Method and apparatus for depositing digital material onto a semiconductor wafer

Abstract

The present invention relates to a microelectronic device (100) formed by dispensing discrete amounts of a mixture (109) of a photoresist resin and a solvent onto a wafer (101) from a drop-on-demand site (108) to form a first photoresist sublayer (112) while the wafer (101) is at a first temperature that allows the photoresist resin to achieve a thickness non-uniformity of less than 10%. The wafer (101) is moved in a first direction under the drop-on-demand site (108) to form the first photoresist sublayer (112). A portion of the solvent in the first photoresist sublayer (112) is removed. When the wafer (101) is at a second temperature that achieves a thickness non-uniformity of less than 10% in the combined first (112) and second photoresist sublayers, a second photoresist sublayer is formed on the first photoresist sublayer (112) using the drop-on-demand site (108). The wafer (101) is moved beneath the drop-on-demand site (108) in a second direction of the second photoresist sub-layer opposite to the first direction.

Description

Technical Field

[0001] The present disclosure relates to the field of microelectronic devices. More particularly, the present disclosure relates to photolithographic processes for forming microelectronic devices. Background Art

[0002] The photolithography process used in semiconductor manufacturing requires applying a photoresist layer to a wafer. Typically, the wafer is covered with a thick layer of photoresist mixed with a solvent, and the wafer is spun in a spin-coating process to shake off the excess photoresist and solvent from the wafer. This is a very inefficient process that wastes most of the photoresist that must then be disposed of, resulting in additional costs. In addition, the spin-coating process leaves photoresist on the edge of the wafer, commonly known as edge beads, which must be removed, resulting in additional process steps and costs. Other methods of applying a photoresist layer to a wafer, such as spray coating, cannot provide a uniform thickness of photoresist across the wafer, thereby limiting the applicability of semiconductor manufacturing processes. Summary of the Invention

[0003] The present disclosure describes a method for forming a microelectronic device. In one embodiment, the disclosed method involves forming a first photoresist sublayer on a wafer using a drop-on-demand site while the wafer is at a first temperature that allows sufficient flow of photoresist in the first photoresist sublayer to achieve a thickness non-uniformity of less than 10%. The first photoresist sublayer is formed while the wafer is moved relative to the drop-on-demand site in a first direction. A portion of the solvent in the first photoresist sublayer is removed. The second photoresist sublayer is formed on the first photoresist sublayer using the drop-on-demand site while the wafer is at a second temperature that allows sufficient flow of photoresist in the second photoresist sublayer to achieve a thickness non-uniformity of less than 10% in the combined first and second photoresist sublayers. The second photoresist sublayer is formed while the wafer is moved relative to the drop-on-demand site in a second direction opposite to the first direction. A portion of the solvent in the second photoresist sublayer is removed. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1A to Figure 1P Stages in an example method of forming a microelectronic device are depicted.

[0005] Figures 2A to 2D is a cross-section of a microelectronic device depicted at a stage in another example formation method.

[0006] Figures 3A to 3C is a cross-section of a microelectronic device depicted at a stage in another example formation method.

[0007] Figure 4is a cross-section of a microelectronic device depicted in another example formation method.

[0008] Figure 5A and Figure 5B is a cross-section of a microelectronic device depicted at a stage in another example formation method.

[0009] Figure 6A and Figure 6B is a cross-section of a microelectronic device depicted at a stage in another example formation method.

[0010] Figure 7A and Figure 7B is a cross-section of a microelectronic device depicted at a stage in another example formation method.

[0011] Figure 8A and Figure 8B is a cross-section of a microelectronic device depicted at a stage in another example formation method. DETAILED DESCRIPTION

[0012] The present disclosure is described with reference to the accompanying drawings. The figures are not drawn to scale and are provided for illustration purposes only. Several aspects of the present disclosure are described below with reference to examples. It should be understood that numerous specific details, relationships, and methods are set forth to provide an understanding of the present disclosure. The present disclosure is not limited by the described ordering of actions or events, as some actions may occur in different orders and / or simultaneously with other actions or events. Furthermore, not all described actions or events are required to implement the methods according to the present disclosure.

[0013] A microelectronic device is formed by forming a photoresist layer on a wafer. The photoresist layer includes a first photoresist sublayer on the wafer and a second photoresist sublayer on the first photoresist sublayer. The first photoresist sublayer is formed by a drop-on-demand site. As the drop-on-demand site dispenses a first discrete amount of a mixture of photoresist and solvent onto the wafer, the wafer moves relative to the drop-on-demand site in a first direction. The wafer is maintained at a first temperature range that allows sufficient flow of the photoresist resin in the first photoresist sublayer, thereby reducing ripples and other non-planar features in the first photoresist sublayer to achieve a thickness non-uniformity of less than 10%, i.e., the standard deviation of the thickness of the first photoresist sublayer is less than 10% of the average thickness of the first photoresist sublayer. The deceleration of the wafer is maintained below a value sufficient to mitigate displacement of the first photoresist sublayer and so as to maintain the thickness non-uniformity below 10%. Having a thickness non-uniformity of the first photoresist sub-layer below 10% may be considered necessary to enable subsequent photolithographic operations using the photoresist layer.Before adding additional photoresist to the photoresist layer, part of the solvent in the first photoresist sub-layer is removed by evaporation.

[0014] As a second discrete amount of a mixture of photoresist and solvent is dispensed onto the first photoresist sublayer at the drop-on-demand site, a second photoresist sublayer is formed by moving the wafer relative to the drop-on-demand site in a second direction opposite to the first direction. The wafer is maintained at a second temperature that allows the photoresist in the second photoresist sublayer to flow sufficiently to achieve a thickness non-uniformity of less than 10% in the combined first and second photoresist sublayers. Deceleration of the wafer is maintained below a value sufficient to mitigate displacement of the second photoresist sublayer and so as to maintain a thickness non-uniformity of less than 10%. Having a thickness non-uniformity of the second photoresist sublayer of less than 10% may also be considered necessary to perform subsequent photolithography operations using the photoresist layer. Before additional photoresist is added to the photoresist layer, a portion of the solvent in the second photoresist sublayer is removed by evaporation.

[0015] Additional photoresist sublayers can be added to the photoresist layer by repeating the steps used to form the first and second photoresist sublayers. The photoresist layer is exposed to patterned ultraviolet (UV) light and developed to remove the photoresist layer exposed to UV light to form a patterned photoresist layer. The patterned photoresist layer is used in the manufacture of microelectronic devices, for example, as a plating mask, implant mask, or etch mask.

[0016] It should be noted that terms such as above and below may be used in this disclosure. These terms should not be construed as limiting the position or orientation of structures or elements, but rather should be used to provide spatial relationships between structures or elements. Similarly, terms such as "inwardly" and "outwardly" refer to directions toward and away from the center of the wafer, respectively.

[0017] Figure 1A to Figure 1P Depicts stages of an example method of forming a microelectronic device. Figure 1A, microelectronic device 100 is part of a wafer 101, which may contain additional microelectronic devices 102. As examples, microelectronic device 100 may be implemented as an integrated circuit, a discrete semiconductor device, a microelectromechanical system (MEMS) device, an electro-optical device, a micro-opto-mechanical system device, or a microfluidic device. As examples, wafer 101 may be implemented as a semiconductor wafer, such as a silicon wafer, a silicon wafer having epitaxial layers of III-V semiconductor materials, a silicon-on-insulator (SOI) wafer, a sapphire wafer having layers of semiconductor materials, a MEMS substrate wafer, or a microfluidic substrate wafer. For example, wafer 101 may have a diameter of 100 millimeters (mm), 125 mm, 150 mm, 200 mm, or 300 mm. Wafer 101 has a first surface 103 having a lateral perimeter 104 that is proximate to the lateral perimeter of wafer 101. Except for regular topological features that may be present in each of microelectronic device 100 and additional microelectronic device 102, first surface 103 is planar or flat. For the purposes of this disclosure, the terms "lateral" and "laterally" refer to directions parallel to the first surface 103, and will be used accordingly in the following examples. The first surface 103 does not extend onto the curved surface of the wafer 101 at the lateral perimeter of the wafer 101. In this example, a coating region 105 of the first surface 103 extends over the microelectronic device 100 and the additional microelectronic device 102, but does not extend to the lateral perimeter 104 of the first surface 103. The coating region 105 may extend to within 1 mm to 3 mm of the lateral perimeter 104, depending on the manufacturing process used to form the microelectronic device 100.

[0018] Wafer 101 is positioned on wafer holder 106. Wafer holder 106 may comprise, for example, aluminum or stainless steel, with a vacuum port (not shown) or mechanical clamps (not shown) holding wafer 101 in place. Wafer holder 106 is configured to heat wafer 101, for example, via one or more heaters 107.

