Lift-off method and chemical liquid tank

A lift-off procedure is provided which enables prevention of damage to a wiring pattern caused by contact of a metal being peeled off from a wafer with a wiring pattern at a time of lift-off procedure. A wafer having a surface on which a pattern is formed which contains a pattern portion to be removed is soaked into a chemical liquid at an angle at which the surface faces downward.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lift-off procedure and lift-off device capable of reducing a failure in wiring in the lift-off procedure being one of wiring forming processes to form a semiconductor device on a wafer.

2. Description of the Related Art

Conventionally, a lift-off procedure is available as one of methods for forming a semiconductor device.

FIG. 10is a diagram showing configurations of a conventional lift-off device. In a general lift-off device, as shown inFIG. 10, on an exclusive jig such as a wafer chuck30is mounted a wafer31with a portion where a metal is adhered and a pattern is formed being faced upward and a chemical liquid is spewed from a chemical liquid nozzle32while the wafer substrate31is being rotated to remove unwanted metal together with a resist. Thereafter, in order to wash away unwanted metal, a rinsing liquid is spewed from a rinsing liquid nozzle33for cleaning.

Additionally, another conventional lift-off device is also available in which a wafer is put into a tank containing a chemical liquid and unwanted metal, together with a resist, is removed while the tank is being shaken.

However, in the case of the above method shown inFIG. 10, since the portion where a metal is adhered on the wafer is faced upward, when the lift-off procedure is performed, a metal portion being removed from a metal face easily comes into contact with a wiring pattern causing a scratch on the wiring pattern. Moreover, if the lift-off procedure is performed with a pattern face being faced upward, a metal in the course of the lift-off procedure comes into contact with the wiring pattern, which causes the wiring pattern to be scratched in some cases. The scratched wiring produces a defective outward appearance and, since a part of the wiring is scraped out, a problem of migration or a like occurs.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention to provide a lift-off procedure which enables contact between a metal portion to be removed while the lift-off procedure is performed and a wiring pattern to be avoided, an exclusive jig and a chemical liquid tank employed in the above lift-off procedures.

According to a first aspect of the present invention, there is provided a lift-off method comprising a step of:

soaking a wafer having a surface on which a pattern containing a pattern portion to be removed is formed into a chemical liquid to remove the pattern portion to be removed at an angle at which the surface faces downward.

In the foregoing, a preferable mode is one wherein the angle at which the wafer is soaked into the chemical liquid is within a range between 90 degrees to 270 degrees relative to a horizontal line.

Also, a preferable mode is one wherein the step further comprises a step of placing each of a plurality of wafers including the wafer at a wafer cassette to be soaked into the chemical liquid, on which a plurality of wafers are arranged at specified intervals.

Also, a preferable mode is one wherein the step further comprises a step of attaching each of a plurality of wafers including the wafer to a jig to be soaked into the chemical liquid, which has a pressing nail used to partially press the surface of the wafer except the pattern, by the pressing nail.

Also, a preferable mode is one wherein the step further comprises a step of making a flow of the chemical liquid so that the flow is formed in a specified direction on the surface of the wafer.

Also, a preferable mode is one wherein the step further comprises a step of placing each of a plurality of wafers including the wafer at a wafer cassette to be soaked into the chemical liquid, on which a plurality of wafers are arranged at specified intervals.

Also, a preferable mode is one wherein the step further comprises a step of attaching each of a plurality of wafers including the wafer to a jig to be soaked into the chemical liquid, which has a pressing nail used to partially press the surface of the wafer except the pattern, by the pressing nail.

According to a second aspect of the present invention, there is provided a lift-off method comprising steps of:

putting up a trash collecting net to collect a pattern portion to be removed which has been peeled off from a pattern of a wafer in a chemical liquid tank having a columnar shape in a direction reaching an axial center from an internal side wall of the chemical liquid tank and being filled with a chemical liquid used to remove the pattern portion from the wafer having a surface on which a pattern containing the pattern portion to be removed is formed;

attaching the wafer to an internal side wall of the chemical liquid tank so that the surface of the wafer faces inward in the chemical liquid tank; and

forming a flow of the chemical liquid in a specified direction on the surface of the wafer.

