectively, as shown in FIG. 7.

[0036] As shown in FIG. 7, the Cu-interconnect 745 may be formed by annealing the Cu 640, adjacent the remaining portions 725A and 725B of the one or more barrier metal layers 525A and copper seed layer 525B (FIGS. 5 and 6), to the first conductive structure 140. The anneal process may be performed in a traditional tube furnace, at a temperature ranging from approximately 100-500° C., for a time period ranging from approximately 10-180 minutes, in a nitrogen-containing ambient that may comprise at least one of N₂, H₂, Ar, NH₃, and the like. Alternatively, the anneal process may be a rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 100-500° C. for a time ranging from approximately 10-180 seconds in a nitrogen-containing ambient that may comprise at least one of N₂, H₂, Ar, and the like.

[0037] As shown in FIG. 8, the low K second dielectric layer 130 may be planarized, as needed, using chemical mechanical polishing (CMP) techniques. Planarization would leave the planarized low K second dielectric layer 130 adjacent the Cu-interconnect 745 and above the etch stop layer 110, forming a Cu-interconnect layer 800. The Cu-interconnect layer 800 may comprise the Cu-interconnect 745 adjacent the densified regions 430 of the second dielectric layer 130. The Cu-interconnect layer 800 may also comprise the etch stop layer 110. As shown in FIG. 8, the Cu-interconnect layer 800 may also comprise an etch stop layer 820 (also known as a “hard mask” and typically formed of silicon nitride, Si₃N₄, or SiN, for short) formed and patterned above the second dielectric layer 130 and above at least a portion of the Cu-interconnect 745.

[0038] As shown in FIG. 9, the Cu-interconnect layer 800 may be an underlying structure layer (similar to the structure 100) to a Cu-interconnect layer 900. The Cu-interconnect layer 900 may comprise a Cu-filled trench 940 adjacent a densified region 945 of a planarized low K dielectric layer 935, and an intermetal via connection 910. The intermetal via connection 910 may be a Cu structure similar to the first Cu structure 140, and the intermetal via connection 910 may be annealed to the Cu-filled trench 940 in a similar fashion to the anneal described above in relation to the formation of the Cu-interconnect 745 (FIG. 7). The Cu-interconnect layer 900 may also comprise the etch stop layer 820 and/or etch stop layer 915 and/or etch stop layer 920 (also known as “hard masks” and typically formed of silicon nitride, Si₃N₄, or SiN, for short) formed and patterned above the planarized low K dielectric layers 925 and/or 935, respectively. The etch stop layer 920 may also be formed above at least a portion of the Cu-filled trench 940.

[0039] As shown in FIG. 10, an MOS transistor 1010 may be an underlying structure layer (similar to the structure 100) to a Cu-interconnect layer 1000. The Cu-interconnect layer 1000 may comprise Cu-filled trenches 1020 and copper intermetal via connections 1030 adjacent densified regions 1050 of a planarized low K dielectric layer 1040. The copper intermetal via connections 1030 may be Cu structures similar to the first Cu structure 140, and the copper intermetal via connections 1030 may be annealed to the second Cu structures 1020 in a similar fashion to the anneal described above in relation to the formation of the Cu-interconnect 745 (FIG. 7).

[0040] As shown in FIG. 11, a first dielectric layer 1105 and a first conductive structure 1125 (such as a copper intermetal via connection) may be formed above a structure 1100 such as a semiconducting substrate. However, the present invention is not limited to the formation of a Cu-based interconnect above the surface of a semiconducting substrate such as a silicon wafer, for example. Rather, as will be apparent to one skilled in the art upon a complete reading of the present disclosure, a Cu-based interconnect formed in accordance with the present invention may be formed above previously formed semiconductor devices and/or process layer, e.g., transistors, or other similar structure. In effect, the present invention may be used to form process layers on top of previously formed process layers. The structure 1100 may be an underlayer of semiconducting material, such as a silicon substrate or wafer, or, alternatively, may be an underlayer of semiconductor devices (see FIG. 20, for example), such as a layer of metal oxide semiconductor field effect transistors (MOSFETs), and the like, and/or a metal interconnection layer or layers (see FIG. 19, for example) and/or an interlayer dielectric (ILD) layer or layers, and the like.

