Patent Publication Number: US-2015086716-A1

Title: Printing of colored pattern using atomic layer deposition

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to co-pending U.S. Provisional Patent Application No. 61/883,095, filed on Sep. 26, 2013, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Field of Art 
     The disclosure relates to forming a layer of material on a substrate using a printer head that performs atomic layer deposition (ALD) on the substrate. 
     2. Description of the Related Art 
     Instead of using conventional semiconductor manufacturing processes, substrates for electronic devices may also be printed with various patterns using various types of materials. Common printing equipments may be used to print ink or other materials on selected areas of the substrate. The printing of patterns is not limited solely to decorative or ornamental features on the substrate, and sometimes printing may be used to form electronic components such as thin film transistor (TFT) or resistors. The process of printing components or features generally has the advantage of producing high-precision components at a low cost. 
     Atomic layer deposition (ALD) is one way of depositing material on a substrate. ALD uses the bonding force of a chemisorbed molecule that is different from the bonding force of a physisorbed molecule. In ALD, source precursor is adsorbed onto the surface of a substrate and then purged with an inert gas to remove physisorbed molecules of the source precursor while retaining chemisorbed molecules of the source precursor on the substrate. As a result, physisorbed molecules of the source precursor (bonded by the Van der Waals force) are desorbed from the substrate. However, chemisorbed molecules of the source precursor are covalently bonded, and hence, these molecules are strongly adsorbed in the substrate and not desorbed from the substrate. 
     The chemisorbed molecules of the source precursor (adsorbed on the substrate) react with and/or are replaced by molecules of reactant precursor. Then, the excessive precursor or physisorbed molecules are removed by injecting the purge gas and/or pumping the chamber, obtaining a final atomic layer. 
     SUMMARY 
     Embodiments relate to printing a pattern on a substrate by using a printer head that injects source precursor and reactant precursor onto the substrate. On areas of the substrate exposed to both the source precursor and the reactant precursor, a layer of material forms the pattern by atomic layer deposition (ALD). A first actuator causes the printer head to move along a first axis parallel to a surface of the substrate. A second actuator causes the printer head to move along a second axis parallel to the surface of the substrate. The movement of the printer head by the first and second actuatord deposits the pattern on the substrate. A conduit is connected to the printer head to provide the source precursor and the reactant precursor to the printer head. 
     In one embodiment, a controller controls at least a parameter associated with a thickness of the layer of the material deposited on the substrate. 
     In one embodiment, different portions of the pattern exhibit different colors based on the different thickness of the layer of material. 
     In one embodiment, a third actuator causes the printer head to move towards or away from the substrate. 
     In one embodiment, the printer head injects purge gas onto the substrate to remove at least excess source precursor from the surface of the substrate. The purge gas is provided by the conduit. 
     In one embodiment, the printer head includes a body. The body is formed with a first injection chamber for injecting the source precursor onto the substrate, and a second injection chamber surrounding the first injection chamber. The second injection chamber injects the reactant precursor onto the substrate. 
     In one embodiment, the body is further formed with a channel, a first exhaust and a second exhaust. The channel is open towards the substrate to inject purge gas onto the substrate. The channel is formed between the first injection chamber and the second injection chamber. The first exhaust formed between the first injection chamber and the channel discharges excess source precursor not chemisorbed on the substrate. The second exhaust formed between the channel and the second injection chamber discharges at least excess reactant precursor not chemisorbed on the substrate. 
     In one embodiment, the body is formed with a first constriction zone and a second constriction zone. The first constriction zone is formed for connecting the first exhaust and the first injection chamber. The first constriction zone has a height smaller than a width of the first injection chamber. The second constriction zone is formed for connecting the second exhaust and the second injection chamber. The second constriction zone has a height smaller than a width of the second injection chamber. 
     Embodiments also relate to a printer head assembly including a printer head and a conduit. The printer head includes a body formed with a first injection chamber and a second injection chamber. The first injection chamber injects first gas onto a substrate. The second injection chamber surrounds the first injection chamber and injects second gas onto the substrate. The second gas reacts or replaces molecules of the first gas adsorbed on the substrate to form a layer of material on the substrate. The conduit is connected to the printer head to provide the first gas and the second gas to the printer head. 
