PMOS AND NMOS TRANSISTORS

BACKGROUND CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority and benefit from United States

Provisional Patent Application No. 62/372,669, filed August 9, 2016, for

"HETEROGENEOUS INTEGRATED PMOS AND NMOS DEVICES FOR CMOS CIRCUITRY," the entire contents of which are incorporated in their entirety herein by reference.

TECHNICAL FIELD

[0002] Embodiments of the subject matter disclosed herein generally relate to a semiconductor device including monolithically integrated PMOS and NMOS transistors and a method of producing such semiconductor devices.

DISCUSSION OF THE BACKGROUND

[0003] As more capabilities are being added to electronic devices, there is a need to accommodate more transistors within a defined area of the electronic devices. This can be addressed by reducing the amount of surface area occupied by transistors, which allows increased transistor density. There is also a need to reduce the size of electronic devices, which likewise can be achieved by reducing the surface area occupied by transistors. However, reducing the surface area occupied by a transistor typically requires reducing the channel length, which can result in undesirable effects, commonly referred to as short channel effects.

[0004] Moreover, as the number and types of devices that are battery powered continues to increase, there is also a desire to reduce the power consumption of transistors.

[0005] Accordingly, there is a need for semiconductor devices that have reduced surface area, reduced power consumption, and do not experience the short channel effects typically encountered when reducing the channel length.

SUMMARY

[0006] According to an embodiment, there is a method for producing a semiconductor device. The method involves forming a first transistor having a silicon substrate and a gate, and forming a second transistor, having a germanium substrate, on top of the first transistor. The second transistor is formed by forming a first gate of the second transistor on top of, and electrically coupled to, the gate of the first transistor, bonding the germanium substrate to the first gate of the second transistor so that the bonding does not damage the first transistor, and forming a second gate of the second transistor on the germanium substrate.

[0007] According to another embodiment, there is a semiconductor device, which includes a first transistor having a silicon substrate, and a second transistor having a germanium substrate. The second transistor comprises a first gate arranged on a first side of the germanium substrate and a second gate arranged on a second side of the germanium substrate. The first gate of the second transistor is arranged on a gate of the first transistor with an electrically conductive contact arranged between the first gate of the second transistor and the gate of the first transistor.

[0008] According to a further embodiment, there is a method for producing a semiconductor device. The method involves forming a first transistor having a gate on a silicon substrate. The silicon substrate includes a source, drain, and channel. The method also includes forming a second transistor having a first gate arranged on a first side of a germanium substrate and a second gate arranged on a second side of the germanium substrate. The germanium substrate includes a source, drain, and channel. The second transistor includes a dielectric interposed between the first gate of the second transistor and the germanium substrate and the formation of the second transistor comprises bonding the germanium substrate to the dielectric so that the bonding does not damage the first transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

[0010] Figure 1 is a cross-sectional view illustrating an integrated circuit with stacked dual gate p-type metal-oxide-semiconductor (PMOS) and n-type metal-oxide- semiconductor (NMOS) according to an embodiment;

[0011] Figure 2 is a flow chart illustrating a method for manufacturing monolithically integrated PMOS and NMOS devices according to an embodiment; [0012] Figure 3 is a flow chart illustrating a method for manufacturing monolithically integrated PMOS and NMOS devices using silicon and germanium semiconductors according to an embodiment;

[0013] Figures 4A-4I are cross-sectional views illustrating manufacturing of monolithically integrated PMOS and NMOS devices according to an embodiment;

[0014] Figure 5 is a cross-sectional view illustrating an inverter formed from monolithically integrated PMOS and NMOS transistors according to an embodiment; and

[0015] Figure 6 is a perspective view of a stacked, heterogeneous CMOS circuit configured as a CMOS inverter according to an embodiment.

DETAILED DESCRIPTION

[0016] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention.

Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of semiconductor devices.