[0041] In a dual-damascene copper process flow, according to various embodiments of the present invention, as shown in FIGS. 11-18, a second dielectric layer 1120 is formed above the first dielectric layer 1105 and above the first conductive structure 1125. A third dielectric layer 1130 is formed above the second dielectric layer 1120. A patterned photomask 1150 is formed above the third dielectric layer 1130, using photolithography, for example. The first dielectric layer 1105 has an etch stop layer (ESL) 1110 (also known as a “hard mask” and typically formed of silicon nitride, Si₃N₄, or SiN, for short) formed and patterned thereon, between the first dielectric layer 1105 and the second dielectric layer 1120. Similarly, the second dielectric layer 1120 has an etch stop layer 1115 (also typically formed of SiN) formed and patterned thereon, between the second dielectric layer 1120 and the third dielectric layer 1130.

[0042] As will be described in more detail below in conjunction with FIG. 14, the first etch stop layer 1110 and a second etch stop layer 1115 define a lower (via) portion of the copper interconnect formed in the dual-damascene copper process flow. If necessary, the third dielectric layer 1130 may be planarized using chemical-mechanical planarization (CMP). The third dielectric layer 1130 has a hard mask layer 1160 (typically also SiN) formed and patterned thereon, using the patterned photomask 1150, the hard mask layer 1160 being disposed between the third dielectric layer 1130 and the patterned photomask 1150.

[0043] The first, second and third dielectric layers 1105, 1120 and 1130 may be formed from a variety of “low dielectric constant” or “low K” (K is less than or equal to about 4) dielectric materials. The low K first, second and third dielectric layers 1105, 1120 and 1130 may be formed by a variety of known techniques for forming such layers, e.g, a chemical vapor deposition (CVD) process, a low-pressure CVD (LPCVD) process, a plasma-enhanced CVD (PECVD) process, a sputtering process, a physical vapor deposition (PVD) process, a spin-on coating process (such as a spin-on glass process), and the like, and may each have a thickness ranging from approximately 1000 Å-5000 Å, for example.

[0044] The low K first, second and third dielectric layers 1105, 1120 and 1130 may be formed from a variety of low K dielectric materials, where K is less than or equal to about 4. Examples include Applied Material's Black Diamond®, Novellus® Coral®, Allied Signal's Nanoglass®, JSR's LKD5104, and the like. In one illustrative embodiment, the low K first, second and third dielectric layers 1105, 1120 and 1130 are each comprised of Applied Material's Black Diamond®, each having a thickness of approximately 5000 Å, each being formed by being blanket-deposited by a PECVD.

[0045] As shown in FIG. 12, the patterned photomask 1150 is trimmed, using a controlled photoresist trim, for example, forming a trimmed photomask 1250. The patterned photomask 1150 may be trimmed by ashing, using a molecular oxygen (O₂) ashing, for example. Approximately 100-500 Å of the patterned photomask 1150 may be trimmed by the ashing.

[0046] As shown in FIG. 13, a densification implant 1300 (indicated by the arrows) may be implanted into the low K third dielectric layer 1130 to form a densified region 1330 in the low K third dielectric layer 1130 above at least a portion of the first conductive structure 1125. The densification implant 1300 increases the density of the low K third dielectric layer 1130 in the densified region 1330 by about 5-50%, and, hence, reinforces and strengthens the low K third dielectric layer 1130 in the densified region 1330 prior to etching.

[0047] In various illustrative embodiments, the densified region 1330 may be formed by being implanted with a densification dose of silicon (Si), silicon dioxide (SiO₂), germanium (Ge), and the like. The densification dose of the densification implant 1300 may range from about 5.0×10¹³−2.0×10¹⁵ions/cm²at an implant energy ranging from about 5-50 keV. The densified region 1330 may be subjected to a rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 400-1000° C. for a time ranging from approximately 5-60 seconds. The RTA process may activate the densification implant 1300 and reinforce the densification process.

[0048] As shown in FIG. 14, a metallization pattern is then formed by using the etch stop layer 1110, and the hard mask layers 1115 and 1160 (FIGS. 13-14). For example, first and second openings, such as via 1420 and trench 1425, for conductive metal lines, contact holes, via holes, and the like, are etched into densified regions (such as the-densified region 1330 in FIG. 13) of the third dielectric layer 1130. Densified sidewalls 1430, portions of the densified region 1330 (FIG. 13), remain adjacent sides 1440 of the opening 1425. The densification implant 1300 increases the density of the densified sidewalls 1430 of the opening 1425, and, hence, reinforces and strengthens the densified sidewalls 1430 of the opening 1425.

