JPH0550272A - Method and device for removing thin film - Google Patents

Abstract

PURPOSE:To allow the sure decision of the end state of thin film removal by comparing the intensity of the ultrasonic waves generated at the time of irradiation with pulse laser beams with a reference value. CONSTITUTION:The part on a substrate 1 where the thin film is desired to be removed is irradiated with the pulse laser beams. The position slightly apart from this position is irradiated with the continuous laser beam from a probe laser beam source 8. The intensity of the pulse laser beam with respect to the intensity of the generated ultrasonic waves is measured. An optimum irradiation condition is previously deduced from the irradiation intensity of the pulse laser beam at the point where the intensity of the ultrasonic waves changes sharply and the thin film removal is executed under the optimum condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film removing method using laser light.

[0002]

2. Description of the Related Art In recent years, since a laser process technique does not require a resist process, the process can be shortened in a process of locally processing only a specific portion on a substrate in a thin film removing technique of a semiconductor manufacturing process. Due to its advantages, it is an important technology for practical use. Among these, LSI
The technique for removing a film such as SiO ₂ , SiN, or phosphorus-doped glass (PSG) used for the insulating film is particularly important for forming a contact hole with a lower layer wiring when forming a multilayer wiring. For example, by combining a laser CVD technique for directly forming a metal line on a substrate with a local removal technique for an insulating film, it becomes possible to correct a wiring design mistake at the time of LSI development on the completed LSI. The period can be greatly shortened.

Regarding the above wiring correction technique, for example,
It is described in detail in the Institute of Electrical Engineers of Japan OQD-89-49 published by September, 1989 by Morishige et al. According to this paper, as a method of forming an insulating film contact hole on a wiring, the insulating film is irradiated with a transparent visible pulsed laser light so that the wiring under the insulating film absorbs the laser light and one of the wiring upper layer portions is exposed. There is shown a method of vaporizing the part and indirectly evaporating the insulating film by the generated pressure. Compared with other methods, this method has excellent features such that the device configuration can be simplified and various types of insulating films used in LSI and the like can be supported. However, since this method is premised on the evaporation of a part of the wiring in principle, there has been a problem how to minimize the damage of the wiring.

[0004]

According to the above-mentioned paper, the irradiation intensity of the pulsed laser light is ± 10 of the optimum value.
It has been pointed out that it is necessary to keep it within the range of about%. However, in this method, since the optimum irradiation intensity depends on the material of the wiring and the size of the wiring such as width and thickness, the optimum irradiation intensity can be obtained over all of the various wiring structures required in the wiring correction phase. It was not easy to remove the thin film. For example, if the thin film is removed with an intensity that greatly exceeds the optimum irradiation intensity, the underlying wiring will be broken, and if the irradiation intensity is not sufficient, processing will not occur,
There is a problem in that it is not easy to distinguish whether or not the thin film removal is completed by simply observing the processed state optically, because a clean processed shape cannot be obtained.

It is an object of the present invention to remove a thin film with a constant irradiation intensity, which is not easy with a conventional thin film removing method utilizing evaporation, for various wiring structures. Another object of the present invention is to provide an excellent thin film removal method capable of reliably determining the end state of processing.

[0006]

The first invention of the present application is
In a thin film removal method of irradiating a required portion on a substrate on which an absorber layer and a thin film formed of wiring are sequentially formed, and removing the thin film by utilizing volume expansion due to temperature rise of the absorber layer, Intensity of ultrasonic waves generated during irradiation of the pulsed laser light by irradiating continuous laser light in the vicinity of the required portion and causing the return light from the vicinity of the continuous laser light and the incident continuous laser light to interfere with each other. Is detected and the intensity of the ultrasonic wave is compared with a reference value to determine the final state of thin film removal.

In a second invention of the present application, in the above-mentioned thin film removing method, the irradiation intensity of the pulsed laser light is gradually increased from the intensity lower than the threshold irradiation intensity at which thin film removal occurs, and the substrate is irradiated, The intensity of the generated ultrasonic waves,
The ratio of the intensity of the pulsed laser light is measured, and the optimum irradiation intensity value required for thin film removal is set to 1 by using the irradiation intensity of the pulsed laser whose intensity ratio deviates from the value in the low intensity range as a reference value. The thin film removing method is characterized in that a thin film is removed by irradiating the pulsed laser light with the optimum irradiation intensity as a value obtained by multiplying by a constant value in the range of 1 to 1.5.

