Microelectronic device transfer and cleaning with ultraviolet laser

Abstract

A method (100) for ultraviolet laser transfer and cleaning of microelectronic devices includes transferring (102) a microelectronic device (110) from a donor substrate (120) to a receiving substrate (130) and cleaning (104) the microelectronic device (110) after the transfer. Prior to transfer, the microelectronic device (110) is coupled to the donor substrate (120) through a sacrificial layer (112) comprising gallium. The first ultraviolet laser beam (180) ablates the sacrificial layer (112) to release the microelectronic device (110) from the donor substrate (120) leaving a gallium residue (114) on a newly exposed surface (116) of the microelectronic device (110). The second ultraviolet laser beam (190) ablates the gallium residue (114) to clean the microelectronic device (110). The first ultraviolet laser beam (180) and the second ultraviolet laser beam (190) may be generated by the same ultraviolet laser (170). The laser ablation of the gallium residue omits a wet chemical step as compared to liquid etch and can be performed by the same laser device for transfer. Laser cleaning is particularly advantageous when the receiving substrate is not resistant to liquid etching.

Description

[0001] priority

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 309,458, filed on February 11, 2022, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present invention generally relates to substrate-to-substrate transfer of microelectronic devices by laser lift-off ablation of gallium nitride layers. In particular, the present invention relates to the removal of residual gallium after laser lift-off. Background Art

[0004] To meet consumer demand for thinner, lighter, and higher-performance electronic devices, the microelectronics industry is working to make smaller microelectronic devices. For example, to make high-resolution LED displays, micro-light-emitting diodes (μLEDs) with dimensions less than 70 microns x 70 microns and as small as about 3 microns x 3 microns are being developed. μLED displays are an emerging display technology that is expected to have higher brightness, lower power consumption, and faster response times than organic LED displays and liquid crystal displays.

[0005] Wafer-scale manufacturing has long been the most cost-effective mass production method for microelectronic devices, enabling millions of identical microelectronic devices to be manufactured simultaneously on the same wafer. Although individual microelectronic devices can be separated from a wafer by dicing the wafer in some cases, thinner form factors can be achieved by separating the microelectronic devices from the wafer entirely. Therefore, wafer-scale manufacturing of microelectronic devices may involve one or more steps to separate the microelectronic devices from the substrate. For example, one type of microelectronic device (e.g., a red LED) may be grown at a high density on a growth wafer, then separated from the growth wafer and implemented at a lower density on a substrate of a final device (e.g., a color display), perhaps in combination with other types of microelectronic devices (e.g., blue LEDs and green LEDs) grown on other growth wafers. After growing at least some layers of the microelectronic device on the growth wafer, the production of microelectronic devices also often involves processing the top and bottom of the microelectronic device. This double-sided processing may require one or more operations to transfer the microelectronic device from one substrate to another to flip it over. In addition, pick-and-place techniques can be used to replace a failed microelectronic device in an array of microelectronic devices.

[0006] Laser lift-off has emerged as a promising transfer technology. The laser lift-off process releases a microelectronic device from a substrate by laser ablation of a sacrificial layer located between the substrate and the microelectronic device. Laser lift-off typically utilizes ultraviolet (UV) light generated by an excimer laser, and can release a microelectronic device from a substrate with a single laser pulse. Laser lift-off can be applied to a single individual microelectronic device, a subset of the total number of microelectronic devices on a substrate, or all microelectronic devices on a substrate. In laser lift-off of multiple microelectronic devices, the laser beam can scan a selected portion of the substrate to release the microelectronic devices one by one, or a larger area laser pulse can be applied to multiple microelectronic devices simultaneously. The larger area laser pulse can be masked to specifically expose the footprint of each microelectronic device.

[0007] Transfer of microelectronic devices can utilize laser lift-off in a stamp-based transfer scheme, a bond-release scheme, or a laser-induced forward transfer scheme. In the stamp-based scheme, the microelectronic device is released from the donor substrate by laser lift-off and picked up from the donor substrate by an elastomeric stamp. The stamp then places the microelectronic device on the receiving substrate. In the bond-release scheme, the microelectronic device is first bonded to the receiving substrate and then released from the donor substrate. In the laser-induced forward transfer scheme, the receiving substrate is kept at a certain distance from the microelectronic device, and the ablation of the sacrificial layer not only releases the microelectronic device from the donor substrate, but also pushes the microelectronic device through the gap to the receiving substrate. The bond-release and laser-induced forward transfer schemes neatly eliminate the need to use robotic equipment to handle individual microelectronic devices during the transfer process.

