Method to modulate the surface roughness of a plated deposit and create fine-grained flat bumps
The present invention relates to a plating bath consisting of a plating solution, accelerating agent and a suppressing agent and a method of forming contact formations on a semiconductor substrate. In an embodiment, the deposition of contact formations occurs in a two step deposition process wherein the deposition process has different deposition rates. Furthermore, the present invention includes a method of forming smooth, flat contact formations for use in electronic packages.
1) Field of Invention
Embodiments of this invention relate to a method for the formation of contact formations, particularly for use on semiconductor substrate and a system utilizing such contact formations.
2) Description of Related Art
Integrated circuits are formed on semiconductor substrates, such as wafers. The wafers are then sawed (or “singulated” or “diced”) into microelectronic die, also known as semiconductor chips, with each chip carrying a respective integrated circuit. Each semiconductor chip is then mounted to a package, or carrier, substrate. Often the packages are then mounted to circuit boards, such as motherboards, which may then be installed in computing systems.
The package substrate provides structural integrity to the semiconductor chips and are used to connect the integrated circuits electrically to the motherboard. On the side of the package substrate connected to the motherboard, there are contact formations, such as Ball Grid Array (BGA) solder balls, which are soldered to the motherboard. Electric signals are sent through the BGA solder balls into and out of the package. On the other side of the package substrate, there are other smaller contact formations used to connect the die to the package substrate. A modern trend for these contact formations is the use of “copper bumps” which are formed on bonding pads on the die. An underfill material, such as an epoxy or paste, may also be present between the die and the packages.
Copper bumps are typically formed using an electroplating process. The formation of the bumps begins within a depression on the surface of the die. This depression leads to a dimple or other formations on the surface of the copper bumps opposite the die. It is this dimpled surfaced which is used to connect the die to the packages.
This dimple may allow material, such as solder, underfill material, or even air, to get caught between the copper bump and the package substrate when the chip-to-package connections are made. This trapped material weakens the strength of the mechanical bond between the die and package substrates and results in a decrease in the maximum amount of current that can be conducted through the copper bumps.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention relates to plating of a semiconductor structure by use of an inventive copper bath composition. Because of the inventive use of the copper bath composition, grain size is controlled and the presence of voids is reduced. Additionally, because of the inventive use of the copper baths composition, an article results in the form of an inventive contact structure.
The seed layer 40 may be made of a conductive material such as, for example, copper, silver, gold, nickel, and or cobalt and may be deposited using PVD, CVD, ALD, electroless plating, and electroplating. The seed layer 40 may have a thickness of, for example, between 10 and 10,000 nanometers and may be formed directly over the adhesion layer 38. Due to the shape of the adhesion layer 38 and the passivation layer 28, the seed layer 40 may have a depression 42 and an upper surface thereof. In an embodiment, the seed layer 40 is a base metal layer.
The semiconductor die 10 may undergo a pre-wet and or pre-plating etch treatment prior to electroplating. A pre-wet process may entail immersing semiconductor die 10 in a solution, such as DI water, and allowing exposure to the openings in semiconductor die 10 to the solution to avoid air bubbles and other defects in the semiconductor die 10. The pre-plating etch process may involve etching the openings in semiconductor die 10 with a solution, such as sulfuric acid, to remove native oxide.
The composition of the plating bath 56 is preferably an aqueous electroplating composition. It comprises copper, at least one acid, selected from sulfuric, methane sulfonic, amidosulfuric, aminoacetic, flouroboric, and mixtures thereof and the like, at least one halogen ion, and at least two agents selected from an accelerating agent and a suppressing agent.
A preferred range of copper ions in the plating bath 56 is from about 0.1 mole/L to about 1.5 mole/L, preferably from about 0.2 mole/IL to about 1 mole/L, and more preferably about 0.23 mole/L.
