Abstract:
A method of fabricating a passivation layer and a passivation layer for an electronic device. The passivation layer includes at least one passivation film layer and at least one nanoparticle layer. A first film layer is formed of an insulating matrix, such as aluminum oxide (Al 2 O 3 ) and a first layer of a noble metal nanoparticle layer, such as a platinum nanoparticle layer, is deposited on the first film layer. Additional layers are formed of alternating film layers and nanoparticle layers. The resulting passivation layer provides a thin and robust passivation layer of high film quality to protect electronic devices, components, and systems from the disruptive environmental conditions.

Description:
This application claims the benefit of U.S. Provisional Application No. 61/786,959, filed Mar. 15, 2013, the entire disclosure of which is herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to electronic devices including integrated circuits and more particularly to a passivation layer for an integrated circuit. 
     BACKGROUND 
     The production of integrated circuits includes the formation of passivation layers which provide electrical stability by isolating certain features of the integrated circuits from undesirable electrical and chemical conditions. In general, a passivation layer is formed of silicon mononitride (SiN) or silicon carbide (SiC) as a thick film. These types of passivation layers, however, are only sufficient to act as barrier against certain environmental conditions. In the face of other environmental conditions, these types of passivation layers are not sufficiently robust to prevent the environmental conditions from affecting the integrated circuit. Consequently, thick films are not always a possible alternative when manufacturing certain types of integrated circuits. 
     In addition, the use of these types of passivation layers can influence the operation of the integrated circuit. For instance, the operation of a sensor fabricated as an integrated circuit is influenced. In addition, the described materials, SiN and SiC are only suitable, if the passivating film is of high quality. To achieve a high quality film, high deposition temperatures greater than five-hundred (500) degrees Celsius (C) are required. These temperatures are often not compatible with the device or circuit requiring protection. 
     Consequently, there is a need for a passivation layer for use in the fabrication of integrated circuits, electrical devices and components including micro-electrical mechanical systems (MEMS) devices. 
     SUMMARY 
     The present disclosure relates to the field of integrated circuit including microelectromechanical systems and devices, including micromachined systems and devices, configured to sense a wide variety of conditions including pressure, sound, and environmental conditions such as humidity. MEMS devices in different embodiments include sensors and actuators typically formed on or within a substrate such as silicon. Devices other than sensors can also benefit from the use of the described passivation layer and the method of fabricating a passivation layer. For instance, micromachined pressure sensors and accelerometers can also benefit. Consequently, the described passivation layer and method of manufacture improves the use and operability of integrated circuits, including sensors, pressure sensors and accelerometers, experiencing disruptive environmental conditions and often harsh environment conditions. 
     In addition, the passivation layer is provide for optical elements, as the layer can be extremely thin and due to its composite nature is very robust. Optical elements include among others touch screens, user interfaces, and lenses. 
     The described passivation layer and method of fabrication provides a thin and robust passivation layer of high film quality. In one embodiment, the passivation layer can be formed by using deposition temperatures of approximately less than three-hundred degrees (300) C. In another embodiment, the passivation layer is formed with the application of lower temperatures, as low as about one-hundred (100) degrees C. Therefore, the passivation layer in different embodiments is applied to all types of circuits and sensors. In addition, disposable devices, including for instance bio sensors and lab-on-a-chip devices which incorporate one or more laboratory functions on an integrated circuit incorporate the disclosed passivation layer in some embodiments. In addition, such devices including plastic incorporate the passivation layer. The film also is realized in a bio-compatible manner in some embodiments. The deposition method via atomic layer deposition allows extremely conformal deposition and allows protection of systems with high aspect-ratios/high topography. 
     A method of forming an electronic device in one embodiment includes forming a base portion including a sensor layer, forming a first insulating layer on an upper surface of the sensor layer using atomic layer deposition (ALD), depositing a first plurality of noble metal nanoparticles on an upper surface of the first insulating layer, and forming a second insulating layer on portions of the upper surface of the first insulating layer and on the first plurality of noble metal nanoparticles by ALD. 
     An electronic device in one embodiment includes a base portion, and a passivation layer on the sensor portion, the passivation layer including an insulating base layer formed by atomic layer deposition (ALD) on a surface of the base portion, a matrix of insulating material and noble metal nanoparticles formed on the base layer using ALD, and an insulating cap layer formed by ALD on the matrix. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts a transmission electron microscope (TEM) image of an electronic device including a passivation layer with a matrix having a first thickness. 
         FIG. 2  shows a magnified view of the TEM image of  FIG. 1  illustrating an insulating material portion and a nanoparticle portion of the matrix. 
