Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS20050194255 A1
Publication typeApplication
Application numberUS 10/793,990
Publication dateSep 8, 2005
Filing dateMar 4, 2004
Priority dateMar 4, 2004
Publication number10793990, 793990, US 2005/0194255 A1, US 2005/194255 A1, US 20050194255 A1, US 20050194255A1, US 2005194255 A1, US 2005194255A1, US-A1-20050194255, US-A1-2005194255, US2005/0194255A1, US2005/194255A1, US20050194255 A1, US20050194255A1, US2005194255 A1, US2005194255A1
InventorsChandra Tiwari
Original AssigneeTiwari Chandra S.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Self-activated electroless metal deposition
US 20050194255 A1
Abstract
A method of plating metal, such as to form a metal interconnect on a semiconductor assembly is described. The metal plating process is a one-step, self-activating (self-initiating) electroless process utilized to deposit metal, such as nickel on varying types of metal substrates, such as tungsten and copper substrates, by adjusting the pH and temperature of a metal based liquid bath solution.
Images(9)
Previous page
Next page
Claims(37)
1. A method of forming a self-initiating bath for the forming of a metal connection to a metal substrate comprising:
forming a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;
adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (EO reducing agent) is greater than the net oxidation potential sum (|EO|) of the oxidation potential of the substrate metal (EO substrate metal) plus the reduction potential of the complexed metal (EO complexed Metal); and
maintaining a bath solution temperature and the pH at sufficient levels to cause the bath solution to operate as the self-initiating bath.
2. The method of claim 1, wherein the metal substrate comprises Copper or Tungsten.
3. The method of claim 1, wherein the complexed metal comprises complexed nickel (Ni).
4. The method of claim 1, wherein the complexing agent comprises Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
5. The method of claim 1, wherein the reducing agent comprises Ammonium Hypophosphite.
6. The method of claim 1, wherein the reducing agent comprises Dimethylaminoborane (DMAB).
7. The method of claim 1, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
26 g/l of Ammonium Hypophosphite; and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
8. The method of claim 7, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.
9. The method of claim 1, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
4 g/l of Dimethylaminoborane (DMAB); and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
10. The method of claim 9, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.
11. A method of forming a metal interconnect on a semiconductor assembly comprising:
subjecting a metal substrate to a metal deposition bath solution with a pH level and an operating temperature level, the metal deposition bath solution comprising comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;
adjusting the pH level of the bath solution such that an oxidation potential of the reducing agent (EO reducing agent) is greater than the net oxidation potential sum (|EO|) of the oxidation potential of the substrate metal (EO substrate metal) plus the reduction potential of the complexed metal (EO complexed Metal); and
maintaining the operating temperature level and the pH at sufficient levels to cause the bath solution to operate as the self-initiating bath.
12. The method of claim 11, wherein the metal substrate comprises Copper or Tungsten.
13. The method of claim 11, wherein the complexed metal comprises complexed nickel (Ni).
14. The method of claim 11, wherein the complexing agent comprises Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
15. The method of claim 11, wherein the reducing agent comprises Ammonium Hypophosphite.
16. The method of claim 11, wherein the reducing agent comprises Dimethylaminoborane (DMAB).
17. The method of claim 11, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
26 g/l of Ammonium Hypophosphite; and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
18. The method of claim 17, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.
19. The method of claim 11, wherein the bath solution comprises:
26 g/l of NiSO40.6H2O;
4 g/l of Dimethylaminoborane (DMAB); and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
20. The method of claim 9, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.
21. A method of depositing a first metal on a second metal by a one step self-initiating bath comprising:
forming a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;
adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (EO reducing agent) is greater than the net oxidation potential sum (|EO|) of the oxidation potential of the substrate metal (EO substrate metal) plus the reduction potential of the complexed metal (EO complexed Metal); and
maintaining a bath solution temperature and the pH at sufficient levels such that oxidation potential sum (|EO|) is great enough to reduce the first metal and thus displace the second metal with the first metal.
22. The method of claim 21, wherein the second metal comprises Copper or Tungsten.
23. The method of claim 21, wherein the first metal comprises Nickel.
24. The method of claim 21, wherein the complexed metal comprises complexed nickel (Ni).
25. The method of claim 21, wherein the complexing agent comprises Ethylene di-amine tetra-acetic acid (EDTA).
26. The method of claim 21, wherein the reducing agent comprises Hypophosphite.
27. The method of claim 21, wherein the reducing agent comprises Dimethylaminoborane (DMAB).
28. The method of claim 21, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
26 g/l of Ammonium Hypophosphite; and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
29. The method of claim 28, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.
30. The method of claim 21, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
4 g/l of Dimethylaminoborane (DMAB); and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
31. The method of claim 9, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.
32. A method of depositing Nickel by a one step self-initiating bath comprising:
presenting a Copper or Tungsten substrate to a bath solution comprising a complexed metal solution, a complexing agent solution and a reducing agent solution;
adjusting the pH of the bath solution such that an oxidation potential of the reducing agent (EO reducing agent) is greater than the net oxidation potential sum (|EO|) of the oxidation potential of the substrate metal (EO substrate metal) plus the reduction potential of the complexed metal (EO complexed Metal);
maintaining a bath solution temperature and the pH at sufficient levels such that oxidation potential sum (|EO|) is great enough to reduce the nickel and thus displace the Copper of Tungsten substrate with a Nickel nucleation layer; and
continuing the self-activating bath to deposit Nickel on the Nickel nucleation layer.
33. The method of claim 32, wherein the complexed metal comprises complexed nickel (Ni).
34. The method of claim 32, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
26 g/l of Ammonium Hypophosphite; and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
35. The method of claim 34, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 85° C.
36. The method of claim 32, wherein the bath solution comprises:
26 g/l of NiSO46H2O;
4 g/l of Dimethylaminoborane (DMAB); and
23 g/ of Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA).
37. The method of claim 36, wherein the pH of the bath solution is greater than 7.0 and the bath solution temperature is greater than 55° C.
Description
FIELD OF THE INVENTION