In the foregoing, a preferable mode is one wherein the step of forming the flow of the chemical liquid further comprises a step of making a flow in the chemical liquid tank so that the flow is formed in the specified direction.

Also, a preferable mode is one wherein the chemical liquid tank is rotated so that the liquid flow is formed in the specified direction.

Also, a preferable mode is one wherein the internal side wall of the chemical liquid tank is in a shape of cylindrical.

According to a third aspect of the present invention, there is provided a chemical liquid tank being filled with a chemical liquid to remove a pattern portion from a wafer having a surface on which a pattern containing a pattern portion to be removed is formed, the chemical liquid tank comprising;

a spewing port from which the chemical liquid is fed; and

a sucking port to suck the chemical liquid to have the fed chemical liquid flow in a specified direction.

In the foregoing, a preferable mode is one that further comprising a supporting member to have each of surfaces of a pair of the wafers face outward and to support the wafers in a V-shaped manner.

Also, a preferable mode is one wherein the chemical liquid soak a wafer cassette on which a plurality of the wafers is arranged at specified intervals, further comprises a rectification device used to guide a flow of the chemical liquid in the specified direction, to be flowed from the spewing port through the wafer cassette to the sucking port.

With the above configuration, since a surface of the wafer is placed at an angle within a range between 90° to 270° so that the surface of the wafer faces downward, an unwanted pattern portion hangs down under its own weight in a direction of gravity and, as a result, contact of the unwanted pattern portion with a wiring pattern on the wafer can be avoided, thus enabling damage to wiring to be reduced.

Also, the unwanted pattern portion which has begun lift off from the wafer by a liquid flow travelling in a specified direction toward the metal adhered portion of the wafer hangs down under its own weight and by liquid flow of the chemical liquid and, as a result, contact of the unwanted pattern with the wiring can be avoided and thus damage to the wiring can be reduced. Also, by flowing the chemical liquid, an increase in concentration of impurities such as a resist that have dissolved in the chemical liquid can be prevented in a local portion in the chemical liquid where the lift-off is performed and, as a result, lift-off time can be shortened.

Also, by using a wafer cassette used to perform batch processing on a plurality of wafers and by placing the wafer cassette at an angle within the range described above, effective lift-off processing can be achieved. Moreover, by using a method so that a metal does not adhere to an area being hidden by an eaves of the cassette in the wafer, it is made possible to prevent an wanted metal from being sandwiched between the cassette and wafer and lift-off from being interfered.

Also, since lift-off procedure proceeds, by act of circulation of the chemical liquid, in a specified direction along a direction of the circulation, a risk of contact of a metal in the midcourse of the lift-off procedure with a wiring pattern can be lowered. Furthermore, since a metal drifting in the chemical liquid can be collected by a trash collecting net after the lift-off procedure, contact of the metal with the wiring pattern can be avoided and, as a result, damage to the wiring pattern can be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a diagram illustrating a method of a lift-off procedure of a first embodiment of the present invention. A chemical liquid tank1is filled with a chemical liquid3which is used to remove an unwanted pattern from a metal adhered portion7formed on a surface of a wafer2from a pattern containing an unwanted pattern portion to be removed. As shown inFIG. 1, a wafer is soaked in the chemical liquid tank1at an angle at which gravity acts on a surface of the wafer2.

Next, steps of the lift-off procedure are explained. The wafer2is soaked in the chemical liquid tank1at a specified angle and for a specified period of time. In the example shown inFIG. 1, the wafer2is mounted in a manner that a surface of the wafer2is positioned on a side on which the metal adhered portion7is formed and in a slant and downward manner so that gravity acts on the surface of the wafer2.

Then, the wafer2is taken from the chemical liquid tank1. The above specified angle is obtained based on a characteristic described later which exhibits a rate of a failure in wiring relative to an angle of a wafer.

FIG. 9is a diagram showing a characteristic in an experiment using a lift-off method of the present invention, that is, a graph showing a change in a failure rate in wiring relative to an angle at which the wafer2is mounted.

In a graph shown inFIG. 9, each of the figures shown in the graph is an average value and Table 1 shows a portion indicating characteristic figures. The degree “0” (0°) in the table indicates that the surface of the wafer is flat and faces upward.

