The present invention relates generally to a system and method for manufacturing integrated circuits, and more particularly to a system and method for improving the process performance of a contact module.
After the fabrication of devices in an integrated circuit has been accomplished, it becomes necessary to fabricate interconnections between the devices in order to produce a functioning integrated circuit. In a modern fabrication process, optical lithography techniques can be used in the creation of electrical contacts to the source/drain and gate terminals of the devices. The contacts need to pass through dielectric layers that can be used to passivate and isolate the devices.
However, the materials used in the dielectric layers can have different reflectivity properties depending upon their thickness and the wavelength of the light used in the optical lithography process. In order to maximize the accuracy of the lithography process, it is desired to minimize any variations in the reflectivity of the dielectric layer. Variations in the reflectivity of the dielectric material can result in inconsistent behavior in the light used in the lithography process. This inconsistent behavior can reduce precision with which the contacts can be cut through the dielectric layer. Since the reflectivity of the dielectric layer is a function of the thickness of the dielectric layer and the wavelength of the light (which is fixed for a given process), it is desired to make as constant as possible, the thickness of the dielectric layer.
One commonly used technique to minimize variations in the thickness of the dielectric layer is the use high-density plasma, chemical vapor deposition (HDP-CVD) to deposit a dielectric layer and then planarize the dielectric layer with a chemical-mechanical polisher (CMP). The chemical-mechanical polisher uses chemical (solvents) and physical (polishing media and surfaces) techniques to planarize the dielectric layer. Typically, a slurry (containing both chemical and physical polishing media) is applied to a wafer and then a polishing surface (usually a polishing wheel or belt) can be used to polish the wafer, planarizing the wafer in the process.
One disadvantage of the prior art is that while CMP can effectively planarize the wafer, the use of CMP can still result in wafers with a large degree of variation in the thickness of the dielectric layer. Furthermore, there can be a large variation in the thickness of the dielectric layer between different wafers. Additionally, the CMP process can be expensive due to the chemical and physical techniques used to planarize the wafers as well as the additional cleaning steps that are needed to cleanse the wafers after they undergo CMP.
A second disadvantage of the prior art is that HDP-CVD is not an effective technique for filling gaps between devices. The inability to fill the gaps between the devices can prevent the electrical isolation of the devices. This can result in an improperly working integrated circuit.
Another disadvantage of the prior art is that the use of HDP-CVD can result in damage to the devices due to electrical charge and ultra-violet (UV) light used in the HDP-CVD process. The use of HDP-CVD can also cause a loss in the thickness of the contact etch stop layer (CESL). A reduction in the thickness of the CESL can result in the inability of the CESL to stop chemical etch from damaging the devices, due to inadequate thickness.
Yet another disadvantage of the prior art is that the compression of the dielectric layer can result in the relaxation of the strained effect, thereby negating any gains in the driving current performance seen in the use of strained technology.
A further disadvantage of the prior art is that thickness measurements have to be made both before and after the use of the CMP process to ensure that the desired thickness of the dielectric layer is maintained. This is a result of the inability to precisely control the amount of dielectric material removed during the CMP process. For example, the amount of material removed in the CMP process can depend upon the condition of the polishing wheel since the polishing wheel's abrasiveness can decrease with use.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention which provides a system and method for improving the process performance of a contact module.
In accordance with a preferred embodiment of the present invention, a multilayer interlayer dielectric (MID) for a semiconductor device, wherein the semiconductor device comprises a field effect transistor (FET) and a substrate, is provided. The MID comprises a first thickness of the MID covering the FET and a second thickness of the MID over the first thickness of the MID, wherein a thickness ratio of the first thickness of the MID to the second thickness of the MID ranges from about 0.06 to about 0.90 and the MID further comprises a third thickness and a fourth thickness.
In accordance with another preferred embodiment of the present invention, a multilayer interlayer dielectric (MID) for a semiconductor device, wherein the semiconductor device comprises a field effect transistor (FET) and a substrate, is provided. The MID comprises a nitrogen containing layer over the FET and at least one oxygen-containing layer, wherein a thickness ratio of a thickness of the oxygen-containing layer to a thickness of the nitrogen containing layer ranges from about 1.1 to about 1.5 and the MID contains at least four layers.
