JPH01296623A - Thin film elimination - Google Patents

Abstract

PURPOSE:To make it possible to form a microscopic contact hole with a high degree of reproducibility without giving a substantial effect on the wiring of the under layer by a method wherein, after an auxiliary laser beam has been projected on the required part on a substrate for the period, or longer, in which the average heat diffusion distance of a thin film becomes longer than the thickness of the thin film, a pulse laser beam is projected. CONSTITUTION:Before the pulse laser beam emitted from a pulse laser beam source 1, with which a thin film will be removed, is made to irradiate when a transparent thin film, located on a substrate having an absorbing layer under the transparent thin film, a continuous laser beam or an auxiliary laser beam having a long pulse width, emitted by an auxiliary laser beam source 2, is made to irradiate on the part desired to be processed in advance. The irradiation period of the laser beam is set in such a manner that the average heat diffusing distance, which is determined by the irradiation period and the heat diffusivity, becomes longer than the thickness of the thin film in order to add thermal distortion on the whole thickness direction of the thin film which is desired to be removed. As a result, the required processed shape can be formed in an excellent reproducible manner without giving a substantial effect on the wiring layer of the under layer.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for removing a thin film using laser light.

[Conventional technology and its issues] In recent years, in thin film removal technology for semiconductor manufacturing processes,
Dry processes are widely used because they have many advantages in terms of miniaturization of minimum patterns, ease of waste disposal, etc. Among these, laser processing technology is being actively researched because it is effective in shortening the process by locally processing only a specific location on a substrate without using a resist process. In particular, 5i0 is used for LSI insulation films.
2. Removal techniques for films such as SiN and phosphorus-doped silica glass (PSG) are particularly important for forming contact holes with underlying interconnects when forming multilayer interconnects. For example, by combining laser CVD technology, which forms metal lines directly on the substrate, and local removal technology for insulating films, it is possible to correct wiring design mistakes during LSI development directly on the completed LSI. It is believed that this will make it possible to significantly shorten the development period.

Up to now, high-speed thin film removal methods using pulsed laser light include a method in which strong pulsed laser light is absorbed into the thin film and the thin film is instantaneously heated to a high temperature to evaporate; There are two known methods of etching and removing using a gas that causes a chemical reaction with the thin film at high temperatures.

Among these methods, the method using the evaporation effect of laser light is a simple and high-speed thin film processing method, and has been put into practical use for applications such as repairing the foot mask used in the exposure process of LSI manufacturing, but it is also used for processing insulating films. However, the irradiation intensity required to cause transpiration is high, which has the disadvantage of causing significant damage to the underlying wiring layer.

On the other hand, the above etching removal method has the advantage that the irradiation intensity at which processing begins can be reduced compared to the simple evaporation method. As an example of achieving high-speed and fine processing, a 5i02 film was etched away using an ArF excimer laser as a light source and hydrogen as an etching gas, which was developed in 1985.
Journal of Vacuum Science and Technology (J, Vac, Sci, Tech,
) magazine, B 3L 'I~8 pages Ehrlich (Ehr
It has been reported by (l 1ch) et al. According to this document, due to the transient temperature rise due to absorption of pulsed laser light, S! It is described that the temperature of the 02 layer was raised to near its softening point to cause an etching reaction and a removal rate as high as 100 people/pulse was achieved17. The minimum machining υ size at this time is about 0.4 μ, which is an excellent value of 1q.

However, this method has the following drawbacks.

In other words, since insulating films have lower reactivity than semiconductors or metals, the reactive gases that can be used must be highly dangerous gases such as hydrogen or fluorine, and this method cannot be used. These devices have the drawback of being complicated and expensive to ensure safety.

In both of the above-mentioned methods, a laser beam having a wavelength that is absorbed by the thin film to be removed is used, and the thin film is processed by utilizing the temperature rise caused by the absorption of the thin film itself. On the other hand, in order to process a transparent film on an absorber that absorbs the irradiated laser beam, the laser beam is absorbed by the absorber, and the pressure generated by gasification of the absorber is used to process the transparent film. One possible method is to blow away the transparent thin film on top of it. This method was experimentally investigated in the case where a via hole for a contact is formed by processing an insulating film on a small uneven wiring. As a result, it was confirmed that this method has the advantage that the wavelength of the irradiated laser light only needs to be absorbed by the underlying wiring metal, and that an inexpensive visible light source can be used. However, this method has the drawbacks of causing significant damage to the underlying absorbent material and significantly worsening the reproducibility of the processed shape.