[0049] The first and second openings 1420 and 1425 may be formed by using a variety of known anisotropic etching techniques, such as a reactive ion etching (RIE) process using hydrogen bromide (HBr) and argon (Ar) as the etchant gases, for example. Alternatively, an RIE process with CHF₃and Ar as the etchant gases may be used, for example. Dry etching may also be used in various illustrative embodiments. The etching may stop at the etch stop layer 1110.

[0050] As shown in FIG. 15, the trimmed photomask 1250 and the hard mask layer 1160 are then stripped, the etch stop layer 1110 is removed above the first conductive structure 1125, and a thin barrier metal layer of tantalum (Ta) 1525A and a copper seed layer 1525B are applied to the entire surface using vapor-phase deposition (FIG. 15). The barrier metal layer 1525A and the Cu seed layer 1525B blanket-deposit an entire upper surface 1530 of the third dielectric layer 1130 as well as the sides 1440 and bottom areas 1450 of the first and second openings 1420 and 1425, forming a conductive surface 1535, as shown in FIG. 15.

[0051] The barrier metal layer 1525A may be formed of at least one layer of a barrier metal material, such as tantalum or tantalum nitride, and the like. For example, the barrier metal layer 1525A may also be formed of titanium nitride, titanium-tungsten, nitrided titanium-tungsten, or another suitable barrier material. The copper seed layer 1525B may be formed on top of the one or more barrier metal layers 1525A by physical vapor deposition (PVD) or chemical vapor deposition (CVD), for example.

[0052] The bulk of the copper trench-fill is frequently done using an electroplating technique, where the conductive surface 1535 is mechanically clamped to an electrode (not shown) to establish an electrical contact, and the structure 1100 is then immersed in an electrolyte solution containing Cu ions. An electrical current is then passed through the wafer-electrolyte system to cause reduction and deposition of Cu on the conductive surface 1535. In addition, an alternating-current bias of the wafer-electrolyte system has been considered as a method of self-planarizing the deposited Cu film, similar to the deposit-etch cycling used in high-density plasma (HDP) tetraethyl orthosilicate (TEOS) dielectric depositions. In various alternative embodiments, a metal seed layer (other than a Cu seed layer) may be electroplated to form a metal structure in the openings 1220 and 1230 formed above at least a portion of the first conductive structure 1125.

[0053] As shown in FIG. 16, this process typically produces a conformal coating of Cu 1640 of substantially constant thickness across the entire conductive surface 1535. As shown in FIG. 17, once a sufficiently thick layer of Cu 1640 has been deposited, the layer of Cu 1640 is planarized using chemical mechanical polishing (CMP) techniques. The planarization using CMP clears all Cu and barrier metal from the entire upper surface 1530 of the third dielectric layer 1130, leaving the Cu 1640 only in a metal structure such as a Cu-filled trench and via, forming a Cu-interconnect 1745, adjacent remaining portions 1725A and 1725B of the one or more barrier metal layers 1525A and copper seed layer 1525B (FIGS. 15 and 16), respectively, as shown in FIG. 17.

[0054] As shown in FIG. 17, the Cu-interconnect 1745 may be formed by annealing the Cu 1640, adjacent the remaining portions 1725A and 1725B of the one or more barrier metal layers 1525A and copper seed layer 1525B (FIGS. 15 and 16), to the first conductive structure 1125. The anneal process may be performed in a traditional tube furnace, at a temperature ranging from approximately 100-500° C., for a time period ranging from approximately 10-180 minutes, in a nitrogen-containing ambient that may comprise at least one of N₂, H₂, Ar, NH₃, and the like. Alternatively, the anneal process may be a rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 100-500° C. for a time ranging from approximately 10-180 seconds in a nitrogen-containing ambient that may comprise at least one of N₂, H₂, Ar, and the like.