[0008] In laser lift-off, the sacrificial layer that is ablated to release the microelectronic device from the donor substrate is typically made of gallium nitride (GaN). Laser ablation of GaN produces nitrogen gas and liquid gallium. When all the nitrogen gas escapes, a residue of liquid gallium remains on the newly exposed surface of the microelectronic device. For most applications, this residue must be removed because the residue may hamper the performance of the microelectronic device or hinder subsequent processing of the microelectronic device. In particular, when the microelectronic device is a μLED, the residue may block the light emission of the μLED. Gallium residues are typically etched away with a corrosive liquid. For example, with ammonia (NH3) or hydrochloric acid (HCl) solution. SUMMARY OF THE INVENTION

[0010] A method for laser lift-off transfer of microelectronic devices followed by laser cleaning of gallium residues is disclosed herein. In the method, both the transfer and the subsequent cleaning are based on UV laser ablation. First, the transfer is initiated by a UV laser beam, which ablates a sacrificial GaN layer. After the transfer, the UV laser beam ablates the gallium residues. Conveniently, both laser ablation operations can be performed by the same UV laser. The second laser ablation operation for removing the gallium residues replaces conventional etching using corrosive liquids.

[0011] The advantages of the present method are manifold. Some substrates are not resistant to liquid etching. For example, the display backplane of a μLED display may include polymers or other materials that are not resistant to etching by corrosive liquids. Laser cleaning is a viable gallium residue cleaning method in scenarios that are not resistant to corrosive liquids, at least because the ultraviolet laser beam can be selectively applied to each individual microelectronic device that needs to be cleaned. The UV laser beam used for cleaning can be relatively easily sized or masked to expose only the microelectronic devices, so damage to the substrate area by laser ablation can be avoided. Even in the case of substrates that are resistant to corrosive liquids, the present transfer and cleaning method provides convenience and simplicity because it eliminates the wet chemical step and instead applies a second ablation operation after the laser lift-off transfer. Replacing liquid etching with laser ablation has the potential to significantly reduce the overall processing time. In addition, in most cases, the laser cleaning step can be performed with the laser lift-off device and functionality already installed.

[0012] In one aspect, a method for ultraviolet laser transfer and cleaning of a microelectronic device includes the step of transferring the microelectronic device from a first substrate to a second substrate. The microelectronic device is coupled to the first substrate via a sacrificial layer comprising gallium. The transferring step includes releasing the microelectronic device from the first substrate by laser ablating the sacrificial layer using a first ultraviolet laser beam. Such laser ablation leaves gallium residue on the microelectronic device. The method also includes the step of removing at least a portion of the gallium residue on the microelectronic device after the transferring step. The cleaning step includes laser ablating the gallium residue with a second ultraviolet laser beam. The sacrificial layer can be a heterogeneous solid layer. The method can include generating the first ultraviolet laser beam and the second ultraviolet laser beam using the same ultraviolet laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the general description above and the detailed description of the preferred embodiments below, serve to explain the principles of the invention.

[0014] Figure 1A -D shows a method for UV laser transfer and cleaning of microelectronic devices according to an embodiment.

[0015] Figure 2 A laser beam configuration is shown for laser cleaning of a plurality of microelectronic devices on a receiving substrate in a multi-device extension of the cleaning step of the method of FIG. 1 , according to an embodiment.

[0016] Figure 3Another laser beam configuration for laser cleaning of multiple microelectronic devices on a receiving substrate in a multi-device extension of the cleaning step of the method of FIG. 1 is shown according to an embodiment, wherein UV radiation is applied only to the microelectronic devices without exposing adjacent portions of the receiving substrate.

