METHOD OF PREPARING ACTIVE SILICON REGIONS FOR CMOS OR OTHER DEVICES
A method of preparing active silicon regions for CMOS devices includes providing a structure including a silicon substrate (210, 410) having formed thereon first and second silicon diffusion lines (110, 420), both of which include first and second silicon layers (211, 213, 421, 423), a silicon germanium layer (212, 422), and an electrically insulating layer (214, 424). The method further includes forming an oxide layer (430) in first and second regions of the structure, forming a polysilicon layer (510) over the oxide layer, removing the polysilicon layer from the first region and depositing oxide (610) therein in order to form an oxide anchor, removing the polysilicon layer from the second region, removing the silicon germanium layer, filling the first and second gaps with an electrically insulating material (910), and depositing oxide in the second region.
The disclosed embodiments of the invention relate generally to silicon-on-insulator formation schemes, and relate more particularly to the formation of anchor structures supporting the silicon-on-insulator formation.
BACKGROUND OF THE INVENTIONThe semiconductor manufacturing industry has long been focused on the miniaturization of microelectronic devices. One strategy that has been used to continue the miniaturization trend is known as silicon-on-insulator, or SOI. This technique uses a substrate having an electrically insulating layer in between layers of silicon as a means to improve performance due to, for example, the reduction of parasitic device capacitance. SOI technology does have certain limitations, such as those that arise as a result of the difficulty in controlling film thicknesses, resistances, and other parameters. As device scaling advances these limitations become increasingly problematic.
Silicon-on-nothing (SON) technology, in which a silicon film is epitaxially grown on a sacrificial silicon germanium (SiGe) layer that, when removed, leaves an air gap underneath the film, is in many respects a way of overcoming the limitations of SOI. Yet SON comes with its own set of issues, including silicon corrosion in the source/drain (S/D) regions and the degradation in selectivity during SiGe removal etching. For example it has been found that plasma damage on silicon exposed to an oxide dry etch process can cause top silicon loss during SiGe etching.
The disclosed embodiments will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying figures in the drawings in which:
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.
DETAILED DESCRIPTION OF THE DRAWINGSIn one embodiment of the invention, a method of preparing active silicon regions for CMOS devices comprises providing a structure having a first region and a second region. The structure comprises a silicon substrate having formed thereon a first silicon diffusion line and a second silicon diffusion line, both of which comprise a first silicon layer, a silicon germanium layer over the first silicon layer, a second silicon layer over the silicon germanium layer, and an electrically insulating layer over the second silicon layer. The structure also comprises a trench between the first and second silicon diffusion lines.
The method further comprises forming an oxide layer in the first and second regions, forming a polysilicon layer over the oxide layer in the first and second regions, removing the polysilicon layer from the first region and depositing oxide therein in order to form an oxide anchor in the first region, removing the polysilicon layer from the second region, removing the silicon germanium layer from the first and second diffusion lines in order to create a first gap in the first diffusion line and a second gap in the second diffusion line, filling the first gap and the second gap with an electrically insulating material, and depositing oxide in the second region.
Embodiments of the invention help solve at least some of the issues that complicate SON technology which, as mentioned above, include silicon corrosion in the S/D regions and degradation in selectivity during SiGe removal etching. As an example, loss of selectivity is minimized for embodiments of the invention because top silicon and sidewalls are not exposed to oxide dry etching. As another example, the SiGe removal etch is performed prior to formation of the gate in order to reduce interactions between plasma processes and SiGe etching, thus reducing or eliminating the problem of silicon corrosion.
The foregoing and other features of embodiments of the invention represent significant advances in CMOS manufacturing technology. For example, the absence of top silicon damage enables aggressive body thickness scaling. Furthermore, the selection of gate materials and structures becomes much more flexible when the gate is formed after SiGe etch so that there is no impact of SiGe etching on gate structures. (As one example, this allows the use of high-k metal gate materials.) Also, standard bulk transistor processes can be used with minimal changes because SOI formation is finished during trench process.
