JPH0312454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive ion etching method and other dry etching methods that utilize discharge activated species, and more particularly to a dry etching method whose subject matter is an etching gas composition suitable for semiconductor manufacturing.

In semiconductor manufacturing, as shown in Figure 1,
Various materials such as Si and Al deposited on base SiO _{2 1} 2
The important step is to form a pattern using photoresist and SiO ₂ as a mask 3. In recent years, the integration density of ICs has increased, and accordingly, reactive ion etching methods that can form highly accurate patterns with small dimensional conversion differences from masks, that is, with steep edges, are being put into practical use. In addition to high processing accuracy, such dry etching requires a difference in etching speed with respect to the underlying material, that is, good selectivity. Furthermore, it is practically important that no defects such as so-called etching residues remain on the etched surface.

Conventionally, to etch Si, metals, etc. on SiO ₂ , a mixed gas in which gases such as O ₂ and Cl ₂ are added to halogenated carbon such as CF ₄ , CF ₃ Br, and CCl ₄ has been used. In this case, it is the halogen of the halogenated carbon that combines with the material 2 to be etched and etches it. and halogenated carbon C or CX _o
(X represents halogen in general) is a surplus substance,
If left as is, it will accumulate on the Si surface. The additive gas combines with this C to generate volatile CO, CO ₂ , CX ₄ , etc. to remove C, contributing to the continuation of etching and improving the selectivity with respect to the underlying SiO ₂ . There is.

In addition, in reactive ion etching, there is a physical reaction in which a reactive mixed gas adsorbed on the surface of the material to be etched receives ion bombardment, becomes active and bonds with the material to be etched, and reactive species such as radicals generated in the plasma. There is also a chemical reaction in which the etching material moves to the surface of the material to be etched and combines with the material to be etched. The former allows directional etching by aligning the direction of ion bombardment, while the latter provides isotropic etching. Looking at this for a mixed system of the halogen carbon and additive gases O ₂ and Cl ₂ , we find that when the additive gas is increased,
In the case of O ₂ , X radicals are increased in the plasma by the reaction CX ₄ +O ₂ →CO or CO ₂ +4X. similar
In the case of Cl ₂ as well, X radicals increase due to the reaction CX ₄ +2Cl ₂ →CCl ₄ +4X·, and Cl radicals from the added gas Cl ₂ itself also increase. As a result, halogen radicals increase in the plasma, the rate of chemical reaction increases, and as shown in FIG. 1, an undercut 4 due to isotropic etching is caused.

However, if the amount of added gas is reduced so that there is no undercut, a pattern with steep edges 24 can be obtained as shown in FIG. Sometimes there is no progress at all. This is due to the following reasons. In a mixed gas of halogenated carbon CX ₄ and O ₂ or Cl ₂ ,
CX _o deposition is always occurring at the same time as etching. This means that the surface of the material to be etched can be inspected for ESCA (Electron Spectroscopy for
It has also been clarified by chemical analysis). The additive gas is effective in removing this excess CX _o , and in a situation where this is insufficient, if there is a foreign substance on the surface of the material to be etched that can become a nucleus for CX _o deposition, the CX _o deposited there will grow and become the etching mask 6. As a result, etching residue 5 is generated.

In this way, in the conventionally used mixed gas of halogenated carbon and O ₂ or Cl ₂ , the amount of added gas is regulated from both the undercut 4 and the etching residue 5, making it possible to realize good etching. The disadvantage was that the composition of the mixed gas was limited.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a reactive ion etching method that selectively etches polysilicon with respect to silicon oxide without producing etching residues based on the etching gas composition.

Another object of the present invention is to provide a dry etching method that is free from etching residues, has a high selectivity with respect to the underlying material, and can realize a good etched shape.

That is, the present invention provides a reactive ion etching device that has opposing electrodes to which high-frequency power can be applied, and that generates glow discharge by applying high-frequency power and etches a material to be etched placed on the electrodes. This dry etching method is characterized by introducing a mixed gas consisting of gas and oxygen gas to selectively etch polysilicon in the material to be etched with respect to silicon oxide.

The present inventors have found that conventional carbon (CX _o ) deposition is caused by the use of halogenated carbon, and that etching mainly using halogen gases such as F ₂ and Cl ₂ can reduce carbon deposition. We first investigated the etching characteristics of Cl ₂ gas, thinking that this is the basis for preventing this.

