This application claims the benefit of the filing date of European Patent Application Serial No. EP09290314.5, filed Apr. 29, 2009, the entire disclosure of which is hereby incorporated herein by this reference.
The invention relates to a method for transferring a layer from a donor substrate onto a handle substrate and for reclaiming the surface of the donor substrate for reuse.
The so-called SMART CUT™ process, illustrated in
The remaining part 117 of the donor substrate 101, also called the negative, can be recycled and again used in the SMART CUT™ type process as a new donor or handle substrate. The SMART CUT™ type SOI fabrication process has a significant economic advantage due to this recycling process. Indeed, the process provides an optimized use of the raw material for instance silicon wafers.
The negative 117 (
The step 123 of the negative 117 typically has a thickness of about 100 Å to 10,000 Å of silicon, mostly between 1000 Å to 3000 Å, and 100 Å to 10,000 Å of silicon oxide and has a width w in the lateral direction of the order of 0.5 mm to 3 mm.
Prior to the reuse of the negative 117 as donor substrate 103 or handle substrate 101, the surface roughness of the inner region 121 needs to be reduced and the protruding residual topography 119a and 119b needs to be removed. The removal needs to be complete as any remaining protruding material can create particle contamination when during a thermal treatment an exfoliation in the chamfered region occurs due the presence of the remaining ion implanted region 129. Methods to do so are, for example, known from EP 1 156 531 A1 and U.S. Pat. No. 7,402,520 B2. Typically, the following process is applied to get rid of the protruding residual topography: The reclaiming process of negative 117 starts with a de-oxidation step to remove the oxide layer 125 on top of the protruding residual topography on the edge of the remainder 117 as well as on the side 131 and on its backside 133. The de-oxidation can, for example, be carried out using a HF bath, wherein the acid consumes the oxide layer 125, 131 and 133. Subsequently, a first polishing step of the edge region of substrate 1 is carried out to at least partially remove the protruding silicon part 127 on the edge. Then a double-sided polishing (DSP) step is carried out to improve the surface roughness in the interior region 121 but also to further remove the step 123 in the direction of the protruding residual topography 119a and 119b, but also to remove residues remaining form the ion implantation. Finally, to obtain a suitable surface roughness on the front surface of the remainder 117, a chemical mechanical polishing step (CMP) is carried out.
Even though, it is possible to obtain a recycled substrate with the described reclaiming process and which can be reused in the SMART CUT™ process, it is an object of the present invention to provide an improved and more economic reclaiming process that no longer needs the double-sided polishing step to reclaim the remainder of the donor substrate. Indeed, the DSP process step has the major disadvantage that, during polishing, up to 10 μm (5 μm on each side of the substrate) of material are removed to get rid of the protruding residual topography 119a and 119b.
This object is achieved with the method according to claim 1. Accordingly, the method comprises the steps of a) providing a donor substrate, in particular a semiconductor substrate, and a handle substrate each with chamfered edge regions, b) forming a predetermined splitting area at a depth h inside the donor substrate, c) attaching, in particular by bonding, the donor and the handle substrate to obtain a donor-handle compound, wherein no attaching occurs between the two substrates in the chamfered edge regions of the donor and handle substrates, then d) etching the chamfered region such that at least a layer of about the thickness h is removed from the donor substrate in the region where no attaching occurred, then e) detaching a remainder of the donor substrate from the donor handle substrate, wherein detachment occurs at the predetermined splitting area and f) reusing the remainder of the donor substrate, in particular after the surface treatment step. According to a preferred embodiment, during step d), a layer with a thickness of more than h is removed.
Thus, unlike in the process of the prior art, the remainder of the donor substrate will no longer present a protruding portion 119a, 119b as illustrated in
Preferably, the method can use a donor substrate comprising a dielectric layer and, in this case, can furthermore comprise a step g) carried out between steps c) and d) which consists in removing the dielectric from the donor substrate at least in the chamfered region but not in the attached region. Thus, even in the presence of a dielectric used to form a semiconductor on insulator substrate with the mentioned process, it is still possible to achieve the advantages of the method as, not only the chamfered region of the donor substrate itself but also of its dielectric layer, is removed prior to detaching.
It has to be pointed out that the removal step to remove the dielectric layer does not represent an additional step which has to be carried out. Indeed, in the prior art, the dielectric layer is also removed during reclaiming. Thus, compared to the prior art, step g) is simply moved from after detachment to prior to detachment.
According to a variant, the handle substrate can comprise a dielectric layer. In this case, the dielectric layer is provided by the handle substrate to form a semiconductor on insulator substrate. This variant has the advantage that one only has to remove the material of the substrate in step d) to achieve the advantages of the invention, as no additional dielectric layer is provided on the donor substrate. Thus, in this variant, less process steps are necessary compared to the variant which provides the dielectric via the donor substrate.
Advantageously, the dielectric layer can be an oxide, in particular a silicon oxide. This oxide layer can be provided either by a thermal process or by deposition. Advantageously, steps e) and/or g) can be a wet or dry etching step. This is a more economic material removal step than the edge polishing and double-sided polished step as used in the prior art.
