JP3400694B2 - Silicon wafer etching method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for etching a silicon wafer, and more particularly to a method for etching a silicon wafer after slicing, lapping and grinding with an alkaline solution.

[0002]

2. Description of the Related Art In the process of manufacturing a silicon wafer, a silicon wafer sliced from single crystal silicon is
After lapping or grinding, it is etched or washed with a chemical solution in order to remove crystal strain and surface stains generated in those steps. This etching or cleaning includes so-called acid etching using an acid solution as a chemical solution and alkali etching using an alkali solution. For acid etching, a mixed acid which is a mixed solution of nitric acid, hydrofluoric acid and acetic acid is generally used. For alkaline etching, a caustic aqueous solution such as sodium hydroxide or potassium hydroxide is used.

In acid etching using mixed acid, hydrofluoric acid, nitric acid, acetic acid, etc., which are more expensive than caustic alkali such as sodium hydroxide, potassium hydroxide, etc., are used, and a large amount of mixed acid is required, resulting in high cost. Moreover, the mixed acid is a strong acid and is highly corrosive, which makes it difficult to handle and has many safety problems. Further, acid etching using a mixed acid has a high etching rate, so that it is difficult to uniformly etch the wafer, and there is a problem that the flatness of the wafer is deteriorated. Therefore, recently, even if the etching rate is slower than in the case of using a mixed acid, it is easier to perform more uniform etching, and alkali etching using an alkali solution that is less likely to deteriorate the flatness of the wafer is It tends to be used more often.

[0004]

However, in the etching using an alkaline solution, unlike the above-mentioned acid etching, anisotropic etching occurs, which causes a new problem that an etch pit is formed depending on the crystal orientation. .
Briefly explaining the etch pits, cracks (generally referred to as fractured layers) occur on the wafer surface due to processing by loose abrasive grains in the lapping step performed before etching. The purpose of etching is to remove the fractured layer, but deep ones remain as etch pits after etching. Even without a fractured layer, etch pits may occur due to the difference in etch speed depending on the crystal orientation. In such a case, the shape of the etch pit becomes an inverted pyramid-shaped depression or an inverted triangular pyramid-shaped dent. When a low-concentration alkaline solution is used, problems such as deterioration of the shape of the silicon wafer and fogging on the surface of the silicon wafer occur. To solve this, an extremely high-concentration alkaline solution (about 45% or more) is used. It was necessary to use the high-concentration caustic solution) of 1.) at high temperature. Further, when a high-temperature low-concentration alkali is used for safety in handling, the above-mentioned etch pits are likely to appear large, and naturally, it is difficult to set etching conditions or handle in order to avoid it. There was a problem that

The inventors of the present invention avoid, as much as possible, the appearance of etch pits on the wafer surface, which is a problem of conventional alkaline etching, without using a high-concentration alkaline solution, and inevitably generate an etch. We have conducted diligent research to develop an etching method that can control the size of pits to be as small as possible, and that can obtain a wafer with a good surface condition in which deterioration of the wafer shape and generation of fogging on the wafer surface are suppressed. As a result, it was found that the above object can be achieved by using a caustic aqueous solution for etching to which a small amount of alkali nitrite is added, and the present invention has been completed based on this finding. Therefore, it is an object of the present invention to avoid the occurrence of large etch pits as described above, to suppress the deterioration of the wafer shape and the occurrence of fogging on the wafer surface, and as a result, a clean and flat wafer without crystal distortion or surface contamination. It is to provide an alkali etching method capable of obtaining a surface.

[0006]

According to the present invention, in a method of etching a silicon wafer with an alkaline solution, etching is performed using a caustic aqueous solution containing an alkali nitrite salt. A method is provided. The present invention is characterized by using a caustic aqueous solution containing a small amount of alkali nitrite as an etching chemical in the case of alkali etching a silicon wafer after slicing, lapping and grinding. . In such etching using an alkaline aqueous solution containing an alkali nitrite, it is possible to control the size of the etch pits on the silicon wafer surface to be smaller than that in the case of using an aqueous solution containing a single caustic alkali, and it is possible to generate fogging. It is also possible to prevent

[0007] Although the mechanism of the above-mentioned action and effect, which is exhibited by the addition of alkali nitrite, has not been sufficiently clarified, the alkali nitrite is an aqueous solution of nitrite anion and Na ⁺ , K ^+, etc. Alkali metal cations of the alkali metal cations and some of them exist in a molecular state, and each of these ions and molecules have a reversible equilibrium relationship and have a slight buffering action against strong alkali. It is presumed that this is because the crystal orientation anisotropy when attacking the silicon element inside is relaxed.