TABLE 1Wafer angleFailure rate in wiring0°12.5%90°2.0%180°3.6%

As shown in Table 1, when an angle of a wafer is 0°, that is, when the wafer2is placed so as to face upward and to be in a horizontal state, the failure rate in wiring becomes 12.5%. When the wafer angle is 90°, the failure rate in wiring is 2.0% and when the wafer angle is 180°, the failure rate in wiring is 3.6%. Therefore, in the cases where the wafer angle is 90° or 180°, the failure rate in wiring is lowered remarkably when compared with the case where the wafer angle is 0°.

Moreover, as is apparent fromFIG. 9, in a range of the wafer angle being 90° and 180°, the failure rate in wiring is lowered gradually and, in a range of the wafer angle being 90° to 180° at which a position of the wafer becomes horizontal with its surface being faced downward, since gravity acts on the unwanted pattern portion which is peeled from the wafer2, a peeling effect can be achieved which can be obtained in the conventional technology.

A main reason for the above is that a degree of action of downward force produced by gravity differs by an angle.

Moreover, in a range from 180° to 360° which is not shown in a graph inFIG. 9, from the viewpoint of peeling-off action obtained at angles within the range of 0° to 180°, it is clear that the curve given in the characteristic graph shown inFIG. 9is turned up.

The above result shows that the wafer2is preferably placed at an angle in the range “A” of 180° from 90° through 180° to 270° shown in FIG.1.

A reason for using the above range of the angle is as follows. In the conventional case, since the wafer is placed in a manner that its surface faces upward to be horizontal at an angle of 0°, peeling of the metal adhered portion7is difficult only by being soaked into a chemical liquid and shaking processing or a like is required. In contrast, according to the present invention, by placing a wafer at an angle at which its surface faces downward relative to 90°, when lift-off processing is performed, gravity causes the metal adhered portion7being a pattern portion to be removed to hang down in a direction being acted on by gravity and therefore the metal adhered portion7can be smoothly peeled off, without requiring the shaking process. Then, while being peeled off, since the unwanted metal adhered portion7hangs down mainly in a gravity direction, a scratch on a wiring pattern formed in its vicinity can be prevented.

With the above configurations, by placing the wafer2in the chemical liquid tank1as described above, the unwanted pattern portion7having started lifted off from a surface of the wafer2hangs down under its own weight, which serves to facilitate the easy peeling, and therefore contact between the unwanted pattern portion and the wiring pattern is reduced and, as a result, it is possible to reduce damage to the wiring pattern.

Second Embodiment

FIG. 2is a diagram illustrating a method of a lift-off procedure of a second embodiment of the present invention. In the second embodiment, as in the case of the first embodiment, a wafer2is placed in the chemical liquid tank1filled with a chemical liquid3at a specified angle at which a surface of a metal adhered portion7faces downward in a slant manner. The chemical liquid tank1of the second embodiment includes a spewing port12used to receive the chemical liquid3and a sucking port13for sucking the chemical liquid3used to have a supplied chemical liquid3flow in a specified direction. The spewing port12and the sucking port13are mounted in such a manner that a flow of the chemical liquid3is formed in a specified direction relative to the metal adhered portion7of the wafer2.

The specified angle at which the wafer2is placed is, as in the case of the first embodiment, within a range of an angle, that is, between 90° to 270°. The spewing port12and sucking port13are placed so as to respond to the specified angle.

The “specified direction” of the flow of the chemical liquid3denotes a direction in which a vortex does not occur in the flow of the chemical liquid3having struck the metal adhered portion7.

The spewing port12and sucking port13are so constructed that the flow of the chemical liquid3has a width enough to allow the metal adhered portion7of the wafer2to be covered and have a shape and structure so as to have the chemical liquid3flow in a specified direction.

In the lift-off procedure of the second embodiment, the wafer2is arranged in the chemical liquid tank1in a manner that following two conditions (1) and (2) are satisfied.

(1) To place the wafer2in the chemical liquid tank1at the specified angle described in the first embodiment so that the metal adhered portion7faces downward.

