Patent Application
20120086054
1. Field of the Invention
The present invention generally relates to a semiconductor structure and the method for making the same. In particular, the present invention is directed to a semiconductor structure whose source contact plug and drain contact plug have relatively asymmetric element properties as well as a method for fabricating a semiconductor structure.
2. Description of the Prior Art
In a regular semiconductor structure, a gate structure is used to control the on and off state of a current passing through the source and the drain which are disposed at two sides of the gate structure. Because the source and the drain are respectively disposed in the substrate at two sides of the gate structure and covered by an interlayer dielectric layer, a source contact plug and a drain contact plug are still needed to respectively penetrate the interlayer dielectric layer to form an electrical connection of the source and the drain to an outer circuit.
In order to increase the operational performance of the semiconductor elements, a conductive material of lower electric resistance, such as metals, is usually used in the source contact plug and the drain contact plug. Besides, traditionally each one of a single semiconductor element uses an independent source contact plug and an independent drain contact plug to independently control the semiconductor element. That is, in the prior art, the same source contact plug and drain contact plug are located at two sides of the gate structure so the source contact plug and the drain contact plug at two sides of the gate structure always have symmetric element properties.
However, with the trend of pursuing elements to be as small as possible, the intrinsic resistance within the source contact plugs and drain contact plugs due to the overly decreased critical dimension becomes too large to support the current to maintain a normal on and off state, which jeopardizes the desirable operational performance of the semiconductor elements.
A slot structure for the source contact plugs and the drain contact plugs to be disposed at two sides of the gate structure has been proposed to exhibit a symmetric layout structure. Albeit the slot layout structure seemingly reduces the total electric resistance to be able to support a larger current, serious sequels to this happen. For example, the slot structure may have serious and adverse interactions such as coupling with the gate structure. In such a way, the operational performance of the semiconductor elements does not improve at all.
In view of this, a novel semiconductor structure is still needed. Such novel semiconductor structure not only supports a larger current but also avoids some adverse consequences. In this way, problems such as overly decreased critical dimension, the extreme intrinsic resistance within the source contact plugs and drain contact plugs and deteriorated operational performance of the semiconductor elements can be thoroughly solved.
Accordingly, the present invention proposes a novel semiconductor structure. This novel semiconductor structure not only supports a larger current but also avoids some adverse consequences. In this way, problems such as overly decreased critical dimension, the extreme intrinsic resistance within the source contact plugs and drain contact plugs and deteriorated operational performance of the semiconductor elements can be thoroughly solved.
The present invention in a first aspect proposes a semiconductor structure. The semiconductor structure of the present invention includes a substrate, a gate structure, a source, a drain, a source contact plug and a drain contact plug. The gate structure is disposed on the substrate. The source and the drain are respectively disposed in the substrate at two sides of the gate structure. The source contact plug is disposed above the source and electrically connected to the source. The drain contact plug is disposed above the drain and electrically connected to the drain. One feature of the present invention resides in the relatively asymmetric element properties of the source contact plug and the drain contact plug so that the electric resistance of the source contact plug or the drain contact plug can be decreased. The element property may be at least one of a shape, a size, a material, a stress, an aspect ratio and a quantity.
The present invention in a second aspect proposes a semiconductor structure. The semiconductor structure of the present invention includes a substrate, a gate structure, a source, a drain, a source contact plug and a drain contact plug. The gate structure is disposed on the substrate. The source and the drain are respectively disposed in the substrate at two sides of the gate structure. The source contact plug is disposed above the source and electrically connected to the source. The drain contact plug is disposed above the drain and electrically connected to the drain. Another feature of the present invention resides in the relatively asymmetric element properties of the source contact plug and the drain contact plug so that the capacitor effect of the source contact plug or the drain contact plug on the gate structure can be decreased. The element property may be at least one of a shape, a size, a material, a stress, an aspect ratio, a quantity and a distance to the gate structure. Preferably, the capacitor effect of the source contact plug on the gate structure is larger than that of the drain contact plug on the gate structure.
The present invention in a third aspect proposes a method for fabricating a semiconductor structure. First a substrate is provided. Second, a gate structure is formed on the substrate. Later, a source and a drain are respectively formed in the substrate and adjacent to the gate structure. Then, a source silicide and a drain silicide are formed in the substrate and on the source and on the drain. Afterwards, an interlayer dielectric layer is formed to cover the gate structure, the source and the drain. Next, a plurality of contact holes are formed in the interlayer dielectric layer to expose the source and the drain. Thereafter, at least a source contact plug and a drain contact plug are respectively formed in the interlayer dielectric layer and to respectively electrically connect the source and the drain. The source contact plug and the drain contact plug have at least a relatively asymmetric element property to decrease the capacitor effect of the source contact plug or of the drain contact plug on the gate structure, and/or to decrease the electric resistance of the source contact plug or the drain contact plug. The element property may be at least one of a shape, a size, a material, a stress, an aspect ratio, a distance to the gate structure and a quantity.
