SLOTTING TOOL, AND THIN FILM SOLAR CELL SLOTTING METHOD AND SCRIBING DEVICE USING SAME

Technical Field

The present invention relates to a slotting tool, a slotting method and a scribing device using the slotting tool when an integrated thin film solar cell, such as a chalcopyrite compound-based integrated thin film solar cell, is manufactured.

Here, chalcopyrite compounds include CIGSS (Cu(In, Ga)(Se, S)₂) and CIS (CuInS₂) in addition to CIGS (Cu(In, Ga)Se₂).

Background Art

Thin film solar cells using a chalcopyrite compound semiconductor as a light absorbing layer generally have an integrated structure where a number of unit cells are connected in series on a substrate.

A conventional manufacturing method for a chalcopyrite compound-based integrated thin film solar cell is described below. Figs 6(a) to 6(c) are schematic diagrams showing the manufacturing steps for a CIGS thin film solar cell. First, as shown in Fig 6(a), an Mo electrode layer 2, which is to become a lower electrode on the + side, is formed on an insulating substrate 1 made of soda lime glass (SLG) or the like in accordance with a sputtering method, and after that a slot S for separating lower electrodes is created by carrying out a scribing process on the thin film solar cell substrate before a light absorbing layer is formed.

Next, as shown in Fig 6(b), a light absorbing layer 3 made of a compound semiconductor (CIGS) thin film is formed on the Mo electrode layer 2 in accordance with a vapor deposition method, a sputtering method or the like, on top of this a buffer layer 4 is formed of a ZnS thin film or the like for heterojunction in accordance with a CBD method (chemical bath deposition method), and on top of this an insulating layer 5 is formed of a ZnO thin film. Then, a slot M1 for a contact between electrodes, which reaches the Mo electrode layer 2, is created in accordance with a scribing process in the thin film solar cell substrate before a transparent electrode layer is formed at a location away from the slot S for separating lower electrodes by a predetermined distance to the side.

Next, as shown in Fig 6(c), a transparent electrode layer 6 made of a ZnO:Al thin film is formed on top of the insulating layer 5 as an upper electrode so as to provide a solar cell substrate with function layers required for power generation using photovoltaic conversion, and then a slot M2 for separating electrodes, which reaches the Mo electrode layer 2 in the lower portion, is created in accordance with a scribing process.

During the above described process for manufacturing an integrated thin film solar cell, a laser scribing method and a mechanical scribing method have been used as the technology for creating slots M1 and M2 for separating electrodes through a scribing process.

In accordance with a laser scribing method, as disclosed in Patent Document 1, for example, a slot for separating electrodes is created through irradiation with a laser beam emitted by exciting an Nd:YAG crystal by means of a continuous discharge lamp, such as an arc lamp. In the case where a slot is created in a thin film solar cell substrate after the formation of a light absorbing layer in accordance with this method, however, there is a risk that the photovoltaic conversion properties of the light absorbing layer 3 may deteriorate due to the heat from the laser beam while scribing.

As disclosed in Patent Documents 2 and 3, for example, mechanical scribing methods relate to a technology for creating a slot for separating electrodes by moving the cutting edge of a slotting tool, such as a metal needle with the tip being tapered, while being pressed against the substrate with a predetermined amount of pressure. Currently, such a mechanical scribing method is widely used.

Prior Art Documents

Patent Documents

• Patent Document 1: Japanese Unexamined Patent Publication H11 (1999)-312815
• Patent Document 2: Japanese Unexamined Patent Publication 2002-094089
• Patent Document 3: Japanese Unexamined Patent Publication 2004-115356

Summary of the Invention

Problem to Be Solved by the Invention

In the mechanical scribing methods as disclosed in Patent Documents 2 and 3, the cutting edge of a slotting tool is tapered as a needle, and strictly speaking, the tip to be pressed against thin film solar cells is approximately horizontally flat so as to provide a wide contact area. That is to say, as shown in Fig 7, the tip is in a truncated cone form. A slotting tool 8' having such a form is moved in the direction Y along a line to be scribed while being pressed against a thin film (any type of functional layer, such as an upper or lower electrode or a light absorbing layer) on a thin film solar cell substrate in which a slot is to be created, and thus a slot is created.

