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# Large-area integration of two-dimensional materials and their heterostructures by wafer bonding

## Abstract

Integrating two-dimensional (2D) materials into semiconductor manufacturing lines is essential to exploit their material properties in a wide range of application areas. However, current approaches are not compatible with high-volume manufacturing on wafer level. Here, we report a generic methodology for large-area integration of 2D materials by adhesive wafer bonding. Our approach avoids manual handling and uses equipment, processes, and materials that are readily available in large-scale semiconductor manufacturing lines. We demonstrate the transfer of CVD graphene from copper foils (100-mm diameter) and molybdenum disulfide (MoS2) from SiO2/Si chips (centimeter-sized) to silicon wafers (100-mm diameter). Furthermore, we stack graphene with CVD hexagonal boron nitride and MoS2 layers to heterostructures, and fabricate encapsulated field-effect graphene devices, with high carrier mobilities of up to $$4520\;{\mathrm{cm}}^2{\mathrm{V}}^{ - 1}{\mathrm{s}}^{ - 1}$$. Thus, our approach is suited for backend of the line integration of 2D materials on top of integrated circuits, with potential to accelerate progress in electronics, photonics, and sensing.

## Results

### Wafer-level transfer of graphene/hBN heterostructures

To demonstrate the viability of our methodology for wafer-level transfer of 2D materials and formation of large-area van der Waals heterostructures, we integrated graphene/hBN heterostructures (see “Methods” for details of the process and materials). We characterized the transferred layers using van der Pauw (vdP) devices, noncontact terahertz (THz) near-field spectroscopy, and Raman spectroscopy (Fig. 2). In short, consecutive transfers of multilayer hBN from copper foil and monolayer graphene from copper foil, both synthesized by CVD, formed a graphene/hBN heterostructure on a 100-mm-diameter silicon wafer. First, we attached the hBN on copper foil (2.5 cm × 2.5 cm) to the adhesive on the spin-coated target wafer by wafer bonding. After etching away the copper in FeCl3 solution and rinsing in deionized water, we placed the monolayer graphene on a copper foil (100 mm diameter) on top of the target wafer and performed a second bonding process in a vacuum atmosphere. Finally, etching in FeCl3 uncovered the transferred layers. Due to the difference in the size of the growth substrates, the graphene/hBN heterostructure in the center of the wafer is surrounded by a monolayer of graphene on BCB. Note that in the heterostructure, neither the graphene nor the top surface of the hBN was in contact with polymers or adhesives at any time. Moreover, the second transfer was performed in a vacuum and at elevated temperature, which reduces the amount of water and gas molecules that may get trapped between the layers. Residuals of copper and the copper etchant are still potential contaminants at the interlayer interface, which potentially can affect the properties of the heterostructure60. Next, we integrated Ti/Au electrodes and patterned the 2D material heterostructure to vdP devices, which allow electrical material characterization on the target wafer (Fig. 2a). Four-point probe measurements of a total of 27 vdP devices yielded the graphene sheet resistance (Rsh), carrier density (n), and mobility of majority charge carrier (μ) of the transferred graphene layer, both for graphene resting on BCB and for graphene resting on hBN (Fig. 2b) (see “Methods”). In both cases, all measured devices were functioning and we found a similar Rsh (630 ± 90 and 600  ±  90 Ω sq−1, respectively), whereas the n and μ showed differences for graphene resting on BCB and on hBN, respectively. The carrier density in the graphene on BCB was lower than for graphene on hBN ($$(3.7 \pm 0.7) \times 10^{12}$$ and $$(4.9 \pm 0.2) \times 10^{12}\,{\mathrm{cm}}^{ - 2}$$), while the mobility was higher for graphene on BCB than for the graphene on hBN ($$2800 \pm 100$$ and $$2000 \pm 200\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$). For the transferred graphene monolayer resting on BCB, the extracted mobilities are in the higher range of previously reported values for polycrystalline CVD graphene transferred on large areas from polycrystalline copper substrates by various methods, including wet transfer with polymeric carrier layers42,61, face-to-face transfer by bubble formation62 and lamination50. The mobility in our graphene/hBN heterostructure is similar to values reported by Pandey et al.63 and Shautsova et al.64, who encapsulated graphene in CVD hBN using wet and dry transfers. In accordance with these works, our results indicate that current large-area CVD hBN substrates typically do not increase the mobility in polycrystalline graphene, thus contrasting several studies on single crystals of graphene and hBN29,30,65,66. We emphasize that for a meaningful comparison, the initial graphene quality before the transfer is of crucial importance. Our measurements suggest slightly lower mobility in the graphene/hBN heterostructure than for graphene on BCB. Since we performed the measurements on the same wafer containing graphene from the same growth substrate, which was exposed to the same fabrication processes, we conclude that the substrate below the graphene (hBN and BCB, respectively) is mainly responsible for the discrepancy in material characteristics. For our materials, the microscopic surface roughness of hBN on Cu foil is ~50% higher than for graphene on Cu foil (root mean square (RMS): 264 and 176 nm, respectively, see Supplementary Fig. 3). This difference might cause local strain variations in the covering graphene layer, which reduces charge carrier mobility67. In addition, large topography of the transferred materials may potentially cause problems for very high-resolution lithography. Using growth substrates with lower surface topography may mitigate this issue68,69,70.

