JPH0456451B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a dry etching method applied to the manufacture of semiconductor devices, masks, etc., in which a film is removed by reactive gas plasma, and the process is completed. This invention relates to a dry etching method that is easily detected.

(b) Background of the technology In order to increase the scale of semiconductor integrated circuit devices, miniaturization of patterns and higher integration are being promoted.The microfabrication technology to realize these patterns is the technology of patterning resist. This is a composite technology that uses this as a mask to etch a semiconductor substrate or the like.

As an etching method in the manufacturing process of semiconductor devices, wet etching using a chemically selected solution has been widely used based on good technological accumulation, but it is necessary to improve etching accuracy in order to miniaturize patterns. In order to reduce the complexity of the process and to protect the environment, wet etching is being replaced by dry etching.

(c) Conventional techniques and problems The techniques collectively called dry etching methods include:
The etching mechanism includes those based on chemical reactions, those based on physical reactions, and those based on chemical and physical reactions.

The physical dry etching method is an etching method that utilizes the spatter phenomenon that occurs when ions with large kinetic energy collide with a solid surface. This method involves masking the surface of the sample in advance with a patterned material with a low etching rate and irradiating the entire surface of the sample with a uniform ion beam, usually called sputter etching. There is an ion beam etching method in which the surface is selectively scanned with an ion beam. These methods are suitable for microfabrication because they can suppress undercuts under the mask by using a uniform incident ion beam with uniform directionality, but they have poor selectivity with respect to the material to be processed, and There is a high risk of damage from ion bombardment.

An example of a chemical dry etching method is a plasma etching method. The low-temperature gas plasma normally used in plasma etching is obtained by introducing a suitable reactive gas into a reaction tube at a pressure of about 0.1 to 10 [Torr] and applying high-frequency power to it. Although the degree of ionization of this low-temperature gas plasma is low, it contains atoms and molecules that have been brought into an excited state through various collision processes. Atoms and molecules in such an excited state have high chemical activity, and a chemical reaction occurs between them and the atoms on the sample surface that come into contact with the gas plasma, and as a result of this reaction, volatile substances are formed, which causes the formation of volatile substances on the sample surface. Atoms are removed from the surface and etched.

Although this plasma etching method has selectivity with respect to the material to be processed, the etching direction is isotropic and the microfabriability is poor.

In the above-described sputter etching method, an inert gas is used as the atmosphere, but by using a reactive gas, chemical and physical reactions coexist, resulting in increased selectivity for the material to be processed. It is possible to increase the etching rate for the obtained and further intended materials. This etching method is called a reactive ion etching method or a reactive sputter etching method, and in many cases plasma is formed by applying high frequency power. This etching method allows anisotropic etching with less undercut.

Dry etching methods that have been put to practical use in the manufacturing process of semiconductor integrated circuit devices are often optimized by combining the etching methods described above, and the etching mechanism is not simple.

Reliably detecting the end point of the dry etching process in this manner is extremely important for etching reliability and for automating the etching apparatus. For this purpose, many end point detection means have conventionally been used depending on the dry etching method, material, and other conditions. Examples of conventionally known detection means are as follows.

(b) Chemical luminescence method that utilizes the light emitted when silicon (Si) reacts with active species; (b) Optical measurement that uses an ellipsometer to measure the refractive index, absorption coefficient, and film thickness of the film to be etched. (3) A laser detection method that detects the reflected interference waveform by irradiating a laser beam onto a sample; (4) A method that detects the emission spectrum that occurs when particles excited by an electric discharge lose energy. (e) Infrared absorption spectrometry, which passes infrared rays into the discharge space to measure the absorption spectrum by molecules in the discharge space; (f) Mass spectrometry of exhaust gas, etc. to determine the intensity of a specific mass spectrum. Mass spectrometry that detects changes, (g) Probe method that applies voltage to a probe placed in a discharge space and judges changes in plasma state based on current-voltage characteristics, and (h) Before and after etching. The discharge impedance method uses changes in the discharge impedance during etching, and the pressure change method detects pressure changes before and after etching (re)aluminum (Al). and so on.

The dry etching method as described above is also suitable for the manufacturing process of masks used in manufacturing semiconductor devices. In other words, a chromium (Cr) film of about 70 [μm] is deposited or sputtered on a high-quality glass substrate, and an etching process is performed to form a mask pattern using, for example, carbon tetrachloride (CCl ₄ ) and oxygen. By using gas plasma using a mixed gas with (O ₂ ), it is possible to form a pattern with less dimensional change than the conventional wet etching method using, for example, ceric ammonium nitrate.

As a method for detecting the end point of the dry etching process for this chrome mask, methods such as irradiating laser light and detecting the reflected light can be applied, but it is necessary to adjust the irradiation position depending on the pattern, and mass spectrometry Laws and other methods are not easy to implement. In order to avoid the complexity of detecting the end point, the dry etching execution time may be standardized and managed based on time, but the actual time required may vary depending on the size of the area to be removed by etching. Because of this, the margin time is usually excessive, which reduces etching accuracy and is also a waste of time.

