JPH05100435A - Thin film removal method - Google Patents

Abstract

PURPOSE:To prevent a resist layer around the removal region from being exposed to flare generated at the time of partially removing the resist layer on a wafer by irradiation with energy beams. CONSTITUTION:The surface of a resist layer 21 is coated with a protective film 20 which hardly transmits ArF excimer laser beams for resist removal, e.g. a PVP film. The energy density of ArF excimer laser beams is regulated in accordance with the ArF excimer laser beam absorbing characteristics of the protective film 20. By irradiation with such ArF excimer laser beams from the top of the film 20, the film 20 and the resist layer 21 within a desired region (removal region) are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention selectively irradiates a thin film (photoresist layer) deposited on a substrate such as a semiconductor wafer or a glass plate with an energy beam to expose a desired portion of the thin film. It concerns the method of removal.

[0002]

2. Description of the Related Art In a photolithography process for manufacturing a semiconductor device, a partial beam including an alignment mark (positioning mark) provided on a wafer along with an exposure region is irradiated with a light beam to emit light from the mark. By photoelectrically detecting information, the pattern of the reticle or mask to be overlaid and exposed is relatively aligned with the wafer (exposure region). Usually, wafer alignment is performed by irradiating an alignment mark with a light beam and photoelectrically detecting reflected light, scattered light, diffracted light, or the like generated from the mark.

However, since the resist is inevitably applied to the wafer before exposure, the alignment mark is detected through the resist layer (thickness of 1 to 2 μm). When the alignment is performed through the projection optical system of the exposure apparatus (TTL method: Through The Lens),
Since the projection optical system has strong chromatic aberration, it is necessary to use exposure light (for example, i-line, KrF excimer laser, etc.) also during alignment, but of course most of the exposure light is absorbed by the resist, There is an inconvenience that the optical information generated from the alignment mark is weakened by the influence of the resist layer.

Further, since the alignment mark has a minute step structure, it is inevitable that the resist layer has a non-uniform thickness around the mark. Therefore, there is a problem in that the alignment accuracy may be lowered due to the interference effect peculiar to the thin film being prominent near the mark, or the unevenness of the resist film thickness being asymmetric on both sides of the mark.

Further, when a multilayer resist is used to achieve a finer pattern, a phenomenon may occur in which the alignment mark itself becomes optically invisible under the illumination wavelength (exposure wavelength). Securing is a difficult problem. Therefore, prior to the alignment operation, it is considered to partially remove the resist by irradiating the resist layer above the mark with a high energy beam in the ultraviolet region such as an excimer laser. The mechanism of this resist removal is that when a resist made of an organic polymer material is irradiated with high-intensity short-pulse ultraviolet light such as an excimer laser, the molecular bond of the resist in the irradiated part that absorbs the laser is broken and decomposed and scattered. It is considered to be based on the ablation process. In the removal by this ablation, the cross section of the removed portion is sharp, and thermal damage /
There are advantages such as no distortion.

Here, a conventional resist removing apparatus will be described with reference to FIG. FIG. 5 is a block diagram showing a schematic configuration of a conventional device, in which a laser beam LB emitted from a laser light source 1 and having an oscillation wavelength in the ultraviolet region is emitted from a variable diaphragm 2.
After being shaped into a predetermined beam shape by, most of the light passes through the beam splitter 3 and reaches the shutter 4.

The shutter 4 passes or blocks the laser beam LB, and the laser beam transmitted through the shutter 4 is reflected by the mirror 5 and then enters the objective lens 6. Then, the laser light LB is imaged by the objective lens 6,
The aperture shape of the variable diaphragm 2 is formed on the wafer 7,
Irradiate the upper resist layer. The molecular bond of the portion of the resist irradiated with the laser beam LB is cut by the energy of the laser beam LB, and further becomes gas or fine particles and scatters from the resist layer. The variable diaphragm 2 is configured such that its opening portion is variable according to the shape and size of the region (at least a partial region including the alignment mark) on the wafer 7 from which the resist layer should be removed.