We used terahertz time-domain spectroscopy (THz-TDS) to further characterize the electrical properties and homogeneity of the wafer-level transferred graphene and large-area graphene/hBN heterostructure. The THz-TDS measurements are recorded in transmission mode using a photoconductive near-field detector71,72 (see “Methods”), which records the amplitude and phase information of a THz signal traveling through the sample. Scanning across the sample surface yields spatially resolved images of the graphene sheet resistance on wafer scale. For our measurements, we set the spatial resolution to 500 µm by adjusting the distance of the near-field detector to the sample and the pitch between acquisition sites. The spatial resolution is significantly larger than the intrinsic length scale that is probed by the THz-TDS. This transport length is estimated by the distance lD, which a charge carrier transverses during one cycle of the alternating THz field73. For our sample and setup, we estimate $$l_{\mathrm{D}}\,\approx \,60 - 100\,{\mathrm{nm}}$$ (see Supplementary information for calculation). The map of the graphene sheet resistance on a 100-mm-diameter wafer after transfer and formation of the graphene/hBN heterostructure indicates a uniform coverage and successful transfer on the entire wafer (Fig. 2c). The sheet resistance in the marked region averages to $$450 \pm 50\,{\Omega}\,{\mathrm{sq}^{-1}}$$, and is similar for both underlying materials ($$450 \pm 20$$ and $$440 \pm 20\,{\Omega}\,{\mathrm{sq}^{-1}}$$ for BCB and hBN, respectively), which is in line with the measurements of the vdP devices shown in Fig. 2b. These values are similar to the values reported for polycrystalline graphene that was transferred from polycrystalline copper substrates using various methods42,50,63. Rahimi et al.61 reported a higher mean value of $$2600\;{\Omega}\,{\mathrm{sq}^{-1}}$$, which originated from lower residual doping. Note that the THz near-field measurement in Fig. 2c was performed on a different sample with high-resistivity Si than the vdP measurements in Fig. 2a, b to avoid absorption of the THz signal by the substrate. At the lateral transition between the graphene/hBN heterostructure and the monolayer graphene (i.e., the outer edges of the heterostructure), the graphene sheet resistance is increased and less uniform. This variation was most likely caused by surface inhomogeneities in the BCB layer that resulted from a partly detached edge region of the hBN on copper foil in the first transfer. This effect is known to occur in wafer bonding of compliant substrates where the contact area of the wafer chuck is smaller than the substrate. Precise adjustment of the contact area between the wafer bonder and the donor substrate to the size of the copper foil should improve the lateral interface between regions with different layer stacks.

We performed Raman measurements to extract detailed information about the local graphene quality, including the relationship between doping and nanometer-scale strain variations, by analyzing the positions of the Raman G (ωG) and 2D (ω2D) peaks and the full-width at half-maximum of the 2D peak (Γ2D)74,75,76. In particular, stress variations are of interest since they limit the charge carrier mobility in high-quality graphene, a crucial parameter for high-performance graphene devices67. In Fig. 2d, we plot the correlation map of ωG and ω2D for the acquired Raman spectra of the transferred graphene placed on BCB (triangles) and on hBN (filled circles), respectively. The location of the acquisition sites on the wafer is marked in Fig. 2c. The single open circle represents the G and 2D peak positions of intrinsic graphene, which is neither doped nor strained ($$\omega _{\mathrm{G}} = 1582\;{\mathrm{cm}}^{ - 1}$$, $$\omega _{2{\mathrm{D}}} = 2670\;{\mathrm{cm}}^{ - 1}$$)74. Hole doping of graphene shifts ωG and ω2D with a relative slope of 0.7 (dashed line), while strain results in a relative shift with a slope of 2.2 (solid line)75. For both substrate materials on our sample, the peak locations indicate slightly tensile strain and predominant hole doping. For graphene on BCB, the charge carrier doping is more pronounced than for graphene on hBN, while the peak locations are less scattered and more confined within a smaller area. Our observation of hole doping and reduced doping level of the graphene when placed on hBN compared to placement on polymeric substrate materials agrees with literature77. However, multilayer hBN grown by CVD does not have the same strong effect as exfoliated hBN, which restores almost intrinsic conditions77. The color scale of the data points in Fig. 2d represents Γ2D and averages to $$28.8 \pm 3.6\;{\mathrm{cm}}^{ - 1}$$ for graphene on BCB and $$27.3 \pm 3.8\;{\mathrm{cm}}^{ - 1}$$ for graphene on hBN. Both values indicate the decent quality of the graphene with little strain variations within the spot of the Raman excitation laser.

