A silicon oxide highly selective etching solution

Abstract

This invention provides a highly selective etching solution for silicon oxide. The etching solution, by mass percentage, comprises the following components: 1-6% hydrofluoric acid, 10-30% ammonium fluoride, 0.01-0.1% surfactant, and the balance being ultrapure water. The surfactant is a mixture of organic amine compounds and phosphate-containing compounds, preferably long-chain organic amines. Through the combined use of surfactants, the etching of the metal layer can be more efficiently suppressed, with an etching selectivity exceeding 20. Simultaneously, this etching solution can rapidly penetrate into the deep porous structure of silicon oxide, completely etching the silicon oxide within the deep holes, thus meeting process requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of etching solutions, and in particular relates to a silicon oxide high-selectivity etching solution. Background Art

[0002] In micro-electromechanical systems (MEMS), silicon oxide is generally used as a sacrificial layer and aluminum is used as a metal connection. The most commonly used process structure is to deposit a metal aluminum film on silicon, and then deposit a layer of silicon dioxide. A deep hole is first etched using a dry etching process, and then the silicon oxide in the deep hole is removed using wet etching until the aluminum layer. During the wet etching process, it is required to completely etch the silicon oxide in the hole and reduce the etching of the aluminum layer to avoid affecting the electrical performance of the chip.

[0003] Wet etching of silicon oxide is generally accomplished using a buffered oxide etchant, but the buffered oxide etchant cannot effectively penetrate into the deep holes to completely etch the silicon oxide layer, and the etching rate for aluminum is too fast, resulting in an uneven pitting surface, which in turn affects its electrical properties. Summary of the invention

[0004] The invention provides a silicon oxide high-selectivity etching solution, which can quickly infiltrate deep holes to completely etch silicon oxide and suppress the etching rate of the etching solution on metals.

[0005] The technical solution of the present invention is a silicon oxide high-selectivity etching solution, which comprises the following components by mass percentage: 1-6% hydrofluoric acid, 10-30% ammonium fluoride, 0.01-0.1% activator, and the balance is ultrapure water; wherein the activator is a mixture of an organic amine compound and a compound containing a phosphoric acid group.

[0006] Furthermore, the mass ratio of the organic amine compound to the compound containing a phosphoric acid group is 80-90:10-20.

[0007] Furthermore, the organic amine compound is an organic amine with a long carbon chain, wherein C≥5.

[0008] Furthermore, the long carbon chain organic amine is one or a combination of pentylamine, hexylamine, heptylamine, n-octylamine, isooctylamine, diisooctylamine, trioctylamine, nonylamine, decylamine, 2-ethylhexyloxypropylamine, and 1,5-dimethylhexylamine; preferably n-octylamine.

[0009] Furthermore, the phosphate group-containing compound is one or a combination of phosphoric acid, pyrophosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium pyrophosphate, ammonium tripolyphosphate, and hydroxyethylidene diphosphonic acid; preferably ammonium phosphate.

[0010] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 2-5%.

[0011] Furthermore, the mass fraction of hydrofluoric acid in the etching solution is 4%.

[0012] Furthermore, the mass fraction of ammonium fluoride in the etching solution is 15-30%.

[0013] Furthermore, the mass fraction of ammonium fluoride in the etching solution is 20%.

[0014] The invention also relates to application of the etching solution in etching of silicon oxide deep hole structures.

[0015] The present invention has the following beneficial effects:

[0016] 1. In the present invention, a long carbon chain organic amine is used as a surfactant, which has good solubility in the etching solution. The surfactant has high surface activity and can significantly reduce the surface tension of the etching solution. The etching solution has good wettability and performs excellently in silicon oxide deep trench and deep hole etching.

[0017] 2. The end of the long carbon chain organic amine active agent contains a free amino group, and the lone pair of electrons on the nitrogen can form a complex adsorption effect with the empty d orbital on the aluminum surface. The long carbon chain has an electron-donating effect, which increases the density of the electron cloud on the amino surface, thereby enhancing its adsorption with aluminum and inhibiting aluminum etching. In addition, the phosphate-based aluminum etching inhibitor has a small molecular volume, and the oxygen ions at the end have a good complexing effect. The combination of long-chain active agents and short-chain inhibitors can be more closely adsorbed and spread on the aluminum surface, blocking the attack of hydrofluoric acid, and thus effectively inhibiting aluminum etching and improving the etching selectivity of silicon oxide to aluminum. The etching selectivity of silicon oxide to aluminum can reach more than 20. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the deep hole structure diagram before etching.

[0019] Figure 2 This is a diagram of the fully etched TEOS structure.

[0020] Figure 3 This is a structural diagram of TEOS that is not completely etched. DETAILED DESCRIPTION

[0021] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0022] The present invention provides multiple etching solution formulas for illustration, as shown in Table 1.

[0023] Table 1

[0024]

[0025]

[0026] In order to verify the etching selectivity of the etching solution for silicon oxide and metal in the above embodiments and comparative examples, a single-layer TEOS film and AlCu were used to collect the etching rate. The specific objects were silicon oxide (TEOS) and 2% copper-doped aluminum sheets. The structure before etching was as follows: Figure 1 The specific etching conditions are stirring immersion etching, the etching time is 3 minutes, and the etching temperature is 23°C. The TEOS layer after dry etching of the deep hole structure is observed by SEM to see whether the etching is complete. When the etching effect is ideal, the structure of TEOS being completely etched is shown in Figure 2 However, when the etching solution has poor selectivity, TEOS is often not completely etched, such as Figure 3 shown.

