Fluid ejection device and method of fabricating the same

A fluid ejection device includes a first substrate having a first crystal orientation, a second substrate having a second crystal orientation, bound to the first substrate, a manifold through the first and second substrates, a chamber formed in the second substrate, connected with the manifold, and a plurality of nozzles connecting to the chamber, wherein the first crystal orientation is different from the second crystal orientation. A method of fabricating the same is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and more specifically to a fluid ejection device and a method of fabricating the same.

2. Description of the Related Art

Strong basic solutions, such as TMAH, KOH, or NaOH, are commonly used as etching solutions in silicon fabrication processes. Such solutions offer different etching performance for various monosilicon crystal planes. Although etching performance for various crystal planes may have slight distinctions due to different kinds or concentration of etching solution, or different etching temperatures, the etching rates for various crystal planes is approximately (111)<(110)<(100), specifically, the etching rate for crystal plane (111) is far slower than for others.

FIG. 1andFIG. 2illustrate the etching performance of a strong basic solution for various crystal planes. Referring toFIG. 1, the crystal plane (100) is etched to form an anisotropic etching track with an included angle of 54.7° in substrate10. InFIG. 2, which shows the etching result of the crystal plane (111), a vertically anisotropic etching track is formed in substrate10.

Therefore, a manifold with a back opening larger than a front opening is formed in the chip (100) while etching the back thereof is performed, for example, a back opening width of a manifold with a front opening width of about 200 μm is enlarged to about 1100˜1200 μm during etching the back of the chip. Thus, the manifold formed in chip (100) occupies the majority of a wafer, and substantially reduces the available area thereon.

Additionally, during assemble, a chip must provide sufficient space for binding with a cartridge. Generally, the width of the binding region at the left and right sides of a chip is about 1200 μm respectively. Thus, a chip should provide a bottom region width of at least 3500˜3600 μm for fabricating a fluid ejection device, thereby reducing availability in the bottom area thereon.

Currently, the original substrate (100) is replaced by a substrate (111) to reduce the back opening size of a manifold. Nevertheless, although the back opening width thereof can be reduced due to specific etching performance, the manifold shape may slant to result in an unexpected chamber shape, deteriorating the dispersion effect of the device.

Referring toFIG. 3, a conventional fluid ejection device comprises a silicon substrate10, a manifold20used to transport fluid, chambers30formed in both sides of the manifold20to store fluid, and a plurality of nozzles40installed on the device surface to ejection fluid.

According to the above device structure, the back opening is larger than the front opening of the manifold, thus the back opening occupies the majority of the wafer, and substantially reduces the available area thereon.

Additionally, a conventional fabrication method for a fluid ejection device is disclosed in the following description, and illustrated inFIGS. 4ato4b.Referring toFIG. 4a, a substrate10, such as a silicon substrate with crystal orientation (100) is provided. A patterned sacrificial layer20is formed on the substrate10. The sacrificial layer20is composed of BPSG, PSG, or silicon oxide, preferably PSG. Subsequently, a patterned structural layer30is formed on the substrate10to cover the patterned sacrificial layer20. The structural layer30includes silicon oxide nitride formed by chemical vapor deposition (CVD).

Next, a patterned resist layer40is formed on the structural layer30as an actuator, such as a heater. The resist layer40comprises HfB2, TaAl, TaN, or TiN. A patterned isolation layer50is then formed to cover the substrate10and the structural layer30, and a heater contact45is formed thereon. Subsequently, a patterned conductive layer60is formed on the structural layer30to fill the heater contact45to form a signal transmission line62. Finally, a protective layer70is formed on the isolation layer50and the conductive layer60, exposing the conductive layer60to form a signal transmission line contact75, thereby facilitating the subsequent packaging process.

Subsequently, referring toFIG. 4b, the back of the substrate10is etched by wet etching using KOH as an etching solution to form a manifold80, and exposes the sacrificial layer20. The sacrificial layer20is then etched by HF to form a chamber90. Finally, the protective layer70, the isolation layer50, and the structural layer30are then etched in order to form a nozzle95connecting the chamber90.

The back opening is larger than the front opening of the manifold80due to the specific crystal orientation (100) of the substrate10, and thereby occupies excessive bottom area on the wafer.

SUMMARY OF THE INVENTION

In order to solve the conventional problems, an object of the invention is to provide a fluid ejection device to effectively reduce the size of a back opening of a manifold, and control a chamber shape by providing a double substrate layer.

To achieve the above objects, the invention provides a fluid ejection device including a first substrate having a first crystal orientation, a second substrate having a second crystal orientation, bound to the first substrate, wherein the first crystal orientation is different from the second crystal orientation, a manifold through the first and second substrates, a chamber formed in the second substrate, connected with the manifold, and a plurality of nozzles connecting the chamber.