Since a slotting tool with the tip portion being in a truncated cone form is used so as to provide a large contact area with the thin film, a slot can be created relatively stably. Meanwhile, the thin film can be greatly and irregularly peeled due to friction resistance through the large contact area and an unnecessary portion may be removed, which may lead to such a problem that the properties and the yield of the solar cell may lower.

It is necessary to make the degree of peeling of a thin film constant, particularly in order to make the quality of the product (efficiency in photovoltaic conversion and the like) fit its design and in order to make the reproducibility high by keeping the width of the scribe line constant. In order to do so, the degree of peeling can be adjusted to a certain extent by adjusting the load under which the cutting edge is pressed in accordance with the properties of the thin film. However, the pressure against the surface of the thin film changes uniformly, and thus fine adjustment is very difficult.

In addition, the above described cutting edge of the slotting tool is in a truncated cone form having a tapered surface. Accordingly, in the case where the cutting edge that has been worn down or chipped is ground, the diameter of the cutting edge may increase, and as a result the width of the scribed slot may be greater than that before grinding. Therefore, the same cutting edge cannot be used over a long period of time or repeatedly, and thus there is a problem that it is wasteful.

Thus, an object of the present invention is to provide a slotting tool with which a slot with a constant width can be created and products can be processed while keeping the quality, such as efficiency in photovoltaic conversion, uniform and with a high yield when slots for separating electrodes are created in a chalcopyrite compound-based integrated thin film solar cell substrate (for example, a precursor before the formation of a transparent electrode) and other integrated thin film solar cells, or slots for a contact between upper and lower electrodes are created in any type of functional layer, such as a light absorbing layer formed between upper and lower electrodes.

Means for Solving Problem

In order to achieve the above described object, the slotting tool for an integrated thin film solar cell according to the present invention is formed of: a body in rod form; and a cutting edge region formed at a tip of the body, wherein the cutting edge region is formed of a long, rectangular bottom, a front surface and a rear surface which rise from the short sides of the bottom, and a pair of sides, left and right sides, which rise at a right angle from the long sides of the bottom and are parallel to each other, and the corner formed of either a front or rear side and the bottom is used as a cutting edge.

In addition, in order to achieve the above described object, in accordance with the method for slotting an integrated thin film solar cell according to the present invention, a slotting tool is moved over an integrated thin film solar cell substrate along a line to be scribed on the above described solar cell substrate with the cutting edge of the slotting tool being pressed against the above described solar cell substrate so that a scribe line is created on the above described solar cell (for example, any type of functional layer at least including a light absorbing layer, in particular any functional layer that includes at least a light absorbing layer of the precursor before the formation of a transparent electrode layer), wherein the above described slotting tool comprises: a body in rod form; and a cutting edge region formed at a tip of the body, wherein the cutting edge region is formed of a long, rectangular bottom, a front surface and a rear surface which rise from the short sides of the bottom, and a pair of sides, left and right sides, which rise at a right angle from the long sides of the bottom and are parallel to each other, and the corner formed of either a front or rear side and the bottom is used as a cutting edge, and the long axis of the rectangular bottom is in the direction in which the above described slotting tool is moved, and the above described slotting tool is inclined in the direction in which the above described slotting tool is moved so that the angle formed between the front or rear surface of the cutting edge region and the surface of the solar cell to be processed is in a range from 50 degrees to 80 degrees, preferably from 65 degrees to 75 degrees.

Effects of the Invention

The slotting tool according to the present invention makes it possible to create a slot with a constant width when a slot for separating electrodes is created in an integrated thin film solar cell, or a slot for a contact between upper and lower electrodes is created in any type of functional layer, such as a light absorbing layer formed between upper and lower electrodes, and thus the yield increases. In the case where the cutting edge is worn down, the cutting edge can be repaired by grinding the bottom and the front or rear surface, if necessary. In particular, the left and right sides of the cutting edge portion are parallel to each other, and therefore the width between the left and right side of the blade does not change even if the bottom is ground. As a result, the width of the scribed slot can be kept the same as that before grinding.