Because the dry/wet etch selectivity of poly-silicon on oxide and nitride is very high, poly-silicon can be utilized to form an anchor structure without severe dry etch damage. Upfront formation of a SON structure also can reduce the interaction between previous processes with SiGe etching. Advantageously, as has been mentioned, the methods of preparing active silicon regions for CMOS devices that are disclosed herein perform SiGe etching prior to gate formation, protect top silicon (e.g., with a nitride layer) during the entire process, and form an anchor structure without ever exposing it to an oxide dry etch.
Referring now to the drawings,
As illustrated in
CMOS device 100 comprises a silicon substrate 210 on which is formed diffusion line 110. Diffusion line 110 comprises a silicon layer 211, an electrically insulating layer 212 over silicon layer 211, a silicon layer 213 over electrically insulating layer 212, an electrically insulating layer 214 over silicon layer 213, and an electrically insulating layer 215 over electrically insulating layer 214. An oxide 220 fills the rest of the space in regions A-A and B-B. Diffusion line 110 passes through both regions A-A and B-B, as may be seen by its presence in both the left and the right portions of
As an example, electrically insulating layers 212, 214, and 215 can comprise an oxide, a nitride, or some other dielectric material. In a particular embodiment, electrically insulating layer 212 comprises an oxide, electrically insulating layer 214 also comprises an oxide, and electrically insulating layer 215 comprises a nitride. In one embodiment, electrically insulating layers 214 and 215 may be combined into a single electrically insulating layer comprising an oxide, a nitride, or the like.
As illustrated in
A step 320 of method 300 is to form an oxide or other electrically insulating layer over the diffusion line in both the first region and the second region. As an example, the oxide layer can be similar to an oxide cap 430 that is shown in
A step 330 of method 300 is to form a polysilicon layer over the oxide layer in the first and second regions. As shown in
A step 340 of method 300 is to remove the polysilicon layer from the first region, e.g., using a dry etch or the like, and to deposit oxide therein in order to form an oxide anchor in the first region. The result is shown in
In one embodiment, the polysilicon layer is planarized using a chemical mechanical polish (CMP) or similar operation prior to its removal. While not required, such planarization helps to provide a more flat topography that is beneficial for subsequent polysilicon patterning.
A step 350 of method 300 is to remove the polysilicon layer from the second region. This finishes the oxide anchor structure. Notably, and advantageously, top silicon (the future location of active silicon devices) and sidewalls have to this point not been exposed to plasma. The selectivity of polysilicon etching against oxide or nitride is very high, so negligible loss of the oxide anchor is expected during polysilicon removal and oxide cap etch. Since the selectivity of polysilicon etching against oxide and nitride is very high, the loss of the oxide anchor structure during polysilicon removal will be negligible.
As an example, step 350 may be performed using a selective wet etch. The result is shown in
A step 360 of method 300 is to remove the silicon germanium layer from the diffusion line in order to create a gap therein. As an example, the gap, sometimes called a backside gap, can be similar to a gap 810 that is first shown in
It should be understood that the oxide anchor supports top silicon in both region A-A and in region B-B since top silicon is one piece (extending through both regions). Mechanical strength allows the oxide anchor to hold top silicon in both regions while being itself confined to region A-A.
A step 370 of method 300 is to fill the gap with an electrically insulating material. As an example, the electrically insulating material can be similar to an electrically insulating material 910 that is first shown in
As an example, electrically insulating material 910 can comprise an oxide (including the same oxide as that used for oxide anchor 610). As another example, electrically insulating material 910 can comprise a high-k dielectric material (i.e., a material having a dielectric constant of approximately 10 or greater). In general, the makeup of electrically insulating material 910 depends on its fill capability and on what properties it must have according to design parameters.
In one embodiment, excess portions of electrically insulating material 910 are subsequently removed, as shown in
Of course, in embodiments where electrically insulating material 910 is the same material as that used for oxide anchor 610 (i.e., also an oxide) then electrically insulating material 910 and oxide anchor 610 are indistinguishable from each other and appear as a single layer. In some such embodiments, furthermore, no portion of electrically insulating material 910 need be removed. In general, excess insulator layer portions need not be removed if the electrically insulating material is compatible with subsequent processes.