[0017] Figure 4 Another laser beam configuration for laser cleaning of multiple microelectronic devices on a receiving substrate in a multi-device extension of the cleaning step of the method of FIG. 1 is shown according to an embodiment, also applying UV radiation only to the microelectronic devices without exposing adjacent portions of the receiving substrate.

[0018] Figure 5 is an image of a microelectronic device on a substrate demonstrating the performance of one embodiment of the method of FIG. 1 . DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring now to the drawings, wherein like parts are indicated by like numerals, Figures 1A-1D is a cross-sectional diagram illustrating a method 100 for UV laser transfer and cleaning of microelectronic devices. Figure 1A The transfer step 102 of the method 100 is shown, Figure 1B shows the result of the transfer step 102, Figure 1C A subsequent cleaning step 104 of method 100 is shown, Figure 1D The final result of method 100 is shown. Figures 1A-1D In the illustrated embodiment, the method 100 is applied to a single microelectronic device 110. The method 100 can be easily extended to multiple devices 110.

[0021] Device 110 may be a μLED, a photodiode, a complementary metal oxide semiconductor circuit, or another microelectronic device. The lateral dimensions of device 110, for example, Figure 1B The width 118W indicated in FIG. 1 may be less than about 100-200 microns, and is typically, but not necessarily, greater than about 0.1 microns. In one embodiment, the width 118W is in the range of 1 to 100 microns. Figure 1B The height 118H of the device 110 shown in FIG. 1 may be tens of microns or less.

[0022] like Figure 1AAs shown, the transfer step 102 includes releasing the device 110 from the donor substrate 120 by laser lift-off, i.e., by laser ablating the sacrificial layer 112 using a UV laser beam 180. Prior to laser lift-off, the layer 112 couples the device 110 to the surface 122 of the donor substrate 120. The layer 112 may be a sacrificial layer for the device 110. The layer 112 is made substantially or entirely of GaN. During the transfer step 102, the donor substrate 120 and the receiving substrate 130 are arranged such that the surface 122 of the donor substrate 120 faces the surface 132 of the receiving substrate 130, wherein the device 110 is located between the surfaces 122 and 132. To achieve laser lift-off, the UV laser beam 180 is directed through the donor substrate 120 to irradiate and ablate the layer 112.

[0023] The UV laser beam 180 may be generated by a UV laser 170 (e.g., an excimer laser). The wavelength of the UV laser beam 180 may be less than 320 nanometers (nm) to effectively ablate the layer 112, such as in the range of 190 to 320 nm. In one embodiment, the UV laser beam 180 is pulsed, and the transfer step 102 ablates the layer 112 using a single pulse of the UV laser beam 180. In another embodiment, the transfer step 102 ablates the layer 112 using a sequence of pulses of the UV laser beam 180. The energy density delivered to the layer 112 by the UV laser beam 180 may be between 600 and 1500 mJ / cm2. 2 ), and layer 112 may have a thickness 112T in the range between 0.5 and 5 nm.

[0024] The donor substrate 120 can withstand and be transparent to UV light. The donor substrate 120 is made of, for example, quartz or sapphire. The receiving substrate 130 may or may not be UV transparent. In one case, the receiving substrate 130 is a final device substrate, such as a display backplane. In this case, the receiving substrate 130 may include a polymer or be essentially composed of a polymer. The final device substrate (whether or not it is a display backplane) may also include one or more functional layers. In another case, the receiving substrate 130 is an intermediate substrate for further processing the device 110 before transferring to another substrate (which may be the final device substrate). In this case, the material composition of the receiving substrate 130 can be similar to the material composition of the donor substrate 120 so that the device 110 can be laser transferred from the receiving substrate 130. The receiving substrate 130 may not be resistant to corrosive liquid etching, for example due to the presence of polymers or functional layers.

[0025] Figure 1AA forward transfer embodiment of the transfer step 102 is shown. In this forward transfer embodiment, the donor substrate 120 and the receiving substrate 130 are arranged such that there is a non-zero gap 140 between the device 110 and the receiving substrate 130 while the device 110 is still coupled to the donor substrate 120. Laser ablation of the layer 112 releases the device 110 from the donor substrate 120 and pushes the device 110 toward the surface 132 of the receiving substrate 130. The surface 132 may include an adhesive that bonds the device 110 to the surface 132 after transfer, or the device 110 may stay in place on the surface 132 until bonded to the surface 132 by, for example, soldering.

