Patent Application
20080024558
The embodiments of a primer layer can be better understood with reference to the following drawings showing an embodiment of an inkjet printing system. The elements of the drawings may not be to scale relative to each other. Rather, emphasis has instead been placed upon clearly illustrating the embodiments of the primer layer in the embodiment of an inkjet printing system. Certain dimensions have been exaggerated in relation to other dimensions in order to provide a clearer illustration and understanding of the present disclosure. Furthermore, like reference numerals designate corresponding similar parts through the several views.
a illustrates a cross sectional diagram of a chamber layer over the developed primer layer showing a relatively small surface topography according to an exemplary embodiment of an inkjet printing system.
b illustrates a cross sectional diagram of a chamber layer over an unpatterned primer layer showing a relatively large surface topography according to an exemplary embodiment of an inkjet printing system.
Primer layers can be useful in promoting adhesion between two layers. An example without a primer layer may occur where, a first layer may be a substrate and the second layer may be a protective overcoat. If the overcoat is applied to the substrate, the overcoat may peel, delaminate, blister, etc.
Separation of the overcoat from the substrate may be due to physical, chemical, or other types of incompatibilities between two materials. Also, the separation may be due to thermal cycling whereby the substrate and the overcoat expand at different rates. Thermal cycling may occur during manufacture of a product, use of the product, and the like. Separation may also be due to other factors.
A primer layer may be used as an intermediate layer between a substrate and a protective overcoat. The primer can have adhesion properties which are compatible with both the substrate and the protective overcoat thereby increasing the overall bond strength between the substrate and the protective overcoat. Increased bond strength may result in less peeling, blistering, delamination, etc. of the protective overcoat from the substrate. The intermediate primer layer can also serve to limit the interfacial stress between the substrate and the protective overcoat. Distributing the stress through the primer layer may also reduce the peeling, blistering, delamination, and the like.
In some embodiments, conductive and/or dielectric films may be deposited on the surface of a substrate, for example, in an integrated circuit. The films on the substrate may form topography. Adding a primer layer to a surface may promote adhesion and absorb stress, although primer layers over a surface may not substantially reduce surface topography. In some situations, it may be desirable to create a coating which does not substantially translate the topography of a film on a substrate to the topography of a surface layer, which may result in a substantially planar top surface. For instance, in an inkjet print-head, a relatively flat planar surface topography allows ejected ink from spatially arranged nozzles to strike paper with less misdirection. An inkjet print-head may be formed from an integrated circuit which may have topographical variations. Reducing topographical variations in a subsequent layer, such as an orifice layer over the integrated circuit can control the directionality of the ejected ink thereby increasing print quality and reducing the likelihood that the ink will mix.
For at least these reasons, it is desirable to retain the stress absorbing and adhesion promoting properties of a primer layer while also using the primer layer to aid in surface planarization thereby reducing topographical surface variations.
Exemplary embodiments which aid planarization using a primer layer while retaining the adhesion and stress reducing properties of the primer layer are described in reference to the following figures.
Semiconducting, dielectric and conducting layers may form control logic 108 on the substrate 102. The control logic 108 serves to command a drop of ink from an inkjet print-head. The control logic 108 may contain: transistors formed from doped semiconductors; interconnects formed from conductors such as aluminum and gold; and insulating layers formed from dielectric materials such as oxides of silicon, silicon carbide, silicon nitride and the like.
An ejector 104 may be used to eject ink from an inkjet print-head. The ejector 104 may be formed from a heater resistor in the case of a thermal inkjet print-head, a piezoelectric drive element in a piezoelectric inkjet print-head, an electromechanical drive element, or other types of drive elements. A transistor (not shown) in the control logic 108 may turn on and off the ejector 104. A thermal inkjet heater resistor may be formed from tantalum, aluminum, tungsten, alloys of tantalum, aluminum, tungsten, or other types of materials or alloys.
Connector 106 serves to conduct current and voltage from the thin film control logic 108 to the ejector 104. Connector 106 may have electrical conductors such as aluminum and may have electrical dielectrics such as silicon nitride, silicon carbide, and other oxides of silicon. The dielectrics may serve as electrical insulators between electrical conductors and also to passivate the electrical conductors, thereby protecting the electrical conductors from corrosion of ink. Tantalum can be applied to the electrical conductors and may aid adhesion. Tantalum may also be used for cavitation protection on the ejector 104. The ejector 104, connector 106, and control logic 108 may all together be considered a first layer 110 having a topography on a substrate 102.