[0017] Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0018] According to an embodiment there is a method for producing a semiconductor device. Specifically, referring to Figures 1 and 2, the method involves forming a first transistor 1 10 having a silicon substrate 102 and a gate 1 12 (step 210) and forming a second transistor 120, having a germanium substrate 104, on top of the first transistor 1 10 (step 220). The formation of the second transistor involves forming a first gate 1 14 of the second transistor 120 on top of, and electrically coupled to, the gate 1 12 of the first transistor 1 10 (step 220A). In one application, first gate 1 14 is directly coupled (electrically and mechanically) to the gate 1 12. The germanium substrate 104 is then bonded to the first gate 1 14 of the second transistor 120 so that the bonding does not damage the first transistor (step 220B). Finally, a second gate 122 of the second transistor 120 is formed on the germanium substrate 104 (step 220C). Accordingly, the semiconductor device 100 includes a single gate n-type metal- oxide-semiconductor (NMOS) transistor 1 10 on a silicon substrate 102 and a dual gate p-type metal-oxide-semiconductor (PMOS) transistor 120 on a germanium substrate 104.

[0019] A semiconductor device with a dual gate PMOS transistor 120 arranged on top of a single gate NMOS transistor 1 10 reduces the surface area occupied by these two transistors. Further, the dual gate PMOS transistor 120 not only reduces the surface area of the PMOS transistor 120 but also addresses the short channel effects normally encountered by reducing the transistor channel length. [0020] Additional details of a method of manufacturing a semiconductor device with a dual gate PMOS transistor formed on top of a single gate NMOS transistor will now be described in connection with the flow chart of Figure 3 and the cross-sectional views of Figures 4A-4I.

[0021] Initially, a silicon substrate 402 is doped to form a channel 403 (step 305 and Figure 4A). The silicon substrate 402 can be, for example, a silicon-on-insulator (SOI) substrate. A dielectric 404 is formed on the channel 403 (step 310 and Figure 4B), a gate 406 is formed on the dielectric 404 (step 315), and then a protective coating 408 is formed on at least the dielectric 404 (step 320). The dielectric 404 can be, for example, a high-K dielectric, comprising hafnium silicate, zirconium silicate, hafnium dioxide, and/or zirconium dioxide. The silicon substrate 402 is then doped to form a source and drain 405A and 405B (step 325). The protective coating 408 can be in the form of, for example, a nitride spacer, and is intended to protect the dielectric from the doping used to form the source and drain 405A and 405B.

[0022] A dielectric 410 is then formed on the protective coating and the semiconductor substrate 402 (step 330 and Figure 4C), and an electrical conducting layer 412 is formed on the dielectric 410 (step 335). The electrical conducting layer 412 can be non-metallic or metallic (e.g., a copper metal or alloy). The dielectric 410 provides a planarized surface for the second transistor. The dielectric 410 can be a spin-on dielectric and the formation of the dielectric 410 can involve etching the dielectric 410, chemically and/or physically, to level the dielectric 410 at a height approximately near the height of the gate 406. The first gate 414 of the second transistor is then formed on the electrical conducting layer 412 (step 340 and Figure 4D).

[0023] A dielectric 416, such as a high-K dielectric, is formed over the dielectric 410 of the first transistor, the contact metal 412, and the first gate 414 of the second transistor (step 345 and Figure 4E). A second dielectric 418 is then formed over the dielectric 416 to provide a planarized surface for the germanium substrate (step 350 and Figure 4E). The dielectric 418 can be a spin-on dielectric and the formation of the dielectric 418 can involve etching the dielectric 418, chemically and/or physically, to level the dielectric 418 at a height approximately near the height of the first gate 414 of the second transistor.

[0024] A germanium substrate 420 of the second transistor is then bonded to the planarized dielectric 418 so that the bonding does not damage the first transistor (step 355 and Figure 4F). The germanium substrate 420 may be patterned to isolate the first transistor. The germanium substrate 420 can be comprised of, for example, single crystal germanium. Damage to the first transistor occurs when the first transistor is subjected to certain high temperatures and affects the performance of the first transistor. One type of damage to the first transistor can be silicidation of the first transistor. Silicidation, as well as other types of damage to the first transistor, can be prevented during bonding in a number of different ways. One way to prevent damage is to use a low temperature during bonding, such as a bonding process that operates at or below 250° C, and in some embodiments one that operates at or below 200° C. Bonding processes operating above 250° C can also be employed so long as the heating is localized and does not occur across the entire surface of the dielectric 418. The types of wafer bonding that can be employed include, but are not limited to, direct bonding, surface activated bonding, plasma activated bonding, anodic bonding, eutectic bonding, glass frit bonding, adhesive bonding, thermocompression bonding, reactive bonding, and/or transient liquid phase diffusion bonding. The wafer bonding allows the placement of a single crystal semiconductor layer, such as single crystal germanium in the dual gate structure.