This invention relates to electroless deposition processes to form semiconductor devices. The invention particularly relates to electroless nickel deposition methods to fabricate conductive interconnects for semiconductor devices.

BACKGROUND OF THE INVENTION

The performance characteristics and reliability of integrated circuits have become increasingly dependent on the structure and attributes of the vias (openings) and interconnects which are used to carry electronic signals between semiconductor devices on integrated circuits or chips. Advances in the fabrication of integrated circuits have resulted in increases in the density and number of semiconductor devices contained on a typical chip. Interconnect structure and formation technology has lagged behind these advances, however, and is now a major limitation on the signal speed of integrated circuits.

Deposition of a metal layer generally occurs through one of the following techniques; chemical vapor deposition (CVD); physical vapor deposition (PVD), also known as sputtering; or electrochemical deposition. CVD involves high temperatures, which can lead to cold creep effects (of the metal) and an increased chance of impurity contamination over other methods, while sputtering has problems yielding sufficient step coverage and density at small line widths. Electrochemical deposition has its problems as well as it requires continuous seeding, which is a big challenge in high aspect ratio vias.

Nickel has been used to fill vias and a typical method of depositing nickel is by electroless deposition. To deposit nickel in vias, a thin conformal seed of conducting material like titanium (Ti) or titanium nitride (TiN) is deposited, which is then activated by activation based solutions, typically palladium (Pd). The Pd is adsorbed in the seed layer, which acts as a nucleation site for nickel deposition. In very high aspect ratio vias, the top of the vias can pinch off before the vias are completely filled, thus leaving voids which might have some nickel bath solution trapped within. The trapped nickel bath solution can burst in further processing of the wafer at elevated temperatures, resulting in a fractured interconnect or a partially filled via, that will also increase the resistance of the interconnect.

