JP3123254B2 - Back etching equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a thin film (generally referred to as a membrane) used as an electromagnetic wave transmitting film or a barrier film for maintaining a vacuum, and furthermore (typified by ULSI production). The present invention can also be applied to a manufacturing apparatus for a so-called X-ray exposure mask used as an original for duplicating an extremely fine pattern.

[0002]

2. Description of the Related Art There is known a method in which a thin film is provided between a vacuum and the atmosphere in order to extract an electromagnetic wave generated in a vacuum, and the vacuum is maintained. In some cases, a thin barrier film is used to maintain the vacuum in a window for observing the inside of the vacuum device while maintaining a vacuum or irradiating a sample in a vacuum with light from the outside.

In the manufacture of semiconductor integrated circuits, the development of X-ray exposure technology using X-rays has been progressing along with the miniaturization of elements due to the progress of photolithography technology. Exposure masks are also being developed. The X-ray exposure mask has an X-ray absorption pattern formed on an X-ray transparent thin film.

An example of a method of forming a vacuum holding film or an X-ray transparent thin film of an X-ray exposure mask is shown in FIGS. 3 to 5 using sectional views of the film to be formed. A thin film 2 for a membrane is formed on a silicon substrate 1 by a sputtering method, a vacuum evaporation method, or another so-called vapor phase growth method (FIG. 3). An etching mask thin film 3 is formed on the surface opposite to the formed film surface (FIG. 4), and a silicon substrate 1 is formed.
Is etched away with an organic alkali solution such as ethylenediamine, an inorganic alkali solution such as sodium hydroxide, or an acid-based etchant such as a hydrofluoric acid solution to form a thin film held on the silicon substrate 1 (FIG. 5).

[0005] The etching of the silicon substrate is called back etching, and the formed thin film is called a membrane. In the X-ray exposure mask, an X-ray absorption pattern 21 is formed on the membrane as shown in the sectional view of FIG.

In the back etching step, an etching apparatus as shown in FIG. 7 is conventionally used. According to this apparatus, the etching solution is heated by the heater, and the heat continues to be transmitted to the outside through the wall surface of the back etching solution tank 22. For this reason, since the temperature and temperature distribution of the etching solution tend to be non-uniform, the etching rate also tends to be non-uniform in the surface of the material to be etched.
Further, the liquid pressure by the etching liquid is applied from the upper side, while the atmospheric pressure is applied from the lower side, and the load is unbalanced. From these facts, if the silicon is not sufficiently etched and remains somewhat unevenly on the membrane near the end point of the etching, stress exceeding the limit is locally concentrated in the membrane. There is a high risk that the membrane will eventually be destroyed.

Further, when the etching solution 18 leaks, the etching solution 18 extends around the side surface or the pattern surface 4 on the front side, so that, for example, when there is a pattern on the front surface, Also has the problem that the pattern is damaged. Further, as described above, the etching solution 18 is stored above the silicon base material, and at the end of etching, only the membrane in the region to be etched withstands the load caused by the hydrostatic pressure of the etching solution 18. Therefore, if the film thickness of the membrane is too thin, there is still a risk that the membrane will be broken.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a back etching process for forming a membrane using a substrate as a support. Eliminates the instability of the etchant temperature due to heat escaping from the substrate and equipment,
Furthermore, if there is a portion of the surface (such as an X-ray exposure mask) that needs to be prevented from being damaged, damage due to leakage of the etchant is prevented, and damage to the membrane that is likely to occur at the end of the back etching process is prevented. An object of the present invention is to provide a back etching apparatus which can easily and stably form a membrane.

[0009]

Means provided by the present invention in order to solve the above-mentioned problem is that a material portion on the other surface side of a substrate on which a thin film is formed is removed by etching, In a back etching apparatus for producing a membrane supported by the base material, at least, an inner tank for back etching and an outer tank for maintaining a liquid temperature, wherein the base material is a part of a vessel wall, and an etching solution is charged. At least a part of the inner tank for back etching is immersed in the outer tank for maintaining temperature containing the temperature maintaining liquid, and the etchant that can leak from the inner tank for back etching contains the outer tank for maintaining temperature. A back etching apparatus characterized in that the back etching apparatus is held in a state of being diffused into a medium temperature holding liquid.