The purpose of the present invention is to be able to form fine contact holes with high reproducibility without significantly affecting the underlying wiring, which was difficult with conventional thin film removal methods using etching or evaporation. It is an object of the present invention to provide an excellent thin film removal method that is safe and does not require the use of dangerous gases, and allows a simple device configuration.

[Means for Solving the Problems] The present invention irradiates a pulsed laser beam onto a desired portion of a substrate on which an absorber layer and a thin film are sequentially formed, and utilizes volumetric expansion due to temperature rise of the absorber layer. The thin film removal method for removing the thin film is characterized in that the auxiliary laser light is irradiated to a desired part of the substrate for a period of time such that the average thermal diffusion distance of the thin film is longer than the thickness of the thin film, and then the pulsed laser light is irradiated. This is a thin film removal method.

[Function] In all conventional methods, thin films were removed only by irradiation with pulsed laser light, but when removing a transparent thin film on a substrate that has an absorber layer under the transparent thin film, the present invention is effective. Now, before irradiating the pulsed laser beam to remove the thin film,
Continuous laser beam or long pulse width auxiliary laser beam,
The difference is that the area to be processed is irradiated in advance.

By irradiating the auxiliary laser beam in advance, stress due to thermal strain is generated in the desired portion of the thin film to be removed. The present invention
When irradiated with pulsed laser light for a-film removal in the presence of this stress, compared to the case without this stress, it has a remarkable effect on reducing damage to the base of the thin film and improving processability and reproducibility of thin film removal. It is based on ♀ cat IC knowledge with Kaaru.

The laser light used in advance to apply stress must satisfy the following conditions. In other words, the irradiation time is
In order to apply thermal strain to the entire thickness of the thin film you want to remove,
It is necessary to select a material so that the average thermal diffusion distance determined from the irradiation time and the thermal diffusivity of the thin film is longer than the thickness of the thin film. When irradiating the auxiliary laser beam by selecting the irradiation time in this way, the energy of the laser beam absorbed by the absorber layer becomes heat and is transmitted to the thin film above it, causing the surface of the thin film and the upper part of the absorber layer to A large temperature gradient is formed between the two, and a large thermal strain can be applied to the thin film.

It also goes without saying that the intensity must be lower than the intensity at which removal of the thin film occurs.

In addition, as a means to achieve the above effect using the conventional method without using an auxiliary laser beam, is it possible to increase the pulse width of the pulsed laser beam that removes the thin film so as to satisfy the above irradiation time? It has the following drawbacks and is not practical. In other words, when forming via holes in an insulating film on wiring, the thermal diffusivity of the insulating film to be removed is generally an order of magnitude higher than that of the metal film that is the absorber layer, so the thickness of the thin film is If the pulse width of the pulsed laser beam used for thin film removal is set to be long so that the action of applying stress in the entire direction and the action of removing the thin film are simultaneously performed, the processed shape will change due to heat diffusion in the absorber. This may result in the wire becoming significantly larger than the diameter, or causing significant damage to the underlying wiring layer.

In contrast, in the method of the present invention, the application of stress to the thin film and the removal of the thin film are performed using separate laser beams, so the pulse width of the pulsed laser beam for removing the thin film can be shortened. A desired processed shape can be formed with good reproducibility without significantly affecting the underlying wiring layer.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. This embodiment is necessary because the present invention is applied to the formation of a microhole for a contact hole in a PSG thin film on N. Outgoing light from a pulsed laser light source 1 composed of a second harmonic generation light source of an Nd:YAG laser is reflected by a first mirror 3, passes through a second mirror 4 and a lens 5, and is delivered to an X-Y stage. 7
The upper substrate 6 is irradiated. Further, the auxiliary laser light emitted from the auxiliary laser light source 2 is reflected by the second mirror 4, passes through the lens 5, and is condensed and irradiated onto the substrate 6.

The auxiliary laser beam and the pulsed laser beam are combined by the second mirror 4, and are configured to be able to irradiate the same position on the substrate 6 with an irradiation beam diameter of one beam. Furthermore, a television camera 8 for observation and a monitor television 9 are provided to monitor the machining position and the machining shape.