### Stacking of graphene layers by repeated transfer

The recent discovery of specific twist angles between two graphene layers that give rise to astonishing properties such as unconventional superconductivity, correlated insulation, and magnetism24,25,26 has spurred great interest in new methods for well-controlled fabrication of double-layer graphene. Furthermore, the stacking of two or multiple layers of 2D materials is of interest for controlling the stiffness of nanoelectromechanical devices78,79.

We performed two consecutive transfers of monolayer (1-layer) graphene from their copper growth substrates to a 100-mm-diameter silicon wafer to demonstrate that our transfer methodology is suitable for high-yield formation of double-layer (2-layer) graphene on large areas (we avoid the term bilayer graphene to distinguish these films from Bernal stacked materials, see “Methods” for process details). First, we transferred CVD graphene from a quarter of a 100-mm copper foil to the center of the target wafer with BCB. For the second transfer, we used a full 100-mm copper foil with CVD graphene. To provide a reference for THz spectroscopy, we removed the graphene on parts of the growth substrate before transfer (left side of the wafer in Fig. 3a). The spatially resolved map of the sheet resistance (Rsh) in Fig. 3c reveals a uniform coverage of graphene on the wafer without major defects. Decreased Rsh in the center clearly distinguishes 1- and 2-layer graphene on the target wafer and confirms the presence of double-layer graphene. We attribute the difference in the 1-layer graphene Rsh between these experiments and the dataset presented in Fig. 2 to a dissimilarity in graphene quality before transfer. The graphene sheet in Fig. 3a that forms the 1-layer region on the target wafer was from a different batch than the graphene sheet used in Fig. 2. To characterize the 1- and 2-layer graphene on the silicon wafer, we extracted the position of the G and 2D peaks from Raman measurements and plotted the correlation map of ωG and ω2D (Fig. 3b). In both regions, the peak positions were clustered with little spread. The measurements indicate hole doping in the graphene, which is consistent with our measurements on graphene/hBN heterostructures in Fig. 2d. We found that the 1-layer graphene (triangles) experienced tensile strain, while the 2-layer graphene (circles) was strained compressively. However, the peak location for 2-layer graphene might also be influenced by weak interactions between the stacked layers. The full-width at half-maximum of the 2D peak (Γ2D) (coloration of data points) is similar in both regions and averages to $${\it{\Gamma}}_{2{\mathrm{D}},\;1 {\mbox{-}} {\mathrm{layer}}} = 33.5 \pm 4.6\;{\mathrm{cm}}^{ - 1}$$ and $${\it{\Gamma}}_{2{\mathrm{D}},\;2 {\mbox{-}} {\mathrm{layer}}} = 32.3 \pm 4.9\;{\mathrm{cm}}^{ - 1}$$, suggesting minor variations in strain and comparably few defects, hinting at potentially high charge carrier mobility.

### Field-effect graphene devices

We fabricated and evaluated top-gated field-effect devices on 100-mm-diameter silicon wafers using four photolithography layers and conventional processing technology (Fig. 3d, details see “Methods”). The extracted sheet resistance and charge carrier mobility as a function of the gate voltage of a typical device (Fig. 3d, left) show the expected characteristic behavior of gated graphene devices80 (see “Methods” for measurement details), where the mobility is zero at the Dirac point due to a zero of the transconductance. At this point, the charge carriers convert from electrons to holes or vice versa. In our measurements, the mobility is not exactly zero because of the limited number of data points. The maximum field-effect mobility of holes from 16 devices averages to $$2600 \pm 1300\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$ with values up to $$4520\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$. The mobilities are in the same range as for identical reference devices with the same type of graphene that were fabricated on top of both BCB and quartz substrates ($$2800 \pm 900$$ and $$1700 \pm 700\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$, respectively) using conventional wet transfer (see Supplementary information). These results indicate that (1) the graphene transfer by adhesive wafer bonding using BCB yields similar final graphene quality as conventional wet transfer and that (2) BCB as substrate material yields similar graphene properties as common dielectric substrates such as quartz. The mobilities of the field-effect graphene devices on BCB were comparable to the mobilities of the vdP devices shown in Fig. 2b, which were solely fabricated by noncontact processes to avoid potential material damage during device fabrication. This similarity suggests that the quality of the transferred graphene is preserved during device manufacturing with multiple processing steps such as high-temperature Al2O3 deposition, multiple lithographic layers, metal depositions, and etching processes. Consequently, these results suggest that our transfer methodology is compatible with large-scale manufacturing of graphene devices using conventional semiconductor process technologies.