[0010] In another preferred embodiment,
The back etching apparatus is characterized in that the base material is silicon.

When the back etching apparatus according to the present invention is used, first, the substrate is attached to the inner tank for back etching with the surface to be etched inside, and then an etching solution is poured into the inner tank for back etching. Into an outer tank for maintaining the liquid temperature. The order in which the temperature maintaining liquid is put into the outer tank for holding liquid temperature may be either the pre-step or the post-step when the inner tank for back etching is put into the outer tank for holding liquid temperature. The back etching is performed while adjusting the temperature to be uniform and constant by the liquid temperature holding outer tank containing the temperature holding liquid. Then, when the back etching is completed and the membrane is taken out, the membrane is simultaneously discharged using a discharge means for the temperature holding liquid and a discharge means for the etching liquid (both not shown).

The liquid amounts of the temperature holding liquid and the etching liquid need to be adjusted from the membrane portion to the respective liquid levels so that the liquid pressure applied to the membrane portion is substantially balanced in consideration of the specific gravity of the two. . Particularly preferred is a case where the specific gravities of the two can be regarded as substantially equal. By making the liquid level heights of the two substantially equal, the above adjustment can be simplified. Also, when the back etching is completed and the membrane is taken out, the liquid pressure applied to the membrane portion is discharged in such a manner that the hydraulic pressure applied to the membrane portion is substantially balanced in consideration of the specific gravity of the both.

[0013]

In the method of manufacturing a membrane supported on a silicon substrate, the back etching is not uniform in the plane in the back etching step of manufacturing the membrane, and there is a possibility of destruction of the film. In the case of an X-ray exposure mask, if a liquid leaks, the pattern is destroyed.

During the back etching, the inner tank for the back etching was immersed in the outer tank for maintaining the liquid temperature so as to keep the etching rate constant and to eliminate the instability in forming the membrane. Also, when the etchant leaks, the leaked liquid diffuses into the temperature holding solution, so that it can be prevented from sneaking into the front surface of the base material, and the portion (pattern to avoid damage due to etching) can be prevented. Etc.) can be prevented.

Further, the pressure applied to the membrane could be reduced by adjusting the height of the etching solution and the temperature maintaining solution.

Hereinafter, the concept of the back etching apparatus of the present invention and the back etching method using the back etching apparatus of the present invention will be described.

FIG. 1 shows a first example of the back etching apparatus of the present invention. FIG. 1 shows a state in which the etching liquid 18 is put into the inner tank 7 for back etching and the silicon substrate 1 is being back etched. A mask thin film 3 for back etching is formed on the silicon substrate 1, and a gasket 5 for preventing leakage of the etching solution 18 is inserted between the inner tank 7 for back etching and the thin film 3 for mask for back etching.

As the etching solution 18, an organic etching solution such as ethylenediamine, an inorganic alkali solution such as sodium hydroxide or potassium hydroxide, or an acid etching solution such as a hydrofluoric acid aqueous solution can be used.

The inner tank 7 for back etching is immersed in the temperature holding liquid 17 of the outer tank 9 for holding the liquid temperature. An etching solution heater 14 and an etching solution temperature sensor 13 are installed in the inner tank 7 for back etching. The etchant is heated during etching.

The temperature holding liquid 17 is filled in the outer tank 9 for holding the liquid temperature up to almost the same height as the etching liquid. Temperature holding liquid 1
At least one temperature holding liquid inflow / outflow portion 19 through which the liquid passes through the support base 8 is formed so that the 7 comes into contact with the pattern surface 4. The temperature holding liquid 17 is heated to substantially the same temperature as the etching liquid 18.

At the time of back etching, the etching solution 1
The liquid temperatures of the liquid 8 and the temperature holding liquid 17 are measured by the temperature sensor 13 for the etching liquid and the temperature sensor 15 for the temperature holding liquid, respectively. Control heating and keep constant.