The X-Y stage 7 is used to precisely position the processing position. The structure of the substrate is thermally oxidized 5i0 on a Si substrate.
2, width 3mm, thickness 1. O! A JIn N wiring is formed, and a PSG film having a thickness of 21 Jfn is deposited thereon by thermal CVD. The wavelength of the laser light emitted from the pulsed laser light source 1 is 532 nm, the pulse width is 10 nS,
The auxiliary laser light source 2 is composed of an Ar (argon) ion laser, and the emission timing of the pulsed laser light source 1 and the auxiliary laser light source 2 is controlled by a control unit 10. Using this configuration, we compared the processed shape, reproducibility, and degree of damage to the underlying wiring between cases where auxiliary laser light was not used and cases where auxiliary laser light was used.

First, a case will be described in which no auxiliary laser light source is used. The threshold irradiation intensity for PSGI film removal is 200 HW/c.
m2, and it was possible to remove the thin film with good reproducibility at irradiation intensity of 230 MW/cm2 or more, but with irradiation intensity of 230 HW/cm2 or more, the underlying N wiring was severely damaged, and in most cases, the wiring was damaged. Also, the processing diameter of PSG film is 5t.
A drawback was observed that the diameter of the beam was about ttn, which was large compared to the irradiation beam diameter. Further, when the irradiation intensity was set to 230 MW/cm2 or less, disconnection of the N wiring was eliminated, but there was a drawback that there was a large variation in the processed shape and it was difficult to confirm whether or not a hole was formed.

From these facts, it was found that the conventional method of removing a thin film using only pulsed laser light is not suitable as a practical method for removing a thin film.

Next, a case will be described in which, after irradiation with the auxiliary laser light of the present invention, pulsed laser light for removing a thin film is irradiated. The intensity of the auxiliary laser light from the auxiliary laser light source 2 was set to 10) IW/cm 2 in order to avoid processing or the like on the substrate. In addition, the irradiation time of the auxiliary laser light is determined to be 200 ns or more based on the thermal diffusivity and thickness of the PSG film, and from the condition that the average thermal diffusion distance is longer than the thickness of the PSG film, so the irradiation time of the auxiliary laser light is 1 It was a song. The timing of the irradiation was such that first, the auxiliary laser light was irradiated once, and at the timing when the auxiliary laser light was cut off, the pulsed laser light was irradiated from the pulsed laser light source 1.

As a result, the threshold irradiation intensity at which processing of the thin film occurs is as low as 80 cm2, and at an irradiation intensity of around 100 cm2, it is O,hn on the N surface and 1.4 cm on the surface of the PSG film. It was found that circular via holes with a tapered diameter could be formed with good reproducibility. In addition, the damage depth of the N wiring is 1500
It was found that the thickness was about 8.8 mm, which was sufficiently thin compared to the original thickness of the N wire, and was kept to a level that would pose no problem for practical use17.

In the manner described above, a fine via hole with a diameter of around 1 μm could be formed with high reproducibility without significantly affecting the underlying wiring.

In the above example, the case where the argon ion laser is modulated and irradiated as the auxiliary laser light is described. However, it is not always necessary to modulate the auxiliary laser light into pulses. For example, even if the auxiliary laser light is irradiated before and after the pulsed laser light irradiation, there is no change in the processed shape. However, if the auxiliary laser beam is irradiated onto a portion of the substrate where there is no N wiring, care must be taken because unnecessary damage to the substrate may occur. Further, as the auxiliary laser light source 2, in addition to the argon ion laser, a semiconductor laser, a Q-switch YAG laser, etc. can be used.

[Effects of the Invention] As described above, according to the present invention, even when the thickness of the thin film to be removed is thick, it is possible to perform microfabrication on the order of Yanagi with good reproducibility, and it is possible to perform microfabrication on the order of Yanagi with good reproducibility. Compared to methods that utilize radiation, the required irradiation intensity can be significantly reduced, which has the advantage of minimizing damage to the base. Furthermore, compared to conventional methods that use gases that are reactive with thin films, there is no need to use dangerous gases, so there is an advantage in that the safety of the apparatus can be ensured much more easily.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention.

Claims (1)

[Claims] (1) In a thin film removal method, the thin film is removed by irradiating a pulsed laser beam onto a predetermined portion of a substrate on which an absorber layer and a thin film are sequentially formed, and utilizing volumetric expansion due to a temperature rise of the absorber layer. A method for removing a thin film, which comprises irradiating a desired portion on a substrate with auxiliary laser light for a period of time such that the average thermal diffusion distance of the thin film is longer than the thickness of the thin film, and then irradiating pulsed laser light.