In accordance with another preferred embodiment of the present invention, a method for fabricating a semiconductor device is provided. The method comprises forming a field effect transistor (FET) device on a semiconductor substrate followed by forming a first nitride layer over the semiconductor substrate, forming a first oxide layer over the first nitride layer, and forming a second oxide layer over the first oxide layer. The method further comprises computing a thickness for a third oxide layer and forming the third oxide layer over the second oxide layer.
An advantage of a preferred embodiment of the present invention is that a more uniform planarization of the dielectric layer is possible than when CMP is used, both on a single wafer and across different wafers. This is due to the greater predictability and precision of the processes involved in the present invention.
A further advantage of a preferred embodiment of the present invention is that gaps between devices can be filled more effectively than with HDP-CVD. The better gap fill results in better isolation of devices.
Yet another advantage of a preferred embodiment of the present invention is that the improved driving current performance achieved through the use of strained technology is maintained.
Another advantage of a preferred embodiment of the present invention is that there is no reduction in the thickness of the CESL. With the CESL unaffected by the gap-fill process, the chance of damage occurring to the devices below the CESL during etching is greatly reduced. Thereby, the yield can be increased.
An additional advantage of a preferred embodiment of the present invention is that a thickness measurement after the fabrication of the dielectric layer is no longer necessary. The elimination of the thickness measurement can result in a more rapid integrated circuit fabrication process and a reduction in the fabrication costs.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
a and 3b are diagrams of cross sectional views of a substrate with an interlayer dielectric layer, shown pre and post planarization using the prior art planarization process shown in
a through 6e are diagrams of cross sectional views of a substrate showing various steps in the formation of an interlayer dielectric layer with minimized surface variations, according to a preferred embodiment of the present invention; and
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention will be described with respect to preferred embodiments in a specific context, namely the fabrication of a contact module in an integrated circuit, wherein there is a desire to maximize planarization of a dielectric layer. The invention may also be applied, however, to the fabrication of other layers in an integrated circuit wherein there is a desire to minimize variations in the thickness of the layers.
With reference now to
The data plot shown in
When the reflectivity of the PSG layer (the interlayer dielectric layer) can vary widely as both the function of the thickness of the PSG layer and the thickness of the CESL, it can be difficult to achieve the desired accuracy when using photo lithography to create the openings in the PSG layer to fabricate electrical contacts. With the reflectivity of the PSG layer widely varying, it can become impossible to predict the behavior of the light beams used in photo lithography, therefore, it may not be able to precisely place the location of the openings (or other physical characteristics such as size and depth) in the PSG layer. The desire is then to planarize the PSG layer as uniformly as possible to minimize variations in the thicknesses of the layer. It is possible to minimize thickness variations by maximizing surface uniformity in the two layers. Note that the discussion provided herein focuses on the CESL (an etch stop layer) and PSG (a dielectric layer) layer. However, this should not be construed as limiting the scope of the present invention to these two layers. The discussion can be extended to more than two layers without changing the spirit of the present invention.
With reference now to
The deposition of the interlayer dielectric layer can occur in two steps. In a first step, the goal of the deposition of the interlayer dielectric layer is to fill in any existing gaps between devices. Since the devices are three dimensional, valleys (gaps) can be present between closely spaced devices and unless these valleys (gaps) are filled, electrical charge can readily travel from one device to another. After gaps have been filled in the first step, a second step can result in the deposition of an interlayer dielectric layer with a certain thickness, for example, nine-thousand Å. After the interlayer dielectric layer has been fabricated (block 210), the thickness of the interlayer dielectric layer can be measured (block 215). It can be necessary to measure the thickness of the interlayer dielectric layer deposited previously due to the relative imprecision of the HDP-CVD process. It may not be possible to adequately predict the thickness of the interlayer dielectric layer simply through the amount of time spent in the deposition process, so an actual measurement of the interlayer dielectric layer is necessary.
