JP2679815B2 - Dry etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a dry etching method.

(Prior Art) In integrated circuit technology, 1M memory is already on the market, and 4M and 16M are the focus in development, always pursuing high integration. Silicon trench etching is required as one of the development factors for achieving this super integration. This silicon trench etching has become a technique absolutely necessary for device isolation or reduction of the two-dimensional area of a capacitor cell as the integration degree of IC is improved.
It is well known to those skilled in the art that a triode etcher has received attention as a means for this trench etching. For example, it is described in Japanese Patent Publication No. 57-44749.

(Problems to be Solved by the Invention) However, when trench etching with a high aspect ratio is performed, there are problems such as occurrence of undercut and roughness of side walls. In particular, when an etching gas having a strong isotropic property was used as the main etchant, the occurrence of undercut was remarkably observed under the mask. Thus, regarding the shape, it is necessary to satisfy the desired trench shape such as control of the taper angle and round etching.

The present invention has been made in consideration of the above points, and provides a dry etching method capable of executing a favorable trench etching shape while maintaining a high etching rate and a high selection ratio.

[Configuration of the invention]

(Means for Solving the Problems) According to claim 1 of the present invention, during the step of introducing an etching gas containing SF ₆ into a vacuum container and dry etching silicon in a plasma atmosphere, the etching gas introduced is constant. The dry etching method is characterized by intermittently adding a SiCl ₄ gas having a protective film forming action to the etching gas.

Claim 2 resides in that in Claim 1, in SF _6, SiCl ₄ and SF ₆
The gas flow rate of is less than 1:60, and SiCl ₄ is characterized by repeating addition and no addition at intervals of 5 seconds or less.

(Operation) By intermittently adding a gas that has a protective film-forming effect, the sidewalls inside the trench are protected, that is, the balance between etching and sidewall protection can be optimally maintained, and the trench shape for trench etching can be improved. It is possible to control to a desired good shape.

In particular, when the effect of the gas with the protective film formation effect has a great influence on the trench shape even if the addition of an ultra-small flow rate is used, the flow rate control by the MFC (mass flow controller) is due to the ultra-low flow rate. This is impossible, and it can be effectively carried out by the above-mentioned intermittent addition.

In addition, a change in the trench taper angle when a gas having a protective film forming action is constantly added to the conventional etching gas species,
For example, the disadvantage that the shape of the positive taper trench becomes an inverse taper does not occur, and a change in the taper angle of the trench can be prevented by intermittently adding a gas having a protective film forming action. .

(Example) Next, an example in which the method of the present invention is applied to dry etching by a triode etcher will be described with reference to the drawings.

Airtight container as a vacuum container (1) For example, a concentric container made of Al is used. This container (1) is surface-treated such as alumina (Al ₂ O ₃ ) so that it does not respond to the reaction gas.
It is processed on the surface. In such a container (1), three electrodes (2), (3) and (4) are arranged to face each other in order to generate plasma. That is, disc-shaped first and second electrodes (2) and (3) are provided in the vertical direction, and an intermediate electrode (4) is arranged between these electrode plates (2) and (3). The first and intermediate electrodes (2) and (4) have a mesh structure, which allows gas to pass therethrough. An operating voltage is applied to each of the electrodes (2), (3) and (4) from outside the airtight container (1). For example, high frequency power, for example 13.56 MHz, is applied between the first and second electrodes (2) and (3) and the intermediate electrode (4). This high frequency power is supplied by high frequency power supplies (5) and (6) connected to the first and second electrodes (2) and (3), respectively. Further, a gas introduction pipe (7) is connected to the container (1) so that a gas contributing to etching and a gas having a protective film forming action are supplied between the electrodes (2), (3) and (4). ing. Further, the gas supplied by the gas introduction pipe (5) is a mesh structure of the first and intermediate electrodes (2).
It can be supplied to the surface of silicon (hereinafter referred to as a wafer (8)) which has passed through (4) and is set on the second electrode (3). Further, an exhaust duct (9) is connected to the container (1) to exhaust the gas in the container (1) to form a tri-auto etcher (10).

Furthermore, when the wafer (8) is loaded onto the second electrode (3) and is unloaded from the electrode (3), the electrode (3)
The structure may be relatively movable so as to widen the interval between the intermediate electrodes (4). Further, in order to increase the adhesion rate between the wafer (8) and the surface of the second electrode (3), the second electrode (3) has a structure in which the surface center portion of the second electrode (3) has a curvature in a protruding state, and the peripheral portion is Alternatively, the ring-shaped pressing mechanism may be pressed from above.

Next, the etching method using the triode etcher will be specifically described.