[0019] Wafer holder 106 is configured to transport wafer 101 beneath drop-on-demand site 108. Drop-on-demand site 108 extends across a width at least as wide as coating zone 105. Drop-on-demand site 108 is configured to dispense discrete amounts of a mixture 109 of photoresist resin and solvent. As an example, the discrete amounts of the mixture 109 of photoresist resin and solvent may have an average volume of 10 picoliters (pL) to 50 pL. The mixture 109 of photoresist resin and solvent has a viscosity suitable for dispensing from drop-on-demand site 108. The mixture 109 of photoresist resin and solvent may have a viscosity of 2 centipoise (cp) to 20 cp at 20° C. to 25° C., as measured by a capillary viscometer, such as an Ostwald viscometer. Furthermore, the mixture 109 of photoresist resin and solvent has a surface tension suitable for dispensing from drop-on-demand site 108. The mixture 109 of photoresist resin and solvent can have a surface tension of 20 to 50 dyne / cm as measured by dynamic surface tension measurement at 20° C. to 25° C. The ratio of surface tension to viscosity can be maintained in the range of 50 to 500 cm / sec to provide consistent volumes of discrete amounts of the mixture 109 of photoresist resin and solvent dispensed by the drop-on-demand site 108.

[0020] The mixture 109 of photoresist resin and solvent may have a photoresist resin content of 10 to 20 weight percent, with the remainder of the mixture 109 consisting essentially of solvent. For the purposes of this disclosure, the term "consisting essentially of solvent" encompasses a mixture of photoresist resin and solvent that includes other materials that do not interfere with the formation of the photoresist layer and the photolithographic process performed on the photoresist layer. In addition to the photoresist resin and solvent, the mixture 109 of photoresist resin and solvent contains at most trace amounts of materials. The photoresist resin may include a novolac resin and a photoinitiator, such as quinone diazide. The solvent may include two or more solvents, wherein the concentrations of the solvents are selected to provide a desired viscosity value and a desired surface tension. For example, the solvent may include propylene glycol methyl ether acetate (PGMEA) and gamma butyrolactone (GBL). An example method of preparing the mixture 109 of photoresist resin and solvent may include mixing 100 parts of AZ P4620 photoresist having approximately 35% photoresist resin and 65% solvent (e.g., n-butyl acetate or xylene) with 60 parts of PGMEA and 90 parts of GBL. Other formulations of the mixture 109 of photoresist resin and solvent are within the scope of this example, as are other methods of preparing the mixture 109 of photoresist resin and solvent.

[0021] A mixture 109 of photoresist resin and solvent is provided to a drop-on-demand site 108. The mixture 109 may be provided to the drop-on-demand site 108 by a dispensing system 110, such as Figure 1A Alternatively, the mixture 109 can be provided to the drop-on-demand sites 108 by adding the mixture 109 to individual reservoirs at each drop-on-demand site 108 before processing the wafer 101 .

[0022] The wafer 101 is heated to a temperature within a first temperature range, for example, 45° C. to 50° C. The wafer holder 106 moves the wafer 101 beneath the drop-on-demand site 108 . Figure 1A Wafer holder 106 is depicted beginning to move wafer 101 as indicated by speed increasing arrow 111. Wafer holder 106 may be moving at a speed of less than 500 mm / s. 2 (mm / s 2 ) rate is accelerated.

[0023] refer to Figure 1BAs wafer holder 106 moves wafer 101 beneath drop-on-demand sites 108, drop-on-demand sites 108 dispense a mixture of photoresist resin and solvent 109 onto wafer 101 to form a first photoresist sub-layer 112 on wafer 101, covering coating region 105. Each of drop-on-demand sites 108 dispenses the mixture of photoresist resin and solvent 109 in a first discrete amount having a first average drop volume of 10 pL to 50 pL. For example, each of drop-on-demand sites 108 may dispense the first discrete amount at a first average drop frequency of 2000 to 4000 drops / second. The first photoresist sub-layer 112 is continuous and covers coating region 105. Wafer holder 106 may move beneath drop-on-demand sites 108 at a first constant speed, as indicated by first speed arrow 113. The first constant speed can be selected to provide a desired thickness of the first photoresist sub-layer 112 while maintaining complete coverage of the coating area 105. The first constant speed can be 50 millimeters per second (mm / s) to 150 mm / sec, depending on the first average drop volume and the first average drop frequency. For example, the first photoresist sub-layer 112 has a first average coating thickness of 30 microns to 50 microns, which is the average thickness immediately after the first photoresist sub-layer 112 is formed. The wafer 101 is maintained at a temperature within the first temperature range, which allows the photoresist resin in the first photoresist sub-layer 112 to fully flow after being dispensed onto the wafer 101, thereby reducing ripples and other non-planar features in the first photoresist sub-layer 112 to achieve a thickness non-uniformity of less than 10%. If the temperature of wafer 101 drops to a temperature below the first temperature range, first photoresist sub-layer 112 may exhibit a thickness variation greater than 10% due to insufficient flow of the photoresist resin, resulting in a lateral dimension of several centimeters above coating region 105. If the temperature of wafer 101 increases to a temperature above the first temperature range, first photoresist sub-layer 112 may exhibit a thickness variation greater than 10% due to rapid drying of first photoresist sub-layer 112 before the photoresist resin can sufficiently flow to achieve a uniform thickness, resulting in a lateral dimension of several millimeters above coating region 105. The upper and lower limits of the first temperature range are selected to achieve a thickness non-uniformity of less than 10% in first photoresist sub-layer 112. The upper limit of 50°C and the lower limit of 45°C are selected to provide the desired thickness uniformity for the process parameters disclosed in this example. The upper and lower limits can be adjusted to accommodate the specific mixture of photoresist resin and solvent 109, the thickness of the first photoresist sub-layer 112, or other process parameters. The span of the first temperature range, i.e., the difference between the upper and lower limits, can be 3° C. to 10° C. to achieve consistent uniformity in the first photoresist sub-layer 112.

[0024] Figure 1B The partially formed first photoresist sub-layer 112 is depicted. Optionally, while the mixture 109 of photoresist resin and solvent is being dispensed onto the wafer 101 at the drop-on-demand site 108 to form the first photoresist sub-layer 112, an anti-drying vapor 114 can be introduced above the wafer 101 to reduce solvent loss from the first photoresist sub-layer 112. The anti-drying vapor 114 can include, for example, a chemical similar to or the same as the solvent in the mixture 109 of photoresist resin and solvent in vapor form. The loss of solvent from the first photoresist sub-layer 112 as the drop-on-demand site 108 dispenses the photoresist resin and solvent mixture 109 onto the wafer 101 can result in thickness non-uniformity in the first photoresist sub-layer 112 across the wafer because regions of the first photoresist sub-layer 112 formed earlier in the process can lose more solvent and therefore be thinner than regions of the first photoresist sub-layer 112 formed later in the process. Introducing the anti-drying vapor 114 can advantageously improve the thickness uniformity of the first photoresist sub-layer 112.

[0025] refer to Figure 1C , the wafer holder 106 decelerates to a stop after the first photoresist sub-layer 112 is formed, as indicated by deceleration arrow 115. The wafer holder 106 may be less than 500 mm / s 2 The deceleration rate is decelerated to a stop to reduce the lateral displacement of the first photoresist sub-layer 112. The lateral displacement of the first photoresist sub-layer 112 may result in a thickness non-uniformity of the first photoresist sub-layer 112 across the coating region 105 that is greater than a few percent, which may exceed the process tolerance of the thickness lithography process performed using the first photoresist sub-layer 112.

[0026] refer to Figure 1D, a portion of the solvent in the form of solvent vapor 116 is removed from the first photoresist sub-layer 112. The solvent vapor 116 can be removed by passing a dry nitrogen or dry air environment over the first photoresist sub-layer 112. The wafer 101 can be maintained at a temperature within a first temperature range to promote solvent removal while maintaining a thickness non-uniformity of less than 10%. The solvent is removed within a specified first drying time, as schematically indicated by a stopwatch 117; as an example, the first drying time can be from 1 second to 10 seconds. As an example, between 10 weight percent and 75 weight percent of the solvent in the first photoresist sub-layer 112 can be removed during the first drying time. After additional sub-layers of the mixture of photoresist and solvent 109 are formed over the first photoresist sub-layer 112, additional drying time may be required to remove less than 10 weight percent of the solvent from the first photoresist sub-layer 112. Removing more than 75 weight percent of the solvent from the first photoresist sub-layer 112 may result in poor adhesion of additional sub-layers of the photoresist and solvent mixture 109 formed on the first photoresist sub-layer 112. The thickness of the first photoresist sub-layer 112 may decrease depending on the amount of solvent removed during the first drying time.