Another approach to fill vias by electroless nickel is bottom-up deposition in which nickel grows up from the bottom of the via. This requires selective activation of the substrate at the bottom of the vias.

FIGS. 1-3 depict a typical method to fill a via with nickel using an activation bottom-up approach by electroless deposition. As seen in FIG. 1, a metal pad 11, such as copper or tungsten is formed in substrate 10 and layers of isolation material, including a silicon dioxide (SiO2) layer 12, formed from tetraethyl orthosilicate (TEOS), a second oxide layer 13, formed from a Barrier Low dielectric constant (BLOK) material and silicon nitride (SiNx) layer 14, are formed in sequence over the metal pad 11 and substrate 10. A via 15 is etched into the SiO2 layer 12, the second oxide layer 13 and the SiNx layer 14 to provide access the underlying metal pad 11.

The substrate assembly is dipped into a liquid bath containing a source of a heavy metal, which is typically palladium (Pd). As shown in FIG. 2, the heavy metal Pd 20 becomes an activation source to chemically activate a metal, such as copper or tungsten, to accept nickel formation when the substrate assembly is dipped into a second bath containing Ni. As mentioned, this activation process requires two steps to deposit Ni. For example, in the first step, the metal material (i.e., such as Cu and W) becomes a chemically activated liquid bath containing palladium (i.e., PdCl2/HF, PdSO4/HF, etc.). In the second step, Ni is deposited in the activated material when the substrate assembly is dipped into a liquid bath containing a Ni source.

However, as shown in FIG. 3 the selective activation of the substrate at the bottom of via 15 in many cases is not achievable. A Pd based solution used for activating the bottom of via 15 also randomly activates dielectric materials, such as silicon oxide, silicon nitride, BLOK, etc., that reside both inside and outside the via. This random activation inside via 15 may lead to a discontinuous deposition of nickel 30 that forms a discontinuous plug 31, with the nickel separated by void 32, which will result in a defective interconnect between Cu pad 11 and a subsequently formed upper metal layer.

What is needed is a method to form interconnects with the reduction of voids or even substantially void free interconnects, using nickel as the fill material that has a high selectivity to the metal residing at the bottom of a via, and the interconnects fabricated in integrated circuits of semiconductor devices, a need of which is addressed by the following disclosure of the present invention that will become apparent to those skilled in the art.

SUMMARY OF THE INVENTION

The present invention discloses a metal plating process that is a one-step, self-activating (self-initiating) electroless process utilized to deposit metal, such as nickel on varying types of metal substrates, such as tungsten and copper substrates, by adjusting the pH and temperature of a metal based liquid bath solution. Exemplary implementations of the present invention include methods utilized to deposit nickel on tungsten and copper substrates by adjusting the pH and temperature of a nickel based liquid bath solution based on the amount of a complexing agent concentration and a reducing agent concentration used to make up the bath solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are prior art figures demonstrating a semiconductor fabrication method to form a metal interconnect using the process of chemical activation.

FIG. 4 represents a portion of a semiconductor assembly depicting a cross-sectional view of a semiconductor substrate section showing a conductive plug connecting between a source/drain region of the transistor and a conductive pad and interconnect isolation materials formed thereover.

FIG. 5 is a subsequent cross-sectional view taken from FIG. 4 after the forming and patterning of photoresist over the isolation materials and a subsequent etch to open a via that allows access to the underlying conductive pad.

FIG. 6 is a subsequent cross-sectional view taken from FIG. 5 following the submersion of the semiconductor assembly into a self-activating metal solution.

FIG. 7 is a subsequent cross-sectional view taken from FIG. 6 following the formation of a metal interconnect material formed in the via by utilizing the self-activation metal solution to fill the via by bottom-up electroless deposition.

FIG. 8 is a subsequent cross-sectional view taken from FIG. 7 following a planarization step to form a planar surface on the metal interconnect for further processing of the semiconductor assembly.