When the etching apparatus of the present invention is used, the temperature difference between the inside and outside of the wall of the inner wall 7 for back etching is eliminated, and the amount of heat leaking from the inner tank 7 for back etching is suppressed. Therefore, the liquid temperature of the etching liquid 18 is kept stable, so that the etching can be stably performed without unevenness in the plane. Since the pressures of the etching solution 18 and the temperature holding solution 17 are substantially balanced at the liquid leakage prevention packing 5, the etching solution 18
Although the liquid leaks little to the side, even if there is a liquid leak, the leaked liquid diffuses into the temperature holding liquid 17 and thus has little effect on the pattern surface of the front.

Furthermore, even when the etching is completed and the thin film becomes the above-mentioned membrane, the fluid pressure applied to both sides of the membrane is balanced, and there is no possibility that an unbalanced external force is applied as in the prior art. Therefore, the membrane is not destroyed.

As the gasket 5 for preventing leakage of the etching solution, an organic silicon rubber may be used, and further, a packing such as a fluororesin may be used. The inner tank 7 for back etching and the outer tank 9 for holding the liquid temperature may be made of the same material, but the inner tank 7 for back etching needs to have resistance to the etching solution 18 and is made of metal such as stainless steel, or gold, nickel, A film formed of a metal having resistance such as chromium, and a film formed of a fluororesin can be used. The back etching inner tank 7 may have a conventionally known shape.

It is necessary that the temperature holding liquid 17 does not affect the pattern surface of the front surface, and that the temperature holding liquid 17 can be heated stably to the same degree as the etching liquid 18. For these reasons, ethylene glycol and water can be used as familiar examples.

[0026]

<Embodiment 1> An embodiment of etching using the back etching apparatus of FIG. 1 will be described below. A thin film 3 serving as an etching mask and a thin film 2 for a membrane were formed on a silicon substrate 1 to be etched, and a packing made of silicon rubber was placed in a back etching inner tank 7 as a liquid leakage preventing packing 5. In this embodiment, the thin film 3 serving as an etching mask and the thin film 2 for a membrane are both made of silicon nitride formed by a chemical vapor deposition method, and both have a thickness of about 1.0 μm. The silicon substrate is 0.5
mm in thickness.

When the material to be etched is a mask for X-ray exposure, an X-ray absorption pattern is formed on the thin film 2 serving as a membrane by using a heavy metal such as tantalum, gold, or tungsten. After the silicon substrate 1 was placed in the inner tank 7 for back etching, a 30% aqueous potassium hydroxide solution was filled as an etching solution 18. Thereafter, hot water was poured into the outer tank 9 for maintaining the liquid temperature, and the liquid level was made almost the same as the etching liquid level.

In this embodiment, the inner tank 7 for back etching and the outer tank 9 for holding the liquid temperature are both made of stainless steel.

In the back etching, the etching solution 18 is heated by the etching solution heater 14, the solution temperature is measured by the etching solution temperature sensor 13, and the temperature of the etching solution is reduced to about 90 by feedback control.
The temperature was kept at 0 ° C. The temperature holding solution 17 was maintained at about 90 ° C. in the same manner as the etching solution 18 using a dedicated heater and sensor.

The etching was completed in about one hour, and the membrane was completed. However, the liquid temperature was kept constant, and the etching proceeded in-plane uniformly. Further, even when the etching solution leaked, the opposite side was filled with water, so that the etching solution did not invade the pattern surface 4 and the front portion of the membrane was not affected.

<Embodiment 2> (FIG. 2) is a sectional view of an etching apparatus according to a second embodiment of the back etching apparatus of the present invention. The figure shows a state where the etching of the silicon base material has progressed about half. The etching method is described below.

Using the same material to be etched as in the first embodiment, the material to be etched was sandwiched between the inner tank 7 for back etching and the support 8, and both were connected by the connecting bolt and nut 20. The connecting bolt and nut 20
Were provided in total of 6 sets (4 sets are not shown). A gasket 5 for preventing leakage of the etchant was provided between the material to be etched and the inner tank 7 for back etching, and a cushion 6 was provided between the support base and the material to be etched.

