Patent Publication Number: US-2023138834-A1

Title: 3d printing apparatus and 3d printing method

Description:
PRIORITY STATEMENT 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0149876, filed on Nov. 3, 2021 in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety. 
     FIELD 
     Example embodiments relate to a three-dimensional printing apparatus and a three-dimensional printing method. More particularly, example embodiments relate to a three-dimensional printing apparatus configured to spray droplets on a substrate and cure them to a desired width, and a three-dimensional printing method using the same. 
     BACKGROUND 
     Inkjet printing technology is expandable from conventional coating and selective printing to 3D printing (additive manufacturing). In particular, many attempts have been made to apply it to a semiconductor package field. In order to form a microstructure, after discharging UV curable ink on a substrate, a UV light module may be installed on one side of an inkjet head to irradiate light to cure the ink. However, since the ink is exposed to light while the ink is spread on the substrate due to mechanical limitations of the inkjet head, it is difficult to reduce a size of the microstructure. 
     SUMMARY 
     Example embodiments provide a 3D printing apparatus capable of forming a microstructure having a desired size. 
     Example embodiments provide a 3D printing method using the 3D printing apparatus. 
     According to example embodiments, a 3D printing apparatus includes a substrate stage configured to support a substrate, a droplet ejector including at least one droplet nozzle configured to discharge a photo-curable droplet on the substrate, a first photo curing unit configured to irradiate light to a drop path along which the droplet discharged from the droplet nozzle falls to change a viscosity of the droplet, and a second photo curing unit configured to irradiate light onto the droplet that has landed on the substrate to cure the droplet. 
     According to example embodiments, a 3D printing apparatus includes a substrate stage configured to support a substrate, an inkjet head including at least one droplet nozzle configured to discharge an ultraviolet (UV)-curable droplet on the substrate, a first UV irradiator configured to irradiate UV light in a horizontal direction to a drop path along which the droplet discharged from the droplet nozzle falls to change a viscosity of the droplet, a second UV irradiator configured to irradiate UV light onto the droplet that has landed on the substrate to cure the droplet, and a controller configured to control an irradiation timing of the UV light emitted from the first UV irradiator based on an ejection signal of the droplet ejected from the droplet nozzle. 
     According to example embodiments, a 3D printing apparatus includes a substrate stage configured to support a substrate, a droplet ejector comprising at least one droplet nozzle configured to discharge a photo-curable droplet on the substrate, a first photo curing unit configured to irradiate light to a drop path along which the droplet discharged from the droplet nozzle falls, to change a viscosity of the droplet, and a second photo curing unit configured to irradiate light onto the droplet that has landed on the substrate, to cure the droplet. The first photo curing unit is configured to irradiate the light to different sides of the droplet falling along the drop path. 
     According to example embodiments, in a 3D printing method, a substrate is positioned on a substrate stage. A photo-curable droplet is discharged on a target area of the substrate through at least one droplet nozzle. Light is firstly irradiated to the droplet falling along a drop path to change a viscosity of the droplet. Light is secondarily irradiated onto the droplet that has landed on the substrate to cure the droplet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.  FIGS.  1  to  19    represent non-limiting, example embodiments as described herein. 
         FIG.  1    is a block diagram illustrating a three-dimensional printing apparatus in accordance with example embodiments. 
         FIG.  2    is a cross-sectional view illustrating a distance between a droplet nozzle and a substrate and a distance between the droplet nozzle and a second light irradiator in  FIG.  1   . 
         FIG.  3    is a plan view illustrating a droplet ejector in  FIG.  1   . 
         FIG.  4    is a cross-sectional view illustrating a first photo curing unit in accordance with example embodiments. 
         FIG.  5    is a cross-sectional view taken along the line A-A′ in  FIG.  4   . 
         FIG.  6    is a cross-sectional view taken along the line B-B′ in  FIG.  4   . 
         FIG.  7    is a cross-sectional view illustrating an input portion of an optical fiber module in accordance with example embodiments. 
         FIGS.  8  and  9    are cross-sectional views illustrating a portion of an output portion of an optical fiber module in accordance with example embodiments. 
         FIG.  10    is a plan view illustrating a light emitting portion of a first photo curing unit in accordance with example embodiments. 
         FIG.  11    is a perspective view illustrating a portion of the light emitting portion in  FIG.  10   . 
         FIG.  12    is a plan view illustrating a light emitting portion of a first photo curing unit in accordance with example embodiments. 
         FIG.  13    is a block diagram illustrating a controller of the 3D printing apparatus of  FIG.  1   . 
         FIG.  14    is a cross-sectional view illustrating a first photo curing unit that irradiates light to a droplet discharged from a droplet nozzle. 