FIG. 9 is a simplified block diagram of a semiconductor system comprising a processor and memory device to which the present invention may be applied.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the terms “wafer” and “substrate” are to be understood as a semiconductor-based material including silicon, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a “wafer” or “substrate” in the following description, previous process steps may have been utilized to form regions or junctions in or over the base semiconductor structure or foundation. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, silicon-on-insulator, silicon-on-saphire, germanium, or gallium arsenide, among others.

The following exemplary implementation is in reference to the formation of metal interconnects formed in a semiconductor device and in particular a method to form conductive metal interconnects between metal layers. While the concepts of the present invention are conducive to forming interconnects between metal layers for semiconductor devices, such as memory devices, the concepts taught herein may be applied to other semiconductor processes or non-semiconductor processes like PCB (printed circuit board: Ni deposition on copper), etc., that would likewise benefit from the use of the process disclosed herein. Therefore, the depiction of the present invention in reference to forming conductive metal interconnects between metal layers for semiconductor devices, such as memory devices, is not meant to so limit the extent to which one skilled in the art may apply the concepts taught hereinafter.

In the manufacturing of integrated circuits, many metal levels are used to accommodate the connections required throughout the device and typically these connections or interconnects are made in relatively confined spaces. Generally tungsten, copper or aluminum-copper alloys are used to form metal level interconnects. The metal levels are interposed by vias (or openings), which are typically very deep and difficult to fill. The vias can be created by etching an ILD (inter level dielectric) and a MLD (middle dielectric layer), which can be made of a single dielectric film or many dielectric films of different materials and properties know to those skilled in the art. Thus, one metal level to another metal level (where each metal level uses such metals as W, Cu or Al—Cu) will be interposed by vias.

Referring now to FIG. 4, an assembly is processed to the point where transistor structures are formed into a conductive silicon substrate 40, the transistor structures made up of transistor gates 41 that are separated from the underlying silicon substrate. Source/drain implant regions 42 span between the gates and a transistor isolation material 43, such as borophosphosilicate gate (BPSG) is formed over the transistor structures. A conductive plug 45, made from materials such as tungsten (W) is formed in an opening (or via) through the BPSG and connects to a poly plug 44, which in turn connects to a source/drain region 42 of the transistor. The surface of the W plug and the BPSG is planarized and a metal pad 46, preferably made of copper (Cu) or tungsten, is formed on the W plug 45 and makes connection therewith.

In this example, Cu is selected for the metal pad, though W may be used as well. Interconnect isolation materials, comprising SiO2 layer 47, second oxide layer 48 and SiNx layer 49 are sequentially formed over metal pad 46. The isolations materials may vary in the type of materials, the number of materials used (a single material may be used) and the order of material placement, depending on what is used in a given fabrication process. The three isolation materials used in this example are selected to demonstrate the effectiveness of the present invention in comparison to the prior art discussed previously.

Referring now to FIG. 5, a photoresist 50 is formed and then patterned over the isolation materials and a subsequent etch to open a via 51 is performed that allows access to the underlying Cu pad 46.

An example of the present invention is depicted in FIGS. 6-8 in conjunction with the processed assembly of FIGS. 4 and 5. Referring now to FIG. 6, the semiconductor assembly is subjected to a bath 60 having a self-activating metal solution comprising nickel (Ni). The activation free process is an electroless bath that can initiate nucleation of Ni in W or Cu, thus forming a Ni monolayer 61 (or Ni nucleation region). FIG. 6 depicts the results of the Ni+ ions displacing the Cu++ ions, which causes the monolayer of Ni 61 to cut into the surface of the Cu pad 46. The activation free Ni electroless process (i.e., self-initiating bath) contains a Ni complexed agent, such as NiSO46H2O, a reducing agent, such as Ammonium hypophosphite or Dimethylaminoborane (DMAB) (if used), a complexing agent such as Ethylene di-amine tetra-acetic acid (EDTA), succinic acid, etc., and a stabilizing agent (if desired).

