Laser beam machining system

A laser beam machining system including a chuck table for holding a work, and a laser beam irradiation unit for irradiating the work held on the chuck table with a laser beam, wherein the laser beam irradiation unit includes: a pulsed laser beam oscillator for oscillating a pulsed laser beam; a condenser for condensing the pulsed laser beam oscillated from the pulsed laser beam oscillator; a laser beam scanning unit disposed between the pulsed laser beam oscillator and the condenser and operative to deflect the pulsed laser beam to be inputted to the condenser; and a laser beam reshaping unit which ids disposed between the pulsed laser beam oscillator and the laser beam scanning unit and by which the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped into a top hat shape.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser beam machining system by which laser beam machining with a uniform depth can be applied to a work.

2. Description of the Related Art

In the process of manufacturing a semiconductor device, a plurality of regions are demarcated by planned split lines called streets which are arranged in a lattice pattern on a face side of a roughly circular disk-like semiconductor wafer, and devices such as ICs and LSIs are formed respectively in the demarcated regions. Then, the semiconductor wafer is cut along the streets to split it into the regions provided with the devices, thereby producing individual semiconductor chips. In order to manufacture devices with smaller size and higher functions, a module structure has been put to practical use in which a plurality of semiconductor chips are stacked and bonding pads of the stacked semiconductor chips are connected to each other. The module structure is so configured that the semiconductor wafer is provided with through-holes (via holes) at its portions provided with electrodes, and the through-holes (via holes) are filled up with a conductive material, such as aluminum and copper, for connection with the electrodes (refer to, for example, Japanese Patent Laid-open No. 2003-163323).

The through-holes (via holes) provided in the semiconductor wafer as above-mentioned are generally formed by use of a drill. However, the through-holes (via holes) provided in the semiconductor wafer have small diameters of 100 to 300 μm, and boring by use of a drill has the problem of poor productivity. In order to solve this problem, the present applicant has proposed in Japanese Patent Application No. 2005-64867 a laser beam machining system by which minute holes can be efficiently formed in a work such as a semiconductor wafer.

The laser beam machining system thus proposed includes machining feed amount detection means for detecting the relative machining feed amounts of a chuck table holding a work thereon and laser beam irradiation means, storage means for storing the X and Y coordinate data on minute holes to be formed in the work, and control means for controlling the laser beam irradiation means on the basis of the X and Y coordinate data on the minute holes stored in the storage means and a detection signal sent from the machining feed amount detection means, wherein the work is irradiated with one pulse of a laser beam when the portion, corresponding to the X and Y coordinate data on the minute hole to be formed in the work, of the work has been brought to a position directly under a condenser of the laser beam irradiation means. However, in order to form a through-hole in the work, the same portion of the work must be irradiated with a pulsed laser beam a plurality of times. Therefore, the use of the above-mentioned laser beam machining system is not necessarily satisfactory in regard of productivity, since movement of the work must be carried out a plurality of times.

In order to meet the above-mentioned requirement, the present applicant has proposed in Japanese Patent Application No. 2005-362236 a laser beam machining system including laser beam irradiation means including acousto-optical deflection means using an acousto-optical device, wherein a laser beam oscillated by laser beam oscillation means is deflected when passing through the acousto-optical device, whereby the same work position of the work is irradiated with the laser beam while performing machining feeding of the work.

In the method of forming a laser beam-machined hole by irradiating a semiconductor wafer with a laser beam from the back side of the semiconductor wafer as above-mentioned, the same portion of the semiconductor wafer must be irradiated with the laser beam a plurality of times, and the irradiation must be so controlled as not to open a hole in the electrode, called bonding pad, formed on the face side of the semiconductor wafer. However, the energy distribution of the laser beam is a Gaussian distribution such that the energy is strongest at the center and is decreased toward the outer peripheral area. Therefore, the machining proceeds most at the central portion of the laser beam with which the work is irradiated, so that it is impossible to form a laser beam-machined hole with a uniform depth. Thus, there is the problem that the electrode (bonding pad) is melted at the central portion of the laser beam, resulting in formation of a hole there.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a laser beam machining system by which a substrate of a wafer is efficiently provided with laser beam-machined holes reaching electrodes, without opening any hole in the electrodes, by forming the laser beam-machined holes which are uniform in depth.

In accordance with an aspect of the present invention, there is provided a laser beam machining system including a chuck table for holding a work, and laser beam irradiation means for irradiating the work held on the chuck table with a laser beam, wherein the laser beam irradiation means includes: a pulsed laser beam oscillator for oscillating a pulsed laser beam; a condenser for condensing the pulsed laser beam oscillated from the pulsed laser beam oscillator; laser beam scanning means disposed between the pulsed laser beam oscillator and the condenser and operative to deflect the pulsed laser beam to be inputted to the condenser; and laser beam reshaping means which is disposed between the pulsed laser beam oscillator and the laser beam scanning means and by which the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped into a top hat shape.

Preferably, the laser beam reshaping means is composed of an aspherical lens. Alternatively, the laser beam reshaping means may be composed of a mask provided with a hole which permits a central portion of the pulsed laser beam oscillated from the pulsed laser beam oscillator to pass therethrough.

A collimation lens by which the laser beam reshaped by the laser beam reshaping means is corrected into a parallel laser beam may be disposed between the laser beam reshaping means and the laser beam scanning means.

Preferably, the laser beam scanning means is composed of acousto-optical deflection means. Alternatively, the laser beam scanning means may be composed of a galvano-scanner.

According to the present invention, the laser beam irradiation means includes the pulsed laser beam oscillator for oscillating a pulsed laser beam, the condenser for condensing the pulsed laser beam oscillated from the pulsed laser beam oscillator, and the laser beam scanning means disposed between the pulsed laser beam oscillator and the condenser and operative to deflect the pulsed laser beam to be inputted to the condenser. Therefore, irradiation with a plurality of pulses of the pulsed laser beam can be conducted at a predetermined work position even in the condition where the work held on the chuck table is being moved in the machining feed direction. As a result, via holes can be formed efficiently.

