US 7482670 B2
A semiconductor device having high tensile stress. The semiconductor device comprises a substrate having a source region and a drain region. Each of the source region and the drain region includes a plurality of separated source sections and drain sections, respectively. A shallow trench isolation (STI) region is formed between two separated source sections of the source region and between two separated drain sections of the drain region. A gate stack is formed on the substrate. A tensile inducing layer is formed over the substrate. The tensile inducing layer covers the STI regions, the source region, the drain region, and the gate stack. The tensile inducing layer is an insulation capable of causing tensile stress in the substrate.
1. A semiconductor device comprising:
a substrate having a source region and a drain region, each of the source region and the drain region includes a plurality of completely separated sections, wherein the plurality of completely separated sections in both the source region and drain region are of the same conductivity type, wherein the plurality of completely separated sections in the source region are interconnected together, and wherein the plurality of completely separated sections in the drain region are interconnected together;
a shallow trench isolation (STI) region formed between each two completely separated sections of the source region and between each two completely separated sections of the drain region;
a gate stack formed on the substrate; and
a tensile stress inducing layer formed over the substrate, the tensile stress inducing layer covering the STI regions, the source region, and the drain region.
2. The semiconductor device of
a silicide layer formed over the source region, the drain region, and the gate stack and wherein the tensile stress inducing layer formed over the substrate is formed over the silicide layer.
3. The semiconductor device of
4. The semiconductor device of
a contact interconnected to the gate stack.
5. The semiconductor device of
6. The semiconductor device of
7. The semiconductor device of
8. The semiconductor device of
9. The semiconductor device of
10. The semiconductor device of
11. The semiconductor device of
This is a divisional application of U.S. patent application Ser. No. 10/815,911, filed on Mar. 31, 2004, now U.S. Pat. No. 7,101,765 B2.
The embodiments of the invention relate to techniques for mechanically stressing the channel of a metal oxide semiconductor (MOS) transistor structure, and more particularly, to an N-Channel MOS transistor, to yield enhanced drive current.
A MOS transistor is the basic building block of digital, integrated circuit components such as processors and memory. The MOS transistor is often described as a three terminal device, with metal lines being provided to its source and drain semiconductor regions and its gate electrode. These lines are part of patterned, metal layers of an integrated circuit die and are insulated from each other via interlayer dielectrics. When used as a switch, the MOS transistor is “turned on” when its drive current in a so-called channel region, between its source and drain regions, is enabled via a voltage applied to its gate electrode.
One way to achieve faster switching of a MOS transistor is to design the device so that the mobility and velocity of its charge carriers in the channel region are increased. An appropriate type of stress in the channel region of an n-channel metal oxide semiconductor (NMOS) transistor is known to improve carrier mobility and velocity, which results in increased drive current for the transistor.
Tensile stress (also known as “strain”) in a lateral direction may be obtained by forming a nitride etch stop layer below the first layer of inter-layer dielectric (also referred to as ILD0) to create stress in the channel that lies directly below the etch stop layer. See Ito et al., “Mechanical Stress Effect of Etch-Stop Nitride and Its Impact on Deep Submicron Transistor Design”, IEDM-2001, pp. 433-436. To achieve increased drive current via increased carrier mobility and velocity, thicker nitride layers may be used to meet higher, specified stress levels. However, thicker nitride layers can present manufacturing difficulties as well as reliability concerns.
Another technique for obtaining tensile stress in a MOS transistor is to build the transistor structure in a silicon substrate that has been grown on top of a relaxed SiGe buffer layer. The buffer layer pulls the silicon layer above it, to induce tensile stress in the silicon layer. This structure, however, may require a relatively complex and expensive manufacturing process.
The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. It should be noted that references to “an” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. In the drawings:
Exemplary embodiments are described with reference to specific configurations and techniques. Those of ordinary skill in the art will appreciate the various changes and modifications to be made while remaining within the scope of the appended claims. Additionally, well known elements, devices, components, circuits, process steps and the like are not set forth in detail.
Exemplary embodiments of the present invention pertain to a way to enhance tensile stress (or strain) in a semiconductor device such as an NMOS transistor by increasing tensile stress contribution in Z direction (device width) and in Y direction (device length). In one embodiment, a nitride etch stop layer (NESL) is used as a tensile inducing layer.
Of these three components, the Dxx is generally small and difficult to modulate, the Dzz is normally weak because the only region where the nitride etch stop layer can pull the active silicon in the Z direction is at the very edge of the device so that its effect is not uniform and the pulling action can happen only if a discontinuity exist in the form of a negative shallow trench isolation (STI) step height (STI recess). For this reason currently, little attention is paid to this potential stress component since it cannot be effectively be controlled and exploited. On the other end the Dyy which is the main component of the stress is able to enhance transistor performance with respect to an equivalent transistor which makes no use of the tensile capping layer but is limited by the ability of the tensile layer to stretch a relatively large volume of silicon.
