TWI462153B - Separation method of epitaxial substrate - Google Patents

Description

Separation method of epitaxial substrate

The present invention relates to a separation method, and more particularly to a method for separating an epitaxial substrate.

The blue/green light emitting diode (LED) is based on the sapphire epitaxial substrate used for the purpose of heat dissipation, and the related artisan skilled in the art uses wafer bonding technology (wafer). Bonding, in which a gallium nitride (GaN) epitaxial film layer structure of a light-emitting diode element is bonded to a heat dissipation substrate (or a conductive substrate) in advance, and further using a laser lift-off method (laser lift-off) ) to crack the buffer layer between the GaN epitaxial film layer structure and the sapphire epitaxial substrate, so that the gallium nitride epitaxial film layer structure is removed from the sapphire epitaxial substrate to solve the problem of poor heat dissipation, or even A light-emitting diode of a vertical feedthrough is produced.

With the development and evolution of the epitaxial substrate separation technology, those skilled in the art are quite time consuming in manufacturing and the equipment cost is high in view of the laser stripping method; therefore, those skilled in the art are familiar with the epitaxial substrate. Separation and other related technologies have developed wet etching in the past five years to replace the aforementioned laser lift-off method. It mainly utilizes the concept of selective etching, using a wet etchant to remove a sacrificial layer connected between the sapphire epitaxial substrate and the GaN epitaxial film layer structure. The sacrificial layer is usually zinc oxide (ZnO), yttrium oxide (SiO ₂ ), or aluminum indium gallium nitride (Al _x In _y Ga _1-xy N, 0≦x, y≦1). For the techniques of separating the sapphire epitaxial substrate by the above wet etching method, reference may be made to the technical contents disclosed in the invention patents such as TWI355099, TW200945416, TW201025673, and TW201201269.

Although the above wet etching method can replace the laser lift-off method to solve the heat dissipation problem often plagued by the related art in the field of light-emitting diodes, a vertical-conducting light-emitting diode structure can be obtained. However, the overall luminous efficiency of the light-emitting diode still depends on the epitaxial quality of the gallium nitride (GaN) epitaxial film layer structure during the epitaxial process. In other words, once the gallium nitride (GaN) epitaxial film layer structure has excellent epitaxial quality, the light-emitting diode has excellent internal quantum efficiency to improve its luminous efficiency. It is well known to those skilled in the art that if a wet etching method is to be used to solve the heat dissipation problem or even a vertical-conducting light-emitting diode is required, the epitaxial substrate and the gallium nitride (GaN) epitaxial film must be used. The sacrificial layer is formed (or stretched) between the layer structures. However, the material selection of the sacrificial layer often determines the quality of the gallium nitride (GaN) epitaxial film layer structure that is deposited thereon. Therefore, those skilled in the art of solving the heat dissipation problem by the wet etching method or even the vertical conduction light-emitting diodes know that once the material selected for the sacrificial layer is unfavorable for the upper (GaN) epitaxy When the epitaxial quality of the film structure is concerned, the relevant technicians must appropriately sacrifice part of the epitaxial quality under consideration of time and equipment cost.

According to the above description, it is a problem to be solved by those skilled in the art that the epitaxial quality of the gallium nitride (GaN) epitaxial film layer structure can be preserved while saving time and equipment cost.

Accordingly, it is an object of the present invention to provide a method of separating an epitaxial substrate.

Therefore, the method for separating an epitaxial substrate of the present invention comprises the steps of: (a) depositing a buffer layer composed of strontium oxide (Sc ₂ O ₃ ) on an epitaxial substrate; (b) After the step (a), an epitaxial film layer structure is formed on the buffer layer, and the epitaxial film layer structure is composed of a material mainly composed of gallium nitride; (c) in the step (b) Thereafter, a heat dissipation substrate is attached to the epitaxial film layer structure; and (d) after the step (c), the buffer layer is used as a sacrificial layer, and the sacrificial layer is removed by a wet etchant to The epitaxial film layer structure is separated from the epitaxial substrate, and the wet etchant is an acid agent selected from the group consisting of nitric acid (HNO ₃ ), hydrochloric acid (HCl), hydrofluoric acid. (HF), and a mixture of the foregoing acid agents.