In the third application of the present invention, a pulse laser light source, an XY stage for holding a substrate to be processed, and an irradiation portion on the substrate are observed while irradiating a required portion of the substrate with the pulse laser light. An irradiation observation optical system, an attenuator that changes the irradiation intensity of the pulsed laser light, and a thin film removal device that includes a control unit that controls the operation of each unit, in the vicinity of the irradiation portion of the pulsed laser light, An interference unit that irradiates continuous laser light from a probe laser light source and causes the incident continuous laser light and the return light from the substrate to interfere with each other, and output from the interference unit due to ultrasonic waves generated when the pulsed laser light is irradiated. A pulse height storage unit that stores the pulse height of a signal, and calculates the ratio of the output from the pulse height storage unit and the irradiation intensity of the pulsed laser light to obtain a threshold irradiation intensity that causes thin film removal. The value of the intensity ratio observed when the irradiation intensity of the pulsed laser light is gradually increased from the low intensity range is set to 1 with respect to the irradiation intensity deviating from the value of the ratio in the low intensity range. The thin film removing apparatus is provided with a control unit for removing the thin film with a value obtained by multiplying a constant value in the range of 1 to 1.5 as the optimum irradiation intensity required for thin film removal.

[0009]

The present invention is characterized by utilizing the photoacoustic method to measure the characteristics of the process of thin film removal or the portion to be processed for thin film removal in a non-contact manner before monitoring or before processing. .. The photoacoustic method irradiates the thin film on the substrate with a pulsed laser to obtain the absorption coefficient of the thin film,
It is known as a method for obtaining the sound velocity in a thin film by detecting an acoustic signal at a position away from the irradiation unit. In the present invention, the value of the ratio of the intensity of the pulsed laser light to the intensity of the generated ultrasonic waves is slightly lower than the threshold irradiation intensity at which thin film removal occurs from the irradiation intensity region that is much lower than the threshold irradiation intensity at which thin film removal occurs. The phenomenon that abruptly changes when it reaches the irradiation intensity range and the irradiation intensity at which thin film removal occurs is that it generates ultrasonic waves that are more than two orders of magnitude stronger than the intensity of ultrasonic waves generated in the region lower than the threshold irradiation intensity. Since it was newly found, the point that it was applied to predict the optimum irradiation intensity by utilizing these characteristics or to judge the quality of the processing state at the end of processing is the principle of the conventional method and apparatus. Is different.

FIG. 2 is a diagram showing the relative positional relationship on the substrate 1 of the pulsed laser light 103 for thin film removal and the continuous laser light 101 for measurement in the thin film removal method of the present invention. The return light 102 of the continuous laser light reflected from the wiring 106 on the substrate 1 returns to the reverse optical path, and the interference unit 13
Then, the up-and-down vibration of the wiring 106 on the substrate, which occurs when the pulsed laser light is irradiated, is detected.

FIG. 3 shows the relationship between the monitor signal intensity of ultrasonic waves detected by the interference unit 13 and the irradiation intensity of pulsed laser light. In the irradiation intensity range (A) where the intensity of the pulsed laser light is much lower than the threshold for thin film removal, the monitor signal intensity increases linearly with the intensity of pulsed laser light irradiation, but is slightly lower than the threshold intensity for thin film removal. It was found that in the region (B) where the irradiation intensity was extremely low, the gradient became steep, and in the intensity (C) at which thin film removal occurred, the monitor signal intensity became significantly large. In the region (A), ultrasonic waves are generated by the local thermal expansion of the wiring due to the pulse laser irradiation, whereas in the region (B), the upper thin film is not removed, but the wiring is partially removed. It is speculated that in the region (C) where components other than the thermal expansion component are added due to vaporization, a burst sound is generated when the thin film is removed. In the present invention, by detecting the rising point (a) of the region (B), the optimum processing strength is predicted, and the quality of the final state of thin film removal is determined from the strength of the ultrasonic waves generated during thin film removal. Can be determined.

[0012]

Embodiments 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. In this embodiment, the present invention is applied to the formation of contact hole fine holes in the SiN film on the A1 wiring.

