JP2001269636A - Method and device for laser cleaning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer cleaning method and device therefor capable of easily and surely removing the deposits on the surface of substrate. SOLUTION: The laser cleaning method for removing the deposits (20) on the surface (18A) of substrate (18) by irradiating the substrate (18) fixed to a specimen holder (13A) with a laser beam (12A), consists of irradiating a contact segment (18B) of the substrate (18) and the deposits (20) with the laser beam (12A) diagonally with the substrate (18), thereby thermally expanding the deposits (20) and removing the deposits (20) from the substrate (18).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for laser cleaning, and more particularly to a novel improvement for efficiently removing minute deposits such as metal particles existing on the surface of a semiconductor wafer.

[0002]

2. Description of the Related Art Conventionally, wet cleaning (RCA cleaning) using a solvent has been performed in order to clean minute deposits on a silicon wafer. In addition, as shown in FIG. 9, a laser beam 3 is radiated perpendicularly to the substrate 1 in order to remove minute attachments 2 on the silicon wafer 1.

However, with the miniaturization of the size of the VLSI, it is necessary to remove fine particles of about 0.1 μm in the future.
It is said that current wet cleaning is difficult to handle. On the other hand, a cleaning method using a laser has been disclosed as a method for removing fine particles of about 0.1 μm. The following method can be used as a method for removing fine particles adhered on a silicon wafer substrate by laser beam irradiation.

A) Allen method (US Pat. No. 4,987,2)
This method is a cleaning method using a CO ₂ laser and water. This method involves immersing a substrate in water, infiltrating water between a contaminant and the substrate surface, and rapidly heating by laser pulse irradiation. Is a method for evaporating water and removing contaminants such as contaminants from a substrate.

B) Tum method (A.C. Tam et al., J. Appl. Phys. 71 (7), March 1992)
This method is a method of removing contaminants by using a laser and a liquid medium as in the Allen method. I as a laser
An r: YAG laser or a KrF excimer laser is used, and alcohol and water are used as a liquid medium.

C) Radiance patent (Tokuhyohei 8-5096)
In this method, a contaminant is removed by irradiating the substrate with a laser beam and simultaneously supplying a laminar flow of an inert gas onto the surface of the substrate.

Japanese Patent Application Laid-Open No. Hei 7-225300 discloses a method and an apparatus for removing surface deposits by using a laser. In this reference, a CO ₂ laser is obliquely irradiated on the surface deposits. Describes removing surface deposits by scattering the surface deposits by ablation.

[0008]

Since the conventional apparatus is configured as described above, there are the following problems. That is, all of the cleaning methods a) to c) are intended to remove by adding a liquid or gas to the laser beam irradiation, and the processing steps are complicated. Further, in the methods a) and b), since a liquid is used, there is a possibility that impurities contained in the liquid become contaminants. Furthermore, in the invention described in Japanese Patent Application Laid-Open No. 7-225300, a laser oscillator that can scatter the surface deposits by ablation is required. There has been a demand for an apparatus and method capable of reliably removing surface deposits with the configuration.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In particular, the present invention is directed to a method of adjusting the incident angle of a laser beam on a substrate to thermally expand an adhered substance to separate the liquid from the substrate surface. Enables efficient removal of fine particles without using gas or gas.

[0010]