[0026] exist Figure 1A In a bond-release embodiment of the transfer step 102 not shown in FIG, the donor substrate 120 and the receiving substrate 130 are arranged so that the device 110 is sandwiched between the donor substrate 120 and the receiving substrate 130 before transfer (corresponding to a zero gap 140 between the device 110 and the receiving substrate 130). Laser ablation of the layer 112 releases the device 110 from the donor substrate 120 and leaves the device 110 on the surface 132 of the receiving substrate 130. The device 110 can be bonded to the surface 132 before laser lift-off from the donor substrate 120, such as by an adhesive or welding. Alternatively, the device 110 can stay in place on the surface 132 after laser lift-off until bonded to the surface 132 by, for example, welding.

[0027] The method 100 can also be used for a stamp-based transfer scheme. When the method 100 is applied to a stamp-based transfer scheme, the receiving substrate 130 is grasped to the side of the device 110 ( Figure 1A The seal on the vertical side of the

[0028] like Figure 1B As shown, the transfer step 102 results in the device 110 being coupled to the surface 132 of the receiving substrate 130. The surface 116 of the device 110 faces away from the surface 132. In the transfer step 102, the surface 116 is exposed by laser ablating the layer 112. However, the laser ablating of the layer 112 in the transfer step 102 leaves gallium residue 114 on the surface 116. At least initially, the gallium residue 114 is liquid because the melting temperature of gallium metal is 30°C. The gallium residue 114 can form a continuous coating (e.g., Figure 1B as shown), a collection of droplets, or a combination thereof.

[0029] In the cleaning step 104, as Figure 1C As shown, a UV laser beam 190 is directed onto the surface 116 to ablate the gallium residue 114, thereby removing the gallium residue 114 from the surface 116, as shown in FIG. Figure 1DThe wavelength of UV laser beam 190 can be in the range of 190 to 320 nm and can be the same as the wavelength of UV laser beam 180. In a particularly advantageous embodiment, each of UV laser beams 180 and 190 is generated by UV laser 170, so that the same laser system performs transfer step 102 and cleaning step 104. Alternatively, UV laser beam 190 is generated by a laser source different from the laser source used in transfer step 102.

[0030] The energy density delivered by UV laser beam 190 in cleaning step 104 may be less than the energy density delivered by UV laser beam 180 in transfer step 102 to prevent UV laser beam 190 from ablating or otherwise damaging device 110. In one embodiment of method 100, the energy density delivered by UV laser beam 190 in cleaning step 104 is no more than 85% (e.g., between 25% and 85%) of the energy density delivered by UV laser beam 180 in transfer step 102. In another embodiment, the energy density delivered by UV laser beam 190 in cleaning step 104 is between 500 and 1000 mJ / cm 2 between.

[0031] Depending on the material of receiving substrate 130 (and any objects disposed on surface 132 in addition to device 110), it may be preferable or even necessary to limit the irradiation of UV laser beam 190 to only surface 116. Therefore, in one embodiment of cleaning step 104, the lateral size and shape of UV laser beam 190 is matched to the lateral size and shape of surface 116. For example, Figure 1C As shown, Figure 1C The width 194 of the UV laser beam 190 in the plane of the device 110 matches the width 118W of the surface 116 in the same plane. The UV laser beam 190 may be masked to match the shape of the surface 116, such as a rectangle. In the transfer step 102, the size and shape of the UV laser beam 180 may be set to match the footprint of the layer 112 in a similar manner and for similar reasons. Referring again to the cleaning step 104, a portion of the surface 116 may be particularly optically sensitive, such as a light emitting or light collecting area, which is only a subset of the surface 116. In this case, the size and shape of the UV laser beam 190 may be set to avoid irradiating this sensitive portion of the surface 116, such as the width 194 is less than the width 118W. In other cases applicable to light emitting or light collecting embodiments of the device 110, the relevant light transmissive area may be only a subset of the surface 116. In this case, the size and shape of the UV laser beam 190 may be set to match the light transmissive area of ​​the surface 116. In these cases as well, the width 194 may be less than the width 118W.