Referring now to FIG. 7, the self-activation process continues to deposit Ni fill 71 on the Ni nucleation region until the process is stopped once the via 51 is filled. The self-activation process demonstrated in this example of the present invention provides a one step process for filling a via with nickel by utilizing the self-activation metal solution to fill the via by a bottom-up electroless deposition.

Referring now to FIG. 8 a planarizing step is performed to form a planar surface on the metal interconnect 81, which is typically desirable for further processing of the semiconductor assembly. The fabrication process then continues to complete the substrate assembly or device.

The exemplary embodiment has been discussed in reference to a self-activation method of forming a Ni interconnect for use in semiconductor assemblies, such as memory devices. However, the concepts taught in the exemplary embodiments, may be utilized by one of ordinary skill in the art to form such metal interconnects for use in most all semiconductor applications. For example, the present invention may be applied to a semiconductor system, such as the one depicted in FIG. 9, the general operation of which is known to one skilled in the art.

FIG. 9 represents a general block diagram of a semiconductor system comprising a processor 90 and a memory device 91 showing the basic sections of a memory integrated circuit, such as row and column address buffers, 93 and 94, row and column decoders, 95 and 96, sense amplifiers 97, memory array 98 and data input/output 99, which are manipulated by control/timing signals from the processor through control 92.

The principles used to determine the controlling parameters of a self-initiating baths of the present invention are demonstrated in the following examples. Two baths were created to be self-initiating baths, including the solution concentrations of which are first characterized by the following general bath solution.

General Bath Solution:

    • Metal Complexed Agent (g/l)+Reducing Agent (g/l)+Complexing Agent (g/l).
      Also, the complexing agent may be Ethylene di-amine tetra-acetic acid (EDTA), Potassium salt of EDTA, or Ammonium salt of ETDA.
      Hypophosphite Based Bath:
    • (A) NiSO46H2O (26 g/l)+Ammonium Hypophosphite (26 g/l)+Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA) (23 g/l),
      • pH>7.0, temperature>85° C.;
        DMAB Based Bath:
    • (B) NiSO46H2O (26 g/l)+Dimethylaminoborane (DMAB) (4 g/l)+Potassium salt of EDTA (23 g/l),
      • pH>7.0, temperature>55° C.

Keys to providing a self-activation or a self-initiation process in the above recipes are pH and temperature as demonstrated hereinafter. The proposed mechanism for the self-initiation to occur is that if the oxidation potential of a reducing agent (EO reducing agent) is higher than the oxidation potential sum (|EO|) of the oxidation potential of the substrate metal (EO substrate metal) plus the reduction potential of the complexed metal (EO complexed Metal), in this case Ni (EO complexed Ni), then nucleation can be achieved by a displacement of the substrate metal by Ni with the help of a reducing agent. The reducing agent is adsorbed at the substrate metal, thus resulting in a net positive potential for oxidation at the adsorption site. Therefore, if the net oxidation potential (|EO|) is great enough to reduce Ni, the metal substrate can then be displaced by Ni.

The following example demonstrates Ni deposition in copper (metal substrate) from a complexed Ni (Ni++complexed by complexing agent) and hypophosphite (reducing agent). The oxidation/reduction potentials of the following reactions can be obtained from most chemistry sources available to those skilled in the art.

First, the oxidation of a Cu substrate is demonstrated in reaction (1).
Cu→Cu+++2e , E O Cu=−0.34V  (1)

Second, the reduction of complexed Ni is demonstrated in reaction (2). (For simplicity taking Ammonium complex of Ni.)
[Ni(NH3)6]+++2e →Ni+6NH3 (aq), E O complexed Ni=−0.49V  (2)

A key is to make both reactions (1) and (2) occur in a forward direction (thermodynamically not feasible as such but backward reactions are possible by displacement of Ni by Cupric ion), the reducing agent used must have a potential EO reducing agent, greater than an EO of 0.83V as demonstrated in the following calculation.
E O =|E O Cu +E O complexed Ni|,
Then substituting in the above values for EO cu+EO complexed Ni,
E O=|−0.34V+−0.49V|=0.83V.