Furthermore, in the case where two cutting edges are formed at the front and rear corners of the slotting tool, the direction in which the tool is attached is changed when one cutting edge is worn down or broken so that the other cutting edge can be used as a new cutting edge.

In accordance with the method for manufacturing an integrated thin film solar cell according to the present invention, a slotting tool in such a form that cutting edges are formed at the corners between the bottom and the front surface as well as between the bottom and the rear surface is used for patterning, and therefore the front or rear surface of the slotting tool is inclined relative to the substrate in the direction in which the slotting tool is moved so that the cutting edges at the corners make contact with the substrate through linear contact, which is close to point contact, and thus the thin film can be peeled smoothly. In particular, the front or rear surface of the cutting edge portion of the slotting tool is inclined towards the direction in which the slotting tool is moved in such a manner that the angle between the front or rear surface and the upper surface of the substrate is within a range from 50 degrees to 80 degrees, preferably from 65 degrees to 75 degrees, and thus a linear and clean scribe line can be created without interruptions due to the bouncing of the cutting tool when it rides on shavings of the film (in the case where the angle of inclination is smaller than the above described set range of values) or without irregular peeling of the thin film due to a high load for pressing (in the case where the angle of inclination is greater than the above described set range of values).

It is preferable for the angle of the cutting edges formed between the bottom and the front surface as well as between the bottom and the rear surface of the slotting tool to be a right angle. When a cutting edge that has been worn down is ground, it can be ground at a right angle relative to the axis of the body so that the bottom and the front and rear surfaces form right angles, and therefore grinding becomes easy

It is preferable for the slotting tool to be formed of a hard metal or diamond.

This makes it possible for the life of the tool to be long with little deformation, and therefore a scribing process with high precision is possible over a long period of time.

Brief Description of the Drawings

• Fig 1 is a perspective diagram showing a scribing device for an integrated thin film solar cell according to one embodiment of the present invention;
• Fig 2 is a perspective diagram showing the slotting tool according to the present invention;
• Fig 3 is a diagram showing an enlargement of the bottom of the above described slotting tool;
• Figs 4(a) to 4(c) are schematic diagrams showing the angles of inclination at which the slotting tool according to the present invention is attached and the corresponding states of the solar cell substrate on which a scribe line is created;
• Fig 5 is a diagram showing the comparison of the states of the solar cell substrate in which scribe lines are created using a conventional slotting tool and the slotting tool according to the present invention;
• Figs 6(a) to 6(c) are schematic diagrams showing the steps of manufacturing a general CIGS-based thin film solar cell;
• Fig 7 is a perspective diagram showing an example of a conventional slotting tool;
• Fig 8 is a perspective diagram showing the slotting tool according to another embodiment of the present invention;
• Fig 9 is a perspective diagram showing an enlargement of the bottom of the slotting tool in Fig 8;
• Fig 10 is a diagram showing an enlargement of the bottom of the slotting tool in Fig 8;
• Figs 11(a) and 11(b) are diagrams showing the state of a cutting edge portion during scribing;
• Fig 12 is a perspective diagram showing the slotting tool according to still another embodiment of the present invention; and
• Fig 13 is a perspective diagram showing an enlargement of the bottom of the slotting tool in Fig 12.

Best Mode for Carrying Out the Invention

(First Embodiment)

In the following, the present invention is described in detail in reference to the drawings showing the preferred embodiments.

Fig 1 is a perspective diagram showing a scribing device SC for an integrated thin film solar cell using the slotting tool according to an embodiment of the present invention. The scribing device SC is provided with a table 18 which is moveable in the lateral direction (direction Y) and rotatable by 90 degrees and by an angle θ in the horizontal plane, where the table 18 basically forms a means for holding a solar cell substrate W.