         FIG.  15    is a cross-sectional view illustrating a second photo curing unit that irradiates light onto a droplet that has landed on a wafer. 
         FIG.  16    is a plan view illustrating a microstructure formed on the wafer in  FIG.  15   . 
         FIG.  17    is a cross-sectional view illustrating a first photo curing unit that irradiates light to droplets discharged from a plurality of droplet nozzles in accordance with example embodiments. 
         FIG.  18    is a cross-sectional view illustrating a microstructure formed on a wafer in accordance with example embodiments. 
         FIG.  19    is a flowchart illustrating a 3D printing method in accordance with example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, example embodiments will be explained in detail with reference to the accompanying drawings. 
       FIG.  1    is a block diagram illustrating a three-dimensional printing apparatus in accordance with example embodiments.  FIG.  2    is a cross-sectional view illustrating a distance between a droplet nozzle and a substrate and a distance between the droplet nozzle and a second light irradiator in  FIG.  1   .  FIG.  3    is a plan view illustrating a droplet ejector in  FIG.  1   . 
     Referring to  FIGS.  1  to  3   , a three-dimensional printing apparatus  10  may include a substrate stage  20  configured to support a substrate such as a wafer W, a droplet ejector  30  installed over the substrate stage  20  to eject droplets having photo-curability on the substrate, a first photo curing unit or first photo curing system  100  configured to change physical properties of the droplet by firstly irradiating light onto the droplet ejected from the droplet ejector  30 , and a second photo curing unit or second photo curing system  200  configured to cure the droplet by secondarily irradiating light on the droplet that has landed on the substrate. In addition, the three-dimensional printing apparatus  10  may further include a controller  400  configured to control operations of the substrate stage  20 , the droplet ejector  30 , the first photo curing unit  100  and the second photo curing unit  200 . 
     In example embodiments, the three-dimensional printing apparatus  10  may spray droplets on the substrate such as the wafer W and curing it to have a desired width in order to manufacture a three-dimensional structure. The three-dimensional printing apparatus  10  may include an inkjet printing apparatus for 3D printing. 
     For example, the three-dimensional printing apparatus  10  may be used to form fine structures such as support spacers that are disposed in a peripheral region of a memory die between vertically stacked memory dies (chips), such as a high bandwidth memory (HBM) device. Additionally, the three-dimensional printing apparatus  10  may be used to form a fine structure such as a dam structure that is disposed on one surface of a redistribution wiring layer of a panel level package. The dam structure may be provided around each of electrodes of a capacitor that are exposed on one surface of the redistribution wiring layer to protect them from the outside. The capacitor may include a land-side capacitor (LSC) type capacitor. 
     In example embodiments, the substrate stage  20  may support the wafer W on which the droplet lands. The three-dimensional printing apparatus  10  may include at least one driver configured to move the substrate stage  20  and the droplet ejector  30  relative to each other. For example, the driver may move the substrate stage  20  in a first direction (X direction) and move the droplet ejector  30  in a second direction (Y direction) perpendicular to the first direction. Additionally, the driver may move the second photo curing unit  200  in the first direction (X direction) or the second direction (Y direction). 
     The controller  400  may output a driving pulse signal to the driver to move the wafer W in the first direction (X direction) and move the droplet ejector  30  in the second direction (Y direction), and as will be described below, may control operations of the first photo curing unit  100  and the second photo curing unit  200  to be in synchronization with a jetting trigger signal of the droplet ejector  30 . Accordingly, the substrate stage  20  may move relative to each of the droplet ejector  30  and the second photo curing unit  200 . Thus, the droplet ejector  30  may eject a droplet at a desired position on the wafer W, and the second photo curing unit  200  may irradiate light onto the droplet that has impacted the wafer W to cure the droplet. 
     In example embodiments, the droplet ejector  30  may include at least one droplet nozzle  32  as a droplet discharger that ejects a photo-curable droplet  50  on the wafer W. For example, the droplet ejector  30  may include an inkjet head. Alternatively, the droplet ejector may include a dispenser. 
     When the droplet ejector  30  includes an inkjet head, since it is easy to control the discharge amount of the droplet  50  and the droplet  50  can reach a fine area, there is an advantage that a fine structure can be formed in a desired shape and size. Hereinafter, a case in which an inkjet head is used as the droplet ejector will be described. 
