CN109585615B - Method for stripping a gallium nitride epitaxial layer from a substrate - Google Patents

Abstract

The present disclosure relates to a method for stripping a gallium nitride epitaxial layer from a substrate, the method comprising: growing a gallium nitride epitaxial layer on a patterned sapphire substrate by MOCVD or MBE deposition; A support sheet larger than the area of the gallium nitride epitaxial layer is adhered to the upper surface of the gallium nitride epitaxial layer through an adhesive and cured; stressing the interface between the gallium nitride epitaxial layers and the support sheet as a whole to peel off the patterned sapphire substrate; and by applying the stress to the interface between the gallium nitride epitaxial layer and the support sheet The adhesive is heated so that the adhesive melts and separates the gallium nitride epitaxial layer from the support sheet.

Description

Method for stripping a gallium nitride epitaxial layer from a substrate

technical field

The present disclosure relates to a semiconductor component and a manufacturing method thereof, and in particular, to a method for stripping an epitaxial layer of gallium nitride.

Background technique

With the wide application of GaN materials in LED devices, it is expected that a larger area of GaN wafers can be obtained in one epitaxial process. However, the process of separating the large-area wafer on the substrate will cause partial damage to the wafer, which will result in a relatively high defect rate in the subsequent cutting process of the wafer. Therefore, it is desirable to provide a method for smoothly separating the device wafer and the substrate without damaging the device wafer as much as possible.

SUMMARY OF THE INVENTION

The present disclosure aims to solve the above and/or other technical problems and to provide a method for stripping a gallium nitride epitaxial layer from a substrate, the method comprising: depositing by MOCVD or MBE on a patterned sapphire substrate growing a gallium nitride epitaxial layer; adhering a support sheet with an area equal to or greater than the area of the gallium nitride epitaxial layer on the upper surface of the gallium nitride epitaxial layer through an adhesive; stressing the interface between the layer and the patterned sapphire substrate so that the gallium nitride epitaxial layer and the support sheet are integrally peeled off from the patterned sapphire substrate; and by applying stress to the gallium nitride epitaxial layer and the support sheet The adhesive at the interface therebetween is heated so that the adhesive melts and separates the gallium nitride epitaxial layer from the support sheet.

The method for peeling a gallium nitride epitaxial layer from a substrate according to the present disclosure further comprises: prior to adhering a support sheet to the upper surface of the gallium nitride epitaxial layer through an adhesive, chemically- The gallium nitride epitaxial layer is thinned by a mechanical polishing method (CMP) to obtain a gallium nitride epitaxial layer with a predetermined thickness.

A method for stripping a gallium nitride epitaxial layer from a substrate according to the present disclosure, further comprising: by applying horizontal lateral physical stress to a side of an interface between the gallium nitride epitaxial layer and the patterned sapphire substrate separate the two.

The method for peeling the gallium nitride epitaxial layer from the substrate according to the present disclosure further comprises: by aligning the gallium nitride epitaxial layer with the patterned sapphire substrate from one side of the patterned sapphire substrate The interface is laser irradiated to separate the two.

A method for peeling a gallium nitride epitaxial layer from a substrate according to the present disclosure, wherein the supporting sheet having an area equal to or greater than that of the gallium nitride epitaxial layer is adhered to the nitrogen by an adhesive The upper surface step of the gallium nitride epitaxial layer includes: coating the upper surface of the gallium nitride epitaxial layer with a layer of wax or low melting point metal in a molten state; attaching a support sheet to the wax layer or the low melting point metal layer ; Place the gallium nitride epitaxial layer, the support sheet and the wax layer or the low melting point metal layer in an inert gas environment and keep it at a temperature at which the wax layer or the low melting point metal layer is in a molten state for 3-10 minutes; As well as reducing the ambient temperature, the wax layer or the low melting point metal layer solidifies.

A method for peeling a gallium nitride epitaxial layer from a substrate according to the present disclosure, wherein the heating of the adhesive at the interface between the gallium nitride epitaxial layer and the support sheet is performed by directly applying The gallium nitride epitaxial layer and the support sheet are placed on a hot plate for heating. .

