# Patent

## Title
Cleaning solution, cleaning method and damascene process using the same

## Abstract

A cleaning solution is provided. The cleaning solution includes (a) 0.01-0.1 wt % of hydrofluoric acid (HF); (b) 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid; (c) 0.05-0.5 wt % of ammonium fluoride (NH4F); (d) a chelating agent containing a carboxylic group; (e) triethanolamine (TEA); (f) ethylenediaminetetraacetic acid (EDTA); and (g) water for balance.

## Background
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a cleaning solution, a cleaning method and a damascene process using the same.
2. Description of Related Art
A Dual damascene process is a technology widely applied in a semiconductor process. To reduce the RC delay caused by a parasitic capacitance, the current dual damascene process adopts an ultra low-k (ULK) material as a dielectric layer. Further, with the minimization of the device, a titanium nitride (TiN) hard mask layer is formed on the dielectric layer, and then the required patterns are precisely transferred to the dielectric layer by utilizing different etching selectivities of the TiN hard mask layer and the dielectric layer.
The pattern transfer is usually achieved by a dry etching process. However, during the etching process, the reactive gases passing into a reaction chamber may also undergo a polymerization reaction. Therefore, the organic polymer formed from the polymerization reaction is deposited on the surface of the device. Moreover, the reactive gases used for etching the dielectric layer are mostly fluorine-containing gases. These fluorine-containing gases may react with the TiN hard mask layer to produce titanium fluoride (TiFx) on the surface of the device, and thus, a profile change of the device, abnormal conduction, leakage or short circuiting between film layers is caused, and the reliability of the device is accordingly reduced.
The effect produced by the polymer and titanium fluoride residues is particularly significant in the deep sub-micro fabrication process. Further, upon the study, the post-etch cleaning process may effect the conduction ability of the device by etching the exposed metal lines below the dual damascene opening, cause a profile change by swelling the dielectric layer with the cleaning solution, or lead to an increase in the dielectric constant. Therefore, the post-etch cleaning process has become a very important step in the duel damascene process.
SUMMARY OF THE INVENTION
The present invention provides a cleaning solution to effectively remove the residues containing a plurality of species.
The present further invention provides a damascene process to reduce the surface damage (copper loss) of the conductive layer, avoid damages of the dielectric layer or an increase in the dielectric constant, or prevent bridges between the dual damascene structures, and thus, the reliability of the semiconductor device is enhanced.
The present invention also provides a cleaning method to effectively remove the residues containing a plurality of species.
The present invention provides a cleaning solution including: 0.01-0.1 wt % of hydrofluoric acid (HF); 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid; 0.05-0.5 wt % of ammonium fluoride (NH4F); a chelating agent containing a carboxylic group; triethanolamine (TEA); ethylenediaminetetraacetic acid (EDTA); and water for balance.
According to an embodiment of the present invention, the strong acid includes sulfuric acid (H2SO4) or hydrochloric acid (HCl).
According to an embodiment of the present invention, the chelating agent containing the carboxylic group includes oxalic acid.
According to an embodiment of the present invention, the cleaning solution consists of (a) to (g).
The present invention further provides a damascene process. A substrate having a conductive layer and a cap layer sequentially thereon is provided. A dielectric layer and a metal hard mask layer are sequentially formed on the cap layer. The metal hard mask layer, the dielectric layer and the cap layer are sequentially etched, so as to form an opening exposing the conductive layer. A post-etch cleaning process is performed with a cleaning solution. The cleaning solution includes: 0.01-0.1 wt % of hydrofluoric acid; 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid; 0.05-0.5 wt % of ammonium fluoride; a chelating agent containing a carboxylic group; triethanolamine; ethylenediaminetetraacetic acid; and water for balance. Thereafter, A conductive material is filled in the opening. The metal hard mask layer is removed.
According to an embodiment of the present invention, the strong acid includes sulfuric acid or hydrochloric acid.
According to an embodiment of the present invention, the chelating agent containing the carboxylic group includes oxalic acid.
According to an embodiment of the present invention, the cleaning solution consists of (a) to (g).
According to an embodiment of the present invention, the opening includes a dual damascene opening, a via opening or a contact opening.
According to an embodiment of the present invention, the metal hard mask layer includes titanium, titanium nitride, tantalum, tantalum nitride, tungsten, tungsten nitride, or a combination thereof.
According to an embodiment of the present invention, the cap layer includes silicon nitride, silicon oxynitride or silicon carbide.
According to an embodiment of the present invention, the dielectric layer comprises an ultra low-k material.
According to an embodiment of the present invention, the damascene process further includes forming a buffer layer after the step of forming the dielectric layer and before the step of forming the metal hard mask layer the buffer layer includes silicon oxide or silicon oxynitride.
According to an embodiment of the present invention, the damascene process further includes forming another cap layer after the step of forming the metal hard mask layer, wherein the another cap layer includes silicon carbide, silicon nitride or oxynitride silicon.
The present invention also provides a cleaning method suitable for a semiconductor process with to-be-removed residual species including refractory metal, fluorine, oxygen, silicon, carbon and copper. The cleaning method includes performing a first cleaning process with a cleaning solution. The cleaning solution includes: 0.01-0.1 wt % of hydrofluoric acid; 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid; 0.05-0.5 wt % of ammonium fluoride; a chelating agent containing a carboxylic group; triethanolamine; ethylenediaminetetraacetic acid; and water for balance.
According to an embodiment of the present invention, the strong acid includes sulfuric acid or hydrochloric acid.
According to an embodiment of the present invention, the chelating agent containing the carboxylic group includes oxalic acid.
According to an embodiment of the present invention, the cleaning solution consists of (a) to (g).
According to an embodiment of the present invention, the cleaning method further includes immediately performing a second cleaning process with DI water after the step of performing the first cleaning process.
According to an embodiment of the present invention, the cleaning solution can effectively remove the residues containing a plurality of species.
According to an embodiment of the present invention, the damascene process can reduce the surface damage (copper loss) of the conductive layer, avoid damages of the dielectric layer or an increase in the dielectric constant, or prevent bridges between the dual damascene structures, and thus, the reliability of the semiconductor device is enhanced.
According to an embodiment of the present invention, the cleaning solution can effectively remove the residues containing a plurality of species.
In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below.



BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIGS. 1A to 1E schematically illustrate cross-sectional views of a damascene process according to an embodiment of the present invention.



DESCRIPTION OF EMBODIMENTS
An embodiment of the present invention provides a cleaning solution. The cleaning solution includes hydrofluoric acid (HF), a strong acid, ammonium fluoride (NH4F), a chelating agent containing a carboxylic group, triethanolamine (TEA), ethylenediaminetetraacetic acid (EDTA) and water.
In the cleaning solution, the content of hydrofluoric acid is 0.01-0.1 wt %. The content of the strong acid is 1-5 wt %. The strong acid is an inorganic acid with pKa value less than −1.74, such as sulfuric acid (H2SO4) or hydrochloric acid (HCl). The content of ammonium fluoride is 0.05-0.5 wt %. The chelating agent containing the carboxylic group includes oxalic acid, for example. The rest of the cleaning solution is water. The water is de-ionized (DI) water. In an embodiment, the cleaning solution consists of hydrofluoric acid, the strong acid, ammonium fluoride, the chelating agent containing the carboxylic group, triethanolamine, ethylenediaminetetraacetic acid and water, and other components are not included.
The cleaning solution can be applied to a damascene process. A dual damascene process is taken as an example in the following.
FIGS. 1A to 1E schematically illustrate cross-sectional views of a damascene process according to an embodiment of the present invention.
Referring to FIG. 1A, a substrate 10 having a conductive layer 20 and a cap layer sequentially thereon is provided. The conductive layer 20 includes Cu, CuAl alloy or CuAlSi alloy, for example. The cap layer 30 includes silicon nitride, silicon oxynitirde or silicon carbide, for example. Thereafter, a dielectric layer 40, a buffer layer 50, a metal hard mask layer 60, and a cap layer 65 are sequentially formed on the cap layer 30. The dielectric layer 40 includes an ultra low-k (ULK) material, for example. The ultra low-k material is a material with a dielectric constant of 2.5-2.7 or lower. The ultra low-k material includes Black diamond (Trademark of AMAT), or Dense ULK (Trademark of NOVELLUS) for example. The material of the buffer layer 50 is different from that of the dielectric layer 40. The buffer layer 50 includes silicon oxide or silicon oxynitride, for example. The metal hard mask layer 60 includes metal or metal nitride, such as titanium, titanium nitride, tantalum, tantalum nitride, tungsten, tungsten nitride, or a combination thereof. The cap layer 65 is to protect the metal hard mask layer 60 and includes silicon nitride, silicon oxide, silicon oxynitirde or silicon carbide, for example.
Referring to FIG. 1B, a dual damascene opening 70 is formed in the cap layer 65, the metal hard mask layer 60, the buffer layer 50, the dielectric layer 40 and the cap layer 30 by photolithography and etching processes. The bottom of the dual damascene opening 70 exposes the conductive layer 20. The dual damascene opening 70 is formed by a laterally extending trench 72 disposed at an upper position and a vertically extending via opening 74 disposed at a lower position. The method of forming the dual damascene opening 70 includes forming the via opening 74 prior to the trench 72, or forming the trench 72 prior to the via opening 74. The etching gases for the etching process usually include fluorine, so as to remove the metal such as refractory metal in the metal hard mask layer 60. During the etching process, polymer is usually formed on the sidewall of the dual damascene opening 70. Moreover, in the etching process, the copper loss problem occurs due to the formation of copper oxide (CuOx) or CuOxFy on the surface of the conductive layer 20 (e.g. copper layer) exposed by the dual damascene opening 70. Therefore, after the step of forming the dual damascene opening 70, the to-be-removed residual species include refractory metal, fluorine, oxygen, silicon, carbon and copper.
Referring to FIG. 1C, a chemical cleaning process 80 (or a post-etch cleaning process) is performed with the above-mentioned cleaning solution, so as to remove the residues on the substrate 10 as well as the damaged surface of the conductive layer 20. The cleaning solution consists of hydrofluoric acid, the strong acid, ammonium fluoride, the chelating agent containing the carboxylic group, triethanolamine, ethylenediaminetetraacetic acid and water, and other components are not included. The components and contents in the cleaning solution are described above, and the details are not iterated herein. The chemical cleaning process 80 can be performed at room temperature, such as 20 to 50° C., for example. The time period of the chemical cleaning process 80 is 60 to 120 seconds, for example.
