POLY GATE EXTENSION DESIGN METHODOLOGY TO IMPROVE CMOS PERFORMANCE IN DUAL STRESS LINER PROCESS FLOW

Abstract

An integrated circuit and method with dual stress liners and with NMOS transistors with gate overhang of active that is longer than the minimum design rule and with PMOS transistors with gate overhang of active that are not longer than the minimum design rule.

Claims

1. An integrated circuit, comprising: a vertically adjacent n-channel (NMOS) transistor and p-channel (PMOS) transistor with an NMOS active, an NMOS gate, a PMOS active, and a PMOS gate; a first NMOS gate overhang of active nearest to the PMOS transistor that is larger than a first PMOS gate overhang of active nearest to the first NMOS transistor.

2. The integrated circuit of claim 1, wherein the first NMOS gate overhang of active crosses a midway point between the NMOS active and the PMOS active.

3. The integrated circuit of claim 1, wherein the first PMOS gate overhang of active does not cross a midway point between the NMOS active and the PMOS active.

4. The integrated circuit of claim 1, wherein a second NMOS gate overhang of active farthest from the PMOS transistor is greater than a minimum design rule for NMOS gate overhang of active.

5. The integrated circuit of claim 1, wherein a second PMOS gate overhang of active farthest from the NMOS transistor is at a minimum design rule for PMOS gate overhang of active.

6. The integrated circuit of claim 1, wherein the first NMOS gate overhang of active is in the range of 50 nm to 200 nm.

7. The integrated circuit of claim 4, wherein the second NMOS gate overhang of active is in the range of 50 nm to 200 nm.

8. An integrated circuit, comprising: an n-channel (NMOS) transistor with an NMOS active region and an NMOS gate; a p-channel (PMOS) transistor with a PMOS active region and a PMOS gate, wherein the NMOS transistor and PMOS transistor are vertically adjacent to each other; a first NMOS gate overhang of active nearest to the PMOS transistor is greater than 50 nm and a first PMOS gate overhang of active nearest to the first NMOS transistor is less than 30 nm.

9. The integrated circuit of claim 8, wherein the first NMOS gate overhang of active crosses a midway point between the NMOS active and the PMOS active.

10. The integrated circuit of claim 8, wherein the first PMOS gate overhang of active does not cross a midway point between the NMOS active and the PMOS active.

11. The integrated circuit of claim 8, wherein a second NMOS gate overhang of active farthest from the PMOS transistor is greater than a minimum design rule for NMOS gate overhang of active.

12. The integrated circuit of claim 8, wherein a second PMOS gate overhang of active farthest from the NMOS transistor is at a minimum design rule for PMOS gate overhang of active.

13. The integrated circuit of claim 8, wherein the first NMOS gate overhang of active is in the range of 50 nm to 200 nm.

14. The integrated circuit of claim 11, wherein the second NMOS gate overhang of active is in the range of 50 nm to 200 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 Vertically adjacent NMOS and PMOS transistors.

[0009] FIG. 2 Graph of NMOS transistor electron mobility versus NMOS gate overhang of active.

[0010] FIG. 3 PMOS transistors formed according to principles of the invention.

[0011] FIG. 4A and 4B are plan views of a PMOS transistor embodiment of the principles of the invention

[0012] FIG. 5A and 5B are plan views of an NMOS transistor embodiment of the principles of the invention

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0013] The present invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide an understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention. The present invention is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with the present invention.

[0014] FIG. 1 shows an NMOS and a PMOS transistor with a dual stress liner (DSL) boundary 32 between them. The NMOS transistor gate 24 overlies an n-active area 20. The PMOS transistor gate 26 overlies a p-active area 22. A DSL boundary 32 typically lies about midway between the NMOS and PMOS transistor active regions 20 and 22 and lies parallel to the current flow in the transistors. The gate extension or gate overhang of active for the NMOS transistor 34 and for PMOS transistors 36 are typically equal. To conserve space, minimum design rules for gate overhang of active for the NMOS 34 and PMOS 36 transistors and the minimum gate tip-to-tip space 42 are used for vertically adjacent NMOS and PMOS transistors. In an example 28 nm CMOS technology, gate overhang of active design rule for the NMOS and PMOS transistors is 25 nm, the gate tip-to-tip design rule space is 50 nm. The DSL to active design rule space is 50 nm.

[0015] In integrated circuits, the majority of transistors may not be vertically adjacent. For example, there may be open area next to many transistors in an integrated circuit above the NMOS transistor (next to DSL boundary 38) and below the PMOS transistor (next to DSL boundary 40) as is illustrated in FIG. 1 and FIG. 3.