After assembling the inner tank 7 for back etching, the material to be etched, and the support 8, an etching solution 18 was injected. Thereafter, it was immersed in the liquid temperature holding outer tank 9 and set. Water was previously heated to 90 ° C. and poured as a temperature maintaining liquid 17 into the liquid temperature maintaining outer tank 9.

In the back etching, the etching solution 18 was heated by the etching solution heater 14, the solution temperature was measured by the etching solution temperature sensor 13, and the solution temperature was maintained at about 90 ° C. by controlling the heater. The temperature holding solution 17 was also maintained at about 90 ° C. The etching solution 18
The back etching was performed by agitating the stirrer 12 so that each of the temperature maintaining liquid 17 and the temperature maintaining liquid 17 had a uniform temperature distribution in each tank.

The back etching was completed in about 1 hour, and the membrane was completed. However, the liquid temperature was kept constant, and the progress of the back etching was uniform in the plane.

Also, when the etching solution 18 leaks, the opposite side is filled with water, so that the etching solution does not enter the pattern surface 4 and the front side portion of the membrane is not affected. Was.

[0037]

According to the back etching apparatus of the present invention, if the back etching step of producing a membrane by the back etching method of the present invention is performed, the uniformity of the etching rate during the back etching can be maintained. It was possible to prevent problems such as breakage of the membrane due to the material remaining partially on the membrane. Also, if used for back etching of the mask for X-ray exposure, even if the etchant leaks, the leaked liquid diffuses into the temperature holding liquid, so that it is possible to prevent the base material from sneaking into the front surface. In addition, the reliability of back etching is improved.

Further, since the pressures of the etching solution and the temperature holding solution are substantially balanced on both surfaces of the membrane, the pressure applied to the membrane after etching is almost equal on both surfaces, and there is a fear that the membrane may be broken by the pressure. lost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a back etching apparatus according to the present invention, using a cross-sectional view.

FIG. 2 is an explanatory view showing another embodiment of the back etching apparatus according to the present invention, using a cross-sectional view.

FIG. 3 is a sectional view showing a conventional method for forming a membrane in the order of steps.

FIG. 4 is a sectional view showing a conventional method of forming a membrane in the order of steps.

FIG. 5 is a sectional view showing a conventional method for forming a membrane in the order of steps.

FIG. 6 is an explanatory diagram showing an X-ray exposure mask using a cross-sectional view.

FIG. 7 is an explanatory diagram showing an example of a conventional back etching apparatus in a cross-sectional view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon base material 2 ... Thin film for membranes 3 ... Thin film for etching masks 4 ... Pattern surface 5 ... Packing for preventing liquid leakage 6 ... Cushion 7 ... Inside for back etching Tank 8 ... Support stand 9 ... Outer tank for maintaining liquid temperature 10 ... Outer lid 11 ... Inner lid 12 ... Agitator 13 ... Temperature sensor for etching liquid 14 ... For etching liquid Heater 15: Temperature sensor for temperature-maintaining liquid 16: Heater for temperature-maintaining liquid 17: Temperature-maintaining liquid 18: Etching liquid 19: Penetration part for entering / exiting temperature-maintaining liquid 20: For connection Bolt and nut 21 ・ ・ ・ X-ray absorption pattern 22 ・ ・ ・ Back etching liquid tank 23 ・ ・ ・ Support plate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-241419 (JP, A) JP-A-3-214730 (JP, A) JP-A-6-13293 (JP, A) 121135 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/306 C23F 1/00-3/06

Claims (2)

(57) [Claims] 1. A back etching apparatus for removing a material portion on the other surface side of a base material on which a thin film is formed by etching to produce a membrane supported by the base material, wherein at least the base material is It consists of a back etching bath and the liquid temperature holding outer tub be part of the wall, etching
At least the inner tank for back etching which contains
An outer tank for maintaining the temperature of the liquid, a part of which is filled with a temperature maintaining liquid.
Immersed inside and from the inner tank for back etching
Leakage of etchant temperature holding solution in outer tank for temperature holding
A back etching apparatus characterized in that the back etching apparatus is held in a state of being diffused into the substrate. 2. The back etching apparatus according to claim 1, wherein said base material is silicon.