Method of forming patterned metalization on patterned...

Details Method of forming patterned metalization on patterned... Method of forming patterned metalization on patterned...

2001-05-21

2004-01-13

Goudreau, George (Department: 1763)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S613000, C438S669000, C438S671000, C438S673000, C438S725000, C438S697000, C438S699000, C438S717000, C438S734000, C438S736000

Reexamination Certificate

active

06677227

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the field of semiconductor processing. More particularly the present invention relates to etch back methods for forming sensor contacts during thin film semiconductor processing.
BACKGROUND OF THE INVENTION
The microelectromechanical systems (MEMS) are being manufactured using process steps often found in traditional semiconductor processes. MEMS fabrication services are becoming widely used in many desirable developmental variations. The use of MEMS technology often presents difficult challenges when integrating MEMS devices into and with compatible semiconductor devices and processes. The semiconductor processes cover many types of devices and materials. One such semiconductor device and process is complementary metal oxide silicon (CMOS) technology. The CMOS process has been traditionally used for fabricating fast low power digital devices. Most MEMS devices are analog type devices. Complete system designs often require the speed and accuracy of modern digital computer processing systems that are coupled to the real world using analog input and output devices. Complete system designs lead to the integration of digital devices and analog devices on a chip with the advantage of an economy of scale. However, such integration of different devices and the corresponding different process steps must be accomplished with inherent compatibility. Many analog devices operate using gold connector contacts because gold is a good electrical conductor that is also non-corrosive and durable. Aluminum is a good conductor, but is highly corrosive, and not desirable for use as an exposed conducting contact. Gold is a large atom, and gold atomic migration through the lattice structures of semiconductor devices often leads to a decrease in the mean time between failure as gold atoms function as an impurity when migrating from an original deposition site. Though highly conductive, gold and silver impurities near the gate junctions of metal oxide silicon (MOS) transistors can lead to premature failures. Hence, in CMOS semiconductor circuits, often polysilicon, aluminum, and tungsten are used as conductors to avoid the migration problem when using gold or silver.
A sensor contact metal, such as gold or tungsten, can be deposited in a contact via well leading to a semiconductor device in a preexisting semiconductor circuit. For example, a sensor contact metal can be deposited over the contact via well with a potentially corrosive analog sensor then being deposited onto the sensor contact metal. The sensor contact metal can then be covered by a deposited protection layer to protect the sensor and contact metal from corrosion when the sensor is exposed to the environment. As a preexisting example, a silicon substrate may have an aluminum conducting etch run that is covered by an insulation layer such as silicon dioxide. During photoresist application, mask exposure and development, a contact via is formed through the photoresist. Photoresist is usually applied by spinning a coating onto a silicon wafer. The silicon dioxide layer is then etched in the location of the photoresist via to form the contact via through the silicon dioxide layer. The photoresist layer is then removed leaving the silicon dioxide layer over the aluminum conductor excepting for the contact via through the silicon dioxide layer. The formation of the contact via through the silicon dioxide layer to the conductor etch run of the semiconductor is an initial starting process point for depositing sensor contact metal upon a buried conductor etch run, prior to then depositing the sensor on the contact metal. The metal sensor contact is deposited as a layer and then patterned. The metal sensor contact should have profile that mates to the profile of the contact via well and extends up and over the insulation layer for contact with the sensor. Often, the metal contact will have a dimple over the contact via well as the metal is deposited evenly over the contour of the contact via well. Various processes have been used to accurately form the profile of the metal sensor contact during well filing.
The tape liftoff process applies an adhesive tape to the deposited sensor contact metal layer. The adhesive tape makes adhesive contact with the sensor contact metal except over the contact via where the dimple is created in the surface of the metal sensor contact layer. As the contact metal being is deposited down into the contact via well, a surface dimple is created. As the adhesive tape is pulled away from the metal sensor contact layer, the contact layer is removed, except where the dimples are located. Hence, the metal sensor contact survives and remains in the contact via wells. The tape liftoff process is imprecise in forming a metal sensor contact profile and creates ragged edges and stresses in the metal contact, leading to separation failures. Liftoff patterning processes require stepped slopes in the contact wells and constrain the metalization layer to small thicknesses. The Liftoff processes are incompatible with good step coverage and deposition techniques, such as sputtering.
The subtractive process also first deposits a metal sensor contact layer. Patterned photoresist portions are formed over the contact wells, exposing the metal contact layer but not over the contact well. The metal sensor contact layer is removed by a dissolving solution. The metal sensor contact layer is dissolved save the protected metal sensor contacts under the patterned photoresist portions. Then, the pattern photoresist portions are removed exposing the metal sensor contacts that have upwardly extending flanges created on the side walls of the metal contact via and lying upon the insulating layer. The problem with subtractive process is that during the metal sensor contact layer removal step, the metal sensor contacts are undercut under the edges of the pattern photoresist portions leading to imprecise metal sensor contact profiles and flange formation. The metal sensor contacts may also fail to sufficiently adhere to the subsequently deposited sensor.
The chlorobenzene liftoff process uses a single photoresist layer to create large sized sensor contact profiles, the flanges of which can be large. The chlorobenzene liftoff process creates a lip in the photoresist layer that can be damaged during sputtering or heated depositions leading to imprecise formation of the sensor contact profiles. Chemical hazards are disadvantageously created when using exotic and unfamiliar chemicals, such as chlorobenzene, to modify the photoresist.
The multiple layer photoresist process uses multiple layers of photoresist that when respectively repeatedly applied, exposed and then developed, create a thick photoresist via through which the metal sensor contact is deposited to create a unique gold contact profile. The multiple layer photoresist process suffers from the repeated photoresist steps and requires very accurate process controls.
As such, conventional techniques for contact formation disadvantageously suffer from imprecise formations leading undesirable profiles of the metal sensor contact. Often, the metalization layer, including the metal contact can have undesirable contours, such as the metal contact dimples. Conventional etch back methods have been used to remove undesirable surface contours of previously patterned layers. The etch back methods are used for ensuring continuous step coverage and for reflattening the surface for further high resolution photolithography. That is, the etch back method is applied to previously patterned layers. In the case of the CMOS planar etch back method, a metal contact layer, such as tungsten, is deposited over the contact well creating a dimple in the metal layer over the contact well. Because further processes may require substantially flat surfaces, the dimple is removed by a planar etch back process. An insulating layer, such as glass, is reflowed by heat, onto a metal layer. Phosphosilicate glass is applied by chemical vapor deposition and can be reflowed at high temperat

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