     Embodiments also relate to a method of forming a pattern on a substrate. Source precursor is injected onto a surface of a substrate via a printer head. Reactant precursor is injected onto the surface via the printer head. The printer head is moved along a path on a substrate while controlling at least a parameter associated with a thickness of layer deposited on the substrate by reaction or replacement of molecules of the source precursor with molecules of the reactant precursor on the surface. Excess source precursor and reactant precursor from the surface of the substrate are discharged via the printer head. Deposition rate of the film can be changed by controlling how 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Figure (FIG.)  1  is a schematic diagram of a printing device using atomic layer deposition (ALD), according to one embodiment. 
         FIG. 2  is a perspective view of a printer head and a conduit for providing gases to the printer head, according to one embodiment. 
         FIG. 3A  is a cross sectional diagram of a printer head taken along line A-B of  FIG. 2 , according to one embodiment. 
         FIG. 3B  is a cross sectional diagram of the printer head taken along line C-D of  FIG. 2 , according to one embodiment. 
         FIG. 4  is a cross sectional diagram of a printer head, according to another embodiment. 
         FIG. 5  is a top view of a substrate printed with patterns, according to one embodiment. 
         FIG. 6  is a cross sectional diagram of a substrate printed with material of different thicknesses to exhibit different colors, according to one embodiment. 
         FIG. 7  is a schematic diagram illustrating the degree of freedom for the printer head, according to one embodiment. 
         FIG. 8  is a flowchart illustrating a method of forming a pattern of material with different thickness, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments are described herein with reference to the accompanying drawings. Principles disclosed herein may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the features of the embodiments. 
     In the drawings, like reference numerals in the drawings denote like elements. The shape, size and regions, and the like, of the drawing may be exaggerated for clarity. 
     Embodiments relate to depositing a layer of material at different thicknesses on a substrate using atomic layer deposition (ALD) to form patterns that exhibit different colors. The patterns may be formed using a printer head that moves in a two-dimensional plane over the substrate along a path while injecting precursor gases onto the substrate. Patterns are formed on the substrate along the path along which the printer head moves. The refraction of light incident on the layer of material on the substrate causes the deposited material to exhibit different colors. The color change is caused by thin-film interference caused by interference with light waves reflected by the upper and lower boundaries of the deposited material. 
     Figure (FIG.)  1  is a schematic diagram of a printing device  100  using atomic layer deposition (ALD), according to one embodiment. The printing device  100  may include, among other components, a printer head  116 , a conduit  120 , arms  104 ,  108 ,  138  and mechanisms  130 ,  134 ,  140  for moving the arms  104 ,  108 ,  138 . The printer head  116  is secured to the arm  108 , which is in turn mounted on the arm  104  via a linear motor  134 . 
     The arm  108  moves in Y-direction by the operation of an actuator such as linear motor  134  and the arm  104  moves in X-direction by the operation of another actuator such as motor  130 . The arm  138  may move in Z-direction by the operation of an actuator such as linear motor  140  to change the vertical locations of the arms  104 ,  108  and the printer head  116 . By moving the printer head  116  vertically, the location of the printer head  116  can be moved closer to the substrate  112  or moved away from the substrate  112  to adjust distance h between the printer head  116  and the substrate  112 . While loading or unloading the substrate  112 , the printer head  116  can be raised to facilitate the loading or unloading operation. The distance h can also be finely tuned to produce better quality deposition on the substrate  112 . 
     As the arms  104 ,  108  are operated, the printer head  116  and the conduit  120  move along a path  126  in a two-dimensional plane (defined by X-direction and Y-direction) above a substrate  112 , and deposits a layer of material on the substrate  112  to form a pattern  124 . The path  126  may include linear segments, non-linear segments and a combination of both linear and non-linear segments. In the example of  FIG. 1 , the printer head  116  moves along a path  126  by the operation of the linear motor  134  and the motor  130 . The linear motor  134  and the motor  130  may receive signals from a controller  150  to coordinate the movement along the path  126  and also control the speed of the printer head  116 . 
     The conduit  120  provides gases for performing ALD on the substrate  112  to the printer head  116 . The conduit  120  may be made of flexible material and includes multiple channels for separately routing the gases to the printer head  116 . The conduit  120  may also include one or more channels for discharging excess materials injected onto the substrate  112 . The conduit  120  may be connected to a valve assembly that controls gas flow to the conduit  120 . 
