Method of transferring micro devices and device transfer assembly

A method of transferring micro devices includes: aligning a detachable transfer plate to a carrier substrate with micro devices thereon by an alignment assistive mechanism which is detachably assembled with the detachable transfer plate; contacting the detachable transfer plate to the micro devices on the carrier substrate by the alignment assistive mechanism; picking up the micro devices from the carrier substrate; detaching the detachable transfer plate with the micro devices thereon from the alignment assistive mechanism; moving the detachable transfer plate with the micro devices thereon to be assembled to another alignment assistive mechanism above a receiving substrate to form a device transfer assembly; aligning the micro devices on the detachable transfer plate with the receiving substrate; and transferring the micro devices to the receiving substrate by the another alignment assistive mechanism through the detachable transfer plate.

BACKGROUND

Field of Invention

The present disclosure relates to a method of transferring micro devices and a device transfer assembly.

Description of Related Art

Traditional technologies for transferring of devices include transferring from a transfer wafer to a receiving substrate by wafer bonding. One such implementation is “direct bonding” involving one bonding stage of an array of devices from a transfer wafer to a receiving substrate, followed by removal of the transfer wafer. Another such implementation is “indirect bonding” which involves two bonding/de-bonding stages. In indirect bonding, a transfer head may pick up an array of devices from a donor substrate, and then bond the array of devices to a receiving substrate, followed by removal of the transfer head.

In recent years, many researchers and experts try to overcome difficulties in making a massive transfer of devices (i.e., transferring millions or tens of millions of devices) possible for commercial applications. Among those difficulties, cost reduction, time efficiency, and yield are three of the important issues.

SUMMARY

According to some embodiments of the present disclosure, a method of transferring micro devices is provided. The method includes: aligning a detachable transfer plate to a carrier substrate with micro devices thereon by an alignment assistive mechanism which is detachably assembled with the detachable transfer plate; contacting the detachable transfer plate to the micro devices on the carrier substrate by the alignment assistive mechanism; picking up the micro devices from the carrier substrate by the detachable transfer plate; detaching the detachable transfer plate with the micro devices thereon from the alignment assistive mechanism; moving the detachable transfer plate with the micro devices thereon to be assembled to another alignment assistive mechanism above a receiving substrate to form a device transfer assembly, in which the micro devices face the receiving substrate; aligning the micro devices on the detachable transfer plate with the receiving substrate; and transferring the micro devices to the receiving substrate by the another alignment assistive mechanism through the detachable transfer plate.

According to some embodiments of the present disclosure, a device transfer assembly is provided. The device transfer assembly includes an alignment assistive mechanism and a detachable transfer plate. The alignment assistive mechanism has a first portion fixed at a place and a second portion which is movable at least in one axis. The detachable transfer plate is detachably assembled on the second portion of the alignment assistive mechanism. The detachable transfer plate is configured to pick up a micro device from a carrier substrate or to place the micro device to a receiving substrate. The detachable transfer plate includes at least one recess thereon, and the at least one recess is configured to accommodate another micro device on the carrier substrate not to be picked up.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings.

Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

In various embodiments, the description is made with reference to figures. However, certain embodiments may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, etc., in order to provide a thorough understanding of the present disclosure. In other instances, well-known semiconductor processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the present disclosure. Reference throughout this specification to “one embodiment,” “an embodiment” or the like means that a particular feature, structure, configuration, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrase “in one embodiment,” “in an embodiment” or the like in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments.