Besides, according to the present invention, the laser beam irradiation means includes the laser beam reshaping means which is disposed between the pulsed laser beam oscillator and the laser beam scanning means and by which the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped. Therefore, the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped into a top hat shape, and the energy distribution is made uniform at the tip of the laser beam, so that a laser beam-machined hole with a uniform depth can be formed. Accordingly, in forming via holes in a wafer, the substrate of the wafer can be provided with laser beam-machined holes reaching the electrodes, without opening any hole in the electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the laser beam machining system configured according to the present invention will be described more in detail below, referring to the attached drawings.FIG. 1shows a perspective view of the laser beam machining system configured according to the present invention. The laser beam machining system shown inFIG. 1includes a stationary base2, a chuck table mechanism3which is disposed on the stationary base2so as to be movable in a machining feed direction (X-axis direction) indicated by arrow X and which holds a work, a laser beam irradiation unit support mechanism4disposed on the stationary base2so as to be movable in an indexing feed direction (Y-axis direction) indicated by arrow Y orthogonal to the direction (X-axis direction) indicated by arrow X, and a laser beam irradiation unit5disposed on the laser beam irradiation unit support mechanism4so as to be movable in a direction (Z-axis direction) indicated by arrow Z.

The chuck table mechanism3includes a pair of guide rails31,31disposed on the stationary base2in parallel to the machining feed direction (X-axis direction) indicated by arrow X, a first sliding block32disposed on the guide rails31,31so as to be movable in the machining feed direction (X-axis direction) indicated by arrow X, a second sliding block33disposed on the first sliding block32so as to be movable in the indexing feed direction (Y-axis direction) indicated by arrow Y, a cover table35supported on the second sliding block33by a hollow cylindrical member34, and a chuck table36as work holding means. The chuck table36includes a suction chuck361formed from a porous material so that a work, for example, a circular disk-like semiconductor wafer is held on the suction chuck361by suction means (not shown). The chuck table36thus configured is rotated by a pulse motor (not shown) disposed in the hollow cylindrical member34. Incidentally, the chuck table36is provided with a clamp362for fixing an annular frame which will be described later.

The first sliding block32is provided in its lower surface with a pair of guided grooves321,321to be fitted to the pair of guide rails31,31, and is provided on its upper surface with a pair of guide rails322,322formed in parallel along the indexing feed direction (Y-axis direction) indicated by arrow Y. The first sliding block32thus configured, with its guided grooves321,321fitted to the pair of guide rails31,31, can be moved in the machining feed direction (X-axis direction) indicated by arrow X along the pair of guide rails31,31. The chuck table mechanism3in the embodiment shown in the figure has machining feeding means37for moving the first sliding block32in the machining feed direction (X-axis direction) indicated by arrow X along the pair of guide rails31,31.

The machining feeding means37includes a male screw rod371disposed in parallel to and between the pair of guide rails31and31, and a drive source such as a pulse motor372for rotatingly driving the male screw rod371. The male screw rod371has one end rotatably supported by a bearing block373fixed to the stationary base2, and has the other end connected on a power transmission basis to an output shaft of the pulse motor372. Incidentally, the male screw rod371is in screw engagement with a female screw through-hole formed in a female screw block (not shown) provided to project from a lower surface of a central part of the first sliding block32. Therefore, as the male screw rod371is driven by the pulse motor372to rotate normally and reversely, the first sliding block32is moved in the machining feed direction (X-axis direction) indicated by arrow X along the guide rails31,31.

The laser beam machining system in the embodiment shown in the figure includes machining feed amount detection means374for detecting the machining feed amount of the chuck table36. The machining feed amount detection means374is composed of a linear scale374adisposed along the guide rail31, and a reading head374bdisposed on the first sliding block32and moved along the linear scale374atogether with the first sliding block32. The reading head374bof the feed amount detection means374sends a pulse signal, having one pulse per 1 μm in the embodiment shown, to control means which will be described later. The control means to be described later detects the machining feed amount of the chuck table36by counting the pulses in the pulse signal inputted.

Incidentally, in the case where the pulse motor372is used as the drive source for the machining feeding means37, the machining feed amount of the chuck table36can also be detected by counting the driving pulses of a control means (described later) for outputting a driving signal to the pulse motor372. In addition, in the case where a servo motor is used as the drive source for the machining feeding means37, the machining feed amount of the chuck table36can also be detected by supplying control means (described later) with a pulse signal outputted by a rotary encoder for detecting the rotating speed of the servo motor and counting the pulses in the inputted pulse signal by the control means.

The second sliding block33is provided in its lower surface with a pair of guided grooves331,331to be fitted to the pair of guide rails322,322provided on the upper surface of the first sliding block32, so as to be movable in the indexing feed direction (Y-axis direction) indicated by arrow Y through the fitting of the guided grooves331,331to the pair of guide rails322,322. The chuck table mechanism3in the embodiment shown in the figure includes first indexing feeding means38for moving the second sliding block33in the indexing feed direction (Y-axis direction) indicated by arrow Y along the pair of guide rails322,322provided on the first sliding block32.

The first indexing feeding means38includes a male screw rod381disposed in parallel to and between the pair of guide rails322and322, and a drive source such as a pulse motor382for rotatingly driving the male screw rod381. The male screw rod381has one end rotatably supported by a bearing block383fixed to the upper surface of the first sliding block32, and has the other end connected on a power transmission basis to an output shaft of the pulse motor382. Incidentally, the male screw rod381is in screw engagement with a female screw through-hole formed in a female screw block (not shown) provided to project from a lower surface of a central part of the second sliding block33. Therefore, as the male screw rod381is driven by the pulse motor382to rotate normally and reversely, the second sliding block33is moved in the indexing feed direction (Y-axis direction) indicated by arrow Y along the guide rails322,322.

The laser beam machining system in the embodiment shown in the figure includes indexing feed amount detection means384for detecting the indexing process feed amount of the second sliding block33. The indexing feed amount detection means384is composed of a linear scale384adisposed along the guide rail322, and a reading head384bdisposed on the second sliding block33and moved along the linear scale384atogether with the second sliding block33. The feed amount detection means384sends a pulse signal, having one pulse per 1 μm in the embodiment shown in the figure, to control means which will be described later. The control means to be detected later detects the indexing feed amount of the chuck table36by counting the pulses in the pulse signal inputted.