[0027] refer to Figure 1E , the wafer holder 106 can laterally move the wafer 101 by a first lateral distance 118 that is less than a lateral separation 119 between adjacent drop-on-demand sites 108. For purposes of this disclosure, the term "lateral" refers to a direction parallel to the first surface 103 of the wafer 101. The first lateral distance 118 and the lateral separation 119 are perpendicular to the direction of movement of the wafer 101 and the wafer holder 106 beneath the drop-on-demand sites 108. Before forming additional sub-layers of the photoresist and solvent mixture 109 on the wafer 101, the wafer holder 106 can laterally move the wafer 101 by the first lateral distance 118 to improve thickness uniformity of the combined sub-layers.

[0028] refer to Figure 1F The wafer 101 is heated to a temperature within a second temperature range that may be the same as the first temperature range. The wafer holder 106 moves the wafer 101 under the drop-on-demand site 108. Figure 1F The wafer holder 106 is depicted beginning to move the wafer 101, as indicated by the speed-increasing arrow 120. Removing a portion of the solvent from the first photoresist sub-layer 112 can reduce the displacement of the first photoresist sub-layer 112 during acceleration or deceleration, such that the wafer holder 106 can move the wafer 101 at a speed greater than the reference speed after the first photoresist sub-layer 112 is formed but before a portion of the solvent is removed. Figure 1C The rate of acceleration of the disclosed deceleration rate.

[0029] refer to Figure 1GAs wafer holder 106 moves wafer 101 beneath drop-on-demand sites 108, drop-on-demand sites 108 dispense a mixture 109 of photoresist resin and solvent onto wafer 101 to form a second photoresist sub-layer 121 on first photoresist sub-layer 112, thereby covering coating region 105. Each of drop-on-demand sites 108 dispenses the mixture 109 of photoresist resin and solvent in a second discrete amount having a second average drop volume of 10 pL to 50 pL. The second discrete amount can have a volume equal to the volume of the first discrete amount. For example, each of drop-on-demand sites 108 can dispense the second discrete amount at a second average drop frequency of 2000 to 4000 droplets / second. The second average drop frequency can be equal to the first average drop frequency. Second photoresist sub-layer 121 is continuous and covers coating region 105. Wafer holder 106 may be moved at a second constant speed beneath on-demand drop site 108, as indicated by second speed arrow 122. The second constant speed may be selected to provide a desired thickness of second photoresist sub-layer 121 while maintaining complete coverage of coating region 105. The second constant speed may be 50 mm / s to 150 mm / s, depending on the second average drop volume and the second average drop frequency. The second constant speed may be equal to the first constant speed. For example, second photoresist sub-layer 121 may have a second average coating thickness of 30 to 50 microns, which is the average thickness immediately after formation of second photoresist sub-layer 121. Wafer 101 is maintained at a temperature within the second temperature range, which allows the photoresist resin in second photoresist sub-layer 121 to fully flow after being dispensed onto first photoresist sub-layer 112, thereby reducing ripples and other non-planar features in second photoresist sub-layer 121 to achieve a thickness non-uniformity of less than 10%. Figure 1G The second photoresist sub-layer 121 is depicted as being formed midway. Optionally, while the mixture 109 of photoresist resin and solvent is being dispensed onto the wafer 101 at the drop-on-demand site 108 to form the second photoresist sub-layer 121, an anti-drying vapor 114 may be introduced onto the wafer 101 to reduce solvent loss from the second photoresist sub-layer 121, thereby obtaining a reference Figure 1B The benefits of disclosure.

[0030] refer to Figure 1H , the wafer holder 106 decelerates to a stop after the second photoresist sub-layer 121 is formed, as indicated by deceleration arrow 123. The wafer holder 106 may be less than 500 mm / s 2 The deceleration rate is decelerated to a stop to reduce the lateral displacement of the second photoresist sub-layer 121. This is because the second photoresist sub-layer 121 may tend to shift during the deceleration, which is similar to the tendency of the first photoresist sub-layer 112 to shift, as shown in FIG. Figure 1Cpublic.

[0031] refer to Figure 1I , a portion of the solvent in the form of solvent vapor 116 is removed from the second photoresist sub-layer 121. The solvent vapor 116 can be removed by a similar method used to remove the solvent vapor 116 from the first photoresist sub-layer 112, as described with reference to FIG. Figure 1E Wafer 101 may be maintained at a temperature within a second temperature range to facilitate solvent removal while maintaining thickness non-uniformity below 10%. The solvent is removed within a specified second drying time, as schematically indicated by stopwatch 117; as an example, the second drying time may be 1 to 10 seconds and may be equal to the reference drying time. Figure 1E The first drying time discussed above. As an example, between 10 weight percent and 75 weight percent of the solvent in the second photoresist sub-layer 121 may be removed during the second drying time. After an additional sub-layer of the mixture of photoresist and solvent 109 is formed on the second photoresist sub-layer 121, removing less than 10 weight percent of the solvent from the second photoresist sub-layer 121 may require additional drying time. Removing more than 75 weight percent of the solvent from the second photoresist sub-layer 121 may result in poor adhesion of the additional sub-layer of the mixture of photoresist and solvent 109 formed on the second photoresist sub-layer 121. The thickness of the second photoresist sub-layer 121 may decrease depending on the amount of solvent removed during the second drying time.

[0032] refer to Figure 1J , a third photoresist sub-layer 124 may optionally be formed on the second photoresist sub-layer 121. The wafer holder 106 may be moved laterally by less than 1 / 8 of the distance between adjacent drop-on-demand sites 108. Figure 1E The wafer holder 106 can be moved to position the wafer 101 relative to the lateral distance of the lateral separation 119 (not shown). Figure 1A Before forming additional sub-layers of the photoresist and solvent mixture 109 on the wafer 101, the wafer holder 106 may be moved laterally to improve the thickness uniformity of the combined sub-layers.

[0033] The wafer 101 may be heated to a temperature within a third temperature range that may be the same as the first temperature range or the second temperature range. The wafer holder 106 moves the wafer 101 under the drop-on-demand site 108, for example, as shown in FIG. Figure 1F Removing a portion of the solvent from the second photoresist sub-layer 112 can reduce the displacement of the second photoresist sub-layer 121 during acceleration or deceleration, so that the wafer holder 106 can be formed after the first photoresist sub-layer 112 and the second photoresist sub-layer 121 are formed and after the portion of the solvent is removed (as shown in FIG. Figure 1D and Figure 1I Public) before with greater than reference Figure 1C and Figure 1H The rate of acceleration of the disclosed deceleration rate.

[0034] As wafer holder 106 moves wafer 101 beneath drop-on-demand sites 108, drop-on-demand sites 108 can dispense a mixture of photoresist resin and solvent 109 onto wafer 101 to form a third photoresist sub-layer 124 on second photoresist sub-layer 121, thereby covering coating region 105. Each of drop-on-demand sites 108 dispenses the mixture of photoresist resin and solvent 109 in a third discrete amount having a third average drop volume of 10 pL to 50 pL. The third discrete amount can have a volume equal to that of the first or second discrete amount. For example, each of drop-on-demand sites 108 can dispense the third discrete amount at a third average drop frequency of 2000 to 4000 droplets per second. The third average drop frequency can be equal to the first or second average drop frequency. The third photoresist sub-layer 124 is continuous and covers coating region 105. Wafer holder 106 may move at a third constant speed beneath on-demand droplet location 108, as indicated by third speed arrow 125. The third constant speed may be selected to provide a desired thickness of third photoresist sub-layer 124 while maintaining complete coverage of coating region 105. The third constant speed may be 50 mm / s to 150 mm / s, depending on the third average droplet volume and the third average droplet frequency. The third constant speed may be equal to the first constant speed or the second constant speed. For example, third photoresist sub-layer 124 may have a third average coating thickness of 30 to 50 microns, which is the average thickness immediately after formation of third photoresist sub-layer 124. Wafer 101 is maintained at a temperature within a third temperature range to achieve a thickness non-uniformity of less than 10%, as disclosed with reference to first photoresist sub-layer 112 and second photoresist sub-layer 121. Figure 1J The third photoresist sub-layer 124 is depicted as being formed midway. Optionally, while the mixture 109 of photoresist resin and solvent is being dispensed onto the wafer 101 at the drop-on-demand site 108 to form the third photoresist sub-layer 124, an anti-drying vapor 114 may be introduced onto the wafer 101 to reduce solvent loss from the third photoresist sub-layer 124, thereby obtaining a reference Figure 1B After the third photoresist sub-layer 124 is formed, the wafer holder 106 may be decelerated, as shown in FIG. Figure 1C and Figure 1H The third photoresist sub-layer 124 is partially removed of the solvent, as shown in FIG. Figure 1D and Figure 1I public.

