JPH0628253B2 - Etching method - Google Patents

Description

The present invention relates to an etching method, and more particularly to a dry etching method suitable for forming fine grooves with high accuracy.

[Prior Art] A dry etching method using plasma of a reactive gas is used for processing a fine pattern of a semiconductor integrated circuit or the like. Typical examples of the etching gas include isotropic etching gases such as Si or GaAs, such as F ₂ and SF.
₆ , NF ₃ , XeF ₂ , CF ₄ , as anisotropic etching gas,
CF ₃ Cl, CF ₂ Cl ₂ , CFCl ₃ , Cl ₂ , CCl ₄ , CB
rF ₃ , CIF _3, etc. are known. For these etching gases, see, for example, JP-A-51-130173.
No. 5, JP-A-52-9648, JP-B-57-13137.
No., etc.

Since isotropic etching is mainly performed by electrically neutral particles, it is difficult to perform highly accurate processing according to the mask dimensions. Therefore, when it is desired to make the fine processing or the etching shape vertical, anisotropic etching has been performed by using ions accelerated from the plasma toward the surface of the material to be etched. A method called reactive dry etching is representative of this method. As an etching gas, etching by electrically neutral particles is unlikely to occur, and etching proceeds only by the action of ions.

[Problems to be Solved by the Invention] In the above conventional technique, since etching is performed by ions accelerated by a negative DC bias, there is a problem of damage to the substrate due to ion bombardment, and accelerated ions collide with gas molecules. However, there was a problem of side etching caused by changing direction and colliding with Si, or different etching conditions between lots because oxygen adsorbed on the furnace wall was knocked out.

Among the above problems, as a method for reducing the ion damage, SF _{6 which} is an isotropic etching gas and anisotropic etching gases such as Cl ₂ , CCl ₄ , CClF ₅ and SiCl _{4 are used.}
A mixed gas with the above is also used. However, even in these cases, the problem of side etching cannot be solved, and the etching shape tends to change depending on the mixed gas ratio and etching conditions.

An object of the present invention is to provide an etching method using a mixed gas that solves this problem.

[Means for Solving Problems] The above-mentioned object is to provide SF ₆ , CF ₄ ,
At least one gas selected from the group consisting of NF ₃ , XeF ₂ and F ₂ and an anisotropic etching gas (C
This can be achieved by using a mixed gas containing, as a main component, at least one kind of gas selected from the group consisting of XF ₂ ) ₂ , (CX ₂ F) ₂ and (CX ₃ ) ₂ . However, the above X is at least one selected from the group consisting of Cl, Br, I and H.

Among these gases, SF ₆ is more preferable as the isotropic etching gas and (CBrF ₂ ) ₂ is more preferable as the anisotropic etching gas from the viewpoint of easy availability of the gas.

[Operation] Various ions and neutral particles are contained in the plasma in the dry etching. Among them, substances mainly containing C and S adhere to the surface of the substrate as reaction residues and hinder the etching. On the other hand, since various ions are accelerated and collide with the surface of the substrate, they not only etch the substrate, but also remove these deposits. The etching using the mixed gas of the isotropic etching gas and the anisotropic etching gas makes good use of the above-mentioned two functions to perform etching in which the etching shape is vertical as shown in FIG.

Specifically, when the high-frequency power is extremely low, the ions are not sufficiently accelerated and thus the deposits that are reaction residues are removed, but the etching of the substrate by the ions is very small. However, the part from which the deposit is removed is easily etched by the highly reactive neutral particles F (mainly contained in the isotropic etching gas). Thus
The etching shape depends on the ion directivity because the etching is performed more and more in a portion where the ions are bombarded. That is, when most of the ions are vertically incident on the substrate, the etching shape is vertical, but when the ions collide with gas molecules and scatter in the middle, the shape is not vertical. As shown in FIG. 2 and FIG. It will be as shown. For example, the gas pressure is 10
When the ion sheath width is 1 mm at Pa, it is said that about 60% of the ions collide with gas molecules during acceleration and are scattered, changing the direction. Therefore, it is necessary to reduce the influence of scattering as much as possible, and as a method therefor, in addition to lowering the gas pressure to sufficiently increase the mean free path and lowering the high frequency power to reduce the ion energy at the time of collision, It is important to choose ions that have a scattering angle that is as small as possible.

The mixed gas according to the present invention described above satisfies the above conditions. That is, the anisotropic etching gas (for example, (CBrF ₂ ) ₂ ) in the above mixed gas becomes two CBrF ₂ ⁺ ions and neutral particles when the C—C bond is cut. This is a heavy ion having a molecular number of about 130, and the same applies to the gas according to the present invention other than (CBrF ₂ ) ₂ which satisfies the above requirements.