When considering the reducing agent, the oxidation potential is considered in the acidic or basic regime to determine if it is greater than 0.83V. Taking the reducing agent of hypophosphite in an acidic regime, hypophosphite has an oxidation potential (EO hypophosphite) of 0.50V, which is less than required as demonstrated in reaction (3).
H2PO2 +H2O+H2PO3+2H+++2e , E O hypophosphite=0.50V  (3)
Hence, Ni cannot be deposited from the above acidic system and a self-initiating bath cannot be achieved (EO hypophosphite=0.50V<0.87V).

However, hypophosphite in a basic regime has an oxidation potential of 1.57V as demonstrated below in reaction (4).
H2PO2 +3OH→HPO3 +2H2O+2e, EO hypophosphite=1.57V  (4)
Thus, hypophosphite in a basic regime can be used for a self-initiating bath that will allow Ni to displace Cu as the oxidation potential for hypophosphite (EO hypophosphite) of reaction (4) of 1.57V is greater than 0.83V (the absolute value sum of the potential EO of reactions (1) and (2)).

A complexing agent can also be chosen to help self-initiation and added to an electroless bath such that it helps in oxidizing the substrate metal. For example, comparing the oxidation of Cu in reactions (5) and (6), EDTA can help Cu oxidize.
Cu+2NH3→[Cu(NH3)2]++e, EO Cu=−0.11V  (5)
Cu+EDTA4−→[CuEDTA]+2e , E O Cu=0.216V  (6)

The results from reactions (5) and (6) show that reaction (6) will be preferred over reactions (1) above, or (5) as reaction (6) can occur in a forward direction thermodynamically while reactions (1) or (5) are not favored. However, the complexing agent will also change the reduction potential of complexed Ni. Therefore, the selection of the complexing agent should be such that the (absolute value) sum of the oxidation potential of the substrate metal and the reduction potential of complexed Ni is minimal for the complexing agents utilized.

As demonstrated above, the pH for hypophosphite based baths needs to be greater than 7.0 (basic) in order to increase the oxidation potential of hypophosphite (as shown, the oxidation potential is approximately three times greater in a basic regime than in acidic regime), so that the bath will become self-initiating and allow Ni to displace Cu.

In like manner using the steps as outlined above, it is determined that a DMAB based bath with a pH greater that 7.0 has enough oxidation potential (EO DMAB>0.87V) to initiate nucleation. When using a self-initiating bath to deposit Ni in W substrates, the bath temperature will be higher and the various solution concentrations will also be adjusted, but the same concepts apply to depositing Ni in W substrates as depositing Ni in Cu substrates.

Bath temperature must also be considered for maintaining a self-initiating bath. Referring back to the examples of two baths that can be used, again listed as bath (A) and (B) below in the form of the general bath solution makeup.

General Bath Solution:

    • Ni Complexed Agent (g/l)+Reducing Agent (g/l)+complexing Agent (g/l).

Hypophosphite Based Bath:

    • NiSO4.6H2O (26 g/l)+Ammonium Hypophosphite (26 g/l)+Potassium salt of Ethylene di-amine tetra-acetic acid (EDTA) (23 g/l),
    • pH>7.0, temperature>85° C.;

DMAB Based Bath:

    • NiSO4.6H2O (26 g/l)+DMAB (Dimethylaminoborane) (4 g/l)+Potassium salt of EDTA (23 g/l),
    • pH>7.0, temperature>55° C.

As shown in bath (A) the temperature is determined to be greater than 85° C., while the temperature for bath (B) must be greater than 55° C. in order to maintain a self-initiating bath. These temperatures depend on the concentrations of bath components, i.e., the Ni++ source (complexed Ni), the complexing agent, the reducing agent and the stabilizing agent (if used). For example, in bath (A) for (26 g/l) of NiSO46H2O, (23 g/l) Potassium salt of EDTA, (26 g/l) of Ammonium Hypophosphite, the bath temperature was determined to be greater than 85° C. (the stabilizing agent, if used will also affect temperature). If the g/l of Ammonium Hypophosphite is increased the temperature required for the bath will decrease. Thus, the solution volume of each concentration must be adjusted along with the bath temperature in order to maintain a self-initiating bath. As mentioned, if desired, a stabilizer concentration may also be added to the bath in order to minimize any Ni plating within the bath by controlling the Ni nucleation as the stabilizer is absorbed in the surface and prohibits Ni plating.

