TECHNICAL FIELD

The present disclosure relates to a semiconductor layer of gallium nitride (GaN) or mixed nitride of gallium and other metal and its formation method. Furthermore, the present disclosure relates to an electronic or opto-electronic device including the layer, a nitride semiconductor substrate and its manufacturing method. The technical field of the present disclosure may be, in broad senses, defined as a semiconductor stacking structure for forming a nitride semiconductor layer with few crystal defects and high quality on a substrate and its formation method.

BACKGROUND ART

Nitride semiconductor of elements in Group III or V in the periodic table occupies an important position in the field of electronic and opto-electronic devices, and this field will be more important in the future. In practice, nitride semiconductor has a wide range of applications, ranging from laser diodes (LDs) to transistors that can operate at high frequency and high temperature. Furthermore, the range of applications includes ultraviolet light detectors, elastic surface wave (SAW) devices and light emitting diodes (LEDs).

For example, gallium nitride is known as a suitable material for applications of blue LEDs or high temperature transistors, but is being widely studied for the use of microwave electronic devices but not limited thereto. Furthermore, as stated herein, gallium nitride has a wide range of applications including gallium nitride-based alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) and aluminum indium gallium nitride (AlInGaN).

In devices using nitride semiconductor such as gallium nitride, the most frequently used substrate for growing a nitride semiconductor layer is a “heterogeneous” substrate such as sapphire, silicon carbide (SiC), and silicon. However, because these heterogeneous substrate materials have a lattice constant mismatch and a difference in thermal expansion coefficient with nitride, a nitride semiconductor layer grown on the heterogeneous substrate includes many crystal defects such as dislocation. The defect acts as a key factor that degrades the performance of nitride semiconductor devices such as LEDs.

Because a sapphire substrate has a higher thermal expansion coefficient than gallium nitride, when gallium nitride is grown at high temperature and then cooled down, compressive stress is applied to a gallium nitride epitaxial layer. Because a silicon substrate has a lower thermal expansion coefficient than gallium nitride, when gallium nitride is grown at high temperature and then cooled down, tensile stress is applied to a gallium nitride epitaxial layer. For this reason, a substrate warpage phenomenon occurs, and to prevent substrate warpage, the substrate thickness increases. The use of a thick substrate only contributes to the reduced superficial phenomenon, and is not technology that reduces the stress of a thin film itself. If the stress of a thin film itself is reduced, an advantage is that a thin substrate can be used. Furthermore, to separate a chip from a fabricated LED, a substrate needs to be ground while leaving about 100 μm, and in this circumstance, if a thin substrate can be used, great benefits will be gained in the aspect of LED production.

In some cases, the nitride semiconductor layer formed on the heterogeneous substrate should be separated from the heterogeneous substrate according to the need, and prior art proposed laser lift-off. However, even though a laser lift-off process is used, substrate warpage occurs due to a difference in thermal expansion coefficient between a sapphire substrate and nitride semiconductor, or a nitride semiconductor layer is melted using a laser and peeled off, so a side effect is the occurrence of thermal stress during the process due to high temperature heat at a local area. The laser lift-off process involves thermal and mechanical deformation and decomposition of nitride semiconductor. Due to laser beam impacts, the nitride semiconductor layer is susceptible to defects such as cracks and the nitride semiconductor layer may be damaged, and further, the nitride semiconductor layer is prone to breakage, and thus, the process is unstable.

Therefore, there is the demand for a substrate separation method with high reliability or a method for obtaining a high quality nitride semiconductor substrate or nitride semiconductor device.

DISCLOSURE

Technical Problem

The problem to be solved by the present disclosure is to provide a semiconductor stacking structure that forms a high quality nitride semiconductor layer with reduced stress applied to the nitride semiconductor layer when growing the nitride semiconductor layer and is easy to separate the nitride semiconductor layer from a substrate with no need for laser lift-off, and a method and apparatus for separating a nitride semiconductor layer using the same.

Technical Solution

To solve the above problem, a semiconductor stacking structure according to the present disclosure includes a monocrystalline substrate of a heterogeneous material from nitride semiconductor, an inorganic thin film including a leg portion contacting with the substrate to define a cavity between the inorganic thin film and the substrate and an upper surface portion extending from the leg portion parallel to the substrate, wherein at least a part of the inorganic thin film is crystalized with the same crystal structure as the substrate, and a nitride semiconductor layer grown from the crystalized inorganic thin film on the cavity.