### Transfer of MoS2 and MoS2/graphene heterostructures

Our proposed transfer methodology is generic and applicable to a broad spectrum of 2D materials available on various types of growth substrates. We demonstrated this versatility by transferring a multilayer of CVD MoS2 from a SiO2/Si growth substrate to a 100-mm-diameter silicon wafer (see “Methods” for parameters of film growth and transfer). First, we bonded the centimeter-sized MoS2/SiO2/Si substrate to a BCB-coated 100-mm-diameter target wafer. Next, we submerged the bonded stack in a potassium hydroxide (KOH) solution, which permeated into the MoS2/SiO2 interface and detached the MoS2 from its growth substrate. This process took tens of seconds, after which the MoS2 remained transferred on top of the BCB layer of the target wafer. The surface roughness of the transferred MoS2 (RMS: 1.9 nm; measurement area: 25 µm × 25 µm) remained low compared to the original surface roughness of the MoS2 on the growth substrate (RMS: 0.8 nm; measurement area: 5 µm × 5 µm). Typical Raman spectra prior transfer (Fig. 4a) exhibited the characteristic E12g and A1g modes of pristine MoS2 at 384.6 and 409.1 cm−1, respectively, which are in good agreement with reported values for MoS29,81,82,83. After transfer, we found the peaks at 384.7 cm−1 (E12g) and 407.2 cm−1 (A1g), that is, without detectable shifts in the position of the E12g mode within the accuracy of our Raman setup. Since the E12g mode is highly sensitive to uniaxial strain84, we conclude that the strain in the transferred MoS2 film was the same as present on the growth substrate and was not significantly affected by our transfer methodology. In contrast, the A1g mode is sensitive to changes in the substrate material, which could cause the observed shift of 1.8 cm−1 85,86. To further investigate the quality of the transferred MoS2 film, we compare the average of 25 normalized photoluminescence (PL) intensity spectra of pristine and transferred MoS2 (Fig. 4b). Before transfer, we found two prominent peaks at 1.821 and 1.968 eV, which correspond to A and B excitonic transitions, respectively87. After transfer, we observed a drastic increase in the A/B intensity ratio since the B-excitation vanishes. A high A/B intensity ratio indicates a high quality of the MoS2 film88. The A exciton transition energy is blue-shifted by 13 meV to 1.834 eV (see Supplementary Fig. 11 for statistics), which we attribute to the change of the substrate material from SiO2 (before transfer) to BCB (after transfer)86. The additional features of the PL intensity between 1.96 and 1.97 eV are Raman modes of the underlying BCB, and hence do not belong to the excitonic transitions in the MoS2 (see Supplementary information for the Raman spectrum of BCB). We formed MoS2/graphene heterostructures by stacking a centimeter-sized layer of MoS2 onto a sheet of graphene in two consecutive transfers (see “Methods”). The map of the graphene sheet resistance extracted from THz spectroscopy indicated the presence of graphene in both the MoS2/graphene heterostructure and its surroundings ($$1030 \pm 520$$ and $$1910 \pm 280\,{\Omega}\,{\mathrm{sq}}^{-1}$$, respectively). In the region of the MoS2/graphene heterostructure, Rsh is significantly reduced. Since the high sheet resistance of a sole MoS2 layer is not directly detectable in this measurement, we speculate that interactions between graphene and MoS2 caused this variation. Raman and PL spectroscopy of the MoS2/graphene heterostructure confirmed the presence and integrity of both materials (Fig. 4d and Supplementary information). The position of the 2D peak of graphene (ω2D) averaged to $$2681.9 \pm 1.8\;{\mathrm{cm}}^{ - 1}$$ with a full-width at half-maximum ($${\it{\Gamma}}_{2{\mathrm{D}},{{\mathrm{MoS}}_2}/{\mathrm{gr}}}$$) of $$30.3 \pm 3.9\;{\mathrm{cm}}^{ - 1}$$. This value is in good agreement with the results in Fig. 3, which hints at the integrity of the graphene even after stacking. The Raman E12g mode of MoS2 exhibited a minor shift from $$384.26 \pm 0.17$$ to $$385.16 \pm 0.35\;{\mathrm{cm}}^{ - 1}$$, while the position of the A1g mode remained unchanged ($$408.06 \pm 0.28\;{\mathrm{cm}}^{ - 1}$$) (see Supplementary information on material characterization prior to transfer). The averaged PL spectrum featured the distinct peaks of A and B excitonic transitions in MoS2 with high A/B ratio and superimposed Raman modes of BCB. We further demonstrated the versatility of the methodology by reversing the order of stacked materials, which formed graphene/MoS2 heterostructures by successfully transferring graphene onto previously transferred MoS2 layers (see Supplementary information). Taken together, the Raman and PL measurements confirm that the layer quality of MoS2 is preserved during the transfer and the stacking to heterostructures. Hence, our methodology is potentially suitable for large-area transfer of MoS2 films and their heterostructures.