     The droplet ejector  30  may include a liquid supply unit configured to supply a photo-curable liquid, the droplet nozzle  32  configured to eject the liquid from the liquid supply unit into droplets having predetermined diameters, and a piezoelectric element configured to drive the droplet nozzle  32 . The inkjet head driver may output a control signal such as a trigger signal to the piezoelectric element, and the piezoelectric element may modulate the pressure inside the droplet nozzle  32  in response to the trigger signal to eject the droplet  50 . The inkjet head driver may be controlled by a droplet control portion or module of the controller  400 , and the injection timing, diameter, and exit speed of the droplets from the droplet nozzle  32  may be adjusted according to the control signal of the controller  400 . 
     For example, a diameter of the droplet nozzle  32  may be within a range of 15 μm to 40 μm. The liquid may include an ultraviolet (UV) curable resin. In this case, the first photo curing unit  100  may serve as a first UV irradiator, and the second photo curing unit  200  may serve as a second UV irradiator. Although in the drawings, the droplet ejector is illustrated as including the droplet nozzle having a nozzle shape, is not limited thereto, and the droplet nozzle may have a hole shape. 
     The droplet ejector  30  may include at least one inkjet head block  31  provided with droplet nozzles  32  installed therein. The droplet nozzles  32  may be arranged in an array shape at predetermined intervals. For example, a length of the inkjet head block  31  may be within a range of 60 cm to 80 cm, and a width of the inkjet head block  31  may be within a range of 30 cm to 40 cm. The inkjet head block  31  may include tens to thousands of droplet nozzles  32 . The droplet nozzles  32  may be installed in the inkjet head block  31  to be arranged in one row, two rows, three rows or four rows, for example. 
     As illustrated in  FIG.  3   , in the inkjet head block  31 , first to third nozzle arrays  32   a ,  32   b  and  32   c  may be arranged in the second direction (Y direction) perpendicular to the first direction (X direction). Each of the first to third nozzle arrays  32   a ,  32   b  and  32   c  may include droplet nozzles  32  that are arranged to be spaced apart from each other by a predetermined interval or spacing S along the first direction (X direction). For example, the spacing distance between the droplet nozzles  32  adjacent to each other may be within a range of 100 μm to 150 μm. The first to third nozzle arrays  32   a ,  32   b  and  32   c  may simultaneously or sequentially eject the droplets  50  in response to ink ejection signals (trigger signals). 
     As illustrated in  FIG.  2   , a gap G 1  between the droplet nozzle  32  of the droplet ejector  30  and the wafer W may be within a range of 1 mm to 2 mm. The first to third nozzle arrays  32   a ,  32   b  and  32   c  may respectively eject the droplets  50  onto first to third regions on the wafer W that are spaced apart from each other at regular intervals. The ejected droplets  50  may each fall on the wafer W after falling along a drop path. 
     In example embodiments, the first photo curing unit  100  may irradiate light onto the drop path of the droplet  50  discharged from the droplet nozzle  32  to change the physical properties of the droplet (primary curing). The first photo curing unit  100  may irradiate light to the droplet  50  before the droplet  50  impacts the wafer W. The first photo curing unit  100  may irradiate light in a horizontal direction perpendicular to the vertical direction (Z direction) toward the droplet  50  falling in the vertical direction (Z direction). The first photo curing unit  100  may include optical elements for irradiating ultraviolet light. 
     As will be described below, the first photo curing unit  100  may include a plurality of optical fibers for directing the light from the ultraviolet light source toward the drop path. Output terminals of the optical fibers as a light emitting portion  136  of the first photo curing unit  100  may be disposed between the droplet nozzle  32  and the wafer W to emit ultraviolet light in the horizontal direction toward the droplet  50  falling along the drop path. The light emitting portion  136  of the first photo curing unit  100  may be installed in or on a flange  34  fixed to a lower portion of the inkjet head block  31 . The light emitting portion  136  may be installed under the flange  34  to irradiate the ultraviolet light in the horizontal direction toward the droplet  50  falling along the drop path between the droplet nozzle  32  and the wafer W. 
     The light emitting portion  136  may irradiate the ultraviolet light in the horizontal direction or in a direction inclined downward by a predetermined angle with respect to the horizontal direction. An angle adjusting mechanism may be installed inside or on the flange  34  or the light emitting portion  136  to adjust an angle of the light emitted from the light emitting portion  136 . 
     Since the liquid used in the inkjet head has a relatively low viscosity, it can spread very well on the surface of the wafer W after it lands on the wafer W having a hydrophilic surface. The first photo curing unit  100  may firstly curing the droplet  50  having a low viscosity before landing on the wafer W to increase the viscosity of the droplet  50 . Accordingly, by reducing the spread of the droplet  50  on the wafer W, it may be possible to form a fine structure having a relatively narrow line width. 
