KR20080079999A - Etching method and ethching composition used in the same - Google Patents

Abstract

An etching method of silicon nitride is provided to suppress the damage and precipitation of silicon oxide caused by a high-purity phosphoric acid, and to use a phosphoric acid etching solution stably for a long period. An etching method of silicon nitride is performed by using a composition containing a phosphorus compound, a boron compound, a silicon compound, and/or fluorides thereof, and water. The boron is contained in an amount of 0.001-10wt%. The silicon is contained in an amount of 0.001-0.01wt%. The fluorine is contained in an amount of 0.010-0.050wt%. The etching is carried out at the temperature ranging from 120 °C to 180 °C.

Description

Etching method and composition for etching used for it {ETCHING METHOD AND ETHCHING COMPOSITION USED IN THE SAME}

The present invention relates to a composition for etching silicon nitride. Furthermore, this invention relates to 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. In the semiconductor manufacturing process, there is a process in which only silicon nitride is selectively etched without damaging silicon oxide. At present, high purity phosphoric acid is mainly used in this process. However, in high-purity phosphoric acid, when used at a high temperature of 150 ° C. or more, there is a problem that silicon oxide damage is large.

As a method of suppressing damage to silicon oxide, phosphoric acid to which high-purity phosphoric acid or hexafluorosilic acid in which silicon is dissolved has been proposed (see Patent Documents 1 to 3). However, hexafluorosilicic acid is a substance which is easy to volatilize, and hexafluorosilicic acid volatilates at the use temperature of 150 degreeC or more, and the stable addition effect was not acquired, and continuous use of etching liquid was difficult. Moreover, when hexafluoro silicic acid was added, precipitation of an insoluble silicon compound from an etching solution accelerated | stimulated and there existed a problem for industrial use.

On the other hand, in the semiconductor wet etching apparatus, etching is performed while circulating the etching liquid to remove impurities and the like in the etching liquid in order to keep clean. Also in the etching of the silicon nitride by the heated phosphoric acid aqueous solution, the method of filtration cycling and removing a precipitate is similarly proposed (patent document 4). However, there is a problem that the precipitated silicon oxide adheres to a semiconductor wafer or the like before being filtered.

As a method of etching silicon nitride at a temperature of 100 ° C. or less, a method of adding fluorosilic acid or fluorosilicate to an etching solution consisting 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 of silicon oxide, which is another semiconductor material, is large and there is a problem for use in the semiconductor process. In particular, when used at a high temperature, the adverse effect is more remarkable.

As described above, there has been no etching composition capable of selectively etching silicon nitride at a high temperature for a long time.

[Patent Document 1] Japanese Unexamined Patent Publication No. 6-349808

[Patent Document 2] Japanese Unexamined Patent Publication No. 2000-133631

[Patent Document 3] Japanese Unexamined Patent Publication No. Hei 8-64574

[Patent Document 4] Japanese Patent Application Laid-Open No. 3-20895

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to prevent damage and precipitation of silicon oxide by high-purity phosphoric acid and to reduce the replacement frequency of the phosphate etching solution, that is, the phosphoric acid etching solution can be stably used for a long time. It is providing the etching method of silicon nitride.

As a result of earnestly examining the etching of silicon nitride, the present inventors found that the etching composition containing phosphorus compound, boron compound, silicon compound and / or their fluoride and water suppresses silicon oxide damage and precipitation than the conventional phosphoric acid etching solution. It was found that the silicon nitride can be etched away stably over a long period of time, and the present invention has been completed.

In the etching method of the present invention, the selectivity to etching of silicon nitride is high, there is no excessive dissolution or precipitation of silicon oxide in the etching for a long period of time, and silicon nitride can be selectively etched, so productivity is high.

The present invention is explained in more detail below.

The silicon nitride etching method of the present invention includes phosphorus compounds, boron compounds, silicon compounds and / or fluorides thereof; And the composition containing water.

Phosphorus compounds and / or fluorides thereof used in the etching method of the present invention are phosphoric acid and phosphorus fluoride, but there are no particular restrictions on the phosphoric acid and phosphorus fluoride used, and those generally distributed can be used.

