JP5332197B2 - 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. However, hexafluorosilicic acid is a substance that volatilizes easily, and at a use temperature of 150 ° C. or higher, hexafluorosilicic acid is volatilized, a stable addition effect cannot be obtained, and the etching solution continues. It was difficult to use. Further, when hexafluorosilicic acid is added, insoluble silicon compounds are precipitated from the etching solution earlier, which causes a problem in industrial use.

  On the other hand, in a semiconductor wet etching apparatus, etching is performed while filtering and circulating an etching solution to remove dust and the like in the etching solution in order to keep it clean. In the etching of silicon nitride with a heated phosphoric acid aqueous solution, a method for removing precipitates by filtration and circulation has also been proposed (Patent Document 4). However, the deposited silicon oxide has a problem of adhering to a semiconductor wafer or the like before being filtered.

  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, in the etching composition in which both hydrofluoric acid and nitric acid are added to phosphoric acid, the damage to silicon oxide, which is another semiconductor material, is large, and there is a problem in using it in a semiconductor process. In some cases, the adverse effects were even more pronounced.

  As described above, there has been no etching composition that can selectively etch silicon nitride stably at a high temperature for a long period of time.

JP-A-6-349808 Japanese Patent Laid-Open No. 2000-136331 JP-A-8-64574 Japanese Patent Publication No. 3-20895

  In view of the above problems, the object of the present invention is to suppress damage and precipitation to silicon oxide by high-purity phosphoric acid and to reduce the frequency of replacement of the phosphoric acid etching solution, that is, to stabilize the phosphoric acid etching solution over a long period of time. It is in providing the etching composition which can be used for.

  As a result of intensive studies on etching of silicon nitride, the present inventors have found that an etching composition comprising a phosphorus compound, a boron compound and / or a fluoride thereof, and water is more oxidized than a conventional phosphoric acid etching solution. It has been found that material damage and precipitation can be suppressed, and silicon nitride can be stably removed by etching for a long period of time, and the present invention has been completed.

  The present invention is described in further detail below.

  The silicon nitride etching composition of the present invention comprises a phosphorus compound, a boron compound and / or a fluoride thereof, and water.

  Phosphorus compounds used in the etching composition of the present invention are phosphoric acid and phosphorous fluoride, but phosphoric acid and phosphorous fluoride to be used are not particularly limited, and those that are generally available can be used. .

Examples of the phosphorus fluoride used in the etching composition of the present invention include phosphorous trifluoride, phosphorus pentafluoride, fluorophosphates such as HPF ₆ , HPO ₂ F ₂ , and H ₂ PO ₃ F, ammonium fluorophosphate, and the like. And at least one selected from the group consisting of fluorophosphates.

Examples of the boron compound used in the etching composition of the present invention include boric acid, borate salts such as ammonium borate, boron trifluoride, HBF ₄ , HBF ₃ (OH), HBF ₂ (OH) ₂ , HBF. It is preferably at least one selected from the group consisting of fluoroborates such as (OH) ₃ and fluoroborates such as ammonium fluoroborate.

  The etching composition of the present invention comprises phosphoric acid, 0.001 to 10 wt% boron compound and / or phosphorus fluoride, 1 to 30 wt% water, 0.001 to 1 wt% boron compound, A composition consisting of 15 to 30% by weight of water is particularly preferred.

  If the boron compound and / or phosphorus fluoride is less than 0.001% by weight, the effect of suppressing the precipitation of silicon oxide is small, and if more than 10% by weight of boron compound and / or phosphorus fluoride is added, silicon oxidation A material that should not be etched such as a film is easily etched. If the amount of water is less than 1% by weight, the etching rate of silicon nitride is low. If the amount of water exceeds 30% by weight, the boiling point of the etching composition is lowered, and the temperature suitable for etching cannot be maintained. Industrially, the boron compound and / or phosphorus fluoride is particularly preferably in the range of 0.01 to 0.2% by weight.

  The boron content of the etching composition of the present invention is preferably 0.014% by weight or more, more preferably from the viewpoint of etching rate of silicon nitride, suppression of precipitation of silicon oxide, and stability of selectivity. Particularly preferred are 014 wt% to 10 wt%, 0.014 wt% to 5 wt%.

It is preferable to add a soluble silicon compound to the etching composition of the present invention. When a soluble silicon compound is added, damage to the silicon oxide film can be reduced. As the soluble silicon compound, silicic acid, silicate, hexafluorosilicate, hexafluorosilicate, alkoxysilanes such as tetraethoxysilane and tetramethoxysilane, and alkylsilanes such as methyltrimethoxysilane are particularly preferable. Even if other soluble silicon compounds are used, there is no problem. 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 to 0.5% by weight, particularly preferably 0.001 to 0.1% by weight. If added at 0.5% by weight or more, silicon oxide may be precipitated.