Incidentally, in the case where the pulse motor382is used as the drive source for the indexing feeding means38, the indexing feed amount of the chuck table36can also be detected by counting the driving pulses of control means (described later) for outputting a driving signal to the pulse motor382. Besides, in the case where a servo motor is used as the drive source for the first indexing feeding means38, the indexing feed amount of the chuck table36can also be detected by sending a pulse signal outputted from a rotary encoder for detecting the rotating speed of the servo motor to control means (described later) and counting the pulses in the inputted pulse signal by the control means.

The laser beam irradiation unit support mechanism4includes a pair of guide rails41,41disposed on the stationary base2in parallel along the indexing feed direction (Y-axis direction) indicated by arrow Y, and a movable support base disposed on the guide rails41,41so as to be movable in the direction indicated by arrow Y. The movable support base42is composed of a movable support part421disposed on the guide rails41,41so as to be movable, and a mounted part422mounted to the movable support part421. The mounted part422is provided on its side surface with a pair of parallel guide rails423,423extending in the direction (Z-axis direction) indicated by arrow Z. The laser beam irradiation unit support mechanism4in the embodiment shown in the figure includes second indexing feeding means43for moving the movable support base42in the indexing feed direction (Y-axis direction) indicated by arrow Y along the pair of guide rails41,41.

The second indexing feeding means43includes a male screw rod431disposed in parallel to and between the pair of guide rails41and41, and a drive source such as a pulse motor432for rotatingly driving the male screw rod431. The male screw rod431has one end rotatably supported by a bearing block (not shown) fixed to the stationary base2, and has the other end connected on a power transmission basis to an output shaft of the pulse motor432. Incidentally, the male screw rod431is in screw engagement with a female screw hole formed in a female screw block (not shown) provided to project from a lower surface of a central part of the movable support part421constituting the movable support base42. Therefore, as the male screw rod431is driven by the pulse motor432to rotate normally and reversely, the movable support base42is moved in the indexing feed direction (Y-axis direction) indicated by arrow Y along the guide rails41,41.

The laser beam irradiation unit5in the embodiment shown in the figure includes a unit holder51, and laser beam irradiation means52attached to the unit holder51. The unit holder51is provided with a pair of guided grooves511,511to be slidably fitted to the guide rails423,423provided on the mounted part422, and is supported so as to be movable in the direction (Z-axis direction) indicated by arrow Z, through fitting of the guided grooves511,511to the guide rails423,423.

The laser beam irradiation unit5in the embodiment shown in the figure includes moving means53for moving the unit holder51in the direction (Z-axis direction) indicated by arrow Z along the pair of guide rails423,423. The moving means53includes a male screw rod (not shown) disposed between the pair of guide rails423and423, and a drive source such as a pulse motor532for rotatingly driving the male screw rod. As the male screw rod (not shown) is driven by the pulse motor532to rotate normally and reversely, the unit holder51and the laser beam irradiation means52are moved in the direction (Z-axis direction) indicated by arrow Z along the guide rails423,423. Incidentally, in the embodiment shown in the figure, the laser beam irradiation device52is moved upwards when the pulse motor532is driven to rotate normally, and the laser beam irradiation device52is moved downwards when the pulse motor532is driven to rotate reversely.

The laser beam irradiation means52shown in the figure includes a hollow cylindrical casing521disposed substantially horizontally. As shown inFIG. 2, a pulsed laser beam oscillation means61, output regulating means62, and a condenser63for condensing a pulsed laser beam which is oscillated from the pulsed laser beam oscillation means61and of which the output is regulated by the output regulating means62. The pulsed laser beam oscillation means61is composed of a pulsed laser beam oscillator611, and cycle frequency setting means612annexed thereto.

The pulsed laser beam oscillator611is composed of a YVO4 laser or YAG laser oscillator in the embodiment shown in the figure, and oscillates a pulsed laser beam LB having such a wavelength (for example, 355 nm) as to be absorbed by the work formed of silicon or the like. The cycle frequency setting means612sets the frequency of the pulsed laser beam oscillated from the pulsed laser beam oscillator611. The energy distribution of the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61configured as above-mentioned is a Gaussian distribution LBG. The output regulating means62regulates the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61to a predetermined output. The condenser63includes a direction changing mirror631for changing the direction of the pulsed laser beam LB to a downward direction, and a condenser lens632for condensing the laser beam direction-changed by the direction changing mirror631, and is attached to the tip of the casing521.

The laser beam irradiation means52in the embodiment shown in the figure includes a laser beam scanning means64disposed between the output regulating means62and the condenser63and operative to deflect the pulsed laser beam to be inputted to the condenser63. The laser beam scanning means64is composed of a first acousto-optical deflection means65for deflecting the laser beam oscillated by the pulsed laser beam oscillation means61in a machining feed direction (X-axis direction), and a second asousto-optical deflection means66for deflecting the laser beam oscillated by the laser beam oscillation means61in the indexing feed direction (Y-axis direction).

The first acousto-optical deflection means65includes a first asousto-optical device651for deflecting the laser beam oscillated by the laser beam oscillation means61in the machining direction (X-axis direction), a first RF oscillator652for producing an RF (radio frequency) to be impressed on the first acousto-optical device651, a first RF amplifier653for amplifying the power of the RF produced by the first RF oscillator652and impressing the amplified RF on the first acousto-optical device651, a first deflection angle regulating means654for regulating the frequency of the RF produced by the first RF oscillator652, and a first output regulating means655for regulating the amplitude of the RF produced by the first RF oscillator652. The first acousto-optical device651can regulate the angle of deflection of the laser beam correspondingly to the frequency of the RF impressed thereon, and can regulate the output of the laser beam correspondingly to the amplitude of the RF impressed thereon. Incidentally, the first deflection angle regulating means654and the first output regulating means655are controlled by a control means which will be described later.