A bridge 19 that goes over the table 18 is formed of supports 20 and 20 on both sides of the table 18 and a guide bar 21 that runs in the direction X. A holder support 23 is attached so as to be moveable along the guide 22 formed on the guide bar 21 and moves in the direction X when the motor 24 is driven.

The holder support 23 is provided with a scribing head 7, and a holder 9 for holding a slotting tool 8 that scribes the surface of the thin film on a solar cell substrate W mounted on the table 18 is provided to the bottom of the scribing head 7. The angle at which the holder 9 is attached to the scribing head 7 can be adjusted, and the angle between the slotting tool 8 and the solar cell substrate W can be adjusted by adjusting this angle of attachment.

In addition, cameras 10 and 11 are respectively provided to bases 12 and 13, which are moveable in the directions X and Y. The bases 12 and 13 move along the guide 15 that runs in the direction X on top of a support 14. The cameras 10 and 11 can be manually operated in order to be moved upwards and downwards so that the focus of images can be adjusted. The images taken by the cameras 10 and 11 are displayed on monitors 16 and 17.

An alignment mark for positioning is provided on the surface of the solar cell substrate W mounted on the table 18, and the position of the solar cell substrate W can be adjusted by taking images of the alignment mark with cameras 10 and 11. Concretely, images of the alignment mark on the surface of the solar cell substrate W supported by the table 18 are taken with cameras 10 and 11 so that the location of the alignment mark is identified. On the basis of the identified location of the alignment mark on the surface of the solar cell substrate W, the direction of the misalignment when the solar cell substrate W is mounted is detected, and the misalignment is rectified by rotating the table 18 by an appropriate angle.

Whenever the table 18 is moved in the direction Y by a predetermined pitch, the scribing head 7 is lowered so that the cutting edge of the slotting tool 8 is pressed against the surface of the solar cell substrate W, and the scribing head 7 is moved in the direction X in this state, and thus the surface of the solar cell substrate W is scribed in the direction X. In the case where the surface of the solar cell substrate W is scribed in the direction Y, the table 18 is rotated by 90 degrees, and then the same operation as in the above is carried out.

Figs 2 and 3 show the slotting tool 8 used in the present invention. Fig 2 is a perspective diagram as viewed from the bottom, and Fig 3 is a diagram showing an enlargement of the bottom of the slotting tool 8. This slotting tool 8 has a body 81 in cylindrical form, which basically becomes an attachment portion to the scribing head 7, and a cutting edge region 82 integrally formed in this tip portion through a discharging process or the like, and is made of a hard material, such as a hard metal or diamond. The cutting edge region 82 has a rectangular bottom 83, a front surface 84 and a rear surface 85 that rides at a right angle from the short sides of the bottom 83, and the left and right sides 88 and 89 that ride at a right angle from the long sides of the bottom 83 are parallel to each other. The corners formed between the bottom 83 and the front surface 84 as well as between the bottom 83 and the rear surface 85 provide cutting edges 86 and 87, respectively.

It is preferable for the width L1 between the left and right of the bottom 83 to be 50 µm to 60 µm, but it is possible for it to be 25 µm to 80 µm in accordance with the width of the scribed slot, if necessary. In addition, it is preferable for the effective height of the cutting edge region 82, that is to say, the height L2 of the left and right sides 88 and 89 as well as the front and rear surfaces 84 and 85 of the cutting edge region, to be approximately 0.5 mm. Furthermore, it is preferable for the diameter of the body 81 in cylindrical form to be approximately 2 mm to 3 mm. Here, the body 81 of the slotting tool 8 is not limited to a cylindrical form, and it is possible for it to be quadrilateral or polygonal in the cross section.

In the case where the above described slotting tool 8 is used for processing, the slotting tool 8 is attached to the scribing head 7 in such a state that the long axis of the bottom 83 of the cutting edge region 82 is directed in the direction in which the tool moves and the front surface 84 or the rear surface 85 of the cutting edge portion 82 is inclined by a predetermined angle relative to the solar cell substrate W. In this case, it is preferable for the angle of inclination to be in a range from 50 degrees to 80 degrees, and it is more preferable for it to be in a range from 65 degrees to 75 degrees.