## Discussion

We have demonstrated a generic methodology for transfer and large-area integration of 2D materials and their heterostructures on wafer level, which is compatible with conventional semiconductor fabrication lines. Our approach avoids manual handling of released layers and relies only on tools, processes, and materials that are already established in the semiconductor industry. To illustrate its applicability, we manufactured graphene devices on a 100-mm-diameter silicon, performed a statistical analysis of the material characteristics, and demonstrated that our transfer method is, in principle, compatible with the conventional process technology. THz near-field inspection confirmed the uniform coverage of graphene in large areas while the evaluation of vdP devices yielded a high charge carrier mobility of up to $$2800 \pm 100\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$, which is among the highest reported values for similar substrate sizes and graphene quality. As representatives for transition metal dichalcogenides, we demonstrated the transfer of MoS2. Raman and PL spectroscopy indicated little strain in both transferred graphene and MoS2. We fabricated top-gated field-effect graphene devices ($$\mu = 2600 \pm 1300\,{\mathrm{cm}}^2\,{\mathrm{V}}^{ - 1}\,{\mathrm{s}}^{ - 1}$$), which required multiple lithography steps in combination with conventional deposition and etching processes after the transfer. This result demonstrates that the proposed transfer process is compatible with large-scale device manufacturing without causing significant deterioration in the quality of the 2D material.

The transfer method replicates the surface topography of the growth substrate of the 2D material in an adhesive layer on the target wafer by molding at low viscosity of the adhesive. After removal of the growth substrate, the 2D material remains on the target wafer in the same shape as it was synthesized on the growth substrate. This feature minimizes defects or additional strain in the 2D material by avoiding deformation. In addition, it reduces wrinkles, which may result from excess material due to different surface topography of the growth substrate and the target wafer. We hypothesize that this feature contributes to preserving similar mechanical properties of the transferred 2D materials. The ability of the adhesive layer to mold repeatedly allows the stacking of 2D materials to heterostructures. In this case, merely the bottommost 2D material is in contact with the adhesive layer. This ensures that the other 2D materials and the interfaces between layers are not contaminated by polymer residuals. To demonstrate this capability, we fabricated graphene/hBN heterostructures, double-layer graphene, and MoS2/graphene heterostructures on large areas by consecutive transfers. In the resulting stacks, Raman, PL, and THz spectroscopy confirmed the uniform coverage and high quality of the graphene and MoS2 layers.

We anticipate that our transfer methodology is applicable to 2D materials in general, independent of the size and the type of growth substrate. Consequently, the barrier is comparatively low for the industry to consider this methodology for the integration of 2D materials on top of conventional IC and microsystem device substrates in the back end of the line. Hence, we expect that our methodology has the potential to accelerate advancements in fundamental 2D material science, as well as in a wide range of application areas, spanning over electronics, sensing, and photonics.

## Methods

### Transfer of graphene

First, a 2.5 µm-thick adhesive layer of BCB (Cyclotene 3022-46, Dow Inc.) was spin-coated at 5000 r.p.m. on the 100-mm target wafer. A softbake on a hot plate at 100 °C for 4 min removed solvents and solidified the adhesive layer. Next, the target wafer was brought in proximity to a 100-mm sheet of monolayer CVD graphene on copper foil (Graphenea Inc.) with the graphene facing the BCB layer. This stack was bonded in a commercial wafer bonder (SB8, SÜSS MicroTec SE) at 190 °C for 20 min using a bond force of 3 kN (bond pressure: 0.95 bar) in a nitrogen atmosphere. Etching the copper foil in FeCl3 solution and rinsing in deionized water for 30 min uncovered the graphene, transferred to the target wafer.