The second acousto-optical deflection means66includes a second acousto-optical device661for deflecting the laser beam oscillated by the laser beam oscillation means61in the indexing feed direction orthogonal to the machining feed direction (X-axis direction), a second RF oscillator622for producing an RF to be impressed on the second acousto-optical device661, a second RF amplifier663for amplifying the power of the RF produced by the RF oscillator662and impressing the amplified RF on the second acousto-optical device661, second deflection angle regulating means664for regulating the frequency of the RF produced by the second RF oscillator662, and second output regulating means665for regulating the amplitude of the RF produced by the second RF oscillator662. The second acousto-optical device661can regulated the angle of deflection of the laser beam correspondingly to the frequency of the RF impressed thereon, and can regulate the output of the laser beam correspondingly to the amplitude of the RF impressed thereon. Incidentally, the second deflection angle regulating means664and the second output regulating means665are controlled by control means which will be described later.

The laser beam irradiation device52in the embodiment shown in the figure includes laser beam absorbing means67for absorbing the laser beam deflected by the first acousto-optical device651, as indicated by broken line inFIG. 2, in the case where an RF having a predetermined frequency is impressed on the first acousto-optical device651.

The laser beam scanning means64in the embodiment shown in the figure is configured as above-mentioned, and its operation will be described below. In the case of a voltage of 10 V, for example, is impressed on the first deflection angle regulating means654of the first acouso-optical deflection means65and an RF having a frequency corresponding to 10 V is therefore impressed on the first acousto-optical device651, the pulsed laser beam oscillated from the pulsed laser beam oscillation means61is deflected as indicated by solid line inFIG. 2, to be condensed into a condensation point Pa. Besides, in the case where a voltage of 15 V, for example, is impressed on the first deflection angle regulating means654and an RF having a frequency corresponding to 15 V is therefore impressed on the first acousto-optical device651, the pulsed laser beam oscillated from the pulsed laser beam oscillation means61is deflected as indicated by dot-dash line inFIG. 2, to be condensed into a condensation point Pb which is displaced by a predetermined angle to the left side inFIG. 2along the machining feed direction (X-axis direction) from the above-mentioned condensation point Pa.

On the other hand, in the case where a voltage of 5 V, for example, is impressed on the first deflection angle regulating means654and an RF having a frequency corresponding to 5 V is therefore impressed on the first acousto-optical device651, the pulsed laser beam oscillated from the pulsed laser beam oscillation means61is deflected as indicated by two-dotted chain line inFIG. 2, to be condensed into a condensation point Pc which is displaced by a predetermined amount to the right side inFIG. 2along the machining feed direction (X-axis direction) from the condensation point Pa. Further, in the case where a voltage of 0 V, for example, is impressed on the first deflection regulating means654of the first acousto-optical deflection means64and an RF having a frequency corresponding to 0 V is therefore impressed on the first acousto-optical device651, the pulsed laser beam oscillated from the pulsed laser beam oscillation means61is led to the laser beam absorbing means67, as indicated by broken line inFIG. 2. Thus, the laser beam deflected by the first acousto-optical device651is deflected in the machining feed direction (X-axis direction) correspondingly to the voltage impressed on the first deflection angle regulating means654.

Incidentally, like the first acousto-optical deflection means65, the second acousto-optical deflection means66can also deflect the pulsed laser beam oscillated from the pulsed laser beam oscillation means61, in the indexing feed direction (Y-axis direction; the direction perpendicular to the surface of the sheet ofFIG. 2) orthogonal to the machining feed direction (X-axis direction), by regulating the voltage impressed on the second deflection angle regulating means664and thereby regulating the frequency of the RF impressed on the second acousto-optical device661. Therefore, by operating the first acousto-optical deflection means65and the second acousto-optical deflection means66so as to sequentially deflect the pulsed laser beam in the X-axis direction and the Y-axis direction, it is possible to perform a trepanning process in which the spot S of the pulsed laser beam is moved in an annular pattern as shown inFIG. 3Bor the spot S of the pulsed laser beam is moved in a vortex pattern as shown inFIG. 3B.

Now, another embodiment of the laser beam scanning means64will be described below, referring toFIGS. 4 and 5. The laser beam scanning means64shown inFIGS. 4 and 5is composed of a galvano-scanner64a. The galvano-scanner64aconstituting the laser beam scanning means64is composed of a pair of a first mirror641and a second mirror642which are disposed in parallel and opposite to each other with a predetermined spacing therebetween as shown inFIG. 5, and an angle regulating actuator643for regulating the disposition angles of the first mirror641and the second mirror642. The angle regulating actuator643has its rotating shaft644connected on a power transmission basis to a connected part between the pair of the first mirror641and the second mirror642. The angle regulating actuator643is controlled by control means which will be described later, whereby the disposition angles of the pair of the first mirror641and the second mirror642are changed in the range from the condition indicated by dot-dash lines to the condition indicated by two-dotted chain lines. In the case where the pair of the first mirror641and the second mirror642are positioned in the condition indicated by solid lines inFIG. 4, the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61is condensed into a condensation point Pa, as indicated by solid line inFIG. 4.

Besides, in the case where the pair of the first mirror641and the second mirror642are positioned in the condition indicated by dot-dash lines inFIG. 4, the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61is condensed into a condensation point Pb which is displaced by a predetermined amount to the right side inFIG. 4along the machining feed direction (X-axis direction) from the above-mentioned condensation point Pa, as indicated by dot-dash line inFIG. 4. Further, in the case where the pair of first mirror641and the second mirror642are positioned in the condition indicated by two-dotted chain lines inFIG. 4, the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61is condensed into a condensation point Pb which is displaced by a predetermined amount to the left side inFIG. 4in the machining feed direction (X-axis direction) from the condensation point Pa, as indicated by two-dotted line inFIG. 4. Incidentally, by use of an fθ lens as the condenser lens632of the condenser63, the laser beams indicated by slid line, dot-dash line and two-dotted chain line inputted from the direction changing mirror631to the condenser lens632in parallel can be condensed in parallel. In addition, in the case where it is desired for the pulsed laser beam LB oscillate from the pulsed laser beam oscillation means61to be displaced also in the indexing feed direction (Y-axis direction; in the direction perpendicular to the surface of the sheet ofFIG. 2) orthogonal to the machining feed direction (X-axis direction), it suffices to dispose another galvano-scanner on the optical path, with a phase of 90 degrees relative to the galvano-scanner64a.