[0025] The germanium substrate 420 is doped to form the channel 421 of the second transistor (step 360 and Figure 4G). A dielectric 424 is formed on the channel 421 (step 365 and Figure 4H) and a second gate 422 of the second transistor is formed on the dielectric 424 (step 370). A protective coating 425, which can be in the form of a nitride spacer, is applied to at least the dielectric 424 to protect it from the subsequent doping (step 375). Finally, the germanium substrate is doped to form the source and drain 426A and 426B (step 380). Accordingly, the method produces a semiconductor device having a dual gate PMOS 434 having a germanium substrate 420 formed on a single gate NMOS 432 formed on a silicon substrate 402.

[0026] A semiconductor device including monolithically integrated PMOS and NMOS transistors, such as those described above and/or manufactured according to the methods described above, may be used to form CMOS logic gates, such as NAND or NOR logic gates, or an inverter. Figure 5 illustrates one example of a semiconductor device in the form of an inverter formed from monolithically integrated PMOS and NMOS transistors. An inverter 500 may be configured using an integrated circuit (IC) similar to that shown in Figure 4I. Inputs and outputs to the integrated circuit may be provided through vias, lines, and/or other conductors coupled to various structures of the integrated circuit. A ground node may be coupled through via 502 to a source or drain in the silicon substrate 402 of the first transistor. A power supply (VDD) node may be coupled through via 504 to a source or drain in the germanium substrate 420 of the second transistor. An input node (IN) may be coupled through via 506 to the second gate 422 of the second transistor. An output node (OUT) may be coupled through line and via 508 to a source or drain of the germanium substrate 420 of the second transistor and a source or drain of the silicon substrate 402 of the first transistor. Further, in this embodiment, a planarized dielectric 524 is formed on top of the second gate 422 of the second transistor.

[0027] Although an inverter is shown in Figure 5, the dual gate design and manufacturing of same may be applied to other logic circuitry. The design may improve density of the circuitry and may reduce power dissipation in the circuitry. These improvements are particularly advantageous in, for example, mobile applications, where complicated electronic circuitry is integrated in a small area and power dissipation is a concern.

[0028] A dual gate design for PMOS circuitry in a logic gate may reduce short channel effects experienced by conventional transistor structures that reduces performance. Thus, the dual gate design of a logic gate, such as shown in the examples of Figures 1 and 5, may have better subthreshold slope, lower leakage current, and better drain-induced barrier lowering (DIBL). The top and bottom gate of the germanium-based PMOS circuitry may improve likelihood of complete inversion of the channel area in the silicon substrate of the first transistor, thus providing improved performance of the device. Additionally, the dual gate design improves the switching performance by reducing the switching current and/or reducing the turn-on time for the germanium-based PMOS circuitry. This reduces the power dissipation in the circuits, and thus improve battery life of mobile devices built from the dual gate logic circuitry.

[0029] A perspective view of a semiconductor device in the form of an inverter formed from monolithically integrated PMOS and NMOS transistors is illustrated in Figure 6. An inverter 600 may include a ground input node 618 coupled to the semiconductor substrate 602 of the first transistor and a power supply (Vdd) input node 616 coupled to the germanium substrate 604 of the second transistor. An input signal may be applied to an input node 612. The inverter 600 may invert the value received at the input node 612, and output the inverted results at an output node 614. For example, when a logic Ί ' is applied to the input node 612, a logic '0' may be output at the output node 614.

[0030] The disclosed embodiments provide methods of producing a semiconductor device including monolithically integrated PMOS and NMOS transistors. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. [0031] Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

[0032] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.