Based on the device structure of the invention, the substrate (111) is first etched to form a vertical etching track therein, as it will reduce the back opening width of the manifold. The substrate (100) is then etched to form another etching track therein, controlling the shape of the subsequently formed chamber.

Another object of the invention is to provide a method of fabricating the fluid ejection device, including the following steps. A first substrate having a first crystal orientation is provided. A second substrate having a second crystal orientation is provided to bind to the first substrate, wherein the first crystal orientation is different from the second crystal orientation. Subsequently, a patterned sacrificial layer is formed on the second substrate, as a predetermined region where at least one chamber is subsequently formed.

Next, a patterned structural layer is formed on the second substrate to cover the patterned sacrificial layer. A manifold through the first and second substrates is then formed to expose the patterned sacrificial layer. Subsequently, the sacrificial layer is removed to form the chamber. The chamber is continuously etched to enlarge the volume thereof so as to occupy a portion of the second substrate. Finally, the structural layer is etched to form at least one nozzle connecting the chamber.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 5a˜5cillustrate the method of fabricating the fluid ejection device according to the invention.

InFIG. 5a, in which the initial step of the invention is illustrated, a first substrate500and a second substrate510are provided, wherein the first substrate500is a silicon substrate with crystal orientation (111) and the second substrate510is a silicon substrate with crystal orientation (100). The thickness ratio of the first substrate500and the second substrate510is about 10:1, wherein the thickness of the first substrate500is about 500˜675 μm, and the thickness of the second substrate510is about 30˜50 μm.

The second substrate510binds to the first substrate500by direct binding or medium binding, wherein the direct binding temperature is about above 1000° C., and the medium is oxide.

Subsequently, referring toFIG. 5b, a patterned sacrificial layer520is formed on a first plane5001of the second substrate510. The sacrificial layer520is composed of BPSG, PSG, or silicon oxide, preferably PSG. The thickness of the sacrificial layer520is about 5000˜20000 Å. The sacrificial layer520is a predetermined region where at least one chamber is subsequently formed.

Next, a patterned structural layer530is formed on the second substrate510to cover the patterned sacrificial layer520. The structural layer530may include silicon oxide nitride formed by CVD. The thickness of the structural layer530is about 0.5˜2 μm. Additionally, the structural layer530comprises a low-stress material, and the stress thereof is about 50˜200 MPa.

Subsequently, a patterned resist layer540is formed on the structural layer530, as a fluid ejection actuator, such as a heater, thereby driving fluid out of subsequently formed nozzles. The resist layer540comprises HfB2, TaAl, TaN, or TiN, and is preferably TaAl.

A patterned isolation layer550is then formed to cover the structural layer530, and a heater contact555is formed. Subsequently, a patterned conductive layer560is formed on the isolation layer550to fill the heater contact555to form a signal transmission line. Finally, a protective layer570is formed on the second substrate510to cover the isolation layer550and the conductive layer560, exposing the conductive layer560to form a signal transmission line contact580, thereby facilitating the subsequent packaging process.

Subsequently, referring toFIG. 5c, a series of etching steps are performed. First, a second plane5002of the first substrate500is etched to form a portion of the manifold590by anisotropic wet etching using TMAH, KOH, or NaOH as an etching solution.

During the above etching, the substrate500with crystal orientation (111) is etched to form a vertical etching track therein, thus reducing the back opening width of the manifold, and significantly increasing the available area on the first substrate500.

Next, the second substrate510with crystal orientation (100) is etched to achieve the manifold fabrication, and exposes the sacrificial layer520. The shape of subsequently formed chambers can be controlled by the manifold structure through the first and second substrates.

The narrow opening width of the manifold590is about 160˜200 μm. Compared to the related art wherein the back opening width is about 1100˜1200 μm, the occupied area on the chip bottom of the present invention is significantly reduced. Additionally, the manifold590connects to a fluid storage tank.

Next, the sacrificial layer520is etched to form chambers600by HF, and subsequently etched by a basic etching solution, such as KOH or NaOH, to enlarge the volume thereof, thus occupying a portion of the second substrate510.

Finally, the protective layer570, the isolation layer550, and the structural layer530are etched in order by laser or reactive ion etching (RIE) to form nozzles610connecting to the chambers600which are connected to the manifold590.

Additionally, if the resolution of a single row of chambers is 300 dpi, resolution can be increased to 600˜1200 dpi by staggering each row of chambers in the embodiment.

In conclusion, the double substrate layer structure of the present invention can reduce the occupied area on a chip bottom, and provide preferable chamber shape to stably eject fluid.