Light emitted from a pulse laser light source 4 composed of a second harmonic generation light source (pulse width 5 ns, 532 nm) of an Nd: YAG laser is attenuated by an attenuator 6 and a beam pattern is shaped by an aperture 22. The lens 3 transfers the pattern of the aperture 22 onto the substrate 1 through the first beam splitter 14 and the second beam splitter 15, and irradiates the pattern. Further, the second beam splitter 15 and the lens 3 include the illumination light source 21 and the camera 19,
A combination of the TV 20, the third beam splitter 16, the fourth beam splitter 17, and the eyepiece lens 18 constitutes an observation optical system. The substrate 1 is configured so that the laser light irradiation unit can be moved to an arbitrary position on the substrate by the XY stage 2. The continuous laser light from the probe laser light source 8 composed of a He-Ne laser light source is split by the fifth beam splitter 10 and is split by the first beam splitter 14.
From the pulse laser beam irradiation part on the substrate 1 by the lens 3 after being reflected by the second beam splitter 15.
It is configured to irradiate the wiring at a position on the substrate which is separated by 0 μm in the horizontal direction.

The return light of the continuous laser light from the substrate 1 interferes with the light of the probe laser light source 8 between the fifth beam splitter 10 and the reflecting plate 12, and its intensity change is P
It is configured to be detected by the photodetector 11 of the IN photodiode. A unit including the probe laser light source 8, the fifth beam splitter 10, the reflection plate 12, and the photodetector 11 constitutes an interference unit 13, and the interference unit 1
3 is configured to be held by the YZ stage 9 and capable of minutely changing the optical path so that the irradiation position of the continuous laser light on the substrate 1 becomes a flat portion such as the central portion of the wiring.

The output signal of the photodetector 11 stores the wave height in the wave height storage unit 7, and the wave height data is input to the control unit 5. The control unit 5 includes a pulse laser light source 4, an attenuator 6, an aperture 22 and an XY.
The operation of the stage 2 and the YZ stage 9 is controlled.

Next, the operation sequence in this embodiment will be described.

First, the XY stage 2 is moved, and the substrate 1 is moved so that the irradiation position of the pulsed laser light is the surface of the wiring (2 μm width × 0.6 μm thickness) on the substrate 1 where thin film removal is desired. To do. Next, the XY stage 9 is moved and finely adjusted so that the continuous laser light from the probe laser light source 8 is reflected on the flat portion of the wiring surface 10 μm away from the position. Next, the size of the aperture 22 is set to 2 μm in which the size of the pulse laser irradiation portion on the substrate is the same as the width of the wiring.
It is set to have a rectangular shape of × 2 μm. The threshold irradiation intensity at which thin film removal occurs is 10 for A1 wiring of this width.
Since it is around 0 MW / cm ² , first, the initial value of the irradiation intensity of the pulsed laser light on the substrate is set to 50 by the attenuator 6.
Set to MW / cm ² . Next, set the repetition rate of the pulsed laser light source to 5 Hz, and set the irradiation intensity to 5 MW each time.
The intensity of the harmonic wave generated at the time of pulsed laser beam irradiation is detected by the detector 11 while increasing / cm ² by 1 / cm ^2, and the relationship between the pulsed laser beam irradiation intensity and the generated harmonic wave intensity is measured. Since the obtained waveform has a shape as shown in FIG. 3, the irradiation of the pulsed laser light is temporarily stopped at a stage beyond the point a where the gradient in the weak irradiation intensity range changes, and the pulsed laser light to be irradiated next is of the irradiation intensity, for the best illumination intensity 117MW / cm ^2, which corresponds to 1,3 times the intensity of 90MW / cm ^2, which corresponds to an irradiation intensity of a point in the case of the wiring, the pulsed laser beam 1 shot irradiated Then, the thin film removal is completed. Cross-sectional area of wiring is 2μm in the same sequence
Optimum irradiation intensity is 130M for width x 1μm thickness
It was predicted to be W / cm ² . In this way, the thin film was removed, and the damage to the wiring due to the thin film removal was evaluated as the change in the wiring resistance value before and after the thin film removal. It was possible to reproducibly suppress the value of the substrate to a very low value of about 0.1Ω within the measurement error range. According to these results, in the conventional method, thin film removal is performed based on the wiring data at the time of LSI creation and the optimum value predicted from preliminary experiments of thin film removal.
It shows that the resistance increase value of the wiring varies within the range of several Ω, and that there is a problem in reproducibility that machining sometimes does not occur, but a great improvement can be obtained.