### Formation of graphene/hBN heterostructures

A 100-mm wafer was spin-coated with a 2.5-µm-thick layer of BCB (Cyclotene 3022-46, Dow Inc.; spinning speed: 5000 r.p.m., softbake: 100 °C for 4 min). A 2.5 cm × 2.5 cm sheet of multilayer hBN (thickness: 2–5 nm) synthesized by CVD on copper foil (2D Semiconductors Inc.) was placed on top of the target wafer (hBN facing the BCB layer) and bonded at 190 °C for 20 min at a bond force of 250 N (bond pressure: 4 bar) in a nitrogen atmosphere. Etching of the copper foil in FeCl3 and subsequent rinsing in deionized water for 30 min uncovered the hBN, transferred to the target wafer. To form a graphene/hBN heterostructure, a 100-mm sheet of CVD graphene on copper foil was placed on top of the target wafer and bonded at 190 °C for 20 min (bond force: 3 kN, bond pressure: 0.95 bar, vacuum atmosphere). Etching of the copper foil in FeCl3 and rinsing in deionized water for 30 min uncovered the graphene, which formed a graphene/hBN heterostructure with the previously transferred hBN.

### Formation of 2-layer graphene

A 2.5-µm-thick adhesive layer of BCB (Cyclotene 3022-46, Dow Inc.) was spin-coated at 5000 r.p.m. on the 100-mm target wafer. Softbake on a hot plate at 100 °C for 4 min removed solvents and solidified the adhesive layer. The target wafer was brought in proximity to a quarter of a 100 mm sheet of monolayer CVD graphene on copper foil (Graphenea Inc.) with the graphene facing the BCB layer. This stack was bonded in a commercial wafer bonder (Suss-SB8) at 190 °C for 20 min using a bond force of 600 N (bond pressure: 3.1 bar) in a nitrogen atmosphere. Etching of the copper foil in FeCl3 solution and rinsing in deionized water for 30 min uncovered the graphene, transferred to the target wafer. To form 2-layer graphene, a 100-mm sheet of CVD graphene on copper foil was placed on top of the target wafer and bonded at 190 °C for 20 min (bond force: 3 kN, bond pressure: 0.95 bar, vacuum atmosphere). Etching of the copper foil in FeCl3 and rinsing in deionized water for 30 min uncovered the graphene, which formed 2-layer graphene with the previously transferred layer. Note, the bond force was adapted to account for the difference in size of the growth substrates. To form reference areas for THz spectroscopy, the 100-mm copper foil was cut into two pieces and graphene was partially removed from one piece by etching in O2 plasma prior transfer. During transfer, both parts were placed side by side, covering the entire target wafer.

### Fabrication and evaluation of vdP devices

A graphene/hBN heterostructure was formed on an oxidized 100-mm silicon wafer (100 nm SiO2) (see above). Thermal evaporation of 20 nm Ti and 200 nm Au through a shadow mask formed electrodes (300 µm × 300 µm) on top of the transferred graphene layer. Ablation by a pulsed femtosecond laser electrically insulated individual vdP devices with an edge length of ~3 mm. These noncontact processes prevent potential material degradation by lithographic layers in contact with the graphene. For device characterization, the wafer was resting on an electromagnet (Wuxue Wen Fang Electric Co. Ltd, model WF-P25/20), which was placed inside a probe station (Cascade Microtech Inc.). Four-point probe measurements of the voltage across the device edge (device current: 100 µA), and the Hall voltage (device current: 1 mA at 1.28 ± 0.17 V; magnetic flux: 28.8 mT) yielded the sheet resistance, carrier density, and mobility of the transferred graphene. Electrical measurements were performed under ambient conditions at room temperature, using a parameter analyzer (Keithley SCS4200).

### Fabrication and evaluation of top-gated field-effect devices

Graphene-based top-gated field-effect devices were fabricated on a 100-mm silicon wafer. First, large-area graphene (10 cm × 10 cm) was transferred by adhesive wafer bonding (see above). Contacts to graphene were fabricated by sputter deposition of 25 nm Ni and e-beam evaporation of 135 nm Al, followed by a lift-off process in acetone (60 °C, 30 min) (1st photolithography layer). The graphene sheet was then patterned by etching in oxygen plasma (2nd photolithography layer)). As a top-gate dielectric, 40 nm Al2O3 was deposited by atomic layer deposition and top-gate electrodes were fabricated by e-beam evaporation of 10/150 nm Ti/Al (3rd photolithography layer). To access the graphene metal contacts under Al2O3, reactive ion etching with SF6 and O2 was used to open vias through the Al2O3 (4th photolithography layer). All resist layers were removed by immersion in acetone (60 °C, 30 min). In this process sequence, the first and second lithographic layers were in direct contact with the graphene, which may have degraded the graphene quality. However, encapsulation of the graphene before fabricating the contacts eliminates this potential source of degradation89. Electrical measurements were performed under ambient conditions at room temperature. The sheet resistance (Rsh) was measured by 4-probe vdP method with top gating. A current (I12) was forced between electrodes 1 and 2 (Fig. 3d), while the voltage drop between electrodes 3 and 4 (V34) was measured. The sheet resistance (Rsh) was calculated by90