[0035] refer to Figure 1K , a fourth photoresist sub-layer 126 may optionally be formed on the third photoresist sub-layer 124. The wafer holder 106 may be moved laterally by less than 1 / 8 of the distance between adjacent drop-on-demand sites 108. Figure 1E The wafer holder 106 can be moved to position the wafer 101 relative to the lateral distance of the lateral separation 119 (not shown). Figure 1E Before forming additional sub-layers of the photoresist and solvent mixture 109 on the wafer 101, the wafer holder 106 may be moved laterally to improve the thickness uniformity of the combined sub-layers.

[0036] The wafer 101 may be heated to a temperature within a fourth temperature range that may be the same as the first temperature range, the second temperature range, or the third temperature range. The wafer holder 106 moves the wafer 101 under the drop-on-demand site 108, for example, as shown in FIG. Figure 1F Removing the portion of the solvent from the third photoresist sub-layer 124 can reduce the displacement of the third photoresist sub-layer 124 during acceleration or deceleration, so that the wafer holder 106 can be formed with a thickness greater than the reference thickness after the first photoresist sub-layer 112 and the second photoresist sub-layer 121 are formed. Figure 1C and Figure 1H The rate of acceleration of the disclosed deceleration rate.

[0037] As the wafer holder 106 moves the wafer 101 beneath the drop-on-demand sites 108, the drop-on-demand sites 108 dispense a mixture of photoresist resin and solvent 109 onto the wafer 101 to form a fourth photoresist sub-layer 126 on the third photoresist sub-layer 124, thereby covering the coating area 105. Each of the drop-on-demand sites 108 dispenses the mixture of photoresist resin and solvent 109 in a fourth discrete amount having a fourth average drop volume of 10 pL to 50 pL. The fourth discrete amount can have a volume equal to the volume of the first discrete amount, the second discrete amount, or the third discrete amount. For example, each of the drop-on-demand sites 108 can dispense the fourth discrete amount at a fourth average drop frequency of 2000 droplets / second to 4000 droplets / second. The fourth average drop frequency can be equal to the first average drop frequency, the second average drop frequency, or the third average drop frequency. The fourth photoresist sub-layer 126 is continuous and covers the coating area 105. The wafer holder 106 can move at a fourth constant speed under the drop-on-demand site 108, as indicated by fourth speed arrow 127. The fourth constant speed can be selected to provide a desired thickness of the fourth photoresist sub-layer 126 while maintaining complete coverage of the coating area 105. The fourth constant speed can be 50 mm / s to 150 mm / sec, depending on the fourth average drop volume and the fourth average drop frequency. The fourth constant speed can be equal to the first constant speed, the second constant speed, or the third constant speed. For example, the fourth photoresist sub-layer 126 has a fourth average coating thickness of 30 to 50 microns, which is the average thickness immediately after the fourth photoresist sub-layer 126 is formed. The wafer 101 is maintained at a temperature within a fourth temperature range to achieve a thickness non-uniformity of less than 10%, as disclosed with reference to the first photoresist sub-layer 112 and the second photoresist sub-layer 121 . Figure 1K The fourth photoresist sub-layer 126 is depicted as being formed midway. Optionally, while the mixture 109 of photoresist resin and solvent is being dispensed onto the wafer 101 at the drop-on-demand site 108 to form the fourth photoresist sub-layer 126, an anti-drying vapor 114 may be introduced onto the wafer 101 to reduce solvent loss from the fourth photoresist sub-layer 126, thereby obtaining a reference Figure 1B After the fourth photoresist sub-layer 126 is formed, the wafer holder 106 may be decelerated, as shown in FIG. Figure 1C and Figure 1H The portion of the solvent in the fourth photoresist sub-layer 126 can be removed, as shown in FIG. Figure 1D and Figure 1I public.

[0038] Figure 1LWafer 101 is depicted after formation of first, second, third, and fourth photoresist sub-layers 112, 121, 124, and 126. First, second, third, and fourth photoresist sub-layers 112, 121, 124, and 126 provide at least a portion of a photoresist layer 128 on first surface 103 of wafer 101. Photoresist layer 128 covers coating area 105 but does not extend to the lateral perimeter 104 of first surface 103. In addition to first, second, third, and fourth photoresist sub-layers 112, 121, 124, and 126, photoresist layer 128 may also include additional photoresist sub-layers (not shown). Additional photoresist sub-layers may be formed as disclosed with reference to first photoresist sub-layer 112, second photoresist sub-layer 121, third photoresist sub-layer 124, or fourth photoresist sub-layer 126. Forming photoresist layer 128 by the method of this example can advantageously reduce the amount of photoresist resin consumed, compared to forming photoresist layer 128 by a spin coating process in which most of the photoresist resin is spun off from wafer 101 and discarded. Figure 1M to Figure 1P is a cross-section of the microelectronic device 100 depicted at a stage of a subsequent step in an example formation method.

[0039] refer to Figure 1M , the chip 101 of this example may include a substrate 129, such as a semiconductor substrate or a sapphire substrate. The chip 101 may include a bonding pad 130, which is conductive. The bonding pad 130 may include, for example, aluminum or copper. The chip 101 may further include a plating seed layer 131 on the substrate 129 and the bonding pad 130. The plating seed layer 131 extends to the first surface 103 of the chip 101. The plating seed layer 131 is conductive and electrically contacts the bonding pad 130. As an example, the plating seed layer 131 may include an adhesion sublayer that contacts the substrate 129 and the bonding pad 130, an optional barrier sublayer on the adhesion sublayer, and a low resistance sublayer on the barrier sublayer. The adhesion sublayer may include titanium or tungsten to provide the desired adhesion of the plating seed layer 131 to the substrate 129 and the bonding pad 130. The low resistance sublayer may include copper to provide a surface suitable for subsequent plating processes. The barrier sublayer, if present, may contain nickel, cobalt, or molybdenum to reduce diffusion of copper from the low resistance sublayer into the wafer 101 .

[0040] The photoresist layer 128 contacts the plating seed layer 131. The photoresist layer 128 includes a first photoresist sub-layer 112, a second photoresist sub-layer 121, a third photoresist sub-layer 124, and a fourth photoresist sub-layer 126.

[0041] The wafer 101 is placed in a photolithography tool 132, which includes a light source 133 and an optical element 134. Figure 1M 13. A photomask 135 is disposed in the optical path between the light source 133 and the optical element 134 in the photolithography tool 132. The photomask 135 has a light-blocking geometry 136 that reduces the transmission of UV light 137.

[0042] UV light 137 is generated by light source 133 and is incident on photomask 135. Portions of UV light 137 are transmitted through photomask 135 in areas not blocked by light-blocking geometry 136 and are incident on optical element 134. Portions of UV light 137 are focused onto photoresist layer 128, exposing the photoresist resin in first photoresist sub-layer 112, second photoresist sub-layer 121, third photoresist sub-layer 124, and fourth photoresist sub-layer 126 in the areas of bump bond studs 138 over bond pads 130. The photoresist resin exposed by UV light 137 is converted from a cyclic ketone to a carboxylic acid.

[0043] refer to Figure 1N , a positive tone development process using a developer solution 139 dissolves Figure 1M The developer solution 139 removes the photoresist layer 128 that is not exposed to the UV light 137, that is, in the area of ​​the bump bond studs 138. The developer solution 139 may include an alkaline aqueous solution such as tetramethylammonium hydroxide (TMAH) or potassium hydroxide (KOH). The developer solution 139 does not remove the large amount of photoresist layer 128 that is not exposed to the UV light 137, thereby leaving the photoresist layer 128 that is not exposed to the UV light 137 in place on the wafer. After the developer solution 139 dissolves the photoresist layer 128, the wafer 101 and the photoresist layer 128 are rinsed and dried.

[0044] In an alternative version of this example, using a negative tone photolithography process, the development process may dissolve the photoresist layer 128 that was not exposed by the UV light 137, thereby leaving the photoresist layer 128 that was exposed by the UV light 137 in place on the wafer.

[0045] refer to Figure 1O, a plating process using a plating bath 140 is used to form copper pillars 141 on the plating seed layer 131 in the area of ​​the bump bond pillars 138. The plating bath 140 contains copper ions that are plated onto the plating seed layer 131 and the partially formed copper pillars 141. The plating process can be implemented as an electroplating process or an electroless plating process. After the copper pillars 141, the photoresist layer 128 is removed, thereby exposing the plating seed layer 131. The photoresist 128 can be removed by any combination of a dry process using oxygen free radicals and a wet process using an organic solvent such as 1-methyl-2-pyrrolidone (NMP). After the photoresist layer 128 is removed, the plating seed layer 131 exposed by the copper pillars 141 is removed. The plating seed layer 131 can be removed by a wet etching process using one or more acidic aqueous solutions. The copper in the plating seed layer 131 can be removed using an aqueous solution such as ferric chloride. The titanium and tungsten in the plating seed layer 131 may be removed by, for example, an aqueous solution containing nitric acid or concentrated hydrogen peroxide.

