JPS61296721A - Fine processing of single crystal silicon - Google Patents

Abstract

PURPOSE:To give roundness to an angular upper corner edge produced by vertical etching of an Si substrate by applying a laser beam of visible ray range or ultraviolet ray range to the Si substrate after vertical etching. CONSTITUTION:A thermal oxide film 5 is formed on P-type (100) Si substrate 4. Then a pattern is formed with a positive type photoresist 6 and the thermal oxide film 5 is subjected to oriented etching by using the photoresist 6 as a mask. After the resist 6 is removed, the single crystal Si substrate 4 is etched and dipped into a buffer fluoric acid solution and the thermal oxide film 5 is removed and then an ArF excimer laser beam is applied. With this process, the Si surface layer is melted and an angular upper corner edge can be rounded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a method for microfabrication of single crystal silicon.

[Technical background of the invention and its problems]

The integration of semiconductor integrated circuits is still increasing at a rate of four times every two years, and design dimensions are about to enter the bumikron range.

In the case of dynamic memory, where the memory cell is composed of one transistor and one capacitor, and stores one bit depending on whether or not the capacitor is charged, in order to perform stable operation and suppress soft errors (- indicates that the capacitor is 30 to 5 QFF). In order to secure the above capacitance while pattern dimensions become smaller, it is necessary to make the gate oxide film thinner. However, there is a limit to the thinning of the gate oxide film, so St substrates are A so-called trench-horizontal recapacitor has been proposed in which capacitors are formed vertically by deep trenching. , a gate oxide film 2 is formed on the bottom and side surfaces, and then polycrystalline Si 3 is buried to form an electrode.

However, when monocrystalline Si is processed by reactive ion etching, the upper and lower ends become angular, as can be seen in FIG. In these angular parts,
Due to the concentration of stress, the quality of the oxide film is poor and can cause leaks when used as a capacitor. This leakage is a major problem in memory cells, leading to poor memory retention. In order to prevent leakage, it is necessary to round the angular portions, but conventionally there has been no method for rounding the upper end portion 1.

[Purpose of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for rounding an angular top edge after vertical etching.

[Summary of the Invention] The present invention provides that after vertical etching of a Si substrate, s
It is characterized by irradiating the t-substrate with laser light in the visible or ultraviolet region.

〔Effect of the invention〕

According to the present invention, the Si substrate absorbs laser light and melts and recrystallizes in a very short time, so that the angular portion of the upper end becomes rounded.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

First, a P-type (IOO) Si substrate 4 is subjected to hydrogen combustion oxidation at 950° C. to form a thermally oxidized M5 of 850 OA.

Next f: A pattern is formed using a positive photoresist 6, and the thermal oxide film 5 is directionally etched using this resist as a mask. Etching of the thermal oxide film 5 was carried out using an ordinary cathode-coupled reactive ion etching device using CHF as the gas (see Fig. 1(a)).
). Thereafter, the resist 6 was removed using a plasma ashing device. Next, the substrate was placed in a cathode-coupled reactive ion etching device, and CBrFl gas was introduced.
, single crystal 8 at pressure 0.04 Torr RF power 600W
The i-substrate 4 was etched (FIG. 2(b)).

Next, the Si substrate 4 was immersed in a buffered hydrofluoric acid solution to remove the thermal oxide film 5, and then irradiated with human rF excimer laser light. The ArF excimer laser light is a pulse laser with a wavelength of 193 nm and a pulse width of approximately 10 SeC, and the energy per pulse is 0. IJ/J with lens 5 wit”
The light was focused at angle j2 and irradiated with 20 pulses per area. At C2, the Si surface layer melts and the upper corner becomes rounded as shown in FIG. 2(C).

Next, a pre-oxidation treatment is performed to form a gate oxide film 7 in a dry oven at 950° C. (film thickness 200 Å), and then polycrystalline Si 8 is formed by vapor phase growth method 1. Then, P
After performing phosphorus diffusion for 10 minutes at 1000°C in an oC/2 atmosphere, the substrate 4 was immersed in a buffered hydrofluoric acid solution, and the oxide film formed on the polycrystalline Si8 surface (-) was removed during the phosphorus diffusion. Next, a positive photoresist was applied, a gate electrode was patterned, and polycrystalline Si8 was etched using CF410 mixed gas plasma (FIG. 2(d)).

FIG. 3 is a diagram showing the current-voltage characteristics of the Mizohori recapacitor thus formed. It is clear that the current value is smaller for the substrate whose upper end is rounded due to the sputtering action, and there is no leakage.

In this embodiment, sputtering was performed using M, but it goes without saying that a similar effect can be produced using any gas other than M, provided that it is inert to Si.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing the process of forming a Mizohori capacitor as an embodiment of the present invention, FIG. 2 is a diagram showing a cross section of the Mizohori capacitor, and FIG. 3 is a diagram showing current-voltage characteristics. It is. 1...Si substrate 2...Gate oxide film 3.
...Polycrystalline St electrode 4...Si substrate 5...Thermal oxide film 6...Positive photoresist...
・Gate oxide film 8... Polycrystalline Si electrode (7317
) Patent Attorney Kensuke Chika (and 1 other person) Figure 2

Claims (3)

[Claims] (1) a step of sequentially depositing a first thin film and a thin film of a photosensitive agent on a silicon substrate; a step of printing and developing a pattern on the thin film of the photosensitive agent using a lithography process to form a pattern of the photosensitive agent; etching the first thin film using the pattern as a mask; then directional etching the silicon substrate using the first thin film as a mask; and after removing the first thin film, applying a laser beam to the silicon substrate. A method for microfabrication of single crystal silicon, comprising a step of irradiating light. (2) The method for microfabrication of single crystal silicon according to claim 1, wherein the laser beam has a wavelength in the visible and ultraviolet regions. (3) The method for microfabrication of single-crystal silicon according to claim 1, wherein the step of irradiating the laser beam is performed under an ultra-high vacuum.