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the disclosure and together with the description serve to explain the principles of the disclosure.

1 is a schematic cross-sectional view of an assembly containing a gallium nitride epitaxial layer to be separated according to an embodiment of the present disclosure;

2 is a scanning electron micrograph of an assembly containing a gallium nitride epitaxial layer to be separated according to the present disclosure;

3 is a schematic diagram illustrating the overall separation of an assembly containing a gallium nitride epitaxial layer to be separated from a substrate according to the present disclosure.

4 is a schematic diagram illustrating a separation support sheet in an assembly containing a gallium nitride epitaxial layer to be separated according to the present disclosure.

Detailed ways

Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. Where the following description refers to the drawings, the same numerals in different drawings refer to the same or similar elements unless otherwise indicated. The implementations described in the illustrative examples below are not intended to represent all implementations consistent with this disclosure. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present disclosure as recited in the appended claims.

The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. As used in this disclosure and the appended claims, the singular forms "a," "the," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will also be understood that the term "and/or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

It should be understood that although terms such as "parallel" or "perpendicular" are used in the present disclosure, it does not mean that the two are completely theoretically parallel or perpendicular, but a parallel relationship within a reasonable range (for example, the angle between the two is within 10 millidegrees) or vertical relationship (for example, the angle between the two is within 10 millidegrees of 90 degrees). When referring to the drawings in the following detailed description, the spatial labels "top," "bottom," "upper," "lower," "vertical," "horizontal," etc. may be used. For example, when referring to the figures, "vertical" may be used to refer to a direction perpendicular to the surface of the substrate, and "horizontal" may be used to refer to a direction parallel to the surface of the substrate. "Top," "top," or "above" may be used to refer to the vertical direction away from the substrate, while "lower," "bottom," or "below" may be used to refer to the vertical direction toward the substrate. Such references are for teaching purposes and are not intended to be absolute references to embodied devices. The embodied device may be spatially oriented in any suitable manner, which may differ from the orientation shown in the figures. The word "if" as used herein can be interpreted as "at the time of" or "when" or "in response to determining" depending on the context.

In order for those skilled in the art to better understand the present disclosure, the present disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1 , an epitaxial layer 120 is grown on a patterned sapphire substrate 110 having an array of trenches and stripes patterned across the surface of the sapphire substrate 110 . The trapezoidal fringe array includes a plurality of generally flat surfaces, at least some of which are covered by a mask material (not shown) that prevents crystal growth from sapphire. The surfaces of the groove and stripe arrays can be oriented in different directions. The crystal growth surface may be approximately parallel to the c-plane facets of the sapphire according to some embodiments. The gallium nitride semiconductor may continue to grow from the crystal growth surface 115 at different locations until the separated gallium nitride blocks merge on the patterned features on the sapphire substrate to form a continuous first gallium nitride epitaxial layer 120, as shown in FIG. 1 shown. The gallium nitride semiconductor may extend partially or fully across the sapphire substrate and form a "flat" "surface to be machined" on the substrate 110 on which epitaxial growth may continue to obtain integrated devices.

The trapezoidal stripes of the patterned sapphire substrate 110 are formed by etching in a conventional manner. For example, a patterned resist (eg, a soft resist, a polymer resist, or eg a hard resist, a patterned inorganic material) is formed on top of the patterned sapphire substrate 110 in alignment with the crystallographic orientation of the sapphire substrate. The PSS substrate 110 used in the present disclosure may be a patterned sapphire substrate 110 as disclosed in Chinese Patent Publication No. CN106233429A, and after the pattern is etched, the resist is removed. For good crystal growth, select surfaces of the sapphire substrate may be masked with a high temperature conformal coating (not shown) formed by pass-through deposition of silicon dioxide or silicon nitride by CVD or PECVD. A high temperature conformal coating of typically about 10 nm to about 50 nm may be formed on selected surfaces of the patterned sapphire substrate 110 . Then, a resist layer (not shown) is formed on the high temperature conformal coating by photolithography or shadow evaporation by means of shadowing, so as to form a resist layer on the high temperature conformal coating except for the c-plane surface. etch layer. Subsequently, by selective anisotropic dry etching, the high temperature conformal coating at the surface not shielded by the resist is etched away, exposing the crystal growth surface of the sapphire substrate. The etchant is subsequently removed from other locations. Thus, only the crystal growth surface is exposed and the other parts are covered by the high temperature conformal coating of the PSS substrate. The fabrication of the PSS substrate used in the present disclosure is a prior art, and thus will not be described in detail here.