[0046] refer to Figure 1P , an optional barrier layer 142 may be formed on the copper pillars 141, and solder bumps 143 may be formed on the barrier layer 142. Solder bumps 143 may include tin. For example, solder bumps 143 may include a eutectic alloy of tin, copper, and silver. Barrier layer 142 may include nickel, cobalt, or molybdenum to reduce diffusion of copper from the copper pillars 141 into the solder bumps 143 and to reduce diffusion of tin from the solder bumps 143 into the copper pillars 141. Barrier layer 142 may be formed, for example, by plating. Solder bumps 143 may be formed by plating or by dispensing solder paste onto barrier layer 142 and then heating the solder paste in a solder reflow process.

[0047] Figures 2A to 2D is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 2A , the microelectronic device 200 is part of a wafer 201, which may contain additional microelectronic devices (not shown). The microelectronic device 200 may be implemented as a reference Figure 1A The chip 201 may be implemented as a microelectronic device 100 of the present invention. Figure 1A The wafer 101 of FIG. 1 is a wafer of any of the disclosed wafer formats. The wafer 201 has a first surface 203 having a lateral perimeter 204 that is proximate to the lateral perimeter of the wafer 201. In this example, a coating region 205 of the first surface 203 extends over the microelectronic device 200 and additional microelectronic devices but does not extend to the lateral perimeter 204 of the first surface 203. The coating region 205 may extend to within 1 mm to 3 mm of the lateral perimeter 204, depending on the fabrication process used to form the microelectronic device 200.

[0048] The wafer 201 moves under a drop-on-demand station 208. The drop-on-demand station 208 extends across a width at least as wide as the coating area 205. The drop-on-demand station 208 dispenses discrete amounts of a mixture 209 of a photoresist resin and a solvent onto the wafer 201 to form a first photoresist sub-layer 212 on the first surface 203, e.g., as described with reference to FIG. Figures 1A to 1C The first photoresist sub-layer 212 is continuous and covers the coating area 205. The first applied thickness 244 of the first photoresist sub-layer 212 over the coating area 205 has a non-uniformity of less than 10%. Before any solvent is removed from the first photoresist sub-layer 212, the first applied thickness 244 can be 30 microns to 50 microns.

[0049] In the present example, discrete amounts of the mixture 209 of photoresist resin and solvent are dispensed by the drop-on-demand site 208 between the coating area 205 and the lateral perimeter 204 of the first surface 203 at a frequency that is lower than the frequency used by the drop-on-demand site 208 in the coating area 205, such that the thickness of the first photoresist sub-layer 212 decreases from a first applied thickness 244 at the lateral perimeter of the coating area 205 to zero in a tapered region 245 that extends outwardly a lateral distance of 100 microns to 1 mm from the lateral perimeter of the coating area 205. Additionally, the first photoresist sub-layer 212 does not extend into a wafer edge exposed (WEE) region 246 that extends inwardly a lateral distance of 1 mm to 3 mm from the lateral perimeter 204 of the first surface 203. Figure 2A The tapered region 245 is depicted as being wider than the WEE region 246 to more clearly depict the tapered profile of the first photoresist sub-layer 212 in the tapered region 245. The first photoresist sub-layer 212 has a tapered profile in the tapered region 245 because the first photoresist sub-layer 212 is formed from discrete amounts of the photoresist resin and solvent mixture 209. The tapered profile in the tapered region 245 advantageously enables the photoresist resin and solvent mixture 209 to coalesce due to surface tension without forming an edge bead thicker than the first applied thickness 244. The first photoresist sub-layer 212 adheres to the wafer 201 in the tapered region 245 against shrinkage of the photoresist resin and solvent mixture 209 due to surface tension, thereby maintaining the thickness of the first photoresist sub-layer 212 no greater than the first applied thickness 244. Forming the first photoresist sub-layer 212 by abruptly terminating the dispensing of the photoresist resin and solvent mixture 209 at the WEE region 246 can undesirably result in the formation of edge beads. The edge beads interfere with the photolithographic and other fabrication processes used to form the microelectronic device 200.

[0050] refer to Figure 2B, a portion of the solvent in the form of solvent vapor 216 is removed from the first photoresist sub-layer 212. The solvent vapor 216 may be removed by a process similar to that of reference numerals. Figure 1D The process of the disclosed process removes the solvent. As an example, between 10 weight percent and 75 weight percent of the solvent in the first photoresist sub-layer 212 can be removed. The thickness of the first photoresist sub-layer 212 in the coating area 205 can be reduced to a first desolvation thickness 247 based on the amount of solvent removed. The thickness of the first photoresist sub-layer 212 in the tapered region 245 is reduced to zero such that the thickness of the first photoresist sub-layer 212 in the tapered region 245 does not exceed the first desolvation thickness 247. Furthermore, the portion of the solvent removal from the first photoresist sub-layer 212 is performed without sudden pressure or temperature changes such that the first photoresist sub-layer 212 does not extend into the WEE region 246.

[0051] refer to Figure 2C , the wafer 201 moves under the drop-on-demand station 208. The drop-on-demand station 208 dispenses discrete amounts of a mixture 209 of a photoresist resin and a solvent onto the wafer 201 to form a second photoresist sub-layer 221 on the first photoresist sub-layer 212, for example, as described in reference Figure 1E to Figure 1H The second photoresist sub-layer 221 is continuous and covers the coating area 205. The second applied thickness 248 of the second photoresist sub-layer 221 above the coating area 205 has a non-uniformity of less than 10%. Before any solvent is removed from the second photoresist sub-layer 221, the second applied thickness 248 can be 30 to 50 microns. Discrete amounts of the photoresist resin and solvent mixture 209 are dispensed from the on-demand droplet site 208 into the tapered area 245 at a lower frequency than in the coating area 205, such that the thickness of the second photoresist sub-layer 221 decreases from the second applied thickness 248 to zero in the tapered area 245. In addition, the second photoresist sub-layer 221 does not extend into the WEE area 246. The second photoresist sub-layer 221 has a tapered profile in the tapered area 245 formed by a process similar to the tapered profile of the first photoresist sub-layer 212. The second photoresist sub-layer 221 adheres to the first photoresist sub-layer 212 and the wafer 201 in the tapered region 245 against shrinkage of the mixture 209 of photoresist resin and solvent due to surface tension, thereby maintaining the thickness of the second photoresist sub-layer 221 to be no greater than the second coated thickness 248 .

[0052] refer to Figure 2D , a portion of the solvent in the form of solvent vapor 216 is removed from the second photoresist sub-layer 221. The solvent vapor 216 may be removed by a process similar to that of reference 2. Figure 1DThe process of the disclosed process removes the solvent. As an example, between 10 weight percent and 75 weight percent of the solvent in the second photoresist sub-layer 221 can be removed. The thickness of the second photoresist sub-layer 221 in the coating area 205 can be reduced to a second desolvated thickness 249 based on the amount of solvent removed. The thickness of the second photoresist sub-layer 221 in the tapered region 245 is reduced to zero such that the thickness of the second photoresist sub-layer 221 in the tapered region 245 does not exceed the second desolvated thickness 249. In addition, the portion of the solvent removal from the second photoresist sub-layer 221 is performed without sudden pressure or temperature changes such that the second photoresist sub-layer 221 does not extend into the WEE region 246.

[0053] The first photoresist sub-layer 212 and the second photoresist sub-layer 221 provide at least a portion of a photoresist layer 228 on the wafer 201. Additional photoresist sub-layers of the photoresist layer 228 may be formed by similar means to those described in reference 2. Figures 2A to 2D The disclosed method is formed on the wafer 201 such that the thickness of the photoresist layer 228 is reduced to zero in the tapered region 245 and the photoresist layer 228 does not extend into the WEE region 246. Forming the photoresist layer 228 using the method of this example can advantageously reduce the manufacturing cost and complexity of the microelectronic device 200 by eliminating the requirement for an edge bead removal process, which would be required if the photoresist layer 228 were formed by a spin coating process.

[0054] Figures 3A to 3C is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 3A , microelectronic device 300 is part of a wafer 301, which may contain additional microelectronic devices (not shown). Microelectronic device 300 may be implemented as a reference Figure 1A The chip 301 may be implemented as a reference Figure 1A The wafer 301 may be any of the wafer formats disclosed herein. The wafer 301 has a first surface 303 that extends to a lateral perimeter (not shown) of the wafer 301. In this example, a coating region 305 of the first surface 303 extends over the microelectronic device 300 and additional microelectronic devices but does not extend to the lateral perimeter of the wafer 301.

