JPH02183524A - Plasma ashing method - Google Patents

Abstract

PURPOSE:To prevent explosion of a resist film and enable the resist film due to ashing to be eliminated by setting the temperature of a substrate to be at low temperature until the surface layer of the resist film is eliminated and then to a high temperature after the elimination. CONSTITUTION:When a substrate 1 has a resist film 11 that is a cured and modified surface layer 11a, a reaction gas excited by oxygen plasma, etc., introduced from a introduction port 2 is operated on the resist film 11 without lighting an infrared lamp 5 initially. Then, after the surface layer 11a is decomposed/ vaporized and is eliminated due to chemical reaction with oxygen radical and reaction gas, the lamp 5 is lit, the substrate 1 is heated, chemical reaction with oxygen radical or radical of reaction gas is promoted, and then the resist film 11 is eliminated readily. Thus, the resist film 11 with stress internally can be eliminated without explosion due to heat stress.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a plasma ashing method for removing a resist film coated on a semiconductor substrate by ashing (ashing) it using plasma.

(Prior art) In order to process minute IC circuits, a resist film with a circuit pattern formed thereon is provided on the surface of a semiconductor substrate, and the underlying insulating film, semiconductor film, or metal film is etched through the resist film. things are being done.

The resist film is removed from the substrate surface after the etching process is completed, and there are two methods for removing it: wet processing using chemicals such as hydrogen peroxide and organic solvents, and oxygen plasma to remove the resist film. There is a dry processing method that involves ashing.

Many of the chemicals used in the wet treatment method are harmful to the human body, and care must be taken to maintain the safety of the removal work and prevent pollution of the waste liquid, which is troublesome. In addition, the chemicals used contain some impurities, which cause defects and contamination of semiconductor circuit patterns, making them unsuitable for microfabrication of ultra-LSIs and the like.

The dry processing method includes Cx1lyNz applied to a substrate.
The resist film is reacted with oxygen radicals generated in oxygen plasma, and the resist film is exposed to CO□, N02 and N20.
Since it is removed by decomposition and vaporization, it does not generate harmful substances to the human body unlike wet processing methods, and it does not contain impurities, so it is suitable for microfabrication of substrates.

A specific example of the dry processing method is as shown in FIGS. 1 and 2, in which a substrate (1) coated with a resist film is provided with a reactive gas inlet 2) and a vacuum exhaust port (3). A hot plate (7) equipped with a temperature-controlled embedded heater (6) or above an infrared lamp (5) in a vacuum processing chamber (4).
), and oxygen gas introduced from the inlet (2) or a reactive gas mixed with a small amount of CF4, N2 or The radicals of the other reactive gases are removed by reacting with the resist on the heated substrate (1), decomposing and vaporizing the resist film, and discharging it from the exhaust port (3) using a vacuum pump. .

In the case shown in Fig. 1, the substrate (1) placed on the rack (8) in the vacuum processing chamber (<4) is heated by the infrared lamp (5) in about 5 seconds as shown by curve A in Fig. 3. heated to a temperature of The temperature of the substrate (1) is managed by an infrared thermometer (9) that detects infrared rays thermally radiated from the surface of the substrate (1) and converts it into temperature.
Feedback the output signal to the power supply of the lamp (5),
The temperature of the substrate (1) is maintained at a constant temperature by controlling the power.

In addition, in the case shown in Figure 2, the substrate (1) is given heat by thermal contact with the hot plate (7), and is heated to a predetermined temperature after about 10 seconds as shown by curve B in Figure 4. Ru. The hot plate (7) is equipped with a thermocouple thermometer (IO
The temperature is controlled at a constant temperature.

(Problem to be Solved by the Invention) With the miniaturization of circuits, it is becoming more common to locally implant impurity ions into the surface of the substrate (1) using a resist film coated on the substrate (1) as a mask. This is becoming more and more common. In this case, as seen in Figure 5,
The surface layer (11a) of the resist film qv used as a mask is hardened and altered by the ion beam, and it begins to contain stress within it. Then, as shown in Fig. 6, the resist film (11) may explode due to sudden thermal stress.The resist film (11) due to this explosion may be damaged on the substrate (1) or in the vacuum processing chamber. (1) remains as a duct and residue, which becomes an obstacle in performing fine processing on the substrate (1).

According to the inventor's experiments, the lower limit explosion temperature of the resist film (11) is in the range of about 70 to 160°C, although it varies depending on the ion implantation conditions and the type of resist. It turns out that the thicker the material, the more likely it is to explode.

An object of the present invention is to propose a method for removing a resist film by ashing without causing it to explode.

(Means for Solving the Problems) In the present invention, a substrate coated with a resist film is provided in a vacuum processing chamber, and the resist film is removed by ashing in oxygen plasma while heating the substrate. and controlling the temperature of the substrate at a low temperature until the surface layer of the resist film is removed, and then ashing at a high temperature to remove the resist film, so that the resist film is removed without causing an explosion. I did it like that.