$$R_{{\mathrm{sh}}} = \frac{{V_{34}}}{{I_{12}}}\frac{\pi }{{\ln 2}}$$
(1)

and the mobility (μ) was then derived by

$$\mu = \frac{1}{{C_{\mathrm{G}}}}\frac{{{\mathrm{d}}G_{{\mathrm{sh}}}}}{{{\mathrm{d}}V_{\mathrm{G}}}}$$
(2)

where

$$G_{{\mathrm{sh}}} = \frac{1}{{R_{{\mathrm{sh}}}}}$$
(3)

and VG and CG are the gate voltage and the capacitance of the dielectric per unit area (k = 7 for Al2O3), respectively.

### Raman spectroscopy of graphene

Raman measurements were conducted using a confocal Raman microscope (alpha 300R, WITec GmbH), equipped with a 532-nm laser, which was coupled to the microscope using a single-mode optical fiber. A power meter in the optical path determined the laser power (0.6 mW), which ensured a high reproducibility of the experiments. The laser power was chosen to stay in the noninvasive regime91. The microscope was connected to a 600 mm ultrahigh-throughput spectrometer (UHTS 600) using a photonic fiber. An 1800 g mm−1 grating was used for the dispersion and an EMCCD camera for the detection of the scattered light. To compensate the topography of the substrate, a ×50 objective with a NA of 0.5 was chosen for the measurements. Note that we have used a high-resolution 1800 g mm−1 grating in combination with the 600 mm spectrometer to obtain more intense signals with a pixel resolution of 0.1 cm−1 @ 2800 relative cm−1. For each measurement site, the spectra were acquired in areas of 25 µm × 25 µm with 25 single spectra per line and 25 lines per site (integration time: 3 s). Peak positions were extracted by a Lorentzian fit. To ensure the validity of the extracted values, only data with a peak intensity exceeding a threshold of ten counts and sufficient separation to the noise level were considered.

### THz near-field spectroscopy

We used THz-TDS in transmission mode to measure the sheet resistance of the transferred graphene on the target wafer. The samples were prepared on high-resistivity wafers with a resistivity of >104 Ω·cm, to avoid inadvertent absorption of the THz signal by the target wafer. For the measurements, we used a THz pump/probe setup equipped with a femtosecond fiber laser (generating pulses of 100 fs duration and 780 nm center wavelength) to pump a terahertz emitter and to gate a photoconductive near-field micro-probe detector (TeraSpike TD-800-X-HR-WT). By measuring the THz transmission through the sample, we extracted the local sheet resistance of the graphene71,72. Lateral scanning of the sample with the tip of the near-field detector held at close distance yielded a spatially resolved map of the graphene sheet resistance with a pixel size of a few hundred micrometer. See Supplementary information for a description of the setup and the estimation of the pixel size.

### Synthesis of MoS2 monolayers

The MoS2 films were grown in a CVD furnace with a 40 mm-diameter quartz tube as the reactor, similar to that described by Luo et al. 92. In short, the SiO2/Si growth substrates were located 12–15 cm downstream from the center of the heated tube (500 mm). MoS2 powder (Alfa Aeasar, 99% purity) was loaded into a quartz boat and placed in the center of the quartz tube of the furnace. The furnace was purged by forming gas (Ar 95%/H2 5%). For the growth, the furnace temperature was ramped up to 950 °C within 30 min, which was then maintained for 60 min. After the growth, the quartz tube was cooled down within 4 h. The growth yielded quasi-continuous films of MoS2 multilayers, with micrometer-sized domains.

### Transfer of MoS2

First, a 2.5-µm-thick adhesive layer of BCB (Cyclotene 3022-46, Dow Inc.) was spin-coated at 5000 r.p.m. on the 100-mm target wafer. A softbake on a hot plate at 100 °C for 4 min removed solvents and solidified the adhesive layer. Next, a multilayer of MoS2, grown on SiO2/Si chips (10 mm × 7 mm), was placed on top of the BCB layer (MoS2 facing the target wafer) and surrounded by silicon dummy chips of the same height to ensure a uniform force distribution during the bonding process. This stack was bonded at 190 °C for 20 min using a bond force of 400 N (bond pressure: 2 bar) in a nitrogen atmosphere, which attached the MoS2 layer on its growth substrate to the target wafer. Etching in O2/SF6 plasma cleaned the edges of the growth substrate from potential BCB residuals. Submersion of the bonded stack in KOH solution detached the growth substrate from the MoS2 layer by permeation of KOH into the MoS2/substrate interface within tens of seconds. The MoS2 layer remained transferred on the target wafer.