Because of the relatively asymmetric element properties which the source contact plug and the drain contact plug have, the capacitor effect of the source contact plug or of the drain contact plug on the gate structure can be independently adjusted, or alternatively, the electric resistance of the source contact plug or the drain contact plug can be independently adjusted as well. These modifications of the novel semiconductor structure may allow a larger operational current owing to lower electric resistance, or a minor capacitor to the gate structure without jeopardizing the original performance of the semiconductor element. In such a way, the present invention is able to practically solve problems such as overly decreased critical dimension, the extreme intrinsic resistance within the source contact plugs and drain contact plugs or deteriorated operational performance of the semiconductor elements, which the technical field currently suffers.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
The present invention provides a novel semiconductor structure. The source contact plug and the drain contact plug in the light of each individual semiconductor element have at least one relatively asymmetric element property so that the element properties of the source contact plug or the drain contact plug can be independently adjusted. As a result, the capacitor effect of the source contact plug or of the drain contact plug on an individual gate structure, or the electric resistance of the source contact plug or the drain contact plug can be properly adjusted. The novel semiconductor structure of the present invention accordingly allows a larger operational current, or exhibits less capacitor to an individual gate structure to maintain an optimal performance of the semiconductor element.
The present invention in a first aspect provides a novel semiconductor structure.
The source 120 and the drain 130 are respectively disposed in the substrate 101 at two sides of the gate structure 110. The source 120 and the drain 130 may be formed by implantation of dopants into the substrate 101 at two sides of the gate structure 101, or an epitaxial material along with dopants are filled in the recesses in the substrate 101 at two sides of the gate structure 110 in order to apply a suitable stress to the gate channel. The source contact plug 140 is disposed above the source 120, penetrates the interlayer dielectric layer 160 and is electrically connected to the source 120. The drain contact plug 150 is disposed above the drain 130, also penetrates the interlayer dielectric layer 160 and is electrically connected to the drain 130. The interlayer dielectric layer 160 is usually an insulating material or the combination of various insulating materials, such as the combination of silicon oxide, nitride, carbide, and a low-k insulating material.
One of the features of the present invention resides in that the source contact plug 140 and the drain contact plug 150 have at least one relatively asymmetric element property to decrease the electric resistance of the source contact plug 140 or to decrease the electric resistance of the drain contact plug 150. Optionally, the source contact plug 140 may have a lower electric resistance, or alternatively the drain contact plug 150 may have a lower electric resistance. However, in any case the source contact plug 140 and the drain contact plug 150 always have substantially relatively different electric resistances because the source contact plug 140 and the drain contact plug 150 have an asymmetric element property. Preferably, the source contact plug 140 may have a lower electric resistance than the drain contact plug 150.
The afore-mentioned element property may be any suitable element property, such as at least one of or some of a shape, a size, a material, a stress, an aspect ratio and a quantity of the source contact plug 140 and the drain contact plug 150. The inventors discover that with the source region, namely the source 120, the source contact plug 140 and its silicide 170, and the drain region, namely the drain 130, the drain contact plug 150 and its silicide 170, each has different responses to different design rules. When the source contact plug 140 and the drain contact plug 150 have relatively different element properties, different responses can be observed with respect to the source contact plug 140 and to the drain contact plug 150 so the desired effects may be attained. Because the source contact plug 140 and the drain contact plug 150 may have various element properties, some demonstrative examples are given here to elaborate some of possible element properties.
Shape
Optionally, the source contact plug 140 and the drain contact plug 150 may be dimensionally or geometrically asymmetric. For example, one of the source contact plug 140 and the drain contact plug 150 may be in a shape of a single square and the other may be in a shape of a slot. A slot may at least go parallel with the channel width or preferably extend to the entire source or drain so the length may be at least twice as large as the width. On the other hand, a single square may be an asymmetric layout structure that an individual gate structure has several single squares, as shown in
Size
Optionally, the size of the source contact plug 140 and the drain contact plug 150 may be asymmetric. For example, one of the sizes, such as width or length, of the source contact plug 140 and the drain contact plug 150 may be larger than the other one.
Material
Optionally, the conductive materials of the source contact plug 140 and the drain contact plug 150 may be different, so the electric resistances are different. For example, different conductive materials, such as Cu or W, are used, or they may have barrier layers of different composition or thickness.