Example A plasma etching apparatus having an anode coupling type parallel plate electrode was used as an etching apparatus, and a mixed gas of SF ₆ and C ₂ Br ₂ F ₄ was used as a gas to etch Si using a resist as a mask. It was The electrode of the etching equipment is 20 cm in diameter, and the high frequency power supply frequency is 13.56M.
Hz.

First, an object to be etched is placed on the electrode, the etching chamber is evacuated to 10 ^-1 Pa or less, and then SF ₆ is added to 32 _SCCM , C ₂
Br ₂ F ₄ was introduced at 8 _SCCM , and etching was performed for 20 minutes at a high frequency power of 0.03 W / cm ² while keeping the inside of the chamber at 10 Pa. The etching rate at this time is 100 nm / min
And etching was performed to a depth of 2 μm. FIG. 1 is an etching cross-sectional view, and thus almost vertical etching was possible. The width of the etching hole is 0.5 μm. The mixing ratio of SB ₆ and C ₂ Br ₂ F ₄ is 4: 1 in the above example, but it is preferably in the range of 3: 1 to 20: 1 under normal vacuum and high frequency power.

Similar results were obtained when the etching mask 2 was made of SiO ₂ or Si ₃ N ₄ in addition to the resist. The etching selectivity (ratio of etching rate to Si) is about 15 for resist, SiO ₂ and
It was 100 or more for Si ₃ N ₄ . However, when the etching was performed under the condition that the high frequency power exceeded 0.30 W / cm ² , the etching selection ratio became smaller as the power became higher. From this viewpoint, the high frequency power is preferably 0.3 W / cm ² or less.

Even when H ₂ or He is further mixed in a mixed gas of SF ₆ and C ₂ Br ₂ F _4, a good cross-sectional shape can be obtained, which is preferable. It is considered that these have a small mass, and therefore their influence is small even if they collide with CBrF ₂ ⁺ ions having a molecular weight of about 130.

As other etching gases, isotropic etching gases such as CF ₄ , NF ₃ , XeF ₂ and F ₂ and anisotropic etching gases such as (CClF ₂ ) ₂ , (CCl ₂ F) ₂ and (CC) are used.
l ₃ ) ₂ , (CIF ₂ ) ₂ , (CBr ₂ F) _{2 and the} like are SF ₆ ,
It showed the same characteristics as C ₂ Br ₂ F ₄ . However, with the gas containing Cl, there was a tendency to be side etching depending on the etching conditions. This is because the heavy ions are further decomposed into light ions. When a mixed gas of SF ₆ and CCl ₄ was used for comparison, a narrow range, such as a side etching at a mixing ratio of CCl ₄ of 15% or more, or at a mixing ratio of 5% and a pressure of 0.1 Torr or more Only good etching shape could be obtained.

A good etching shape was obtained when NF ₃ , CF ₄ , XeF ₂ and F ₂ were used instead of SF ₆ , but the condition range was slightly narrower than that of SF ₆ . It was considered that this was due to the difference in how reaction residues attached to the substrate adhered.

From the above results, by performing plasma etching using a mixed gas of a highly reactive isotropic etching gas typified by SF ₆ and an anisotropic etching gas containing heavy ions that are easily dissociated symmetrically, It became clear that etching of fine and deep holes can be processed with high precision. In this case, it is more preferable to perform plasma etching with relatively low high frequency power.

The above gases may be used as a mixture of three or more kinds, and the above X is not only one kind in the same molecule but also B
Needless to say, it may contain plural kinds of elements such as r and Cl.

EFFECTS OF THE INVENTION According to the present invention, since etching can be performed with a very low high frequency power, the resist can be used as it is as an etching mask, and the thickness of the resist can be small.
In addition, there is no concern that oxygen adsorbed on the wall will be sputtered and adversely affect, so that there is an effect that ultrafine processing can be performed with high reproducibility. Further, there is an effect that the ion impact on the substrate is eliminated and the device characteristics are improved.

When the ions decomposed by plasma are heavier, the effect of reducing the etching condition dependency is smaller than that when light ions are used.

[Brief description of drawings]

FIG. 1 is an etching cross-sectional view obtained by the present invention, and FIGS. 2 and 3 are etching cross-sectional views when affected by ion scattering. 1 ... Si substrate, 2 ... resist, 3 ... etching hole.

Claims (2)

[Claims] 1. A method of plasma etching an object to be etched placed in an etching chamber using a mixed gas, the step of exhausting the etching chamber, and the mixed gas of SF ₆ and (CBrF ₂ ) _{2 in} the etching chamber. An etching method comprising: a step of introducing the material; and a step of etching the object to be etched with a high frequency power of 0.3 Wcm ² or less using a mixed gas of SF ₆ and (CBrF ₂ ) ₂ . 2. The etching method according to claim 1, wherein at least one of He and H ₂ is added to the mixed gas of SF ₆ and (CBrF ₂ ) ₂ .