JPS62163331A - Wet etching method - Google Patents

Abstract

PURPOSE:To etch the inner wall of a groove as a recessed section without approximately etching the upper surface of a semiconductor wafer by positioning water only in the recessed section of the wafer, dissolving a water-soluble etching gas to the water and forming an etching liquid only in the recessed section. CONSTITUTION:An silicon wafer 4 is dipped in pure water 6 and pure water is also admitted to a groove 5 as a recessed section, water droplets on the upper surface of pure water are scattered by centrifugal force, and water 6 is left only in the groove 5. The wafer 4 is brought into a reaction chamber, and hydrogen fluoride gas 8 as a water-soluble etching gas is introduced to the reaction chamber. Hydrogen fluoride gas 8 dissolves to water 6 remaining in the groove, and is changed into hydrofluoric acid as an etching liquid 9. Nitrogen dioxide gas 10 as a second etching gas is introduced to the reaction chamber. Nitrogen dioxide gas 10 also dissolves in water 6 remaining in the groove 5, and is turned into nitric acid as an etching liquid 11. When a fixed time passes and nitric acid is brought to predetermined concentration, nitrogen dioxide is removed from the reaction chamber. The next reaction is generated in the groove 5, and silicon on the inner wall of the groove 5 is etched.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to wet etching methods used, for example, to form integrated circuits on semiconductor wafers.

2. Description of the Related Art In recent years, with the aim of improving the degree of integration of integrated circuits, attempts have been made to utilize semiconductor wafers not only as flat surfaces but also as three-dimensional structures to form circuits. As one of these methods, attempts have been made to form deep grooves with a nearly rectangular cross section, which are recesses, on the surface of a semiconductor wafer. When forming these grooves, small irregularities are created on the side and bottom surfaces of the grooves, and it is necessary to smooth these out. Conventionally, a wet etching method in which the grooves are immersed in an etching solution has been mainly used.

An example of the conventional wet etching method mentioned above will be explained below with reference to FIG.

A silicon semiconductor wafer 1 having grooves 2 as recesses is immersed in an etching solution 3 as shown in FIG. Groove 2
has a width of 1 μm and a depth of 2 μm. The etching solution is a mixture of hydrofluoric acid and nitric acid. When the semiconductor wafer 1 is immersed in the etching solution 3, the upper surface of the semiconductor wafer 1,
All surfaces of groove 2, including the sides and bottom, are etched. When the predetermined etching is completed, the semiconductor wafer 1 is taken out from the etching solution and washed with pure water to remove the etching solution from the semiconductor wafer 1. Finally, the semiconductor sea urchin
・Wet etching is completed by drying 1, but this drying is performed by blowing nitrogen gas diagonally from above while spin drying. FIG. 2(b) shows the state after completion of wet etching.

In FIG. 2, the dashed line indicates the original wafer surface.

Problems to be Solved by the Invention However, in the above configuration, the top surface of the wafer also comes into contact with the etching solution as well as the inside of the groove as a recess.
This method has the problem that not only the inner wall of the groove to be etched but also the upper surface of the wafer is wasted to approximately the same thickness.

In view of the above-mentioned problems, the present invention provides a ware etching method capable of etching the inner walls of grooves as recesses without etching the upper surface of the wafer.

Means to Solve the Problems In order to solve the above problems, the present invention first makes water exist only in the four main parts of the semiconductor wafer, and then temporarily flows a water-soluble etching gas. The etching gas is dissolved in the water present in the recess to form an etching solution, which is an aqueous solution of the etching gas, and then the etching gas is removed, and the inner wall of the recess is etched with the etching solution after being left for a predetermined period of time. It is characterized by selectively etching the concave portions of the semiconductor wafer by removing the etching solution present in the etching solution.

Function The present invention has the above-mentioned configuration, in which water is allowed to exist only inside the recess formed in the main part of the semiconductor wafer, and a water-soluble etching gas is dissolved therein to form an etching solution that is an aqueous solution of the etching gas. With this method, the etching solution can be present only in the recesses, thereby hardly etching the upper surface of the semiconductor wafer.
The inner wall of the recess can be etched to a predetermined thickness.

Embodiment A wet etching method according to an embodiment of the present invention shown in FIG. 1 will be explained with reference to the drawings.

First, as shown in FIG. 1(-), a silicon unicorn 1 (hereinafter abbreviated as unicorn) 4 is immersed in pure water 6, and the groove 5 serving as a recess is also filled with pure water. Groove 6 is 1pm wide and 2μ deep.
It is m. Next, this Uninow 4 is rotated using a known single-wafer type spin dryer, and water droplets on the upper surface are blown off by centrifugal force, leaving water 6 only inside the grooves 5. The rotation conditions for spin drying are 500 to 11,000 rpm and 5 to 15 seconds. Next, this UniNo 4 is placed in a reaction chamber, and hydrogen fluoride gas 8 as a water-soluble etching gas is introduced into the reaction chamber and exposed to it as shown in FIG. 1(C). Hydrogen fluoride gas 8 is generated by heating fluorite and sulfuric acid and introduced into the reaction chamber using nitrogen gas as a carrier gas. reaction chamber, gas generation chamber,
Gas inlet pipes, etc. are made of fluorine resin and polyvinyl chloride. The hydrogen fluoride gas 8 is dissolved in the water 6 remaining inside the groove to become hydrofluoric acid as an etching solution 9. When the hydrofluoric acid reaches a predetermined concentration after a predetermined time has elapsed, the hydrogen fluoride gas 8 is removed from the reaction chamber.