Three exposed primer areas 310 are shown between the connectors 106 for illustrative purposes. There may be more or less than three exposed primer areas 310 between the connectors 106. The exposed primer areas 310 between the connectors 106 may form the base of pillars. The pillars may be circular shaped, square shaped, rectangular shaped or have another shape. The pillars may serve to filter particles from ink in an inkjet print-head. The pillars may also serve to filter particles from a liquid in an inkjet print-head. The liquid may be ink, but is not limited to ink. The liquid may be a chemical binder, a chemical fixer, an assay, and the like.
However, the exposed primer areas 310 may be located in other areas. Thus the exposed primer areas 310 are not restricted to being placed between the connectors 106. For example, the exposed primer areas 310 may be located on a portion of a substrate 102 which does not have control logic 108 or other features such as a layer of tantalum and gold which may be used on a print-head for passivation purposes. In one embodiment of a print-head, the height of tantalum and gold is about 1.7 microns. Thus, exposed primer areas 310 may be formed on a portion of the substrate 102 where tantalum and gold is absent in order to aid in planarizing the thickness of subsequent layers. In other words, the exposed primer areas 310 may be used to compensate for the thickness of the tantalum and gold layers in areas where tantalum and gold is not present.
In one embodiment of a print-head, the exposed primer areas 310 to compensate for the about 1.7 micron height of tantalum and gold are circular shaped with a diameter of about 39 microns and a thickness of about 4 microns. The circular shaped structure having a thickness forms a cylinder. One or more of these cylinders may be placed adjacent to each other in areas where tantalum and gold is absent. 40 percent of the area may be uniformly filled with the cylinders. This 40 percent area fill may be used to compensate for the thickness of a tantalum and gold layer in areas where tantalum and gold is not present.
However, the patterned primer features 402 may be located in other areas. Thus the patterned primer features 402 are not restricted to being placed between the connectors 106. For example, the patterned primer features 402 may be located on a portion of a substrate 102 which does not have control logic 108 or other features such as a layer of tantalum and gold which may be used on a print-head for passivation purposes. In one embodiment of a print-head, the height of tantalum and gold is about 1.7 microns. Thus, patterned primer features 402 may be formed on a portion of the substrate 102 where tantalum and gold is absent in order to aid in planarizing the thickness of subsequent layers. In other words, the patterned primer features 402 may be used to compensate for the thickness of the tantalum and gold layers in areas where tantalum and gold is not present.
In one embodiment of a print-head, the patterned primer features 402 compensate for the about 1.7 micron height of the tantalum and gold and are circular shaped with a diameter of about 39 microns and a thickness of about 4 microns. The circular shaped structure forms a cylinder. One or more of these cylinders may be placed side by side where about 40 percent of the area lacking tantalum and gold is uniformly filled with the cylinders. This 40 percent area fill may be used to compensate for the thickness of a tantalum and gold layer in areas where tantalum and gold is not present.
The patterned primer features 402 partially cover the control logic 108 and the connector 106 layers. The patterned primer features 402 may overlap the connector layers 106 and the control logic 108 a lateral distance (D1) 404 and (D2) 406 respectively. These lateral distances (D1) 404 and (D2) 406 may be different. If the lateral distance (D2) 406 is greater than about 10 times the thickness of a height difference (D3) 408 then the stress within the patterned primer feature 402 and the stress of subsequent layers at the topographical boundary interface may be reduced. As an example, a topographical boundary occurs between the substrate 102 and the control logic 108 layer as indicated by the height difference (D3) 408 of the topographical boundary.
This partial coverage of the patterned primer feature 402 having a lateral distance (D2) 406 can increase the interfacial adhesion and reduce stress within the patterned primer features 402. The partial coverage having a lateral distance (D2) 406 may also reduce the stress between the control logic 108 layer and a subsequent layer applied over the control logic 108 layer. Similarly, the partial coverage of the patterned primer features 402 may increase interfacial adhesion and reduce stress within the patterned primer features 402 and between the connector 106 layer and a subsequent layer applied over the connector 106 layer.