Stress
Optionally, the source region and the drain region may generate different stress on the gate structure 110. Different ways may be used to generate different stress. For example, different epitaxial materials along with dopants are filled in the recesses which are formed in the source region and the drain region, or either one recess is filled to generate different stress to the gate structure 110. On the other hand, the bottoms of the source contact plug 140 and the drain contact plug 150 may extend into the epitaxial materials to be lower than the gate dielectric layer in the gate structure 110. In addition, to adjust the thickness ratio of the barrier layer to the plug material, or to adjust the formation parameters of the barrier layer, such as physical vapor deposition (PVD), chemical vapor deposition (CVD), temperature or pressure . . . etc. may also adjust the needed stress.
Or, a stress layer, such as a contact etching-stop layer, may be optionally used to cover the gate structure 110 to generate different stress. At the moment, the bottoms of the source contact plug 140 and the drain contact plug 150 may penetrate the stress layer. Of course, the source contact plug 140 and the drain contact plug 150 may respectively penetrate the stress layer in an asymmetric way, such as different shapes or sizes of the openings, to accomplish the feature of asymmetric element property of the present invention.
Aspect Ratio
Optionally, the aspect ratios of the source contact plug 140 and the drain contact plug 150 may be asymmetric. For example, the sizes of the openings of the contact holes for preparing the source contact plug 140 and the drain contact plug 150 may be different so that the aspect ratios of the two are asymmetric. Or for instance, the contact plugs may include a plug material, namely a conductive material and a barrier material or a plug material, namely a conductive material alone. The barrier material may be Ti, TiN or the combination thereof.
Quantity
Optionally, the quantity of the source contact plug 140 and the drain contact plug 150 may be asymmetric. For example, one is more than the other.
In any case, the electric resistance of the source contact plug 140 and the drain contact plug 150 is substantially distinctive as long as the source contact plug 140 and the drain contact plug 150 have a relatively asymmetric element property so the present invention is able to practically solve problems such as overly decreased critical dimension, the extreme intrinsic resistance within the source contact plugs and drain contact plugs or deteriorated operational performance of the semiconductor elements, which the technical field currently suffers.
The present invention in a second aspect provides another semiconductor structure.
The source 120 and the drain 130 are respectively disposed in the substrate 101 at two sides of the gate structure 110. The source 120 and the drain 130 may be formed by implantation of dopants into the substrate 101 at two sides of the gate structure 110, or an epitaxial material along with dopants are filled in the recesses in the substrate 101 at two sides of the gate structure 110 in order to apply a suitable stress to the gate channel. The source contact plug 140 is disposed above the source 120, penetrates the interlayer dielectric layer 160 and is electrically connected to the source 120. The drain contact plug 150 is disposed above the drain 130, also penetrates the interlayer dielectric layer 160 and is electrically connected to the drain 130. The interlayer dielectric layer 160 is usually an insulating material, such as silicon oxide.
One of the features of the present invention resides in that the source contact plug 140 and the drain contact plug 150 have at least one relatively asymmetric element property to adjust the capacitor effect of the source contact plug 140 on the gate structure 110 or the capacitor effect of the drain contact plug 150 on the gate structure 110 to reach an optimal result. Optionally, the source contact plug 140 may have less capacitor effect on the gate structure 110, or alternatively the drain contact plug 150 may have less capacitor effect on the gate structure 110. However, in any case the source contact plug 140 and the drain contact plug 150 always have substantially different effect on the gate structure 110 because the source contact plug 140 and the drain contact plug 150 have an asymmetric element property. Preferably, the drain contact plug 150 has less capacitor effect on the gate structure 110 than the source contact plug 140 to the gate structure 110.
The afore-mentioned element property may be any suitable element property, such as at least one of or some of a shape, a size, a material, a stress, an aspect ratio, a quantity and a distance to the gate structure 110 of the source contact plug 140 and the drain contact plug 150. The inventors discover that with the source region, namely the source 120, the source contact plug 140 and its silicide 170, and the drain region, namely the drain 130, the drain contact plug 150 and its silicide 170, each has different responses to different design rules. When the source contact plug 140 and the drain contact plug 150 have different element properties, different responses can be observed with respect to the source contact plug 140 and to the drain contact plug 150 so the desired effects may be attained. Because the source contact plug 140 and the drain contact plug 150 may have various element properties, some demonstrative examples are given here to elaborate some of possible element properties.
Distance
Optionally, the distance to the gate structure 110 from the source contact plug 140 and from the drain contact plug 150 may be asymmetric. Generally speaking, a greater distance means less capacitor effect. For example, one of the source contact plug 140 and the drain contact plug 150 may have a relatively greater distance to the gate structure 110 and the other may have a relatively shorter distance to the gate structure 110 to get the desired effects.
Other properties such as shape, size, material, stress, aspect ratio and quantity may refer to the above corresponding descriptions. In any case, the capacitor effect of the source contact plug 140 on the gate structure 110 or the capacitor effect of the drain contact plug 150 on the gate structure 110 is substantially distinctive as long as the source contact plug 140 and the drain contact plug 150 have an asymmetric element property so the present invention is able to practically solve problems such as overly decreased critical dimension, the adverse capacitor effect of the source contact plug 140 and of the drain contact plug 150 on the gate structure or deteriorated operational performance of the semiconductor elements, which the technical field currently suffers.
