JPH01214122A - Plasma processing method - Google Patents

Abstract

PURPOSE:To reduce a microwave reflection in a vacuum vessel and to stabilize a plasma process by generating a plasma by using a magnetic field of predetermined intensity and a pulselike microwave in processing gas introduced into the vessel, and specifying the relationship between a microwave outputting period and stopping period when processing a material to be processed by using the gas. CONSTITUTION:A vacuum vessel 1 is evacuated to a predetermined vacuum degree, processing gas is introduced into an ion generation chamber 1a, the vessel 1 is evacuated to a desired vacuum degree, and an annular magnetic field is then generated by an annular magnetic coil 6. Then, a pulselike microwave is generated from a microwave output unit 4, introduced to the chamber 1a, electrons are spirally moved by the synergistic action between the magnetic field and the microwave, accelerated by a cyclotron resonance, a high ionization plasma is generated near the lower opening 7 of the chamber 1, and a semiconductor wafer 2 is processed by acceleration ion therein. With this construction, when the microwave output period per one pulse period is 1 and its stopping period is x, the relationship of 3<=x<=10 is satisfied.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a plasma processing method.

(Prior Art) Conventionally, as a method for plasma processing objects to be processed such as semiconductor wafers, ECR (Electronic Carbon Processing) has been used.
yclotron Re5onance) plasma processing method is used.

As this ECR plasma processing method, for example, in the ECR etching method, due to the interaction of a magnetic field and microwave,
Electrons are made to move in a spiral and accelerated under conditions of electron cyclotron resonance, the accelerated electrons collide with the processing gas to generate plasma, and the ions in this plasma are extracted to etch the object to be processed. It's a method.

In this way, in the ECR etching method, the accelerated electrons in the ion source undergo spiral motion, which increases the probability of ionization of neutral particles due to electron impact in the ion source. Highly ionized plasma can be generated in a vacuum, and etching processing can be performed in a high vacuum atmosphere.

By the way, with the recent increase in the degree of integration of semiconductor devices, high accuracy is required in the formation of fine patterns. That is, in order to faithfully reproduce the dimensions of the etching mask pattern to be used as a photoresist formed in the mask pattern transfer process, as shown in FIG. It is desirable that the etched cross section of the etching mask 3 has an anisotropic shape.

However, when etching is performed in a high degree of vacuum, as shown in Figure 7, the incident ions a collide and scatter with reaction products and other neutral species, causing the direction of incidence to be bent. There has been a problem in that a so-called undercut phenomenon occurs in which the material collides with the side wall of the section and etches the side wall.

Therefore, in conventional ECR etching, the problem of undercutting has been solved by creating a low vacuum atmosphere in the vacuum chamber, for example, 10-' Torr or less, to reduce the probability of collision of incident ions.

(Problem to be solved by the invention) However, as mentioned above, EC
When performing R-etching, there is a problem that the etching rate decreases, and if an attempt is made to lengthen the etching time without solving this problem, the problem arises that the temperature of the object to be processed increases and the resist deteriorates. Ta.

In addition, in conventional ECR etching, the microwave output is applied continuously until the processing operation is completed, as shown in Figure 8. There are limits to improving the conversion efficiency of plasma generation energy from processing gas.
Excess microwave energy appears as reflected waves in the ion generation chamber inside the vacuum container.

When such reflected waves occur, the state of the plasma becomes unstable, leading to a decrease in the etching rate and the occurrence of uneven etching, resulting in the problem that stable processing cannot be performed.

In order to prevent the generation of reflected waves, it has been considered to make the ion extraction port from the ion generation chamber, which is the plasma generation area, smaller, but since the amount of ions flowing out is small, it is difficult to process in a short time. The problem is that the object to be processed must be moved closer, which improves the etching rate but reduces etching uniformity, and moving the object away improves uniformity but conversely reduces the etching rate. occurred.

The present invention was made to solve the above-mentioned problems, and it enables stable processing in a high vacuum atmosphere, reduces microwave reflection in the processing chamber, and enables stable ECR plasma processing. The purpose is to provide a possible plasma processing method.

[Structure of the Invention] (Means for Solving the Problems) The plasma method of the present invention introduces a processing gas into a vacuum container serving as a processing chamber, and generates an interaction between a magnetic field of a predetermined strength and pulsed microwaves. In the plasma processing method, in which the introduced processing gas is turned into plasma and the object to be processed is processed with the generated plasma, one pulse period of the microwave has a microwave output period of 1,
The process is characterized by adding pulsed microwaves that satisfy 3≦X≦10, where X is the microwave stop period.

(Function) By applying microwaves for plasma generation in the form of pulses with predetermined intervals, stable processing is possible in a high vacuum atmosphere, and reflection of microwaves within the processing chamber is reduced, resulting in stable processing. This makes it possible to perform plasma processing with

(Example) Hereinafter, an example in which the method of the present invention is applied to ECR etching will be described with reference to the drawings.

The stepped cylindrical vacuum container 1 has an ion generation chamber lax for ionizing processing gas in the small cylindrical part at the top, and a mounting table 3 on which the object to be processed, such as a semiconductor wafer 2, is placed in the large cylindrical part at the bottom. It consists of a processing chamber 1b in which a

A microwave waveguide 5 connected to a microwave output section 4 that outputs pulsed microwaves with a predetermined cycle is attached to the top surface of the vacuum vessel 1. The waveguide 5 outputs pulsed microwaves. It is guided into the ion generation chamber 1a. An annular magnetic coil 6 is disposed on the outer surface of the ion generation chamber 1a of the vacuum container 1 to form a donut-shaped magnetic field within the ion generation chamber 1a.