The thickness of the interlayer dielectric layer is needed to determine how much of the interlayer dielectric layer needs to be removed via chemical-mechanical polishing (CMP), which is used to planarize the interlayer dielectric layer (block 220). As discussed earlier, CMP uses both chemical and mechanical means to polish the interlayer dielectric layer. A polishing slurry, possibly containing both chemical solvents and polishing media, can be applied to the interlayer dielectric layer and then a mechanical polisher, typically a polishing wheel or belt, mechanically polishes the interlayer dielectric layer. The amount of polishing can be dependent upon the reactiveness and abrasiveness of the polishing slurry, the abrasiveness of the mechanical polisher, the amount of force applied by the mechanical polisher, the operating speed of the mechanical polisher, the amount of time spent polishing, the wear on the mechanical polisher, and so forth. Since there are many factors that can contribute to the effectiveness of the CMP process, an advanced process control (APC) may be needed to achieve accurate results. The APC may involve accurate timing controls of the CMP process as well as control over the polishing slurry and measurements of the thickness of the interlayer dielectric layer. Additionally, the APC can take into account the amount of time that the mechanical polisher (the polishing wheel or belt) has been in use since it was last replaced, the amount of time that the polishing slurry has been in use, and so on. This can be important because the effectiveness of the polish can depend on the amount of wear on the mechanical polisher as well as the frequency of reuse of the polishing slurry.
Even with the use of the APC, it can be relatively difficult to accurately predict the amount of dielectric material that has been removed from the interlayer dielectric layer. Therefore, after the CMP process (block 220), it may be necessary to once again measure the thickness of the interlayer dielectric layer (block 225). In addition to verifying the thickness of the interlayer dielectric layer and making sure that the thickness is within specifications, it may also be possible to measure the variation in the interlayer dielectric layer. After the interlayer dielectric layer has been planarized, the fabrication of the integrate circuit can continue to completion.
As discussed previously, disadvantages of the process 200 may include: thickness variation can still be significant after CMP planarization (with a non-uniformity of approximately 10 percent), the gap fill performance of the HDP-CVD process is not very good, charge damage and ultra-violet damage can occur to the CESL due to the HDP-CVD process, the HDP-CVD process can result in a reduction of the thickness of the CESL, the CMP process can be expensive due to expensive materials and multiple process steps, the thickness of the interlayer dielectric layer has to be measured both before and after the CMP process in order to obtain good performance, and the compression of the interlayer dielectric layer can result in the relaxation of the strained effect which was purposely applied to the substrate to obtain better driving current performance.
With reference now to
A contact etch stop layer (CESL) 335, applied over the fabricated device, can be used to prevent the propagation of an etch from damaging the fabricated device. An interlayer dielectric layer 340 can then be deposited over the fabricated device. As an example, in a modern fabrication process, phosphorous-doped silicon glass (PSG) or undoped silicon glass (USG) can be used as the material for the interlayer dielectric layer 340 and can be applied via a high-density plasma chemical vapor deposition (HDP-CVD) process. Note that due to the three-dimensional properties of the fabricated device, a bump 342 may be present in the interlayer dielectric layer. Note that for purposes of planarization, the interlayer dielectric layer 340 can be applied to a thickness (shown as span 345) that may be greater than the actual desired thickness since the CMP process can result in a reduction of the thickness of the interlayer dielectric layer 340. For example, the interlayer dielectric layer 340 can be applied to a thickness of approximately nine-thousand Å.
With reference now to
With reference now to
Clearly, the use of CMP to planarize the interlayer dielectric layer does not yield very good results. The resulting interlayer dielectric layer, while smoother than an interlayer dielectric layer that has not been planarized, retains significant variations, possibly enough to result in the fabrication of poor quality contacts.
With reference now to
The process 500 can begin after the devices have been fabricated onto a substrate and prior to the fabrication of interconnections (electrical connectors) between the devices. After the fabrication of the devices, a CESL can be deposited over the devices (block 505). According to a preferred embodiment of the present invention, silicon nitride (e.g. SiNx, x is less than about 2) can be used as the CESL layer and can be deposited using either low-pressure chemical vapor deposition (LP-CVD) or plasma enhanced chemical vapor deposition (PE-CVD) techniques. However, other materials can be used as the CESL layer as long as they react sufficiently differently to the etch material used to etch the interlayer dielectric layer (specifically, they are relatively inactive to the etch material) so that they can protect the devices and the substrate from the etch material.