(2) To place the wafer2in the chemical liquid tank1so that the chemical liquid3travelling between the spewing port12and sucking port13placed in the chemical liquid tank1flows in a specified direction along the metal adhered portion7.

The chemical liquid3is flown from the spewing port12to the sucking port13so that the flow of the chemical liquid3travels in a specified direction along the metal adhered portion7.

After a specified time, the wafer2is taken out from the chemical liquid tank1.

Thus, in the second embodiment, in addition to the method described in the first embodiment, the lift-off procedure is performed while the chemical liquid3flows.

According to the second embodiment, since the chemical liquid3flows in a specified direction, the metal adhered portion7hanging down in a downward direction is induced to be directed to the specified direction which enables an unwanted pattern portion to be easily peeled off. Thus, by placing the wafer2in a downward direction and by inducing the pattern portion to hang down in a specified direction, it is possible to prevent damage to a wiring pattern conventionally caused by a shaking process of a wafer.

According to the second embodiment, by placing the wafer2in such the way as described above, since an unwanted metal having started to be lifted off from the wafer2easily hang down in a downward direction under its own weight or by flowing of the chemical liquid3, contact of the unwanted metal with a wiring pattern is reduced and, as a result, damage to the wiring can be prevented. Moreover, by having the chemical liquid3flow in such the manner as described above, since an increase in the concentration of impurity such as a resist or a like having dissolved in the chemical liquid3in a local portion on which the lift-off procedure is performed can be inhibited, lift-off time is shortened.

Third Embodiment

FIG.3(a), FIG.3(b), and FIG.3(c) are diagrams illustrating a method of a lift-off procedure according to a third embodiment of the present invention. In the third embodiment, a lift-off procedure is carried out by performing batch processing on a plurality of pieces of wafers.

FIG.3(a) is a diagram explaining operations of the lift-off procedure. FIG.3(b) is a cross sectional view of a cassette case with wafers being mounted of FIG.3(c) taken along a line A—A. FIG.3(c) is a cross sectional view of the cassette case, with wafers being mounted, of FIG. (b) taken along a line B—B. FIG.3(d) is a bottom plan view in FIG.3(d).

Steps of the procedure in the third embodiment will be explained.

As shown in FIG.3(b) and FIG.3(c), a plurality of pieces of wafers on which the lift-off procedure is to be performed is placed in a general-type wafer cassette8being configured to be opened at its one end such as A82M manufactured by Fluoroware Corp., or a like.

At this point, a portion6of the wafer2shown in FIG.3(d) to which a metal is not adhered is placed on an eaves5so that the metal adhered portion7facing downward is inserted between a pair of eaves5mounted at equal intervals from an upper to lower portions on a wall side of the wafer cassette8, as shown in FIG.3(c).

The wafer cassette8having the wafers2is placed into the chemical liquid tank1at a specified angle.

The chemical liquid tank1includes a plurality of spewing ports23adapted to supply a chemical liquid3into the chemical liquid tank1and a sucking port24adapted to suck the supplied chemical liquid3. The plurality of the spewing ports23are mounted on a wall side of the chemical liquid tank1in an aligned manner. The sucking port24is attached to a bottom wall on the chemical liquid tank1.

The above wafer cassette8is placed at a specified angle relative to the spewing port23in such a manner that a flow4of the chemical liquid3spewed from the above spewing port23travels along the metal adhered portion7of the wafer2facing downward. The liquid flow4having passed through the wafer cassette8is sucked into the sucking port24in a sucking direction to the sucking port24.

The wafer cassette8is placed at an angle that does not disturb the flow of the chemical liquid3, that is, at an angle that does not produce a vortex in the flow of the chemical liquid3. This causes the lift-off procedure on the metal adhered portion7to proceed almost equally on each of the wafer2in the wafer cassette8.

Next, lift-off procedure employed in the embodiment is described. As shown in FIG.3(a), the wafer cassette8having a plurality of pieces of wafers2is placed in the chemical liquid tank1at a specified angle.

The liquid flow4that has been diverted for every wafer2from each of spewing ports23is formed in the metal adhered portion7in a specified direction in which the vortex does not occur and, while the liquid flow4strikes the metal adhered portion7, travels along the metal adhered portion7. The liquid flow4spewed from the wafer cassette8is sucked into the sucking port24.