Returning toFIG. 2, the laser beam irradiation device52in the embodiment shown in the figure includes laser beam reshaping means68disposed between the output regulating means62and the laser beam scanning means64and operative to reshape the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator61into a top hat shape, and a collimation lens69disposed between the laser beam reshaping means68and the laser beam scanning means64and operative to correct the laser beam reshaped by the laser beam reshaping means68into a parallel laser beam. The laser beam reshaping means68in the embodiment shown inFIG. 2is composed of an aspherical lens681. The aspherical lens681reshapes the energy distribution of the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61from the Gaussian distribution into the top hat shape.

The collimation lens69is composed of a convex lens691in the embodiment shown inFIG. 2. The convex lens691is so disposed that the focal position of the convex lens691is positioned in the focal position of the aspherical lens681. More specifically, where the focal length (f1) of the aspherical lens681is 40 mm and the focal length (f2) of the convex lens691is 40 mm, the convex lens691is disposed at a position spaced from the aspherical lens681by a spacing (d1) of 80 mm. With the focal length (f1) of the aspherical lens681, the focal length (f2) of the convex lens691and the spacing (d1) between the aspherical lens681and the convex lens691set in this manner, the focal length of the lens set consisting of the aspherical lens681and the convex lens691becomes infinite, so that the laser beam reshaped by the aspehrical lens681serving as the laser beam reshaping means68is corrected into a parallel laser beam by the convex lens691.

Now, an embodiment in which the collimation lens69is composed of a concave lens692will be described below, referring toFIG. 7. In the case where the collimation lens69is composed of the concave lens692and where the focal length (f1) of the aspherical lens681is 40 mm and the focal lens (f3) of the concave lens692is −30 mm, the concave lens692is disposed at a position spaced from the aspherical lens681by a spacing (d2) of 10 mm. With the focal length (f1) of the aspherical lens681, the focal length (f3) of the concave lens692and the spacing (d2) between the spherical lens681and the concave lens692set in this manner, the focal length of the lens set consisting of the aspherical lens681and the concave lens692becomes infinite, so that the laser beam reshaped by the aspherical lens681serving as the laser beam reshaping means68is corrected into a parallel laser beam by the concave lens692. Incidentally, where the collimation lens69consists of the concave lens692, the spacing (d2) between the aspherical lens681and the concave lens692can be set small.

Now, another embodiment of the laser beam reshaping means68will be described below, referring toFIG. 8. The laser beam reshaping means68shown inFIG. 8is composed by use of a mask682provided with a hole682ahaving a diameter of φ500 μm, for example. When the mask682provided with the hole682ahaving a diameter of φ500 μm is thus used, only a central portion of the pulsed laser beam LB oscillated from the pulsed laser beam oscillation means61is permitted to pass through the hole682a, so that the energy distribution of the pulsed laser beam LB is reshaped into a top hat shape. In addition, a convex lens693as the collimation lens69is disposed so that the focal position of the convex lens693is positioned in the hole682aof the mask682. Specifically, in the case where the focal length (f4) of the convex lens693is 500 mm, the convex lens693is disposed at a position spaced from the mask682by a spacing (d3) of 500 mm. With the convex lens693as the collimation lens69thus disposed so that the focal position of the convex lens693is positioned in the hole682aof the mask682, the laser beam having passed through the hole682aof the mask682is corrected into a parallel laser beam by the convex lens693. Incidentally, in the embodiment shown inFIG. 8, let the focal length of the condenser lens652of the condenser63be f5, then the size of the image formed through condensation of light by the condenser lens632will be changed by a factor of f5/f4.

Returning toFIG. 1, the laser beam machining system in the embodiment shown in the figure includes image pickup means11disposed at a front end part of the casing521and operative to detect a work region to be subjected to laser beam machining by the laser beam irradiation device52. The image pickup means11includes not only an ordinary image pickup device (CCD) for imaging by use of visible rays but also infrared (IR) illumination means for irradiating the work with IR rays, an optical system for capturing the IR rays radiated by the IR illumination means, an image pickup device (IR CCD) for outputting an electrical signal corresponding to the IR rays captured by the optical system, and so on, and an image signal obtained through image pickup (imaging) is sent from the image pickup means11to control means which will be described later.

The laser beam machining system in the embodiment shown in the figure includes control means20. The control means20is composed of a computer, including a central processor unit (CPU)201for performing arithmetic processes according to a control program, a read-only memory (ROM)202storing the control program and the like, a random access memory (RAM)203capable of reading and writing of data for storing the results of arithmetic operations, etc., a counter204, an input interface205, and an output interface206. The input interface205of the control means20is supplied with detection signals from the machining feed amount detection means374, the indexing feed amount detection means384, the image pickup means11, etc. Control signals are outputted from the output interface of the control means20to the pulse motor372, the pulse motor382, the pulse motor432, the pulse motor532, the pulsed laser beam oscillation means61and the output regulating means62of the pulsed laser beam oscillation means52, the deflection angle regulating means654and the output regulating means655constituting the first acousto-optical deflection means65, the deflection angle regulating means664and second output regulating means665constituting the second acousto-optical deflection means66, etc. Incidentally, the random access memory (RAM)203includes a first storage region203afor storing design value data on the work which will be described later, and other storage areas.