A step 380 of method 300 is to deposit oxide in the second region. The result of step 380 is a structure identical or very similar to CMOS device 100 that is shown in
As an example, the structure can be similar to CMOS device 100, the first region can be similar to region A-A, and the second region can be similar to region B-B, all of which are shown in
A step 1120 of method 1100 is to form an oxide or other electrically insulating layer in the first and second regions. As an example, the oxide layer can be similar to oxide cap 430 that is shown in
A step 1130 of method 1100 is to form a polysilicon layer over the oxide layer in the first and second regions. As an example, the polysilicon layer can be similar to polysilicon layer 510 that is shown in
A step 1140 of method 1100 is to remove at least a portion of the polysilicon layer from the second region, thus forming a polysilicon anchor in the first region. The result is shown in
Steps 1110, 1120, and 1130 of method 1100 resulted in structures that were identical or very similar to corresponding structures at corresponding stages of method 300, described above. The discussion of steps 1110, 1120, and 1130 thus referred to figures that were first introduced during the discussion of method 300. Beginning at step 1140, method 1100 diverges from method 300 in certain respects and for this reason step 1140 and subsequent steps of method 1100 will no longer refer back to earlier figures, referring instead to
As illustrated in
As an example, silicon substrate 1210, diffusion lines 1220, silicon layer 1221, SiGe layer 1222, silicon layer 1223, oxide layer 1224, and nitride layer 1225 can be similar to, respectively, silicon substrate 410, diffusion line 420, silicon layer 421, SiGe layer 422, silicon layer 423, oxide layer 424, and nitride layer 425, all of which are shown in
CMOS device 1200 also comprises a polysilicon layer 1240 in both region A-A and region B-B. The removal of a portion of polysilicon layer 1240 from region B-B that takes place in step 1140 of method 1100 results in the formation of a polysilicon anchor 1241 in region A-A that is an example of the polysilicon anchor mentioned above in connection with step 1140. A hard mask 1250 protects polysilicon anchor 1241 during the dry etch (or similar operation) that removes portions of polysilicon layer 1240 from region B-B. As an example, hard mask 1250 can be similar to hard mask 520 that is shown in
A step 1150 of method 1100 is to remove the silicon germanium layer from the first and second diffusion lines in order to create a first gap in the first diffusion line and a second gap in the second diffusion line. As an example, the first gap can be similar to a gap 1310 and the second gap can be similar to a gap 1320, both of which are shown in
It should be understood that the polysilicon anchor supports top silicon in both region A-A and in region B-B since top silicon is one piece (extending through both regions). Mechanical strength allows the polysilicon anchor to hold top silicon in both regions while being itself confined to region A-A.
A step 1160 of method 1100 is to fill the first gap and the second gap with an electrically insulating material. As an example, the electrically insulating material can be similar to an electrically insulating material 1410 that is shown in
A step 1170 of method 1100 is to remove the polysilicon anchor. The result is shown in
A step 1180 of method 1100 is to fill the first and second regions with oxide. The result of step 1180 is a structure identical or very similar to CMOS device 100 that is shown in
Although the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made without departing from the spirit or scope of the invention. Accordingly, the disclosure of embodiments of the invention is intended to be illustrative of the scope of the invention and is not intended to be limiting. It is intended that the scope of the invention shall be limited only to the extent required by the appended claims. For example, to one of ordinary skill in the art, it will be readily apparent that the methods for preparing active silicon regions discussed herein may be implemented in a variety of embodiments, and that the foregoing discussion of certain of these embodiments does not necessarily represent a complete description of all possible embodiments.
Additionally, benefits, other advantages, and solutions to problems have been described with regard to specific embodiments. The benefits, advantages, solutions to problems, and any element or elements that may cause any benefit, advantage, or solution to occur or become more pronounced, however, are not to be construed as critical, required, or essential features or elements of any or all of the claims.