Since each of the wafers2is attached to the wafer cassette8in such a manner that gravity acts on the metal adhered portion7, an unwanted portion of the pattern on the wafer2starts to be peeled off from a corner of the wafer cassette7by the liquid flow4and then gradually and increasingly by further continued liquid flow4and, as a result, hangs down by gravity. Moreover, the liquid flow4travelling in a specified direction acts on a portion hanging down which causes the portion hanging down to be peeled off apace.

Since the liquid flow4is controlled so as to travel in a specified direction in the chemical liquid tank1, damage to wiring pattern existing in a vicinity of the unwanted pattern caused by the portion hanging down is effectively inhibited.

Setting is made possible in a manner that such the flow of the chemical liquid3occurs according to a need. At this point, as shown in FIG.3(d), the wafer2is preferably placed in a manner that the metal does not adhere physically to an area6being hidden by an eaves5. For example, when the metal is formed by a deposition device, deposition is performed with the area6being hidden by the eaves5being masked.

Thus, according to the third embodiment of the present invention, even if lift-off procedure is performed by batch processing of a plurality of pieces of wafers, same effects obtained in the first and second embodiments can be achieved. Moreover, as described above, by taking a measure so that an unwanted metal does not adhere to an area being hidden by an eaves on the wafer, it is made possible to prevent lift-off procedure from being interfered by unwanted metal being sandwiched between a substrate of the wafer and the eaves on the wafer cassette.

Modified Embodiment of Third Embodiment

FIG. 8is a side view illustrating a method of lift-off procedure according to modified embodiment of the third embodiment of the present invention. In the modified embodiment of the third embodiment, as in the case of the third embodiment, batch processing is performed on a plurality of pieces of wafers2. The method employed in the modified embodiment differs from that used in the third embodiment in that a rectification device20is mounted in the chemical liquid tank1.

Next, lift-off procedure employed in the embodiment is described below.

As in the case of the third embodiment, a wafer cassette8in which a plurality of wafers2is placed is attached to the rectification device20in the chemical liquid tank1as shown in FIG.8.

The rectification device20includes a spewing port23to spew a chemical liquid3fed from a device (not shown) used to form a liquid flow4and a diverting pipe21having a plurality of exits used to form the liquid flow4to each of wafers2connecting to the spewing port23. Each of exits of the diverting pipe21is so constructed that a vortex flow is not produced by contact of the liquid flow4with the metal adhered portion7. The rectification device20is placed in a vicinity of the wafer cassette8so that the liquid flow4is not disturbed. The sucking port24is provided in the chemical liquid tank1to form a natural flow of the chemical liquid3.

The liquid flow4of the chemical liquid3shown inFIG. 8travels in a manner that it forms an approximately S-shaped flow and, therefore, a speed of the liquid flow4travelling through an upper step of the wafer cassette8becomes almost equal to that of the liquid flow4travelling through a lower step of the wafer cassette8. Therefore, a speed, liquid pressure, and amount of the liquid flow4striking the metal adhered portion7among wafers2become almost equal to one another and the lift-off procedure in the wafer cassette8proceeds in the same ways accordingly.

Next, lift-off procedure employed in the embodiment is described. As shown inFIG. 8, the wafer cassette8on which a plurality of pieces of wafers2is placed is mounted on the rectification device20in the chemical liquid tank1.

The chemical liquid3is flown from the spewing port23into the diverting pipe21with pressure. The liquid flow4diverted to each of the wafers2by the diverting pipe21is rectified in a specified direction in which a vortex occurs in the metal adhered portion7of each wafer2, while striking the metal adhered portion7, travels along the metal adhered portion7. The liquid flow4having passed through the wafer cassette8is sucked into the sucking port24.

As described above, the liquid flow4formed in the chemical liquid tank1strikes corners of the metal adhered portion7and has the metal adhered portion7be peeled off. The peeled portion is further peeled off by subsequent liquid flow4.