     In one embodiment, a silicon substrate is used as the substrate  112 , and an oxide is deposited to form the pattern  124 . By changing the thickness of the oxide, the color reflected from the pattern can be changed, as described below in detail with reference to  FIG. 6  and Table 1. 
     Although  FIG. 1  illustrates an example where the printer head  116  moves in both X-direction and Y-direction while the substrate  112  remains stationary, in other embodiments, the printer head  116  may move in only X or Y direction while the substrate  112  is moved in Y or X direction. Alternatively, the printer head  116  may remain stationary while the substrate  112  is moved in both X and Y directions to form patterns on the substrate  112 . 
     Further, a heater (not shown) may be provided below or near the substrate  112  to heat the substrate  112 . The heating of the substrate  112  promotes the reaction between the source precursor and the reactant precursor to promote formation of a layer of material on the substrate  112 . 
     In one embodiment, the printer head  116  is moved in the two-dimensional plane manually by operating personnel instead of using motors or other actuating mechanisms. 
       FIG. 2  is a perspective view of the printer head  116  and the conduit  120  for providing gas to the printer head  116 , according to one embodiment. In the embodiment of  FIG. 2 , the printer head  116  has a cylindrical shape and is formed with chambers and channels for routing gases for injection or discharging excess gases from the substrate  112 . The shape of the printer head  116  of  FIG. 2  is merely illustrative and the printer head  116  may be in various other shapes (e.g., a rectangular column shape). The printer head  116  is kept at a predetermined height above the substrate but preferably does not come in touch with the substrate  112  to prevent damage to the material deposited on the substrate  112 . 
     The conduit  120  is connected to sources of various gases via valves  210 ,  220 . The valves  210 ,  220  can be switched on or off to selectively connect the conduit  120  to the sources of the gases. The valves  210 ,  220  may also be controlled to adjust the amount of gas provided to the printer head  116 . When conduits are disconnected from the sources, the gases are no longer injected onto the substrate  112 , and hence, no pattern is formed on the substrate  112 . By shutting on or off the valves  210 ,  220 , discontinuous line segments can be formed on the substrate  112  using the printer head  116 . The operation of the valves  210 ,  220  may be controlled by the controller  150 . 
       FIG. 3A  is a cross sectional diagram of the printer head  116  taken along line A-B of  FIG. 2 , according to one embodiment. The bottom of the body  360  is separated from the top surface of the substrate  112  by a distance of h. The body  360  of the printer head  116  is formed with channels  312 ,  314 ,  318  to convey gases to the bottom of the printer head  116 . 
     The channel  312  is formed in the outer periphery of the body  360 . In one embodiment, the channel  312  carries reactant precursor gas received via the conduit  120 . The reactant precursor gas may include radicals. The reactant precursor travels via perforations or slit  330  to an injection chamber  336  having a width of W E1 . The substrate  112  is injected with the reactant precursor below the injection chamber  336 . As a result, the source precursor may react or replace source precursor adsorbed on the substrate  112  and form a layer of material on the substrate  112 . 
     The reactant precursor moves through a constriction zone  352  and is discharged via an exhaust  342 . The constriction zone  352  has a height H E1  that is smaller than the width W E1  of the injection chamber  336 . In one embodiment, the height H E1  is from 1 mm to 4 mm. Due to the reduced size of passage in the constriction zone  352 , the speed of the reactant precursor in the constriction zone  352  is increased while the pressure of the reactant precursor is decreased in the constriction zone  352  compared to the reactant precursor in the injection chamber  336 . Thus, the flow of the reactant precursor through the constriction zone  352  facilitates the removal of excess reactant precursor (e.g., reactant precursor molecules physisorbed on the substrate  112 ) while leaving the deposited material intact on the substrate  112 . 