After the PSS substrate as described above is prepared, the first gallium nitride epitaxial layer 120 may be performed using MOCVD. The temperature in the reaction chamber may be ramped to a higher temperature to anneal the buffer layer for a period of time before the growth of the first gallium nitride epitaxial layer 120 begins. In some embodiments, the temperature may be increased to a value between about 1000°C and about 1100°C. The annealing time may be from about 1 minute to about 10 minutes. In some cases, the temperature can be increased to a value between 1000°C and 1100°C, and the annealing time can be from about 1 minute to about 10 minutes.

Subsequently, epitaxial growth of the first gallium nitride epitaxial layer 120 is performed using metal organic chemical vapor deposition (MOVCD). In some embodiments, molecular beam epitaxy (MBE) methods, vapor phase epitaxy (VPE) methods, or atomic layer deposition may be used. The growth of the first gallium nitride epitaxial layer 120 may be performed at a temperature of about 1000°C to about 1100°C, for example, may be performed at a temperature of about 1030°C. During growth of the first gallium nitride epitaxial layer 120, the chamber pressure may be maintained at about 100 mbar to about 250 mbar. The flow rate of the parent material _NH3 may be about 1 slm to about 4 slm, and the flow rate of the parent material trimethylgallium (TMGa) may be about 30 seem to about 50 seem.

In order to reduce the number of defects on the surface of the first gallium nitride epitaxial layer 120 . One typically prepares a buffer layer on the exposed crystal surface to form integrated circuit grade GaN before growing the first gallium nitride epitaxial layer 120 on the PSS substrate 110 . According to some embodiments, the PSS substrate 110 can grow a GaN or AlN buffer layer at a low temperature after cleaning, eg, below about 600°C. The cleaning process is carried out in a conventional manner. The specific process of the buffer layer is not repeated here, and can be performed with reference to the prior art. It should be noted that the buffer layer is not an essential constituent element of the present disclosure.

Subsequently, the growth of the III-nitride material is continued on the flat surface of the first gallium nitride epitaxial layer 120 to epitaxially grow a second gallium nitride epitaxial layer (not shown). In order to facilitate subsequent processes, the second gallium nitride epitaxial layer is grown by a hydride vapor phase epitaxy (HVPE) method, so that a thicker second gallium nitride epitaxial layer can be grown better and faster. HVPE equipment has the advantages of simple equipment and fast growth rate (up to 700-800 μm/h), and can grow uniform and large-sized GaN thick films (dislocation density is only 10 ⁴ /cm ² ). The present disclosure employs conventional hydride vapor phase epitaxy (HVPE) methods for growth. Since the second gallium nitride epitaxial layer is continued to grow on the first gallium nitride epitaxial layer 120, cracks during the thickness increase process of the conventional hydride vapor phase epitaxy (HVPE) method rarely occur. The thickness of the second gallium nitride epitaxial layer grown by a hydride vapor phase epitaxy (HVPE) method is not less than 100 microns. However, in order to facilitate the processing in subsequent steps, the thickness of the second gallium nitride epitaxial layer 130 is not less than 200 microns. Alternatively, the thickness of the second gallium nitride epitaxial layer is not less than 500 microns. Alternatively, the thickness of the second gallium nitride epitaxial layer may be 1 mm or even thicker.