     In example embodiments, the second photo curing unit  200  may irradiate light onto the droplet  50  that has landed on the wafer W to cure the droplet (secondary curing). The second photo curing unit  200  may irradiate light in the vertical direction (Z direction) toward the droplet  50  that has landed on the wafer W. The second photo curing unit  200  may include a UV head that is installed to be spaced apart from the inkjet head block  31  in the horizontal direction to irradiate ultraviolet light. 
     For example, a gap G 2  between the droplet nozzle  32  of the droplet ejector  30  and a light irradiator of the second photo curing unit  200  may be at least 60 mm. After the droplet  50  ejected from the droplet nozzle  32  lands on the wafer W, the wafer W may be moved under the second photo curing unit  200  by the stage driver, and then, the second photo curing unit  200  may irradiate light onto the droplet on the wafer W under the second photo curing unit  200 . In this case, after about 300 ms after discharging the droplet, the second photo curing unit  200  may irradiate the droplet with light. 
     Hereinafter, the first photo curing unit will be described in detail. 
       FIG.  4    is a cross-sectional view illustrating a first photo curing unit in accordance with example embodiments.  FIG.  5    is a cross-sectional view taken along the line A-A′ in  FIG.  4   .  FIG.  6    is a cross-sectional view taken along the line B-B′ in  FIG.  4   . 
     Referring to  FIGS.  4  to  6   , a first photo curing unit  100  may include a light source  110  to generate light and include an optical fiber module  130  having a plurality of optical fibers  131  configured to direct light from the light source  110  toward a droplet  50  between a droplet nozzle  32  and a wafer W. The first photo curing unit  100  may further include a clamp  120  connecting the light source  110  and the optical fiber module  130 . 
     The light source  110  may include an ultraviolet light source, a laser light source, etc., e.g., as a UV head. The light generated by the light source  110  may be determined or selected according to the material of the droplet  50  to be cured. 
     The optical fiber module  130  may include a cable  132  accommodating the optical fibers  131 , an input portion  134  and an output portion  136 . The input portion  134  of the optical fiber module  130  may be connected to the light source  110  by the clamp  120 . The clamp  120  may align the UV head with an optical axis of the optical fiber module  130 . For example, a diameter of the optical fiber  131  may be 600 μm or less. 
     A plurality of the optical fibers  131  may be accommodated within the cable  132 , and light from the light source  110  may be inputted through input terminals of the optical fibers  131  and outputted through output terminals of the optical fibers  131 . The input portion  134  of the optical fiber module  130  may have a circular cross-sectional shape in order to minimize light loss, and the output portion  136  of the optical fiber module  130  may have a rectangular cross-sectional shape extending in one direction in consideration of the positions or the like of the droplets  50  discharged from a plurality of droplet nozzles  32 . Since the cross-sectional shape of the output portion  136  of the optical fiber module  130  can have various shapes, the light output from the output portion  136  may be formed to have a desired shape. 
     Since the cable  132  of the optical fiber module  130  has flexibility, the output portion  136  of the optical fiber module  130  may be installed at a desired position. As illustrated in  FIG.  1   , the output portion  136  of the optical fiber module  130  as a light emitting portion of the first photo curing unit  100  may be fixedly installed in a lower portion of the inkjet head block  31  by the flange  34 . Accordingly, the output portion  136  of the optical fiber module  130  may be arranged between the droplet nozzle  32  and the wafer W to irradiate the ultraviolet light in the horizontal direction toward the droplet  50  falling along the drop path. 
     The irradiation time, power (output), intensity of illumination, light emission channel, etc. of the light emitted by the first photo curing unit  100  may be controlled by a light controller of the controller  400 . As will be described below, the power of the light may be determined according to the material of the droplet that strikes the wafer W. 
     The injection timing, diameter, and exit speed of the droplets from the droplet nozzle  32  may adjust according to the control signal of the controller  400 . 
       FIG.  7    is a cross-sectional view illustrating an input portion of an optical fiber module in accordance with example embodiments.  FIGS.  8  and  9    are cross-sectional views illustrating a portion of an output portion of an optical fiber module in accordance with example embodiments.  FIG.  7    is a cross-sectional view taken along the line A-A′ in  FIG.  4   .  FIGS.  8  and  9    are cross-sectional views taken along the line B-B′ in  FIG.  4   . 
     Referring to  FIGS.  7  to  9   , the number of optical fibers  131  may be changed, and output terminals of the optical fibers  131  in an output portion  136  of an optical fiber module  130  may be arranged in an array form. 