     To cause sufficient Bernoulli effect in the constriction zone  352 , the height H E1  of the constriction zone  352  is smaller than ⅔ of the width W E1 , and more preferably smaller than ⅓ of the diameter W E1 . The constriction zone  352  also enables the reactant precursor to form self-sustaining laminar flow to cause the reactant precursor to react or replace the source precursor in a uniform manner. The constriction zone  352  reduces leaking or diffusion of reactant precursor beyond outer wall  337  of the printer head  116  by facilitating discharge of the reactant precursor through the exhaust  342  due to pressure at the constriction zone  352  that is lower than the pressure gap (with height of h) between the outer wall  337  and the substrate  112 . In some embodiments, outer wall  337  protrudes downwards and forms the outer periphery of the reactor  116  to reduce leaking or diffusion of reactant precursor. Whenever the printer head is moving, the printer head injects the reactant precursor on the substrate  112  across an area corresponding to an outer diameter of D R . 
     The channel  314  is formed near center axis O—O′ of the printer head  116 . In one embodiment, the channel  314  carries source precursor. The source precursor in the channel  314  is injected into an injection chamber  338  via a perforation  332 . The injection chamber  338  has a diameter of W E2 . The portion of the substrate  112  below the injection chamber  338  is injected with the source precursor. Part of the injected source precursor is adsorbed on the substrate  112  while remaining excess source precursor is discharged via the constriction zone  354  to an exhaust  344 . In some embodiments, some portions of excess source precursor may remain on the surface of the substrate for increasing the deposition rate of material on the substrate. The constriction zone  354  has a height H E2  that is smaller than the diameter W E2  of the injection chamber  338 . 
     As a result, the pressure of the source precursor drops and the speed of the source precursor increases as the source precursor passes through the constriction zone  354 , facilitating removal of excess source precursor (e.g., source precursor molecules physisorbed on the substrate  112 ) while leaving source precursor molecules chemisorbed on the substrate  112  intact. 
     To cause sufficient Bernoulli effect in the constriction zone  354 , the height H E2  of the constriction zone  354  is smaller than ⅔ of the diameter W E2 , and more preferably smaller than ⅓ of the diameter W E2 . In one embodiment, the height H E2  is from 1 mm to 4 mm. The constriction zone  354  also enables the source precursor to form self-sustaining laminar flow to adsorb the source precursor in a uniform manner. When the printer head  116  moves on the substrate  112 , an area with diameter Ds is exposed to the source precursor. 
     The remaining source precursor is discharged via the exhaust  344 . In the example of  FIG. 3A , a portion of the substrate having a diameter Ds is exposed to the source precursor when the printer head  116  and the substrate  112  remain stationary. The diameter Ds represents the smallest width of a pattern that can be formed on the substrate  112  using the printer head  116 . A printer head with a larger diameter Ds will deposit a pattern with a thicker line feature covering a larger surface area of the substrate  112  whereas a printer head with a smaller diameter Ds will deposit a patter with a finer line feature covering a smaller surface area of the substrate  112 . 
     The channel  318  carries separation gas (e.g., inert gas such as Argon). The separation gas forms an air curtain between the portion of the printer head  116  injecting the source precursor and the portion of the printer head  116  injecting the reactant precursor. In this way, the mixing of the source precursor and the reactant precursor is prevented from occurring at places other than on the substrate  112 . Hence, formation of particles due to the reaction between source precursor and the reactant precursor can be prevented. Moreover, the separation gas also functions as purge gas that removes all or some of the physisorbed molecules of the source precursor or reactant precursor by controlling the flow rate of the purge gas while keeping at least chemisorbed molecules of the source precursor or reactant precursor intact on the substrate  112 . Remaining physisorbed molecules on the substrate may increase the deposition rate of the material on the substrate  112 . 
     As the printer head  116  moves over the substrate  112 , a portion of the substrate  112  below the printer head  116  is exposed to a series of gas. Assuming that the printer head  116  moves in the direction identified by arrow  311 , the substrate  112  below the printer head  116  is sequentially exposed to the reactant precursor, separation gas (purge gas), the source precursor, the separation gas and then the reactant precursor. That is, the area represented by diameter Ds is exposed to the source precursor, the purge gas and then the reactant precursor. As a result of the reaction between the source precursor and the reactant precursor, a layer of material in the form of a line feature is deposited on the substrate  112 . 
     In one embodiment, the distance h is either a function of diameter Ds or may be set to a fixed value, for example, less than 1 mm. For example, the distance h is set to a value less than one tenth of Ds to minimize the precursor leak through this gap. 
