JP3260039B2 - Manufacturing method of ferroelectric wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric wafer, and more particularly to a method for manufacturing a ferroelectric wafer comprising a single crystal of lithium tantalate and lithium niobate which is useful as a substrate for a surface acoustic wave device. It is about.

[0002]

2. Description of the Related Art Ferroelectric wafers such as lithium tantalate single crystal and lithium niobate single crystal are used as substrates for surface acoustic wave devices, but these wafers have mirror-polished surfaces on which surface waves propagate. However, it is generally considered that the back side is finished by roughening to prevent spurious due to reflection of bulk waves. However, when the finish on the front side and the back side is different as described above, the wafer is largely warped due to a difference in remaining processing strain.
In order to reduce the distortion due to the roughening of the back side and to improve the warpage of the wafer, there is known a method of performing an etching treatment using a solution such as hydrofluoric nitric acid after the roughening (Japanese Patent Publication No. Sho 56).
-36808).

[0003] However, single crystals such as lithium tantalate and lithium niobate are chemically stable, and the etching rate is very low even with a strong acid such as hydrofluoric nitric acid. Generally 60 to 110
It is performed by heating to ° C.

[0004]

However, these single crystal wafers are affected by the anisotropy of the coefficient of thermal expansion and the piezoelectricity, pyroelectricity, and ferroelectric properties of the ferroelectric material, and the effect of the strained layer due to roughening. The problem is that many wafers are cracked due to the temperature difference when they are easily broken and are put into an etching solution heated from room temperature or when they are taken out of the etching solution and washed with water at room temperature, and the yield is greatly reduced. Has become. Therefore, there is a method of raising the temperature and gradually cooling the wafer while the wafer remains in the etching solution. However, this method is disadvantageous in that it is time-consuming, inefficient, and unsuitable for mass production processing.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a ferroelectric wafer which solves such disadvantages and problems, and includes a method for etching a ferroelectric wafer before and after an etching tank. A stepwise heated or cooled tank is provided, and a temperature difference when the wafer is put in and taken out of the etching tank is set to 35 ° C. or less.

That is, the present inventors have studied various methods for preventing cracks in the etching treatment of ferroelectric wafers, and have described in detail the occurrence of cracks in the etching process of single crystal wafers such as lithium tantalate and lithium niobate. The cracks were observed immediately after the wafer was placed in the heated etching solution and immediately after the wafer was taken out of the etching solution and placed in the washing tank. In particular, the C-axis component was observed in the thickness direction of the wafer. It is found that cracks easily occur in the rotating Y-cut plate containing, and that the wafer is thinner and the back surface roughness is more easily cracked. For this, a tank heated or cooled stepwise before and after the etching solution tank is found. If the temperature difference between when the wafer is put in and out of the etching solution and the temperature difference is within 35 ° C Make sure that the obtained results of the present invention has been completed. This will be described in more detail below.

[0007]

The present invention relates to a method for manufacturing a ferroelectric wafer, which is used for etching a ferroelectric wafer made of a single crystal such as lithium tantalate or lithium niobate as described above. Before and after, steps are provided for heating or cooling tanks, wafers are sequentially inserted into these tanks, and the temperature difference when the wafers are taken in and out of the etching solution is set to 35 ° C or less. For example, there is an advantage that a great effect is obtained in reducing cracks during the etching process of the ferroelectric wafer.

The present invention relates to a method for manufacturing a ferroelectric wafer, and thus to a method for manufacturing a ferroelectric wafer made of a single crystal such as lithium tantalate or lithium niobate, which transmits a surface wave on the surface side. The wafer is mirror-polished and the back side is roughened to prevent spurious emission due to reflection of bulk waves. This wafer is etched with hydrofluoric nitric acid or the like to improve its warpage. ,this is
It is performed under heating of 60-110 ° C. This is because the wafer is very susceptible to cracking due to the anisotropy of the coefficient of thermal expansion and the strained layer caused by roughening, and the yield is greatly reduced. There was a problem.

Therefore, when the cracks were examined, it was found that the cracks occurred immediately after the wafer was put in the heated etching solution and immediately after the wafer was taken out of the etching solution and put in the washing tank. In particular, it has been found that cracks easily occur in a rotating Y-cut plate containing a C-axis component in the thickness direction of the wafer, and that the thinner the wafer and the larger the back surface roughness, the easier it is to crack. It is considered that many cracks occur due to the influence of the anisotropic thermal expansion coefficient of the wafer and the ferroelectric properties of piezoelectricity, pyroelectricity, and strain due to rough surface processing due to a large temperature change. .

Therefore, in this regard, a plurality of water tanks heated or cooled to an intermediate temperature are prepared before and after the etching tank, and when the wafers are sequentially immersed in these water tanks, these water tanks are heated or cooled stepwise. Although it is cooled and the temperature difference between them is reduced, this cracking can be reduced, but it is not clear how best to obtain this one-stage temperature. As a result of continuing to study with various changes in the temperature difference, this was 35 ° C.
It was found that a large effect can be obtained in reducing the cracking of the wafer.

