JPS6339095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry etching apparatus for finely processing semiconductors and the like using reactive gas ions.

Films such as polycrystalline silicon (Poly-Si) and silicon nitride (Si ₃ N ₄ ) used in the manufacturing process of integrated circuits are
Recently, a dry method called plasma etching has been used instead of a wet method using a fluoro-nitric acid solution. The outline of the plasma etching method is to introduce Freon-based gas into a vacuum chamber, apply high-frequency power at a pressure of 0.1 to 1 Torr to generate gas plasma, and SiF ₄ is etched by active fluorine in the gas plasma. Etching is achieved by creating and exhausting this. This method has various advantages, such as the ability to use photoresist directly as an etching mask, and is often employed in the manufacture of integrated circuits. However, since this method performs isotropic etching, for example, as shown in _FIG .
When the -Si film 2 is etched using the photoresist 3 as a mask, an undercut is created under the photoresist 3 by the thickness of the poly-Si film 2. Therefore, this method requires a minimum pattern size of 3 to 4μ for LSL.
It is only used for devices with a diameter of 1 to 2 μm.
It cannot be applied to VLSI, which aims to be a device with this pattern. This undercut is caused by the fact that etching is performed only by chemical reaction.

In contrast, a reactive sputtering etching method that incorporates a physical sputtering effect has recently been studied. As shown in Fig. 2, this method uses a metallic vacuum container 11, evacuates the inside to 10 ^-6 Torr or less using a diffusion pump, etc., and then
A reactive gas having a C-F bond such as CF ₄ , C ₂ F ₆ , or C ₃ F ₈ is introduced and adjusted to a pressure of about 10 ^-3 Torr, and a 13.56M
Gas plasma 14 is generated by applying high frequency power 13 of Hz.
The sample 16 placed on the sample stage 15 on the electrode 12 is etched. 17 and 18 are valves connected to the gas introduction system and exhaust system, respectively;
9 is an insulating spacer made of Teflon or the like. In conventional plasma etching methods, the etching rate of Si is always higher than that of _SiO2 , but with this method,
When using CF ₄ gas, when the sample stage 15 is made of quartz, the etching rate is almost the same for Si and SiO ₂ , and when the sample stage 15 is made of Teflon or carbon, the etching rate is approximately the same.
It has been reported that SiO ₂ is etched approximately 5 times faster than Si (S. Matsuo et al., Jap.JA
P.vol16, No.1P.175 (1977)). According to this method, the photoresist is used as a mask and Poly-
When etching a Si film, it is etched with almost no undercuts.

However, in this method, since the sample is in the plasma, the radiant heat of the plasma, power loss, and
The sample temperature rises rapidly during etching due to the impact of ions accelerated at 1000V, and not only the sample but also the photoresist is altered and etched. As a result, the edges of the photoresist recede, and although there is no undercut, the minimum dimensions of the pattern created are approximately the same as those obtained by the plasma etching method described above. Furthermore, although this method results in a steep etching cross section, it is impossible to perform tapered etching to prevent disconnection of wiring, for example. Furthermore, in order to continuously perform poly-Si/SiO ₂ /Si etching using this method, it is necessary to change the gas and
The work is extremely difficult as the sample stage must be changed.

Therefore, the present inventors first separated the discharge part and the material-to-be-etched part in a vacuum container, and, for example,
We proposed a method in which plasma is generated by discharging C ₂ F ₆ gas, and only reactive cations are extracted from this plasma and guided to the area where the material to be etched is placed.

FIG. 3 is a diagram showing a simple schematic structure of a dry etching apparatus in which the discharge section and the etched material placement section are separated.

The dry etching apparatus 30 is roughly composed of a discharge chamber 31 and an etching chamber 32.
A filament cathode 33 is disposed within the discharge chamber 31, and by applying voltage from an AC power source 34 between the anode and the wall of the discharge chamber 31, a discharge is generated within the discharge chamber 31. There is.
Two electrodes 35 and 36 having a large number of through holes are provided at the openings of the discharge chamber 31 and the etching chamber 32, and an annular insulating member is interposed between the electrodes 35 and 36. It is constructed to maintain airtightness. In this way, the discharge chamber 31 and the etching chamber 32 are communicated with each other. Of the two electrodes 35 and 36, the electrode 35 is a grid held at a positive high potential, and the electrode 36 is a grid held at zero potential, and the ions generated in the discharge chamber 31 by these electrodes are is accelerated and guided into the etching chamber 32.

On the other hand, a holding mechanism 38 is provided within the etching chamber 32 to hold the object 37 to be etched.

According to the dry etching method using this device, the ion extraction acceleration voltage and SiO ₂ , Poly-Si
The relationship between etching speed and photoresistor etching speed is as shown in FIG. As is clear from the figure,
While the etching rate of SiO ₂ increases monotonically, in the case of Poly-Si, the etching rate is small up to 600V, increases rapidly above that, and reverses to that of SiO ₂ at about 900V. Therefore, this method uses the same gas and simply changes the ion extraction acceleration voltage to produce Poly-Si/Si.
Etching of SiO ₂ /Si system can be performed continuously. Furthermore, since the sample is separated from the plasma, desired taper etching is possible by allowing the sample stage to rotate and revolve, and the sample can also be water-cooled. The low etching rate of the photoresist in FIG. 4 is considered to be a result of this water cooling.