The wafer (8) is loaded onto the second electrode (3) and set at a predetermined position. Next, from the gas introduction pipe (7), etching reaction gas, for example, SF ₆ gas flow rate 60S
CCM, an O ₂ gas flow rate of 40 SCCM, and a Kr gas flow rate of 100 SCCM are supplied into the container (1) to keep the pressure inside the airtight container (1) at a constant pressure, for example, 0.6 TORR. At this time, the supply gas passes through the first electrode (2) as described above, further passes through the intermediate electrode (4), and is supplied to the wafer (8) on the second electrode (3),
It is exhausted by the exhaust duct (9). At this time, the first and second electrodes (2) and (3) with respect to the intermediate electrode (4),
High-frequency power of 13.56MHz, for example, 40 for the first electrode (2)
0W, 200W to the second electrode (3) high frequency electrode (5) (6)
Apply from At this time, a gas having a protective film forming action, for example, a SiCl ₄ gas flow rate of 1 SCCM is intermittently added while the etching gas introduced from the gas introduction pipe (7) is kept constant.

A trench etching shape due to the influence of this intermittent operation is shown in FIG. The figure (a) shows the case where a gas having a protective film forming action, for example, SiCl ₄ is not added. That is, S
The figure shows the case of only F ₆ , O ₂ , and Kr gas species.
_{When 4} is always added with 1 SCCM. (C) The figure shows SiCl _{4 1} SCCM
The figure shows the case where the operations of 1 min addition and 1 min non-addition were repeated. In (d), SiCl ₄ 1SCCM is added for 10 seconds and without addition for 10 seconds, and in (e), SiCl ₄ 1SCCM is added for 5 seconds and 5s.
The change in trench shape when each operation without ec is repeated is shown. In the figure (a), an undercut occurs under the SiO ₂ mask. At this time, the etching rate was 1.8 μm / min. In addition, as shown in (b), Si
When Cl ₄ 1SCCM is constantly added, the undercut shown in (a) disappears, but the trench shape largely changes from the positive taper to the reverse taper in (a). Next, when SiCl ₄ is intermittently added as shown in FIG.
Although no undercut is seen, the trench shape is changed and the side wall is undulated as in the case of FIG. Therefore, if the time for adding or not adding SiCl ₄ is shortened, there is no undercut as shown in Fig. (D) and finally (e), and there is a good positive taper and good etching such as round etching. The shape is obtained. Further, the etching rate in FIG. 6 (e) is 1.8 μm / min as in the case of FIG. 4 (a), and the high etching rate can be maintained without any decrease in the etching rate. As can be seen from these figures, the shape of the anisotropic trench etching using low temperature plasma can be improved by intermittently adding a gas having a protective film forming action.

In the above example, addition of a gas having a protective film forming action,
Although the ratio of no addition was 1: 1, the present invention is not limited to this, and the optimum value can be freely determined by adapting to various processes such as 2: 1 and 3: 1.

Furthermore, although the triode etcher has been described in the above embodiment, it can be applied to either a bipolar etcher or an ECR etcher.

As described above, according to this embodiment, the side wall inside the trench is protected by intermittently adding the gas having the protective film forming action, that is, the balance between the etching and the side wall protection can be kept optimal. The trench shape of the trench etching can be done without lowering the etching rate,
It is possible to control to a desired good shape.

In particular, when the effect of the gas having a protective film forming effect has a great influence on the trench shape even if the addition of an ultra-small flow rate is performed, the flow rate control by MFC is impossible because of the ultra-fine flow rate. Yes, it can be effectively performed by the above-mentioned intermittent addition.

In addition, there is no inconvenience such as a change in the trench taper angle when a gas having a protective film forming action is constantly added to the conventional etching gas species, for example, a positive taper trench shape becomes an inverse taper. A change in taper angle of the trench can also be prevented by intermittently adding a gas having a generating action in time.

〔The invention's effect〕

As described above, according to the present invention, anisotropic etching of a desired trench shape having a high aspect ratio can be performed while maintaining a high selection ratio and a high etching rate.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a trench etcher for explaining an embodiment of the method of the present invention, and FIG. 2 is a diagram for explaining a groove shape of trench etching by the method of FIG. 1 ... container, 2,3,4 ... electrode, 5,6 ... high frequency power supply, 7 ... gas introduction pipe.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-60-126835 (JP, A) JP-A-61-263225 (JP, A) JP-A-62-102529 (JP, A) JP-A-60- 50923 (JP, A) JP 62-7130 (JP, A) JP 63-115338 (JP, A)

Claims (2)

(57) [Claims] 1. A step of introducing an etching gas containing SF ₆ into a vacuum container and performing a dry etching of silicon in a plasma atmosphere, the etching gas to be introduced is kept constant and a protective film forming action is applied to the etching gas. SiCl ₄
A dry etching method characterized by intermittently adding a gas. 2. The dry etching according to claim 1, wherein the gas flow rate ratio of SiCl ₄ and SF ₆ is 1:60 or less, and SiCl ₄ is repeatedly added and not added at intervals of 5 seconds or less. Method.