Method and structure having monolithic heterogeneous integration of compound semiconductors with elemental semiconductor

A semiconductor structure having compound semiconductor (CS) device formed in a compound semiconductor of the structure and an elemental semiconductor device formed in an elemental semiconductor layer of the structure. The structure includes a layer having an elemental semiconductor device is disposed over a buried oxide (BOX) layer. A selective etch layer is disposed between the BOX layer and a layer for a compound semiconductor device. The selective etch layer enables selective etching of the BOX layer to thereby maximize vertical and lateral window etch process control for the compound semiconductor device grown in etched window. The selective etch layer has a lower etch rate than the etch rate of the BOX layer.

TECHNICAL FIELD

This disclosure relates generally to the monolithic heterogeneous integration of compound semiconductors with elemental semiconductor such as Si (as in CMOS) and Ge.

BACKGROUND AND SUMMARY

As is known in the art, recent advances in monolithic heterogeneous integration of compound semiconductor (CS) devices (including Group III-V devices composed of InP, GaAs, GaN, or AlN containing materials)with elemental semiconductor devices, such as Si based CMOS, have enabled compound semiconductor devices to be grown in etched windows on modified silicon on insulator (SOI) substrates and fabricated within a few microns of neighboring CMOS devices. Ideally, the resulting CS devices are co-planar or nearly co-planar with the CMOS in order to enable the use of standard back-end CMOS processing techniques to complete process integration. In this approach, compound semiconductor devices are grown on modified Silicon-On-Insulator (SOI) variants with compound semiconductor growth supports that are one of the following:the SOI handle substrate (which may be Si, SiC, Sapphire or other elemental or compound semiconductor)a template layer that has been grown directly on the SOI handle substratea template layer that was layer transferred to the handle substratea template layer that has been layered transferred and ends up sandwiched (i.e., buried) between two oxide layers in the SOI.

Generalized outlines of two of these modified SOI variants are shown inFIGS. 1A-1Fand2A-2F, for gallium nitride (GaN) and gallium arsenide (GaAs) or gallium nitride (GaN), respectively, integrated with CMOS. InFIGS. 1A-1F, the GaN/CMOS integration is accomplished by growing the GaN device in a window directly on the window exposed portion of the handle wafer, e.g., Si, SiC, or Sapphire. On the other hand, for the GaAs (or InP)/CMOS integration ofFIGS. 2A-2F, the GaAs devices are grown on a window exposed portion of the template layer that is otherwise buried between two oxide layers in the SOI structure. It should be noted that the buried template layer could be any compound or elemental semiconductor such as Si, Ge, InP, GaAs, GaN, or AlN. Alternately, the figures could have been drawn with the GaN devices grown on an exposed portion of the buried template layer, and the GaAs (or InP) devices grown directly on the handle substrate.

More particularly, it is noted that for both SOI variants, a substrate (or handle) of, for example, silicon, SiC or sapphire is provided with a buried oxide (BOX) layer of silicon dioxide on the surface of the substrate. In the case the GaN structure, a top layer of silicon (Top Si) is formed on the BOX layer and then the CMOS devices are formed in the top silicon layer as shown inFIG. 1F; and in the case of the GaAs or InP structure, a buried CS template layer is sandwiched between a pair of BOX layers (i.e., a lower BOX layer2(BOX2) and an upper BOX layer1(BOX1) and then the CMOS devices are formed in the top silicon layer, as shown inFIG. 2.

The monolithic approach to heterogeneous integration that is outlined inFIGS. 1A-1Fand2A-2F face many challenges including:

1. vertical and lateral windows etch repeatability

2. the impact of CS growth temperatures on CMOS device parameters

3. impact of growing CS devices on non-native substrates and templates on CS device reliability

4. layer cross contamination during SOI wafer manufacture, III-V growth, and process anneal steps

5. CS to CMOS heterogeneous interconnect fabrication

As mentioned above, heterogeneous integration on modified SOI wafers (as shown inFIGS. 1A-1Fand2A-2F) suffers from limited process control/repeatability related to etching windows into the SOI so that CS devices can be grown. The limited process control/repeatability of the windows etching process impacts two areas that are the following:

1. the quality of the CS devices grown

2. the minimum possible spacing between CMOS and CS devices

The process shown inFIG. 2Babove is shown in more detail inFIGS. 2B-1through2B-3. Thus, as shown inFIG. 2B-1, the top oxide layer is first etched with a fluoride containing plasma. The etch is a non-selective etch and penetrates into the Top Si. Next, a fluoride-oxide containing plasma is used to selectively remove the remaining Top Si and selectively expose the BOX layer, as shown inFIG. 2B-2. Next, the upper portion of the exposed BOX layer is dry etched with fluoride containing plasma (as shownFIG. 2B-3); it being noted that a thin portion of the BOX layer remains. This thin BOX layer is then removed with a final wet HF etch.