The present invention in a third aspect provides a method for fabricating a semiconductor structure.
First, please refer to
Later, as shown in
Afterwards, as shown in
Next, as shown in
Optionally, a source silicide/drain silicide 170 may be formed before or after multiple contact holes 161 are formed to be respectively disposed in the substrate 101 and on the source 120 and on the drain 130. If the source silicide/drain silicide 170 are formed on the source 120 and on the drain 130 before multiple contact holes 161 are formed, a suitable metal 171 is used to entirely cover the substrate 101, the gate structure 110, the source 120 and the drain 130 before the contact etching-stop layer 162 and the interlayer dielectric layer 160 are formed, as shown in
Or alternatively, a suitable metal is used to fill the contact holes 161 after multiple contact holes 161 are formed if the source silicide/drain silicide 170 are formed on the source 120 and on the drain 130 after multiple contact holes 161 are formed. Later, a thermo step is carried out to make the exposed silicon atoms react with the metal to form the source silicide/drain silicide 170, as shown in
Thereafter, at least a source contact plug 140 and a drain contact plug 150 are formed in the interlayer dielectric layer 160 to respectively electrically connect the source 120 and the drain 130. The source contact plug 140 and the drain contact plug 150 have at least one asymmetric element property. If the contact etching-stop layer 162 is present, the source contact plug 140 and the drain contact plug 150 penetrate the contact etching-stop layer 162 and the source contact plug 140 and the drain contact plug 150 still have the asymmetric element property.
The afore-mentioned element property may be any suitable element property, such as at least one of or some of a shape, a size, a material, a stress, an aspect ratio, a quantity and a distance to the gate structure 110 of the source contact plug 140 and the drain contact plug 150. The inventors discover that with the source region, namely the source 120, the source contact plug 140 and its silicide 170, and the drain region, namely the drain 130, the drain contact plug 150 and its silicide 170, each has different responses to different design rules. When the source contact plug 140 and the drain contact plug 150 have asymmetric element properties, different responses can be observed with respect to the source contact plug 140 and to the drain contact plug 150 so the desired effects may be attained. Because the source contact plug 140 and the drain contact plug 150 may have various asymmetric element properties, some demonstrative examples are given here to elaborate some of possible element properties.
Distance
Optionally, when a photoresist (not shown) is used to go with lithographic and etching steps to form multiple contact holes 161, the layout pattern on the reticle may be designed to control the relative position between the contact holes 161 and the gate structure 110 so the distance to the gate structure 110 from the source contact plug 140 and from the drain contact plug 150 are asymmetric.
Shape
Optionally, when a photoresist (not shown) is used to go with lithographic and etching steps to form multiple contact holes 161, the layout pattern on the reticle may be designed to control the contact holes 161 to be asymmetric, so the resultant source contact plug 140 and the drain contact plug 150 may be dimensionally or geometrically asymmetric, as shown in
Size
Optionally, when a photoresist (not shown) is used to go with lithographic and etching steps to form multiple contact holes 161, the layout pattern on the reticle (not shown) may be designed to control the sizes of the contact holes 161 to be asymmetric, so the resultant size of the source contact plug 140 and the drain contact plug 150 are asymmetric.
Material
Optionally, the plug materials for filling contact holes 161 may be different, so the resultant electric resistances of the source contact plug 140 and the drain contact plug 150 are different. For example, different conductive materials, such as Cu or W, are used.
Stress
Optionally, the source region and the drain region may generate different stress on the gate structure 110. For example, different epitaxial materials or dopants are used. Or, a stress layer, such as a contact etching-stop layer, may be optionally used to cover the gate structure 110 to generate different stress.
Aspect Ratio
Optionally, the aspect ratios of the source contact plug 140 and the drain contact plug 150 may be asymmetric. For example, the sizes of the openings of the contact holes for preparing the source contact plug 140 and the drain contact plug 150 may be different, or the materials in the contact holes may be different, so that the aspect ratios of the two are asymmetric.
Quantity
Optionally, the quantity of the source contact plug 140 and the drain contact plug 150 may be asymmetric. For example, one is more than the other.
In any case, the electric resistance of the source contact plug 140 and the drain contact plug 150 or the capacitor effect on the gate structure 110 is substantially distinctive as long as the source contact plug 140 and the drain contact plug 150 have asymmetric element properties so the present invention is able to practically solve problems such as overly decreased critical dimension, the extreme intrinsic resistance within the source contact plugs and drain contact plugs or deteriorated operational performance of the semiconductor elements, which the technical field currently suffers.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