Preferably, steps e) and g) can be performed using a non-selective and/or isotropic etching solution. Using the non-selective etching process, both the dielectric layer and the underlying part of the donor substrate, for instance a semiconductor material, can be removed in one step. By using an isotropic etching solution, the process is furthermore simplified as varying etching rates, depending on the crystallographic directions which are different in the chamfered region compared to the rest of the substrate, do not have to be taken into account. This simplifies the control of the process.
The dielectric material removal step, independent of whether the dielectric layer is removed from the donor and/or the handle substrate (in case a dielectric is also present on the handle substrate), does not have an impact on the quality of the buried dielectric layer as this one is sandwiched between donor and handle substrate.
Advantageously, during step d), a layer with a thickness of about 100 Å to 10,000 Å, in particular 1000 Å to 3000 Å, can be removed in the non-attached region of the donor substrate. Compared to the double-sided polishing step mandatory in the prior art during which a large amount of material, namely in the order of 5 μm on each side, had to be removed to get rid of the protruding portions, the material removal in the process according the invention can be less so that one donor substrate can be reused more often, for instance, more than ten times, compared to the prior art process. This is also made possible by the fact that the reclaimed donor substrate remains within the semi-standard concerning the substrate dimensions.
Preferably, steps d) and/or g) can be carried out at a temperature of less than 500° C., preferably at less than 350° C. Thus, the whole process until detachment is carried out at low temperature so that no detachment can occur in the non-attached regions which could lead to unwanted particle contamination of the final product.
According to a preferred embodiment, the surface treatment step can, at most, comprise a polishing step, in particular a CMP polishing and a cleaning step before and/or after the polishing step. Thus, compared to the prior art, a greatly simplified reclaiming process can be carried out. The polishing step is used to get the desired surface quality of the reclaimed remainder of the donor substrate, typically a mirror polished quality, and the cleaning steps, as known in the art, make the reclaimed donor substrate ready for reuse. Thus, instead of a three-level reclaiming process: i) edge polishing, ii) double-sided polishing, iii) mirror polishing plus the various cleaning steps, the invention provides the possibility to carry out the reclaiming process with only one simple mirror polishing step.
In this context, the term “about the thickness h” used in claim 1 relates to thickness that are such that the remainder can be planarized using only a CMP process. This means that a layer is removed in step d) of claim 1 that has a thickness of at least h minus about 50 nm. This would lead to a protruding region in the remainder of the donor substrate with a height of about 50 nm, which can be dealt with by a simple CMP polishing step.
Advantageously, during CMP polishing, a layer of less than 3 μm, preferably less than 1 μm, can be removed from the surface where detachment occurred. As mentioned above, this limited material removal brings the advantage that one donor substrate can be reused more often, in particular, more than ten times, in the layer transfer process.
Advantageous embodiments will be described in combination with the enclosed Figures.
a through 1c illustrate a prior art layer transfer process according to the SMART CUT™ technology;
a through 2d illustrate a first embodiment of the inventive method;
a through 3e illustrate a second embodiment of the inventive method; and
a through 4d illustrate a third embodiment of the inventive method.
a through 2d illustrate a first embodiment of the inventive method for transferring a layer from a donor substrate onto a handle substrate.
It should nevertheless be mentioned that the handle substrate 101 can be any suitable handle substrate, in particular a silicon wafer, but also a glass or quartz type substrate. The donor substrate 103 can be a semiconductor substrate, in particular one out of a silicon, a silicon carbide, a silicon germanium, a gallium nitride or a germanium substrate and the isolating dielectric layer 105 can be one out of silicon dioxide, silicon nitride, silicon oxynitride or Al2O3, etc.
In the following, the inventive method will be described, without being limited to this particular choice, to a handle substrate 101 being a silicon wafer, a donor substrate 103 being a silicon wafer and the dielectric layer 105 being a silicon dioxide.
b illustrates the source-handle compound 201 obtained after an etching step during which the dielectric layer 105 has been removed from the back side 203, the side 205 but also the chamfered regions 207 and 209 of the donor substrate. A dielectric layer 105′ remains sandwiched between the donor substrate 103 and the handle substrate 101 and forms the future buried oxide layer.
In this embodiment, the material removal is achieved with an etching step. The etching can be a dry or a wet etching suitable to remove the dielectric oxide layer which typically has a thickness of up to 1000 nm, but typically has a thickness of 10 nm to 200 nm.
Subsequently, as illustrated in
The etching is carried out such that material is removed from the chamfered region 207′ and 209′ at least of the donor substrate 103 and such that the removed layer has a thickness h1 corresponding to the depth h of the predetermined splitting area 107. Typically the material removal not only occurs in the chamfered region but also on the side and on the back side of the donor substrate 103 and also in the chamfered region 211 and 213 of the handle substrate 101.