The inventors have recognized that both of these issues stem from the fact that in order to achieve the minimum spacing between CMOS and CS devices, one must dry etch most of the Top oxide/Top Si/BOX stack and leave a minimal amount of BOX (above the CS template surface).

The final wet etch removal of a thin residual BOX layer is necessary because in most cases complete dry etch removal of the buried oxide would result in a damaged template surface for CS growth. This in turn would result in higher defects in the CS devices that may suffer from performance and reliability issues (impacting area 1 above). On the other hand, the hydrofluoric acid solutions used for final BOX removal will substantially laterally etch both the top oxide layers (above the CMOS) and BOX if wet etch times are long (impacting area 2 above). As a result, the amount of BOX left after the dry etch process should be as thin as possible, so as to minimize wet etch times.

A poorly controlled dry etch of the BOX could result in either an over etch of the BOX resulting in a complete dry etch process (impacting area 1 above), or in an under etch of the BOX that would leave more oxide than expected for wet etch removal (impact areas 1 or 2 above). If the wet etch time of the under dry etched case is not adjusted, and residual oxide is present in the windows, then the CS devices will fail to nucleate properly during growth (impacting area l above) in windows. If the wet etch time is adjusted to remove the oxide, but it is lengthened too much, than the lateral etching of the oxide may be excessive (impacting area 2 above)

In accordance with the present disclosure, a layer having an elemental semiconductor device is disposed over aburied oxide (BOX) layer. A selective etch layer is disposed between the elemental semiconductor device layer and a layer for a compound semiconductor device. The selective etch layer enables selective etching of the BOX layer to thereby maximize vertical and lateral window etch process control for the compound semiconductor device grown in the etched window.

In one embodiment, a semiconductor structure is provided having CMOS transistor and a compound semiconductor device. The structure includes: a compound semiconductor growth support for the compound semiconductor having the compound semiconductor device therein; a selective etch layer on the compound semiconductor growth support; and a silicon layer disposed over the selective etch layer, the silicon layer having disposed in portions thereof the CMOS transistors. A window formed through other portions of the silicon layer and underlying portions of the selective etch layer exposes a portion of the compound semiconductor growth support. The compound semiconductor is disposed over the exposed portion of the compound semiconductor growth support.

In one embodiment, the selective etch layer is aluminum oxide (Al2O3), silicon nitride (SiNx), aluminum nitride (AlN), hafnium oxide, or zirconium oxide or a plurality of layers having combinations of aluminum oxide (Al2O3), silicon nitride (SiNx), aluminum nitride (AlN), hafnium oxide, or zirconium oxide.

In one embodiment, the compound semiconductor growth support is silicon (Si), SiC or sapphire.

In one embodiment, the compound semiconductor growth support is a compound or elemental semiconductor.

In one embodiment, the compound semiconductor growth support is Ge, InP, GaAs, GaN, or AlN.

The overall thickness of the selective etch layer or layers and the remaining buried oxide are selected to minimize or eliminate any additional buried oxide thickness relative to typical SOI buried oxide thicknesses, which, in turn, widens the process windows available during modified SOI manufacture, CS/CMOS process integration, and CS growth processes.

DETAILED DESCRIPTION

Referring now toFIG. 3, a cross sectional sketch of a semiconductor structure10having compound semiconductor (CS) device12, here for example, a III-V device formed in a compound semiconductor18, such as, for example, a GaAs, GaN or InP transistor and an electrically connected elemental semiconductor device14, here for example a pair of silicon devices, more particularly CMOS transistors, formed in an elemental semiconductor layer26is shown.

After formation of the elemental semiconductor devices14and a top silicon dioxide layer28, and prior to the formation of the compound semiconductor (CS) device, a structure is provided having compound semiconductor growth layer or support16(sometimes also referred to herein as substrate16), here a substrate of, for example, silicon, SiC or sapphire. The support16has disposed on the upper surface thereof a first buried oxide (BOX) layer20of silicon dioxide. A selective etch layer22, here for example, aluminum oxide (Al2O3) or aluminum nitride (AlN), is disposed on the selective etch layer22. A second buried oxide (BOX) layer24of silicon dioxide is disposed on selective etch layer22. A top elemental semiconductor layer26, here silicon is disposed on the second buried oxide (BOX) layer24. A top silicon dioxide layer28is disposed on the top elemental semiconductor layer26.