Next, nitrogen dioxide gas 10 is used as the second etching gas.
is introduced into the reaction chamber and the wafer 4 is exposed to it as shown in FIG. 1(C). Nitrogen dioxide gas 10 and water 6 remaining inside the groove 5
The etching solution 11 becomes nitric acid. When the nitric acid reaches a predetermined concentration after a predetermined period of time, nitrogen dioxide is removed from the reaction chamber.

The following reaction occurs inside the groove 5, and the silicon on the inner wall of the groove 5 is etched.

3Si+4HNO3J-18HF→3H2S IF6+
4No+8H20 After a predetermined amount of etching is completed after leaving the wafer 4 for a predetermined time, the wafer 4 is immersed in pure water to remove the etching solution, and then the wafer 4 is dried using a spin dryer. The rotation conditions at this time are 2000-300 Or pm and 24
0 to 360861C, and at the same time, nitrogen gas is blown diagonally from above to remove the scallops inside the groove 6. FIG. 1(d) shows the state after the water inside the groove 5 has been removed, and 10 is a groove whose inner wall has been etched to smooth out small irregularities on the inner surface. The broken line indicates the surface of the original groove 5. As described above, according to this embodiment, hydrogen fluoride gas and nitrogen dioxide gas are introduced and dissolved in water, so that almost no silicon etching reaction occurs on the top surface of the wafer where there is no water, and the recesses are The etching reaction occurs only inside the groove 6, and only the inner wall of the groove 6 can be etched.
It can smooth out small irregularities on the inner wall.

Next, a second embodiment of the present invention shown in FIG. 2 will be described.

First, a silicon wafer 22 having a deep groove 21 with a nearly rectangular cross section as a recess is placed in a diffusion furnace and a thermal oxide film 23 is formed on the surface by pyrogenic method as shown in FIG. 2A). The wafer 22 is immersed in pure water to fill the grooves 21 with water. Next, spin dry the water droplets on the top surface of the groove 21.
Leave water only inside. Thereafter, this wafer 22 is placed in a reaction chamber, and hydrogen fluoride gas as an etching gas and nitrogen gas as a carrier gas are introduced into the reaction chamber, and the hydrogen fluoride is dissolved in the water remaining inside the groove 21 to form hydrofluoric acid. . When the concentration of hydrofluoric acid reaches a predetermined concentration after being left for a predetermined time, the hydrogen fluoride gas is removed. Further, the groove 21 of the wafer 22 is left for a predetermined period of time.
The thermal oxide film on the inner wall of the trench 21 is etched by the hydrofluoric acid inside the trench. After the thermal oxide film on the inner wall of groove 21 is removed, the wafer is immersed in pure water to remove hydrofluoric acid and stop etching. This wafer 22 is spin-dried while blowing nitrogen gas obliquely from above, so that the inside of the groove 21 is dried.

FIG. 3(b) shows the state after the wet etching method has been applied, in which the thermal oxide film 23 formed on the entire surface of the wafer 22 is removed by etching only the inside of the groove 21, and the upper surface of the wafer 22 is etched. It is possible to leave only the thermal oxide film 23 without using a mask.

Effects of the Invention According to the present invention, the upper surface of the wafer can be etched by making water exist only in the recesses of a semiconductor wafer, dissolving a water-soluble etching gas in the water, and generating etching liquid only inside the recesses. Only the inner wall of the recess can be etched without etching.

Therefore, small irregularities on the inner wall can be smoothed out without etching the wafer surface. Further, it is possible to easily form a film only on the upper surface of a semiconductor having a recess, excluding the recess, without using a mask.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a wet etching method in a first embodiment of the present invention, FIG. 2 is an explanatory diagram of a wet etching method in a second embodiment of the present invention, and FIG. 3 is an explanatory diagram of a conventional wet etching method. It is an explanatory diagram. 4.22...Wafer, 5,21...Groove, 6...Pure water, 8.10...Etching gas, 9,11... ...Etching liquid. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (2)

[Claims] (1) Etching, which is an aqueous solution of etching gas, by making water exist only in the recesses formed in the main parts of the semiconductor wafer, and then temporarily flowing a water-soluble etching gas to dissolve it in the water existing in the recesses. After that, the etching gas is removed, and the inner wall of the recess is etched with the etching liquid by leaving it for a predetermined period of time, and then the etching liquid existing in the recess is removed, thereby selectively etching the recess of the semiconductor wafer. A wet etching method characterized by etching. (2) The wet etching method according to claim 1, wherein the semiconductor wafer is a silicon wafer, and the etching gas is hydrogen fluoride or a gas containing hydrogen fluoride and nitride oxide as main components.