Since each of the wafers2is placed on the wafer cassette8in a manner that gravity acts on the metal adhered portion7, an unwanted metal portion of the peeled-off wafer2hangs down due to the gravity. The liquid flow4acts on the portion hanging down in a specified direction, thus causing the portions hanging down to be peeled off rapidly. Since the liquid flow4is formed in a specified direction, it is possible to effectively prevent a wiring pattern existing in the vicinity of the metal adhered portion7from being damaged by the portion hanging down.

As in the case of the third embodiment, setting is made possible in a manner that such the flow of the chemical liquid3occurs according to a need. At this point, it is desirous to place the wafer2in a manner that the metal does not adhere physically to an area being hidden by an eaves5. For example, when the metal is formed by a deposition device, deposition is performed with the area being hidden by the eaves5being masked.

Next, effects by the modified embodiment of the third embodiment are described. Same effects obtained in the first to third embodiments may be achieved in the modified embodiment of the third embodiment as well. Moreover, a speed, liquid pressure, and amount of the liquid flow4striking the metal adhered portion7among wafers2can be made almost equal to one another.

Fourth Embodiment

A fourth embodiment will be described by referring toFIG. 4to FIG.5. In the fourth embodiment, an example in which batch processing is performed on a plurality of pieces of wafers. FIG.4(a) and FIG. (b) are diagrams showing configurations of a jig exclusively used in the fourth embodiment of the present invention.

FIG. 5is a diagram explaining a lift-off operation of the fourth embodiment of the present invention. FIG.5(a) is a cross-sectional view of a chemical liquid tank1seen from a spewing port12in FIG.5(b), taken along a line A-A′. FIG.5(b) is a cross-sectional view of the chemical liquid tank1in FIG.5(a) taken along a line B-B′.

In the fourth embodiment, as in the third embodiment, a method of batch processing to be performed to carry out the lift-off procedure on a plurality of pieces of wafers2and its device are provided.

The exclusive jig9, as shown in FIG.4(a) and FIG.4(b), includes a substrate18having a size of a wafer being larger than that of the wafer2. As shown in FIGS.4(a) and4(b), a wafer pressing nail16is placed in an upper position and at a left and right positions on a surface of the substrate18and a wafer pressing nail17is placed in a lower position. The wafer pressing nail17being placed in the lower position and being formed so as to have a large width and to be dividable is adapted to partially press a portion6to which a metal is not adhered on a side making up a partially lacking portion of a wafer's circular shape. Moreover, the wafer pressing nail16being formed so as to be narrower than that of the wafer pressing nail17is adapted to partially press another portion6having no metal on the wafer2. One of the divided member of the wafer pressing nails16and17is fixed to the substrate18and is connected to another divided member of the wafer pressing nails16and17while pressing the wafer2.

As shown in FIG.4(a), the exclusive jig9shown in FIG.4(a) is attached to a H-shaped supporting member and the wafer2is soaked in the chemical liquid tank1with the metal adhered portion7being faced downward in a manner that gravity acts on the metal adhered portion of the wafer2. At this point, as shown in FIG.5(b), a pair of a measuring rule-shaped spewing ports12adapted to cover all pieces of wafers2on the supporting member15being arranged in parallel is mounted in an upper portion on a wall side of the chemical liquid tank1and a sucking port13is mounted at a bottom of the chemical liquid tank1in a manner that the liquid flow4strikes the metal adhered portion7and then flows in a specified direction to be sucked in the sucking port13. A collecting device (not shown) used to collect unwanted resists and metal films having peeled from the wafer2is embedded at the sucking port13.

Next, lift-off processing employed in the embodiment is described. As shown in FIG.5(a), the exclusive jig9is attached to the supporting member15in a manner that the metal adhered portions7on a pair of the wafers2are V-shaped which face outside and, by using the supporting member15, the exclusive jig9is soaked in the chemical liquid tank1.

By having the liquid flow4travel from the spewing port12to the sucking port13and by having the liquid flow4act, in a specified direction, on the resists and/or unwanted patterns hanging down in a direction of gravity, the resists and/or unwanted wirings are peeled off from the wafer2.

When the lift-off procedure of the fourth embodiment is performed, in order to form the liquid flow4that travels toward the metal adhered portion7in a specified direction, as shown in FIG.5(a), an angle for attaching an exclusive jig9to the supporting member15, a direction of the metal adhered portion7, a position of the spewing port12and sucking port13, a speed of spewing the chemical liquid3, an amount of a spewed liquid, or a like are adjusted.