Figs 4(a) to 4(c) are schematic diagrams showing the results of the experiment of slotting a solar cell substrate W using a slotting tool 8 in terms of the relationship between the angle at which the slotting tool 8 was attached and the state of the processed solar cell substrate W.

• Fig 4(a) shows the results of scribing when the slotting tool 8 was attached at a preferable angle of inclination in a range from 50 degrees to 80 degrees or in a more preferable range from 65 degrees to 75 degrees. The slot M created in the solar cell substrate W was linear and clear along the scribe line without extra peeling.
• Fig 4(b) shows the results of scribing when the slotting tool 8 was attached at an angle of inclination of less than 50 degrees. The cutting edge of the slotting tool 8 rode on shavings of the film and bounced, and as a result the processed slot M had an interruption.
• Fig 4(c) shows the results of scribing when the slotting tool 8 was attached at an angle of inclination that exceeded 80 degrees. The processed slot M had irregular peeling of the thin film due to the high load for pressing the slotting tool 8.

According to the present invention, the front surface 84 or the rear surface 85 of the slotting tool 8 is inclined in the direction in which the slotting tool 8 moves relative to the solar cell substrate W so that the corner formed between the front surface and the bottom surface or between the rear surface and the bottom, that is to say, the cutting edge 86 or the cutting edge 87, makes contact with the solar cell substrate W through line contact, which is close to point contact, and thus the thin film can be peeled smoothly. In particular, the slotting tool 8 is inclined in the direction in which the slotting tool 8 moves so that the angle between the front surface 84 or the rear surface 85 in the cutting edge region and the upper surface of the substrate W is within a range from 50 degrees to 80 degrees, preferably from 65 degrees to 75 degrees, and thus it becomes possible to create a linear and clean scribe line without interruptions due to the bouncing of the cutting tool when it rides on shavings of the film or without irregular peeling of the thin film due to a high load for pressing.

In addition, the slotting tool 8 has two cutting edges 86 and 87 in the front and rear corners, and therefore the direction in which the slotting tool 8 is attached is changed when one cutting edge is worn down or broken so that the other cutting edge can be used as a new cutting edge. Furthermore, the bottom 83 as well as the front and rear surfaces 84 and 85, if necessary, can be ground so as to repair the cutting edges in the case where the two cutting edges are worn down.

Fig 5 is an image where scribe lines created using a conventional slotting tool and scribe lines created using the slotting tool according to the present invention are compared. In the case where the slotting tool according to the present invention was used for scribing at an angle of inclination in a range from 65 degrees to 75 degrees, it was obvious that clean scribe lines with a constant width were created in comparison with the prior art.

Though in the above described embodiment the scribing process was carried out by moving the scribing head 7 in the direction X, the same scribing process is possible as long as either the scribing head 7 or the solar cell substrate W moves relative to the other. The scribing head 7 may be moved in the direction X or Y with the solar cell substrate W being in a fixed state, or only the solar cell substrate W may be moved in the direction X or Y without moving the scribing head 7.

Though a representative embodiment of the present invention is described in the above, the present invention is not necessarily limited to the structure in the above described embodiment and may be modified. For example, the angle of the cutting edges formed between the bottom and the front surface as well as between the bottom and the rear surface may be slightly obtuse, though a right angle is preferable as described in the above embodiment.

(Second Embodiment)

Next, a slotting tool that is a modification of that of the first embodiment is described. As described in reference to Figs 4(a) to 4(c), the slotting tool 8 shown in Figs 2 and 3 is inclined when scribing so that the angle formed between the front surface 84 of the slotting tool 8 and the surface to be processed (scribing angle) is within an appropriate angle range, and thus a continuous slot with a constant width can be created.