A wafer cleaning method according to the present invention is directed to a laser cleaning method for irradiating a substrate fixed to a sample stage with a laser beam to remove deposits on the surface of the substrate. A method of removing the attached matter from the substrate by irradiating the laser beam obliquely to the substrate to a contact portion with the attached matter to thermally expand the attached matter, and removing the attached matter from the substrate. By irradiating the laser beam to the contact portion in the normal direction, horizontal direction, obliquely downward direction or vertically downward direction, is a method of removing the attached matter from the substrate surface, and the surface of the substrate An angle between the incident direction of the laser beam and the incident direction is in a range of 10 ° to 30 °, and further, a plurality of laser beams are applied to the contact portion from a plurality of directions. How to Further, the laser cleaning device of the present invention includes a laser oscillator, an attenuator for attenuating a laser beam emitted from the laser oscillator, an optical system for shaping a laser beam output from the attenuator, Provided on the output side of the system, a sample stage for fixing the substrate, the laser oscillator, attenuator and control means for controlling the drive of the sample stage,
In a laser cleaning device for irradiating a substrate fixed to a sample stage with a laser beam to remove an adhering substance on the surface of the substrate, the laser is oblique to the substrate at a contact portion between the substrate and the adhering substance. By irradiating a beam and thermally expanding the attached matter, the attached matter is removed from the substrate, and the normal of the substrate is directed horizontally, obliquely downward or vertically downward. By irradiating the laser beam to the contact portion, the attached matter is removed, and the angle between the surface of the substrate and the incident direction of the laser beam is 10 ° to 30 °.
And a configuration in which a plurality of laser beams are applied to the contact portion from a plurality of directions.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a laser cleaning apparatus and apparatus according to the present invention will be described below in detail with reference to the drawings.

First, the present invention will be schematically described. Whereas the conventional laser cleaning method is a means for removing the deposit by ablation or adding a liquid and multiplying the evaporation of the liquid to remove the deposit, the laser cleaning method of the present invention employs a laser beam. Is applied to the silicon wafer (substrate) in an oblique direction, thereby applying thermal energy to the contact portion between the silicon wafer and the attached matter, causing rapid thermal expansion between the silicon wafer and the attached matter, and removing the attached matter. It is a method of removing.

The force f (cleaning force) per unit area applied to the deposit by the laser beam is given by the following equation for each of the silicon wafer and the deposit.
(YFLu et al., AppL Sur. Sic. 120
(1997), pp. 317-322) f = γE △ T (1) γ: linear thermal expansion coefficient E: elastic coefficient ΔT: temperature rise of the contact part due to laser beam irradiation

As a laser beam device, a pulsed laser oscillator is suitable because a continuous wave laser may damage a silicon wafer. In particular, among the pulse laser oscillators, a wavelength band having a large photon energy and a high light absorption to many substances (ArF: 193n), such as an excimer laser oscillator such as ArF or KrF, is used.
m, KrF: 248 nm).

[0015] However, as described above, the difficulty of removing the deposits is as follows.
This is related to the temperature rise (ΔT) at the time of laser beam irradiation on the silicon wafer and the attached matter, and ΔT largely depends on the light absorption rate of the substance. For example, the deposit is metal (Al, Ni, etc.)
If a substance to be absorbed excimer laser as, the effect due to the oblique illumination is large, deposit SiO ₂
In the case of a substance that hardly absorbs the excimer laser (that is, transmits or reflects) as described above, there is no effect of oblique irradiation. Therefore, it is necessary to select an appropriate laser wavelength depending on the object to be removed. Furthermore, the removal target is effective for substances (metal particles) and spherical particles having a larger coefficient of thermal expansion than equation (1).

Next, the wafer cleaning apparatus and method according to the present invention will be specifically described. FIG. 1 is a configuration diagram showing an embodiment of a wafer cleaning apparatus according to the present invention, and is a top view schematically showing an apparatus for cleaning a silicon wafer. This device uses a KrF laser oscillator 10
(Laser oscillator), attenuator 11 (attenuator), optical system 12, processing chamber 13, sample table 13A, gate valve 14
A, 14B, a transfer chamber 15, a cassette chamber 16, and a PC controller 17 (control means). A substrate such as a silicon wafer 18 is fixed to the sample stage 13A. Further, the apparatus is compatible with vacuum, and the processing chamber 13,
The transfer chamber 15 and the cassette chamber 16 are connected by gate valves 14A and 14B, respectively.

In FIG. 1, the silicon wafer 18 is disposed so that its normal 18C faces in the horizontal direction.
Laser beam 10 emitted from KrF laser oscillator 10
A becomes a laser beam 12A via the optical system 12,
The laser beam 12A is applied to the silicon wafer 18 fixed on the sample table 13A.

Here, since FIG. 1 is a top view, it seems that the laser beam 12A is irradiated perpendicularly to the surface of the silicon wafer 18, but actually, it is irradiated obliquely from above. Things. In such a case, it is necessary to irradiate the contact portion 18B between the silicon wafer 18 and the deposit 20 with the laser beam 12A.
Instead of irradiating A, the periphery of the contact portion 18B may be irradiated with the laser beam 12A.

