JPS6062125A - Plasma etching method - Google Patents

Abstract

PURPOSE:To improve the efficiency of an etching reaction by modulating the application of high-frequency power from the outside and intermittently executing a reaction in which an introducing gas is converted into an active seed. CONSTITUTION:A reactive gas is introduced into a sealed vessel 31 from an introducing hold 32, and removed from an exhaust hole 33. An upper electrode 30 is grounded, and a material to be etched 34 is placed on a lower electrode 35. Power is applied to the electrode 35 from a high-frequency power supply 39 through a breaker 36. The breaker 36 is controlled by a pulse generator 37, and can turn high-frequency power ON-OFF by arbitrary frequency. Consequently, a reaction between the material to be etched and active seeds is progressed during a time when the supply of energy from the outside is stopped till the next period by intermittently executing a reaction in which an introducing gas is converted into the active seeds. A re-decomposition in plasma of a reaction product is prevented by further removing a volatile reaction product, and the efficiency of an etching reaction can be improved.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to the active species and material to be etched generated in the plasma generated by applying high frequency (including microwave) power to a reactive gas introduced into a closed container. The present invention relates to a plasma etching method in which a material to be etched is etched using a physicochemical reaction with a material to be etched.

[Technical background of the invention and its problems]

Generally, in electronic materials, mainly materials for manufacturing semiconductor devices, an etching process is often used to form four turns in a predetermined device. In this etching process, corrosion using liquid chemicals such as acids and alkalis (wet etching) has conventionally been mainly used. In recent years, plasma etching methods, in which etching is performed in a gas phase, have come into wide use due to its controllability and safety. This plasma etching applies high-frequency (including microwave) power to a reactive gas containing halogen, etc., excites a discharge, and utilizes a physicochemical reaction between the formed active species and the material to be etched. is converted into volatile compounds and exhausted as a gas phase.

By the way, plasma etching can be broadly classified into the following two types. In other words, when the surface of the material to be etched is directly exposed to plasma, and when the plasma generation area and the material to be etched are placed in separate locations, the active species created in the plasma region are introduced to the surface of the material to be etched, resulting in the etching. This is when a reaction occurs. In the case of direct exposure to plasma, the following problems arise. That is, as shown in FIG. 1, is the material 12 to be etched in the closed container 11 directly exposed to the plasma region 14?
Or, even when separated by the shield 13, it is very close to the plasma. In such a situation, the elementary reactions in the plasma are considered to be mainly as follows. As shown in FIG. 2, the reactive gas 22 introduced through the gas introduction hole 21 is activated within the plasma region 23 and becomes highly reactive active species 24. This and the material to be etched 25
reacts to form a reaction product 26, which is removed through the exhaust hole 27, thereby progressing the etching. At this time, since the reaction product 26 on the gas introduction hole 21 side passes through the plasma region again, there is a high rate of re-decomposition due to the impact of ions and electrons.

Atoms (molecules) of the etched material re-decomposed in this way
28 is again attached to the material surface. Since the etching reaction consists of a collection of such elementary reactions, the following two reactions occur.
point is essentially the problem.

(a) The reaction products 26 undergo re-decomposition in the plasma region 23 and adhere to the material surface, resulting in a decrease in etching efficiency. Further, since the gas flow is in the direction shown by the arrow in FIG. 2, re-decomposition and re-deposition occur more frequently in the downstream region of the gas flow, resulting in non-uniform etching.

(b) The gas species introduced through the gas introduction hole 21 is activated, combines with the material, and is consumed, resulting in a shortage of active species in the downstream region of the gas flow, causing non-uniform etching.

[Purpose of the invention]

In the present invention, the presence of gas flow is unavoidable in plasma etching equipment, and etching tends to be non-uniform in the upstream and downstream regions of the gas flow (the cause of this is the non-uniform presence of active species in the plasma). In view of the fact that the reaction products undergo re-decomposition when passing through the plasma region again and re-deposit on the material surface, the external energy supply that is the source of active species formation is modulated. This aims to create a temporal non-uniformity, thereby eliminating the spatial non-uniformity, and to provide a plasma etching method with excellent etching efficiency and uniformity.

[Summary of the invention]

In the present invention, external high frequency (microwave, R
Adio Frequency (abbreviated as RF) By modulating the power application and making the reaction that converts the introduced gas into active species intermittently, active species are uniformly created in the plasma, and energy from the outside is not absorbed until the next cycle. While the supply is stopped, the reaction between the material to be etched and the active species is allowed to proceed, and volatile reaction products are removed to prevent the reaction products from being decomposed again in the plasma, thereby slowing down the etching reaction. This is designed to increase efficiency.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. The device used in this example was a normal parallel plate type etching apparatus as shown in Fig. 3, with a closed container (vacuum chamber)
A reactive gas is introduced into the chamber through an introduction hole 32, and reaction products and excess gas are removed through an exhaust hole 33. The upper electrode 3Q is grounded, and the material to be etched 34 is placed on the lower electrode 35. This lower electrode 35 has
Power is applied via a circuit breaker 36 and a matching network 38 from a high frequency power source 39 of, for example, 1'3.56 MHz. The circuit breaker 36 is controlled by a pulse generator 37, and can turn on and off the high frequency power at an arbitrary period.