Referring now toFIGS. 3A-3F, a window30is then formed through layers28,26,24,22, and20to expose a portion of the compound semiconductor growth supportor substrate16for compound semiconductor18. More particularly, the window30is formed using a series or sequence of etches. First, a non-selective, fluoride containing plasma dry etch is used to remove portions of the top silicon dioxide layer28and expose an underlying portion of the top silicon layer26. Next, a selective fluorine-oxygen containing plasma dry etch is used to remove the underlying portions of the top silicon layer26to thereby expose underlying portions of the second buried oxide layer24. Next, a selective fluorine containing plasma etch is used to remove the underlying portions of the second buried oxide layer24. It is noted that the second buried oxide layer24etch rate is much higher than the etch rate of the underlying portions of the selective etch layer22in fluorine containing plasmas. The selective etch layer22(sometimes also referred to herein as an etch stop layer) acts as an etch stop during BOX dry etch, then occurs one of the following depending on the modified SOI variant: the etch stop layer22is then selectively dry etched to reveal the final layer which is to be wet etched; or the etch stop layer22itself is wet etched to reveal the III-V growth surface.

The current example outlined inFIGS. 3A-3Fis the former of the two selective etch cases, so aBCl3/Cl2gas chemistry selective etch is used to remove the underlying portions of the selective etch layer22to thereby expose underlying portions of buried oxide layer20. Next a wet etch, here for example, a hydrofluoric acid containing solution is used to remove the exposed portions of the first buried oxide layer20and thereby expose a portion of the compound semiconductor growth support16. Next, the compound semiconductor18is formed on the exposed portion of the support16. Next, the compound semiconductor (CS) device12is formed in the upper portion of the compound semiconductor18. The completed structure is shown inFIG. 3.

From this baseline modified SOI structure and approach to windows etching additional variants can be derived. Many more variants are shown inFIGS. 4-9. InFIG. 4, the second buried oxide layer26is removed fromFIG. 3. InFIG. 5, the first buried oxide layer20is removed fromFIG. 3. InFIG. 6, the etch layer22is silicon nitride (SiNx). InFIG. 7, the etch layer22is a composite layer of lower layer22aof Al2O3or AlN and an upper layer22bof SiNx. The SiNx layer is also etched in fluorine containing plasmas, but its etch rate is manipulated relative to the other layers through its deposition method and conditions, subsequent thermal treatment, and composition of fluorine gas chemistry used to etch SiNx. It should be understood that the variations inFIGS. 4 through 6may be used with the composite layers22a,22bfor the etch layer22. InFIG. 8the compound semiconductor growth support16′ for the compound semiconductor18is a buried compound semiconductor (CS) template (compound semiconductor growth support) layer16′bdisposed on an additional buried oxide layer16′a. The compound semiconductor growth support16′ is on the substrate16, as shown. It should be understood that all of the variations described above inFIGS. 3 through 7may be used in the structure shown inFIG. 8. InFIG. 9, the compound semiconductor growth support16″ for the compound semiconductor18is a buried oxide layer16″aon the substrate16, a SiNx layer16″bon the buried oxide layer16″a, an Al2O3 or SiN layer16″con the SiNx layer16″b, a buried oxide layer16″don the Al2O3 or SiN layer16″c. and a buried compound semiconductor (CS) template (compound semiconductor growth support) layer16″edisposed on the buried oxide layer16″d. It should be understood that all of the variations described above inFIGS. 3 through 8may be used in the structure shown inFIG. 9.

The SiNx in this additional BOX stack is deposited by plasma enhanced chemical vapor deposition (PECVD), chemical vapor deposition (CVD), or by atomic layer deposition (ALD). The aluminum oxide (Al2O3) layer is deposited by ALD, sputter deposition, thermal oxidation of aluminum to Al2O3, or by PECVD as part of the buried oxide layer formation of the modified SOI fabrication process. Finally, the SiO2in this stack can be thermal SiO2, if the CS growth surface is Si, or PECVDSiO2if the CS growth surface is a non-Si template layer.

The SiNx also provides wet and dry etch selectivity relative to the SiO2and Al2O3and thereby help minimize lateral process bias caused the dry and wet etching windows processes. The Al2O3(primarily etched BCl3/Cl2containing plasmas) and SiO2(primarily etched fluorine containing plasmas) on the other hand, act primarily as selective dry etch stops relative to each other. Nitrided interfaces may be used in place of SiNx. Surfaces may be nitrided through NH3, N2, or other nitrogen containing gas plasma treatments.

A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, the selective etch layer may be silicon nitride (SiNx), aluminum nitride (AlN), hafnium oxide, or zirconium oxide or a plurality of layers having combinations of aluminum oxide (Al2O3), silicon nitride (SiNx), aluminum nitride (AlN), hafnium oxide, or zirconium oxide. Further, different dielectric layers, such as a silicon nitride layer, may be used in place of the BOX layer24. Accordingly, other embodiments are within the scope of the following claims.