As will be apparent from the examples described below, addition of salts other than alkali nitrite such as sodium nitrate, potassium nitrate, lithium nitrate and the like will not achieve the above-mentioned effects of the present invention. Can not. Further, when an alkali nitrite salt is added to a caustic alkali solution, the etching rate tends to be slightly lowered. Therefore, adding too much is not a good idea from the viewpoint of productivity drop.
It is preferable to limit the addition to the amount by weight or less. In addition, so-called alkali etching using an alkaline solution has advantages that the shape of the silicon wafer does not deteriorate and it is cheaper than acid etching using a mixed acid or the like.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The etching method for a silicon wafer according to the present invention is characterized by an etching agent used therein, that is, a compounding component of an alkaline solution. In the present invention, examples of the alkaline component to be added to the alkaline solution include caustic alkalis to be added to ordinary alkaline etching, that is, sodium hydroxide, potassium hydroxide and lithium hydroxide. Sodium hydroxide is most commonly used because high purity products are relatively inexpensive to obtain.

The caustic alkali concentration is 15 to 30.
Weight percentages, preferably in the range of 15 to 20 weight percent, are generally used. The caustic alkali used in the present invention may be a high-purity caustic alkali used for conventional ordinary alkali etching, and is not particularly limited, but impurities such as nickel ion, copper ion, chromium ion, and iron can be used. It is preferable that the content of metal ions such as ions is as low as possible, and it is more preferable to use a metal ion having a total content of 50 ppb or less.

Examples of the nitrite alkali salt added to the caustic solution as an essential component of the present invention include lithium nitrite salt, sodium nitrite salt, potassium nitrite salt and the like. In the present invention, of course, one kind of the above caustic alkali salts may be used alone, but two or more kinds may be used in combination. Among these, it is preferable to use sodium nitrite, which is a relatively inexpensive and highly-pure product with stable quality. The purity of the alkali nitrite used is preferably 95% or more, more preferably 99% or more, and particularly preferably the content of metal ions such as nickel ions, copper ions, chromium ions and iron ions is as low as possible. The total content of the metal ions is preferably 50 ppb or less. The amount of alkali nitrite added to the aqueous solution of caustic alkali varies slightly depending on the concentration of caustic alkali in the solution, but is usually 0.05 to 10 based on the solution after addition of the alkali nitrite.
% By weight, preferably 0.1 to 5.0% by weight. When the amount of alkali nitrite added is less than 0.05% by weight, there is almost no effect due to the addition, while 10% by weight
If it is added over the range, the etching rate becomes too slow and the productivity is lowered.

In the present invention, the silicon wafer after slicing, lapping and grinding is usually heated to a temperature of 20 to 110 ° C., preferably 70 to 90 ° C. using the above alkaline solution for etching, and the depth of the wafer surface is usually 5 Etching is performed to about 30 μm. More specifically,
A silicon wafer loaded on a carrier is placed in an etching treatment tank filled with the above alkaline solution of the present invention, for example, an alkaline aqueous solution containing 15 to 30% by weight of sodium hydroxide and 0.1 to 5.0% by weight of sodium nitrite. Dip and rotate the wafer with the carrier at a temperature of 60 to 90 ° C. to bring the wafer to a thickness of 10 to 30 from its surface.
Etch to about μm. After the etching, the wafer is washed with pure water in a water washing tank, then dried and sent to the next step.

[0013]

[Examples] "Example 1" An alkaline aqueous solution for etching containing a sodium hydroxide concentration of 20% by weight and sodium nitrite of 2.0% by weight was prepared, and an etching treatment tank (solution filling capacity of 40 liters, a rectangular treatment tank) was prepared. ). A wafer having a diameter of 8 inches, which has been subjected to double-sided lapping, is loaded into a carrier and immersed in this filling tank, and the wafer is rotated (10 rpm) in the solution with a liquid temperature of 90.
Etching was performed at 10 ° C. for 10 minutes. After the etching-processed wafer is transferred to a washing bath and washed and dried, the wafer surface etching rate, the state of etch pits on the wafer surface after treatment, and the degree of deterioration of the wafer shape before and after etching (ΔTTV: Total thichness) variation
Each) was evaluated. The results are shown in Table 1. The number of evaluation wafers in the examples including the present example and the comparative example is 10
The number of sheets is shown in Table 1.