         FIG. 3  depicts a TEM image of another electronic device including a passivation layer with a matrix having a second thickness. 
         FIG. 4  shows a magnified view of the TEM image of  FIG. 3  illustrating an insulating material portion and a nanoparticle portion of the matrix. 
         FIGS. 5-8  depict a process for forming a passivation layer on a base portion of an electronic device. 
     
    
    
     DESCRIPTION 
     For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one of ordinary skill in the art to which this disclosure pertains. 
       FIGS. 1-4  depict transmission electron microscope (TEM) images of an electronic device  100  including a passivation layer  102 . The electronic device  100  includes a base portion  104  on which the passivation layer  102  is formed. While depicted as being formed on an upper surface of the base portion  104 , the passivation layer  102  may be formed additionally and/or alternatively on sides of the base portion  104 . 
     The passivation layer  102  includes a base layer  106  formed with an insulating material using a process such as ALD, although PVD is used in another embodiment. In the embodiment of  FIGS. 1-2 , the base layer  106  is of Al 2 O 3  formed to provide a thickness on the order of 5-6 nm. In other embodiments, the base layer is a few angstroms in thickness. 
     A matrix  108  including noble metal nanoparticles  110  (which appear as large dark circular objects, particularly in  FIGS. 2-4 ) and insulating material  112  (which is similar in appearance to the base layer  106 ) is located above the base layer  106 . In  FIG. 2 , five layers of noble metal nanoparticles  110  can be discerned. Each layer of nanoparticles is separated from the adjacent layer of nanoparticles by a layer of insulating material, resulting in four intermediate layers of insulating material. The noble metal nanoparticles  110  in this embodiment are platinum noble metal nanoparticles with a diameter of about 4 nm. The total thickness of the matrix  108  is about 24.2 nm. Accordingly, each layer of insulating material (like the layer  16 ) is about 1 nm in thickness. 
     In  FIGS. 3 and 4 , approximately seven layers of the noble metal nanoparticles  110  can be discerned. Similar to the layers of the nanoparticles shown in  FIG. 2 , each layer of the nanoparticles shown in  FIGS. 3 and 4  is separated from the adjacent layer of nanoparticles by a layer of insulating material, resulting in six intermediate layers of insulating material. The noble metal nanoparticles  110  in this embodiment are similarly platinum noble metal nanoparticles with a diameter of about 4 nm. Accordingly, the total thickness of the matrix  108  shown in  FIGS. 3 and 4  is greater than 24.2 nm. 
     In the embodiments of  FIGS. 1-4 , a cap layer  114  of insulating material is provided above the uppermost layer of noble metal nanoparticles. In some embodiments, the cap layer  114  is of similar thickness and material as the base layer  106 . In other embodiments, the cap layer  114  is about the same thickness as the intermediate insulation layers, or thinner. 
     The passivation layer  104  prevents electrical short circuiting of different sensor/device areas. Platinum is described as being used as the noble metal nanoparticle in the foregoing example, but other noble metals such as gold (Au) are known to be extremely inert against harsh or disruptive environments such as those that are chemically aggressive. Accordingly, in other embodiments nanoparticles of other noble metal are used. In other embodiments using other noble metals, the nanoparticles are preferably substantially the same size as the platinum nanoparticles of  FIGS. 1-4 . Materials other than noble metal are also known to be resilient against harsh or disruptive environments. Accordingly, in other embodiments nanoparticles of material other than noble metal, such as Aluminum, Titanium, Titanium Nitride, Tungsten, and Ruthenium, are used. In addition, while Al 2 O 3  is described as being used for the insulation material, in other embodiments other insulating materials, including Hafnium Oxide (HfO 2 ) and Zirconium Dioxide (ZrO 2 ), or combinations thereof, are used. The term “electronic device” is not meant to be limiting to any one specific device and includes devices such as a sensor, an integrated circuit, and an interposer. Accordingly, the term “base portion” as used herein can include any portion of a sensor, an integrated circuit, an interposer, or the like on which a passivation layer is formed. 
       FIGS. 5-8  depict a process for forming a passivation layer on a base portion  150 , which in one embodiment includes an outer layer of silicon. Referring initially to  FIG. 5 , a base layer  152  is deposited on the base portion  150 . The base portion  150  in one embodiment is formed in accordance with any desired process. In some embodiments, the base portion  150  is an outer layer of the sensor area, or even a membrane of a sensor area. 