[0016] As is shown in the graph in FIG. 2, the performance of an NMOS transistor in an integrated circuit with DSL is enhanced by increasing the NMOS gate overhang 34 and 35 of active. As shown in FIG. 2 the performance of an NMOS transistor in a 28 nm CMOS technology may be increased by more than 1.5% by extending the gate from about 25 nm overlap to about 200 nm overlap.

[0017] In an example embodiment for a 28 nm CMOS technology with the DSL boundary is 50 nm from the NMOS transistor active, increasing the NMOS gate overhang of active (35 in FIG. 1) from 25 nm to approximately 200 nm increases the mobility of the electrons in the channel by approximately 1.75% resulting in an increase of NMOS transistor drive current (performance) by approximately 1.75%.

[0018] The mobility of holes in a PMOS transistor may be improved by reducing the gate overhang of active 36 and 37. Since the PMOS gate overhang of active 36 and 37 is typically drawn at minimum design rule, little space is available for improving PMOS performance. For PMOS transistors, optimum performance is achieved by reducing the PMOS gate overhang 36 and 37 to the minimum allowed by the design rule.

[0019] As shown in FIG. 3, if the gate overhang of active for the NMOS 34 and PMOS 36 and gate tip-to-tip space 42 are not drawn at minimum design rule between the vertically adjacent NMOS and PMOS transistors, the gate overhang of active for the NMOS transistor 34 may be increased and the gate overhang of active for the PMOS transistor 36 may be decreased to improve the performance of the NMOS and PMOS transistors.

[0020] If additional space is available above the NMOS transistor the gate overhang 35 of active may be additionally extended above the NMOS transistor as shown in FIG. 3 to enhance the NMOS transistor. When the NMOS gate in a 28 nm technology is extended to about 200 nm the performance of the NMOS transistor is improved by about 1.75%. The PMOS gate overhang of active 36 and 37 may be reduced to minimum design rule to maximize PMOS transistor performance.

[0021] As shown in FIG. 4A a narrow width PMOS transistor 60 may be drawn adjacent a wide PMOS transistor 58 or transistors, 58 and 62. In these instances it is common practice to extend the gate 52 overhang of active 48 to the same gate length as the adjacent wide PMOS transistors 58 and 62 as part of optical proximity correction (OPC).

[0022] As is illustrated in FIG. 4B, the performance of the PMOS transistor 60 may be enhanced by decreasing the gate overhang 52 of active 48 to the minimum allowed by design rule and forming a OPC dummy gate extension 56. This may be accomplished by forming a gap 54 between the PMOS gate 50 and the OPC dummy gate extension 56.

[0023] As shown in FIG. 5A a narrow width NMOS transistor 82 may be drawn adjacent a wide NMOS transistor 80 or transistors, 80 and 84. In these instances it is common practice to provide an OPC dummy gate extension 78 above the narrow transistor 82 gate 70 as part of the OPC correction. As shown in FIG. 5A the OPC dummy gate extension 78 may be separated from the gate 70 by a gap 76.

[0024] As is illustrated in FIG. 5B, the performance of the narrow NMOS transistor 82 may be enhanced by eliminating the gap 76 and joining the gate 70 to the OPC dummy gate extension 78 to increase the NMOS gate overhang 74 of active 72.

[0025] If desired, in a high performance integrated circuit technology with DSL, the gate overhang of active design rule may be larger for NMOS transistors than for PMOS transistors to take advantage of the improvement in NMOS transistor performance with increased gate overhang of active. This design rule may be in the base set of design rules or may be implemented in design for manufacturing (DFM) guidelines.

[0026] Vertically adjacent NMOS and PMOS transistor layout would appear as in FIG. 3 for these design rules when NMOS gate overhang of active 34, PMOS gate overhang of active 36, and gate tip-to-tip space 42 are all at minimum design rule. For example, a base design rule set for 28 nm technology may have NMOS gate overhang of active 34 design rule equal to 25 nm and PMOS gate overhang of active 36 design rule equal to 25 nm whereas the DFM design rules may have NMOS gate overhang of active 34 design rule in the range of 50 nn to 200 nm and PMOS gate overhang of active 36 design rule of 30 nm or less.

[0027] Some CMOS technologies that use double pattern for forming the transistor gate pattern. The first pattern is a dark geometry pattern which defines the gate length and the second pattern is a clear geometry pattern which separates the gates of vertically adjacent transistors. In this process the second pattern may be aligned to PMOS active to minimize the PMOS gate overhang of active 36 and to maximize the NMOS gate overhang of active 34, depending upon the location of a DSL boundary.

[0028] Those skilled in the art to which this invention relates will appreciate that many other embodiments and variations are possible within the scope of the claimed invention.