"Wafer evaluation test method" (1) Etching rate (etching rate: μm / mi
n): (thickness before etching−thickness after etching) / etching time Note that the thickness of the wafer may be measured as an average thickness and a center thickness, but in the case of the present embodiment, the average thickness measurement value (wafer center and outer circumference). 4 points at equal intervals on the circumference of 20 mm from the inside were adopted (5 points in total). (2) Etch pit state evaluation test (μm): The shape of the etch pit is observed with a differential interference microscope, and its width is measured with the micrograph. (3) Wafer shape deterioration degree evaluation test (ΔTTV / (μ
m)): difference between the thickest part and the thinnest part of the wafer (TT
V: Total Thickness Value) is displayed as a difference before and after etching, that is, ΔTTV (change amount of TTV) = TTV after etching−TTV before etching.

Example 2 A sodium nitrite concentration of 0.
An alkaline aqueous solution for etching was prepared in the same manner as in Example 1 except that the amount was 5% by weight, and a wafer was subjected to etching treatment in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 3] A sodium nitrite concentration of 5.
An alkaline solution for etching was prepared in the same manner as in Example 1 except that the amount was 0% by weight, and the wafer was etched.
Evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 4 An alkaline solution for etching was prepared in the same manner as in Example 1 except that the sodium hydroxide concentration was 30% by weight and the sodium nitrite concentration was 3.0% by weight, and the wafer was similarly etched. It processed and evaluated like Example 1.

[Example 5] An alkaline solution for etching was prepared in the same manner as in Example 1 except that the sodium hydroxide concentration was 15% by weight and the sodium nitrite concentration was 1.0% by weight, and the wafer was similarly etched. It processed and evaluated like Example 1.

[Example 6] An alkaline solution for etching was prepared in the same manner as in Example 1 except that the concentration of potassium hydroxide was 30% by weight and the concentration of kalium nitrite was 3.0% by weight. Example 1 except that the time was 5 minutes
The wafer was subjected to etching treatment in the same manner as in 1. and the obtained wafer was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 A 20% by weight aqueous sodium hydroxide solution containing no sodium nitrite was prepared and treated in the same manner as in Example 1, and the resulting wafer was evaluated in the same manner as in Example 1. The results are shown in Table 1.

"Comparative Example 2" The sodium nitrite concentration was set to 1
An alkaline solution for etching was prepared in the same manner as in Example 1 except that the content was changed to 0.0% by weight, and the wafer was subjected to etching treatment, and evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 An alkaline solution for etching was prepared in the same manner as in Example 1 except that 2% by weight of sodium nitrate was added instead of sodium nitrite, and the wafer was subjected to an etching treatment. Evaluated to. The results are shown in Table 1.

Comparative Example 4 The sodium sulfite concentration was adjusted to 0.
An alkaline solution for etching was prepared in the same manner as in Example 5 except that the amount was changed to 05% by weight, and the wafer was subjected to etching treatment in the same manner and evaluated in the same manner as in Example 5.

[0024]

[Table 1]

[0025]

As described above, according to the present invention, when a silicon wafer after slicing, lapping and grinding is alkali-etched, an aqueous solution obtained by adding an alkali nitrite salt to an aqueous caustic alkali solution is used as an etching chemical. Compared with the case of using an alkaline etching chemical solution containing only caustic, the etching rate is hardly reduced, the number of etch pits generated on the silicon wafer surface is small, and the size of the generated etch pits is small. The effect is that it can be controlled to be small and the occurrence of fogging on the wafer surface can be avoided.

Continuation of front page (56) Reference JP-A-5-102122 (JP, A) JP-A-9-137155 (JP, A) JP-A-9-82677 (JP, A) JP-A-10-310883 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21 / 304,21 / 306,21 / 308

Claims (6)

(57) [Claims] 1. A method of etching a silicon wafer, which comprises etching with a caustic aqueous solution containing an alkali nitrite salt in the method of etching a silicon wafer. 2. The method for etching a silicon wafer according to claim 1, wherein the alkali nitrite salt is at least one selected from lithium nitrite salt, sodium nitrite salt and potassium nitrite salt. . 3. The method of etching a silicon wafer according to claim 2, wherein the alkali nitrite is sodium nitrite. 4. The etching of a silicon wafer according to claim 1, wherein the alkali nitrite is added so that the concentration of the aqueous caustic alkali solution after the addition of the salt is 0.05 to 10% by weight. Method. 5. The method for etching a silicon wafer according to claim 1, wherein the caustic alkali concentration in the caustic aqueous solution is 15 to 30% by weight. 6. 15 to 20% by weight of sodium hydroxide,
6. A silicon wafer is etched at 60 to 90 [deg.] C. using an alkaline aqueous solution containing 0.1 to 5.0% by weight of sodium nitrite.
2. A method for etching a silicon wafer according to any one of 1.