An etching method using such an ECR etching apparatus will be explained below.

First, the inside of the vacuum container 1 is set to a predetermined degree of vacuum, and a processing gas is introduced into the ion generation chamber 1a from a gas introduction part (not shown) to create a vacuum atmosphere of the degree of vacuum necessary for processing, for example, 10' Torr. , a current is passed through the annular magnetic coil 6 to form an annular magnetic field of, for example, 875 Gauss.

After that, for example, 2.
Microwaves of 45 GHz are guided into the ion generation chamber 1a in a pulsed manner, for example, at intervals of 16 m5 as shown in FIG.

In this way, the interaction between the magnetic field and the zero microphone wave causes the electrons to move in a spiral motion, and the electrons are accelerated by cyclotron resonance, generating highly ionized plasma near the lower opening 7 of the ion processing chamber 1a, and inside the generated plasma. A predetermined etching process is performed using accelerated ions.

By the way, in this example, as mentioned above, the method of outputting microwaves in pulsed form is used, and by outputting pulsed microwaves in this way and generating plasma intermittently, high vacuum conditions such as Even under a vacuum atmosphere of 10' Torr, the occurrence of undercuts during etching could be suppressed, and anisotropic etching could be performed. At this time,
By further lengthening the pulse period, the occurrence of this undercut can be further reduced, but at the same time, there is a risk of lowering the etching rate. Increasing the microwave output did not cause a decrease in the etching rate.

Furthermore, by adding pulsed microwaves, the efficiency of energy conversion from microwave energy to plasma generation energy increases, making it possible to reduce the generation of reflected waves and eliminate the various problems caused by these reflected waves. I was able to solve it.

Therefore, as shown in Figure 4, we determined the relationship between the ratio of the pulse width per pulse period of the microwave (active period) to the inactive period X (duty factor) and the generation rate of reflected waves. The results are shown in FIG.

FIG. 5 is a diagram showing the generation rate of reflected waves when the microwave pulse duty is varied while a magnetic field of 875 Gauss is applied to the grid section 7, which is the plasma generation section in the vacuum vessel 1. , as shown in the same figure, the inactive period X per pulse period is 3 times the pulse width ~
It was observed that when the magnification was up to 10 times, the reflected wave generation level was lower than that of the conventional continuous output method.

This is because the pulse interval is too short below x-3.
This is because the next pulse is guided before the plasma disappears, and as a result, plasma is generated continuously as in the conventional continuous output method.On the other hand, when x-10 is exceeded, In order to maintain the etching rate, it is necessary to make the microwave output extremely high, and with microwaves of such high output, not all of the energy is converted into plasma, and the surplus energy of the microwave appears as reflected waves. This is because it ends up happening.

Furthermore, in this case, a problem arises in that the etching rate decreases due to a decrease in energy conversion efficiency.

Therefore, it has been found that when the pulse duty ratio of the microwave is set to 1, the inactive period X may be set to 3 to 10.

In this way, by applying microwave output at a predetermined pulse period, anisotropic etching is possible even in a vacuum atmosphere of high vacuum, e.g. 10' Torr, and furthermore, the energy of microwave energy - plasma generation energy can be By improving the conversion efficiency, reflected waves of microwaves in the vacuum chamber are reduced, the etching rate and etching uniformity are improved, and stable processing can be performed.

As for the microwave pulse output method, with a 60Hz power supply, a single-phase half-wave rectified voltage may be applied to the magnetron, or a single-phase full-wave (80Hz) voltage may be used to increase the power efficiency.
a+S pulse) or a three-phase full-wave commutator smoothing circuit may be used.

Further, the method of the present invention is not limited to the above-mentioned etching method, but can be applied to any method using a plasma processing method, such as an ECRCVD apparatus.

[Effects of the Invention] As explained above, according to the plasma processing method of the present invention, stable processing is possible in a high vacuum atmosphere, and the reflection of microwaves in the processing chamber is reduced, resulting in stable processing. Plasma treatment becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an ECR etching apparatus to which the method of the present invention is applied, FIGS. 2 and 3 are diagrams showing the state of microwave pulse output in the embodiment, and FIG. FIG. 5 is a diagram showing the relationship between the pulse duty ratio of the microwave and the generation rate of reflected waves in the example, and FIG. 6 is a diagram for explaining the pulse width per pulse and the inactive period. FIG. 7 is a partial cross-sectional view of a semiconductor wafer showing directional etching, FIG. 7 is a partial cross-sectional view of a semiconductor wafer showing etching that causes undercuts, and FIG. 8 is a view showing the state of microwave output in a conventional method. 1... Vacuum container, 2... Semiconductor wafer, 4... Pulse microwave output section, 6...
...Annular magnetic coil. Applicant Chill Thermco Co., Ltd. Agent Patent Attorney Satoshi Suyama - Figure 1 Figure 1 Mars Tenko 1 Figure 2 1 Mars Thinking Day Figure 3 1:4 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Scope of Claims] Processing gas is introduced into a vacuum container serving as a processing chamber, and the introduced processing gas is turned into plasma by the interaction between a magnetic field of a predetermined strength and pulsed microwaves, and the generated plasma In a plasma processing method for treating a workpiece, one pulse period of the microwave satisfies 3≦x≦10, where the microwave output period per pulse period is 1 and the microwave stop period is x. A plasma processing method characterized by processing by applying pulsed microwaves that cause