Reference is made toFIGS. 1 to 2G.FIG. 1is a schematic flow chart of a method100of transferring the micro devices210according to some embodiments of the present disclosure.FIGS. 2A to 2Gare schematic cross-sectional views of intermediate stages of the method100of transferring the micro devices210according to some embodiments of the present disclosure. The method100begins with operation110in which a detachable transfer plate220is aligned to a carrier substrate230with micro devices210thereon by an alignment assistive mechanism240which is detachably assembled with the detachable transfer plate220(as referred toFIG. 2A). The method100continues with operation120in which the detachable transfer plate220is in contact with the micro devices210on the carrier substrate230by the alignment assistive mechanism240(as referred toFIG. 2B). The method100continues with operation130in which the micro devices210are picked up from the carrier substrate230by the detachable transfer plate220(as referred toFIG. 2C). The method100continues with operation140in which the detachable transfer plate220with the micro devices210thereon is detached from the alignment assistive mechanism240(as referred toFIG. 2D). The method100continues with operation150in which the detachable transfer plate220with the micro devices210thereon is moved to be assembled to another alignment assistive mechanism340above a receiving substrate350to form a device transfer assembly2000, and the micro devices210face the receiving substrate350(as referred toFIG. 2E). The method100continues with operation160in which the micro devices210on the detachable transfer plate220are aligned with the receiving substrate350by the another alignment assistive mechanism340which controls a position of the detachable transfer plate220(as referred toFIGS. 2E and 2F). The method100continues with operation170in which the micro devices210are transferred to the receiving substrate350by the another alignment assistive mechanism340through the detachable transfer plate220(as referred toFIG. 2F), and then the micro devices210are released from the detachable transfer plate220(as referred toFIG. 2G). In operation150, since there is only the detachable transfer plate220with the micro devices210thereon is moved or conveyed to be aligned with the receiving substrate350, a throughput of transferring the micro devices210is enhanced because the detachable transfer plate220is smaller, lighter, and simpler in structure compared to the alignment assistive mechanism240. Furthermore, there may be a plurality of different detachable transfer plates each with one type of micro devices thereon prepared for operations150,160, and170, such that times for waiting the operations110,120,130, and140to be completed can be omitted in some embodiments to increase efficiency and flexibility of operations.

Reference is made toFIGS. 3A to 3C.FIGS. 3A to 3Care schematic cross-sectional views of optional stages of the method100of transferring the micro devices210according to some embodiments of the present disclosure. In some embodiments, after picking up the micro devices210from the carrier substrate230, the detachable transfer plate220is inspected. The inspection may include marking a misplace M1(seeFIG. 3B) or an absence M2(seeFIG. 3C) of at least one micro device210on the detachable transfer plate220to enhance quality control. In some embodiments, the detachable transfer plate220is inspected after the detachable transfer plate220with the micro devices210thereon is detached from the alignment assistive mechanism240. An inspection device400used for said inspection may be an optical microscope, but should not be limited thereto. It is noted that normally the micro devices210from the same carrier substrate230are the same type (e.g., they are all blue micro light-emitting diodes, but should not be limited thereto) because the micro devices210as mentioned come from the same epitaxial layer grown from a growth substrate, and then the growth substrate is removed by, e.g., laser lift-off (LLO).

Reference is made toFIG. 4.FIG. 4is a schematic cross-sectional view of the detachable transfer plate220according to some embodiments of the present disclosure. In some embodiments, the detachable transfer plate220is made of fused silica or glass with a glue layer222thereon configured to grip the micro devices210. In some embodiments, the glue layer222is an ultraviolet (UV) curable glue layer or an UV release glue layer, but should not be limited thereto. An adhesive force applied to the micro devices210by the glue layer222can be reduced after the glue layer222is irradiated by UV light. Therefore, in the above embodiments, the micro devices210may be picked up by the detachable transfer plate220through the adhesive force exerted by the detachable transfer plate220, and then the adhesive force between the detachable transfer plate220and the micro devices210are reduced before the micro devices210are transferred to the receiving substrate350.

Reference is made toFIGS. 5A and 5B.FIGS. 5A and 5Bare schematic cross-sectional views of optional stages of the method100of transferring the micro devices210according to some embodiments of the present disclosure. In some embodiments, liquid500is formed between the micro devices210and the receiving substrate350during transferring the micro devices210to the receiving substrate350, such that the micro devices210and the contact pads352on the receiving substrate350are respectively gripped together by the capillary force produced by two opposite surfaces of the liquid500when the micro devices210are placed in proximity to the contact pads352. The liquid500can be formed on surfaces of the contact pads352facing the micro devices210or on surfaces of the micro devices210facing the contact pads352. The liquid500can also be formed on both of the surfaces of the micro devices210and the surfaces of the contact pads352as mentioned. In some embodiments, the capillary force is greater than the adhesive force before the adhesive force is reduced. In some embodiments, the capillary force is greater than the adhesive force after the adhesive force is reduced. In some embodiments, a temperature of the receiving substrate350is lowered such that the liquid500is frozen before the micro devices210are released from the detachable transfer plate220. Specifically, the frozen liquid500provides a force to grip the micro devices210, and the micro devices210are then released from the detachable transfer plate220. In some embodiments, the force provided by the frozen liquid500is greater than the adhesive force before the adhesive force is reduced. In some embodiments, the force provided by the frozen liquid500is greater than the adhesive force after the adhesive force is reduced.