In the case where the slotting tool 8 is new, however, the thin film adjacent to the slot sometimes peels, causing the width of the slot to be partially wider even when the scribing angle is set to an appropriate value for use. Furthermore, Mo films tend to scratch relatively easily. In the case where the slotting tool 8 is not new, a similar problem arises once in a while.

Thus, the slotting tool 8 is further improved, and a slotting tool having such a structure that a slot with a constant width can be created stably while preventing the thin film adjacent to the slot from being peeled and the film in the layer below the thin film to be slotted is hardly scratched is prepared.

The slotting tool according to the second embodiment of the present invention is made of: a body in rod form; and a cutting edge region in rectangular parallelepiped form formed at a tip of the body, wherein the cutting edge region is formed of five planes: a rectangular bottom surrounded by a pair of short sides and a pair of long sides; front and rear surfaces rising at a right angle relative to the bottom from the two short sides of the bottom; and left and right sides rising at a right angle relative to the bottom from the two long sides of the bottom, cutting edges in the longitudinal direction are formed at the corner between the front surface and the right side as well as at the corner between the front surface and the left side, a cutting edge in the lateral direction is formed at the corner between the bottom and the front surface, and the corner between the bottom and the right side as well as the corner between the bottom and the left side are rounded.

Thus, the slotting tool according to the present invention is used for slotting in such a manner that the slotting tool is inclined in the direction in which the slotting tool moves so that the cutting edge in the corner between the front surface and the bottom is made to make contact with a surface to be processed for scribing in such a state as being pressed.

In the slotting tool according to the second embodiment, the corner between the bottom and the right side and the corner between the bottom and the left side are rounded, and thus these corners are not sharp enough to peel the thin film when these corners make contact with the thin film during scribing, and therefore a clean linear slot can be created.

Concretely, the thin film can be completely prevented from being irregularly peeled (see Fig 4(c)), which would sometimes occur when these corners make contact with the thin film.

In the above described slotting tool according to the second embodiment, the corner between the bottom and the front surface may have an inclined surface. The slotting tool has an inclined surface from the beginning, and thus the inclined surface is pressed against the surface to be processed for scribing from the first use. The slotting tool with an inclined surface being created is similar to a slotting tool which did not originally have an inclined surface (see Fig 2) and is continuously used for a while so as to be in such a state that the corner between the bottom and the front surface is worn down. Accordingly, the slotting tool can be used for scribing from the beginning in the same state as that of the slotting tool that has been worn down. Concretely, a cutting edge that is too sharp may locally apply pressure to a surface to be processed and there is a risk that the Mo film may be damaged, and the inclined surface can prevent the pressure from being concentrated in a local point.

In addition, it is preferable for the angle formed between the inclined surface and the bottom of the slotting tool according to the second embodiment to be within a range from 10 degrees to 40 degrees. In the case where the angle formed between the inclined surface and the bottom is within this range, the angle formed between the front surface and the surface to be processed (scribing angle) is between 50 degrees (the angle formed between the inclined surface and the bottom is 40 degrees) and 80 degrees (the angle formed between the inclined surface and the bottom is 10 degrees) when the inclined surface of the slotting tool is made to make contact with the surface to be processed, and thus the angle can be set to be in such a range that a clean scribing process is possible as described in reference to Fig 4(a).

In addition, in the slotting tool according to the second embodiment, a cutting edge in the longitudinal direction may be formed in the corner between the rear surface and the right side as well as in the corner between the rear surface and the left side, and at the same time a cutting edge in the lateral direction may be formed in the corner between the rear surface and the bottom.

In the case where one side is broken or greatly worn down, the cutting edge can be switched with the other for continuous use of the slotting tool by switching the front and rear surfaces.

Here, an inclined surface may be created in the corner between the bottom and the rear surface. When an inclined surface is created in the corner between the bottom and the rear surface, the slotting tool is in the same state as being worn down when scribing in the case where the front and the rear are switched, and as a result the quality of the process can be prevented from changing over time.

In the following, the second slotting tool according to the present invention is described in detail in reference to the drawings.