     In one embodiment, the source precursor is Tris[dimethylamino]Silane (3DMAS) and the reactant precursor is O* or (OH)* radicals to deposit a SiO 2  film which is transparent in a visible spectrum. The reaction of such source precursor and the reactant precursor deposits a layer of SiO 2  on the substrate  112 . 
     In other embodiments, O 3 , H 2 O, H 2 O 2 , N 2 O plasma, O 2  plasma, (H 2 +O 2 ) plasma, O 3  plasma, H 2 O plasma or their combination may be used as reactant precursor for depositing an oxide layer on the substrate. NH 3 , NH 2 —NH 2 , N 2  plasma, NH 3  plasma, (N 2 +H 2 ) plasma, N* radical or their combination may be used as reactant precursor for depositing a nitride layer on the substrate. C 2 H 2  plasma, CH 4  plasma, C 6 H 6  plasma, (H 2 +CH 4 ) plasma, C* radical or their combination may be used for depositing a carbonized layer, carbon nano-tube, graphine or graphine oxide on the substrate  112 . 
     In other embodiments, the source precursors are either Tetrakis-dimethylamino Titanium (TDMAT) or titanium tetraisopropoxide (TTIP) for forming a TiO 2  film, and Tetrakis-ethylmethylamino Hafnium (TEMAHf) for forming a HfO 2  film which has a higher refractive indexed a SiO 2  film. The thicknesses of TiO 2  and HfO 2  films on this application may be thinner than the thickness of the SiO 2  film. 
     In other embodiments, the source precursor is injected via the channel  312  into the injection chamber  336  and the reactant precursor is injected via the channel  314  into the injection chamber  338 . In these embodiments, excess reactant precursor is discharged via exhaust  344 , and excess source precursor is discharged via exhaust  342 . 
       FIG. 3B  is a cross sectional diagram of the printer head  116  taken along line C-D of  FIG. 2 , according to one embodiment. The printer head  116  is formed with inlets  362  for receiving the reactant precursor, inlets  364  for receiving the separation gas, and an inlet  366  for receiving the source precursor. The reactant precursor, the separation gas and the source precursor are transferred to the channel  312 , the channel  318  and the channel  314 , respectively, via holes (not shown) formed in the body  360 . 
     The body  360  of the printer head  116  is also formed with exhausts  342 ,  344  for discharging the excess reactant precursor and the excess source precursor, respectively. The exhausts  342 ,  344  are connected to the injection chambers  336 ,  338  via constriction zones  352  and  354 . 
     Although the printer head  116  of  FIGS. 3A and 3B  is illustrated as being symmetric with respect to the axis O—O′, other embodiments may have non-symmetric shape or configuration. 
       FIG. 4  is a sectional diagram of a printer head  400 , according to another embodiment. The printer head  400  includes a first portion  410  and a second portion  420 . The first portion  410  is identical to the printer head  116  of  FIGS. 3A and 3B , and therefore, detailed description thereof is omitted herein for the sake of brevity. The printer head  400  further includes the second portion  420  for injecting purge gas (e.g., inert gas) through channel  422 , perforations or slits  424 , and an injection chamber  428 . The gas in the injection chamber  428  is injected onto the substrate  112  to remove excess reactant precursor or other excess material from the surface of the substrate  112 . In order to enhance the removal process, a constriction zone  438  having the height H E3  smaller than the width W E3  is formed in the printer head  400 . As the purge gas moves through the constriction zone  438 , the pressure of the purge gas drops and the speed of the purge gas increases due to Bernoulli effect. The purge gas and any excess material are discharged via exhaust  442 . 
       FIG. 5  is a top view of a substrate  112  printed with patterns  510 ,  520 ,  530 , according to one embodiment. The patterns  510 ,  520 ,  530  are formed by moving the printer head  116  along a defined path while switching on or off valves  210 ,  220  for injecting precursor materials into the printer head  116 . 