  In the etching composition of the present invention, the silicon content is particularly preferably 0.001 to 0.01% by weight, and the fluorine content is preferably 0.010 to 0.050% by weight, and more preferably the silicon content is 0.004 to 0.005% by weight and fluorine content of 0.016 to 0.020% by weight. When the silicon content is less than 0.001% by weight, the etching rate of silicon oxide at the initial stage of the batch used is high, and the selectivity of the initial batch is low and is not stable. On the other hand, when the content is 0.01% by weight or more, the etching rate of silicon nitride decreases as the batch process is repeated, and the selectivity is difficult to stabilize.

  In the etching composition of the present invention, high selectivity is obtained from the beginning of the batch, and stability is maintained for a long time. The reason why such characteristics are obtained is not necessarily clear, but it is considered that a composite of boron, silicon, and fluorine (hydrofluoric acid) is formed in the etching composition, and an extremely stable state is maintained.

  Nitric acid and / or nitrate is preferably added to the etching composition of the present invention. When nitric acid and / or nitrate is added, damage to the silicon oxide film can be reduced. Especially when phosphorus compounds, boron compounds and / or their fluorides are used in combination with nitric acid and / or nitrates, the variation in selective etching properties of silicon nitride relative to silicon oxide is small and extremely stable even after repeated batch processing. Becomes higher. As the nitrate, it is preferable to use ammonium nitrate.

  The concentration of nitric acid and / or nitrate in the etching composition of the present invention is 0 to 20% by weight, particularly 0.0001 to 10% by weight, more preferably 0.01 to 1% by weight, and particularly 0.01 to 0.2% by weight. % Is preferred. On the other hand, when 20 wt% or more is added, the etching rate of silicon nitride decreases.

  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. By using the etching composition of the present invention, silicon nitride can be selectively and stably etched for a long period of time.

  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.

  When the etching composition of the present invention is used, the silicon concentration in the etching solution increases with the etching of silicon nitride. Therefore, in order to avoid this, a phosphorus compound, a boron compound and / or a fluoride thereof can be additionally added. The boron compound or phosphorus fluoride may be added alone, or may be added as an etching composition of the present invention containing a boron compound and / or phosphorus fluoride.

  In addition, when batch processing is repeated, since some components of the etching composition of the present invention are consumed or volatilized, the effects of the present invention may be reduced, so that the phosphorus compound in the etching composition of the present invention, Any one or more of boron compounds, silicon compounds and / or their fluorides, nitric acid and / or nitrates, and water may be added as appropriate.

  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 highly productive because silicon nitride can be selectively etched without excessive dissolution or precipitation of silicon oxide during long-term etching.

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

Reference example 1
A silicon wafer (15 mm square) having a thickness of 300 nm formed by CVD on 100 g of an etching composition composed of 0.02% fluoroboric acid, 0.002% ammonia, 5% water, and the remaining phosphoric acid, and heat A silicon wafer (15 mm square) having a thickness of 1000 nm was immersed at 150 ° 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. This was repeated 14 batches continuously as one batch. The SiN etching rate of the 14th batch was 6.10 nm / min, and the etching rate of the thermal oxide film was 0.03 nm / min. 1
Even in the fourth batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was slightly etched.

  The etching composition initially started from a state in which no soluble silicic acid was contained, but the composition was in a state containing soluble silicic acid immediately after the start of use. When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, it was improved from 18 in the first batch to 130 in the 14th batch.

Example 2
With further hexafluorosilicic acid composition of the composition containing 0.03% Reference Example 1, it was etched in silicon nitride under the same conditions as in Reference Example 1.

  No precipitation of silicon oxide was observed even in the 14th batch.

  The selectivity between silicon nitride and silicon oxide was 220 from the first batch, which was high from the beginning.

Reference example 3
Using the composition was changed 0.02% fluoroboric acid 0.02% fluorophosphate in the composition of Reference Example 1, it was etched in silicon nitride under the same conditions as in Reference Example 1.

  The SiN etching rate of the 14th batch was 6.00 nm / min, and the etching rate of the thermal oxide film was 0.06 nm / min. Even in the 14th batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was slightly etched.

  The etching composition initially started from a state that does not contain soluble silicic acid, but the composition was in a state containing soluble silicic acid immediately after the start of use. When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, the first batch was 15, but the 14th batch was 100.

Reference example 4
Using the composition was changed 0.02% fluoroboric acid 0.01% fluoroboric acid and 0.01% fluorophosphate in the composition of Reference Example 1, was etched in silicon nitride under the same conditions as in Reference Example 1 It was.