[0027] The etching rate of TEOS is obtained by measuring the thickness of the TEOS film before and after etching using an ellipsometer for a certain period of time. The etching rate of AlCu is obtained by measuring the thickness before and after etching using a four-point probe instrument for a certain period of time. The surface tension of the etching solution is measured using a surface tension meter.

[0028] The specific experimental results are shown in Table 2.

[0029] Table 2

[0030]

[0031]

[0032] As can be seen from Table 2, except for Example 15, the etching selectivity ratios of TEOS and AlCu layers in the other examples are all greater than 20; and the etching liquid in all examples can quickly wet and drill into the deep hole, and completely etch the TEOS layer in the deep hole. In Examples 13 and 14, the amount of octylamine added is increased from 0.04% to 0.08%, but the etching selectivity ratio of TEOS to AlCu does not increase significantly, so the amount of octylamine can be reduced to 0.04%.

[0033] Comparative Example 1 does not contain an organic amine active agent and a phosphate inhibitor, and the etching rate of TEOS is maintained at Nearby, but the etching rate of AlCu increases significantly, resulting in a significant decrease in the etching selectivity of TEOS to AlCu. In addition, without the addition of the activator organic amine, the surface tension of the etching solution increases significantly, and the wettability is poor, resulting in the TEOS in the deep hole not being completely etched. In Comparative Example 2, there is an organic amine activator in the etching solution, so the surface tension of the etching solution is low, and the TEOS in the deep hole can be completely etched, but the etching rate of AlCu is faster because there is no inhibitor of the phosphate group, and the etching selectivity is lower than 11. It can be seen from Comparative Examples 1 and 2 that organic amine can not only increase the wettability of the etching solution but also inhibit the etching rate of AlCu. This is because the end of the organic amine activator contains an amino group, and the lone pair of electrons on it is complexed with the 3d empty orbit of Al and then adsorbed on the surface of Al, inhibiting the etching of Al.

[0034] It can be seen from Comparative Example 3 that when ammonium phosphate Al etching inhibitor is added alone to the etching solution, the etching selectivity of TEOS to AlCu is less than 17, which indicates that the long carbon chain organic amine active agent and ammonium phosphate have a synergistic effect in inhibiting AlCu etching. This is because the octylamine chain is long and has a hydrophobic effect, so it is difficult to adsorb saturatedly on the AlCu surface, and small molecules of ammonium phosphate are required for further adsorption. This mutual synergistic adsorption of large molecules and small molecules effectively inhibits the etching of AlCu, thereby greatly improving its etching selectivity.

[0035] It can be seen from Comparative Example 4 that when butylamine is used as the activator, the surface tension of the etching solution is only 58 mN / m, and the TEOS in the deep hole is not completely etched. This shows that the organic amine activator with a chain length that is too short is too poor in activity, resulting in poor wettability of the etching solution. Therefore, it is necessary to select an organic amine activator with a suitable chain length.

[0036] Obviously, the above embodiments and comparative examples are only examples for clear demonstration, and are not limited to the above embodiments. For those skilled in the art, the above embodiments have many variations or combinations, and it is not necessary and impossible to cite all the embodiments here. Therefore, the changes or modifications based on the above embodiments are still within the protection scope of the present invention.

Claims

1. A silicon oxide highly selective etching solution, characterized in that: The etching solution comprises the following components by mass percentage: 1-6% hydrofluoric acid, 10-30% ammonium fluoride, 0.01-0.1% activator, and the balance is ultrapure water; wherein the activator is a mixture of an organic amine compound and a compound containing a phosphoric acid group; the organic amine compound is an organic amine with a long carbon chain, wherein C≥5, specifically one or a combination of pentylamine, hexylamine, heptylamine, n-octylamine, isooctylamine, diisooctylamine, trioctylamine, nonylamine, decylamine, 2-ethylhexyloxypropylamine, and 1,5-dimethylhexylamine; the compound containing a phosphoric acid group is one or a combination of phosphoric acid, pyrophosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium pyrophosphate, ammonium tripolyphosphate, and hydroxyethylidene diphosphonic acid.

2. The etching solution according to claim 1, characterized in that: The mass ratio of the organic amine compound to the compound containing a phosphoric acid group is 80-90:10-20.

3. The etching solution according to claim 1, characterized in that: The long carbon chain organic amine is n-octylamine.

4. The etching solution according to claim 1, characterized in that: The compound containing a phosphoric acid group is ammonium phosphate.

5. The etching solution according to claim 1, characterized in that: The mass fraction of hydrofluoric acid in the etching solution is 2-5%.

6. The etching solution according to claim 1, characterized in that: The mass fraction of hydrofluoric acid in the etching solution is 4%.

7. The etching solution according to claim 1, characterized in that: The mass fraction of ammonium fluoride in the etching solution is 15-30%.

8. The etching solution according to claim 1, characterized in that: The mass fraction of ammonium fluoride in the etching solution is 20%.

9. Use of the etching solution according to any one of claims 1 to 8 in etching of deep hole structures of silicon oxide.

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