In addition to copper, other metals may be combined with the copper such as refractory metals, noble metals, and other transition metals. Examples of useful refractory metals that may be combined with the copper include vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, rhenium, and the like, and combinations thereof. Examples of useful noble metals that may be combined with the copper include gold, silver. Other useful metals that may be combined with the copper include nickel, palladium, platinum, zinc, ruthenium, rhodium, cadmium, indium, and the like, and combinations thereof. Other useful metals that may be combined with copper include alkaline earth metals such as magnesium and the like. As a whole, the composition of the plating bath 56 contains a preferred range of total metal deposit ions in a range from about 0.01 mole/L to about 1.5 mole/L, preferably from about 0.1 mole/L to about 1 mole/L, and most preferably about 0.23 mole/L. The preferred ratio of copper to any other metal ions is in a range from about 1:1 to about 100: 1, preferably from about 2:1 to about 50:1.
Additionally, the composition of the plating bath 56 may contain mineral acids such as sulfuric, fluoboric, combinations thereof, and the like. The plating bath 56 composition may also contain organic acids such as methane sulfonic (MSA), amidosulfuric, aminoacetic, combinations thereof, and the like. The composition of the plating bath 56 may also contain combinations of mineral acids and organic acids. A preferred concentration range of acids in the inventive plating bath composition I from about 0.1 mole/L to about 4 mole/L, preferably from about 0.15 mole/L to about 3.6 mole/L, and more preferably from about 0.2 mole/L to about 2.6 mole/L. Alternatively, the effective acid content in the inventive plating bath composition mya be expressed by pH in a preferred range from about pH <0 to about pH 14, prefer ably from about pH 0.4 to about pH 3.
The composition of the plating bath 56 may include at least one halogen such as fluorine, chlorine, bromine, iodine, and combinations thereof. Preferably, the composition of the plating bath 56 includes at least one halogen of chloride or bromine. A preferred range of halogens in the plating bath 56 is the range from about 150 micron mole/L to about 3500 micron mole/L, preferably from about 1000 micron mole/L to about 3225 micron mole/L.
Accelerating agents may include a bath composition soluble disulfide or monsulfide organic compound including their mixtures. Once accelerating agent is SPS, 1-propane sulfonic acid, 3,3′-dithio-bis, di-sodium salt, that may include bis-(soldium-sulfopropyl) -disulfide as the di-sodium salt. Another accelerating agent is 1-propanesulfonic acid, 3-[(ethoxy-thiomethyl)thi],-potassium salt. Another accelerating agent is a sulphonated or a phosphonated monosulfide, such as 3-mercapto-1-propanesulfonic acid (MPS) or 2-Mercaptoethanesulfonic acid (MES).
In one embodiment, the accelerating agent comprises a phosphonated disulfide in a concentration range from about 2 micron mole/liter to about 500 micron mole/L, preferably from about 5 micron mole/L to about 250 micron mole/L.
In another embodiment, accelerating agent is selected from a sulfonated monosulphide and a phosphonated monosulfide in a concentration range from about 2 micron mole/L to about 500 micron mole/L, preferably from about 5 micron mole/liter to about 250 micron mole/L.
In another embodiment, the accelerating agent is selected from 3-mercapto-1-propanesulfonic acid, and 2-mercaptoethanesulfonic acid sodium salt in a concentration ranger from about 2 micron mole/L to about 500 micron mole/L, preferably from about 5 micron mole/L to about 250 micron mole/L.
The accelerating agent may also be selected from acylthioureas, thiocarboxylic acid amides, thiocarbamates, thiosemicarbazones, thiohydantoin, mixtures thereof, and the like in a concentration range from about 2 micron mole/L to about 500 micron mole/L, preferably from about 5 micron mole/L to about 250 micron mole/L. The accelerating agent may comprise (O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester, potassium salt.
The suppressing agent is provided in a concentration range from about 0.6 mole/L to about 600 micron mole/L, preferably from about 3 micron mole/L to about 300 micron/L.
In one embodiment, the suppressing agent comprises a cross-linked polyamide in a concentration range from about 0.6 micron mole/L to about 600 micron mole/L, and wherein the cross-linked polyamide has an average molecular weight in a range from about 2,000 gram/mole to about 3,000 gram/mole.