The effect of the invention is that: Sc ₂ O _{3 is} used as a buffer layer when the epitaxial film layer structure (GaN) is formed, on the one hand, the epitaxial quality of the epitaxial film layer structure (GaN) can be improved, on the other hand, Sc ₂ O _{3 is} also used as a sacrificial layer when separating the epitaxial substrate, which is advantageous for saving time cost and equipment cost in the process.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention.

Before the present invention is described in detail, it is to be noted that In the description, similar elements are denoted by the same reference numerals.

Referring to FIG. 1 , a first preferred embodiment of the method for separating an epitaxial substrate of the present invention comprises the steps of: (a) depositing a buffer layer 3 composed of yttrium oxide on an epitaxial substrate 2; After the step (a), an epitaxial film layer structure 4 is formed on the buffer layer 3, and the epitaxial film layer structure 4 is composed of a material mainly composed of gallium nitride (GaN); After the step (b), a heat dissipation substrate 5 is bonded to the epitaxial film layer structure 4; and (d) after the step (c), the buffer layer 3 is used as a sacrificial layer, and a The wet etchant 6 removes the sacrificial layer (ie, the buffer layer 3) to separate the epitaxial film layer structure 4 from the epitaxial substrate 2, and the wet etchant is a group selected from the group consisting of Acid agent: nitric acid, hydrochloric acid, hydrofluoric acid, and a mixture of the foregoing acid agents.

The epitaxial substrate 2 suitable for the step (a) of the first preferred embodiment of the present invention is a group selected from the group consisting of <111> single crystal germanium (Si), heterogeneous epitaxy in <111> single <111> yttrium oxide (Y ₂ O ₃ ) on the wafer, and <0001> gallium nitride on the <0001> sapphire. Preferably, the buffer layer 3 of the step (a) is formed on the epitaxial substrate 2 in the <111>direction; and the epitaxial film layer structure 4 based on the gallium nitride in the step (b) is The <0001> direction is projected on the buffer layer 3.

Preferably, the step (d) is carried out at an operating temperature of between 25 ° C and 65 ° C; in addition, in the first preferred embodiment of the invention, the wet etching Engraving agent 6 is a mixture of nitric acid and hydrofluoric acid. The nitric acid is between 40 vol% and 60 vol% and the hydrofluoric acid is between 40 vol% and 60 vol%, based on the volume percentage of the wet etchant 6.

Referring again to FIG. 1, a second preferred embodiment of the method for separating an epitaxial substrate of the present invention is substantially the same as the first preferred embodiment, except that the wet etchant 6 is hydrochloric acid. a mixture with hydrofluoric acid; between 90 vol% and 60 vol%, and hydrofluoric acid being between 40 vol% and 60 vol%, based on the volume percentage of the wet etchant 6.

It is worth noting here that the wet etchant 6 employed in the step (d) of the preferred embodiment of the present invention exhibits for the sacrificial layer (i.e., the buffer layer 3; Sc ₂ O ₃ ) Selectivity etch characteristics. In other words, an acid agent such as nitric acid, hydrochloric acid, hydrofluoric acid or the like has a fast etching rate for Sc ₂ O ₃ , which does not tend to etch away the epitaxial film layer structure 4. Therefore, the epitaxial film layer structure 4 can be quickly removed from the epitaxial substrate 2; accordingly, the effect of saving process time and equipment cost has been initially achieved.