The KrF laser oscillator 10 includes:
LPX210i, Kr manufactured by Lambda Physik
An F excimer laser (wavelength 248 nm) is used. The optical system 12 shapes the laser beam 10A into a laser beam 12A having a top flat energy distribution. The sample table 13A includes a uniaxial linear movement mechanism and a rotation mechanism. With such a configuration, the entire surface of the silicon wafer 18 can be irradiated with the laser beam 12A. That is, the sample stage 13A can be arbitrarily rotated in any of the directions θx and θy shown in FIG.

The beam spot shape when irradiating the laser beam 12A is 6 mm × 6 mm. The PC controller 17 includes a KrF laser oscillator 10, an attenuator 11,
In addition to controlling the drive of the sample table 13A, the irradiation energy density (100 to 600 mJ / cm ² ) and the laser incident angle (0 to 90 °) can be set arbitrarily.
And the laser oscillation frequency can be changed.

With this configuration, the PC controller 17 can arbitrarily set the beam overlap (the ratio of the overlap of the irradiation range of the laser beam 12A on the wafer when scanning). Here, the incident angle of the laser beam 12A refers to the surface 18A of the wafer 18 and the laser beam 12A as shown in FIG.
The angle formed by the incident direction of A.

FIG. 2 is an enlarged view of a main part in FIG. 1 and a view showing a state where a laser beam 12A is irradiated from a lateral direction. FIG. 3 is an enlarged view of a main part in FIG. FIG. Although FIG. 3 shows the normal 18C of the silicon wafer 18 to be directed vertically upward for convenience of explanation, in actuality, as shown in FIG. 18C is disposed so as to face diagonally downward.

A KrF laser 10 is applied to Ni particles (particle diameter: 3 to 24 μm), which are deposits 20 on the silicon wafer 18.
The laser beam 12A obtained through the attenuator 11 and the optical system 12 was irradiated obliquely, and the number of particles of the attached matter 20 before and after the irradiation was measured by a microscope. As a result, characteristics as shown in FIGS. 4 and 5 were obtained.

FIG. 4 shows the relationship between the irradiation energy density and the removal rate when the incidence angle of the laser beam 12A is changed, and FIG. 5 shows the relationship between the laser incidence angle and the removal rate. . From the characteristics shown in FIGS. 4 and 5, the laser beam 12A was
In the case of irradiating on the top 8, the oblique irradiation (0 ° <incident angle <90 °) is clearly higher in removal rate than the perpendicular irradiation (incident angle 90 °). When the incident angle is small, the Ni particles can be removed with a lower energy density.

However, if the incident angle is made smaller, the irradiation beam area becomes larger than in the case of normal incidence (the incident angle is 90 °), so that the irradiation energy density becomes smaller (for example, when the incident angle is 30 °, The irradiation energy density is halved for normal incidence). Also, since the focal depth of the optical system 12 needs to be long, it is not preferable to unnecessarily reduce the incident angle. In view of this point, as shown in FIG. 5, in order to obtain a high removal rate, the incident angle is 10 ° to 30 °.
It can be seen that the case within the range is optimal.

Even if the incident angle is 90 ° or more, the laser beam 12A is irradiated obliquely, but depending on the angle of the silicon wafer 18 and the irradiation direction of the laser beam 12A, the removed particles are re-applied to the wafer again. There is a risk of adhesion. Therefore, when the laser beam 12A is incident from the lateral direction as shown in FIG. 2, the sample stage 13A is fixed so that the normal 18C of the silicon wafer 18 is obliquely downward, and the laser beam 12A is irradiated.

As shown in FIG. 1, when the normal line 18C of the silicon wafer 18 is oriented in the horizontal direction, the laser beam 12A is incident obliquely from above. In such a case, an appropriate reflector (not shown) or the like is applied to the laser beam 1.
2A, the laser beam 12A
May be guided to the silicon wafer 18, and further, such a reflection plate or the like may be driven by the PC controller 17.