     Each of the patterns  510 ,  520 ,  530  may have different colors by varying the thickness of the material deposited on the substrate  112 .  FIG. 6  is a cross sectional diagram of substrate  112  printed with material  614 ,  618  of different thickness (t 1 , t 2 ) to show different colors, according to one embodiment. By depositing a layer of transparent or semi-transparent material of a different thickness on the substrate  112 , the color of the pattern can be changed due to different refractive characteristics of the deposited material. For example, when SiO 2  of 1000 Å is deposited, the pattern exhibits red-violet (color code: B32F79) color. When SiO 2  of 3450 Å is deposited, the pattern exhibits green (color code: 00FF00) color. When SiO 2  of 1250 Å is deposited, the pattern exhibits blue (color code: 0000FF) color. By using different combinations of colors, a holographic image in color can be patterned on the substrate. 
     The thickness of materials formed on the substrate  112  may be changed by one or more of the following ways. First, the printer head may move over the same path a number of times to deposit a thicker layer of material on the substrate. The color of the deposited material may be changed due to the thickness of the deposited material. Alternatively, the print head may move along a path with junction points or areas where the print head passes through multiple times. In such instance, the layer of material on the junction points or areas would be thicker than other portions of the path. Hence, the color of the deposited material at the junction points or areas will be different from other areas of the deposited material. 
     Second, the portions where the printer head moves at a higher speed are likely to be exposed to a less amount of source precursor and reactant precursor. Hence, a thinner layer of material is likely to be deposited along a path where the printer head moves at a higher speed. By controlling the moving speed of the printer head, a layer of different thickness may be deposited on the substrate, and hence, the color of the deposited material may be varied. 
     Third, the flow rate of the source precursor, the reactant precursor, the purge gas or a combination thereof may be controlled to deposit materials of different thickness on the substrate. For example, the valves  210 ,  220  may be controlled to inject these gases to the printer head at different rates. When the amount of gas injected into the printer head is decreased, the thickness of the deposited layer is also decreased, causing a change in the color of the deposited material. 
     Fourth, the concentration of the source precursor or reactant precursor in the gas injected into channel may be changed. When the concentration of the precursor relative to a carrier gas is higher, a thicker layer of material is likely to be formed on the substrate. 
     Fifth, when radicals are used to as source or reactant precursor, power source for generating radicals may be controlled to increase or decrease the reactivity of the precursor. The radicals may be generated using various ways such as exposing gas to ultra violet rays or generating plasma in a chamber filled with the gas. By controlling parameters associated with power (e.g., voltage level of electrodes for generating plasma), the reactivity of the radicals can be controlled. When the substrate is exposed to radicals of higher reactivity, a thicker layer of material forms on the substrate. 
     Sixth, different precursor material may be injected into the printer head to deposit material of different type or thickness on the substrate. Some precursor tends to deposit a thicker material than other precursors. Hence, by selectively feeding the type of precursor injected by the printer head, materials of different thickness may be formed on the substrate. 
     In some embodiments, a combination of above methods may be used to control the thickness of material deposited on the substrate. The controller  150  may be programmed to adjust one or more of parameters associated with the above methods to control the thickness of the deposited material. 
     Some of many advantages of using ALD to form patterns on the substrate are that the thickness of the deposited material can be tightly controlled, and that the material deposited by ALD is resistant to abrasion or discoloration due to exposure to ultraviolet rays or extreme ultra violet rays. 
     The following table shows examples of various colors that can be expressed by depositing SiO 2  of different thickness on a substrate. 