In another embodiment, the suppressing agent is selected from a polyether such as polyoxyethylene lauryl ether (POE). The suppressing agent may also be a glycol such as polyethylene glycol, polypropylene glycol, combinations thereof, and the like.
The suppressing agent may also be an aromatic compound such as alkoxylated beta-naphtol, alkyl naphthalene sulphonate, combinations, and the like. In one embodiment, the suppressing agent is selected from a polyether, a polyethylene, a naphtol, a sulphonate, a polyamine, a polyimid, and mixtures thereof. In another embodiment, the suppressing agent comprises a beta-naphtol having the structure:
C6H4C6H3—O —(CH2CH3CH2O)n—(CH2—CH2O)m-H,
Wherein n may be equal to 1 and wherein m may be equal to 1 and wherein the molecular weight is in the range from about 800 to about 1,500. The suppressing agent may also be polyethylene oxide. The suppressing agent may also be a nitrogen-containing compound such as polyimines, poly amines, polyamids, combinations and the like. Additionally, the suppressing agent may be cross-combinations of any two up to all of ethers, glycols, double aromatics, polyethylenes, and nitrogren-containing compounds.
The semiconductor substrate 10 may be placed on the substrate support 48 within the liquid container 46 of the electroplating apparatus 44 so that the semiconductor substrate 10 is completely immersed within the plating bath 56. The second electrode 54 may be connected to the semiconductor substrate 10 such that the second electrode 54 is electrically connected to each of the bonding pads 22, or the adhesion layer 38, as illustrated in
Operating conditions according to present invention may be selected depending upon a particular application. The wafer may be contacted by the copper plating bath composition by moving the bath composition in relation to the wafer. For example, the wafer may be rotated. A preferred rotation speed is in the range from about 0 to about 500 rpm. Optionally, the bath composition may be rotated and the wafer held in place. This embodiment allows for the elimination of moving parts in a wafer electroplating chamber with the advantage of reducing the likelihood of particulates contaminating the electroplating bath composition.
In one embodiment, a plating tool containing 1-25 plating chambers is loaded with between 1 and 25 wafers and the inventive copper plating bath composition is flowed at a rate from about 3 L/min to about 60 L/min for each wafer. Where the wafer is rotated, or the solution is rotated, the wafer rotation speed, relative to the solution, is between 0 rpm and about 500 rpm.
Depending upon the specific chemical make-up of the plating bath composition and the preferred plating amount, the temperature is between about 7 C and about 35 C.
As illustrated in
During the electroplating process, the suppressing particles improve wettability and “suppress” the plating rate to prevent a dendritic copper deposit from forming. The accelerating agent may act to increase the electroplating rate. Because of the distribution of the suppressing and accelerating agents illustrated in
Still referring to
As illustrated in
In use, the motherboard 68 may be installed in a computing system. Electric signals such as input/output(IO) signals, are then sent from the integrated circuit within the die 18 through the contact formations 58, into the package substrate 62, and into the computing system through the motherboard 68. Power and ground signals may also be provided to the die 18. The computing system may send similar, or different, signals back to the integrated circuit within the die 18 through the motherboard 68, the package substrate 62, and the contact formations 58.
One advantage is that because of the domed shape and the smooth upper surface of the copper bumps, when the die is attached to the package substrate, the likelihood of any solder material, underfill material, or air being trapped between the copper bump and the package substrate is reduced. Therefore, the mechanical strength of the bond between the copper bumps and the package substrates is increased, resulting in a more reliable electrical connection. Another advantage is that a greater portion of the copper bumps may be an electrical contact with the package substrate, allowing the amount of current that is conducted through each copper bump to be maximized.
Other embodiments may use a plating bath solution that does not contain the suppressing agent. A two-step electroplating process may also be used. The contact formations resulting from this alternative embodiment may not be domed or smooth to the same extent as the copper bump illustrated in
Claims
1. A plating bath consisting of:
- a plating solution; and
- an accelerating agent in said plating solution; and
- a suppressing agent in said plating solution.