The material to be etched is a base SiO ₂ 51, as shown in the etching shape explanatory diagrams in FIGS. 5a and 5b.
Polysilicon 52 doped with phosphorus (P) deposited thereon was used, and resist 53 was used as a mask material. Next, the device used by the inventors was
As shown in the figure. Parallel plate electrodes 32 and 33 facing each other are provided within the chamber 31 . The upper electrode 32 is grounded, and the lower electrode 33 is connected to a 13.56 MHz high frequency power source 35 via a matching box 34. Cooling water W is also made to flow through the lower electrode 33 . An electrode material 36 is placed on the lower electrode, and a material to be etched 37 is placed thereon. Halogen gas (X ₂ ), which is a reactive gas, and oxygen gas (O ₂ ), which is an additive gas, are adjusted to predetermined flow rates by a flow rate regulator (not shown), and are introduced into the chamber from the gas introduction hole 38. Ru. The reaction products of the excess gas in the chamber 31 are exhausted through the exhaust hole 39 by an exhaust system (not shown). Note that the DC bias (cathode drop voltage) that occurs between both electrodes
A device that can detect V _DC ) is attached, but this is also not shown. The material to be etched 37 is etched in a gelatin discharge generated in the chamber by applying high frequency power to this reactive ion etching device.
is etched.

Now, the etching characteristics when using Cl ₂ alone as the reactive gas will be described below. Figure 4 shows the change in etching rate of lindove polysilicon and SiO ₂ with respect to gas pressure when 40 c.c./min of Cl ₂ was introduced and a high frequency power of 0.28 W/mm ² per unit electrode area was applied. The figure shows the change in V _DC . As the pressure increases, the etching rate of phosphorus-doped polysilicon increases, and conversely, the etching rate of SiO ₂ decreases. The change in etching rate of SiO ₂ and the change in V _DC show good agreement.
Since V _DC is considered to be correlated with the strength of ion bombardment, it indicates that SiO ₂ is etched mainly by physical reaction. On the other hand, for phosphorus-doped polysilicon, both physical and chemical reactions are effective; as the pressure increases, Cl radicals increase in the chamber, and the resulting chemical reaction becomes dominant, increasing the etching rate. Fifth
Figure a shows the etched shape of phosphorous-doped polysilicon at 0.04 Torr, and reflecting the fact that physical reactions are dominant in this pressure region, a steep etched shape 24 that matches the dimensions of the mask material is obtained. It is being On the other hand, FIG. 5b shows the etched shape at 0.12 Torr, with a large undercut 4, indicating that chemical reactions are dominant. In the end, this investigation revealed that etching with Cl ₂ gas does not produce etching residue as expected, and that a low pressure of 0.05 Torr or less is sufficient to achieve high-precision machining without undercuts. I also understood. However, when using Cl ₂ gas alone, the etching rate of SiO ₂ increases and the selectivity with the underlying material decreases to ~15
The problem remains that only a certain amount can be taken.

Based on the above knowledge regarding _Cl2 gas etching, the present inventors have developed a dry etching method that has a high selectivity with respect to the underlying material without carbon deposition by using the reactive gas composition as described below. In addition to solving the problems of carbon deposition and selectivity, we were able to realize a dry etching method that enables high-precision processing.

To carry out the etching of the present invention, a single halogen, ie, one or more of F ₂ , Cl ₂ , Br ₂ or I ₂ , is made into a gaseous state and used as the main reactive gas. In this sense, Cl ₂ gas can be particularly preferably used. Carbon deposition can be prevented by using halogen as a reactive gas. Furthermore, in order to perform directional etching that allows for high-precision processing, it is sufficient to perform etching under low pressure as in the research above.
The gas pressure may be determined depending on the desired high-precision machining process or the type of dry etching method employed, taking into account the reaction between the discharge active species and the material to be etched.

Therefore, the object of the present invention can be achieved by finding a suitable additive gas that inhibits the reaction on the SiO ₂ surface in order to reduce the etching rate of SiO ₂ as a base material, and the present inventors have made efforts to As a result of repeated research, we found that O ₂ is effective as an additive gas.

Figure 6 shows the reactive ion etching apparatus described above using Cl ₂ + O ₂ gas, with a total gas flow rate of 40 c.c./
The graph shows the etching rate of phosphorus-doped polysilicon and SiO ₂ as well as the change in V _DC with respect to the amount of O ₂ added when a high frequency power of 0.35 W/cm ² is applied. The gas pressure was kept at a low pressure of 0.05 Torr to achieve directional etching.