FIG. 6 and FIG. 7 are views showing a case where the laser beam 12A is incident from a plurality of directions. In these cases, more heat energy can be given to the contact portion between the silicon wafer 18 and the deposit 20, so that the deposit 20 can be more efficiently removed from the silicon wafer 18. Here, efficient cleaning refers to removing the deposit 20 with a low energy density and a small number of irradiations.

As described above, the deposit 20 removed from the surface of the silicon wafer 18 by thermal expansion is shown in FIG.
Since the normal line 18C of the silicon wafer 18 is directed obliquely downward as shown in FIG. 7, the silicon wafer 18 falls directly below the processing chamber 13 and does not adhere to the silicon wafer 18 again. As means for collecting the adhered matter 20 thus removed, the sample table 13A in the processing chamber 13 is used.
For example, a net-like electrode (not shown) may be provided below the lower part to cause the electrostatic attraction force to be exerted to collect the deposit 20.

In the above description, the laser beam 12
Although the case where the incident angle of A is changed has been described, FIG.
As shown in FIG.
And the angle of incidence of the laser beam 12A may be fixed and the angle of incidence of the laser beam 12A may be set by changing the angle of the sample table 13A while fixing the angle of incidence. In such a case, when the silicon beam 18 is irradiated with the laser beam 12A, the normal 18C of the silicon wafer 18 is inclined downward (see FIG. The sample stage 13A is set so as to face (see FIG. 3). In the above description, the case where the sample table 13A is fixed and the deposit 20 is removed so that the normal line 18C of the silicon wafer 18 faces obliquely downward has been described. However, the present invention is limited to such a form. Instead, the normal 18C of the silicon wafer 18 is moved completely vertically (not shown) or horizontally (ie, FIG. 1).
Even if the sample table 13A is fixed so as to face the same direction as shown in FIG.

As described above, according to the wafer cleaning method and apparatus of the present invention, it is possible to easily and reliably remove the deposits on the silicon wafer. Further, in the above description, a silicon wafer is described as an example, but the present invention is not limited to such a range, and it is possible to similarly remove attached matter on other substrates.

[0032]

The wafer cleaning method according to the present invention is directed to a laser cleaning method for irradiating a substrate fixed to a sample stage with a laser beam to remove extraneous matter on the surface of the substrate. By irradiating the laser beam to the contact portion of the substrate obliquely with respect to the substrate to thermally expand the attached matter, the attached matter is removed from the substrate, so that the attached matter can be efficiently removed. Further, by irradiating the laser beam to the contact portion with the normal of the substrate oriented in the horizontal direction, obliquely downward direction or vertically downward direction, the attached matter is removed from the substrate surface, so that it is simple and reliable. Deposits can be removed. In addition, since the angle between the surface of the substrate and the incident direction of the laser beam is in the range of 10 ° to 30 °, the adherent can be efficiently removed within the range of 10 ° to 30 °. Can be removed. Further, since the plurality of laser beams are applied to the contact portion from a plurality of directions, the attached matter can be more effectively removed. Further, the laser cleaning device of the present invention includes a laser oscillator, an attenuator for attenuating a laser beam emitted from the laser oscillator, an optical system for shaping a laser beam output from the attenuator, A sample stage arranged on the output side of the system, the sample stage fixing the substrate, the laser oscillator, the attenuator and control means for controlling the drive of the sample stage, comprising a laser beam on the substrate fixed to the sample stage. A laser cleaning device for irradiating the substrate with the laser beam obliquely to a contact portion between the substrate and the attached object to irradiate the laser beam on the substrate, thereby thermally expanding the attached object. By doing so, the attached matter is removed from the substrate, so that the attached matter can be efficiently removed. In addition, since the laser beam is applied to the contact portion with the normal line of the substrate directed horizontally, obliquely downward, or vertically downward, the adhering matter is removed, so that the adhering matter is easily and reliably removed. it can. Further, since the angle between the surface of the substrate and the incident direction of the laser beam is set in the range of 10 ° to 30 °, the attached matter can be efficiently removed in the range of 10 ° to 30 °. Further, since a plurality of laser beams are applied to the contact portion from a plurality of directions, the attached matter can be more effectively removed.