Optionally, in order to improve the growth environment of the second gallium nitride epitaxial layer, the surface of the first gallium nitride epitaxial layer 120 may be planarized before the second gallium nitride epitaxial layer 130 is grown, so as to obtain favorable conditions for the first gallium nitride epitaxial layer 130 to grow. GaN epitaxial layer growth surface. For example, chemical-mechanical polishing (CMP) may be used to planarize the surface of the epitaxial first gallium nitride epitaxial layer 120 layer. The planarization may remove about 10% to 20% of the first gallium nitride epitaxial layer 120 . For example, the first gallium nitride epitaxial layer 120 may be grown to a thickness of 30 microns and removed using chemical-mechanical polishing (CMP) of about 3 microns to about 6 microns. In a sense, the first gallium nitride epitaxial layer 120 may be a sacrificial layer of the components of the present disclosure. Therefore, the thickness of the first gallium nitride epitaxial layer 120 may be less than 10 microns. In order to reduce the generation of surface errors due to extensive removal, therefore, extensive polishing removal is not required here to avoid potential subsurface damage caused by the polishing process. Experimental evidence indicates that for typical CMP processes, the depth of polishing damage in GaN ranges from below about 1.5 μm to about 2.6 μm. Thus, according to some embodiments, an initial epilayer thickness of about 30 microns and a CMP removal of about 3 microns to about 6 microns may provide suitable material quality on machined surfaces of GaN.

After obtaining the first gallium nitride epitaxial layer 120 or the second gallium nitride epitaxial layer (in the case of the second gallium nitride epitaxial layer), the outer surface of the gallium nitride epitaxial layer is coated with wax or low-temperature wax in a molten state melting point metal. The melting point of this wax or low melting point metal is usually between 60°C and 90°C. The coating process is carried out in a nitrogen environment, and the temperature is kept slightly higher than the melting point of wax or low melting point metal by about 5-10°C, so that its viscosity coefficient will not be too low to flow and cannot be coated, such as 100-200mPa between. When the upper surface of the first gallium nitride epitaxial layer 120 is fully coated with the adhesive layer 126, the surfaces of the support sheet 130 and the adhesive layer 126 are provided with a certain amount on the opposite side of the support sheet 130 to the adhesive layer 126. The temperature and pressure cause the support sheet to be bonded to the device wafer 120 through the adhesive layer. The thermal expansion coefficient of the material of the support sheet 130 is preferably close to that of the first gallium nitride epitaxial layer 120 to avoid adverse mechanical effects due to different thermal expansion coefficients between the two materials bonded to each other. In some cases, glass is advantageous for transmitting the laser light during the subsequent laser melting lift-off process. The support sheet can also be a metal material or a dielectric material or a semiconductor material, for example, the same semiconductor material as the first gallium nitride epitaxial layer 120 .

For bonding, after the support sheet 130 , the adhesive layer 126 and the first gallium nitride epitaxial layer 120 form an assembly, temperature and pressure need to be applied. The bonding temperature can be lowered below the tolerance of the adhesive 126, eg, between 50°C and 60°C, and the pressure can be between 0.18MPA and 0.20MPA. The duration of the bonding treatment is 5-9 minutes. During the bonding process, the assembly can be placed in a nitrogen atmosphere. It can also be placed in an air environment. Subsequently, the composite body is cooled, and the shear strength of the adhesive layer 126 in the composite body in the cooled state is above 30 MPa.

In general, the step of adhering a support sheet 130 with an area equal to or greater than the area of the first gallium nitride epitaxial layer 120 on the upper surface of the first gallium nitride epitaxial layer 120 through adhesive 126 includes: Coat the upper surface of the first gallium nitride epitaxial layer 120 with a layer of wax or low melting point metal in a molten state; attach the support sheet 130 to the wax layer or the low melting point metal layer 126; The first-mentioned gallium nitride epitaxial layer 120, the support sheet 130, and the wax layer or the low melting point metal layer 126 are placed in an inert gas atmosphere and kept at a temperature such that the wax layer or the low melting point metal layer is in a molten state for 3-10 minutes; and lowering the ambient temperature to allow the wax layer or low melting point metal layer to solidify.

2 is a scanning electron micrograph of an assembly comprising a first gallium nitride epitaxial layer 120, a support sheet 130, and an adhesive layer 126 formed on a PSS substrate in accordance with embodiments of the present disclosure. As shown in FIG. 2 , which clearly shows the first gallium nitride epitaxial layer 120 grown on the PSS substrate 110 . The first gallium nitride epitaxial layer 120 is coated with an adhesive layer 126 . The support sheet 130 is adhered to the upper surface of the adhesive layer 126 .

