JPH0817169B2 - Plasma etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plasma etching method, and more particularly to a plasma etching method suitable for fine etching of a workpiece.

[Conventional technology]

In recent years, with the high integration of silicon integrated circuits, techniques for processing silicon substrates such as isolation by deep silicon trenches and formation of capacitors by deep silicon holes have been put into practical use. In the processing of silicon substrates, the asbestos ratio is high (1: 4 to 1:10), and shape control is especially important.

Conventional silicon substrate etching is performed at a low pressure (1 to 1) by a so-called reactive ion etching (RIE) device.
It was performed using chlorine gas plasma of 0 mTorr). In this case, the anisotropy of etching is secured by strengthening the directionality of ions by etching at a low pressure.

Recently, for example, Chemical Society, Plasma Treatment, Fig. 5, Symposium, 552
Page ~ Page 567 (Proc, of the 5th Sympodium on Plasma P
rocessing, the Electrochemical Soc., as discussed in PP552～567), by a combination of halocarbon-based gas and SF _6, using a so-called side wall protective type process, also attempted etching with an etching apparatus of a cathode couple ing.

[Problems to be Solved by the Invention]

 The problems of the above conventional technology will be described below.

1. Etching by RIE device In this method, chlorine-based gas is used and etching is performed by the reaction between chlorine ions and silicon. This method, in which etching is performed at a low pressure in order to align the directionality of ions, has the following problems.

 The etching rate of silicon is low.

For this reason, a batch type etching apparatus that simultaneously processes a plurality of silicon wafers is used, but the uniformity of the etching rate in the same batch is poor.

Since a large high frequency power is required, the ion energy is large and the silicon substrate is damaged greatly.

2. In etching by the anode coupling device,
As shown in the known example, sufficient anisotropy cannot be obtained.

An object of the present invention is to provide a plasma etching method that is excellent in anisotropy and mass productivity and that causes little damage to a work piece.

[Means for solving the problem]

The above-mentioned object is to perform a plasma etching method by fixing the flow rate ratio of the side wall protection gas containing carbon (C ₂ Br ₂ F ₄ ) and the etching gas, and using chlorine (Cl ₂ ) and argon (Ar) as etching shape control gases. ), Xenon (Xe) and crypto (Kr) gases are mixed at the same time to form a mixed gas into plasma, and the plasma is used to etch the workpiece.

[Action]

The side wall protective gas containing carbon advances the formation of a protective film for side wall protection, and the etching gas advances the etching. Thereto, Cl ₂ as an etching shape control gas, Ar, X
The shape control can be controlled more finely by adding at least one kind of gas selected from e and Kr.

〔Example〕

 An embodiment of the present invention will be described below.

1 to 3 show the processed shape of the silicon substrate 1 by C ₂ Br ₂ F ₄ and SF ₆ gas. Here, C ₂ Br ₂ F ₄ is a sidewall protection gas, and SF ₆ is an etching gas. When the flow rate ratio of SF ₆ is small, silicon substrate 1
As the etching proceeds, the groove width or the hole diameter becomes so-called a forward taper shape. As the flow rate ratio of SF ₆ is increased, the taper angle increases as shown in Fig. 2 and approaches a vertical shape, and finally a vertical shape as shown in Fig. 3 is obtained. The SF ₆ flow rate ratio when this vertical shape is obtained is determined by the wafer size of the silicon substrate 1 to be processed and the area to be etched (area of the portion where the mask is not formed).
-It varies depending on the pattern size and pattern shape and other process conditions, but it is between about 2% and 30%.

Next, when the forward tapered shape as shown in FIG. 4 is changed to the vertical shape as shown in FIG. 5, undercut may occur at the same time. If undercut occurs, a dimension shift occurs even if a vertical shape is obtained, which is not preferable in terms of the deice characteristic. In such cases,
As shown in Fig. 6, under the condition that undercut does not occur
C ₂ Br ₂ F ₄ is fixed at a flow rate ratio of SF ₆ , and Cl ₂ or Ar
Alternatively, when at least one kind of gas selected from Xe and Kr is added, a vertical shape can be obtained without generating an undercut as shown in FIG. in this way
Cl ₂ , Ar, Xe, and Kr play a role in enabling delicate shape control. As shown in FIG. 7, addition of these gases has the effect of rounding the bottom of the groove or hole. This is advantageous in terms of the coverage in the film formation inside the groove / hole in the process subsequent to the groove / hole processing and the problem of stress at the corners of the groove / hole.

Further, as shown in FIG. 8, when only C ₂ Br ₂ F ₄ + SF ₆ is etched, a phenomenon may occur in which the groove or hole becomes thinner as the etching progresses. Also in this case, a vertical shape can be obtained as shown in FIG. 9 by adding at least one kind of gas selected from Cl _2, Ar, Xe and Kr.

FIG. 10 shows a processed shape when the gate material 3 is etched. The gate material 3 can be applied to the following films.

i) Polycrystalline silicon ii) Refractory metal such as tungsten / titanium / molybdenum iii) Silicon compound of ii) iv) Multilayer film of i) and iii) The above examples were obtained by a magnetic field microwave plasma etching apparatus. Although an example has been shown, it is considered that similar characteristics can be obtained by optimizing the process conditions in an apparatus in which gas is converted into plasma and etching is performed by the reaction between the plasma and the workpiece.

Further, although it was emphasized that the present embodiment can be processed vertically, the shape required for processing a silicon deep groove / deep hole varies depending on the purpose of use, and a forward taper may be better in some cases. Also in this respect, according to the present invention, the forward taper to the vertical direction can be easily controlled by controlling the flow rate ratio of C ₂ Br ₂ F ₄ and SF ₆ or the flow rate of the added gas (Cl ₂ , Ar, Xe, Kr). Another advantage is the ability to control the processing shape.

According to the above examples, the shape control is easy in processing the silicon substrate, the silicon etching rate is high,
Also, since it does not require large ion energy, damage is small. Therefore, the silicon substrate can be processed with high productivity.

〔The invention's effect〕

According to the present invention, it is possible to provide a plasma etching method which is excellent in anisotropy and mass productivity and has less damage to a work piece.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 10 show an embodiment of the present invention. FIGS. 1 to 9 are longitudinal sectional views showing etching shapes of silicon substrates, and FIG. It is a longitudinal cross-sectional view showing the etching shape of the gate material film. 1 ... Silicon substrate, 2 ... Mask, 3 ... Gate material film, 4 ... Underlayer film

Claims (1)

[Claims] 1. C ₂ Br ₂ F ₄ as a sidewall protecting gas containing carbon
And SF ₆ as an etching gas are fixed, and at least one of chlorine, argon, xenon, and krypton gas is simultaneously mixed as a gas for controlling the etching shape, and the mixed gas is plasma-converted to generate the plasma. A plasma etching method, characterized in that a workpiece is etched by means of a plasma etching method.