There is a need for an end point detection means that is easy to implement in such embodiments of the dry etching method.

(d) Purpose of the Invention It is an object of the present invention to provide a dry etching method in which a film is removed using reactive gas plasma, in which the completion of intended film removal can be easily detected. do.

(e) Structure of the Invention The object of the present invention is to accommodate a sample to be treated with a film to be removed exposed in a container, introduce a reactive gas to which nitrogen gas is added into the container, and conduct the reaction. Applying high frequency power to a reactive gas to form a gas plasma state, removing the film by the gas plasma, and completing the removal of the film by increasing the reflected power generated in the high frequency power supply circuit. This is accomplished by detecting.

It should be noted that this phenomenon is caused by the fact that it is generally known that when nitrogen gas is introduced into the container and high frequency power is applied, the bias voltage increases. It is presumed that this will lead to a significant increase in waves.

(f) Embodiments of the Invention The present invention will be specifically described below using embodiments with reference to the drawings.

FIG. 1 is a block diagram showing an example of an apparatus suitable for carrying out the present invention. In the figure, 1 is a processing container;
2 is a gas outlet pipe, 3 and 3' are electrodes, 4, 5 and 6 are gas containers, 7 is a regulator, 8 and 8' are shut valves, 9 is a flow meter, 10 is a leak valve, 11 is a vacuum gauge, 12 is a 13 is a vacuum pump, 14 is a high frequency power source, 15 is a reflected power measuring device, 16 is a DC power source, 17 is a system controller, and 18 is a sample to be processed.

When the present invention is applied to pattern formation of a mask having a Cr film on a glass substrate, the gas container 4 is filled with carbon tetrachloride (CCl ₄ ), the gas container 5 is filled with oxygen (O ₂ ),
6. Prepare nitrogen (N ₂ ). The mask grank after the resist development process is transferred to sample 1 to be processed.
8 and placed at a predetermined position on the electrode 3 inside the processing container 1. For example, CCl ₄ and O ₂ at a ratio of about 3:2,
N ₂ is usually 10% of the total flow rate of CCl ₄ and O ₂
Thereafter, it is introduced into the processing container 1 at a ratio of, for example, about 4%, and the pressure inside the processing container is set to a predetermined pressure. In this embodiment, it is set to about 0.1 to 1 [Torr].

Etching is started by applying to the electrodes 3 and 3' a DC voltage of, for example, about 100 [V] with electrode 3' having a positive polarity and the required high frequency incident power, about 500 [W] in this example. do. At this time, impedance matching is performed for the high-frequency incident power, and the reflected power from the electrodes 3 and 3' side to the power source is eliminated to about 0.2% or less with respect to the incident power, that is, the applied power.

Impedance matching is maintained while etching of the Cr film is progressing, but near the end of etching of the Cr film, the impedance between electrodes 3 and 3' changes, causing a mismatch and increasing reflected power with respect to high-frequency incident power. .

If N ₂ is not added to the reaction gas, the reflected power will increase by at most 3 [W] or 0.6 for an incident power of 500 [W], as illustrated by the chain line A in Figure 2. Compared to this, the change in impedance is increased by adding _N2 , and the second
As illustrated by solid line B in the figure, the reflected power is 10 [W]
In other words, it can be about 2%.

The reflected power measuring device 15 accurately detects the reflected power increased in this way, and the system control device 17 stops the dry etching process.

Although the embodiments described above involve etching a Cr film using CCl ₄ and O ₂ as reaction gases, the present invention can also be applied to other types of dry etching processes. For example, Freon (CF) is used as a reaction gas. ₄ ) and oxygen (O ₂ ) may be used.

(g) Effects of the Invention As explained above, according to the present invention, it is possible to easily detect the etching end point of a dry etching method in which a film is removed using reactive gas plasma. The effect of improving the precision and productivity of masks used in manufacturing contributes to the advancement and spread of semiconductor devices, especially large-scale integrated circuit devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus suitable for carrying out the present invention, and FIG. 2 is a diagram showing an example of a time change in the ratio of reflected power to high-frequency incident power. In the figure, 1 is a processing container, 3 and 3' are electrodes,
4, 5 and 6 are gas containers, 13 is a vacuum pump, 1
4 is a high frequency power supply, 15 is a reflected power measuring device, 16
17 is a DC power supply, 17 is a system controller, and 18 is a sample to be processed.

Claims (1)

[Claims] 1. The sample to be treated with the film to be removed exposed is placed in a container, a reactive gas to which nitrogen gas is added is introduced into the container, and high frequency power is applied to the reactive gas to create a gas plasma state. A dry etching method characterized in that the film is removed by the gas plasma, and the completion of the film removal is detected by an increase in reflected power generated in the high frequency power supply circuit.