1. Field of the Invention
This invention relates generally to a semiconductor device and a process for fabricating the same; and more particularly to a structure of a memory device, and a process for fabricating the same.
2. Description of the Related Art
A memory cell of static random access memory (SRAM) usually comprises of a pair of MOS transistors that form a flip-flop, two MOS transistors (transfer gates) that control the connection/disconnection of the output terminal and the data line, and two resistors that act as the load for the flip-flop. However, as the integration level of SRAM has increased in recent years, SRAM is beginning to use memory cells in which the two resistors that act as the load for the flip-flop are replaced by two MOS transistors configured using thin polycrystalline silicon films. A single memory cell is thereby configured using six MOS transistors. As the technology continues to shrink, leakage current of devices is becoming a prime concern as it is indicative of faults in the devices. Such faults may not affect logical behavior and may pass the functional and logical testing, but may malfunction over time, causing reliability hazards. Many of such faults cause elevated quiescent power supply current (IDDQ), which is typically greater than the IDDQ of a fault-free device.
One of the common faults is due to diode leakage. During the fabrication of the share-contact, over etching of the contact opening may occur which may damage the spacer and the STI and also partially remove the LDD and Halo regions so that the metal filled into the contact opening creates the share contact to have contact with Halo region (N-mixing). Consequently, upon application of voltage onto the share contact, instead of enabling S/D(p+) and N-well to generate a p-n junction, leakage occurs via the Halo region (N-mixing) and N-well.
Therefore, one of the objects of the present invention is to develop a structure and a process for fabricating a memory cell for reducing the diode leakage and increasing the reliability of the memory device.
One embodiment realizes a memory cell in which the aforementioned diode leakage may be reduced to improve the reliability of the memory device.
One embodiment provides a process of fabricating a memory cell for reducing the diode leakage for improving the reliability of the memory device.
One embodiment is a structure of the memory cell of a memory device comprising a substrate of first conductive type and a shallow trench isolation (STI) structure; a PMOS and a gate formed over the substrate, wherein the gate is formed over the STI structure; a dielectric layer covering the substrate, the PMOS and the gate; and a contact penetrating the dielectric layer and extending both to the second gate and to the source/drain region of the first gate. The PMOS comprises a gate, Halo regions of first conductive type, LDD of second conductive type and S/D regions of second conductive type formed on both sides of the gate.
One embodiment is a fabrication process comprising at least providing a substrate of first conductive type comprising an active region including and a shallow trench isolation (STI) structure formed therein; forming a first gate and a second gate on the active region and the STI respectively; covering the second gate; forming halo regions of first conductive type, LLD regions of second conductive type, and source/ drain region of second conductive type in the substrate; sequentially forming an etching stop layer and a dielectric layer over the substrate; and forming a contact penetrating the dielectric layer and extending both to the second gate and to the source/drain region of the first gate.
In an embodiment, the step of forming the Halo regions includes disposing a photoresist layer to cover the substrate, the first and second gates, patterning the photoresist layer to expose the first gate, and performing an ion implantation to form the halo regions on both sides of the first gate.
In an embodiment, the halo regions are selectively formed on the sides of the first gate and no halo region is formed in the active region and under the contact. Consequently, a larger source/drain region compared to the conventional source/drain region may be formed. Because no halo regions are formed under the contact area, the p-n junction may be effectively generated upon application of voltage to the contact.
The characteristics and the advantages of the present invention will be apparent from the following description of an embodiment thereof given by way of indicative and non-limiting example with reference to the annexed drawings.
These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout.
In the following description, numerous specific details are set forth such as specific steps and configurations to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details.
Hereinafter a process for fabricating a conventional memory cell may be briefly described.
During the fabrication of the contact opening 134, over etching may occur which may damage the spacers 126 and the STI, and may also partially remove the LDD 104 and halo regions 106 so that the metal layer filled into the contact opening 134 creates the contact 136 to have contact with halo regions 106 (N-mixing). Consequently, upon application of voltage onto the contact, instead of enabling S/D(p+) and N-well to generate a p-n junction, leakage occurs via the halo region (N-mixing) and N-well.
Hereinafter an example structure of a memory cell according to an embodiment is described as follows. This embodiment is exemplified with a static random memory (SRAM) cell device, which may be able to resolve the aforementioned problems of the prior art.
Hereinafter a process for fabricating a memory cell of a memory device is described as follows.
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When over-etching occurs, the contact opening 334 may etch off the etching stop layer 330 and portions of the spacer 326 and gate 320b, and extend to the source/drain region 328. It is to be noted that since no halo region 304 is formed in the substrate 300 under the contact 336 (shown as
The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein, including configurations ways of the recessed portions and materials and/or designs of the attaching structures. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.