The scribing device SC using the second slotting tool can be the same scribing device as described in reference to Fig 1 according to the first embodiment, and therefore the same symbols are attached to the same components and the same descriptions are not repeated.

Next, the slotting tool according to the present invention that is to be attached to a scribing device is described. Figs 8 to 10 are diagrams showing the slotting tool 8a according to one embodiment of the invention, where Fig 8 is a perspective diagram as viewed from the bottom, Fig 9 is a perspective diagram showing an enlargement of the bottom, and Fig 10 is a diagram showing an enlargement of the bottom. The same symbols are attached to the same components as those of the slotting tool 8 that is described in reference to Fig 2.

This slotting tool 8a is formed of a body 81 in cylindrical form, which is an attachment portion to the scribing head 7, and a cutting edge region 82 in rectangular parallelepiped form, which is integrally formed with the tip portion of the body 81 through discharge processing or the like and is made of a hard material, such as a hard metal or diamond.

The cutting edge region 82 has a long rectangular bottom 83 surrounded by a pair of short sides and a pair of long sides, a front surface 84 and a rear surface 85 which rise from the short sides of the bottom 83 so as to be perpendicular to the bottom (in the state before the below described inclined surfaces 90 and 96 are created), and a left side 88 and a right side 89 which rise from the long sides of the bottom 83 so as to be perpendicular to the bottom and are parallel to each other.

The corner between the bottom 83 and the front surface 84 in the cutting edge region 82 is rounded and an inclined surface 90 is created. When a solar cell substrate is slotted, this inclined surface 90 is made to make contact with the surface to be processed of the solar cell substrate, and in this state the slotting tool 8a is moved in the direction parallel to the left side 88 and the right side 89 so that the surface to be processed of the solar cell substrate is scribed. The main reason why the inclined surface 90 is provided is that the surface is scribed with the slotting tool from the beginning in the same state as being worn down. Another reason is to prevent pressure from being locally concentrated since a cutting edge that is too sharp may make pressure be applied locally, and there is a risk that the Mo film may be damaged. Here, though the inclined surface 90 is large in the figures for the sake of convenience of the description, the inclined surface 90 may be smaller than this as long as the inclined surface 90 can be made to make contact with the surface to be processed for scribing. Concretely, the length of the inclined surface 90 between the bottom and the front surface (width of the rounded corner) is approximately 3 µm to 20 µm.

The slotting tool 8a may be moved in the direction parallel to the left side 88 and the right side 89 so as to scribe the surface to be processed of the solar cell substrate in such a state that the corner between the bottom 83 and the front surface 84 of the cutting edge region 82 is made to make contact with the surface to be processed in the case there is no inclined surface 90. In this case, there is a risk that the Mo film may be damaged when the slotting tool 8a is used for the first time, but the corner between the bottom 83 and the front surface 84 is worn down after scribing has been carried out several times, and the risk of the Mo film being damaged is eliminated. Therefore, when the slotting tool is replaced with a new one, Mo metal plates or solar cell substrates that are defective products may be used so as to carry out scribing for several times, and the corner between the bottom 83 and the front surface 84 may be intentionally worn down before the slotting tool is used for processing in order to mass produce products.

In addition, the slotting tool 8a has a rounded corner 91 between the bottom 83 and the left side 88 and a rounded corner 92 between the bottom 83 and the right side 89. It is preferable for the corners to be rounded in accordance with a chamfering process, but it may be a rounding process. The width of the rounded corners (length between the bottom and the left side as well as the length between the bottom and the right side) is approximately 3 µm to 8 µm.

Meanwhile, the corner 93 between the front surface 84 and the left side 88 and the corner 94 between the front surface 84 and the right side 89 are finished as sharp corners without being rounded, and thus are used as cutting edges in the longitudinal direction (vertical direction).