     As illustrated in  FIG.  8   , the output portion  136  of the optical fiber module  130  as a light emitting portion of a first photo curing unit  100  may include first and second light emission channels  131   a  and  131   b  arranged in a vertical direction (Z direction). Some of the output terminals of the optical fibers  131  may be arranged in one row to provide the first light emission channel  131   a . Some of the output terminals of the optical fibers  131  may be arranged in two rows to provide the second light emission channel  131   b . The first light emission channel  131   a  may irradiate light to the droplet  50  at a first height from the wafer W. The second light emission channel  131   b  may radiate light to the droplet  50  at a second height lower than the first height from the wafer W. 
     As illustrated in  FIG.  9   , the output portion  136  of the optical fiber module  130  as the light emitting portion of the first photo curing unit  100  may include first, second and third light emission channels  131   a ,  131   b  and  131   c  arranged in the vertical direction (Z direction). The first light emission channel  131   a  may irradiate light to the droplet  50  at a first height from the wafer W. The second light emission channel  131   b  may radiate light to the droplet  50  at a second height lower than the first height from the wafer W. The third light emission channel  131   c  may radiate light to the droplet  50  at a third height lower than the second height from the wafer W. 
       FIG.  10    is a plan view illustrating a light emitting portion of a first photo curing unit in accordance with example embodiments.  FIG.  11    is a perspective view illustrating a portion of the light emitting portion in  FIG.  10   . 
     Referring to  FIGS.  10  and  11   , an output portion  136  of an optical fiber module  130  as a light emitting portion of a first photo curing unit  100  may have a polygonal shape such as a rectangular shape extending to surround the droplet ejector  30  or the droplet nozzle  32  when viewed in plan view. Output terminals of the optical fibers  131  may be separated from each other to provide the output portion  136  having the rectangular shape. Accordingly, the output portion  136  may irradiate light to different sides of the droplet  50  discharged from a droplet nozzle  32  to increase the amount of light. 
     For example, the output portion  136  and may include first and second emitting portions  136   a  and  136   b  extending in a direction parallel with a first direction (X direction) and facing each other, and third and fourth emitting portions  136   c  and  136   d  extending in a direction parallel with a second direction (Y direction) and facing each other. Only some of the first to fourth emitting portions  136   a ,  136   b ,  136   c  and  136   d  may be selectively operated to emit light. 
       FIG.  12    is a plan view illustrating a light emitting portion of a first photo curing unit in accordance with example embodiments. 
     Referring to  FIG.  12   , an output portion  136  of an optical fiber module  130  may have an annular or ring shape extending to surround the droplet ejector  30  or the droplet nozzle  32  when viewed in plan view. Output terminals of the optical fibers  131  may be separated from each other to provide the output portion  136  having the annular shape. Accordingly, the output portion  136  may irradiate light to different sides of the droplet  50  discharged from the droplet nozzle  32 . 
     Hereinafter, a method of controlling the 3D printing apparatus will be explained. 
       FIG.  13    is a block diagram illustrating a controller of the 3D printing apparatus of  FIG.  1   . 
     Referring to  FIG.  13   , a controller  400  may include a droplet controller  410  configured to control an operation of a droplet ejector  30  and a light controller  420  configured to control operations of first and second photo curing units  100  and  200 . Additionally, the controller  400  may further include a stage controller configured to control an operation of a substrate stage  20 . 
     In example embodiments, the droplet controller  410  may control operations of the droplet nozzles  32  of the droplet ejector  30 . The droplet controller  410  may output a control signal S 1  such as a trigger signal to an inkjet head driver of the droplet ejector  30 . The piezoelectric element of the droplet ejector  30  may eject the droplet  50  by modulating the pressure inside the droplet nozzle  32  in response to the trigger signal. Additionally, the droplet controller  410  may control the injection timing, diameter, and exit speed of the droplets from the droplet nozzle  32 . 
     The light controller  420  may control the operations of the first and second photo curing units  100  and  200 . The light controller  420  may control the irradiation timing, power, intensity of illumination, optical fiber channel, etc. of the light emitted by the first photo curing unit  100 . The light controller  420  may control the irradiation timing, power, intensity of illumination, etc. of the light emitted by the second photo curing unit  200 . 
     In particular, the light controller  420  may include an irradiation timing controller  422 , a power controller  424  and a light emission channel selector  426 . 
     The irradiation timing controller  422  may receive a first control signal S 1  including the trigger signal from the droplet controller  410  (or the inkjet head driver), and may determine a time delay from ejection of droplets to irradiation of light, that is, light irradiation time point (light irradiation time point (μs˜ms)), based on the trigger signal generation time. 
     The power controller  424  may determine the power (0 to 100%) of the light generated from the light source  110  based on the first control signal S 1 . The power of the light may be determined in consideration of a material of the droplet, a rate of change in viscosity, etc. 