[0032] Laser ablation of the gallium residue 114 releases the gallium residue 114 from the surface 116, but may generate gallium particles or even airborne droplets. To prevent such gallium particles or airborne droplets from contaminating the surface 116 or other portions of the receiving substrate 130 (or objects disposed thereon), the method 100 may include exhausting the gallium residue released from the surface 116. Therefore, in addition to one or more laser sources for laser ablation in the transfer step 102 and the cleaning step 104, the apparatus performing the method 100 may also include a pump 178 for collecting and removing the released gallium residue.

[0033] Although Figures 1A-1D 1 , but additional process steps may be performed between the transfer step 102 and the cleaning step 104. In one such extension of the method 100, other microelectronic devices are transferred from other donor substrates to the receiving substrate 130, in which case the cleaning step 104 may be applied to the device 110 and these other microelectronic devices. In one embodiment, the device 110 is a red μLED transferred from a wafer of red μLEDs to the receiving substrate 130, and the method 100 further includes applying the transfer step 102 to green μLEDs on a wafer of green μLEDs and blue μLEDs on a wafer of blue μLEDs, and then applying the cleaning step 104 to each of the red, green, and blue μLEDs.

[0034] In another extension, the method 100 applies the transfer step 102 to a plurality of devices 110 on a donor substrate 120 to transfer each of these devices 110 to a receiving substrate 130, after which the method 100 may apply a cleaning step 104 to each of the transferred devices 110. Optionally, this extension of the method 100 also includes: before applying the cleaning step 104 to all of the transferred devices 110, transferring other devices 110 from one or more other donor substrates 120 to a receiving substrate 130, for example according to the transfer step 102. Alternatively, in the case where different types of devices 110 from different respective donor substrates 120 are to be transferred to the same receiving substrate 130, the method 100 may complete the transfer step and the cleaning step for each type of device 110 before continuing with the transfer and cleaning of the next type of device 110.

[0035] Figure 2 1 is a plan view showing one laser beam configuration 200 for laser cleaning a plurality of devices 110 on a receiving substrate 130 in a multi-device extension of the cleaning step 104 of the method 100. In the configuration 200, a UV laser beam 290 simultaneously irradiates a group of adjacent devices 110 located on the receiving substrate 130. The size and shape of the UV laser beam 290 are set so that its footprint ( Figure 2The shaded area in FIG. 2 ) includes the entire set of devices 110 and any portion of the receiving substrate 130 located between the devices 110. The size and shape of the UV laser beam 290 required to obtain the desired coverage area may include masking. Configuration 200 is suitable when the receiving substrate 130 can withstand the exposure to the UV laser beam 290 required to clean the gallium residue 114 on the device 110, or when UV laser damage to the receiving substrate 130 is acceptable.

[0036] exist Figure 2 In the illustrated embodiment, the group of devices 110 to be cleaned is a 3x3 array of devices 110. Configuration 200 can be adapted to irradiate a different number of devices 110, or even a single device 110. When the group of devices 110 simultaneously irradiated by the UV laser beam 290 is only a subset of the total number of devices 110 to be cleaned, the UV laser beam 290 can be scanned, for example as indicated by arrow 298, to sequentially clean several groups of devices 110. In this way, the UV laser beam 290 can clean a larger subset of the devices 110 located on the receiving substrate 130, or even clean all the devices 110 on the receiving substrate 130. The UV laser beam 290 can be conveniently moved between its pulses. The scanning of the UV laser beam 290 can be customized to skip some devices 110.