Further, since the intensity of the ultrasonic wave generated when the thin film is satisfactorily removed is 100 times stronger than the monitor signal intensity observed at the point a, the above-mentioned optimum irradiation intensity is measured before processing. Even if it is processed,
It was found that the quality of the final state of thin film removal can be easily determined from the intensity of the detected ultrasonic waves.

[0019]

As described above, according to the present invention, in accordance with various wiring structures, the optimum irradiation intensity necessary for surely removing the thin film in each structure can be processed as desired. Measure each wiring in advance,
Since the thin film can be removed, the thin film can be surely removed with a very high yield. In addition, there is an advantage that the quality of the final state of thin film removal can be reliably determined.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relative relationship between irradiation positions on a substrate of pulsed laser light for removing a thin film and continuous laser light for monitoring according to the present invention;

FIG. 3 is a diagram showing a relationship between a pulse laser beam irradiation intensity and a monitor signal intensity.

[Explanation of symbols]

 1 substrate 2 XY stage 3 lens 4 pulse laser light source 5 control unit 6 attenuator 7 wave height memory unit 8 probe laser light source 9 XY stage 10 fifth beam splitter 11 photodetector 12 reflector 13 interference unit 14 First Beam Splitter 15 Second Beam Splitter 16 Third Beam Splitter 17 Fourth Beam Splitter 18 Eyepiece 19 Camera 20 TV 21 Illumination Light Source 22 Aperture

Claims (3)

[Claims] 1. A thin film is removed by irradiating a required portion on a substrate on which an absorber layer made of wiring and a thin film are sequentially formed, with a pulsed laser beam and utilizing volume expansion of the absorber layer due to temperature rise. In the thin film removal method, continuous laser light is irradiated in the vicinity of the required portion, and the continuous laser light that is incident is made to interfere with the return light of the continuous laser light from the vicinity, which occurs when the pulsed laser light is irradiated. The thin film removal method is characterized in that the intensity of the ultrasonic wave to be detected is detected and the intensity of the ultrasonic wave is compared with a reference value to determine the final state of thin film removal. 2. The thin film removing method according to claim 1,
The irradiation intensity of the pulsed laser light is gradually raised from the intensity lower than the threshold irradiation intensity at which thin film removal occurs, and the substrate is irradiated while the intensity of the generated ultrasonic wave and the intensity of the pulsed laser light are measured. An optimum irradiation intensity value required for thin film removal based on the irradiation intensity of the pulse laser whose intensity ratio deviates from the value in the low intensity range is a constant value in the range of 1.1 to 1.5. The thin film removing method is characterized in that the thin film is removed by irradiating the pulsed laser beam with the optimum irradiation intensity. 3. A pulse laser light source, an XY stage for holding a substrate to be processed, and an irradiation observation optical system for observing an irradiation portion on the substrate while irradiating a required portion of the substrate with the pulse laser light. In a thin film removal apparatus comprising an attenuator that changes the irradiation intensity of the pulsed laser light and a control unit that controls the operation of each unit described above, a thin film removal device is provided near the irradiation portion of the pulsed laser light from a probe laser light source. An interference unit that irradiates continuous laser light and interferes the incident continuous laser light with the return light from the substrate, and the wave height of the output signal from the interference unit that is generated by ultrasonic waves when irradiating the pulsed laser light is stored. And a ratio of the output from the wave height storage unit to the irradiation intensity of the pulsed laser light is calculated, and the intensity is gradually reduced from the intensity range lower than the threshold irradiation intensity at which thin film removal occurs. The value of the intensity ratio observed when the irradiation intensity of the pulsed laser light is increased is deviated from the value of the ratio in the low intensity region as a reference value, and 1.1 to 1 is added to the reference value. A thin film removing apparatus, comprising: a control unit for removing a thin film, with a value obtained by multiplying a constant value in the range of 0.5 as the optimum irradiation intensity required for thin film removal.