<Analysis data>

It is well known in the art of epitaxy related art that the epitaxial strain will be generated due to a lattice mismatch between the epitaxial film and the epitaxial substrate, and the theoretical calculation formula is E _mf =[( a _s - a _f ) / a _f ] × 100%; wherein E _mf , a _f , a _s represent the epitaxial strain, the lattice constant of the upper epitaxial film, and the lattice constant of the lower epitaxial substrate, respectively. When a _s > a _f , it represents that the upper epitaxial film is subjected to tensile strain; conversely, when a _f > a _s , it represents that the upper epitaxial film is subjected to compressive strain. Applicants calculated the optimal lattice constant of GaN (0001) a _f =12.94 Å, the optimal lattice constant of Sc ₂ O ₃ (111) a _s =13.81 Å, and calculated the GaN epitaxial film according to the above formula. The tensile strain was 6.74%.

The buffer layer (Sc ₂ O ₃ ) 3 employed to further demonstrate the method of the preferred embodiments of the present invention is advantageous for the epitaxial quality of the epitaxial film layer structure (GaN) 4. Applicants hereby pre-acquire the surface model of Sc ₂ O ₃ (111) epitaxial growth using the first principle calculation method of density functional theory, which has a Sch-terminated Sc ₂ O ₃ (111) surface model and O-terminated Sc ₂ O ₃ (111) surface model; wherein, with oxygen-rich (O-rich) oxygen-terminated Sc ₂ O ₃ (111 The surface model is the most stable surface model.

Further, the influence of the elemental chemical atmosphere on the GaN (0001)/Sc ₂ O ₃ (111) heterointerface was calculated using the aforementioned surface model. Applicants based on the above surface model (ie, the oxygen-terminated Sc ₂ O ₃ (111) surface model), the composition ratio and the epitaxial orientation relationship are Ga ₄₈ N ₄₈ (0001) / / Sc ₄₈ O ₇₂ (111) and Ga ₄₈ N ₄₈ [1010] / / Sc ₄₈ O ₇₂ [211] conditions, the establishment of four sets of atomic structures as shown in Figure 2 (with reference to Annex 1) (ie, GaN (0001) / Sc ₂ O ₃ ( 111) Model of heterogeneous interface structure). Referring to Figure 3 (with reference to Annex 2), the applicant uses the first principle to calculate the interfacial energy (Γ; eV/Å ² ) of four sets of GaN (0001)/Sc ₂ O ₃ (111) heterostructures, where The Ga-polar GaN epitaxial film with N-Sc bond and Ga-O bond at the interface has the lowest interface in the interface structure model of the oxygen-terminated Sc ₂ O ₃ (hereinafter referred to as model 1). can. In addition, the model 1 is in a state of Ga-rich, N-rich, Sc-rich and O-rich. The interface can be compared, and the model 1 has the lowest interface energy (Γ=-0.16 eV/Å ² ) in the atmosphere rich in Ga and O-rich atmosphere.

Finally, according to the above theoretical calculation results, the applicant simulates a high resolution transmission electron microscope (high resolution transmission electron microscope) as shown in FIG. 4 under the condition of rich Ga atmosphere and O-rich atmosphere. HRTEM) image. Referring to Figure 4 (see Appendix 3 for details), the GaN (0001)/Sc ₂ O ₃ (111) heterointerface structure allows the GaN epitaxial film to withstand a tensile strain of 6.74%; however, since the heterointerface bond is N -Sc bond and Ga-O bond (ie, Model 1), which has the lowest heterointerface energy (-0.16 eV/Å ² ) in a Ga-rich atmosphere and an O-rich atmosphere; therefore, the heterogeneity shown in Figure 4 The atomic arrangement of the interface (ie, the imaginary line in FIG. 4) is flat, which represents that the N-Sc bond and the Ga-O bond in the interface atom can effectively alleviate the epitaxial growth of the GaN film in the lattice of the Sc ₂ O ₃ film. By matching, it was confirmed that the present invention uses Sc ₂ O ₃ as a buffer layer for growing a GaN epitaxial film, and a high-quality GaN epitaxial film can be obtained.