After the micro devices210and the contact pads352are gripped together by the capillary force, the liquid500is evaporated such that at least one of the micro devices210is stuck and bound to the contact pads352of the receiving substrate350(back to seeFIG. 2F). In some embodiments, a binding force which binds the micro devices210to the contact pads352is greater than the adhesive force before the adhesive force is reduced. In some embodiments, the binding force which binds the micro devices210to the contact pads352is greater than the adhesive force after the adhesive force is reduced.

Reference is made toFIG. 6.FIG. 6is a schematic cross-sectional view of an optional stage of the method100of transferring the micro devices210according to some embodiments of the present disclosure. In some embodiments, an external pressure P is applied to press the micro devices210and the receiving substrate350during evaporating the liquid500to further assist contacting the micro devices210to the contact pads352such that a better solid phase bonding therebetween can occur. The external pressure P can be applied by the another alignment assistive mechanism340of the device transfer assembly2000to the micro devices210or changing the environmental pressure to press the micro devices210and the contact pads352, but should not be limited thereto.

Reference is made toFIG. 7.FIG. 7is a schematic cross-sectional view of an optional stage of the method100of transferring the micro devices210according to some embodiments of the present disclosure. In some embodiments, micro devices210′ of another type are transferred to the receiving substrate350via another detachable transfer plate220′ with the micro devices210′ of the another type thereon assembled to the another alignment assistive mechanism340. As such, the another alignment assistive mechanism340only needs to be moved by a distance substantially equal to one pitch SP1of sub-pixels arranged in a lateral direction (e.g., in y-axis) during operations of transferring different types of micro devices210and210′ to the contact pads352of the receiving substrate350, so as to save time for moving and aligning the another alignment assistive mechanism340with the receiving substrate350.

Reference is made toFIGS. 7 to 9.FIG. 8Ais a schematic view of one type of the detachable transfer plate220according to some embodiments of the present disclosure.FIG. 8Bis a schematic view of one type of the detachable transfer plate220according to some embodiments of the present disclosure.FIG. 9is a schematic cross-sectional view which illustrates picking up the micro devices210by the detachable transfer plate220according to some embodiments of the present disclosure. In some embodiments, the detachable transfer plate220includes a picked-up portion222A (or a picked-up portion222B) and a base portion224. The picked-up portion222A(222B) has a surface222A-1(or a surface222B-1) configured to pick up the micro devices210. The base portion224is connected with the picked-up portion222A(222B) and opposite to the surface222A-1(222B-1) of the picked-up portion222A(222B). In some embodiments, a Young's module of the picked-up portion222A(222B) is smaller than a Young's module of the base portion224. As such, since the picked-up portion222A(222B) deforms when the detachable transfer plate220contacts the micro devices210, the micro devices210are leveled with the detachable transfer plate220. In this way, each of the micro devices210intended to be picked up can be in contact with the detachable transfer plate220to maintain a presence of grip forces exerted on each of the micro devices210intended to be picked. In other words, when the detachable transfer plate220contacts the micro devices210, a total volume of gaps or a number of the gaps between the detachable transfer plate220and each of the micro devices210intended to be picked up can be decreased. Therefore, it makes the detachable transfer plate220avoid failing in picking up the micro devices210, and increases the successful rate of picking up. Furthermore, the condition on the Young's module as mentioned avoids damages on the micro devices210when the micro devices210are picked up by the picked-up portion222A(222B) of the detachable transfer plate220. A difference between the embodiments illustrated byFIG. 8Aand the embodiments illustrated byFIG. 8Bis a geometric structure of the picked-up portion222A(222B) of the detachable transfer plate220. The picked-up portion222A as shown inFIG. 8Aincludes a plurality of isolated and island-like portions each having the surface222A-1for picking up the micro devices210. Devices or elements not intended to be picked up by the picked-up portion222A can be accommodated in place without the picked-up portion222A which faces the base portion224when the micro devices210are picked up via the surface(s)222A-1. The picked-up portion222B as shown inFIG. 8Bincludes at least one recess222B-2configured to accommodate devices or elements not intended to be picked up by the picked-up portion222B. In some embodiments, the recess(es)222B-2is(are) configured to accommodate at least one micro device210on the carrier substrate not to be picked up (seeFIG. 9). The recess(es)222B-2can also be used to accommodate objects which are already existed on the receiving substrate350. A function of the accommodation as mentioned is also applicable to the embodiments as illustrated byFIG. 8A. There is a continuous surface222B-1on the picked-up portion222B for picking up the micro devices210. In some embodiments, the recess(es)222B-2is(are) fully enclosed by the continuous surface222B-1at a plane of the picked-up portion222B opposite to the base portion224. In some embodiments, the glue layer222as illustrated inFIG. 4may be formed on the surface222A-1(222B-1) of the picked-up portion222A(222B) (not shown inFIGS. 8A and 8B). Briefly, the micro devices210can be selectively picked up by the detachable transfer plate220as illustrated byFIGS. 8A and 8B.