Moreover, as shown in FIG.4(a), the wafer2is set to the exclusive jig9having a greatly expanded contact area between the chemical liquid3and the wafer2, and the exclusive jig9is soaked into the chemical liquid3with the wafer2being faced slant and downward so that gravity acts on a surface of the wafer2and an unwanted pattern is lifted off. Setting is made possible in a manner that such the flow of the chemical liquid3occurs according to a need.

Thus, according to the fourth embodiment, same effects obtained in the third embodiment can be achieved and moreover a valid area for the lift-off procedure in the wafer2can be ensured.

Fifth Embodiment

A fifth embodiment will be described by referring to FIG.6.FIG. 6is a plan view explaining a method of the lift-off procedure according to a fifth embodiment of the present invention.

As shown inFIG. 6, the chemical liquid tank1is so configured that, at least, its internal side wall is cylindrical and a plurality of pieces of wafers2are placed on the side wall so that they are freely detachable. Each of the wafers2is attached in such a manner that its metal adhered portion7faces toward a center of the chemical liquid tank1. On the side wall of the chemical liquid tank1is attached a plurality of trash collecting nets10having a mesh-like shape being put up in a direction toward a center of the chemical liquid tank1and each of the wafers2is placed among trash collecting nets. The trash collecting net10may be made from a synthetic resin, metal or a like and has a function of collecting resists or unwanted metal films floating in the chemical liquid3after it had been peeled from the wafer2and of preventing a necessary wiring pattern on the wafer2from being damaged. In a center of the chemical liquid tank1is placed a flow generating unit such as a screw (not shown), moving blade (not shown) or a like which forms a liquid flow4rotating in one direction as shown inFIG. 6. Aspeed of the liquid flow4produced by the flow generating unit and a diameter of an aperture of a mesh of the trash collecting net10, or a like are determined and set in a manner that the chemical liquid3travelling along the metal adhered portion7flows in a specified direction.

Next, lift-off processing employed in the embodiment is described. The wafer2is attached in a manner that the metal adhered portion7faces toward a center of the chemical liquid tank1in the cylindrical chemical liquid tank1.

The metal adhered portion7on the wafer2is peeled off, beginning with its part existing on a side where it is struck by the liquid flow4. The peeled-off portions are further expanded by the continued liquid flow4and are finally separated. The peeled-off unwanted metal films or resists that have not dissolved in the chemical liquid3are ridden on the liquid flow4and then collected finally by the trash collecting net10.

Thus, according to the fifth embodiment, since lift-off procedures are facilitated in one direction along the liquid flow4by circulation of the chemical liquid3caused by the liquid flow4, a risk of contact of a metal being in a midcourse of the lift-off procedure with a wiring pattern can be reduced. Moreover, by collecting, using the trash collecting net10, the metal drifting in the chemical liquid3after the lift-off procedure, contact of the metal with the wiring pattern can be avoided. As a result, damage to the wiring pattern can be reduced accordingly.

Sixth Embodiment

FIG. 7is a plan view explaining a method of a lift-off procedure according to a sixth embodiment of the present invention. Unlike in the case of the above fifth embodiment, the chemical liquid3in the cylindrical chemical liquid tank1is circulated, in the sixth embodiment, the cylindrical chemical liquid tank1itself is rotated.

The chemical liquid tank1, as shown inFIG. 1, is constructed that, at least, its internal side wall is cylindrical and the wafer2is attached to its side wall or its cylindrical jig in a manner that it is freely detachable. Each of the wafer2is attached in a manner that its metal adhered portion7faces toward a center of the chemical liquid tank1. To the side wall of the chemical liquid tank1is attached a plurality of trash collecting net10having a mesh-like shape each facing toward the center of the chemical liquid tank1and the wafer2is placed among the trash collecting nets10. The trash collecting net10is made of a synthetic resin, metal, or a like and collects unwanted metal films and resists having peeled off from the wafer2and serves not to cause damage to necessary wirings on the wafer2. The chemical liquid tank1or cylindrical jig, as shown inFIG. 7, is provided with a rotating unit (not shown) used to rotate the chemical liquid tank1in one direction.