3 is a schematic diagram illustrating a process for peeling an assembly containing a gallium nitride epitaxial layer from a PSS substrate in accordance with an embodiment of the present disclosure. As shown in FIG. 3 , the assembly including the first gallium nitride epitaxial layer 120 is peeled off from the PSS substrate 110 . The peeling process can adopt laser irradiation, cavity-assisted physical peeling, and thermal stress peeling. Specifically, a laser is used to irradiate the connection interface between the first gallium nitride epitaxial layer 120 and the PSS substrate 110 from the lower part of the PSS to melt the connection interface between the two at a high temperature, so that the first gallium nitride epitaxial layer 120 and the PSS substrate 110 are formed. separation. Alternatively, as shown in FIG. 1 , during the growth process of the first gallium nitride epitaxial layer 120 , a cavity will be formed between the first gallium nitride epitaxial layer 120 and the PSS substrate 110 . The connection between the gallium epitaxial layer 120 and the PSS substrate 110 is fragile due to these cavities, and it is only necessary to apply a certain physical force along the junction of the first gallium nitride epitaxial layer 120 and the PSS substrate 110, that is, the The first gallium nitride epitaxial layer 120 is glassed off from the PSS substrate 110 . Alternatively, a certain thermal stress may be applied between the first gallium nitride epitaxial layer 120 and the PSS substrate 110 to separate the two.

Alternatively, chemical-mechanical polishing (CMP) may be used to grind the lower surface of the first gallium nitride epitaxial layer 120 to form a flat lower surface. Due to the presence of the support sheet, the first gallium nitride epitaxial layer 120 will not be damaged during the grinding process.

4 is a schematic diagram of a process for peeling an assembly containing a gallium nitride epitaxial layer from a PSS substrate in accordance with an embodiment of the present disclosure.

Specifically, since the melting point of the bonding wax is relatively low, the combination of the gallium nitride epitaxial layer 120 , the bonding layer 126 and the support sheet 130 can be directly placed in high-temperature hot water, or sprayed with high-temperature steam. Drain, the three will naturally separate. Alternatively, the external force can be directly applied from the side of the support sheet 130, so that the shear strength generated by the external force between the contact surface of the adhesive layer 126 and the support sheet 130 is greater than the shear strength, such as 35-40MPa, so that the The support sheet 130 is separated from the gallium nitride epitaxial layer 120 . Alternatively, when the supporting sheet 130 is made of transparent glass or has the same material as the gallium nitride epitaxial layer 120, the adhesive layer 126 can be heated by irradiating the adhesive layer 126 with laser light from the side of the supporting sheet 130 opposite to the adhesive layer 126. It is melted, thereby separating the support sheet 130 from the gallium nitride epitaxial layer 120 . Alternatively, the outer surface of the support sheet 130 in the combination of the gallium nitride epitaxial layer 120 , the bonding layer 126 and the support sheet 130 may be placed on a hot plate having a temperature above the melting point of the bonding layer 126 On the above, the assembly is heated from the side of the support sheet 130 , so that the adhesive layer 126 is melted and flows out, thereby separating the support sheet 130 from the gallium nitride epitaxial layer 120 .

As the wax or low melting point metal to be used, commercially available lamination wax or the like can be used. The melting point of these waxes is usually between 60-90°C. These waxes are suitable for bonding various materials such as glass, hard plastics, brass, silicon wafers, quartz crystals and metals, and do not require special preparation of the workpiece surface. In addition, the gallium nitride epitaxial layer 120 can also be firmly bonded during the grinding or polishing process, and is widely used for fixing thin components, such as adhering semiconductor crystals or crystal blanks. Because the adhesive wax 126 has good thermoplastic adhesion and the formed working layer is thin, it can ensure that the gallium nitride epitaxial layer 120 will not be twisted and deformed, and maintain the flatness of the gallium nitride epitaxial layer 120, and the selected melting point is relatively low, such as 65° C. In the case of the same wax, the material structure of the gallium nitride epitaxial layer 120 will not be affected during bonding or separation.