As the laser light for removing such a resist layer, ArF or KrF excimer laser, Nd:
Those having an oscillation line in the wavelength range of 150 nm to 360 nm, such as the third and fourth harmonics of a YAG laser and the second harmonic of an oscillation line of 514.5 nm of an Ar ion laser, are preferable. The wafer 7 is controlled by the stage controller 8 to move two-dimensionally in the x and y directions.
It is placed on the stage 9. The position of the XY stage 9 is constantly detected by a laser interferometer (not shown) or the like, and is fed back to the stage controller 8 as position information. The stage controller 8 drives a motor (not shown) based on the position information from the interferometer in accordance with the positioning command from the system controller 12 (that is, the position information of the alignment mark for removing the resist layer), and the XY stage 9 By moving, the wafer 7 (that is, the alignment mark) can be positioned with respect to the irradiation position of the laser light LB (the optical axis position of the objective lens 6) with an accuracy of about 0.01 μm, for example. There is.

On the other hand, a small amount of the laser beam LB reflected by the beam splitter 3 is collected on the light receiving surface of the irradiation photometer 11 by the condenser lens 10, and the irradiation photometer 11 responds to the light amount (light energy) thereof. The photoelectric signal is output to the system controller 12. System controller 12
Is the laser beam LB of the wafer 7 on the stage controller 8.
To a laser control system 15 for controlling light emission (oscillation) of the laser light source 1 and / or a drive system (not shown) of the shutter 4 while giving a command for positioning to A control signal is given so that the irradiation light amount optimal for removing the resist layer is obtained.

For example, when the laser light source 1 generates a pulse laser such as an excimer laser, the system controller 12 determines the optimum laser output value and the required number of pulses based on the photoelectric signal from the irradiation photometer 11. Is calculated and a control signal corresponding thereto is output to the laser control system 15. When using a pulse laser, it is not necessary to provide the shutter 4 in particular.

On the other hand, when the laser light source 1 emits continuous light, the system controller 12 calculates the optimum laser irradiation energy and the required irradiation time based on the photoelectric signal, and the laser control system regarding the output value. A control signal is sent to 15, and a control signal is sent to the shutter 4 regarding the irradiation time. In addition, the alignment optical system 13 for detecting the alignment mark formed on the wafer 7 is
For example, the alignment measurement of the wafer 7 is performed by an off-axis method together with the mark detector 14 that is fixed at a position different from the objective lens 6 and includes a photoelectric detector and the like. The alignment signal from the mark detector 14 is the system controller 1
2 is supplied.

This alignment signal is generated when a mark provided at a specific position on the wafer 7 is detected. In this embodiment, the system controller 12 uses the position of the XY stage 9 at the time of generation as a reference. By storing as a point, association (global alignment) between the irradiation position of the laser beam LB and an arbitrary point (alignment mark or the like) on the wafer 7 is completed.

[0013]

However, the conventional resist (thin film) removing method as described above has the following problems. First, the optimum energy value of the emitted laser light will be described with reference to FIG. FIG. 4 shows the relationship between the energy density P (horizontal axis) applied to the resist layer and the depth (vertical axis) at which the resist layer is removed by the ablation process. As is clear from this figure, the energy density P (J / cm ² · pulse) per unit pulse of laser irradiation is the threshold P _th.
The resist layer is not removed by the irradiation of laser light until the energy density exceeds P. However, when the energy density P exceeds the threshold P _th , the removal depth of the resist layer increases in proportion to the energy density P. The laser wavelength used at this time is, for example, the KrF excimer laser wavelength (24 nm) for a resist designed with the KrF excimer laser as its photosensitive wavelength.
Those shorter than 8 nm) are suitable. This is because the resist is generally designed to have a small absorption with respect to its photosensitive wavelength, and the resist made of a polymer has a large absorptance as the wavelength of light becomes shorter. For example, as a laser light source, ArF having a wavelength of 193 nm
The threshold value P _{th in} the case of using an excimer laser shows a value of 30 to 40 mJ / cm ² · pulse in a general resist. In the experiment, the energy density per pulse was 100 mJ / cm ²
-For pulse, about 30 pulses of laser irradiation are required to completely remove the resist with a thickness of 1 μm, and the total is 3
It was found that it required J / cm ² .

