JPH0622211B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device including a step of plasma etching silicon.

[Conventional technology]

In the manufacture of silicon semiconductor devices, there are many steps of selectively etching the silicon surface according to a predetermined pattern, but in the manufacture of ICs, LSIs, etc., it is necessary to perform precise processing along a fine pattern. Plasma etching is often employed to increase accuracy.

For plasma etching of silicon, after exhausting the inside of the reaction tube, a halogen-based gas such as CF ₄ gas is used for 0.1 to 10 Torr.
Introduced, high voltage DC or high frequency voltage is applied to generate gas discharge to create gas plasma, in which silicon or silicon oxide film is etched by halogen-based active chemical species. It progresses little and is suitable for processing fine patterns.

[Problems to be solved by the invention]

However, there is a drawback that the discharge is not stable in the initial stage of the discharge and the plasma is not stable. Due to such plasma variations, silicon is not uniformly etched at the initial stage of etching, and variations occur in the way silicon is etched depending on the position within the silicon wafer, or for each silicon wafer, and for each etching lot. There was a point.

The present invention solves the above-mentioned problems and avoids plasma etching variations due to initial discharge variations,
It is an object of the present invention to provide a method for manufacturing a semiconductor device capable of uniformly etching silicon.

[Means for solving problems]

In order to achieve the above-mentioned object, in the present invention, in a method for manufacturing a semiconductor device including a step of plasma etching silicon, a silicon oxide thin film is formed on a portion of a silicon surface to be etched, where a resist is removed by patterning. Then, when there is variation in plasma at the initial stage of plasma etching, the silicon oxide thin film is plasma-etched, and then the silicon is plasma-etched in a stable plasma state.

[Action]

In this way, a silicon oxide thin film is formed on the silicon surface to be etched, plasma etching is performed from above, and the oxide thin film is sequentially etched into silicon,
The oxide thin film is etched at the beginning of plasma etching and before the plasma is stabilized at the beginning of discharge, and the desired silicon is etched after the plasma is stabilized. The oxide thin film has a slower plasma etching speed (about 1/10) than silicon, and even if the discharge varies, there is almost no variation in etching, and the etching surface is uniform. Subsequent etching of silicon is performed with stable plasma, so that etching naturally has no variation, and as a result, it is possible to uniformly plasma-etch silicon while avoiding initial variation in discharge.

〔Example〕

FIG. 1 shows a cross section of a main part of a semiconductor device in the manufacturing process of one embodiment of the present invention. FIG. 1 (a) shows that after the patterning, the A-face to be etched of the resist 2 of the silicon 1 to be etched is silicon. Exposed. (b) shows the silicon oxide thin film 3 formed on the A surface, and (c) shows the silicon oxide thin film 3 and a part of the silicon 1 etched out by performing plasma etching on the A surface. (d)
Is after removing the resist 2.

In the same manner as the plasma asher, that is, by introducing oxygen gas into the reaction tube and applying a high-frequency or direct-current voltage to the A surface of the silicon 1 of FIG. An electric discharge is generated to generate oxygen plasma, and a silicon oxide thin film having a film thickness of about 100 angstroms is grown as shown in (b).

Then, the silicon oxide thin film is etched by etching the surface A of (b) by plasma of halogen-based fluorine gas such as CF ₄ or SF _6, and the silicon 1
Is etched to a predetermined depth to obtain (c). In this plasma etching, the discharge is unstable and the plasma is also unstable in the initial stage, but at this point, the oxide thin film on the surface is etched, and the etching speed is very slow. The difference in etching speed causes almost no problem, and uniform etching can be performed without variation. At the time when the required silicon etching starts, the plasma is in a stable state and does not fluctuate, so the silicon is etched without variations, and variations within wafers, between wafers, and between processing lots occur. No uniform silicon etching can be achieved.

After that, the resist 2 is removed to be in the state of (d), and subsequently, the semiconductor element is manufactured through the required steps, but the plasma etching is always performed uniformly by the action of the silicon oxide thin film according to the present embodiment, Since a fine pattern is also formed with high precision, a semiconductor element having excellent characteristics can be stably obtained.

On the other hand, conventionally, the exposed silicon surface was plasma-etched from the beginning without forming a silicon oxide thin film as shown in FIG. 1 (b).

Therefore, there was a problem that silicon was scattered and etched due to variations in plasma at the initial stage of initiation, but in the present embodiment, by forming a silicon oxide thin film on the silicon surface and then performing plasma etching, etching was performed. The uniform plasma etching is realized by avoiding the influence of the initial plasma variation.

As for the film thickness of the silicon oxide thin film 3 of (b), it is sufficient that the silicon oxide film exists for a short time until the plasma is stabilized at the initial stage of discharge, so an ultrathin film is sufficient, and it may be 200 angstroms or less, about 100 angstroms. Is preferred. Since the etching speed of the silicon oxide film is slow in the etching using the plasma of the halogen-based gas, it is not preferable to form a thicker silicon oxide film than necessary because the etching time becomes longer accordingly.

Although there are various methods for forming the silicon oxide film, the method using oxygen plasma as in the present embodiment is desirable for forming the thin film as described above. By controlling the oxygen gas pressure supplied to the reaction tube and the discharge power, it is easy to control the film thickness, and it is possible to grow a thin film uniformly with a predetermined film thickness. This is because there are many advantages such as being possible.

〔The invention's effect〕

According to the present invention, a silicon oxide thin film is formed on the surface of silicon to be etched, the silicon oxide thin film is plasma-etched when there is a variation in plasma at the beginning of plasma etching, and then silicon is plasma-etched in a stable plasma state. To do. By the action of this oxide thin film, it is possible to avoid variations in etching of silicon due to variations in plasma at the initial stage of plasma etching, and it is possible to perform uniform etching, and it is possible to stably manufacture semiconductor elements with excellent characteristics. became.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a semiconductor device in a manufacturing process according to an embodiment of the present invention. 1 ... Silicon, 3 ... Silicon oxide thin film.

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device including a step of plasma-etching silicon, wherein a silicon oxide thin film is formed on a portion of a silicon surface to be etched where a resist is removed by patterning, and a variation in plasma at the initial stage of plasma etching. A method for manufacturing a semiconductor device, wherein the silicon oxide thin film is plasma-etched when there is a certain state, and then the silicon is plasma-etched in a stable plasma state. 2. A method of manufacturing a semiconductor device according to claim 1, wherein the silicon oxide thin film formed on the silicon surface is grown on silicon by oxygen plasma. 3. A method of manufacturing a semiconductor device according to claim 1, wherein the thickness of the silicon oxide thin film to be formed is 200 angstroms or less.