The phosphorus fluoride used in the etching method of the present invention is selected from the group consisting of fluorophosphates such as phosphorus trifluoride, phosphorus fluoride, HPF ₆ , HPO ₂ F ₂ , H ₂ PO ₃ F, and ammonium fluorophosphate At least one selected is preferred.

The boron compounds and / or fluorides thereof used in the etching method of the present invention may be borates such as boric acid, ammonium borate, boron trifluoride, HBF ₄ , HBF ₃ (OH), HBF ₂ (OH) ₂ , HBF (OH) _3, etc. It is preferable that it is at least 1 sort (s) chosen from the group which consists of fluoroborates, such as fluoroboric acid and ammonium fluoroborate.

The etching method of the present invention is composed of phosphoric acid, 0.001 to 10% by weight of a boron compound and / or phosphorus fluoride, 1 to 30% by weight of water, and 0.001 to 1% by weight of boron compound and 15 to 30% by weight of water. This 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 the boron compound and / or phosphorus fluoride is added more than 10% by weight, materials such as silicon oxide films and the like should not be etched. It becomes easy to etch. Moreover, the etching rate of silicon nitride is low in water less than 1 weight%, and the boiling point of an etching composition falls in water exceeding 30 weight%, and it becomes impossible to maintain the temperature suitable for etching. 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 that can be used in the etching method of the present invention is preferably 0.014% by weight or more, more preferably 0.014% by weight to 10% by weight in view of the etching rate of silicon nitride, the suppression of precipitation of silicon oxide, and the stability of the selectivity. %, 0.014% to 5% by weight is particularly preferred.

The silicon compound of the composition used for the etching method of this invention and / or its fluoride is alkoxysilanes, such as silicic acid, a silicate, hexafluoro silicic acid, a hexafluorosilicate, tetraethoxysilane, tetramethoxysilane, methyltrile, etc. Although alkylsilanes, such as methoxysilane, are especially preferable, you may use other soluble silicon compounds. As a silicate and hexafluorosilicate, an ammonium salt is preferable. As the silicic acid or the silicate, a silicon oxide or the like may be added to sulfuric acid or phosphoric acid, and heated and dissolved. Hexafluorosilicic acid and hexafluorosilicate may use what is industrially distributed, and hydrofluoric acid may be made to react with silicic acid, and this may be used as a salt.

By addition of these silicon compounds, damage to a silicon oxide film can be reduced.

The concentration of the silicon compound in the etching method of the present invention is preferably from 0 to 0.5% by weight, in particular from 0.001 to 0.1% by weight. When 0.5 weight% or more is added, there exists a possibility that a silicon oxide may precipitate.

It is particularly preferable that the silicon content in the etching method of the present invention is 0.001 to 0.01% by weight, and the fluorine content is 0.010 to 0.050% by weight. If the silicon content is less than 0.001% by weight, the etching rate of the silicon oxide in the initial batch batch is high, and the selectivity of the initial batch is low, making it difficult to stabilize. On the other hand, at 0.01 weight% or more, the etching rate of silicon nitride falls with repetition of a batch process, and selection ratio is also hard to stabilize.

In the etching method of the present invention, high selectivity can be obtained from the beginning of the batch, and stability is maintained for a long time. Although the cause of such a characteristic is not necessarily obtained, it is thought that the complex material of boron, silicon, and fluorine (fluoric acid) is formed in an etching composition, and the extremely stable state is maintained.

In the etching method of this invention, it is preferable to add nitric acid and / or nitrate. By adding nitric acid and / or nitrate, damage to the silicon oxide film can be reduced. In particular, when phosphorus compounds, boron compounds and / or their fluorides and nitric acid and / or nitrates are used in combination, even if the batch treatment is repeated, variations in the selectivity of silicon nitride to silicon oxide are small, resulting in extremely high stability. As nitrate, it is preferable to use ammonium nitrate.

The concentration of nitric acid and / or nitrate in the etching method of the present invention is preferably 0 to 20% by weight, in particular 0.0001 to 10% by weight, more preferably 0.01 to 1% by weight, especially 0.01 to 0.2% by weight. On the other hand, when 20 weight% or more is added, the etching rate of a silicon nitride will fall.