[0055] Wafer 301 is referenced Figures 1A to 1CThe disclosed method moves below the drop-on-demand site 308. The drop-on-demand site 308 extends across a width at least as wide as the coating area 305. The drop-on-demand site 308 dispenses a first discrete amount of a mixture 309 of a photoresist resin and a solvent onto the wafer 301 to form a first photoresist sub-layer 312 of a photoresist layer 328 on the first surface 303, for example, as described in reference Figures 1A to 1C The first photoresist sub-layer 312 is continuous and covers the coating area 305 . Figure 3A A first photoresist sub-layer 312 is depicted immediately after a mixture of photoresist resin and solvent 309 is dispensed onto wafer 301 .

[0056] A portion of the solvent in the first photoresist sub-layer 312 is removed, thereby reducing the thickness of the first photoresist sub-layer 312. The portion of the solvent in the first photoresist sub-layer 312 may be removed, as described with reference to FIG. Figure 1D public.

[0057] The first photoresist sub-layer 312 may have an undesirable degree of thickness non-uniformity, which may be due, for example, to unintended variations in the process of dispensing the mixture of photoresist resin and solvent from the drop-on-demand site 308. One possible source of unintended variations in the process of dispensing the mixture 309 may be variations in the volume of the droplets of the mixture 309.

[0058] refer to Figure 3B , measuring the thickness variation of the first photoresist sub-layer 312. The thickness variation can be measured using a profilometer tool 350 having a scanning pen 351, such as Figure 3B Alternatively, the thickness variation can be measured using a non-contact optical tool, such as an optical interferometry tool or a reflectometer tool. Other methods of measuring the thickness variation of the first photoresist sub-layer 312 are within the scope of the present example.

[0059] refer to Figure 3C , wafer 301 is referenced Figure 1E to Figure 1HThe disclosed method moves below the drop-on-demand sites 308. The drop-on-demand sites 308 dispense a second discrete amount of the mixture of photoresist resin and solvent 309 onto the wafer 301 to form a second photoresist sub-layer 321 of the photoresist layer 328 on the first surface 303. In this example, the dispensing of the second discrete amount of the mixture of photoresist resin and solvent 309 is adjusted for each of the drop-on-demand sites 308 to compensate for thickness variations of the first photoresist sub-layer 312, such that the photoresist layer 328 has a thickness uniformity that is better than the thickness uniformity of the first photoresist sub-layer 312 alone. More of the mixture 309 can be dispensed into areas where the first photoresist sub-layer 312 is thinner than the average thickness of the first photoresist sub-layer 312, and less of the mixture 309 can be dispensed into areas where the first photoresist sub-layer 312 is thicker than the average thickness. The dispensing of the second discrete amount of mixture 309 can be adjusted by adjusting the volume of the droplets of mixture 309 , by adjusting the rate at which the droplets are dispensed, or by adjusting both the volume of the droplets and the rate at which the droplets are dispensed. The second photoresist sublayer 321 is continuous and covers the coating region 305 . Figure 3C The first photoresist sub-layer 312 is depicted immediately after the mixture of photoresist resin and solvent 309 is dispensed onto the wafer 301. A portion of the solvent in the second photoresist sub-layer 321 is removed, resulting in a reduction in the thickness of the second photoresist sub-layer 321.

[0060] Adjusting the droplets of mixture 309 to compensate for thickness variations of first photoresist sub-layer 312 can advantageously improve thickness uniformity of photoresist layer 328. Additional photoresist sub-layers of photoresist layer 328 can be formed over the combination of first photoresist sub-layer 312 and second photoresist sub-layer 321, and thickness variations of photoresist layer 328 can be measured. Subsequent photoresist sub-layers of photoresist layer 328 can be formed by adjusting the droplets of mixture 309 to compensate for thickness variations of photoresist layer 328, thereby further yielding the advantage of advantageously improved thickness uniformity.

[0061] Figure 4 is a cross-section of a microelectronic device depicted in another example formation method. Microelectronic device 400 is a portion of wafer 401, which may contain additional microelectronic devices (not shown). Microelectronic device 400 may be implemented as a reference Figure 1A The chip 401 may be implemented as a reference Figure 1AThe wafer 401 may be any of the wafer formats disclosed herein. The wafer 401 has a first surface 403 that extends to a lateral perimeter (not shown) of the wafer 401. In this example, a coating region 405 of the first surface 403 extends over the microelectronic device 400 and additional microelectronic devices but does not extend to the lateral perimeter of the wafer 401.

[0062] Wafer 401 is referenced Figures 1A to 1C The disclosed method moves beneath a drop-on-demand site 408. Drop-on-demand site 408 extends across a width at least as wide as coating zone 405. Drop-on-demand site 408 is configured to dispense a first discrete amount of a mixture 409 of a photoresist resin and a solvent. Drop-on-demand site 408 of the present example includes an ultrasonic transducer 452 that applies ultrasonic energy to the discrete amount of mixture 409 to break each of the discrete amounts of mixture 409 into a plurality of small droplets 453. The discrete amount of mixture 409 may have a volume of 10 pL to 50 pL, while the small droplets 453 may have a volume of 1% to 10% of the volume of the discrete amount of mixture 409. Drop-on-demand site 408 dispenses the discrete amount of mixture 409 in the form of small droplets 453 onto wafer 401 to form a first photoresist sub-layer 412 of photoresist layer 428 on first surface 403. Compared to a single droplet having the entire first discrete amount of mixture 409, small droplet 453 may be as Figure 4 4. The small droplets 453 can thus form a first photoresist sub-layer 412 having a more uniform thickness than if a single droplet of mixture 409 were dispensed for each discrete amount of mixture 409. The first photoresist sub-layer 412 is continuous and covers the coating area 405. Additional photoresist sub-layers of photoresist layer 428 can be formed over the first photoresist sub-layer 412 by similar methods to provide the photoresist layer 428 with a desired thickness.

[0063] Figure 5A and Figure 5B is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 5A , microelectronic device 500 is part of a wafer 501, which may contain additional microelectronic devices (not shown). Microelectronic device 500 may be implemented as a reference Figure 1A The chip 501 may be implemented as a reference Figure 1A The wafer 501 is configured to be any of the wafer formats disclosed herein. The wafer 501 has a first surface 503 that extends to a lateral perimeter (not shown) of the wafer 501. In this example, a coating region 505 of the first surface 503 extends over the microelectronic device 500 and additional microelectronic devices, but does not extend to the lateral perimeter of the wafer 501.

[0064] Wafer 501 is referenced Figures 1A to 1C The disclosed method moves at a constant speed beneath a drop-on-demand site 508. The drop-on-demand site 508 extends across a width at least as wide as the coating area 505. The drop-on-demand site 508 dispenses discrete amounts of a mixture of photoresist resin and solvent 509 in the form of droplets 554 dispensed at a first dispensing frequency onto the wafer 501 to form a first photoresist sub-layer 512 of the photoresist layer 528 on the first surface 503. The first photoresist sub-layer 512 is continuous and covers the coating area 505. The first dispensing frequency can be selected so that the first photoresist sub-layer 512 is formed with sufficient thickness to prevent the mixture of photoresist resin and solvent 509 from pooling and merging on the wafer 501 as the droplets 554 are dispensed. Dispensing droplets 554 at a lower frequency can create undesirable voids in the first photoresist sub-layer 512.

[0065] After the droplet 554 is dispensed onto the wafer 501, a portion of the solvent in the first photoresist sub-layer 512 is removed, thereby causing the thickness of the first photoresist sub-layer 512 to decrease. The portion of the solvent in the first photoresist sub-layer 512 may be removed, as described with reference to FIG. Figure 1D public.

[0066] refer to Figure 5B , wafer 501 is referenced Figure 1E to Figure 1H 5. The disclosed method moves at a constant speed beneath a drop-on-demand station 508. The drop-on-demand station 508 dispenses discrete amounts of a mixture of a photoresist resin and a solvent 509 in the form of droplets 554 dispensed at a second dispensing frequency that is lower than the first dispensing frequency onto the wafer 501 to form a second photoresist sub-layer 521 of the photoresist layer 528 over the first photoresist sub-layer 512. The second photoresist sub-layer 521 is continuous and covers the coating area 505. After the droplets 554 are dispensed onto the wafer 501 to form the second photoresist sub-layer 521, a portion of the solvent in the second photoresist sub-layer 521 is removed, resulting in a reduction in the thickness of the second photoresist sub-layer 521. The second dispensing frequency can be selected such that the second photoresist sub-layer 521 is formed with a thickness that is less than the thickness of the first photoresist sub-layer 512 to provide the desired thickness of the photoresist layer 528. In an alternative version of this example, the second dispensing frequency can be greater than the first dispensing frequency such that the thickness of the second photoresist sub-layer 521 is greater than the thickness of the first photoresist sub-layer 512.