On the other hand, the antireflection coating suitable for the glass material used for the objective lens 6 for irradiating the desired removal region with the laser, for example, silica glass, has a sufficiently low reflectance for the laser light in the ultraviolet region. No one is currently available. Therefore, in the objective lens made of quartz glass with this antireflection coating, flare of about several percent is generated around the laser irradiation region in the removal process.
That is, if the energy density P of the irradiation area of 3J / cm ^2, its becomes the irradiation of a few tens of J / cm ² is carried out to ambient, by partial exposure of the resist layer other than removal region by flare, after There is an inconvenience that the pattern exposure in the process and the resist pattern shape after development are affected. For example, when the resist is a positive type, a film reduction phenomenon may occur, and when the resist is a negative type, the pattern itself may not be formed. In recent years, these phenomena become more prominent in the chemically amplified resist characterized by high sensitivity that has been actively developed.

The present invention has been made in view of the above points, and provides a resist removing method capable of avoiding exposure of the resist surface around the removed region when removing a desired region of the resist by irradiation with an energy beam. The purpose is that.

[0016]

According to the present invention, a resist 21 deposited on a substrate (wafer) 22 is selectively irradiated with an energy beam LB so that a desired portion of the resist 21 (for example, an alignment mark is formed). In the thin film removing method of removing the partial region including the protective film 20, a protective film 20 that is substantially opaque to the energy beam LB is deposited on the surface of the resist 21, and the energy beam is adjusted according to the absorption characteristics of the protective film 20 for the energy beam LB. L
The energy density P of B is adjusted, and the energy beam LB is irradiated from above the protective film 20 to remove the protective film 20 and the resist 21 in a desired portion.

Further, a light beam in a wavelength range that sensitizes the resist 21 (illumination light for pattern exposure, for example, Kr
When the absorptivity of the protective film 20 for F excimer laser) is high, the protective film 20 and the resist 21 are removed by irradiation with the energy beam LB, and then the protective film 20 not removed on the resist 21 is removed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the resist is designed as a KrF excimer laser having a photosensitive property (exposure wavelength) of 248 nm, and an ArF excimer laser (wavelength 193 nm) is used as an energy beam for resist removal. The case will be described as an example. FIG. 3 shows an example of a spectral transmission spectrum of a standard resist for a KrF excimer laser.

By the way, when the resist is partially removed by the irradiation of the ArF excimer laser, for example, light from the resist surface may be reflected by the objective lens and become flare to enter the resist around the removed region. Therefore, in the present embodiment, at least a thin film that is substantially opaque to the ArF excimer laser for resist removal, such as PVP (polyvinylpyrrolidone), which is a water-soluble polymer, is applied to the resist surface as a protective film in the present invention. I will keep it. Here, the spectral transmission spectrum of PVP is shown in FIG. Although the protective film is preferably opaque to the ArF excimer laser, it may have some transmittance as in the PVP shown in FIG. Also, ArF
It is slightly absorptive to excimer lasers.

Now, the removing method of this embodiment will be briefly described with reference to FIG. As shown in FIG. 1A, the substrate (wafer) 22 is irradiated with the ArF excimer laser LB prior to irradiation.
On the surface of the upper resist layer 21, P as a protective film is further formed.
The VP is applied almost uniformly. At this time, PVP (protective film)
Even if 20 is deposited on the entire surface of the resist layer 21, a partial region of the resist surface including the region where the resist should be removed (that is, a constant region centered on the removal region where irradiation by flare is expected) ) Only.

Next, as shown in FIG. 1B, an ArF excimer laser LB is applied from above the protective film 20 to the resist layer 21.
The desired amount of energy is applied to the desired area of the
With 0, the resist layer 21 is removed. At this time, ArF
The protective film 20 and the resist layer 21 in the irradiation region of the excimer laser LB are removed by the ablation phenomenon.