  The SiN etching rate of the 14th batch was 6.00 nm / min, and the etching rate of the thermal oxide film was 0.05 nm / min. Even in the 14th batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was slightly etched.

  The etching composition initially started from a state that does not contain soluble silicic acid, but the composition was in a state containing soluble silicic acid immediately after the start of use. When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, the first batch was 16, but the 14th batch was 120.

Example 5
With further hexafluorosilicic acid composition of the composition containing 0.03% Reference Example 1, it was etched in silicon nitride under the same conditions as in Reference Example 1.

  0.02% fluoroboric acid was added every 4% / batch, and no silicon oxide deposition was observed even in the 14th batch.

  The selectivity between silicon nitride and silicon oxide was 200 from the first batch, and a high selectivity was obtained from the beginning.

Example 6
Etching silicon nitride under the same conditions as in Example 5 using a composition in which 0.02% of fluoroboric acid was changed to 0.05% of fluoroboric acid in the composition of Example 5 and 0.1% of nitric acid was further added. Went.

0.05% fluoroboric acid was added every 4% / batch, the SiN etching rate of the first batch was 5.42 nm / min, and the SiN etching rate of the 12th batch was 5.00 nm / min. The etching rate was 0.01 nm / min. Even in the 12th batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was only slightly etched.

  When the etching selection ratio (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, the first batch was 325, a high selection ratio from the beginning, and the twelfth batch was also 440, maintaining a high selection ratio. It was done.

Example 7
Etching of silicon nitride was performed under the same conditions as in Example 5 using a composition in which 0.1% nitric acid was changed to 1% nitric acid in the composition of Example 6.

The SiN etching rate of the first batch was 5.57 nm / min, the SiN etching rate of the 12th batch was 5.02 nm / min, and the etching rate of the thermal oxide film was 0.02 nm / min. Even in the 12th batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was slightly etched.

  When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, it was 220 for the first batch and 328 for the 12th batch.

Reference Example 8
Change 0.02% fluoroboric acid 0.05% fluoroboric acid in the composition of Reference Example 1, further ammonium nitrate with a composition containing 0.1%, etching of silicon nitride under the same conditions as in Reference Example 1 Went.

The SiN etching rate of the first batch is 5.44 nm / min, the SiN etching rate of the 12th batch is 4.99 nm / min, and the etching rate of the thermal oxide film is 0.01.
nm / min. Even in the 12th batch, no deposition of silicon oxide was observed on the thermal oxide film, and the thermal oxide film was slightly etched.

  The etching composition initially started from a state that does not contain soluble silicic acid, but the composition was in a state containing soluble silicic acid immediately after the start of use. When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, the first batch was 340, which was a high selectivity from the beginning, and the twelfth batch was 441.

Example 9
The same method as in Reference Example 1 except that 0.05% fluoroboric acid was added 4% / batch per batch to the etching composition consisting of 0.03% hexafluorosilicic acid, 2.5% water, and the remaining phosphoric acid. Etching was performed.

  Even when the batch was repeated, the etching rate of silicon nitride was not lowered, and the etching of silicon oxide was maintained at a very low level. The results are shown in FIGS.

Example 10
Etching was performed in the same manner as in Reference Example 1 by further adding 0.1% (1000 ppm) nitric acid to the composition of Example 9.

  Similar to Example 9, there was no decrease in the etching rate of silicon nitride, and the etching of silicon oxide was also maintained at a very low level, but the selectivity was higher than in Example 9, especially after increasing the number of batches. The etching rate is shown in FIGS.

実施例１１
ケイ素０．００４３％、フッ素０．０１７４％、ホウ素０．０１５％（ヘキサフルオロケイ酸０．０２２％、ホウ酸０．０８６％相当）、水３．７５％、残部リン酸からなるエッチング組成物にバッチ毎に０．０５％フルオロホウ酸を４．５％バッチ／毎添加し、１５５℃で評価した他は、参考例１と同じ方法でエッチングを実施した。

Example 11
Etching composition comprising 0.0043% silicon, 0.0174% fluorine, 0.015% boron (equivalent to 0.022% hexafluorosilicic acid, 0.086% boric acid), 3.75% water, and the remaining phosphoric acid Etching was carried out in the same manner as in Reference Example 1 except that 0.05% fluoroboric acid was added to each batch at 4.5% batch / rate and evaluated at 155 ° C.

  With this composition, a constant selectivity was obtained from the first batch, and the etching rate of silicon nitride did not decrease even when the batch was repeated. The results are shown in FIGS.

Example 12
Etching of silicon nitride was performed under the same conditions as in Example 11 except that 0.0039% silicon and 0.0158% fluorine (equivalent to 0.02% with hexafluorosilicic acid) were used.