Carbon tetrachloride CC/4 is used as the reactive gas,
Al was selected as the material to be etched.

After placing the sample 34 in the sealed container 31, it is evacuated, and a reaction gas is introduced to approximately 0%. Etching was carried out under reduced pressure conditions of about I Torr and by applying high frequency power (13.56 MHz) of about 0.2 W per electrode area. The reaction product takes the form of A11XC1ly and is removed from the exhaust hole 33. The applied high frequency power is applied to the circuit breaker 36.
It can be turned on and off periodically by , and can be said to have added Gluc modulation. Lower electrode 3 at this time
FIG. 4 shows the waveform of the high frequency voltage applied to 5. The time tl during which the high frequency is applied and the time t2 during which the high frequency is cut off can be freely set.

FIG. 5 shows the results when high frequency power is continuously applied. This figure shows the relationship between the position within the material to be etched (in this case, an AA film deposited on a 5-inch diameter silicon wafer by the SiQ tuttering method) and the etching rate. Compared to the etching rate near the upstream side of the gas flow within the wafer, which is approximately 1000 νmln,
Near the downstream, it is only about 600 Vmin. As mentioned above, this is because active species contributing to etching are consumed in the upstream region of the gas flow, and in the downstream region, reaction products are re-decomposed in the plasma and re-attached to the wafer surface. One way to eliminate this drawback is to apply RF power intermittently, as shown in FIG. That is, in FIG. 6(,), as shown in the time/applied voltage relationship on the right side of the figure, no RF power is applied (time t 2
), the chamber is uniformly filled with a reaction gas 41. Here, as shown in Fig. 6(b), the RF for a time of 1.0
Application of electrical power activates a portion of the gas species uniformly filled within the chamber. This active species 420 distribution is also uniform. Next, as shown in Fig. 6 (c), the active species and the material to be etched react to form a reaction product 43, but since no RF is applied during this time, the reaction product 43 is exposed to the plasma again. It is removed without being re-decomposed. In order for this situation to occur effectively, many factors are involved, such as gas flow rate, time required for surface reaction, chamber size, etc., but in reality, the time tl shown in Figure 4 is related.
Optimization can be achieved by choosing the value of rt2 well.

FIG. 7 shows the etching rate distribution within the wafer when optimized in this manner. That is, compared to the case of FIG. 5 in which no modulation is applied to RF, the uniformity is clearly improved. Furthermore, at this time, even though t1/(tl+tz)-0.7, that is, the RF application time was about 70% of the total, the etching rate did not decrease, and this was due to the decomposition and re-decomposition of the reaction products. This is because loss due to adhesion is reduced.

This effect brings about advantageous results in addition to improving etching efficiency. That is, in the conventional continuous RF application method, the reaction products are re-decomposed and re-deposited on the inner wall of the chamber other than the wafer, thereby contaminating the chamber and causing dust. In contrast, in the RF modulation application method of the present invention, re-decomposition and re-deposition of reaction products are reduced, so that the chamber can be much less contaminated.

Note that the present invention is not limited to the embodiments, and can be applied in various ways. For example, in the embodiment, the case of etching Al in a parallel plate reactor was used as an example, but it can also be used in other groove-shaped plasma etching such as a barrel quip reactor. It is also effective when etching organic materials such as silicon oxide, silicon nitride, and resist. Although the power application method is a pulse modulation method, other methods such as sine wave modulation are also effective.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to improve the uniformity of plasma etching and improve the etching efficiency.
Furthermore, it is possible to provide a plasma etching method that has advantages such as less contamination of the chamber.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional plasma etching system;
The figure shows the principle of a conventional plasma etching method, Fig. 3 is a configuration diagram of a plasma etching apparatus showing an embodiment of the present invention, Fig. 4 is a diagram of high frequency waveforms used in the same apparatus, and Fig. 5 shows etching by the conventional apparatus. FIG. 6 is an explanatory diagram of the operation of the apparatus shown in FIG. 3, and FIG. 7 is an etching characteristic diagram using the same apparatus. 30... Upper electrode, 3... Sealed container, 32...
Gas introduction hole, 33... Exhaust hole, 34... Wafer to be etched, 35... Lower electrode, 36... Circuit breaker, 3
7... /f/L/S generator, 38... Matching network, 39... High frequency power supply. Appearance agent Patent attorney Takehiko Suzue

Claims (3)

[Claims] (1) When etching the material to be etched by utilizing the physicochemical reaction between the material to be etched and the active species generated in the plasma generated by applying high frequency power to a reactive gas introduced into a sealed container, A plasma etching method characterized by modulating high frequency power. (2) The plasma etching method according to claim 1, wherein the modulation is an intermittent supply (pulse modulation) of the high frequency power. (3) The plasma etching method according to claim 1, wherein the modulation is sinusoidal modulation.