     The light emission channel selector  426  may select at least one of the light emitting channels arranged in the vertical direction in the output portion  136  of the optical fiber module  130 . The light emission channel may be determined in consideration of a time point at which light is irradiated after droplet discharge (height from the substrate). 
     The light controller  420  may output a second control signal S 2  according to the parameters determined by the irradiation timing controller  422 , the power controller  424  and the light emission channel selector  426  to the first photo curing unit  100 , and the first photo curing unit  100  may irradiate light to the droplet  50  based on the second control signal S 2 . 
     Similarly, the light controller  420  may output a third control signal S 3  to the second photo curing unit  200 , and the second photo curing unit  200  may irradiate light onto the droplet that has landed on the wafer W based on the third control signal S 3 . 
       FIG.  14    is a cross-sectional view illustrating a first photo curing unit that irradiates light to a droplet discharged from a droplet nozzle.  FIG.  15    is a cross-sectional view illustrating a second photo curing unit that irradiates light onto a droplet that has landed on a wafer.  FIG.  16    is a plan view illustrating a microstructure formed on the wafer in  FIG.  15   . 
     Referring to  FIG.  14   , a droplet  50  discharged from a droplet nozzle  32  may fall along a drop path P and then land on a wafer W. A light output portion  136  of a first photo curing unit  100  may irradiate light L 1  in a horizontal direction toward the droplet  50  that is falling along the drop path P between the droplet nozzle  32  and the wafer W before the droplet  50  hits the wafer W. 
     When a first time t 1  has elapsed from a discharge time t 0 , the light output portion  136  of the first photo curing unit  100  may irradiate the droplet  50  with light. At this time, a diameter of the droplet  50  may be within a range of 15 μm to 40 μm. As light is irradiated to the droplet  50 , a physical property of the droplet  50 , that is, viscosity may increase. The rate of change in viscosity of the droplet  50  may be determined by the power (output) of light. 
     Then, the droplet  50  having the viscosity increased by the light irradiation may land on a target area of the wafer W at a time point when a second time t 2  has elapsed from the discharge time t 0 . The droplet  50   i  that has landed on the wafer W may spread on the surface of the wafer W. The spread of the impacted droplet  50   i  may be reduced by the increased viscosity so that the impacted droplet has a relatively small diameter D 2 . For example, the diameter D 2  of the impacted droplet  50   i  may be 50 μm or less. A height H of the impacted droplet  50   i  may be 1 μm or less. 
     Referring to  FIGS.  15  and  16   , while the wafer W moves in one direction, the droplet nozzle  32  may discharge the droplets  50  according to a pulse signal, thereby forming a microstructure having a constant width M. 
     After the droplet  50  discharged from the droplet nozzle  32  lands on the wafer W, the wafer W may move under a second photo curing unit  200  by a stage driver and the second photo curing unit  200  may irradiate light L 2  to the droplet  50   i  that has landed on the wafer W. Accordingly, the impacted droplet  50   i  may be changed into a droplet  50   f  cured by light to form the microstructure. The microstructure may have a width M of 50 μm or less. 
     Since the droplet  50  discharged from the droplet nozzle  32  and falling is primarily cured by the first photo curing unit, the time required to be completely cured by the second photo curing unit  200  may be shortened. 
       FIG.  17    is a cross-sectional view illustrating a first photo curing unit that irradiates light to droplets discharged from a plurality of droplet nozzles in accordance with example embodiments. 
     Referring to  FIG.  17   , in example embodiments, an output portion  136  of an optical fiber module as a light emitting portion of a first photo curing unit may include first to third light emission channels  131   a ,  131   b  and  131   c  arranged in a vertical direction (Z direction). Each of the first to third light output channels  131   a ,  131   b  and  131   c  may include portions of output terminals of optical fibers  131 . 
     A plurality of droplet nozzles of a droplet ejector  30  may eject droplets  50  to a first target area R 1  on a wafer W respectively, and the first light emission channel  131   a  may irradiate light L 1   a  toward the droplets  50  at first height h 1  from the wafer W. A plurality of droplet nozzles of the droplet ejector  30  may eject droplets  50  to a second target region R 2  on the wafer W respectively, and the second light emission channel  131   b  may irradiate light L 1   b  toward the droplets  50  at a second height h 2  from the wafer W. A plurality of droplet nozzles of the droplet ejector  30  may eject droplets  50  to a third target region R 3  on the wafer W respectively, and the third light emission channel  131   c  may irradiate light L 1   c  toward the droplets  50  at a third height h 3  from the wafer W. An irradiation timing, output, etc. of the light irradiated from the first to third light emission channels  131   a ,  132   b  and  131   c  may be controlled by a light controller. 
