JP4983422B2 - Etching composition and etching method - Google Patents

Description

  The present invention relates to a silicon nitride etching composition. Furthermore, it is related with the composition which can etch the silicon nitride used for insulating films, such as a semiconductor device and a flat panel display.

  Silicon nitride is a very important compound as a ceramic material and a semiconductor material. Semiconductor manufacturing processes include processes that require selective etching of silicon nitride without damaging the silicon oxide. Currently, high-purity phosphoric acid is mainly used in this process. However, when high purity phosphoric acid is used at a high temperature of 150 ° C. or higher, there is a problem that silicon oxide is greatly damaged.

  As a method for suppressing damage to silicon oxide, high-purity phosphoric acid in which silicon is dissolved or phosphoric acid to which hexafluorosilicic acid is added has been proposed (see Patent Documents 1 to 3). However, when hexafluorosilicic acid is added, the insoluble silicon compound precipitates faster from the etching solution. Therefore, hexafluorosilicic acid cannot be added to sufficiently reduce the damage of silicon oxide, and it can be used industrially. Had a problem.

  As a method of etching silicon nitride at a temperature of 100 ° C. or lower, a method of adding fluorosilicic acid or fluorosilicate to an etching solution composed of phosphoric acid, hydrofluoric acid, and nitric acid is disclosed. However, an etching composition in which hydrofluoric acid and nitric acid are added to phosphoric acid has a large damage to silicon oxide, which is another semiconductor material, and has a problem in use in a semiconductor process. In particular, a mixed acid obtained by adding hydrofluoric acid and nitric acid to phosphoric acid has a more remarkable adverse effect when used at a high temperature.

  Thus, there has been no industrially satisfactory etching composition that can selectively etch silicon nitride without damaging silicon oxide.

JP-A-6-349808 Japanese Patent Laid-Open No. 2000-136331 JP-A-8-64574

  In view of the above problems, an object of the present invention is to provide a composition capable of selectively etching silicon nitride without damaging silicon oxide.

  As a result of intensive studies on etching of silicon nitride, the present inventors have found that the composition for etching silicon nitride contains phosphoric acid, a soluble silicon compound and water, and further contains nitric acid and / or nitrate water, and does not contain hydrofluoric acid. As a result, it has been found that silicon nitride can be etched and removed at high speed without damaging the silicon oxide, and the problem of reprecipitation of silicon oxide can be remarkably improved when the processing batch is used repeatedly. The invention has been completed.

  That is, the present invention is an etching composition for silicon nitride and a method for etching silicon nitride, which contain phosphoric acid, a soluble silicon compound, nitric acid and water, and do not contain hydrofluoric acid.

  The present invention is described in further detail below.

  The etching composition of the present invention is a composition comprising phosphoric acid, a soluble silicon compound, nitric acid and water.

  There is no restriction | limiting in particular in the phosphoric acid in the etching composition of this invention, What is generally distribute | circulating can be used.

  The etching composition of the present invention contains a soluble silicon compound. The soluble silicon compound can reduce damage to the silicon oxide film. As the soluble silicon compound, silicic acid, silicate, hexafluorosilicate, hexafluorosilicate, alkoxysilanes such as tetraethoxysilane and tetramethoxysilane, and alkylsilanes such as methyltrimethoxysilane are particularly preferable. Other soluble silicon compounds can also be used. As the silicate and hexafluorosilicate, ammonium salts are preferable. Silicic acid and silicate may be used by adding silicon oxide or the like to sulfuric acid or phosphoric acid and dissolving them by heating. Hexafluorosilicic acid and hexafluorosilicate may be commercially available, or may be hydrolyzed with silicic acid and further salted. The concentration of the soluble silicon compound in the etching composition of the present invention is preferably 0.001 to 0.5% by weight, particularly 0.001 to 0.2% by weight, and more preferably 0.01 to 0.1% by weight. If added at 0.5% by weight or more, silicon oxide may be precipitated.

  The etching composition of the present invention contains nitric acid and / or nitrate. These nitric acid components can reduce damage to the silicon oxide film. As the nitrate, for example, ammonium nitrate containing no alkali metal is preferable.

  The concentration of nitric acid in the etching composition of the present invention is preferably 0.0001 to 20% by weight, particularly 0.01 to 1% by weight, and more preferably 0.01 to 0.2% by weight. Particularly in the range of 0.01 to 0.1% by weight, a high silicon nitride etching rate and selectivity can be achieved. On the other hand, when 20 wt% or more is added, the etching rate of silicon nitride tends to decrease.

  The etching composition of the present invention does not contain hydrofluoric acid. Hydrofluoric acid increases the etching rate of silicon nitride, but damage to silicon oxide increases to a degree that cannot be ignored, and etching selectivity cannot be obtained.

  The etching composition of the present invention exhibits excellent performance in use for etching silicon nitride, particularly for etching silicon nitride used as an insulating film for semiconductor devices and flat panel displays. In a semiconductor device, silicon nitride is formed on a semiconductor substrate by a CVD method (chemical vapor deposition) or the like, but it is necessary to remove unnecessary portions by etching in order to form elements and circuits. If the etching composition of the present invention is used, silicon nitride can be selectively etched.