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

The temperature of the etching method of this invention is 120-180 degreeC, Preferably it is 130-170 degreeC. At temperatures exceeding 180 ° C, damage is likely to occur to semiconductor materials other than silicon nitride, and at temperatures below 120 ° C, it is difficult to etch silicon nitride at an industrially acceptable rate.

In the etching method of this invention, according to the etching of silicon nitride, the density | concentration of silicon in an etching liquid becomes high. Therefore, to avoid this, phosphorus compounds, boron compounds and / or their fluorides may be further added. The boron compound or phosphorus fluoride may be added alone or as a composition for etching of the present invention containing a boron compound and / or phosphorus fluoride.

Moreover, when repeating a batch process, some components of the etching composition of this invention may be consumed or volatilized, and the effect of this invention may fall, and the phosphorus compound, boron compound, and silicon in the etching composition of this invention may be reduced. Any one or more of the compounds and / or their fluorides, nitric acid and / or nitrates, and water may be used while appropriately added.

In the etching method of the present invention, when etching silicon nitride, the etching may be accelerated by using an ultrasonic wave or the like.

Example

Although this invention is demonstrated further in detail by the following example, this invention is not limited to these.

Example  One

A silicon wafer (square of 15 mm on one side) and a thermal oxide film 1000 having SiN formed in a thickness of 300 nm by CVD method in 100 g of an etching composition consisting of 0.02% of fluoroboric acid, 0.002% of ammonia, 5% of water and the remainder of phosphoric acid. A silicon wafer (square of 15 mm on one side) formed into a film with a thickness of nm was immersed at 150 ° C. for 30 minutes. The wafer was taken out, washed with water and dried, and the film thicknesses of the SiN and thermal oxide films were measured with an optical interference film thickness meter. 14 batches were repeated continuously as this batch. The SiN etching rate at the 14th batch was 6.10 nm / min, and the etching rate of the thermal oxide film was 0.03 nm / min. Also in the 14th batch, precipitation of silicon oxide was not confirmed on the thermal oxide film, and the thermal oxide film was slightly etched.

In the said etching composition, although starting from the state which does not contain soluble silicic acid at first, the composition became the state containing soluble silicic acid immediately after starting use. When the etching selection ratio (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, it improved from 18 in the first batch to 130 in the 14th batch.

Example  2

Silicon nitride was etched on the conditions similar to Example 1 using the composition which added 0.03% of hexafluoro silicic acid to the composition of Example 1 further.

Also in the 14th batch, precipitation of the silicon oxide was not confirmed.

The selection ratio of silicon nitride and silicon oxide was 220 from the first batch, and was a high selection ratio from the beginning.

Example  3

Silicon nitride was etched on the conditions similar to Example 1 using the composition which changed 0.02% of fluoroboric acid to 0.02% of fluorophosphoric acid in the composition of Example 1.

The SiN etching rate at the 14th batch was 6.00 nm / min, and the etching rate of the thermal oxide film was 0.06 nm / min. Also in the 14th batch, precipitation of silicon oxide was not confirmed on the thermal oxide film, and the thermal oxide film was slightly etched.

In this etching composition, it started from the state which does not contain soluble silicic acid at first, but the composition was a state containing soluble silicic acid immediately after starting use. When the etching selection ratio (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.

Example  4

Silicon nitride was etched on the conditions similar to Example 1 using the composition which changed 0.02% of fluoroboric acid into 0.01% of fluoroboric acid and 0.01% of fluorophosphoric acid in the composition of Example 1.

The SiN etching rate at the 14th batch was 6.00 nm / min, and the etching rate of the thermal oxide film was 0.05 nm / min. Also in the 14th batch, precipitation of silicon oxide was not confirmed on the thermal oxide film, and the thermal oxide film was slightly etched.

In this etching composition, it started from the state which does not contain soluble silicic acid at first, but the composition was a state containing soluble silicic acid immediately after starting use. When the etching selection ratio (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

Silicon nitride was etched on the conditions similar to Example 1 using the composition which added 0.03% of hexafluoro silicic acid to the composition of Example 1 further.