By doing so, the ion implanted region 129, present in the chamfered part 207 and 209 illustrated in
The next step consists in a detachment step, the result of which is illustrated in
The effect of the inventive method is even more visible on the remainder 219 of the donor substrate 103 illustrated on the left hand side of
The surface part 221 where detachment occurred has a rather rough surface, with roughness values close to 60 Å to 70 Å like in the prior art. However, due to the fact that the protruding portion is not present, the surface roughness can be improved by a simple CMP polishing process during which less than 3 μm, preferably less than 1 μm, or even only about 50 nm, of material is removed from the surface to obtain the desired surface quality for reuse of the reclaimed remainder 219.
The chemical/mechanical polishing step can be accompanied by standard cleaning processes as in the prior art.
Compared to the prior art, the method according to the first embodiment has the advantage that, after detachment, no protruding portions are present in the edge regions, which is in complete contrast with the prior art, see reference numerals 119a, 119b in
a through 3e illustrate a second embodiment of the inventive method for transferring a layer of a donor substrate 103 onto a handle substrate 101.
The difference between the first embodiment and the second embodiment is that, during the etching of the chamfered region 207″ and 209″ of the donor substrate 103, the material removal goes beyond the depth of the predetermined splitting area 107, 129, as illustrated in
Compared to the first embodiment, the additional material removal has the advantage that it is ensured that all implanted areas 129 present in the chamfered region 207 and 209 are removed.
After the detachment step, the semiconductor on insulator substrate 301, as illustrated on the right hand side of
Unlike the remainder 217 illustrated in
With the second embodiment, the same advantages as can be achieved like with the first embodiment.
According to a variant of the invention, instead of providing a semiconductor on insulator substrate, the process could be carried out without an intervening dielectric layer, which is called a direct silicon bonding process. In this case, the first and second embodiments could be carried out without the step of removing the dielectric 105, as illustrated in
a through 4d illustrate a third embodiment of the invention. This embodiment is slightly different compared to the first and second embodiments as, here, the dielectric layer is provided on the handle substrate side and the donor substrate is a bare semiconductor wafer, for instance a silicon wafer. The materials that can be used in this embodiment correspond to the ones of the first and second embodiment.
The left side of
b illustrates the source handle compound 409 achieved by bonding the donor and the handle substrate 401 and 405. Like in the first and second embodiment on the surface side where bonding occurred a non attached region 411 and 413 can be observed which is due to the chamfered edge region of both substrates.
Subsequently, and as illustrated in
After detachment, achieved by a thermal and/or mechanical treatment, a SOI substrate 415 is obtained comprising a transferred layer 417 and a buried oxide layer 419 still part of the original dielectric layer 407 covering the handle substrate 405. Eventually a deoxidation step could be carried out to remove the dielectric layer 407 except for the buried part 415 to obtain a SOI substrate as illustrated in
The remainder 421 of the original donor substrate 401 has the same structure than the one illustrated in
Finally, according to a variant, the material removal step illustrated in
According to a variant the first till third embodiments can also be carried out without the presence of a buried oxide layer 105′. In the so called direct silicon bonding technology two Si wafers typically one with a 100 and the other one with a 110 surface are bonded together. In this case the process described are carried out in the same way without however the step of removing the oxide by etching. It should furthermore be mentioned that by CMP a remaining protruding portion of about 50 nm, which could be present in the edge region in case the material removal did not go up until h or beyond, can still be removed.
In the following practical examples according to the invention will be described.
Example one according to the invention: a Silicon on Insulator substrate with a buried thermal oxide of thickness 145 nm and a transferred layer of thickness 250 nm is achieved using an etching process of the source handle substrate as illustrated in
Example two according to the invention: a Silicon on Insulator substrate with a buried thermal oxide of thickness 145 nm and a transferred layer of thickness 300 nm is achieved using an etching process with HF/H2O2/H2O and h1=250 nm, with h being 300 nm. The recycling of the remainder is carried out by an EP and CMP step. In this example the HF/H2O2 bath is not selective and both layers the oxide and the silicon can be etched in one step. Edge polishing is performed to get rid of any potential residue of the implanted layer on the edge since material removal did not go up until h or beyond (h1˜h−50 nm), but the remaining 50 nm can also be removed with a CMP step and no EP polishing.
Example three according to the invention: a Silicon on Insulator substrate with a buried thermal oxide of 10 nm thickness and a transferred layer of 250 nm is achieved using a plasma (dry) etch such that h1=h=250 nm+/−5%. During the dry etch, a first plasma based on CF4 or CHF3 etches the oxide and then a second plasma on the basis of SF6 etches the silicon. In this case one of the two substrates, preferably the donor substrate, has one of its main surfaces, called the back surface, on a substrate holder which prevents etching of the back side. In this case the reclaiming of the remainder of the donor substrate comprises an additional deoxidation step to remove the oxide from the back side plus the CMP step polishing the front surface and removing about 1 μm of Silicon.
Example four according to the invention: a Silicon on Insulator substrate with a 145 nm buried insulator layer comprising SiOxNy and one or more SiO2 layers, etched using HF and H3PO4 and then HF/HNO3 such that h1=h=250 nm+/−5%.
Number | Date | Country | Kind |
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09290314.5 | Apr 2009 | EP | regional |