As shown in FIG. 6, V _DC increases as the amount of O ₂ added increases, and the ion bombardment becomes stronger.
Despite this, a trace amount (~5c.c./min: partial pressure ratio~
The etching rate of SiO ₂ is drastically reduced by the addition of O ₂ (12.5%), and remains at a low level even when the amount of O ₂ added is higher than that. This is considered to be because O ₂ is effective in inhibiting the reactions of (1) dissociation of Si and O, and (2) formation of SiCl _o on the SiO ₂ surface. On the other hand, the etching rate of phosphorus-doped polysilicon is hardly affected by the addition of this small amount of O ₂ , but when O ₂ is further increased (9 to cc/min: partial pressure ratio of 22.5 to %), it decreases to the next level. It's coming. This is because (1) separation of Si on the Si surface (2) occurs only when the amount of O ₂ added increases.
This is thought to be because the reaction to form SiCl _o begins to be inhibited by O ₂ .

In Figure 6, the amount of O ₂ added that can achieve the maximum selectivity is about 6 c.c./min (partial pressure ratio 15%), and the selectivity with SiO ₂ at this time is about 100, which is compared to the case without O ₂ addition. This was a marked improvement compared to the ~15 in the case. And since the degree of improvement is remarkable, it is practical to use O ₂
The amount added can be in the range of 2 to 16 c.c./min (partial pressure ratio of 5 to 40%).

FIG. 7 shows a steep shape 24 obtained when the phosphorus-doped polysilicon 72 is etched under the condition of O ₂ =6 c.c./min, which is the maximum selection ratio in FIG. Directional etching can be achieved under a mixed gas, as expected, by applying an appropriately low pressure, as in the case of a halogen gas unit.

For the Cl ₂ +O ₂ mixed gas, almost the same relationship curve was obtained for the silicon nitride base material as in FIG. 6 for SiO ₂ . Its maximum selection ratio is about 60
It was hot. In addition to polysilicon, the materials to be etched include single crystal silicon, amorphous silicon,
It has been found that the present invention is effective when applied to Al, high melting point metals used for electrode wiring such as Mo, W, and Ti formed on wafers, and silicides thereof. It was particularly effective for those doped with impurities.
Although resist is used as the mask material in this example, it should be understood from the above results that good results can be obtained even if SiO ₂ or the like is used as a mask.

In addition, since the high selectivity to the substrate is achieved by the composition of the gas mixture, and perhaps by the nature of the active species generated by the gas mixture in the discharge, it is possible to We believe that it is also effective in etching equipment and ion shower etching equipment,
This was confirmed for the above device. Therefore, this mixed gas can be applied to a dry etching method that utilizes discharge activated species.

As explained above, according to the present invention, since the reactive gas is mainly chlorine gas, etching residue is generated due to carbon deposition, and since oxygen gas is added to it, it is Therefore, the material to be etched can be etched with a high selectivity over a wide range of oxygen gas addition amounts. Further, even if etching is performed under a low pressure that enables desired etching, carbon deposition does not occur as in the conventional method, so that in addition to the above-mentioned effects, conditions for high precision processing can be freely selected. Therefore, the present invention is a useful method for increasing the degree of integration of ICs.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the etching shape with undercut by the conventional method of halogenated carbon;
The figure is an explanatory diagram of an etched shape with etching residue, FIG. 3 is a cross-sectional view of the apparatus used in the embodiment of the present invention, and FIG. 4 is a diagram showing the relationship between gas pressure, etching rate, and V _DC using Cl ₂ simple gas. 5a and 5b are explanatory diagrams of the etching shape by Cl ₂ simple gas, FIG. 6 is a graph showing the relationship between gas composition, etching rate, and V _{DC according to the method of the present invention, and FIG. 7 is a graph showing the relationship between the etching rate and V DC} according to the method of the present invention. FIG. 1,51,71...Oxide or nitride (base material), 2,52,72...Substance to be etched, 3,
53,73...Mask, 4...Undercut,
24... Steep etching end surface, 5... Etching residue, 6... Carbon deposition, 32, 33... Parallel plate electrode, 35... High frequency power source, 37... Etched material, 38... Gas introduction hole.

Claims (1)

[Scope of Claims] 1. A reactive ion etching device having opposing electrodes to which high frequency power can be applied, which generates glow discharge by applying high frequency power and etches a material to be etched placed on the electrodes. , by introducing a mixed gas consisting of chlorine gas and oxygen gas,
A dry etching method characterized by selectively etching polysilicon in a material to be etched with respect to silicon oxide. 2. The dry etching method according to claim 1, wherein the mixed gas is a mixed gas having a partial pressure ratio of oxygen gas of 5 to 40% and a low pressure that allows desired directional etching.