  Although the etching rate of silicon nitride did not decrease even when the batch was repeated (FIG. 6), the etching rate of the thermal oxide film in the first and second batches was 0.05 nm / min or more, which was higher than that of Example 11. (Figure 2)

Example 13
Etching of silicon nitride was performed under the same conditions as in Example 11 except that 0.0051% silicon and 0.0201% fluorine (equivalent to 0.025% with hexafluorosilicic acid) were used.

  The silicon oxide etch was maintained at a low level (FIG. 2), but the silicon nitride etch rate decreased until the third batch (FIG. 1).

Comparative Example 1
Etching was performed in the same manner as in Reference Example 1 except that neither fluoroboric acid nor fluorophosphoric acid was added. The SiN etching rate of the 14th batch was 2.49 nm / min. In the 14th batch, precipitation of silicon oxide was observed on the thermal oxide film, and the thickness of the thermal oxide film was increased.

Comparative Example 2
Etching was performed in the same manner as in Reference Example 1 using an etching composition comprising 0.03% hexafluorosilicic acid, 2.5% water, and the remaining phosphoric acid.

  As the number of batches increased, the etching rate of silicon nitride decreased. The results are shown in FIG.

Comparative Example 3
To the composition of Comparative Example 2, 0.1% hexafluorosilicic acid was sequentially added every batch at 4% / batch.

Even when the batches were repeated, the etching rate of the silicon nitride etching did not decrease (FIG. 5), but silicon oxide was deposited after the fifth batch and could not be used continuously. (Fig. 6)
Comparative Example 4
Etching silicon nitride under the same conditions as in Example 5 using a composition in which 0.02% of fluoroboric acid was changed to 1% of fluoroboric acid and 0.1% of nitric acid was added in the composition of Example 5. It was.

  1.5% fluoroboric acid was added every 4% / batch, the SiN etching rate of the first batch was 45.4 nm / min, and the etching rate of the thermal oxide film was 84.6 nm / min. The SiN etching rate of the 12th batch was 49.0 nm / min, and the etching rate of the thermal oxide film was 70.1 nm / min.

  When the etching selectivity (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, the first batch was 0.5, and the twelfth batch was 0.7, which was an extremely low selectivity.

It is a figure which shows the etching rate of the silicon nitride in the conditions of Examples 11-13. It is a figure which shows the etching rate of the silicon oxide in the conditions of Examples 11-13. It is a figure which shows stability of the etching rate of the silicon nitride in the conditions of Examples 11-13. It is a figure which shows the selection ratio (silicon nitride / silicon oxide) in the conditions of Examples 11-13. It is a figure which shows the etching rate of the silicon nitride in the conditions of Comparative Examples 2 and 3. It is a figure which shows the etching rate of the silicon oxide in the conditions of Comparative Examples 2 and 3. (Negative etch rate indicates silicon oxide deposition.) It is a figure which shows the etching rate of the silicon nitride in the conditions of Examples 9 and 10. It is a figure which shows the etching rate of the silicon oxide in the conditions of Examples 9 and 10.

Claims (9)

At least one selected from the group consisting of boric acid, ammonium borate, boron trifluoride, HBF ₄ , HBF ₃ (OH), HBF ₂ (OH) ₂ , HBF (OH) ₃ , ammonium fluoroborate, phosphoric acid, water And a soluble silicon compound, from the group consisting of boric acid, ammonium borate, boron trifluoride, HBF ₄ , HBF ₃ (OH), HBF ₂ (OH) ₂ , HBF (OH) ₃ , ammonium fluoroborate A composition for etching silicon nitride, wherein at least one selected is 0.001 to 10% by weight. The etching composition according to claim 1, wherein the boron content is 0.014% by weight or more. The soluble silicon compound is at least one selected from the group consisting of silicic acid, silicate, silicon fluoride, silicon chloride, hexafluorosilicic acid, ammonium hexafluorosilicate, tetraethoxysilane, tetramethoxysilane, and methyltrimethoxysilane. The etching composition according to claim 1, wherein the composition is an etching composition. The composition for etching according to claim 1, wherein the soluble silicon compound is 0.001 to 0.1% by weight. The etching composition according to claim 1, wherein the silicon content is 0.001 to 0.01% by weight. The etching composition according to claim 1, further comprising nitric acid and / or nitrate. The etching composition according to claim 6, wherein the nitrate is ammonium nitrate. Nitric acid and / or nitrate is 0.0001-10 weight%, The etching composition in any one of Claims 6-7 characterized by the above-mentioned. A method of etching silicon nitride, wherein the etching composition according to claim 1 is used and etching is performed at 120 ° C. or higher and 180 ° C. or lower.

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