[0067] Figure 6A and Figure 6B is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 6A, microelectronic device 600 is part of a wafer 601, which may contain additional microelectronic devices (not shown). Microelectronic device 600 may be implemented as a reference Figure 1A The chip 601 may be implemented as a reference Figure 1A The wafer 601 is configured to be any of the wafer formats disclosed herein. The wafer 601 has a first surface 603 that extends to a lateral perimeter (not shown) of the wafer 601. In this example, a coating region 605 of the first surface 603 extends over the microelectronic device 600 and additional microelectronic devices but does not extend to the lateral perimeter of the wafer 601.

[0068] Wafer 601 is referenced Figures 1A to 1C The disclosed method moves at a constant speed beneath a drop-on-demand site 608. The drop-on-demand site 608 extends across a width at least as wide as the coating area 605. The drop-on-demand site 608 dispenses a first discrete amount of a mixture of photoresist resin and solvent 609 in the form of first droplets 654 dispensed at a constant frequency onto the wafer 601 to form a first photoresist sub-layer 612 of the photoresist layer 628 on the first surface 603. The first droplets 654 each have a first volume, which may be 10 pL to 50 pL, as an example. The first photoresist sub-layer 612 is continuous and covers the coating area 605. The first volume may be selected so that the first photoresist sub-layer 612 is formed with sufficient thickness to prevent the mixture of photoresist resin and solvent 609 from pooling and coalescing on the wafer 601 as the droplets 654 are dispensed. Dispensing the first drop 654 at a lower volume may create undesirable voids in the first photoresist sub-layer 612 .

[0069] After the first droplet 654 is dispensed onto the wafer 601, a portion of the solvent in the first photoresist sub-layer 612 is removed, thereby causing the thickness of the first photoresist sub-layer 612 to decrease. The portion of the solvent in the first photoresist sub-layer 612 may be removed, as described in reference to FIG. Figure 1D public.

[0070] refer to Figure 6B , wafer 601 is referenced Figure 1E to Figure 1H6. The disclosed method moves at a constant speed beneath a drop-on-demand station 608. The drop-on-demand station 608 dispenses a second discrete amount of a mixture of photoresist resin and solvent 609 in the form of second droplets 655 onto the wafer 601 at a constant frequency to form a second photoresist sub-layer 621 of the photoresist layer 628 on the first photoresist sub-layer 612. The second droplets 655 each have a second volume that is smaller than the first volume. The second photoresist sub-layer 621 is continuous and covers the coating area 605. After the second droplets 655 are dispensed onto the wafer 601 to form the second photoresist sub-layer 621, a portion of the solvent in the second photoresist sub-layer 621 is removed, resulting in a reduction in the thickness of the second photoresist sub-layer 621. The second volume can be selected such that the second photoresist sub-layer 621 is formed with a thickness that is less than the thickness of the first photoresist sub-layer 612 to provide the desired thickness of the photoresist layer 628. In an alternative version of this example, the second volume can be larger than the first volume such that the thickness of the second photoresist sub-layer 621 is greater than the thickness of the first photoresist sub-layer 612.

[0071] Figure 7A and Figure 7B is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 7A , microelectronic device 700 is part of a wafer 701, which may contain additional microelectronic devices (not shown). Microelectronic device 700 may be implemented as a reference Figure 1A The chip 701 may be implemented as a reference Figure 1A In this example, the wafer 701 includes a semiconductor material 756, such as silicon. The semiconductor material 756 may be p-type, such as Figure 7A . Wafer 701 of this example further includes a dielectric layer 757 on semiconductor material 756. Dielectric layer 757 extends to first surface 703 of wafer 701. As an example, dielectric layer 757 may include silicon dioxide, may have a thickness of 5 to 100 nanometers, and may be formed by thermal oxidation of semiconductor material 756. Dielectric layer 757 is sometimes referred to as a pad oxide layer or sacrificial oxide layer. The purpose of dielectric layer 757 is to protect semiconductor material 756 from damage and contamination during the manufacturing process.

[0072] A photoresist layer 728 is formed on the wafer 701 according to any of the examples disclosed herein. The photoresist layer 728 includes at least two photoresist sub-layers; the photoresist layer 728 of the present example includes a first photoresist sub-layer 712 formed on the wafer 701, a second photoresist sub-layer 721 formed on the first photoresist sub-layer 712, a third photoresist sub-layer 724 formed on the second photoresist sub-layer 721, and a fourth photoresist sub-layer 726 formed on the third photoresist sub-layer 724. The photoresist layer 728 is patterned to expose the wafer 701 in the implanted region 758. The photoresist layer 728 may be formed as described in reference to FIG. Figure 1M and Figure 1N The disclosure is generally patterned or patterned by another patterning method.

[0073] Dopant 759 is implanted into the semiconductor material 756 exposed by the photoresist layer 728 to form an implanted region 760 in the semiconductor material 756. Dopant 759 is blocked from the wafer 701 outside the implanted region 760 by the photoresist layer 728. Dopant 759 may be an n-type dopant, such as Figure 7A , such as phosphorus, arsenic, or antimony. In alternative versions of this example, semiconductor material 756 can be n-type, or dopant 759 can be a p-type dopant, such as boron, gallium, or indium. Forming photoresist layer 728 by any of the examples disclosed herein can produce the disclosed advantages, such as reducing the amount of photoresist resin and solvent mixture used compared to spin coating processes and eliminating the need to remove edge beads from the periphery of wafer 701.

[0074] After the dopant 759 is implanted into the semiconductor material 756, the photoresist layer 728 is removed. The photoresist layer 728 can be removed by exposing the photoresist layer 728 to oxygen radicals in an ashing process followed by a wet etching process using an aqueous mixture of sulfuric acid and hydrogen peroxide. Other processes for removing the photoresist layer 728, such as a wet process using NMP, are also within the scope of this embodiment. The dielectric layer 757 can advantageously protect the semiconductor material 756 during the removal of the photoresist layer 728.

[0075] refer to Figure 7B , the wafer 701 is heated by the annealing process 761, and the annealing process 761 activates Figure 7A of the implanted region 760 Figure 7A The implanted dopants 759 are implanted to form n-type regions 762 in the semiconductor material 756. The annealing process 761 may be performed as a furnace anneal, in which case the implanted regions 759 may further diffuse into the semiconductor material 756. Alternatively, the annealing process 761 may be performed as a rapid thermal annealing process, such as a spike anneal or a flash anneal.

[0076] Figure 8A and Figure 8B is a cross-section of a microelectronic device depicted at a stage in another example formation method. Figure 8A , microelectronic device 800 is part of a wafer 801, which may contain additional microelectronic devices (not shown). Microelectronic device 800 may be implemented as a reference Figure 1A The chip 801 may be implemented as a reference Figure 1A The wafer 801 of the present example may be any of the wafer formats disclosed in connection with the wafer 101. In the present example, the wafer 801 includes a substrate 863, which may be implemented as a portion of a fabricated device and may include semiconductor material, metal conductors, and dielectric layers. The wafer 801 of the present example also includes an etch stop layer 864 on the substrate 863. As examples, the etch stop layer 864 may include silicon dioxide, silicon nitride, silicon oxynitride, silicon carbide, silicon carbonitride, or silicon carbon oxynitride. The wafer 801 of the present example further includes a material layer 865 on the etch stop layer 864. The material layer 865 extends to the first surface 803 of the wafer 801. The material layer 865 may include any material that provides structural elements of the microelectronic device 800, such as aluminum, polysilicon, silicon dioxide, or a dielectric material having a lower dielectric constant than silicon dioxide, sometimes referred to as a low-k dielectric material. The etch stop layer 864 has a composition that provides etch selectivity relative to the material layer 865.

[0077] A photoresist layer 828 is formed on the wafer 801 according to any of the examples disclosed herein. The photoresist layer 828 includes at least two photoresist sub-layers; the photoresist layer 828 of the present example includes a first photoresist sub-layer 812 formed on the wafer 801, a second photoresist sub-layer 821 formed on the first photoresist sub-layer 812, a third photoresist sub-layer 824 formed on the second photoresist sub-layer 821, and a fourth photoresist sub-layer 826 formed on the third photoresist sub-layer 824. The photoresist layer 828 is patterned to expose the wafer 801 in the etched area 866. The photoresist layer 828 can be formed as described in reference to FIG. Figure 1M and Figure 1N Forming the photoresist layer 828 by any of the examples disclosed herein can produce the advantages disclosed herein.