Moreover, embodiments and limitations disclosed herein are not dedicated to the public under the doctrine of dedication if the embodiments and/or limitations: (1) are not expressly claimed in the claims; and (2) are or are potentially equivalents of express elements and/or limitations in the claims under the doctrine of equivalents.
Claims
1. A method of preparing active silicon regions for CMOS or other devices, the method comprising:
- providing a structure having a first region and a second region, the structure comprising a silicon substrate having formed thereon a diffusion line that comprises: a first silicon layer, a silicon germanium layer over the first silicon layer, a second silicon layer over the silicon germanium layer; and a mask layer over the second silicon layer;
- forming an oxide layer in the first and second regions;
- forming a polysilicon layer over the oxide layer in the first and second regions;
- removing the polysilicon layer from the first region and depositing oxide therein in order to form an oxide anchor in the first region;
- removing the polysilicon layer from the second region;
- removing the silicon germanium layer from the diffusion line in order to create a gap therein;
- filling the gap with an electrically insulating material; and
- depositing oxide in the second region.
2. The method of claim 1 wherein:
- forming the oxide layer comprises growing the oxide layer in a thermal oxidation process.
3. The method of claim 1 wherein:
- forming the oxide layer comprises depositing the oxide layer using a chemical vapor deposition process.
4. The method of claim 1 further comprising:
- planarizing the polysilicon layer prior to removing it from the first region.
5. The method of claim 4 wherein:
- planarizing the polysilicon layer comprises performing a chemical mechanical polishing operation on the polysilicon layer.
6. The method of claim 1 further comprising:
- removing an excess portion of the electrically insulating material prior to depositing oxide in the second region.
7. The method of claim 1 wherein:
- the electrically insulating material comprises an oxide.
8. The method of claim 1 wherein:
- the electrically insulating material comprises a material having a dielectric constant of approximately 10 or greater.
9. A method of preparing active silicon regions for CMOS or other devices, the method comprising:
- providing a structure having a first region and a second region, the structure comprising: a silicon substrate having formed thereon a first silicon diffusion line and a second silicon diffusion line, both of which comprise: a first silicon layer; a silicon germanium layer over the first silicon layer, a second silicon layer over the silicon germanium layer; and a mask layer over the second silicon layer; and a trench between the first and second silicon diffusion lines;
- forming an oxide layer in the first and second regions;
- forming a polysilicon layer over the oxide layer in the first and second regions;
- removing at least a portion of the polysilicon layer from the second region, thus forming a polysilicon anchor in the first region
- removing the silicon germanium layer from the first and second diffusion lines in order to create a first gap in the first diffusion line and a second gap in the second diffusion line;
- filling the first gap and the second gap with an electrically insulating material;
- removing the polysilicon anchor; and
- filling the first and second regions with oxide.
10. The method of claim 9 wherein:
- removing at least the portion of the polysilicon layer comprises etching away the portion of the polysilicon layer using a dry etch.
11. The method of claim 9 wherein:
- removing the polysilicon anchor comprises etching away the polysilicon anchor using a wet etch.
12. The method of claim 9 wherein:
- the electrically insulating material comprises an oxide.
13. The method of claim 9 wherein:
- the electrically insulating material comprises a material having a dielectric constant of approximately 10 or greater.
14. The method of claim 9 wherein:
- forming the oxide layer comprises growing the oxide layer in a thermal oxidation process.
15. The method of claim 9 wherein:
- forming the oxide layer comprises depositing the oxide layer using a chemical vapor deposition process.
Type: Application
Filed: Dec 31, 2007
Publication Date: Jul 2, 2009
Inventors: Seiyon Kim (Portland, OR), Peter L. D. Chang (Portland, OR), Ibrahim Ban (Beaverton, OR), Willy Rachmady (Beaverton, OR)
Application Number: 11/967,708
International Classification: H01L 21/76 (20060101);