Another stress reduction technique is to overlap the control logic 108 with the patterned primer features 402 a lateral distance (D2) 406 of at least 3 times the thickness (D4) 410 of the patterned primer features 402. The lateral distance (D2) extends from an exposed boundary 412. As an example, the thickness (D4) 410 of the patterned primer features 402 can be 4 microns. Therefore, the overlap lateral distance (D2) 406 of the patterned primer feature 402 is 3 times 4 microns, or 12 microns. The overlap lateral distance (D2) 406 can also be 10 times the thickness (D4) 410 of the patterned primer features 402 to provide more stress reduction. Furthermore, the overlap lateral distance (D2) 406 can be 15 times the thickness (D4) 410 of the patterned primer features 402. Increasing the overlap lateral distance (D2) 406 from 10 to 15 times the thickness (D4) 410 of the patterned primer features 402 may not proportionally increase stress reduction, but can provide margin. Similarly connector 106 may be overlapped with the patterned primer features 402. The overlap lateral distance extends from an exposed boundary 412. The overlap lateral distance (D1) 404 ranges from about 3 to 15 times the thickness (D4) 410 of the patterned primer features 402.
Yet another stress reduction technique is for patterned primer features 402 to have a lateral distance (D5) 414 which is at least 3 times greater than the thickness (D4) of the patterned primer feature 402. The lateral distance (D5) may be 15 times greater than the thickness (D4) to provide for margin.
These techniques of stress reduction may be applied to high stress areas within an inkjet print-head. Other areas in an inkjet print-head which are not subject to high stresses such as the patterned primer features 402 between the connectors 106 may not apply this stress reduction technique.
a illustrates a cross sectional diagram of a chamber layer 502a coating over the patterned primer features 402 according to an exemplary embodiment of an inkjet printing system showing reduced surface topography. The chamber layer 502a has a relatively small peak-to-valley height (H1) 504a of about 0.3 microns on an inkjet print-head. This relatively small peak-to-valley height (H1) 504a decreases the amount of chemical mechanical polishing (CMP) planarization in a subsequent process step thereby saving time and processing materials. The chamber layer 502a may be considered a third layer.
A chamber layer 502a is deposited over the patterned primer features 402. The chamber layer 502a may be about 15 microns thick; however other thicknesses may be used. The chamber layer 502a is used to form a cavity 702 as shown in
If the patterned primer features 402 are spaced apart with a first spacing (S1) 506 of about 250 microns or less, then the chamber layer 502a coats the patterned primer features 402 relatively uniformly. The first spacing (S1) 506 is the distance between the patterned primer features 402. The first spacing (S1) 506 between the patterned primer features 402 may be about 4 microns. Tests have shown that if the distance between the patterned primer features 402 is about 4 microns, a subsequent layer—such as the chamber layer which is over the patterned primer features 402—can planarize the surface of the subsequent layer to less than 0.3 microns. The patterned primer features 402 may be spaced apart about 10 to 12 microns and can result in a subsequent surface planarity of about 0.3 microns.
The patterned primer features 402 translate to reduced surface topography of the chamber layer 502a and therefore can substantially reduce the amount of subsequent chemical mechanical polishing (CMP) processing. As an example,
The patterned primer features 402 between the connectors 106 when spaced apart about 10 microns to 12 microns may trap particles embedded in ink. If particles in the ink are not trapped, the particles may clog nozzles and reduce print quality. The patterned primer features 402 may thus serve to create a filter for ink particles thereby creating a particle tolerant architecture for a print-head. The use of ink is not limiting since an inkjet print-head may also use other fluids or liquids. The patterned primer features 402 serving to trap particles are shown in
b illustrates a cross sectional diagram of a chamber layer 502b over a primer layer 202 according to a prior art exemplary embodiment of an inkjet printing system.
The primer layer 202 is spaced apart by a second spacing (S2) 508 so that ink may be fed through the etched away area 1304 of substrate 102 as shown in
The measured peak-to-valley height (H2) 504b of chamber layer 502b on an inkjet print-head having spacing (S2) 508 is about 3 microns. This relatively large peak-to-valley height (H2) 504b of 3 microns increases the amount of subsequent chemical mechanical polishing (CMP) to planarize the inkjet print-head.
The ratio of the peak-to-valley height (H2) 504b relative to the peak-to-valley height (H1) 504a is; 3 microns divided by 0.3 microns or 10. Therefore, patterned primer features 402 have reduced the surface topography of chamber layer 502 about 10 times. The chamber layer 502 may be considered a third layer.
In act 1404, a second layer such as the primer layer 202 in
In act 1406, a third layer such as a chamber layer 502a may be disposed over the second layer as shown in
The present embodiments of an inkjet printing system show cross sections of two inkjet nozzles for illustration and exemplary purposes. It should be appreciated that a multiplicity of inkjet nozzles may be formed in accordance to the information described herein.
While the present embodiments of an inkjet printing system have been particularly shown and described, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope of the embodiments defined in the following claims. The description of the embodiment is understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element would have to be included in all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither specifically including nor excluding two or more such elements.