Hydrofluoric acid, sulfuric acid and ammonium fluoride in the cleaning solution are for providing fluorine ions and adjusting the pH value. The chelating agent containing the carboxylic group, triethanolamine and ethylenediaminetetraacetic acid in the cleaning solution serve as a chelating agent, resolve the metal complexes in the aqueous solution, and stabilize the surface of the conductive layer to avoid re-oxidation of the conductive layer, and thus, they are regarded as a surface oxidation inhibitor.
In details, sulfuric acid in the cleaning solution hardly reacts with the dielectric layer 40, so that damages of the dielectric layer 40 do not occur. However, sulfuric acid can react with CuOx or CuOxFy on the surface of the conductive layer 20 to form water-soluble copper ions (Cu2+). The copper ions can chelate with the chelating agent containing the carboxylic group, so as to avoid copper loss caused by re-oxidation of the conductive layer 20. Further, sulfuric acid, hydrofluoric acid and ammonium fluoride in the cleaning solution are mixed to form SO3F—, which is a strong nucleophilic reagent to make the Cu—R bonds break and achieve the purpose of removing the residues.
Referring to FIG. 1D, a cleaning process 90 is performed after the step of performing the chemical cleaning process 80. In an embodiment, the cleaning process 90 is performed immediately after the step of performing the chemical cleaning process 80, and no other processes between the cleaning process 90 and the chemical cleaning process 80 are present. The cleaning process 90 is performed with DI water only, and no other components are used. The cleaning process 90 can be performed at room temperature, such as 20 to 30° C., for example. The time period of the cleaning process 90 is 30 to 90 seconds, for example. Thereafter, a baking process is performed. The temperature of the baking process is 200 to 300° C., and the time period of the same is 30 to 60 minutes, for example.
Referring to FIG. 1E, a conductive material (not shown) is formed on the cap layer 65 and the metal hard mask layer 60 filling in the dual damascene opening 70. The conductive material includes copper, for example. Thereafter, a chemical mechanical polishing (CMP) or an etching back process is performed to remove the conductive material on the cap layer 65 and remain the conductive material 100 in the dual damascene opening 70. Afterwards, the cap layer 65, the metal hard mask layer 60, and the buffer layer 50 are removed.
The dual damascene process in the above-mentioned embodiment is provided for illustration purposes, and is not construed as limiting the present invention. The above-mentioned dual damascene opening can also be a via opening or a contact opening only. Therefore, the above-mentioned cleaning solution can be applied to a single damascene process.
Further, the cleaning solution is not limited to apply to a damascene process. The cleaning solution of the present invention can be applied to a semiconductor process with to-be-removed residual species including refractory metal, fluorine, oxygen, silicon, carbon and copper.
Example
An ultra low-k dielectric layer, a silicon oxynitride layer and a titanium nitride layer are sequentially formed on a substrate having a copper layer and a carbide silicon nitride layer thereon. Thereafter, a photolithography process is performed and followed by a dry etching process with fluorine containing gases, so as to form a dual damascene opening. Afterwards, a chemical cleaning process is performed with a cleaning solution (0.06 wt % of hydrofluoric acid, 3 wt % of sulfuric acid, 0.1 wt % of ammonia fluoride, 10 wt % of oxalic acid, 10 wt % of TEA, 0.2 wt % of EDTA and water for balance), and then another cleaning process is performed immediately with DI water.
The result shows that the residues in the process can be effectively removed by performing the chemical cleaning process with the cleaning solution and followed by nother cleaning process with DI water. Moreover, damages are not found on the surface of the dielectric layer or the copper layer, or an increase in the dielectric constant is not caused. Bridges are not observed between the formed dual damascene structures. Thus, the reliability of the semiconductor device can be accordingly enhanced.
Comparative Examples 1 to 6
A dual damascene opening is formed by the method of the above-mentioned Example. Thereafter, a post-etch cleaning process is performed with different cleaning solutions including different components, and immediately followed by another cleaning process with DI water. The results are shown in Table 1.