[0037] Figure 3 Another laser beam configuration 300 for laser cleaning a plurality of devices 110 on a receiving substrate 130 is shown, wherein UV irradiation is applied only to the devices 110 without exposing adjacent portions of the receiving substrate 130. Configuration 300 is another multi-device extension of the cleaning step 104 of method 100. In configuration 300, a group of devices 110 are irradiated by a UV laser beam 390, which is shielded to selectively expose only the devices 110. The UV laser beam 390 is composed of a plurality of beam columns 392, which are arranged at the positions of the devices 110 and the UV laser beam 390. Figure 3 Each column 392 is aligned with a corresponding device 110. The portion 332 of the receiving substrate 130 located between the devices 110 is not irradiated by the UV laser beam 390. Configuration 300 is similar to configuration 200 in other respects and can be applied in a scanning manner, as described above with reference to Figure 2 As shown, for example, by arrow 398. Configuration 300 is preferred over configuration 200 when directly irradiating receiving substrate 130 at an energy density required to clean device 110 would cause unacceptable damage to receiving substrate 130.

[0038] Figure 4Another laser beam configuration 400 is shown for laser cleaning a plurality of devices 110 on a receiving substrate 130, again applying UV radiation exclusively to the devices 110 without exposing adjacent portions of the receiving substrate 130. Configuration 400 is a variation of configuration 300 that uses a plurality of spaced-apart beam columns 492 (in Figure 4 The UV laser beam 490 composed of the UV laser beam 490 (represented as the shaded area in FIG. 1 ) is used to illuminate the array of devices 110 having a lower density than the full array of devices 110 on the receiving substrate 130. Figure 4 In the illustrated embodiment, the density of the array of devices 110 illuminated by the UV laser beam 490 is 25% of the full array density of devices 110 on the receiving substrate 130, wherein the pillars 492 are aligned with one device 110 in each 2x2 block of devices 110. Portions 432 of the receiving substrate 130 not occupied by devices 110 are not exposed to the UV laser beam 490, and devices 110 that are not to be cleaned are also not exposed to the UV laser beam 490. The UV laser beam 490 may be applied in a scanning manner, as described above with reference to Figure 2 As described, for example, as indicated by arrow 498.

[0039] Figure 2 , Figure 3 and Figure 4 The degree of cleaning selectivity demonstrated is not achievable with liquid etching and demonstrates the significant advantages of the present transfer and cleaning methods. In addition, some existing laser lift-off systems are equipped with the ability to shape, size, mask, and scan the UV laser beam, as described above in reference Figure 2 , Figure 3 and Figure 4 As described above, it may be possible to implement these UV laser beam configurations using existing equipment. Although discussed in the context of cleaning step 104, the above reference Figure 2 , Figure 3 and Figure 4 Each of the configurations discussed may also be applied to the transfer step 102 .

[0040] Figure 5 5 is an image 500 of microelectronic devices that, in one embodiment, demonstrates the performance of method 100. Image 500 is a transmission image of an array of microelectronic devices on a receiving substrate after transfer according to transfer step 102 of method 100, including (a) microelectronic devices 510 that have been cleaned according to cleaning step 104 of method 100 and (b) microelectronic devices 520 that have not been cleaned. Figure 5 Not all devices 510 and 520 are labeled, but device 520 is easily identifiable as the dark device in image 500. The dark color of device 520 results from the gallium residue 114 blocking the transmission of light through the device. In contrast, device 510 can transmit light, thereby demonstrating the effectiveness of cleaning step 104.

[0041] In the embodiment of image 500, each device 510 is subjected to a laser beam having a wavelength of 248 nm and an energy density of 900 mJ / cm 2 The energy density required to clean the gallium residue 114 may depend on several factors. One of these factors is the thickness of the sacrificial GaN layer ablated during the transfer step ( Figure 1A Another factor is the degree of cleanliness required in a given application. Certain applications may require a high level of cleaning, while other applications may be able to tolerate a certain amount of gallium residue remaining after the laser cleaning step. For example, in some applications, removal of 80-99% of the gallium residue may be acceptable, so cleaning for these applications can be performed with a lower laser energy density than when a higher level of cleaning is required. We have found that the process window for removing about 99% of the gallium residue is generally quite wide. In one embodiment, we have found that using 700 to 900 mJ / cm 2 This level of cleaning can be achieved with laser energy densities in the range of

[0042] Currently, most laser lift-off processes are based on the ablation of a sacrificial GaN layer. However, the sacrificial layer may have other compositions, such as aluminum gallium nitride (Al x Ga 1-x N), gallium oxide (Ga2O3), amorphous gallium oxide (α-GaO x ) or InGaN (In x Ga 1-x N). The method 100 can be extended to these compositions. Thus, more generally, the layer 112 is a heterogeneous solid layer comprising gallium, and the gallium residue 114 is a residue comprising gallium and possibly other metals.