In the practice of the present invention, it is most preferable to apply the present invention to both heating and cooling, and although it is possible to obtain the effect of either of them,
A greater effect can be obtained when applied during cooling than during heating. Note that this etching process is usually performed after roughening the back surface, but may be performed before or after the front surface is mirror-polished. In any case, the same effect can be obtained according to the present invention. it can. This ferroelectric wafer was applied to a rotating Y-cut plate containing a C-axis component in the thickness direction of the wafer, such as a 36 ° Y-cut lithium single crystal tantalate wafer and a 64 ° Y-cut lithium niobate single crystal wafer. In this case, a greater effect can be obtained.

[0012]

Next, examples of the present invention and comparative examples will be described. Examples 1-3, Comparative Examples 1-3 A 36 ° Y-axis pulled lithium tantalate single crystal having a diameter of 3 inches and grown by the usual Czochralski method is sliced, and both surfaces thereof are # 2,000 silicon carbide abrasive grains. To form a 400-μm thick 36 ° Y-cut wafer. Then, when the back surface of the wafer was lapped with # 240 silicon carbide abrasive grains and roughened, the wafer was warped by 90 to 120 μm due to the difference in processing strain between the front and back surfaces of the wafer.

[0013] In view of this, etching is performed using hydrofluoric acid, which is a commercially available mixture of 50% hydrofluoric acid and 36% hydrochloric acid at a volume ratio of 2: 1.
In this case, a water tank heated or cooled to an intermediate temperature was installed before and after the heated etching tank as needed, and 25 wafers were placed in a Teflon basket at a time. Then, the wafer was immersed in each tank, and the holding time in the water tank at the intermediate temperature was set to 1 minute, and 100 wafers were etched.

In this case, the processing conditions were changed to those of the six conditions shown in Table 1. Under any of the conditions, the warping of the wafer was reduced to 15 μm or less by this etching treatment, and the surface side was mirror-polished. The warpage was also 20 μm or less, and the effect of correcting the warpage by removing the processing strain by this etching treatment was given. In Examples (Examples 1 to 3), wafer cracking was significantly reduced and the yield was improved, but in Comparative Examples 1 to 3 where the temperature was 35 ° C. or higher, the wafer cracks were large and the yield was reduced.

[0015]

[Table 1]

Examples 4 to 6 and Comparative Example 4 A 64 ° Y-axis pulled lithium niobate single crystal having a diameter of 3 inches and grown by the ordinary Czochralski method was sliced, and both surfaces thereof were polished with silicon carbide # 2,000. The grains were wrapped to produce a 400 μm thick 64 ° Y-cut wafer. Then, when the back surface of the wafer was lapped with # 240 silicon carbide abrasive grains and roughened, a warp of 80 to 110 μm was generated due to a difference in processing strain between the front and back surfaces of the wafer.

In view of this, an etching process is performed using a commercially available 50% hydrofluoric acid and 60% nitric acid mixed at a volume ratio of 2: 1 with hydrofluoric nitric acid at a temperature of 60 ° C.
In this case, a water tank heated or cooled to an intermediate temperature was installed before and after the heated etching tank as needed, and 25 wafers were placed in a Teflon basket at a time. The wafers were immersed in each of the tanks, and the holding time in the water tank at the intermediate temperature was set to 1 minute, and 100 wafers were etched.

In this case, the processing conditions were changed to the four conditions shown in Table 2. In any case, the warpage of the wafer was reduced to 15 μm or less by this etching treatment, and the surface side was mirror-polished. The warpage is also 20 μm or less, and the processing distortion is removed by this etching treatment, and the effect of correcting the warp is given. In Examples (Examples 4, 5, and 6), wafer cracking was significantly reduced, and the yield was improved.
In the case of Comparative Example 4 described above, the wafer had many cracks, and the yield was reduced.

[0019]

[Table 2]

[0020]

The present invention relates to a method of manufacturing a ferroelectric wafer, and more particularly to a method of etching a ferroelectric wafer by heating or cooling a wafer processing tank in a stepwise manner. It is characterized in that the temperature difference at the time of taking in and out of the liquid is within 35 ° C., according to which the warpage of the wafer is reduced and the cracking of the wafer due to this etching process is significantly reduced. The advantage of being able to do so is given.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C23F 1/00 H01B 3/12

Claims (3)

(57) [Claims] 1. When etching a ferroelectric wafer, a stepwise heated or cooled tank is provided before and after the etching tank, and the temperature difference when the wafer is taken in and out of the etching solution is within 35 ° C. A method for producing a ferroelectric wafer, comprising: 2. The method for producing a ferroelectric wafer according to claim 1, wherein the ferroelectric wafer is a single crystal wafer of lithium tantalate or lithium niobate. 3. The method for producing a ferroelectric wafer according to claim 1, wherein the ferroelectric wafer is a single crystal wafer of 36 ° Y-cut lithium tantalate or 64 ° Y-cut lithium niobate.