0.02% fluoroboric acid was added every 4% / batch, and the precipitation of the silicon oxide was not confirmed even in 14th batch.

The selectivity ratio of silicon nitride and silicon oxide was 200 from the 1st batch, and high selection ratio was obtained from the beginning.

Example  6

In the composition of Example 5, silicon nitride was etched 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, and 0.1% of nitric acid was further added.

0.05% fluoroboric acid was added every 4% / batch, the SiN etching rate of the first batch was 5.42 nm / min, the SiN etching rate of the 12th batch was 5.00 nm / min, and the etching rate of the thermal oxide film was 0.01 nm /. min. Also in the 12th batch, precipitation of silicon oxide was not confirmed 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, which was a high selectivity from the beginning, and the second batch was 440, and the high selectivity was maintained.

Example  7

Silicon nitride was etched on the conditions similar to Example 5 using the composition which changed 0.1% nitric acid to 1% nitric acid in the composition of Example 6.

SiN etching rate of the 1st batch was 5.57 nm / min, SiN etching rate of the 12th batch was 5.02 nm / min, and the etching rate of the thermal oxidation film was 0.02 nm / min. Also in the 12th batch, precipitation of silicon oxide was not confirmed on the thermal oxide film, and the thermal oxide film was 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 220 and the twelfth batch was 328.

Example  8

In the composition of Example 1, silicon nitride was etched under the same conditions as in Example 1 using a composition in which 0.02% of fluoroboric acid was changed to 0.05% of fluoroboric acid, and 0.1% of ammonium nitrate was further added. .

SiN etching rate of the 1st batch was 5.44 nm / min, SiN etching rate of the 12th batch was 4.99 nm / min, and the etching rate of the thermal oxidation film was 0.01 nm / min. Also in the 12th batch, precipitation of silicon oxide was not confirmed on the thermal oxide film, and the thermal oxide film was slightly etched.

In this etching composition, it started from the state which does not contain soluble silicic acid at first, but the composition was a state containing soluble silicic acid immediately after starting use. The etching selection ratio (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined. The first batch was 340, which was a high selection ratio from the beginning, and the fourth batch was 441.

Example  9

The etching was carried out in the same manner as in Example 1 except that 0.05% fluoroboric acid was added every 4% / batch to the etching composition consisting of 0.03% hexafluorosilicic acid, 2.5% water and the balance of phosphoric acid.

Even if the batch was repeated, there was no decrease in the etching rate of silicon nitride, and the etching of silicon oxide was also maintained at an extremely low level.

Example  10

0.1% (1000 ppm) nitric acid was further added to the composition of Example 9, and etching was performed in the same manner as in Example 1.

As in Example 9, there was no decrease in the etching rate of silicon nitride, and the etching of silicon oxide was also maintained at an extremely low level, but the selectivity was particularly higher than that in Example 9 after repeated drainage.

Batch Selectivity Example 9 (without HNO ₃ ) Example 10 (with HNO ₃ ) One 297 325 2 197 371 3 325 519 4 338 416 5 189 242 8 150 354 10 144 206 11 106 376 12 118 439

Example  11

To an etching composition consisting of 0.0043% silicon, 0.0174% fluorine, 0.015% boron (0.022% hexafluorosilicic acid, 0.086% boric acid), 3.75% water and the balance of phosphoric acid, 0.05% fluoroboric acid per batch was added at 4.5% / batch And except having evaluated at 155 degreeC, it etched by the method similar to Example 1.

In this composition, a constant selectivity could be obtained from the first batch, and even if the batch was repeated, there was no decrease in the etching rate of silicon nitride.

Example  12

Silicon nitride was etched under the same conditions as in Example 11 except that 0.0039% silicon and 0.0158% fluorine (equivalent to 0.02% in hexafluorosilic acid) were used.

Although the etching rate of silicon nitride did not fall even if batch was repeated, the etching rate of the thermal oxidation film of the 1st and 2nd batch was 0.05 nm / min or more, and it was larger than Example 11.