Embodiments of the present invention increases the NMOS performance (e.g., drive current increased at fixed Ioff) above the already enhanced strain silicon device by about 3 to 10% depending on device width. Embodiments of the present invention enhanced tensile stress in the device to increase device performance (e.g., increasing current flow or mobility). As will be apparent, embodiments of the present invention can increase the NMOS performance essentially without additional processes. The embodiments of the present invention thus make them a very attractive approach for future technologies or scaling.
In one embodiment, a semiconductor device 200, e.g., an NMOS transistor, is created to have a multi-narrow sections in a parallel layout. The multi-narrow section layout enhances the tensile stress formed in the device 200 by a tensile stress inducing layer formed on top of the device 200 (
In one embodiment, the nitride etch step layer 212 is conformal. The nitride etch step layer 21 this conforms to the structure formed on the substrate 202. In one embodiment, a silicide layer (not shown) is formed over the sections 204 a-204 c of the source region 204 and the sections 206 a-206 c of the drain region 206. In this embodiment, the nitride etch step layer 212 is formed over the silicide layer.
Dividing the substrate into multiple narrow sections provide more sides in the substrate 202 for the pulling action of the tensile stress inducing layer. And, more stress induced in the substrate leads to higher carrier or current mobility.
At box 904, a shallow trench isolation (STI) region is created between two sections of the source region and between two sections of the drain region forming a device with multi-narrow section layout. There can be more than two sections for each of the source region and the drain region as shown in
At box 906, a gate stack is formed on the substrate. The gate stack is formed approximately between the source and drain region. To form the gate stack, a dielectric layer is formed on substrate. A gate electrode is then formed on the dielectric layer. Methods of creating the gate stack are known in the art.
At box 908, the substrate is implanted to create the source region and the drain region. In some embodiments, spacers may be formed on each side of the gate stack. At box 910, a tensile stress inducing layer is formed over the substrate including all sections of the source region, all sections of the drain region, and the gate stack. The tensile stress inducing layer thus covers the gate stack, the source region, the drain region, and the spacers. The tensile stress inducing layer is also conformal. The tensile stress inducing layer can be formed using chemical vapor deposition or other suitable technique. The tensile stress inducing layer is made of an insulation material capable of causing tensile stress in the substrate. An example of such a tensile stress inducing layer is a nitride etch stop layer. The tensile stress inducing layer can be other strained insulating film that can pull the semiconductor material on which it has been created (the substrate). Additionally, the tensile stress inducing layer is made of a material that has a different etch rate than the material used to make the STI region to allow for selective etching, for example, when vias are created in the tensile stress inducing layer for contacts to the gate stack, source region, and drain region.
In some embodiments, a silicide layer is formed over the source and drain regions as well as the gate stack to improve contact to the source and drain regions and the gate stack. In such embodiments, the tensile stress inducing layer is formed over the silicide layer and over the substrate as previously mentioned.
In some cases, such as in a complementary MOS process flow, a region of semiconductor material that will become the source and/or drain of a p-channel MOS (PMOS) transistor, in the same integrated circuit die or in the same semiconductor wafer for the NMOS structure, may be covered by a suitable layer prior to forming the tensile stress inducing layer. This layer is designed to help avoid inducing tensile stress in the channel of PMOS transistor structures via the tensile stress inducing layer, because tensile stress might not promote higher carrier mobility and velocity in such transistor structures.
At box 912, contact vias are created in the tensile stress inducing layer to allow to contacts to be made to the source, drain, and gate regions. Conductive traces (e.g., metalization) can be formed on top of the tensile stress inducing layer and into the vias to reach the source, drain, and gate regions.
Embodiments of the present invention can be used in conjunction with other methods of creating tensile stress or strain in a semiconductor substrate. For instance, a method of enhancing carrier mobility by creating a tensile strain or stress in silicon material includes forming a layer of silicon on a silicon germanium substrate. The silicon germanium lattice is generally more widely spaced than a pure silicon lattice as a result of the presence of the larger germanium atoms in the lattice. Because the atoms of the silicon lattice align with the more widely spread silicon germanium lattice, a tensile strain is created in the silicon layer. The silicon atoms are essentially pulled apart from one another. In conjunction with the silicon grown on a silicon germanium substrate, the substrate can be divided into many sections and an STI region can be created between each two sections. A tensile stress inducing layer is then formed over the substrate as previously described. The thickness of the tensile stress inducing layer can be controlled so that a particular tensile stress value can be obtained. Embodiments of the present invention thus can be used as a method of creating strain in a semiconductor substrate, alone or in combination with existing methods.
While the invention has been described in terms of several embodiments, those of ordinary skill in the art will recognize that the invention is not limited to the embodiments described. The method and apparatus of the invention, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.
Having disclosed exemplary embodiments, modifications and variations may be made to the disclosed embodiments while remaining within the spirit and scope of the invention as defined by the appended claims.