[0043] The present invention has been described above in the form of preferred embodiments and other embodiments. However, the present invention is not limited to the embodiments described and depicted herein. On the contrary, the present invention is only limited by the claims attached hereto.

Claims

1. A method for ultraviolet laser transfer and cleaning of microelectronic devices, comprising the following steps: transferring a microelectronic device from a first substrate to a second substrate, the microelectronic device being coupled to the first substrate via a sacrificial layer, the sacrificial layer being a heterogeneous solid layer containing gallium, the transferring comprising releasing the microelectronic device from the first substrate by laser ablating the sacrificial layer using a first ultraviolet laser beam, the laser ablation leaving a gallium residue on the microelectronic device; as well as At least a portion of the gallium residue is removed from the microelectronic device after the transferring step, the cleaning comprising laser ablating the gallium residue using a second ultraviolet laser beam. The method of claim 1 , wherein the sacrificial layer comprises gallium nitride.

3. The method according to claim 1 or claim 2, wherein the sacrificial layer is made of gallium nitride.

4. The method according to any one of the preceding claims, further comprising: The first ultraviolet laser beam and the second ultraviolet laser beam are generated by the same ultraviolet laser.

5. The method of claim 4, wherein the ultraviolet laser is an excimer laser.

6. The method according to any one of the preceding claims, wherein the first substrate is a sapphire substrate and the wavelength of the first and second ultraviolet laser beams is between 190 and 320 nanometers.

7. The method according to any one of the preceding claims, wherein the cleaning step further comprises: Gallium residues released from the microelectronic device are removed by laser ablation.

8. The method according to any of the preceding claims, wherein the cleaning step is performed by a single UV laser pulse.

9. The method according to any one of the preceding claims, wherein the energy density of the second ultraviolet laser beam incident on the microelectronic device in the cleaning step is less than the energy density of the first ultraviolet laser beam incident on the sacrificial layer in the transferring step.

10. The method of any one of the preceding claims, wherein the energy density of the second UV laser beam incident on the microelectronic device in the cleaning step is between 25% and 85% of the energy density of the first UV laser beam incident on the sacrificial layer in the transferring step.

11. The method of any of the preceding claims, wherein the transferring step results in the microelectronic device being located on the second substrate with the laser ablated side of the microelectronic device being farthest from the second substrate.

12. A method according to any preceding claim, wherein the second substrate is a display backplane.

13. A method according to any preceding claim, wherein the second substrate comprises a polymer.

14. The method according to any of the preceding claims, wherein the second substrate comprises a functional layer.

15. The method according to any one of the preceding claims, further comprising: The cleaning step is applied to a plurality of microelectronic devices located on the second substrate.

16. The method according to claim 15, further comprising: The plurality of microelectronic devices are simultaneously irradiated with the second ultraviolet laser beam to remove gallium residues on each of the plurality of microelectronic devices.

17. The method according to claim 15, further comprising: The second ultraviolet laser beam is spatially scanned to sequentially irradiate the plurality of microelectronic devices, thereby sequentially removing gallium contaminants on the plurality of microelectronic devices.

18. The method according to any one of the preceding claims, wherein the cleaning step comprises: The second ultraviolet laser beam is selectively applied to the microelectronic device while surrounding areas of the second substrate are not exposed to the second ultraviolet laser beam.

19. A method for ultraviolet laser transfer and cleaning of microelectronic devices comprising the following steps: transferring a microelectronic device from a first substrate to a second substrate, the transferring comprising laser ablating a sacrificial layer coupling the microelectronic device to the first substrate, the sacrificial layer comprising gallium, the laser ablation leaving a gallium residue on the microelectronic device; removing at least a portion of the gallium residue from the microelectronic device after the transferring step, the cleaning comprising laser ablating the gallium residue using a second ultraviolet laser beam; as well as The first ultraviolet laser beam and the second ultraviolet laser beam are generated by the same ultraviolet laser.

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