       FIG.  18    is a cross-sectional view illustrating a microstructure formed on a wafer in accordance with example embodiments. 
       FIGS.  1  and  18   , a three-dimensional printing apparatus  10  may sequentially forms a plurality of stacked layers  60   a ,  60   b ,  60   c  and  60   d  on a wafer W to form a desired three-dimensional microstructure. 
     First, a droplet ejector  30  of the 3D printing apparatus  10  may discharge first droplets having a first photo-curable material on a surface of the wafer W to form a first laminated layer  60   a  extending in one direction. In this case, a power (output) of light emitted by a first photo curing unit  100  may be adjusted to 5 mW. A viscosity of the first droplet on which the light emitted by the first photo curing unit  100  has been irradiated may be 10 cp, and a height of the first laminated layer  60   a  may be 0.3 μm. 
     Then, the droplet ejector  30  may discharge second droplets having a second photo-curable material on the first laminated layer  60   a  to form a second laminated layer  60   b . In this case, the power (output) of light emitted by the first photo curing unit  100  may be adjusted to 10 mW. A viscosity of the second droplet on which the light emitted by the first photo curing unit  100  has been irradiated may be 15 cp, and a height of the second laminated layer  60   b  may be 0.3 μm. 
     Then, the droplet ejector  30  may discharge third droplets having a third photo-curable material on the second laminated layer  60   b  to form a third laminated layer  60   c . In this case, the power (output) of light emitted by the first photo curing unit  100  may be adjusted to 15 mW. A viscosity of the third droplet on which the light emitted by the first photo curing unit  100  has been irradiated may be 15 cp, and a height of the third laminated layer  60   c  may be 0.5 μm. 
     Then, the droplet ejector  30  may discharge fourth droplets having a fourth photo-curable material on the third laminated layer  60   c  to form a fourth laminated layer  60   d . In this case, the power (output) of light emitted by the first photo curing unit  100  may be adjusted to 20 mW. A viscosity of the third droplet on which the light emitted by the first photo curing unit  100  has been irradiated may be 15 cp, and a height of the second laminated layer  60   b  may be 1.0 μm. 
     As mentioned above, the three-dimensional printing apparatus  10  may include the droplet ejector  30  that ejects the droplet  50  having a photo-curable material on the wafer W, and the first photo curing unit  100  as a preliminary photo curing unit configured to irradiate light to the droplet  50  ejected from the droplet ejector  30  and falling along the drop path. In addition, the three-dimensional printing apparatus  10  may further include the second photo curing unit  200  as a main photo curing unit configured to irradiate light onto the droplets that have landed on the wafer W. 
     The first photo curing unit  100  may include the output portion  136  of the optical fiber module  130  as the light emitting portion arranged between the droplet nozzle  32  and the wafer W so as to be adjacent to the droplet nozzle  32  of the droplet ejector  30 . The optical fiber module  130  may include a plurality of optical fibers  131  that direct the light from the light source  110  toward the droplet  50  falling along the drop path. The output terminals of the optical fibers  131  may form the output portion  136  of the optical fiber module  130 . 
     The output portion  136  of the optical fiber module  130  may have a rectangular or annular shape extending to surround the droplet nozzle  32  when viewed in plan view. Accordingly, the output portion  136  may irradiate light to various sides of the droplet  50  discharged from the droplet nozzle  32 . 
     Additionally, the output portion  136  of the optical fiber module  130  may include the first to third light emission channels  131   a ,  131   b  and  131   c  arranged in a vertical direction (Z direction). Each of the first to third light emission channels  131   a ,  131   b  and  131   c  may include the portions of the output terminals of the optical fibers  131 . The position (height) of the droplet  50  to be irradiated by light while falling along the drop path may be determined by adjusting the irradiation timings of the first to third light emission channels  131   a ,  131   b  and  131   c.    
     Thus, the height of the stacked layer, spreadability of the droplet, etc. may be adjusted according to the stacked layers of the microstructure formed on the wafer W, the physical properties of the droplet, etc. 
     Hereinafter, a method of forming a three-dimensional microstructure on a wafer using the above three-dimensional printing apparatus will be explained. 
       FIG.  19    is a flowchart illustrating a 3D printing method in accordance with example embodiments. 
     Referring to  FIGS.  1  to  19   , first, a substrate such as a wafer W may be disposed or positioned on a substrate stage  20  (S 10 ), and a droplet  50  having photo-curability may be discharged or ejected toward a target area of the wafer W through at least one droplet nozzle  32  (S 20 ). 