Here, as is clear from FIG. 2, the protective film
(PVP) 20 is almost incompatible with ArF excimer lasers.
It is transparent and exposes the resist layer 21 by flare.
It is possible to prevent the
However, the relationship shown in FIG. 4 holds. So A
Irradiation with rF excimer laser causes
Energy density when the removal of the resist layer 21 is started
Degree P (J / cm²・ Pulse) threshold_th1Removal of protective film 20
The threshold of the energy density P at the start of
_th2(However, here P_th1<P_th2And)
And the energy density P is a threshold value before the laser irradiation.
P_th2Adjust so that the above is achieved. by this,
Protective film in the irradiation area by irradiation with ArF excimer laser
20 and the resist layer 21 are to be removed together.
It The above threshold P_th1, P_th2Is ArF excimer
Unique to the absorption characteristics of the resist and protective film
It is determined by the target. In addition, the cash register in one desired area
When removing the strike layer, for example, the threshold P_th1, P
_th2Energy density of ArF excimer laser corresponding to
P is made different in each of the protective film 20 and the resist layer 21.
I don't care.

Next, as shown in FIG. 1C, the resist layer 2 other than the desired removal region (more precisely, the laser beam irradiation region).
The protective film 20 remaining on the surface 1 and not removed is physically removed from the surface of the resist layer 21. This completes the resist removal. If the protective film 20 is water-soluble, the protective film 20 can be easily removed by washing with water. If the protective film 20 is almost transparent to the exposure light (KrF excimer laser) like PVP (in other words, if the absorption characteristic (rate) for the KrF excimer laser is low), the resist layer is removed at the end of the removing step. It is not necessary to remove (remove) the protective film 20 that remains without being removed above. At this time, it is desirable that the protective film 20 be one that is also soluble in the resist developing solution. This can be carried out even in the developing step until the protective film 20 is peeled off,
This is because it is not necessary to remove the protective film in a separate step, which makes it possible to reduce costs and improve throughput.

In the above embodiments, P is used as the protective film.
Although the VP is used, any protective film may be used as long as it is substantially opaque to the energy beam for resist removal and is absorptive. For example, a water-soluble polymer PVA (polyvinyl alcohol) to which a water-soluble UV absorber is added may be used. As a water-soluble UV absorber, for example, Viosorb 112 (trade name, manufactured by Kyodo Pharmaceutical Co., Ltd.) is available. Further, in order to reduce the deterioration of the protective film around the laser irradiation region due to the heat generated by the ablation phenomenon due to the laser irradiation, in a special gas atmosphere, for example, He
The resist may be removed in gas.

[0025]

As described above, in the present invention, since the resist is removed by irradiating the energy beam with a film almost opaque to the energy beam for removing the thin film on the resist surface, the energy is removed. The flare of the beam can prevent the thin film around the removed region from being deteriorated, for example, resist exposure to light.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a thin film removing step in an example of the present invention.

FIG. 2 is a diagram showing an example of a spectral transmission spectrum of a protective film used in an example of the present invention.

FIG. 3 is a diagram showing an example of a spectral transmission spectrum of a resist layer used in an example of the present invention.

FIG. 4 is a graph showing the relationship between the energy density of the energy beam for thin film removal and the resist removal depth.

FIG. 5 is a block diagram showing a schematic configuration of a conventional resist removing apparatus.

[Explanation of symbols]

 20 Protective film 21 Resist layer 22 Substrate (wafer) LB Energy beam for resist removal

Claims (4)

[Claims] 1. A thin film removal method for removing a desired portion of a thin film by selectively irradiating a thin film deposited on a substrate with an energy beam, the method comprising: By depositing a substantially opaque protective film, adjusting the energy density of the energy beam according to the absorption characteristics of the protective film for the energy beam, and irradiating the energy beam from above the protective film. A method for removing a thin film, characterized in that the protective film and the thin film in the above portion are removed. 2. The thin film is a photosensitive resist,
When the absorptivity of the protective film with respect to the light beam in the wavelength range that sensitizes the resist is high, the protective film and the resist are removed by irradiation with the energy beam, and then the protective film not removed on the resist is removed. The thin film removing method according to claim 1, wherein 3. The thin film removing method according to claim 1, wherein the protective film is a water-soluble polymer film having absorptivity for the energy beam. 4. When removing a desired portion of the thin film, the thin film is removed by changing the energy density of the energy beam after removing the protective film by irradiation with the energy beam. The thin film removal method according to claim 1.