Self-aligned contacts

#Metal-oxide-semiconductor (MOS) transistors, such as MOS field effect transistors (MOSFET), are used in the manufacture of integrated circuits. MOS transistors include several components, such as a gate electrode, gate dielectric layer, spacers, and diffusion regions such as source and drain regions. An interlayer dielectric (ILD) is typically formed over the MOS transistor and covers the diffusion regions.

#Electrical connections are made to the MOS transistor by way of contact plugs that are typically formed of a metal such as tungsten. The contact plugs are fabricated by first patterning the ILD layer to form vias down to the diffusion regions. The patterning process is generally a photolithography process. Next, metal is deposited in the vias to form the contact plugs. A separate contact plug is formed down to the gate electrode using the same or a similar process.

#One problem that can occur during the fabrication of a contact plug is the formation of a contact-to-gate short. A contact-to-gate short is a short circuit that occurs when the contact plug is misaligned and comes into electrical contact with the gate electrode. One conventional approach to preventing contact-to-gate shorts is by controlling registration and critical dimensions (CDs). Unfortunately, for transistors with gate pitches (gate length+space) at or below 100 nanometers (nm), CD control for gate and contact dimensions needs to be less than 10 nm and the registration control between gate and contact layers also needs to be less than 10 nm to deliver a manufacturable process window. Thus, the likelihood of a contact shorting to a gate is very high. This problem becomes more prevalent as transistor gate pitch dimensions are scaled down further because the critical dimensions become much smaller.

#FIG. 1A illustrates a substrate and two conventional MOS transistors with a correctly aligned trench contact.

#FIG. 1B illustrates a misaligned trench contact formed to a diffusion region of the MOS transistors, resulting in a contact-to-gate short.

#FIG. 2A illustrates a substrate and two MOS transistors having insulator-cap layers atop their respective metal gate electrodes in accordance with one implementation of the invention.

#Described herein are systems and methods of reducing the likelihood of contact-to-gate shorts during the fabrication of metal-oxide-semiconductor (MOS) transistors. In the following description, various aspects of the illustrative implementations will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the illustrative implementations. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative implementations.

#Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.

#FIG. 1A illustrates a substrate 100 and two MOS transistors 101. The MOS transistors 101 include gate electrodes 102, gate dielectric layers 104, and spacers 108. Diffusion regions 106 are formed in the substrate 100. Interlayer dielectrics (ILD), such as ILD layers 110a and 110b, are deposited in the regions between and around the two MOS transistors 101.