After the deposition of the CESL, a second layer of a multilayer interlayer dielectric layer can be formed on top of the CESL. Initially, a first interlayer dielectric layer can be deposited (block 510). The first dielectric layer can be used to specifically cover the devices, which are lying on top of the substrate. The first dielectric layer can fill in any gaps between devices on the substrate, electrically isolating the devices. The first dielectric layer can be formed using undoped silicon glass (USG) using a sub-atmospheric pressure deposition technique (SA-USG) or an atmospheric pressure deposition technique (AP-USG).
After the deposition of the first dielectric layer, a second dielectric layer can be deposited (block 515). The second dielectric layer can be used to help fill out any significant surface irregularities that can be present in the first dielectric layer, such as bumps due to the topology of the devices present on the substrate. The second dielectric layer can be formed using spin-on-coating deposition such as spin on glass (SOG) techniques which has a benefit of the use of centrifugal force to help uniformly distribute the dielectric material across the wafer and can be made from USG. This can produce a dielectric layer with a low variation in overall thickness.
After the formation of the first and the second dielectric layers (blocks 510 and 515), a measurement of the thickness of the two dielectric layers can be made (block 520). A thickness measurement may be made to determine the thicknesses of the two dielectric layers already deposited and to determine how much more dielectric material needs to be deposited to bring the total thickness of the multilayer interlayer dielectric layer to a desired thickness. After the measurement of the thickness of the two dielectric layers, a third dielectric layer can be deposited (block 525). According to a preferred embodiment of the present invention, the third dielectric layer can be used to bring the multilayer interlayer dielectric layer to a desired thickness and can be made from phosphorous doped silicon glass (PSG) or USG and can be deposited using PE-CVD in conjunction with an APC. Since the PE-CVD technique can be highly precise and the thickness of the material deposited using the technique can be accurately predicted based upon the amount of time the technique is used, the APC used to control the deposition of the third dielectric layer can be based solely on the time that the technique is used.
With reference now to
After the device 607 has been fabricated on the surface of the substrate 605, it becomes necessary to provide electrical connections to and from the device 607. However, electrical connections cannot simply be placed on top of the device, namely a multilayer interlayer dielectric layer needs to be formed between the device 607 and the electrical connections to protect the device 607 from the electrical connections and the processing needed to fabricate the electrical connections.
After the formation of the CESL layer 610, a first dielectric layer 620 of the multilayer interlayer dielectric layer can be formed.
After the formation of the first dielectric layer, a second dielectric layer 630 can be formed.
After the completion of the second dielectric layer 630, the overall thickness layer of the multilayer interlayer dielectric layer can be measured (as discussed in block 520 of
e illustrates a fifth step in creating the multilayer interlayer dielectric layer, which is to place the third dielectric layer 640 over the second dielectric layer 630 (as discussed in block 525 of
The completed multilayer interlayer dielectric layer fabricated under the preferred conditions of a preferred embodiment of the present invention (as discussed previously and as shown in
With reference now to
After forming the nitride layer (block 710), a first oxide layer can be formed over the nitride layer (block 715). The first oxide layer can be an initial layer of a multilayer interlayer dielectric, wherein the first oxide layer can be formed using either a SA-CVD or an AP-CVD process. Following the formation of the first oxide layer, a second oxide layer can be formed (block 720). The second oxide layer's primary function can be to fill in any existing gaps in the first oxide layer, which may have arisen due to the three-dimensional topology of the device(s). The second oxide layer can be formed using a SOG process, which can help produce an oxide layer with good gap-fill properties. With the formation of the first and the second oxide layers, an algorithm can be used to compute a thickness of a third oxide layer (block 725). According to a preferred embodiment of the present invention, the algorithm can be an advanced process control application that can be used to determine the thickness of the first and the second oxide layers and the compute the thickness of the third oxide layer based upon the determined thickness and a desired thickness of the first, second, and third oxide layers. Since a process used to form the third oxide layer is very precise, there is a direct relationship between the thickness of the third oxide layer and the amount of time spent in forming the third oxide layer. After computing the needed thickness for the third oxide layer, the third oxide layer can be formed, preferably using either a PE-CVD or HDP-CVD process (block 730).
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. The third dielectric layer can be used to specifically perform the operation of gap filling, i.e., filling the valleys between devices to ensure that the devices are electrically isolated.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.