The laser beam machining system in the embodiment shown in the figure is configured as above, and its operation will be described below, based on an example in which the laser beam irradiation means52shown inFIG. 2is provided.FIG. 9shows a plan view of a semiconductor wafer30as the work to be subjected to laser beam machining. The semiconductor wafer30shown inFIG. 9consists of a silicon wafer, of which the face side30ais provided with a plurality of regions demarcated by a plurality of planned split lines arranged in a lattice pattern, and devices302such as ICs and LSIs are formed respectively in the demarcated regions. All the devices302have the same configuration. Each of the device302is provided on its face side with a plurality of electrodes303(303ato303j) as shown inFIG. 10. Incidentally, in the embodiment shown in the figure, the electrodes303aand303f, the electrodes303band303g, the electrodes303cand303h, the electrodes303dand303i, and the electrodes303eand303jare so located that their positions in the X direction coincide with each other. In the portions of the plurality of electrodes303(303ato303j), via holes extending from the back side10bof the semiconductor wafer30to reach the electrodes303are formed.

The spacing A in the X direction (the left-right direction inFIG. 10) between the electrodes303(303ato303j) in each device302and the spacing B between the electrode303ein one device302and the nearest electrode303ain the other device302, of each pair of devices302adjacent to each other in the X direction (the left-right direction inFIG. 10) with the planned split line301therebetween, are respectively constant in the embodiment shown in the figure. In addition, the spacing C in the Y direction (the upper-lower direction inFIG. 10) between the electrodes303(303ato303j) in each device302and the spacing D between the electrode303f(303j) in one device302and the nearest electrode303a(303e) in the other device302, of each pair of devices302adjacent to each other in the Y direction (the upper-lower direction inFIG. 10) with the planned split line301therebetween, are respectively constant in the embodiment shown in the figure. For the semiconductor wafer30configured in this manner, design value data on the numbers of the devices302arranged in rows E1. . . En and columns F1. . . Fn shown inFIG. 9and on the above-mentioned spacings A, B, C, D are stored in the first storage region203aof the random access memory (RAM)203.

Now, an embodiment of the laser beam machining for forming machined holes (via holes) in the portions of the electrodes303(303ato303j) of each of the devices302formed on the semiconductor wafer30, by use of the laser beam machining system as above-described, will be described below. As shown inFIG. 11, the face side30aof the semiconductor wafer30configured as above-mentioned is adhered to a protective tape50composed of a sheet of a synthetic resin such as polyolefin and mounted to an annular frame40. Therefore, the back side30bof the semiconductor wafer30is set on the upper side. Of the semiconductor wafer30thus supported on the annular frame40through the protective tape50, the protective tape50side is mounted on the chuck table36of the laser beam machining system shown inFIG. 1. Then, the suction means (not shown) is operated, whereby the semiconductor wafer30is held by suction onto the chuck table36through the protective tape50. In addition, the annular frame40is fixed by the clamp362.

The chuck table36with the semiconductor wafer30held thereon by suction as above-mentioned is positioned directly under the image pickup means11by the machining feeding means37. When the chuck table36is positioned directly under the image pickup means11, the semiconductor wafer30on the chuck table36is in the state of being positioned at a position in a coordinate system shown inFIG. 12. Under this condition, an alignment operation is carried out to ensure that the planned split lines301formed in a lattice pattern in the semiconductor wafer30held on the chuck table301are set in parallel to the X-axis direction and the Y-axis direction. More specifically, the semiconductor wafer30held on the chuck table36is imaged by the image pickup means11, and image processing such as pattern matching is conducted, to thereby perform the alignment operation. In this case, though the face side301aprovided with the planned split lines301of the semiconductor wafer30is located on the lower side, the planned split lines301can be imaged on a see-through basis on the side of the back side301bof the semiconductor wafer30, since the image pickup means11has the image pickup means including the IR illumination means, the optical system for capturing the IR rays, the image pickup device (IR CCD) for outputting an electrical signal corresponding to the IR rays captured, and the like.

Next, the chuck table36is moved so that the device302at the leftmost end inFIG. 12in the uppermost row E1of the devices302formed on the semiconductor wafer30is positioned directly under the image pickup means11. Then, further, the electrode303aat the leftmost uppermost position inFIG. 12of the electrodes303(303ato303j) formed on the device302thus positioned is positioned directly under the image pickup means11. Under this condition, when the electrode303athus positioned is detected by the image pickup means11, the coordinate data (a1) thereof are sent to the control means20as first machining feed starting position coordinate data. The control means20stores the coordinate data (a1) into the random access memory (RAM)203as the first machining feed starting position coordinate data (machining feed starting position detection step). In this case, since the image pickup means11and the condenser63of the laser beam irradiation means52are disposed with a predetermined spacing therebetween in the X-axis direction, an X coordinate obtained by adding the spacing between the image pickup means11and the condenser63to the X coordinate in the detected coordinate data is stored.

When the first machining feed starting position coordinate data (a1) in the device302in the uppermost row E1inFIG. 12is detected in this manner, the chuck table36is index fed in the Y-axis direction by the spacing of the planned split lines301and is moved in the X-axis direction, whereby the device302at the leftmost end in the second uppermost row E2inFIG. 12is positioned directly under the image pickup means11. Then, further, the electrode303aat the leftmost uppermost position inFIG. 12of the electrodes303(303ato303j) formed on the device302thus positioned is positioned directly under the image pickup means11. Under this condition, when the electrode303athus positioned is detected by the image pickup means11, the coordinate data (a2) thereof are sent to the control means20as second machining feed starting position coordinate data. Then, the control means20stores the coordinate data (a2) into the random access memory (RAM)203as second machining feed starting position coordinate data. In this case, since the image pickup means11and the condenser63of the laser beam irradiation means52are disposed with a predetermined spacing therebetween in the X-axis direction as above-mentioned, an X coordinate obtained by adding the spacing between the image pickup means11and the condenser63to the X coordinate in the detected coordinate data is stored. Thereafter, the control means20repeatedly performs the indexing feed and the machining feed starting position detection step for all the rows ranging to the lowermost row En, detects the machining feed starting position coordinate data (a3to an) on the devices302formed in each of the rows, and stores the detected data into the random access memory (RAM)203.