After the support sheet 130 is separated from the gallium nitride epitaxial layer 120 , cleaning is convenient because of its low melting point and water solubility. It can be cleaned with plasma water and leaves no residue on the wafer surface.

The process of separating the (2021) GaN epitaxial wafer from the substrate is described above through specific embodiments. The technical solutions described herein can be implemented as methods, of which at least one embodiment has been provided. The actions performed as part of the method may be sequenced in any suitable manner. Accordingly, embodiments may be constructed in which acts are performed in an order different from that shown, which may include performing some acts concurrently, even though the acts are shown as sequential acts in an illustrative embodiment. Furthermore, methods may include more acts than those shown in some embodiments, and fewer acts than those shown in other embodiments.

Although the figures generally show small portions of epitaxially grown GaN layers, it should be understood that large areas or entire substrates may be covered with such epitaxially grown layers. In addition, integrated circuit devices (eg, transistors, diodes, thyristors, light emitting diodes, laser diodes, photodiodes, etc.) can be fabricated using epitaxially grown materials. In some embodiments, integrated circuit devices may be used in consumer electronic devices such as smartphones, tablets, PDAs, computers, televisions, sensors, lighting, displays, and application specific integrated circuits.

Although at least one illustrative embodiment of the invention has been described herein, various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be within the spirit and scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only by the following claims and their equivalents.

Claims (6)

1. A method for stripping a gallium nitride epitaxial layer from a substrate, the method comprising: A first gallium nitride epitaxial layer is grown on the patterned sapphire substrate by MOCVD or MBE deposition and a cavity is formed between the first gallium nitride epitaxial layer and the patterned sapphire substrate, and a first nitride A second gallium nitride epitaxial layer is grown on the upper surface of the gallium epitaxial layer; Adhering a support sheet with an area equal to or greater than that of the second gallium nitride epitaxial layer on the upper surface of the gallium nitride epitaxial layer through an adhesive and performing curing treatment; The first and second gallium nitride epitaxial layers and the support sheet are integrally removed from the patterned sapphire by applying horizontal lateral physical stress to the sides of the interface between the first gallium nitride epitaxial layer and the patterned sapphire substrate peel off the substrate; and By heating the adhesive at the interface between the second gallium nitride epitaxial layer and the support sheet, the adhesive is melted and the second gallium nitride epitaxial layer is separated from the support sheet . 2. The method for stripping a gallium nitride epitaxial layer from a substrate according to claim 1, further comprising: Before the support sheet is adhered to the upper surface of the second gallium nitride epitaxial layer by an adhesive, the second gallium nitride epitaxial layer is thinned by chemical-mechanical polishing method to obtain a predetermined thickness of nitrogen Gallium oxide epitaxial layer. 3. The method for peeling a gallium nitride epitaxial layer from a substrate according to claim 1, wherein said through-bonding a support sheet having an area equal to or greater than that of the second gallium nitride epitaxial layer The step of adhering the agent on the upper surface of the second gallium nitride epitaxial layer includes: Coat the upper surface of the second gallium nitride epitaxial layer with a layer of wax or low melting point metal in a molten state; attaching the support sheet to the wax layer or the low melting point metal layer; The first and second gallium nitride epitaxial layers, the support sheet and the wax layer or low melting point metal layer are placed in an inert gas atmosphere and maintained at a temperature such that the wax layer or low melting point metal layer is in a molten state 3 -10 minutes; and The ambient temperature is lowered to allow the wax layer or low melting point metal layer to cure. 4. The method for stripping a gallium nitride epitaxial layer from a substrate according to claim 1, wherein the said application to the interface between the second gallium nitride epitaxial layer and the support sheet Adhesive heating is performed by directly placing the first and second gallium nitride epitaxial layers and the support sheet on a hot plate. 5. The method for stripping a gallium nitride epitaxial layer from a substrate according to any one of claims 1-4, wherein the curing process is performed in a nitrogen atmosphere. 6. The method for stripping a gallium nitride epitaxial layer from a substrate according to claim 5, wherein the adhesive has a melting point of 60°C-90°C.

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