[0078] The material layer 865 in the etched area 866 is removed by an etchant 867 in a reactive ion etching (RIE) process. The etchant 867 may contain halogen ions, such as fluoride ions, as Figure 8A The photoresist layer 828 prevents the etchant 867 from attacking the material layer 865 outside the etched area 866. Figure 8A The depiction shows the completion of the removal of the material layer 865 in the mid-etch region 866. The RIE process continues until all of the material layer 865 in the etch region 866 is removed. The etch stop layer 864 has a sufficiently low etch rate that the RIE process can be stopped before the etch stop layer 864 in the etch region 866 is removed. In an alternative version of this example, the material layer 865 in the etch region 866 can be removed by a wet etching process.

[0079] After the material layer 865 in the etched area 866 is removed, the photoresist layer 828 is removed. The photoresist layer 828 can be removed by exposing the photoresist layer 828 to oxygen radicals in an ashing process followed by a wet etching process using an aqueous mixture of ammonium hydroxide and hydrogen peroxide. Other processes for removing the photoresist layer 828, such as a wet process using NMP, are also within the scope of this embodiment. Figure 8B The microelectronic device 800 is depicted after the photoresist layer 828 has been removed.

[0080] The various features of the examples disclosed herein may be combined in other embodiments of example methods for forming a microelectronic device. For example, any of the methods can be used to form a photoresist layer having two, three, four, or more photoresist sublayers. Any of the photoresist layers can be formed to have a reduced thickness in a tapered region that extends inwardly toward the WEE region around the lateral periphery of the wafer. Any of the photoresist layers can be formed by varying the frequency or volume of droplets of a mixture of a photoresist resin and a solvent. Any of the photoresist layers can be formed by using ultrasound to break up discrete amounts of a mixture of a photoresist resin and a solvent into a plurality of small droplets. Any of the photoresist layers can be formed by measuring thickness variations after forming one or more photoresist sublayers and adjusting the dispensing of the mixture of the photoresist resin and the solvent during subsequent photoresist sublayer formation to compensate for the thickness variations. Furthermore, in addition to plating masks, implant masks, and etch masks, photoresist layers can also be used in other processes of microelectronic device fabrication.

[0081] Although various embodiments of the present disclosure have been described above, it should be understood that they are presented by way of example only and not by way of limitation. Numerous changes may be made to the disclosed embodiments in accordance with the disclosure herein without departing from the spirit or scope of the present disclosure. Therefore, the breadth and scope of the present invention should not be limited by any of the embodiments described above. Specifically, the scope of the present disclosure should be defined in accordance with the appended claims and their equivalents.

Claims

1. A method of forming a microelectronic device, comprising: Providing a wafer having a first surface with a lateral perimeter, wherein lateral refers to a direction parallel to the first surface, wherein the first surface does not extend onto a curved surface of the wafer at the lateral perimeter of the wafer, and the first surface has a coating area that does not extend to the lateral perimeter; providing a drop-on-demand site configured to dispense droplets of a mixture of a photoresist resin and a solvent onto the wafer, the mixture having a viscosity of 2 to 20 centipoise (cp) and a photoresist resin content of 10 to 20 weight percent, wherein the remainder of the mixture consists essentially of solvent; heating the wafer to a temperature within a first temperature range; moving the wafer in a first direction beneath the drop-on-demand site while the wafer is within the first temperature range and dispensing a first discrete amount of the mixture of photoresist resin and solvent from the drop-on-demand site onto the wafer to form a first photoresist sub-layer of a photoresist layer on the wafer, the first photoresist sub-layer being continuous, the first photoresist sub-layer covering the coating area; after dispensing the first discrete amount of the mixture of photoresist resin and solvent, removing a portion of the solvent from the first photoresist sublayer while the wafer is within the first temperature range; and After removing the portion of the solvent from the first photoresist sublayer, moving the wafer in a second direction opposite to the first direction below the drop-on-demand site while the wafer is within a second temperature range, and dispensing a second discrete amount of the mixture of photoresist resin and solvent from the drop-on-demand site onto the wafer to form a second photoresist sublayer of the photoresist layer on the first photoresist sublayer, the second photoresist sublayer being continuous and covering the coating area.

2. The method of claim 1 , wherein after the first discrete amount of the mixture of photoresist resin and solvent is dispensed onto the wafer, the wafer is moved at a speed not exceeding 500 mm / s. 2 (mm / s 2 ) to a stop at the deceleration rate.

3. The method of claim 1 , wherein the first discrete amounts of the mixture of photoresist resin and solvent each have a volume of 10 picoliters (pL) to 50 pL, and the second discrete amounts of the mixture of photoresist resin and solvent each have a volume of 10 pL to 50 pL. The method of claim 1 , wherein the first temperature range is 45° C. to 50° C., and the second temperature range is 45° C. to 50° C.

5. The method of claim 1 , wherein the first photoresist sublayer is formed to have a thickness that decreases from a first thickness at a lateral periphery of the coating zone to zero in a tapered region extending outward from the coating zone a lateral distance of 100 microns to 1 mm, wherein the first photoresist sublayer does not extend into a wafer edge exposed (WEE) region extending inward from the lateral periphery of the first surface a lateral distance of 1 mm to 3 mm.

6. The method of claim 1, wherein the mixture of photoresist resin and solvent comprises propylene glycol methyl ether acetate (PGMEA) and gamma butyrolactone (GBL).

7. The method of claim 1, wherein the mixture of photoresist resin and solvent has a surface tension of 20 to 50 dyne / cm at 20 to 25°C as measured by a dynamic surface tension measurement method.

8. The method of claim 1, further comprising introducing an anti-drying vapor above the wafer while dispensing the mixture of the photoresist resin and the solvent onto the wafer at the drop-on-demand site to form the first photoresist sub-layer.

9. The method of claim 7 , further comprising moving the wafer laterally in a direction perpendicular to the first direction by a first lateral distance that is less than a lateral separation between adjacent drop-on-demand sites after forming the first photoresist sublayer and before forming the second photoresist sublayer.

10. The method of claim 1, further comprising measuring a thickness variation of the first photoresist sub-layer before forming the second photoresist sub-layer.

11. The method of claim 10, wherein the second discrete amount of the mixture of photoresist resin and solvent dispensed is adjusted to compensate for the thickness variation.

12. The method of claim 1, comprising applying ultrasonic energy to the first discrete quantities of the mixture of the photoresist resin and the solvent to break each of the first discrete quantities into a plurality of small droplets.

13. The method of claim 1 , wherein the first discrete amount of the mixture of photoresist resin and solvent is dispensed at a first dispensing frequency, and the second discrete amount of the mixture of photoresist resin and solvent is dispensed at a second dispensing frequency, the second dispensing frequency being different from the first dispensing frequency.

14. The method of claim 1, wherein the first discrete amounts of the mixture of photoresist resin and solvent each have a first volume, and the second discrete amounts of the mixture of photoresist resin and solvent each have a second volume, the second volume being different from the first volume.

15. The method of claim 1, further comprising: exposing areas of the photoresist layer to ultraviolet (UV) light through a photomask; and The areas of the photoresist layer exposed to UV light are dissolved in a developer solution, thereby leaving the photoresist layer not exposed to the UV light in place on the wafer.

16. The method of claim 1, further comprising: exposing areas of the photoresist layer to UV light through a photomask; and The areas of the photoresist layer not exposed to the UV light are dissolved in a developer solution, thereby leaving the photoresist layer exposed to the UV light in place on the wafer.

17. The method of claim 1, further comprising: patterning the photoresist layer using a photolithography process; and Copper posts are plated on the wafer in areas exposed by the photoresist layer.

18. The method of claim 1, further comprising: patterning the photoresist layer using a photolithography process; and Dopants are implanted into the wafer in the areas exposed by the photoresist layer.

19. The method of claim 1, further comprising: patterning the photoresist layer using a photolithography process; and The material layer of the wafer is etched in the areas exposed by the photoresist layer.

20. The method of claim 1, further comprising: after dispensing the second discrete amount of the mixture of photoresist resin and solvent, removing a portion of the solvent from the second photoresist sublayer while the wafer is within the second temperature range; and After removing the portion of the solvent from the second photoresist sublayer, moving the wafer in the first direction below the drop-on-demand site when the wafer is within a third temperature range, the third temperature range being equal to the second temperature range or the first temperature range, and dispensing a third discrete amount of the mixture of photoresist resin and solvent from the drop-on-demand site onto the wafer to form a third photoresist sublayer of the photoresist layer on the second photoresist sublayer, the third photoresist sublayer being continuous, and the third photoresist sublayer covering the coating area.

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