(Function) To remove the resist film applied to the surface of the substrate,
The substrate is placed in a vacuum processing chamber, and oxygen plasma is introduced into the chamber while being heated to ash the resist film.
At this time, the temperature of the substrate is first controlled to a low temperature and then to a high temperature, so that the surface layer of the resist film, which has been hardened and altered by being irradiated with the ion beam in the initial low temperature state, is not subjected to sudden thermal stress. In other words, it is possible to remove the resist film without causing an explosion, and then rapidly raise the temperature inside the resist film to perform high-speed ashing, thereby eliminating the above-mentioned problems caused by the explosion of the resist film.

(Example) An example of the present invention will be described based on FIGS. 7 to 10 of the drawings. In FIGS. 7 and 8, symbols (1) to 00 refer to the same symbols (1) to (IG) shown in FIGS. 1 and 2, and in FIG. 7, the resist is applied. A semiconductor substrate (1) made of a silicon wafer is placed in a vacuum processing chamber (4) equipped with a reactive gas inlet (2) and a vacuum exhaust port (3).
) shows an example in which the infrared lamp (5) is supported and installed above the infrared lamp (5) with a rack (8).

Further, FIG. 8 shows an example in which a substrate (1) coated with a resist is placed on a hot plate (7) and heated.

In either case, the reactive gas inlet (2) is equipped with a microwave discharge section (2a) or I? which turns the reactive gas into plasma. A discharge means such as an F coil is provided, and oxygen gas or a reactive gas mixed with CF, N2, or N2 is excited by plasma and introduced into the vacuum processing chamber (1). Further, the vacuum exhaust port (3) is connected to a suitable vacuum pump, and the inside of the vacuum processing chamber (1) is
Evacuate to maintain the pressure below 0-'Torr.

In FIG. 7, the substrate (1) has a surface layer (
When the resist film 11a) is hardened and altered and is represented by C The excited reactive gas acts on the resist film (fD), and when the surface layer (11a) is decomposed and vaporized and removed by a chemical reaction with oxygen radicals and reactive gas radicals, the lamp (5) is activated. Lights up and the board (1
) to accelerate the chemical reaction with oxygen radicals and reactive gas radicals, and quickly remove the resist film (I'D).The temperature of the substrate (1) in this case is as shown by curve C in FIG. When the time t1 necessary to remove the surface layer (Ila) has elapsed, the lamp (5) is turned on, and as in the conventional case, the temperature reaches 200°C after about 5 seconds and the resist film (' A quick removal of lv takes place.

In the case of Fig. 8, a plurality of pins (Ie) that are raised and lowered by a lifting device (2) consisting of an air cylinder provided outside the vacuum processing chamber (4) and a hot plate (7
), and the board (1) is initially raised with the pin (
13 to maintain the temperature of the substrate (1) at a low temperature by supporting it above a hot plate (7) at a high temperature, and during this time, the hardened surface layer (Ila) of the resist film (11) is removed. After the removal, the pin a3 is lowered by the lifting device ('lb), the substrate (1) is placed on the hot plate (7), and the remaining resist film (11) is removed while applying heat to the substrate (1). The change in temperature of the substrate (1) in this case is as shown by the curve in Figure 10, and after the time t required to remove the surface layer (11a), the substrate (1) is placed on the hot plate (7). After about 10 seconds, the temperature reaches 200° C. and the remaining resist film ('lv) is removed, as in the case of conventional heating using a hot plate.

In the case shown in FIGS. 7 and 8, the resist film C is
First, the surface layer (11a) is removed at low temperature and then the remaining layer is removed at high temperature, so the resist film (11a) with internal stress is removed (
'l'D can be removed without exploding due to thermal stress, preventing contamination of the substrate (1) and the inside of the vacuum processing chamber (4) with resist film (l flakes), and allowing accurate microcircuit processing. I can do it.

(Effects of the Invention) As described above, according to the present invention, when removing a resist film applied to a substrate by ashing, the temperature of the substrate is kept low until the surface layer of the resist film is removed. Since the resist film is heated to a temperature after the removal, the resist film can be removed by ashing without exploding, and the resist film can be advantageously applied to the production of fine semiconductor circuits.

[Brief explanation of the drawing]

Figures 1 and 2 are cut side views showing the conventional ashing method, Figure 3 is a diagram showing the temperature change of the substrate in the case shown in Figure 1, and Figure 4 is the temperature of the board in the case shown in Figure 2. Diagrams showing changes; FIGS. 5 and 6 are enlarged sectional views of the resist film; FIGS. 7 and 8 are cut side views showing examples of the present invention; FIGS. 9 and 10 are respectively FIG. 8 is a diagram showing temperature changes of the substrate in each case of FIGS. 7 and 8;

Claims (1)

[Claims] In this method, a substrate coated with a resist film is provided in a vacuum processing chamber, and the resist film is removed by ashing in oxygen plasma while heating the substrate. A plasma ashing method characterized by controlling the temperature at a low temperature until the resist film is removed, and then performing ashing at a high temperature to remove the resist film.