The chemical liquid tank1is designed so that a surface of each of the wafers2receives a constant resistance by rotation of the chemical liquid tank1in a specified direction11shown in FIG.7.

Next, lift-off procedure employed in the embodiment is described. The wafer2is attached to the side wall or cylindrical jig among the trash collecting nets10in the cylindrical chemical liquid tank1so that the metal adhered portion7faces toward the center of the chemical liquid tank1.

The chemical liquid tank1is rotated in a specified direction11which causes an end of an unwanted pattern of the metal adhered portion7to curl up by continued receipt of resistance of the chemical liquid3and the curled-up portion receives larger resistance which makes the unwanted pattern be finally peeled off.

The unwanted metal film having been peeled off by the above method is collected by the trash collecting net10in the chemical liquid tank1.

According to the sixth embodiment, by rotating the chemical liquid tank1, the same act of circulation of the chemical liquid3as in the case of the fifth embodiment can be produced and, therefore, the lift-off operations proceed in a specified direction being reverse to a direction of rotation of the chemical liquid tank1which enable reduction in a risk that the metal being in the midcourse of the lift-off procedure comes into contact with the wiring pattern. Moreover, by collecting a metal drifting in the chemical liquid3using the trash collecting net10after it has been peeled off, contact of the metal with the wiring can be avoided and, as a result, damage to a wiring pattern can be reduced.

Other Embodiment

In the first to fourth embodiments, the wafer2on which the metal adhered portion7is soaked in the chemical liquid3with a surface of the wafer2facing toward a slant and downward direction. In the other embodiment, the wafer2may be placed at an arbitrary angle within a range between 90° to 270° so that the surface of the wafer2faces downward. Moreover, in the fifth to sixth embodiment, the chemical liquid tank1having a cylindrical internal side wall is used, however, a chemical liquid tank, when seen from an upper surface, that is, in its plan view, so long as it is circular or polygonal being near to a circular shape and so long as it is constructed in a manner that the chemical liquid3circulates in a constant direction and that a vortex does not occur, can be employed as well, which can provide same effects as obtained in the fifth to sixth embodiment can be achieved.

Next, an example of processes for incorporating the above embodiment is explained.

As shown in the example of processes in Table 2, in the first tank process, DMF (Dimethylforamide) is used as a chemical liquid3and the wafer2is in a “Face Down” state, that is, the wafer2is placed in a manner that its metal adhered portion7faces downward and is then soaked in the chemical liquid3for 120 minutes without being shaken, and a flow of the chemical liquid3is produced in a constant direction. In the first tank process, the same steps as used in the third embodiment can be employed. By performing the first tank step prior to the process of shaking, a larger part of unwanted pattern portions is removed and, as a result, in subsequent process of the shaking process, lift-off procedures can be performed without causing almost no damage to the wiring pattern.

In the second tank step following the above first tank step, the DMF is used and the wafer2is soaked into the chemical liquid3for 15 minutes with the wafer2being in a “Face Up” state, that is, with the metal adhered portion7being faced upward while being shaken.

In the third tank process subsequent to the second tank process, IPA (Isopropyl Alcohol) is used and the wafer2is soaked into the chemical liquid3with the wafer2being in a “Face Up” state while being shaken.

Finally, the wafer2is washed with IPA while being spun In the above example of processes shown in Table 2, the method used in the first tank process is employed as the first tank process. However, instead of this, any method used in the first to second embodiment and in the fourth to sixth embodiment may be employed.

Moreover, in the second and third tanks in the example of processes shown in Table 2, operations of shaking the wafer2with the wafer2being in the “Face Up” state are added, however, instead of this, the wafer2may be soaked with it being in the “Face Up” state without operations of shaking the wafer2. Moreover, a process of forming a liquid flow can be added.

A number of processes and order of processes for the lift-off are not limited to the process example shown in Table 2 and they can be designed in an arbitrary manner, however, it is preferable that the processes used in the above embodiment are incorporated into the first process of the lift-off procedures.

It is thus apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and spirit of the invention.