Particularly, the cavity may consist of a plurality of cavities separated from each other, and may be a line type pattern extending in the direction perpendicular to a direction in which a lateral growth rate of the nitride semiconductor layer is fast. The nitride semiconductor layer may be in combined or non-combined form. The nitride semiconductor layer may be continuous or discontinuous in horizontal direction. The nitride semiconductor layer may consist of at least two films. An inorganic thin film defining cavities such as the above may be further formed between the at least two films.

There is provided a method for separating a nitride semiconductor layer according to the present disclosure. After a sacrificial layer pattern is formed on a monocrystalline substrate of a heterogeneous material from nitride semiconductor, an inorganic thin film is formed on the sacrificial layer pattern. The sacrificial layer pattern is removed from the substrate with the inorganic thin film, to form cavities defined by the substrate and the inorganic thin film. Subsequently, at least a part of the inorganic thin film is crystalized with the same crystal structure as the substrate, and a nitride semiconductor layer is grown from the crystalized inorganic thin film on the cavities. Subsequently, the nitride semiconductor layer is mechanically separated from the substrate.

The growing of a nitride semiconductor layer may include forming the nitride semiconductor layer as a plurality of nitride semiconductor layers separated from each other.

The sacrificial layer pattern may be formed by various methods. The sacrificial layer pattern may be formed by photolithography after applying a photoresist film onto the substrate, or may be formed by nano-imprint after applying resin for nano-imprint onto the substrate. Alternatively, the sacrificial layer pattern may be formed by adhering organic nanoparticles onto the substrate.

Preferably, the forming of an inorganic thin film is performed within the temperature range in which the sacrificial layer pattern is not deformed. The cavities are where the sacrificial layer pattern is removed away. Thus, the cavities conform to the shape and size and two-dimensional array of the sacrificial layer pattern. Accordingly, for the cavities to have the controlled shape and size and two-dimensional array, it is required to set the shape and size and two-dimensional array of the sacrificial layer pattern.

Another method for separating a nitride semiconductor layer according to the present disclosure performs mechanical separation of a substrate and a nitride semiconductor layer in the semiconductor stacking structure according to the present disclosure.

Still another method for separating a nitride semiconductor layer according to the present disclosure performs mechanical separation of a substrate and a nitride semiconductor layer in other semiconductor stacking structure including an interfacial layer with cavities between the substrate and the nitride semiconductor layer even though the semiconductor stacking structure does not follow the present disclosure.

When the nitride semiconductor layer is separated from the substrate using this method, the nitride semiconductor layer may be transferred or moved to vertical or horizontal LEDs or any type of substrates to manufacture LEDs or nitride semiconductor free-standing substrates.

In the method for separating a nitride semiconductor layer according to the present disclosure, the mechanically separating may be performed by a method for separation by applying a force in vertical direction to the substrate and the nitride semiconductor layer, a method for separation by applying a force in horizontal direction, a method for separation by applying a force in relative circular motion, and its combined method.

Particularly, in the case of the method for separation by applying a force in vertical direction to the substrate and the nitride semiconductor layer, it is preferable to perform end point detection by sensing the thickness or pressure at which the substrate and the nitride semiconductor layer are compressed in vertical direction.

The method for separating a nitride semiconductor layer according to the present disclosure may further include, after separating the nitride semiconductor layer from the substrate, transferring the separated nitride semiconductor layer to other substrate or packaging the separated nitride semiconductor layer.

An apparatus for separating a nitride semiconductor layer according to the present disclosure performs mechanical separation of the nitride semiconductor layer from the substrate in the semiconductor stacking structure according to the present disclosure or other semiconductor stacking structure including an interfacial layer with cavities between the substrate and the nitride semiconductor layer even though the semiconductor stacking structure does not follow the present disclosure.

The apparatus may include a pair of separation member as jigs applied respectively to the substrate and the nitride semiconductor layer of the semiconductor stacking structure. The separation members and the semiconductor stacking structure may be temporarily adhered to each other. The temporary adhesion may be any of an adhesive layer, adhesive coating, an adhesive tape, an electrostatic force or a force by vacuum.