Next, a boring step is carried out for boring laser beam-machined holes (via holes) in the portions, corresponding to the electrodes303(303ato303j) formed on each of the devices302, of the semiconductor wafer30. In carrying out the boring step, first, the machining feeding means37and the first indexing feeding means38are operated to move the chuck table36, whereby the portion corresponding to the first machining feed starting position coordinate data (a1) stored in the random access memory (RAM)203is positioned directly under the condenser63of the laser beam irradiation means52. The condition where the portion corresponding to the first machining feed starting position coordinate data (a1) is thus positioned directly under the condenser63is shown inFIG. 13A. Starting from the condition shown inFIG. 13A, the control means20controls the machining feeding means37so as to perform machining feeding of the chuck table36at a predetermined velocity in the direction indicated by arrow X1inFIG. 13Aand, simultaneously, operates the laser beam irradiation means52so as to perform irradiation with a pulsed laser beam through the condenser63for a predetermined time. The energy density of the pulsed laser beam is desirably set at such a value that the semiconductor substrate of silicon or the like can be machined efficiently but bonding pads303are not machined easily, i.e., at a value of 40 to 20 J/cm2.

Incidentally, the condensation point P of the laser beam radiated through the condenser63is adjusted to the vicinity of the face side30aof the semiconductor wafer30. During the predetermined time for which the irradiation with the pulsed laser beam is conducted, the control means20outputs control signals for controlling the first deflection angle regulating means654and the first output regulating means655of the first acousto-optical deflection means65based on a detection signal sent from a reading head374bof the machining feed amount detection means374. Specifically, the control means20outputs such a control signal as to output a driving pulse signal (DS) in the range of 5 to 15 V to the first deflection angle regulating means654. Incidentally, in the boring step in the embodiment shown, the pulsed laser beam is not deflected in the Y-axis direction; therefore, the control means20outputs such a control signal as to impress a voltage of 0 V on the second deflection angle regulating means664of the second asousto-optical deflection means66.

On the other hand, the first RF oscillator652outputs an RF corresponding to control signals from the first deflection angle regulating means654and the first output regulating means655. The power of the RF outputted from the first RF oscillator652is amplified by the first RF amplifier653, before being impressed on the first acousto-optical device651. In addition, the second RF oscillator662also outputs an RF corresponding to control signals from the second deflection angle regulating means664and the second output regulating means665. The power of the RF outputted from the second RF oscillator662is amplified by the second RF amplifier663, before being impressed on the second acousto-optical device661. As a result, the first acousto-optical device651and the second acousto-optical device661deflect the pulsed laser beam, which is oscillated from the pulsed laser beam oscillation means61, within the range from the position indicated by dot-dash line inFIG. 2to the position indicated by two-dotted chain line inFIG. 2.

An example of the machining conditions in the above-mentioned boring step will be described below.

Light source: LD excited Q switch Nd:YVO4

When the boring step is carried out under these machining conditions, a laser beam-machined hole with a depth of about 5 μm per pulse of the pulsed laser beam can be bored in the silicon wafer. Therefore, in order to provide a 50 μm-thick silicon wafer with a machined hole reaching the electrode303, it is necessary to irradiate the wafer with 10 pulses of the pulsed laser beam. Thus, in the above-mentioned machining conditions, the portion, corresponding to the first machining feed starting position coordinate data (a1), of the semiconductor wafer30held on the chuck table36being moved at a machining feed velocity of 300 mm/sec is irradiated with 10 pulses of the pulsed laser beam, whereby a laser beam-machined hole (via hole) reaching the electrode303can be formed in the semiconductor wafer30.

Here, a method for irradiating the portion, corresponding to the first machining feed starting position coordinate data (a1), of the semiconductor wafer30with 10 pulses of the pulsed laser beam in moving the semiconductor wafer30at a machining feed velocity of 300 mm/sec will be described, referring toFIGS. 14Aand14B. In the above-mentioned machining conditions, the cycle frequency of the pulsed laser beam is 50 kHz, so that irradiation with 50000 pulses of the pulsed laser beam takes place in one second (50000 pulses/sec). Therefore, the time taken for irradiation with 10 pulses of the pulsed laser beam is 1/5000 sec. On the other hand, the semiconductor wafer30being moved in the direction indicated by arrow X1at a machining feed velocity of 300 mm/sec is moved by 60 μm in 1/5000 sec. Therefore, it suffices to perform such a control that the laser beam irradiation means52is operated for 1/5000 sec during the movement of the semiconductor wafer30by 60 μm, and, during this period, the first deflection angle regulating means654and the first output regulating means655of the first acousto-optical deflection means65and the second deflection angle regulating means664and the second output regulating means665of the second acousto-optical deflection means66are controlled so that the condensation point of the pulsed laser beam is kept positioned at the position corresponding to the first machining feed starting position coordinate data (a1).

The above-mentioned control can be achieved by a method in which, based on the detection signal from the reading head374bof the machining feed amount detection means374as above-mentioned, the control means20controls the voltages to be impressed on the first deflection angle regulating means654and the first output regulating means655of the first acousto-optical deflection means65and on the second deflection angle regulating means664and the second output regulating means665of the second acousto-optical deflection means66, thereby controlling the frequencies of the RF powers impressed on the first acousto-optical device651of the first acousto-optical deflection means65and the second acousto-optical device661of the second acouto-optical deflection means66. As a result, even in the condition where the semiconductor wafer30is being moved in the machining feed direction X1, the wafer portion corresponding to the first machining feed starting position coordinate data (a1) can be irradiated with the 10 pulses of the pulsed laser beam, so that the laser beam-machined hole304reaching the electrode303can be formed in the semiconductor wafer30at the position corresponding to the first machining feed starting position coordinate data (a), as shown inFIG. 14B. After the wafer portion corresponding to the first machining feed starting position coordinate data (a1) is thus irradiated with the 10 pulses of the pulsed laser beam, the control means20impresses a voltage of 0 V on the first deflection angle regulating means654of the first acousto-optical deflection means65, whereby an RF with a frequency corresponding to 0 V is impressed on the first acousto-optical device651, and the pulsed laser beam oscillated from the pulsed laser beam oscillation means61is led to the laser beam absorbing means67, as indicated by broken line inFIG. 2.