In addition, the inclined surface 90 forms an angle of 10 degrees to 40 degrees with the bottom 83, and preferably forms an angle of 15 degrees to 25 degrees. That is to say, the scribing angle α formed between the front surface 84 and the inclined surface 90 is within a range from 50 degrees to 80 degrees, preferably within a range from 65 degrees to 75 degrees, in the state where the inclined surface 90 makes contact with the surface to be processed. This scribing angle is within a range such that an appropriate scribing process is possible, as described in reference to Fig 4 (a).

Next, a change in the cutting edge of the slotting tool 8a according to the present invention over time is described. Figs 11(a) and 11(b) are diagrams showing the state of a cutting edge portion during scribing, and Fig 11(a) shows a state when the slotting tool 8a is new and Fig 11(b) shows a state after it has been used for a while.

The inclined surface 90 is worn down as the number of times of scribing increases, and the scribing ends up with the use of the inclined surface 90a of which the length has been increased between the front and rear in comparison with the inclined surface 90 when the slotting tool 8a is new. Even though the inclined surface 90 has changed to the inclined surface 90a, the length of the surface contact has slightly changed and the effects on the surface to be processed have not been greatly changed. In addition, the inclined surface 90a has the same width between the left and right as the inclined surface 90 and is parallel to the inclined surface 90, and therefore a stable scribing process can be carried out such that the line width and the scribing angle α are the same even after the slotting tool has been worn down.

The angle 91 between the bottom 83 and the left side 88 and the angle 92 between the bottom 83 and the right side 89 are greatly rounded, and therefore the bottom 83 moves away from the surface to be processed in the case where the slotting tool 8a is inclined for scribing, which has so far been considered to barely affect the quality of processing. Therefore, the corners are made in a sharp state without being rounded. However, the quality of processing is increased when the corners 91 and 92 are rounded. In particular, films are barely peeled in such a manner that used to occasionally happen. Thus, films are barely peeled irregularly when the corners 93 and 94 are kept sharp and other corners 91 and 92 are rounded.

Though the corners 93 and 94 are chamfered as well, the quality of processing deteriorates, thereby causing films to be peeled. The results are summarized in Table 1.

Rounding of corners 91, 92

Rounding of corners 93, 94

Quality of processing

No

No

Film is peeled (Fig 11(c))

Yes

Yes

Film is peeled (Fig 11(c))

Yes

No

Good (Fig 11(a))

That is to say, excellent quality of processing can be gained when the corners 93 and 94 are not rounded and are kept as sharp cutting edges, while the corners 91 and 92 are rounded.

Fig 12 is a perspective diagram showing a slotting tool 8b according to another embodiment, and Fig 13 is a perspective diagram showing an enlargement of the bottom thereof. Here, the same symbols are attached to the same components as in the slotting tool 8a shown in Figs 8 to 10, and the same descriptions are not repeated.

According to the present embodiment, not only the corners on the front surface 84 side but also the corners 97 and 98 on the rear surface 85 side are not rounded and are finished as being sharp so as to provide cutting edges in the longitudinal direction. Furthermore, an inclined surface 96 is created so that the corner 99 between the inclined surface 96 and the rear surface 85 is a cutting edge in the lateral direction.

As a result, a scribing process is possible when the slotting tool moves towards the front surface 84 side, and in addition a scribing process is possible when the slotting tool moves towards the rear surface 85 side when the front and rear are switched, and thus the life of the slotting tool can be doubled.

Though representative embodiments of the present invention are described in the above, the present invention is not necessarily limited to the structure in the above described embodiments, and appropriate modifications and alterations are possible as long as an object of the present invention is achieved and the scope of the invention is not deviated from.

Industrial Applicability

The present invention can be applied to a slotting tool used for the manufacture of an integrated thin film solar cell using a chalcopyrite compound-based semiconductor film, for example.

Explanation of Symbols

W

solar cell substrate

7

scribing head

8, 8a, 8b

slotting tool

81

body

82

cutting edge region

83

bottom

84

front surface

85

rear surface

86

cutting edge

87

cutting edge

88

left side

89

right side

90, 96

inclined surface

91, 92

corner (rounded)

93, 94, 95

corner (cutting edge)

97, 98, 99

corner (cutting edge)