The apparatus may include a driving unit to apply an external force to the semiconductor stacking structure, and a control unit to control the driving unit. The driving unit may apply relative compression, tension, shear, torsion, and its combined external force to the substrate and the nitride semiconductor layer.

The separation apparatus according to the present disclosure may apply the external force while at least one of a pair of separation member is temporarily adhered to the semiconductor stacking structure, the pair of separation member as jigs applied respectively to the substrate and the nitride semiconductor layer of the semiconductor stacking structure. While any of the separation members is fixed, the external force in vertical direction, horizontal direction or rotation may be applied to the other separation member against the remaining one.

Particularly, it is preferable to fix any of the separation members and drive the other in vertical direction against the remaining one to provide a compressive force, and release the compressive force immediately after the nitride semiconductor layer and the substrate are separated by destruction of the inorganic thin film or the interfacial layer. In this instance, the control unit may control the driving unit to stop relative movements of the separation members or move the separation members apart from each other through end point detection for separation of the nitride semiconductor layer and the substrate. A separation sensing unit for the end point detection may be further provided. The separation sensing unit may perform the end point detection by a method for measuring the distance between the separation members or pressure monitoring.

The separation apparatus according to the present disclosure may further include a conveyance apparatus to transfer the separated nitride semiconductor layer to other substrate or package the separated nitride semiconductor layer.

The use of the semiconductor stacking structure according to the present disclosure and the method and apparatus for separating a nitride semiconductor layer using the same contributes to the manufacture of ultraviolet light detectors, elastic surface wave devices, LEDs, LDs, and microwave electronic devices, and can be expanded to modules and systems using the devices. In addition, nitride semiconductor free-standing substrates can be manufactured. Details of other embodiments are included in the detailed description and drawings.

Advantageous Effects

According to the present disclosure, the nitride semiconductor layer is grown on the inorganic thin film on the cavities. The inorganic thin film shares and relieves stress with the nitride semiconductor layer grown thereon, and thus, according to the present disclosure, the nitride semiconductor layer is grown with a low defect density and a high quality. Therefore, a low defect density and high quality nitride semiconductor layer is formed, and the reduced crystal defect density in nitride semiconductor increases the internal quantum efficiency.

Even though stress occurs in the nitride semiconductor layer due to a difference in thermal expansion coefficient between the substrate and the nitride semiconductor layer, stress is locally relieved, and as a consequence, a substrate warpage phenomenon will reduce. Although there is a difference in thermal expansion coefficient between the substrate and the nitride semiconductor layer, the cavities may be compressed or stretched by the nitride semiconductor layer, resulting in reduced stress applied to the nitride semiconductor layer. Accordingly, it is possible to use a relative thin substrate on a large scale substrate.

Particularly, because the sacrificial layer pattern is formed a controlled method such as photolithography or nano-imprint, the cavities are not formed irregularly or at random and are formed by a controlled method, leading to good reproducibility and superior device uniformity. As a result, it is possible to grow a nitride semiconductor epitaxial layer with outstanding properties, and realize opto-electronic devices with high efficiency and high reliability.

Due to the cavities and voids that can be created when forming the nitride semiconductor layer, the substrate and the nitride semiconductor layer are easy to mechanically separate from each other. The nitride semiconductor layer and the substrate can be mechanically separated by a small mechanical force or impact without applying great energy such as a laser. Accordingly, it is easy to separate the nitride semiconductor layer from the substrate even though laser lift-off is not used, making it easy to manufacture vertical LEDs or nitride semiconductor free-standing substrates.

Particularly, because the separation method and apparatus according to the present disclosure separates the nitride semiconductor layer from the substrate by a mechanical force without using a laser, the time and process costs are reduced as compared to a method using a laser, and production efficiency increases.

The present disclosure proposes a new mechanism for a method and apparatus for separating a nitride semiconductor layer from a substrate by a mechanical separation method. An inorganic thin film defining cavities, namely, an artificial nano-structure that can be easily destructed, is formed between the substrate and the nitride semiconductor layer, thereby separating the nitride semiconductor layer from the substrate with no need for an expensive laser device without a deterioration phenomenon caused by a laser.

It is possible to grow the nitride semiconductor layer continuously or discontinuously by adjusting the inorganic thin film structure defining the cavities, the two-dimensional array and the nitride semiconductor layer growth condition, thereby improving the performance of LEDs and reducing production costs.