However, in this method, the etching rate of SiO ₂ is proportional to the ion extraction acceleration voltage.
High etching selectivity of SiO ₂ /Si can be obtained
It is difficult to obtain a high etching rate for SiO ₂ in the range of 600 V or less because the amount of ions is predetermined by the accelerating voltage.

When SiO ₂ /PolySi is etched with a reactive etching gas such as C ₂ F ₆ using a dry etching apparatus as shown in Fig. 3, the selectivity is compared as shown in Fig. 4. However, the etching rate of SiO ₂ is at most 400
It can only be obtained up to about Å/min.

This invention has been made in view of the above points, and provides a dry etching apparatus that extracts reactive ions from plasma to microfabricate a desired material to be etched with a high selectivity and high etching rate. This is what we provide. That is,
This invention generates plasma by discharging a reactive gas containing a halogen element, extracts the ions necessary for etching from this plasma, and guides them to the material to be etched. It is characterized in that after a required amount of ions are drawn out using an accelerating voltage, the ions are decelerated to 900V or less by a deceleration means and guided to the material to be etched.

In this way, by fixing the amount of ions to be extracted and lowering the energy of the extracted ions, it is possible to suppress the physical sputtering effect and take sufficient account of chemical etching, resulting in high selectivity. In addition, etching can be performed at a high etching speed. In this case, an energy analyzer is provided between the ion acceleration means and the ion deceleration means,
By selecting only necessary ions from among the extracted ions, it becomes possible to perform etching with even higher selectivity.

Examples of the present invention will be described below. FIG. 5 is a schematic diagram showing an etching apparatus according to one embodiment, and the entire structure constitutes a vacuum vessel. 51 is a gas inlet port, and when a desired reactive gas containing a halogen element is supplied from this port, a power source 52 (7kV, 100mA) is supplied.
A discharge occurs between the electrode 53 to which the voltage is applied and the casing 54, and plasma 55 is generated. 56 is a spacer made of boron nitride. Reactive cations are extracted from the plasma 55 thus created by the extraction electrode 57 and collected by the main shell lens 58 . 59 and 60 are power supplies (30 kV, 15 mA) applied to the extraction electrode 57 and the main shell lens 58, respectively. The ions extracted and accelerated in this way are transferred to the deceleration electrodes 61, 6
2, 63 so that the speed is gradually reduced. A power source 64 is connected to the deceleration electrodes 61, 62, and 63.
(20kV, 2mA) output with resistors 65, 66, 67
The voltage is divided and applied appropriately. The decelerated ions are then guided to the sample chamber 69 via the neutralization mechanism 68. The neutralization mechanism 68 is, for example, a filament, and neutralizes the ions sent into the sample chamber 69 by attaching electrons to them. 70 is a cryopump, 71 is an insulating glass spacer, and 72 is an insulating rod for fixing the glass spacer. In the sample chamber 69, there is a sample stage 74 that can rotate and revolve by an external drive mechanism 73.
is placed, and the sample (material to be etched) 7 is placed on top of it.
5 is placed. 76 is an exhaust port connected to, for example, a diffusion pump.

In this way, a sufficient amount of reactive ions are drawn out and accelerated in advance, and then guided into the sample chamber by the deceleration system in the next stage, with the amount of ions remaining fixed and only the energy lowered. Therefore, etching caused by sputtering is suppressed, and highly selective etching is performed by chemical action.

The experimental results show that when C ₂ F ₆ gas is used, and it is discharged and extracted with an acceleration voltage of 25 kV, and then a deceleration voltage of 24.8 kV is applied, that is, substantially
When accelerating at 200V, the etching speed of Si is approximately
200 Å/min, while that of SiO ₂ is about 1400 Å/min.
Å/min, and a very large selectivity was obtained.

Furthermore, for the acceleration voltage of the ions in Fig. 4,
As is clear from the characteristic diagram showing the relationship between the etching rates of Poly-Si and SiO ₂ , even when using the device according to the embodiment of the present invention, the actual accelerating voltage is 900V.
SiO ₂ can be selectively etched with respect to Poly-Si under the following conditions. Further, in this case, the etching speed of SiO ₂ can be obtained at a more practical value than in the case of using a dry etching apparatus having no speed reduction means as shown in FIG. 3, as described above.

On the other hand, if we take the case of CF ₄ gas as an example,
The components of reactive ions when this is left are:
78% _CF3 ⁺ , 7.8% _CF2 ⁺ , 4.4% F ⁺ , CF ⁺
3.7%, 3.1% for C ⁺ , 1.9% for _CF2 ⁺⁺ , 0.7% for _CF3 ⁺⁺
It is becoming. Etching under the aforementioned acceleration and deceleration voltage conditions was performed in a state where ions of various components were mixed, and the SiO ₂ /Si
The etching selectivity is still too small for actual device fabrication. Furthermore, among the various ionic components mentioned above, CF ₃ ⁺ is said to be an active species that etches SiO ₂ particularly faster than Si.