In summary, the separation method of the epitaxial substrate of the present invention uses Sc ₂ O ₃ as the buffer layer 3 when the epitaxial film layer structure (GaN) 4 is formed, and on the other hand, the epitaxial film layer structure (GaN) 4 can be improved. The epitaxial quality, on the other hand, also uses Sc ₂ O ₃ as a sacrificial layer for separating the epitaxial substrate 2, which can retain the epitaxial film layer structure (GaN) while saving time and equipment cost. 4 should have the epitaxial quality, so it can achieve the purpose of the present invention.

The above is only the preferred embodiment and the specific examples of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent change according to the scope of the invention and the description of the invention. And modifications are still within the scope of the invention patent.

2‧‧‧ epitaxial substrate

3‧‧‧buffer layer

4‧‧‧ epitaxial film structure

5‧‧‧heated substrate

6‧‧‧ Wet etchant

1 is a schematic flow chart showing a first preferred embodiment and a second preferred embodiment of the method for separating an epitaxial substrate of the present invention; FIG. 2 is a schematic diagram of an atomic structure, illustrating that the applicant uses the simulation software to establish four groups. The atomic model of the GaN (0001)/Sc ₂ O ₃ (111) heterointerface structure; Fig. 3 is a 3D relationship diagram of the interfacial energy (Γ) versus the chemical potential ( Δμ ), illustrating the four heterogeneous interface structures of Figure 2. The interface energy size of the model; and Figure 4 is an alignment diagram illustrating the HRTEM image obtained by the GaN(0001)/Sc ₂ O ₃ (111) heterointerface structure model and the aforementioned model after software simulation.

2‧‧‧ epitaxial substrate

3‧‧‧buffer layer

4‧‧‧ epitaxial film structure

5‧‧‧heated substrate

6‧‧‧ Wet etchant

Claims (4)

A method for separating an epitaxial substrate comprises the steps of: (a) depositing a buffer layer made of yttrium oxide on an epitaxial substrate; (b) after the step (a), stretching on the buffer layer Forming an epitaxial film layer structure, wherein the epitaxial film layer structure is composed of a material mainly composed of gallium nitride; (c) after the step (b), bonding the structure of the epitaxial film layer a heat dissipating substrate; and (d) after the step (c), using the buffer layer as a sacrificial layer, removing the sacrificial layer by a wet etchant to separate the epitaxial film layer structure from the epitaxial substrate The wet etchant is an acid agent selected from the group consisting of nitric acid, hydrochloric acid, hydrofluoric acid, and a mixture of the foregoing acid agents; wherein the epitaxial substrate of the step (a) is selected from the group consisting of Groups of the following: <111> single crystal germanium, heterogeneous epitaxial <111> germanium oxide on <111> single crystal germanium, heterogeneous epitaxial <0001> gallium nitride on <0001>sapphire; The buffer layer of the step (a) is formed on the epitaxial substrate in the <111> direction, and the epitaxial film layer structure mainly composed of gallium nitride in the step (b) is made in the <0001> direction. In the buffer And the interface between the buffer layer and the epitaxial film layer structure of the step (b) is a GaN epitaxial film with a surface of an N-Sc bond and a Ga-O bond, and grows at the end of oxygen. The interface structure of Sc ₂ O ₃ . The method for separating an epitaxial substrate according to claim 1, wherein the step (d) is at an operating temperature of between 25 ° C and 65 ° C. Implementation. The method for separating an epitaxial substrate according to claim 2, wherein the wet etchant is a mixture of nitric acid and hydrofluoric acid; and the nitric acid is 40 vol% based on the volume percentage of the wet etchant Between 60 vol%, hydrofluoric acid is between 40 vol% and 60 vol%. The method for separating an epitaxial substrate according to claim 2, wherein the wet etchant is a mixture of hydrochloric acid and hydrofluoric acid; and the hydrochloric acid is 40 vol% based on the volume percentage of the wet etchant. Between 60 vol%, hydrofluoric acid is between 40 vol% and 60 vol%.