  The temperature when using the etching composition of the present invention is 120 to 180 ° C, preferably 130 to 170 ° C. At temperatures exceeding 180 ° C., damage to semiconductor materials other than silicon nitride is likely to occur, and at temperatures below 120 ° C., it is difficult to etch silicon nitride at an industrially satisfactory rate.

  In addition, when batch processing is repeated, since some components of the etching composition of the present invention are consumed or volatilized, the effect of the present invention may be reduced, so that phosphoric acid in the etching composition of the present invention, You may use, adding suitably one or more components in any one of a soluble silicon compound, nitric acid and / or nitrate, and water.

  When etching the silicon nitride using the etching composition of the present invention, ultrasonic waves may be used to accelerate the etching.

  The etching composition of the present invention has high selectivity for etching silicon nitride, and is useful for forming a semiconductor circuit because there is no problem of reprecipitation of silicon oxide when the treatment batch is repeatedly used.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Examples 1-7
A silicon wafer in which SiN is deposited to a thickness of 300 nm by a CVD method on 100 g of an etching composition composed of 0.04% hexafluorosilicic acid, 3.75% water, nitric acid shown in Table 1, and the remaining 85% phosphoric acid. A silicon wafer (15 mm square) having a thickness of 1000 nm and a thermal oxide film of 1000 nm was immersed at 155 ° C. for 30 minutes. The wafer was taken out, washed with water, and dried, and the film thickness of SiN and the thermal oxide film was measured with an optical interference film thickness meter. The etching rate of silicon nitride, the etching rate of silicon oxide, and the selection ratio (silicon nitride / silicon oxide) are shown in Table 1 and FIG.

  When nitric acid was added, the etching rate decreased in a region where the addition amount was small. Conventionally, it was known that the addition of nitric acid was bad, but as is apparent from FIG. 1, the etching rate was within a specific nitric acid concentration range. It has been found that there is a composition range that significantly increases the selectivity.

Comparative Example 1
It implemented by the same method as Examples 1-7 except not adding nitric acid. The results are shown in Table 1.

実施例８〜１０
実施例１において硝酸のかわりに硝酸アンモニウムを添加した以外は同様な条件でエッチングを実施した。窒化ケイ素のエッチング速度、酸化ケイ素のエッチング速度、選択比率（窒化ケイ素／酸化ケイ素）を表２に記載した。

Examples 8-10
Etching was performed under the same conditions as in Example 1 except that ammonium nitrate was added instead of nitric acid. Table 2 shows the etching rate of silicon nitride, the etching rate of silicon oxide, and the selectivity (silicon nitride / silicon oxide).

比較例２
フッ酸を１％添加した以外は、実施例７と同じ方法で実施した。その結果、酸化ケイ素のエッチング速度は１５．４７ｎｍ／ｍｉｎとなり、選択比は０．７１まで低下した。

Comparative Example 2
The same procedure as in Example 7 was performed except that 1% of hydrofluoric acid was added. As a result, the etching rate of silicon oxide was 15.47 nm / min, and the selectivity was reduced to 0.71.

Example 11
A silicon wafer (15 mm) formed by depositing SiN to a thickness of 300 nm by a CVD method on 100 g of an etching composition comprising 0.03% hexafluorosilicic acid, 2.5% water, 0.1% nitric acid, and the remaining 85% phosphoric acid. A batch process of immersing a silicon wafer (15 mm square) with a thickness of 1000 nm and a thermal oxide film of 1000 nm at 150 ° C. for 30 minutes was repeatedly performed. It was carried out while adding 0.1% hexafluorosilicic acid in increments of 4% per batch. As a reference, batch processing was repeated with the same composition except that no nitric acid was added. The results are shown in FIG.

  When nitric acid was not added, the etching rate of silicon oxide was negative (that is, reprecipitation of silicon oxide) as the number of batch treatments increased, but reprecipitation of silicon oxide was remarkably suppressed when nitric acid was added. .

The relationship of the addition amount of nitric acid of Examples 1-7 and the etching rate of silicon nitride is shown. (The horizontal line in the figure indicates the rate of addition of nitric acid.) The reprecipitation of silicon oxide during repeated batch processing is shown. (Example 11) The case where the etching rate is negative indicates the deposition of silicon oxide.

Claims (6)

A silicon nitride etching composition comprising phosphoric acid, hexafluorosilicic acid , nitric acid and / or nitrate, and water, and containing no hydrofluoric acid. The etching composition according to claim 1 , wherein the nitrate is ammonium nitrate. Hexafluorosilicic acid is 0.001 to 0.5 weight%, The etching composition of Claim 1 or 2 characterized by the above-mentioned. The etching composition according to any one of claims 1 to 3 , wherein nitric acid and / or nitrate is 0.0001 to 10% by weight. A method for etching silicon nitride, wherein the etching composition according to any one of claims 1 to 4 is used and etching is performed at 120 ° C or higher and 180 ° C or lower. A method for etching silicon nitride using the etching composition according to any one of claims 1 to 4 , wherein at least one component selected from the group consisting of phosphoric acid, hexafluorosilicic acid , nitric acid and / or nitrate is added. An etching method characterized by being added and used.

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