     In example embodiments, a controller  400  may control to move the substrate stage  20  on which the wafer W is disposed to a space under a droplet ejector  30 , and then the droplet nozzle  32  of the droplet ejector  30  may eject the droplet  50  to the target area on the wafer W. For example, a gap G 1  between the droplet nozzle  32  of the droplet ejector  30  and the wafer W may be within a range of 1 mm to 2 mm. 
     An inkjet head block  31  of the droplet ejector  30  may include first to third nozzle arrays  32   a ,  32   b  and  32   c  arranged in a second direction (Y direction) perpendicular to a first direction (X direction). The first to third nozzle arrays  32   a ,  32   b  and  32   c  may eject droplets  50  on the first to third regions R 1 , R 2  and R 3  spaced apart at regular intervals on the wafer W, respectively. 
     Then, a first photo curing unit  100  may firstly irradiate light to the droplet  50  falling along a drop path P to increase the viscosity of the droplet  50  (S 30 ). 
     In example embodiments, as illustrated in  FIG.  14   , the droplet  50  discharged from the droplet nozzle  32  may fall along the drop path P and then land on the wafer W. A light emitting portion  136  of the first photo curing unit  100  may irradiate light L 1  in a horizontal direction toward the droplet  50  that is falling along the drop path P between the droplet nozzle  32  and the wafer W before the droplet  50  hits the wafer W. 
     When a first time t 1  has elapsed from a discharge time t 0 , the light emitting portion  136  of the first photo curing unit  100  may irradiate the droplet  50  with light. At this time, a diameter of the droplet  50  may be within the range of 15 μm to 40 μm. As light is irradiated to the droplet  50 , the physical property of the droplet  50 , that is, viscosity may increase. The rate of change in viscosity of the droplet  50  may be determined by the power (output) of the light. 
     Then, the droplet  50  having the increased viscosity by the light irradiation may land on a target area of the wafer W at a time point when a second time t 2  has elapsed from the discharge time t 0 . The droplet  50   i  that has landed on the wafer W may spread on a surface of the wafer W. The spread of the impacted droplet  50   i  may be reduced by the increased viscosity so that the impacted droplet has a relatively small diameter D 2 . For example, the diameter D 2  of the impacted droplet  50   i  may be 50 μm or less. A height H of the impacted droplet  50   i  may be 1 μm or less. 
     Then, a second photo curing unit  200  may secondarily irradiate light onto the droplet  50   i  that has landed on the wafer W to cure the droplet  50   i  (S 40 ). 
     In example embodiments, as illustrated in  FIGS.  15  and  16   , while the wafer W moves in one direction, the droplet nozzle  32  may discharge the droplets  50  according to a pulse signal, thereby forming a microstructure having a constant width M. 
     After the droplet  50  discharged from the droplet nozzle  32  lands on the wafer W, the wafer W may move to a space under the second photo curing unit  200  by a stage driver and the second photo curing unit  200  may irradiate light to the droplet  50   i  that has landed on the wafer W. Accordingly, the impacted droplet  50   i  may be changed into a droplet  50   f  cured by light to form the microstructure. The microstructure may have a width M of 50 μm or less. 
     The above-described steps S 10  to S 40  may be repeatedly performed to sequentially form a plurality of stacked layers on the wafer W to form a desired three-dimensional microstructure. 
     For example, the 3D microstructure may include a plurality of support spacers disposed between stacked memory dies of a high bandwidth memory (HBM) device. The support spacer may be disposed in a peripheral region of the memory die to prevent over-pressing in an edge region in a pressurized reflow process. Since the support spacer is disposed adjacent to solder bumps, the support spacer may be required to have a relatively narrow line width so as not to interfere with the solder bumps. A width of the support spacer may be 50 μm or less, and a height of the support spacer may be within a range of 12 μm to 14 μm. 
     According to another example, the 3D microstructure may include a dam structure disposed on one surface of a redistribution wiring layer of a panel level package (PLP). The dam structure may be provided around LSC-type capacitor pads that are exposed from the surface of the redistribution wiring layer, to protect them from dielectric resin. A width of the dam structure may be 50 μm or less, and a height of the dam structure may be within a range of 20 μm to 30 μm. 
     The above three-dimensional printing method may be used for manufacturing a semiconductor package including semiconductor devices such as logic devices or memory devices. The semiconductor package may include logic devices such as central processing units (CPUs), main processing units (MPUs), or application processors (APs), or the like, and volatile memory devices such as DRAM devices, HBM devices, or non-volatile memory devices such as flash memory devices, PRAM devices, MRAM devices, ReRAM devices, or the like. 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in example embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of example embodiments as defined in the claims.