     The base layer  152  is a layer of insulating material. In one embodiment, the base layer  152  is a thin Al 2 O 3  layer, having a thickness of a few Angstroms. In some embodiments, the base layer  152  is a few nanometers thick. The base layer  152  may be deposited on a base portion formed of a material such as silicon, adjacent to one or more conductors formed on the base portion. The base layer  152  provides a base layer of insulating material which substantially prevents electrical short circuiting of different areas of the devices being formed including MEMS sensors and accelerometers. 
     Formation of the passivation layer continues by using a switched process of atomic layer deposition (ALD). After the base layer of insulating material such as Aluminum Oxide (Al 2 O 3 ) is deposited to form the base layer  152 , a layer of noble metal nanoparticles  154  such as platinum (Pt) is deposited on the base layer  152  as illustrated in  FIG. 6 . The deposition process of the layer of noble metal nanoparticles  154  is controlled in a way that individual nanoparticles  154  are formed. In one embodiment, the nanoparticles  154  are Pt crystals.  FIG. 6  is for illustrative purposes only and the circles representing the nanoparticles  154  do not represent an actual size of the nanoparticles with respect the thickness of the film  152 , nor do the respective locations of the nanoparticles represent the distance between nanoparticles. 
     While the layer of noble metal nanoparticles  154  may be thicker than the base layer  152 , the thickness of the layer of noble metal nanoparticles  154  is controlled to be less than the thickness at which the noble metal coalescences, for instance approximately four (4) nanometers for Pt. Consequently, individual nanoparticles are realized, not a continuous layer, once the process for depositing the layer of nanoparticles  154  is completed. Because the thickness of the layer of noble metal nanoparticles  154  is limited, if a different thickness is desired for a passivation layer, the above steps are repeated, as desired to obtain the desired thickness. 
     For example, as illustrated in  FIG. 7 , a second layer  156  of insulating material is deposited on the layer  152  and on the nanoparticles  154 . If the thicker passivation layer is desired, a second layer of nanoparticles  158  such as platinum nanoparticles is deposited on the second layer  156  (see  FIG. 8 ). The steps are thus repeated as needed to obtain the desired thickness. In some embodiments, a stack of four to fifty or more layers of insulating material and noble metals are used. In one embodiment, the final layer of insulating material is formed to be thicker than any of the intermediate insulating layers to form a cap layer such as the cap layer  114 . 
     Because of the manner in which the various layers in the passivation layer are formed, it is possible to mix materials if desired for a particular application. For example, the different layers of insulation material may be formed using different materials and the different layers of noble metals may be formed with different metals. 
     The nature of the film allows a high protection of the underlying device against attack from harsh or disruptive environments. The platinum particles are chemically extremely inert and thereby not attacked. The insulating Al 2 O 3  matrix is extremely thin, only 0.1-2 nm, and therefore a high aspect ratio structure is obtained, which allows good protection against attack. 
     Those of skill in the art will recognize that the process described with reference to  FIGS. 5-8  in other embodiments is modified to provide a variety of configurations designed for the particular embodiment. 
     The passivation layer and devices which include the passivation layer of the present invention can be embodied in a number of different configurations. The following embodiments are provided as examples and are not intended to be limiting. 
     In one embodiment, a method is provided for fabricating a passivation layer for protection of devices against undesirable environments. The method in one embodiment has a low deposition temperature of less than three-hundred degrees C. In one embodiment, the method is implemented to fabricate complementary metal oxide semiconductor (CMOS) devices and sensors. The method in one embodiment has a deposition temperature of one-hundred degrees or lower so as to allow compatibility to bio-sensors and lab-on-chip systems. 
     In one embodiment, the passivation layer is formed of particles having a high chemical inertness due to utilization of noble metal nanoparticles, including platinum or gold. The method in one embodiment includes an electrically insulating film of platinum-nanoparticles realized by enclosing the particles within an insulating matrix including Al 2 O 3 , HfO 2 , ZrO 2 , or combinations thereof. In one embodiment, the method includes fabricating the passivation layer by use of an ALD process. In one embodiment, the method includes passivation of packaged electronic devices, as a highly conformal deposition process. The method in one embodiment includes passivation of bond-wires and/or passivation of high aspect-ratio structures including micro-fluidic systems. 
     In one embodiment, the method includes a passivation layer having a total film thickness less than 100 nm. The method in another embodiment includes a passivation layer having a total film thickness below 50 nm. In one embodiment, the method includes a passivation layer formed as an optically transparent film, including a low thickness. The method in one embodiment includes a passivation layer for applications in systems with optical detection/readout. 
     The passivation layer described above does not limit to materials including nanoparticles made from noble metals. Other type of materials such as Aluminum, Titanium, Titanium Nitride, Tungsten, Ruthenium are also possible, depending on the application. 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. The passivation layer can be incorporated in a wide range of devices. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.