### Formation of MoS2/graphene heterostructures

First, the silicon target wafer (diameter: 100 mm; resistivity: >104 Ω·cm) was spin-coated with a 2.5 µm-thick BCB layer (Cyclotene 3022-46, Dow Inc., spinning speed: 5000 r.p.m.; softbake: 100 °C for 4 min). A quarter of a 100-mm sheet of monolayer CVD graphene on copper foil (Graphenea Inc.) was bonded to the target wafer with the graphene facing the BCB layer (bond temperature: 190 °C; bond time: 30 min; bond force: 600 N with a resulting bond pressure of 3.1 bar, nitrogen atmosphere). Etching of the copper foil and rinsing in deionized water for 30 min uncovered the transferred graphene on top of the BCB on the target wafer. Next, a multilayer of MoS2 on a SiO2/Si chip (10 mm × 10 mm) was placed on top of the transferred graphene (MoS2 facing the graphene) and surrounded by silicon dummy chips to ensure a uniform force distribution over the wafer during the following bonding process. Bonding at 190 °C for 30 min attached the MoS2/SiO2/Si chip to the target wafer (bond force: 750 N with a resulting bond pressure of 3 bar, vacuum atmosphere). Etching in O2/SF6 plasma cleaned the edges of the chip while a resist mask protected the remaining surface of the target wafer. Submersion of the bonded stack in acetone stripped the resist mask and detached the growth substrate, leaving the MoS2 film transferred on top of the graphene, forming a MoS2/graphene heterostructure.

### Raman and PL measurements of MoS2 films

Raman and PL measurements were carried out in a confocal Raman system (alpha 300, WITec GmbH) in ambient conditions. For all measurements, an excitation laser with a wavelength of 532 nm and a 100× objective was used. For Raman measurements, the excitation power was 1 mW (1800 g mm−1 grating), which achieves a spectral resolution of about 1.2 cm−1. For PL measurements, the excitation power was 0.2 mW (600 g mm−1 grating).

## Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## Code availability

The code that supports the findings of this study is available from the corresponding author upon request.

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## Acknowledgements

This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 825272 (ULISSES—www.ulisses-project.eu), the European Research Council through the Starting Grant M&M’s (No. 277879), Graphene Flagship (785219, 881603), VINNOVA (2017-05108), VR (2015-05112), the Swedish Foundation for Strategic Research (SSF) (GMT14-0071), the German Ministry for Education and Research (BMBF, GIMMIK 03XP0210), the German Ministry for Economic Affairs and Energy (BMWi) and the European Social Fund in Germany (AachenCarbon, FKZ: 03EFLNW199), and the China Scholarship Council (CSC) through a scholarship grant. We thank Daniel Neumaier of AMO GmbH, Aachen for fruitful discussions. Graphene Flagship 2D Experimental Pilot Line (Acronym: 2D-EPL), Grant no. 952792.

## Funding

Open Access funding provided by KTH Royal Institute of Technology.

## Author information

Authors

### Contributions

A.Q., X.W., K.B.G., N.R., G.S. and F.N. conceptualized the methodology. A.Q. performed significant part of the wafer bonding experiments, part of the white-light interferometric measurements, the entire fabrication and evaluation of the vdP devices, SEM inspection, X.W. performed part the wafer bonding experiments and white-light interferometric measurements. S.W. performed and A.Q. evaluated the Raman measurements of graphene/hBN heterostructures, 1-layer graphene and 2-layer graphene. S.S. performed and evaluated the THz spectroscopy and A.Q. analyzed the data statistically. B.U. and Z.W. designed, fabricated, and characterized top-gated field-effect devices from transferred graphene by A.Q. (bonding) and M.O. (wet transfer). S.L. synthesized the MoS2, M.P. and O.H. performed all related Raman and PL measurements. M.P., O.H. and G.S.D. analyzed the spectroscopic measurements of MoS2. M.L., K.B.G., N.R., G.S. and F.N. supervised the project. All authors contributed to drafting and revising the manuscript.

### Corresponding authors

Correspondence to Arne Quellmalz or Frank Niklaus.

## Ethics declarations

### Competing interests

A.Q., X.W., K.B.G., N.R., G.S., and F.N. are co-inventors on a patent application describing a method for 2D material transfer (PCT/EP2020/051831). The other authors have no competing interests.

Peer review information Nature Communications thanks David Mackenzie and the other, anonymous reviewer(s) for their contribution to the peer review of this work. Peer review reports are available.

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Quellmalz, A., Wang, X., Sawallich, S. et al. Large-area integration of two-dimensional materials and their heterostructures by wafer bonding. Nat Commun 12, 917 (2021). https://doi.org/10.1038/s41467-021-21136-0

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