Therefore, using C ₂ F ₆ gas, we installed a magnet between the acceleration system and the deceleration system and conducted _an energy analysis ^.
An etching experiment was carried out under the same conditions as described above. As a result, the etching rate of SiO ₂ is
The etching rate for Si was reduced to about half to 600 Å/min, but the etching rate for Si was reduced to 1/10 to about 20 Å/min, and the selectivity was about 30 times higher, making it possible to apply it to actual device manufacturing. I understood.

FIG. 6 shows a schematic configuration of another embodiment of the present invention which has been improved based on the above experimental results. 81 is a gas inlet, and 82 is an ion source. As explained in the previous embodiment, the ion source 82 ionizes the introduced gas by leaving it alone, but it is not limited to the parallel plate type, but may also be of the dual plasma type, PIG type, Freeman type, or a mixture of these types. Furthermore, a microwave ion source using ECR (electron cyclotron resonance) may be used. 83
is an ion extraction acceleration system, and 84 is an energy analyzer. The energy analyzer 84 separates the ion species by applying a magnetic field to the extracted ions, and only the necessary ions are transferred to the next ion deceleration system 85.
lead to. Then, the ions are decelerated to about 900V or less by the ion deceleration system 85 and guided to the sample chamber 86. A sample stage 88 that can rotate and revolve around its axis by an external drive mechanism 87 is arranged in the sample chamber 86, and a sample 89 is placed on it.
is placed. Reference numerals 90, 91, and 92 are exhaust ports, which are connected to a diffusion pump or the like.

If you place not only one magnet but several magnets side by side as the energy analyzer 84, for example,
It is possible to send a suitable combination of ion species, such as CF ₃ ⁺ and C ⁺ or F ⁺ and C ^+, to the sample chamber 86, thereby making it possible to further improve the etching selectivity. The energy analyzer also serves to prevent the material to be etched from being contaminated by the electrode material sputtered inside the ion source, making it very useful as an etching device for semiconductors.

In the above explanation, the etching of Si and SiO ₂ was taken as an example, but W, which has etching characteristics similar to Si,
The apparatus of the present invention can be similarly applied to heat-resistant metals such as Mo, Nb, and Ti. In addition to CF ₄ and C ₂ F ₆ , the gas to be used may also be a gas having other C-F bonds such as C ₄ F ₈ or CHF ₃ , or even Al.
A gas containing Cl such as CCl ₄ can also be used for etching of Cr and Cr.

As explained above in detail, in the dry etching apparatus according to the present invention, a deceleration means for decelerating the ions to an acceleration voltage of 900 V or less is provided after the means for extracting and accelerating the ions, so that the extracting and accelerating means is sufficient. After extracting a certain amount of ions, the energy of the ions can be lowered by the deceleration means so that the ions reach the material to be etched at an accelerating voltage of 900 V or less while keeping the ion amount fixed. Therefore, according to the present invention, it is possible to balance etching by sputtering and etching by chemical action, and to perform etching with high selectivity and a practical etching rate. Further, by providing an energy analyzer between the ion acceleration means and the ion deceleration means to select necessary ions, etching with even higher selectivity becomes possible.

[Brief explanation of the drawing]

Figure 1 shows Poly etching using a plasma etching device.
-A diagram showing the state of Si etching, Figure 2 is a diagram showing a plasma etching apparatus that takes sputtering action into consideration, and Figure 3 is a dry etching structure in which the discharge part and the etching material placement part are separated without a deceleration means. A schematic configuration diagram of the apparatus, FIG. 4 is a diagram for explaining the characteristics of the dry etching apparatus without the deceleration means shown in FIG. 3, and FIG. 5 is an embodiment of the dry etching apparatus having the deceleration means according to the present invention. FIG. 6 is a schematic diagram showing another embodiment of the present invention. 51... Gas inlet, 53... Electrode, 54...
Housing, 55...Plasma, 57...Extraction acceleration electrode, 58...Mainzel lens, 61, 62,
63...Deceleration electrode, 68...Neutralization mechanism, 69...
... Sample chamber, 74 ... Sample stage, 75 ... Sample (material to be etched), 76 ... Exhaust port, 81 ... Gas inlet, 82 ... Ion source, 83 ... Acceleration system, 84
...Energy analyzer, 85...Deceleration system, 86...
...Sample room.

Claims (1)

[Scope of Claims] 1. An etching target selectively formed on the surface of a sample placed in a vacuum container by chemically reacting the sample with ions generated from a reactive gas introduced into the container. A dry etching apparatus for etching a member includes at least means for extracting and accelerating ions for etching the member to be etched, and ions extracted and accelerated by the extracting and accelerating means.
A dry etching device characterized by having a deceleration means for decelerating to an acceleration voltage of 900V or less. 2. The dry etching apparatus according to claim 1, further comprising means for selecting only desired ions contributing to the chemical reaction after the ions are extracted until they reach the member to be etched. 3. The dry etching apparatus according to claim 1, wherein the table on which the member to be etched is placed has a rotation mechanism.