2. The plating bath of claim 1, wherein said plating solution is selected from the group consisting of methane sulfonic, amidosulfuric, and aminoacetic.
3. The plating bath of claim 1, wherein said accelerating agent is selected from the group consisting of SPS, 1-propane sulfonic acid, 3,3′-dithio-bis, di-sodium salt; 1-propanesulfonic acid, 3-[(ethoxy-thiomethyl_thio],-potassium salt; phosphonated disulfide; sulphonated monosulfide; phosphonated monsulfide.
4. The plating bath of claim 1, wherein said suppressing agent is selected from the group consisting of polyoxyethylene lauryl ether; polyethylene glycol, polypropylene glycol; alkoxylated beta-naphtol; alkyl naphthalene sulphonate.
5. The plating bath of claim 1 further comprising copper.
6. The plating bath of claim 1 further comprising refractory metals, noble metals, transition metals, and halogens.
7. A plating bath consisting of:
- a methane sulfonic; and
- a sulphonated monosulfide; and
- polyethylene glycol; and
- copper; and
- bromine.
8. The plating bath of claim 7 further consists of metal deposit ions.
9. The plating bath of claim 7 further consists of mineral acids.
10. A method consisting of:
- forming an adhesion layer over the top surface of a semiconductor substrate;
- forming a seed layer over the top surface of said adhesion layer;
- patterning a first resist for a bump pattern over said seed layer;
- exposing said semiconductor substrate to a plating bath, wherein said plating bath consists of a plating solution, accelerating agent, and a suppressing agent;
- applying a current to said plating bath, wherein a first metal layer is deposited in said bump pattern;
- removing said first resist;
- etching a first portion of said adhesion layer and said seed layer, wherein the portion of said adhesion layer and said seed layer that remains is directly underneath said first metal layer.
11. The method of claim 10, wherein said first metal layer deposition occurs in a first step and a second step.
12. The method of claim 11, wherein said first step comprises applying a current to said plating bath, wherein said second metal layer is deposited at a rate approximately 69 microns/3600 seconds.
13. The method of claim 11, wherein said second step comprises applying a current to said plating bath, wherein said second metal layer is deposited at a rate approximately 118 microns/3600 seconds.
14. The method of claim 10, wherein said seed layer is a base metal layer.
15. The method of claim 14, wherein said base metal layer comprises titanium copper.
16. The method of claim 10, wherein said first metal layer comprises copper.
17. A method consisting of:
- forming an adhesion layer over the top surface of a semiconductor substrate;
- forming a base metal layer over the top surface of said adhesion layer;
- patterning a first resist for a bump pattern over said base metal layer;
- exposing said semiconductor substrate to a plating bath, wherein said plating bath consists of a plating solution, accelerating agent, and a suppressing agent;
- applying a current to said plating bath, wherein a copper layer is deposited in said bump pattern in a first step and a second step and wherein said first step deposits said copper layer at a rate of approximately 69 microns/3600 seconds and wherein said second step deposits said copper layer at a rate of approximately 118 microns/3600 seconds;
- removing said first resist;
- etching a first portion of said adhesion layer and said base metal layer, wherein the portion of said adhesion layer and said base metal layer that remains is directly underneath said copper layer.
18. The method of claim 17, wherein said semiconductor substrate comprises a passivation layer, and wherein said passivation layer is on the top surface of said semiconductor substrate.
19. The method of claim 17, wherein said adhesion layer comprises titanium.
20. The method of claim 17 further consisting of a pre-wet process prior to forming an adhesion layer over the top surface of said semiconductor substrate.
Type: Application
Filed: Dec 30, 2005
Publication Date: Jul 12, 2007
Inventors: Scott Haight (Portland, OR), Tzuen-Iuh Huang (Portland, OR), Liang Harry (Portland, OR)
Application Number: 11/323,547
International Classification: C25D 5/00 (20060101);