TABLE 1






Components of cleaning solution
Results







Comparative
10 wt % of oxalic acid, 0.1 wt % of
Copper sur-


example 1
ammonia fluoride, 3 wt % of sulfuric acid,
face damage



0.06 wt % of hydrofluoric acid and water




for balance



Comparative
10 wt % citric acid, 0.1 wt % of ammonia
Polymer 


example 2
fluoride, 3 wt % of sulfuric acid, 0.06 wt %
residue



of hydrofluoric acid and water for balance



Comparative
5 wt % of iminodiacetic acid (IDA), 0.1
Polymer 


example 3
wt % of ammonia fluoride, 3 wt % of
residue



sulfuric acid, 0.06 wt % of hydrofluoric
Dielectric 



acid and water for balance
layer damage


Comparative
10 wt % of oxalic acid, 0.2 wt % of EDTA,
Copper sur-


example 4
3 wt % of sulfuric acid, 0.06 wt % of
face damage



hydrofluoric acid and water for balance
Polymer




residue


Comparative
10 wt % of TEA, 0.1 wt % of ammonia
Copper sur-


example 5
fluoride, 3 wt % of sulfuric acid, 0.06 wt %
face damage



of hydrofluoric acid and water for balance



Comparative
5 wt % of iminodiacetic acid, 1 wt % of 
Dielectric


example 6
NH4HF2, 3 wt % of sulfuric acid, 0.06
layer damage



wt % of hydrofluoric acid and water for
Copper sur-



balance
face damage









The present invention has been disclosed above in the preferred embodiments, but is not limited to those. It is known to persons skilled in the art that some modifications and innovations may be made without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be defined by the following claims.

## Claims

1. A cleaning solution, comprising:
(a) 0.01-0.1 wt % of hydrofluoric acid (HF);
(b) 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid;
(c) 0.05-0.5 wt % of ammonium fluoride (NH4F);
(d) a chelating agent containing a carboxylic group;
(e) triethanolamine (TEA);
(f) ethylenediaminetetraacetic acid (EDTA); and
(g) water for balance.

2. The cleaning solution of claim 1, wherein the strong acid comprises sulfuric acid (H2SO4) or hydrochloric acid (HCl).

3. The cleaning solution of claim 1, wherein the chelating agent containing the carboxylic group comprises oxalic acid.

4. The cleaning solution of claim 1, which consists of (a) to (g).

5. A damascene process, comprising:
providing a substrate having a conductive layer and a cap layer sequentially thereon;
sequentially forming a dielectric layer and a metal hard mask layer on the cap layer;
sequentially etching the metal hard mask layer, the dielectric layer and the cap layer, so as to form an opening exposing the conductive layer;
performing a post-etch cleaning process with a cleaning solution, the cleaning solution comprising:
(a) 0.01-0.1 wt % of hydrofluoric acid (HF);
(b) 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid;
(c) 0.05-0.5 wt % of ammonium fluoride (NH4F);
(d) a chelating agent containing a carboxylic group;
(e) triethanolamine (TEA);
(f) ethylenediaminetetraacetic acid (EDTA); and
(g) water for balance;

filling a conductive material in the opening; and
removing the metal hard mask layer.

6. The damascene process of claim 5, wherein the strong acid comprises sulfuric acid (H2SO4) or hydrochloric acid (HCl).

7. The damascene process of claim 5, wherein the chelating agent containing the carboxylic group comprises oxalic acid.

8. The damascene process of claim 5, wherein the cleaning solution consists of (a) to (g).

9. The damascene process of claim 5, wherein the opening comprises a dual damascene opening, a via opening or a contact opening.

10. The damascene process of claim 5, wherein the metal hard mask layer comprises titanium, titanium nitride, tantalum, tantalum nitride, tungsten, tungsten nitride, or a combination thereof.

11. The damascene process of claim 5, wherein the cap layer comprises silicon nitride, carbide silicon nitride or silicon carbide.

12. The damascene process of claim 5, wherein the dielectric layer comprises an ultra low-k material.

13. The damascene process of claim 5, further comprising forming a buffer layer after the step of forming the dielectric layer and before the step of forming the metal hard mask layer, wherein the buffer layer comprises silicon oxide or silicon oxynitride.

14. The damascene process of claim 13 further comprising forming another cap layer after the step of forming the metal hard mask layer, wherein the another cap layer comprises silicon carbide, silicon nitride or oxynitride silicon.

15. A cleaning method, suitable for a semiconductor process with to-be-removed residual species comprising refractory metal, fluorine, oxygen, silicon, carbon and copper, comprising:
performing a first cleaning process with a cleaning solution, the cleaning solution comprising:
(a) 0.01-0.1 wt % of hydrofluoric acid (HF);
(b) 1-5 wt % of a strong acid, wherein the strong acid is an inorganic acid;
(c) 0.05-0.5 wt % of ammonium fluoride (NH4F);
(d) a chelating agent containing a carboxylic group;
(e) triethanolamine (TEA);
(f) ethylenediaminetetraacetic acid (EDTA); and
(g) water for balance.

16. The cleaning method of claim 15, wherein the strong acid comprises sulfuric acid (H2SO4) or hydrochloric acid (HCl).

17. The cleaning method of claim 15, wherein the chelating agent containing the carboxylic group comprises oxalic acid.

18. The cleaning method of claim 15, wherein the cleaning solution consists of (a) to (g).

19. The cleaning method of claim 15, further comprising immediately performing a second cleaning process with DI water after the step of performing the first cleaning process.