JPH0480533B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a method for removing protrusions from an anisotropically etched surface of a silicon semiconductor.

(Prior art and its problems) It is well known that the following measures are taken in manufacturing semiconductor devices using silicon (Si). That is, as shown in FIG. 1a, a required etching pattern is formed on the SiO ₂ film 2 grown on the crystal plane 100 of the Si wafer 1 by a photo process, and then a cleaning method using acid and alkaline solution, such as RCA cleaning, is performed. Perform wet cleaning according to the method. Next, the cleaned material is immersed for a short time in a dilute hydrofluoric acid (HF) solution to remove the natural oxide film on the Si surface to be etched, and then dried. Pyrocatechol - so-called aqueous solution
A method of etching Si using an EPW solution as shown in FIG. 1b is taken, but it is known that the following drawbacks occur in this case.

That is, as shown in FIGS. 1b and 1c (FIG. 1 is a trace of a microscopic photograph), protrusions called micropyramids are formed on the etched surface 3 with attached organic matter or fine metal particles as cores. 4 occurs,
Moreover, since it forms a quadrangular pyramidal structure surrounded by 111 planes as shown in FIG. 1, it remains until the end without disappearing even during etching. This results in drawbacks such as, for example, a reduction in the isolation breakdown voltage yield of dielectric isolation ICs and a reduction in the processing yield of silicon in diaphragm pressure sensors. Research has been carried out to prevent this, but currently the only method available is to mix organic solvents such as isopropyl alcohol into the etching solution, which does not completely remove the micropyramids. You can't get rid of it.

(Object of the Invention) The present invention has been made for the purpose of realizing a smooth etched surface free of micropyramids as described above, and the details thereof will be explained below with reference to the drawings.

(Means and effects for solving the problems) The present invention is to clean a semiconductor wafer that has been subjected to anisotropic etching in which micropyramids have been formed as described above with acid and alkaline solution, dry it, and then anisotropically etch it again. This method is based on an experimental fact that revealed that micropyramids can be eliminated by performing a second etching process by immersing them in a chemical etching solution and at the same time selecting the immersion time. The disappearance of Tsudo is thought to be due to the following reasons.

That is, as mentioned above, the micropyramid is 1
It is a square pyramid surrounded by 11 sides. Therefore, in this state, no matter how much anisotropic etching is performed, it cannot be eliminated. However, after performing anisotropic etching as described above, it is necessary to perform a second anisotropic etching after pre-treatment such as cleaning. Anisotropic etching is performed again with S _i planes other than the 111 plane being exposed at the intersections b of the apex a of 4 and the 111 plane. Therefore, etching is rapidly performed from the apex a and the intersection line b, and the micropyramid 4 is erased. In this case, if the second etching time is too long, the pyramid 4 will be formed again after it disappears. Therefore, appropriate selection of the time is necessary, which according to experiments is less than 10 minutes. Next, the effects of the present invention will be explained using specific examples.

(Effect of the invention) As shown in Figure 2, 3 has 100 crystal planes.
After cleaning the Si _wafer 1 of ~5Ωcmp type by the RCA cleaning method, it is immersed in a 10% aqueous solution of HF to remove the natural oxide film. After this is oxidized to grow the SiO ₂ film 2 as described below, a pattern is formed. Next, after performing wet cleaning using the RCA cleaning method as in the first anisotropic etching, immersion in a 10% HF aqueous solution for 20 seconds removes the natural oxide film on the Si surface to be etched. Remove and dry. Just like that later
EPW solution (Ethylenediamin−Pyrocatictechol−
After the first anisotropic etching was performed by heating and refluxing water for the required time (varies depending on the etching depth), the second etching treatment, which is a feature of the present invention, was performed.

That is, as shown in Figure 2, after cleaning, removing the natural oxide film, and drying using the same method as in the first etching process, the above etching process is performed.
Etching was performed for 5 minutes using EPW solution.

Figures 3a and 3b are comparative diagrams of traced photographs of etched surfaces obtained by the present invention in which anisotropic etching was performed twice as described above and the conventional method in which anisotropic etching was performed only once. It has been clearly shown that the micropyramids 4 produced by the first etching are eliminated by the second etching process of the present invention, which includes pre-treatments such as cleaning and removal of the native oxide film.

Therefore, according to the present invention, it is possible to easily eliminate micropyramids and realize a smooth silicon surface, which improves the yield of dielectrically isolated ICs and facilitates the processing of silicon diaphragm type pressure sensors and silicon sensors such as IS FETs. This has the great effect of achieving high precision and high yield.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional anisotropic etching method for silicon wafers, FIG. 2 is an explanatory diagram of the present invention, and FIG. 3 is an explanatory diagram of the actual state of micropyramid disappearance according to the present invention. 1...Si wafer, 2...SiO ₂ film, 3...etched surface, 4... protrusion (micropyramid).

Claims (1)

[Claims] 1. A silicon semiconductor on which protrusions have been generated on the etched surface by anisotropic etching is subjected to anisotropic etching again for a period during which the protrusions are not regenerated, after pretreatment such as cleaning and removal of a natural oxide film. A method for removing protrusions on an anisotropically etched surface of a silicon semiconductor.