Reference is made back toFIGS. 2A, 2E, 2G, and 7. The above embodiments as illustrated in the present disclosure can be performed by the device transfer assembly2000in which structural features thereof are described as follows. In some embodiments, the device transfer assembly2000includes the alignment assistive mechanism240and the detachable transfer plate220. The alignment assistive mechanism240has a first portion2402fixed at a place and a second portion2404which is movable at least in one axis. Specifically, the alignment assistive mechanism240can be set up in a production line. In some embodiments, the first portion2402can be fixed on a certain place in the production line, but should not be limited thereto. The second portion2404has degrees of freedom in at least z-axis as shown in the figures. The second portion2404can have degrees of freedom in x-axis and y-axis for aligning. The detachable transfer plate220can be detachably assembled on the second portion2404of the alignment assistive mechanism240. The detachable transfer plate220is configured to pick up the micro devices210from the carrier substrate230by the alignment assistive mechanism240or to place the micro devices210on the receiving substrate350by the another alignment assistive mechanism340. In some embodiments, the detachable transfer plate220includes at least one recess220B-2thereon, and the recess220B-2is configured to accommodate another micro device on the carrier substrate230not to be picked up. In some embodiments, some align marks are on the detachable transfer plate220to assist aligning in operations which have been mentioned above.

In some embodiments, the device transfer assembly2000further includes another alignment assistive mechanism340configured to detachably assemble the detachable transfer plate220thereon. The another alignment assistive mechanism340has a first portion3402fixed at a place and a second portion3404which is movable at least in one axis which is similar to the alignment assistive mechanism240and details will not be repeated again. With the above configuration, the alignment assistive mechanism240and the another alignment assistive mechanism340can be substantially fixed at places as mentioned and only the detachable transfer plate220(which is much smaller, lighter, and simpler in structure) is moved or transferred (e.g., along the production line, but should not be limited thereto) from the alignment assistive mechanism240to the another alignment assistive mechanism340through a conveyor2002for example, but should not be limited thereto. As such, the throughput can be enhanced. Besides, since different detachable transfer plates (e.g., the detachable transfer plate220and the detachable transfer plate220′) which carry different types of micro devices (e.g., micro light-emitting diodes of different wavelengths, but should not be limited thereto) can be assembled on the another alignment assistive mechanism340one after another, the another alignment assistive mechanism340only needs to be moved by one pitch SP1of sub-pixels during operations of transferring different types of micro devices to the contact pads352of the receiving substrate350, so as to save time for moving and aligning the another alignment assistive mechanism340to the receiving substrate350.

It is noted that in the above embodiments a number of the detachable transfer plates (e.g., the detachable transfer plates220,220′ . . . etc.) can be different from a number of the alignment assistive mechanisms (the alignment assistive mechanisms240,340). For example, when there are three or more types of micro devices (e.g., the red micro light-emitting diodes, green micro light-emitting diodes, and blue micro light-emitting diodes . . . etc.), there can be corresponding three or more detachable transfer plates included in the device transfer assembly2000, so as to enhancing the throughput of transferring micro devices. Furthermore, times for waiting the operations110,120,130, and140to be completed can be omitted in some embodiments as mentioned to increase efficiency and flexibility of operations.

In summary, embodiments of the present disclosure provide a method of transferring a micro device and a device transfer assembly in which only a detachable transfer plate which is small, light, and simple in structure is moved from a carrier substrate to a receiving substrate. As such, a throughput of transferring micro devices is enhanced and time for alignment is reduced.