[0055] As shown in FIG. 18, the low K third dielectric layer 1130 may be planarized, as needed, using chemical mechanical polishing (CMP) techniques. Planarization would leave the planarized low K third dielectric layer 1130 adjacent the Cu-interconnect 1745 and above the etch stop layer 1115, forming a portion of a Cu-interconnect layer 1800. The Cu-interconnect layer 1800 may comprise the Cu-interconnect 1745 adjacent the densified regions 1430 of the third dielectric layer 1130. The Cu-interconnect layer 1800 may also comprise the first etch stop layer 1110. As shown in FIG. 18, the Cu-interconnect layer 1800 may also comprise an etch stop layer 1820 (also known as a “hard mask” and typically formed of silicon nitride, Si₃N₄, or SiN, for short) formed and patterned above the third dielectric layer 1130 and above at least a portion of the Cu-interconnect 1745.

[0056] As shown in FIG. 19, the Cu-interconnect layer 1800 may be an underlying structure layer (similar to the structure 1100) to a Cu-interconnect layer 1900. In various illustrative embodiments, the Cu-interconnect layer 1900 may comprise a Cu-filled trench 1940 adjacent densified regions 1945 of a planarized low K dielectric layer 1935, an intermetal via connection 1910, and an etch stop layer 1915 between the low K dielectric layers 1935 and 1925. The intermetal via connection 1910 may be a Cu structure similar to the first Cu structure 1125, and the intermetal via connection 1910 may be annealed to the Cu-filled trench 1940 in a similar fashion to the anneal described above in relation to the formation of the Cu-interconnect 745 (FIG. 7). The Cu-interconnect layer 1900 may also comprise the etch stop layer 1820 and/or an etch stop layer 1920 formed and patterned above the planarized low K dielectric layer 1935 and above at least a portion of the Cu-filled trench 1940.

[0057] In various alternative illustrative embodiments, the Cu-interconnect layer 1900 may be similar to the Cu-interconnect layer 1800, the Cu-interconnect layer 1900 having a Cu-interconnect disposed therein (not shown) that is similar to the Cu-interconnect 1745 (FIGS. 17-18), for example. The Cu-interconnect disposed in the Cu-interconnect layer 1900 may be annealed to the Cu-interconnect 1745 disposed in the Cu-interconnect layer 1800 in a similar fashion to the anneal described above in relation to the formation of the Cu-interconnect 1745 (FIG. 17).

[0058] As shown in FIG. 20, an MOS transistor 2010 may be an underlying structure layer (similar to the structure 1100) to a Cu-interconnect layer 2000. The Cu-interconnect layer 2000 may comprise Cu-filled trenches and vias 2020 adjacent densified regions 2050 a planarized low K dielectric layer 2040. The Cu-filled trenches and vias 2020 may be annealed to an underlying conductive structure such as source/drain regions 2015 of the MOS transistor 2010 in a similar fashion to the anneal described above in relation to the formation of the Cu-interconnect 1745 (FIG. 17).

[0059] The dual-damascene copper process flow according to various embodiments of the present invention, as shown in FIGS. 11-18, combines the intermetal via connection formation with the Cu trench-fill formation by etching a more complex pattern before the formation of the barrier metal layer and Cu seed layer and before the Cu trench-fill. The trench etching continues until the via hole (such as the first opening 1420 in FIG. 14) has been etched out. The rest of the dual-damascene copper process flow according to various embodiments of the present invention, as shown in FIGS. 15-18, is essentially identical with the corresponding single-damascene copper process flow according to various embodiments of the present invention, as shown in FIGS. 5-8. Overall, however, the dual-damascene copper process flow according to various embodiments of the present invention significantly reduces the number of processing steps and is a preferred method of achieving Cu-metallization.

[0060] Any of the above-disclosed embodiments of a method of forming a copper interconnect enables a copper interconnect to be formed using conventional damascene techniques in conjunction with densified low K dielectric materials that are far more robust than the conventional low K materials typically used in conventional damascene techniques. The densified low K dielectric materials are far less susceptible to damage during the etching and subsequent processing steps of the conventional damascene techniques than are the conventional low K materials. By forming, a densified low K dielectric layer adjacent the copper interconnect, all of the advantages of using a low K dielectric layer to reduce the capacitance and RC delays between adjacent copper interconnects are retained, without any of the difficulties of forming the copper interconnect using a conventional undensified low K dielectric during the conventional damascene processing.

[0061] The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a−b”) disclosed herein is to be understood as referring to the power set (the set of all subsets) of the respective range of values, in the sense of Georg Cantor. Accordingly, the protection sought herein is as set forth in the claims below.