                             TABLE 1               Oxide               Thickness   COLOR           [Å]   CODE   Color and Comments                                            500   D2B48C    Tan       750   A52A2A   Brown       1000   B32F79   Dark Violet to red violet       1250   2E73F3   Royal blue       1500   ADD8E6    Light blue to metallic blue       1750   D9ECB3    Metallic to very light yellow-green       2000   F9F9C8   Light gold or yellow slightly metallic       2250   DAA520   Gold with slight yellow-orange       2500   F6853D   Orange to Melon       2750   B32F79   Red-Violet       3000   5D3694   Blue to violet-blue       3100   0000FF   Blue       3250   0083AE   Blue to blue-green       3450   00FF00   Light green       3500   84D82E   Green to yellow-green       3650   84C82E   Yellow-green       3750   E2DE2B   Green-yellow       3900   FFFF00   Yellow.       4120   FFB500   Light orange       4260   FA7FC1   Carnation pink       4430   E82362   Violet-red       4650   B32F79   Red-violet       4760   EE82EE   Violet       4800   5D3694   Blue Violet       4930   0000FF   Blue       5020   008080   Blue-green       5200   008846   Green (Broad)       5400   9ACD32   Yellow-green       5600   ADFF2F   Green-yellow       5740   FFFFD2   Yellow to Yellowish (not yellow but is in the               position where yellow is to be expected. At               times is appears to be light creamy gray or               metallic)       5850   FFDE93   Light orange or yellow to pink borderline       6000   FA7FC1   Carnation pink       6300   EE82EE   Violet-red       6800   AE82FF   Bluish (Not blue but borderline between violet               and blue-green. It appears more like a Mixture               between violet-red and blue-green and over-all               looks grayish)       7200   00A080   Blue-green to green (quite broad)       7700   FFFF8C   Yellowish       8000   FFA500   Orange (rather broad for orange)       8200   FA8072   Salmon       8500   B32F79   Dull, light red-violet       8600   EE82EE   Violet       8700   5D3694   Blue-violet       8900   0000FF   Blue       9200   0083AE   Blue-green       9500   84C82E   Dull yellow-green       9700   FFFF00   Yellow to Yellowish       9900   F3770C   Orange       10000   FA7FC1   Carnation Pink       10200   E82362   Violet-red       10500   B32F79   Red-violet       10600   EE82EE   Violet       10700   5D3694   Blue-violet       11000   008846   Green       11100   84C82E   Yellow-green       11200   008846   Green       11800   EE82EE   Violet       11900   B32F79   Red-violet       12100   E82362   Violet-red       12400   FA7FA1   Carnation Pink-Salmon       12500   FFA500   Orange       12800   FFFF00   Yellowish       13200   47B0E3   Sky blue to green-blue       14000   FFA500   Orange       14500   EE82EE   Violet       14500   5D3694   Blue-violet       15000   0000FF   Blue       15100   84C82E   Dull Yellow-green                    
In order to exhibit colors not shown in the above table, segments of the substrate may be deposited with materials with different thicknesses. Each segment of the substrate will reflect different colors, and the combined reflection of from the segments will result in a color different from the color reflected by individual segments.
 
       FIG. 7  is a schematic diagram illustrating the degree of freedom for the printer head  700  according to one embodiment. Although the printer head  116  of  FIG. 1  has three degrees of freedom (X, Y and Z-directions), other embodiments may include printer heads with more or less degrees of freedom. For example, the printer head  700  may have six degrees of freedom by capable of linear movements in X, Y and Z-directions, and rotation in α, β and γ angles. With increased degrees of freedom, the printer head  700  can deposit materials on non-planar surfaces (e.g., curved surfaces). Mechanisms for moving or rotating the printer head  700  may include actuators such as motors, links or hydraulic devices. 
       FIG. 8  is a flowchart illustrating a method of forming a pattern of material with different thickness, according to one embodiment. Source precursor is injected  810  onto a substrate via printer head  116 . Reactant precursor is also injected  820  onto a substrate via printer head  116 . The source precursor and the reactant precursor may be injected into the printer head via valves  210 ,  220  and conduit  120 . 
     Printer head  116  moves along a path on the substrate while controlling one or more parameters associated with the thickness of material deposited on the substrate. The path of the printer head  116  may include straight lines, curves and random shapes. The one or more parameters includes one or more of the following: (i) the speed at which the printer head  116  is moving, (ii) the amount or concentration of source precursor and/or reactant precursor injected into the printer head  116  and (iii) the reactivity of radicals used as source precursor or reactant precursor. By changing these parameters, the thickness of the material deposited on the substrate may be changed, causing different portions of the pattern to exhibit different colors. 
     Excess material is discharged  840  from the substrate by the printer head  116 , for example, by injecting purge gas onto the substrate. The excess material may include, source precursor, reactant precursor and material deposited on the substrate but not chemisorbed on the substrate. The excess material may be discharged using exhausts  342 ,  344 . 
     The sequence of processes illustrated in  FIG. 8  is merely illustrative. Although steps  810  through  840  are illustrated as being performed sequentially, these steps may be performed simultaneously. Additional steps such as injecting purge gas which not illustrated in  FIG. 8  may also be performed. 
     Although the present invention has been described above with respect to several embodiments, various modifications can be made within the scope of the present invention. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention.