NON-CYANIDE BASED Au-Sn ALLOY PLATING SOLUTION

Abstract

The present invention provides a non-cyanide based Au—Sn alloy plating solution capable of performing a Au—Sn alloy plating treatment by a plating solution composition that is neutral and does not contain cyanide. In the present invention, a non-cyanide soluble gold salt, a Sn compound composed of tetravalent Sn, and a thiocarboxylic acid-based compound are contained. The non-cyanide based Au—Sn alloy plating solution of the present invention can further contain sugar alcohols, and, in addition, can further contain a dithioalkyl compound.

Claims

1. A non-cyanide based Au—Sn alloy plating solution, comprising a non-cyanide soluble gold salt, a Sn compound composed of tetravalent Sn, and a thiocarboxylic acid-based compound.

2. The non-cyanide based Au—Sn alloy plating solution according to claim 1, further comprising sugar alcohols.

3. The non-cyanide based Au—Sn alloy plating solution according to claim 1, wherein the thiocarboxylic acid-based compound comprises thiomonocarboxylic acid.

4. The non-cyanide based Au—Sn alloy plating solution according to claim 2, wherein the sugar alcohols comprise—D-(−)sorbitol or xylitol.

5. The non-cyanide based Au—Sn alloy plating solution according to claim 1, further comprising a dithioalkyl compound.

6. The non-cyanide based Au—Sn alloy plating solution according to claim 5, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

7. The non-cyanide based Au—Sn alloy plating solution according to claim 2, wherein the thiocarboxylic acid-based compound comprises thiomonocarboxylic acid.

8. The non-cyanide based Au—Sn alloy plating solution according to claim 3, wherein the sugar alcohols comprise D-(−)sorbitol or xylitol.

9. The non-cyanide based Au—Sn alloy plating solution according to claim 7, wherein the sugar alcohols comprise D-(−)sorbitol or xylitol.

10. The non-cyanide based Au—Sn alloy plating solution according to claim 2, further comprising a dithioalkyl compound.

11. The non-cyanide based Au—Sn alloy plating solution according to claim 3, further comprising a dithioalkyl compound.

12. The non-cyanide based Au—Sn alloy plating solution according to claim 7, further comprising a dithioalkyl compound.

13. The non-cyanide based Au—Sn alloy plating solution according to claim 4, further comprising a dithioalkyl compound.

14. The non-cyanide based Au—Sn alloy plating solution according to claim 8, further comprising a dithioalkyl compound.

15. The non-cyanide based Au—Sn alloy plating solution according to claim 9, further comprising a dithioalkyl compound.

16. The non-cyanide based Au—Sn alloy plating solution according to claim 10, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

17. The non-cyanide based Au—Sn alloy plating solution according to claim 11, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

18. The non-cyanide based Au—Sn alloy plating solution according to claim 12, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

19. The non-cyanide based Au—Sn alloy plating solution according to claim 13, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

20. The non-cyanide based Au—Sn alloy plating solution according to claim 14, wherein the dithioalkyl compound comprises 3,3′-dithiobis(1-propanesulfonic acid) or a salt thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a graph of measurement of current-potential.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an embodiment of the non-cyanide based Au—Sn alloy plating solution according to the present invention will be described based on Examples.

[0030] In the present embodiment, Au—Sn alloy plating solutions of following compositions were examined.

TABLE-US-00001 TABLE 1 Au Sn (A) (B) (C) (D) (E) (F) (G) (H) g/L g/L g/L g/L g/L g/L g/L g/L g/L g/L Example 1 1 2 4.7 0 0 0 0 0 0 0 Example 2 1 2 0 6.1 0 0 0 0 0 0 Example 3 2 2 3.1 0 6.2 0 0 0 0 0 Example 4 1 2 3.1 0 6.2 0 0 0 100 0 Example 5 5 20 31 0 62 9 0 20 0 0 Example 6 3 4 6.2 0 12.3 10.8 20 0 15 5 Comparative 1 2 0 0 0 0 0 0 0 0 example 1 Comparative 3 4 0 0 0 0 0 0 0 0 example 2 Au: Gold sodium sulfite Sn: Potassium stannate (IV) trihydrate (A): Thioglycolic acid (B): Cysteine (C): D(−)-sorbitol (D): 3,3′-dithiobis(1-propanesulfonic acid) sodium (E): N,N-di(2-hydroxyethyl)glycine (F): Sodium sulfate (G): Potassium nitrate (H): Sodium dihydrogen phosphate

[0031] For each plating solution shown in Table 1, a plating treatment was performed, with a test piece made of Cu (2 cm×2 cm) as an object to be plated, and by use of a mesh anode made of Pt/Ti as an anode.

[0032] As evaluation items of each plating solution, stability of the liquid, a Au—Sn precipitation ratio of the plated film and a precipitation efficiency were investigated. The stability of the liquid was evaluated by visual observation of the state of liquid after preparation of each plating solution. A Au—Sn precipitation ratio of the plated film was measured with an X-ray fluorescence thickness meter (SFT-9550), and the precipitation efficiency was calculated from weight difference between test pieces before and after the plating. Evaluation results of each plating solution are shown in Table 2.

TABLE-US-00002 TABLE 2 Liquid Precipita- temper- Current tion ratio Precipitation ature density Au:Sn efficiency Liquid pH ° C. A/dm.sup.2 (%) mg/A .Math. min stability Example 1 8.0 40 0.4 80:20 49.0 Δ Example 2 8.0 40 0.4 79:21 48.5 Δ Example 3 7.0 40 0.5 80:20 48.8 Δ Example 4 7.0 40 0.5 71:29 36.5 Δ Example 5 7.0 40 0.5 75:25 44.0 ◯ Example 6 7.2 50 0.4 79:21 49.0 ⊚ Comparative 8.0 40 0.4 90:10 22.5 X example 1 Comparative 8.0 — — — — XX example 2 Liquid stability: ⊚: no trouble was generated by 6-month neglect after the plating test ◯: slight turbidity was generated by 1-week neglect after the plating test Δ: turbidity was generated by neglect for a while after the plating test X: slight turbidity existed when the plating solution was prepared, and turbidity was generated after the plating test XX: turbidity was generated when the plating solution was prepared

[0033] Further, in Example 6, there was performed a test of precipitating Au by plating in the same amount as the amount of Au contained in the plating solution and replenishing reduced components, as a running treatment of 1 MTO. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Precipitation Precipitation ratio efficiency MTO Au:Sn (%) mg/A .Math. min Liquid stability 0 79:21 49.0 ⊚ 0.25 79.5:20.5 49.0 0.5 80.5:19.5 48.5 0.75 80.3:19.7 48.0 1.0 79.8:20.5 49.0 Plating solution: Example 6 pH: 7.2 Liquid temperature: 50° C. Current density: 0.4 A/dm.sup.2 Liquid stability: ⊚ no trouble was generated by 3-month neglect after the plating test

[0034] As shown by the results in Table 2, in the instance as Comparative Example 1 that contained neither thioglycolic acid nor cysteine being thiocarboxylic acid-based compounds, eutectoid of Sn and precipitation efficiency gave low values and good precipitation was not obtained. Further, in Comparative Example 1, slight turbidity was generated when the plating solution was prepared, and turbidity was generated after the plating test to show an insufficient result of liquid stability. Furthermore, when concentrations of Au and Sn were increased as in Comparative Example 2, turbidity was generated when pH was adjusted, and a plating solution could not be materialized.

[0035] In contrast, as in Examples 1 and 2, in instances that thioglycolic acid and cysteine being thiocarboxylic acid-based compounds were contained, it became possible to perform plating under the eutectic crystal condition of Au:Sn=80:20 at neutral, and stability of the liquid was also good. Moreover, in instances that (A)/Sn=(B)/Sn=2 in molar ratio as in Examples 3 to 6, the result was that plating solutions were materialized without trouble, and arbitrary Au—Sn alloy precipitation ratios were obtained by change of metal concentration or the like. Further, the use of (C) in an appropriate amount made it possible to bring about a more stable state as a plating solution as in Examples 5 and 6.

[0036] Under the condition in Example 6 that gave the best result, as shown by the result in Table 3, it was confirmed that a plating treatment with replenishment of a component was also possible, and that a plating solution having good liquid stability and high industrial practicality could be obtained.

[0037] Finally, there will be described the result of examining the change in precipitation potential owing to a thiocarboxylic acid-based compound. FIG. 1 shows results of performing measurement of current-potential. The measurement of current-potential was performed under conditions described below on the basis of the composition concentration in Example 3.

[0038] pH: 7.0

[0039] Liquid temperature: 40° C.

[0040] W.E.: 2 cm×2 cm test piece (Cu/burnished Ni plating/Au strike)

[0041] R.E.: Ag/AgCl electrode

[0042] C.E.: Pt/Ti mesh anode

[0043] Sweep rate: 2 mV/s

[0044] Measurement liquid: [0045] 1: Sn+(B):D(−)-sorbitol [0046] 2: Sn+(A):thioglycolic acid+(B):D(−)-sorbitol [0047] 3: Au+(B):D(−)-sorbitol

[0048] As shown in FIG. 1, originally, since Sn(IV) and Au(I) have very large difference in precipitation potentials (1, 2 in FIG. 1), it is difficult to obtain eutectoid, and, even if the eutectoid is obtained, the precipitation ratio changes largely by slight change in the condition. However, by use of thioglycolic acid being a thiocarboxylic acid-based compound (3 in FIG. 1), most of difference in precipitation potentials between Sn and Au disappears and it becomes possible to obtain good alloy precipitation.

INDUSTRIAL APPLICABILITY

[0049] According to the present invention, a Au—Sn alloy plating treatment becomes possible without application of a large load to environment and lowering of liquid stability such as deposition generation caused by oxidation of a Sn compound does not occur, and, therefore, a Au—Sn alloy plating treatment of a semiconductor wafer or the like can be performed effectively.