It is desired that the complexing agent and stabilizer concentration be optimumized as a higher concentration of a complexing agent has a negative impact on self-initiation. However, various complexing agents can be used with above systems if the necessary temperature and pH level is maintained. The stabilizer concentration will depend on the feature size of the via fill, thus a lower concentration of a stabilizer is desired as a higher concentration reduces the self-initiation activity of the solution in small features. An increase in temperature also reduces the effect of an increase in the complexing agent concentration or stabilizer concentration.

Other baths can be constructed considering the above criteria. Temperature and concentrations of all components have an impact on self-initiation. The self-initiation regime of the bath depends on the type of substrate material (tungsten or copper) and the method of deposition of the substrate material (Atomic Layer Deposition (ALD), Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), electroplating, etc.).

Main advantages of the self-activation process of the present invention compared to the prior art bottom-up activation process described are: the activation step (using heavy metal activation) is eliminated; less chemicals are used as the need for a heavy metal solution, such as a Pd solution, is eliminated; smaller process tools are required as a process chamber is not needed for activation; fewer process parameters are involved; self-activation is very selective to Cu or W as Ni nucleation in the dielectric materials is eliminated; and the Ni fill on a semiconductor assembly, such as on a silicon wafer, can be re-plated if rework is required.

These advantages allow the self-activation process of the present invention to provide a cost efficient process that will provide a high quality interconnect that is highly desirable in the fabrication of semiconductors.

It is to be understood that, although the present invention has been described with reference to two exemplary embodiments, various modifications, known to those skilled in the art, may be made to the disclosed structure and process herein without departing from the invention as recited in the several claims appended hereto.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7226857 *Jul 30, 2004Jun 5, 2007Micron Technology, Inc.Front-end processing of nickel plated bond pads
US7485948Apr 7, 2006Feb 3, 2009Micron Technology, Inc.Front-end processing of nickel plated bond pads
US7582557Jan 13, 2006Sep 1, 2009Taiwan Semiconductor Manufacturing Co., Ltd.Process for low resistance metal cap
US7777344Apr 11, 2007Aug 17, 2010Taiwan Semiconductor Manufacturing Company, Ltd.Transitional interface between metal and dielectric in interconnect structures
US7795093Jul 29, 2008Sep 14, 2010Micron Technology, Inc.Front-end processing of nickel plated bond pads
US8043961Aug 9, 2010Oct 25, 2011Micron Technology, Inc.Method of forming a bond pad
US8349730Jun 25, 2010Jan 8, 2013Taiwan Semiconductor Manufacturing Company, Ltd.Transitional interface between metal and dielectric in interconnect structures
US8900945Oct 5, 2011Dec 2, 2014Micron Technology, Inc.Method of forming a memory device
Classifications
U.S. Classification205/101
International ClassificationC25D5/00
Cooperative ClassificationC23C18/34, H01L21/76805, C23C18/168, H01L21/288, C23C18/1637, C23C18/1651, H01L21/76874, C23C18/54, H01L21/76879
European ClassificationH01L21/768C4B, C23C18/34, H01L21/768B2C, C23C18/16B8B2, H01L21/288, C23C18/16B8H6, C23C18/54, H01L21/768C3S4, C23C18/16B8D4B
Legal Events
DateCodeEventDescription
Mar 5, 2004ASAssignment
Owner name: MICRON TECHNOLOGY, INC., IDAHO
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:TIWARI, CHANDRA S.;REEL/FRAME:015068/0519
Effective date: 20040302