Example  13

Silicon nitride was etched under the same conditions as in Example 11 except that 0.0049% silicon and 0.0198% fluorine (equivalent to 0.025% in hexafluorosilic acid) were used.

Although etching of silicon oxide was kept at a low level, the etching rate of silicon nitride was seen to be reduced until the third batch.

Comparative example  One

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

Comparative example  2

Etching was carried out in the same manner as in Example 1, using an etching composition consisting of 0.03% of hexafluorosilicic acid, 2.5% of water and the balance of phosphoric acid.

Each time the number of batches was repeated, the etching rate of silicon nitride decreased.

Comparative example  3

For the composition of Comparative Example 2, 0.1% hexafluorosilicic acid was added sequentially in batches every 4% / batch.

Even if the batch was repeated, there was no decrease in the etching rate of silicon nitride etching. However, precipitation of silicon oxide occurred after the fifth batch, and it could not be used continuously.

Comparative example  4

In the composition of Example 5, silicon nitride was etched 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 further added.

1.5% fluoroboric acid was added every 4% / batch, the SiN etching rate of the 1st batch was 45.4 nm / min, and the etching rate of the thermal oxidation film was 84.6 nm / min. The SiN etching rate at the 12th batch was 49.0 nm / min, and the etching rate of the thermal oxide film was 70.1 nm / min.

The etching selection ratio (silicon nitride / silicon oxide) of silicon nitride and silicon oxide in each batch was examined, and the first batch was 0.5 and the 12th batch was 0.7, which was an extremely low selectivity.

1 shows the etching rate of silicon nitride under the conditions of Examples 11 to 13;

2 shows the etching rate of silicon oxide under the conditions of Examples 11 to 13;

3 shows the stability of the etching rate of silicon nitride under the conditions of Examples 11 to 13;

4 shows selectivity (silicon nitride / silicon oxide) under the conditions of Examples 11 to 13;

5 shows the etching rates of silicon nitride under the conditions of Comparative Examples 2 and 3;

FIG. 6 is a diagram showing an etching rate of silicon oxide under the conditions of Comparative Examples 2 and 3 (negative etching rate indicates precipitation of silicon oxide); FIG.

7 shows the etching rates of silicon nitride under the conditions of Examples 9 and 10;

8 shows etching rates of silicon oxide under the conditions of Examples 9 and 10;

Claims (11)

Phosphorus compounds, boron compounds, silicon compounds and / or fluorides thereof; And a method for etching silicon nitride by a composition containing water. The method of etching silicon nitride according to claim 1, wherein the phosphorus compound and / or their fluoride is at least one selected from the group consisting of phosphoric acid, phosphorus fluoride, phosphorus trifluoride, phosphorus fluoride, fluorophosphate and fluorophosphate. The method of etching silicon nitride according to claim 1, wherein the boron compound and / or fluoride thereof is at least one selected from the group consisting of boric acid, boric acid, boron fluoride, boron trifluoride, fluoroboric acid and fluoroborate. The method of claim 1, wherein the silicon compound is silicon halide, hexafluorosilicate, hexafluorosilicate, alkoxysilane, alkylsilane, silicic acid, silicate, silicon fluoride, silicon chloride, ammonium hexafluorosilicate, tetraethoxy A method of etching silicon nitride, which is at least one member selected from the group consisting of silane, tetramethoxysilane, and methyltrimethoxysilane. The method of etching silicon nitride according to any one of claims 1 to 4, wherein the boron content is 0.001 to 10% by weight or more. The method of etching silicon nitride according to claim 1, wherein the silicon content is 0.001 to 0.01% by weight. The method of etching silicon nitride according to claim 1, wherein the fluorine content is 0.010 to 0.050% by weight. The method for etching silicon nitride according to claim 1, further comprising nitric acid and / or nitrate. The silicon nitride etching method according to claim 1, which is etched at 120 ° C or more and 180 ° C or less. The method of etching silicon nitride according to claim 1, further comprising at least one selected from the group consisting of phosphorus compounds, boron compounds, silicon compounds and / or their fluorides, nitric acid and / or nitrates and water. The composition for etching silicon nitride of Claim 1.

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