[Brief description of the drawings]

FIG. 1 is a top view schematically showing a configuration of a wafer cleaning apparatus according to the present invention.

FIG. 2 is an enlarged view showing a main part of the wafer cleaning apparatus according to the present invention.

FIG. 3 is a conceptual diagram showing an enlarged main part of the wafer cleaning apparatus according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship between an irradiation energy density and a removal rate when an incident angle of a laser beam is changed.

FIG. 5 is a characteristic diagram showing a relationship between a laser incident angle and a removal rate.

FIG. 6 is a conceptual diagram illustrating a state where a plurality of laser beams are irradiated.

FIG. 7 is a conceptual diagram illustrating a state where a plurality of laser beams are irradiated.

FIG. 8 is a top view schematically showing a configuration of another embodiment of the wafer cleaning apparatus according to the present invention.

FIG. 9 is a diagram conceptually showing a state in which a laser beam is applied to a deposit by a conventional method.

[Explanation of symbols]

 Reference Signs List 10 KrF laser oscillator (laser oscillator) 10A laser beam 11 attenuator (attenuator) 12 optical system 12A laser beam 13 processing room 13A sample table 14A, 14B gate valve 15 transfer room 16 cassette room 17 PC controller (control means) 18 silicon wafer (Substrate) 18A Surface 18B Contact part 18C Normal 20 Adhered matter 21 Mirror

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shinichi Ishizaka 1-1, Nikkocho, Fuchu-shi, Tokyo F-term in Japan Steel Works, Ltd. (reference) 3B116 AA02 AA03 AB42 BC42 CD01 CD43

Claims (8)

[Claims] 1. A laser cleaning method for irradiating a substrate (18) fixed to a sample stage (13A) with a laser beam (12A) to remove a deposit (20) on a surface (18A) of the substrate (18). In the method, a contact portion (18B) between the substrate (18) and the deposit (20)
The laser beam (12A) obliquely to the substrate (18)
Irradiation to thermally expand the deposit (20),
A laser cleaning method, comprising: removing the deposit (20) from the substrate (18). 2. A normal line (18C) of the substrate (18) is set in a horizontal direction,
The contact portion (18B) diagonally downward or vertically downward
2. The laser cleaning method according to claim 1, wherein the deposit (20) is removed from the surface of the substrate (18) by irradiating the substrate with the laser beam (12A). 3. An angle between the surface (18A) of the substrate (18) and the incident direction of the laser beam (12A) is from 10 ° to 30 °.
The laser cleaning method according to claim 1 or 2, wherein the temperature is within a range up to °. 4. The laser cleaning method according to claim 1, wherein a plurality of laser beams are irradiated on the contact portion from a plurality of directions. 5. A laser oscillator (10), said laser oscillator
An attenuator (11) for attenuating a laser beam (10A) emitted from (10), an optical system (12) for shaping a laser beam output from the attenuator (11), and the optical system ( A sample stage (13A) arranged on the output side of 12) and fixing the substrate (18)
And a control means (17) for controlling the drive of the laser oscillator (10), the attenuator (11) and the sample stage (13A), and the laser is mounted on a substrate (18) fixed to the sample stage (13A). In a laser cleaning device for irradiating a beam (12A) to remove the deposit (20) on the surface (18A) of the substrate (18), a contact portion between the substrate (18) and the deposit (20) ( 18B) by irradiating the laser beam (12A) obliquely to the substrate (18) to thermally expand the attached matter (20), thereby removing the attached matter (20) from the substrate (18). A laser cleaning device. 6. A normal line (18C) of the substrate (18) is set in a horizontal direction,
The contact portion (18B) diagonally downward or vertically downward
6. The laser cleaning apparatus according to claim 5, wherein the deposit is removed by irradiating the laser beam with the laser beam. 7. An angle formed between the surface (18A) of the substrate (18) and the incident direction of the laser beam (12A) is from 10 ° to 30 °.
7. The laser cleaning apparatus according to claim 5, wherein the angle is set to a range of up to °. 8. The laser cleaning apparatus according to claim 5, wherein a plurality of laser beams are irradiated on the contact portion from a plurality of directions.