On the other hand, the control means20is being supplied with a detection signal from the reading head374bof the machining feed amount detection means374, and the detection signal is being counted by the counter204. When the count obtained by the counter204has reached a value corresponding to the interval A in the X-axis direction inFIG. 10of the electrodes303, the control means20controls the laser beam irradiation means52so as to perform the above-mentioned boring step. Thereafter, also, each time the count obtained by the counter204has reached the intervals A and B in the X-axis direction inFIG. 10of the electrodes303, the control means20operates the laser beam irradiation means52so as to perform the boring step. When the boring step has been carried out at the position of the electrode303eat the rightmost end inFIG. 13Bof the electrodes303formed on the device302at the rightmost end in the row E1on the semiconductor wafer30as shown inFIG. 13B, the operation of the machining feeding means37is stopped, thereby stopping the movement of the chuck table36. As a result, the semiconductor wafer30is provided with the laser beam-machined holes304at the portions corresponding to the electrodes303(not shown) as shown inFIG. 13B. The energy distribution of the pulsed laser beam used for irradiation in the boring step is reshaped into the top hat shape by the aspherical lens681serving as the laser beam reshaping means68, so that the energy distribution at the tip of the laser beam is uniform. Therefore, the laser beam-machined holes304reaching the electrodes303can be formed in the substrate of the wafer, without boring any hole in the electrodes303.

Next, the control means20controls the first indexing feeding means38so that the condenser63of the laser beam irradiation means52is put into indexing feeding in the direction orthogonal to the surface of the sheet ofFIG. 13B. On the other hand, the control means20is being supplied with a detection signal from the reading head384bof the indexing feed amount detection means384, and the detection signal is being counted by the counter204. When the count obtained by the counter204has reached a value corresponding to the interval C in the Y-axis direction inFIG. 10of the electrodes303, the operation of the first indexing feeding means38is stopped, thereby stopping the indexing feeding of the condenser63of the laser beam irradiation means52. As a result, the condenser63is positioned directly above the electrode303j(seeFIG. 10) opposite to the above-mentioned electrode303e. This condition is shown inFIG. 15A.

In the condition shown inFIG. 15A, the control means20controls the machining feeding means37so as to perform machining feeding of the chuck table36at a predetermined moving velocity in the direction indicated by arrow X2inFIG. 15Aand, simultaneously, operates the laser beam irradiation means52so as to carry out the boring step. Then, the control means20causes the counter204to count the detection signal sent from the reading head374bof the machining feed amount detection means374as above-mentioned, and, each time the count has reached the intervals A and B in the X-axis direction inFIG. 10of the electrodes303, the control means20operates the laser beam irradiation means52so as to carry out the boring step. When the boring step has been carried out at the position of the electrode303fformed on the device302at the rightmost end in the row E1on the semiconductor laser30as shown inFIG. 15B, the operation of the machining feeding means37is stopped, thereby stopping the movement of the chuck table36. As a result, the semiconductor wafer30is provided with the laser beam-machined holes304at the portions corresponding to the electrodes303as shown inFIG. 15B.

When the via holes304have thus been formed at the portions, corresponding to the electrodes303formed on the devices302in the row E1, of the semiconductor wafer30, the control means20operates the machining feeding means37and the first indexing feeding means38so that the portion, corresponding to the second machining feed starting position coordinate data (a2) stored in the random access memory (RAM)203of the electrode303formed on the device302in the row E2, of the semiconductor wafer30is positioned directly under the condenser63of the laser beam irradiation means52. Then, the control means20controls the laser beam irradiation means52, the machining feeding means37and the first indexing feeding means38so as to carry out the boring step for boring via holes in the semiconductor wafer30at the positions of the electrodes303formed on the devices302in the row E2. Thereafter, the boring step is carried out for boring via holes in the semiconductor wafer30at the positions of the electrodes303formed on the devices302in the rows E3to En. As a result, the laser beam-machined holes304are formed in the semiconductor wafer30at the positions of all the electrodes303formed on the devices302.

Incidentally, in the boring step, irradiation of the semiconductor wafer30with the pulsed laser beam is not conducted for the regions of the intervals A and the regions of the intervals B in the X-axis direction inFIG. 10. For not performing the irradiation of the semiconductor wafer30with the pulsed laser beam in this manner, the control means20impresses a voltage of 0 V on the first deflection angle regulating means654of the first acousto-optical deflection means65. As a result, an RF with a frequency corresponding to 0 V is impressed on the first acousto-optical device651, whereby the pulsed laser beam (LB) oscillated from the pulsed laser beam oscillation means61is led to the laser beam absorbing means67as indicated by broken line inFIG. 2, so that the semiconductor wafer30is not irradiated with the pulsed laser beam.

Now, another embodiment of laser beam machining conducted by operating the first acousto-optical deflection means65and the second acousto-optical deflection means66of the laser beam irradiation means52will be described below, referring toFIGS. 16A and 16B. In the condition where the work held on the chuck table36is subjected to machining feeding, the first acousto-optical deflection means65and the second acousto-optical deflection means66are operated so as to sequentially deflect the pulsed laser beam in the X-axis direction and in the Y-axis direction and to regulate the output of the pulsed laser beam, thereby irradiating the work with the pulsed laser beam. As a result, two-dimensional machining such as trepanning is applied to the work so as to form a plurality of via holes304, as shown inFIG. 16A, whereby a hole305with a desired size can be opened in the work, as shown inFIG. 16B. Even in the case where the hole305with a desired size is opened by the trepanning process in this manner, the energy distribution at the tip of the laser beam is uniform, since the energy distribution of the pulsed laser beam used for irradiation has been reshaped into the top hat shape by the aspherical lens681serving as the laser beam reshaping means68. Therefore, the laser beam-machined holes304reaching the electrodes303can be formed in the substrate of the wafer, without opening any hole in the electrodes303.

While examples of forming laser beam-machined holes by use of the laser beam machining system according to the present invention have been shown above, the laser beam machining system of the present invention is suitable for forming a laser beam-machined groove or grooves having a uniform depth over the whole width thereof, or for removing an insulating film coating the surface of a wafer, by a predetermined width, without damaging the wafer.