KR100664039B1 - Nitride compound semiconductor device manufacturing method - Google Patents

Abstract

A method of fabricating a nitride semiconductor device is provided to minimize a loss of Mg by breaking coupling of Mg-H which is generated during a growth process and then activating the layer in a p type. A GaN layer containing Mg as an impurity is deposited on a substrate with nitride layers by using NH3 gas and H2 gas at high temperature to form a GaN:Mg layer(20). A protective layer(30) is deposited on the GaN:Mg layer. The GaN:Mg layer is irradiated by an excimer laser through the protective layer to break coupling of Mg-H. The excimer laser is irradiated under a nitrogen atmosphere. The excimer laser is irradiated in a pulse mode to activate the GaN:Mg layer.

Description

Nitride semiconductor device manufacturing method {NITRIDE COMPOUND SEMICONDUCTOR DEVICE MANUFACTURING METHOD}

1 is a cross-sectional view showing a p-GaN layer activation process of an embodiment of the present invention.

Figure 2 is a cross-sectional view showing a p-GaN layer activation process of another embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

10: lower element layer 20: GaN: Mg layer (before activation)

25: p-GaN layer (after activation) 30: protective layer

The present invention relates to a method for manufacturing a nitride semiconductor device, in particular using an excimer laser that can be carried out quickly at low temperature instead of a high temperature low-temperature heat treatment is performed to activate the p-type GaN: Mg (GaN containing Mg) after growth. The present invention relates to a nitride semiconductor device manufacturing method for activating a GaN: Mg layer in p-type.

Group III nitride semiconductors have been applied to optical devices including blue / green light emitting diodes (LEDs) and electronic devices that are high-speed switching and high-output devices such as MOSFETs and HEMTs. In particular, a light emitting device using a group III nitride semiconductor has a direct transition band gap corresponding to a region from visible light to ultraviolet light, and high efficiency light emission can be realized. Therefore, the semiconductor is mainly used as an LED or a laser diode (LD).

Among the group III nitride semiconductors, gallium nitride (GaN) is typically used, which is grown on a substrate by a crystal growth method, and is activated in a p-type or n-type according to a doped material to be composed of a PN junction diode. However, the present technology cannot produce a single crystal substrate having a lattice structure that is sufficient to directly grow the nitride semiconductor (GaN), such as sapphire (Al ₂ O ₃ ) single crystal or silicon carbide (SiC) single crystal. Substrates made of dissimilar materials are used.

For example, in the case of forming a light emitting device on a sapphire substrate, a GaN buffer layer is formed at low temperature without doping to easily eliminate lattice mismatch on the sapphire substrate, and an impurity such as Si is implanted while the GaN layer is grown thereon. To form an n-type GaN layer. Then, an active layer is formed on one of various structures (a single active layer, a quantum well structure, a multi-quantum well structure, etc.), and a P-type GaN layer is formed by implanting Mg with impurities while growing a GaN layer thereon. Subsequently, the LED device is configured by further performing a necessary process and forming a current diffusion layer or an electrode.

Here, in the growth method of the p-type GaN layer, ammonia (NH ₃ ) is used as a precursor of nitrogen, and H ₂ is used as a carrier gas. At this time, since the ammonia is very thermally stable, only a few% of ammonia is pyrolyzed even at 1000 ° C. or higher, contributing to GaN growth as a nitrogen source.

Therefore, high temperature growth is inevitable in order to increase pyrolysis efficiency, and a V / III fraction of 4,000 to 10,000 is generally used for good crystallinity of GaN growth. Here, the V / III ratio refers to the number of moles of the group III element and the group V element which are passed through the reaction furnace when the group III-V compound semiconductor crystal is grown by metal organic chemical vapor deposition (MOCVD). It is the ratio of the mole number of the molecule to contain. For example, in the case of growing gallium nitride using TMGa and ammonia, the fraction means the ratio of the number of moles of TMGa and the number of moles of ammonia passed through the reaction furnace.

As shown in the following formula, a large amount of ammonia used for GaN growth releases a large amount of hydrogen as a by-product, and Mg-H by combining with M ₂ injected during p-type GaN growth together with H ₂ used as a carrier gas. Will form. This causes the p-type GaN layer to be deactivated by the insulator after growth.

NH ₃ → N + H + H ₂

In general, the inactive p-type GaN thin film immediately after growth is activated through a heat treatment process such as Low Energy Electron Beam Irradiation (LEEBI) or high temperature annealing (Rapid Temperature Annealing, Furnace Annealing) to obtain p-type characteristics. However, since the device structure has to be exposed for a long time at a high temperature, the process has problems such as reduced yield by process time, reduced activation efficiency due to external diffusion of Mg concentrated on the surface during heat treatment, and formation of oxygen compounds by oxidation of Mg. This happens.

Even with the recent response to the use of H ₂ instead of the N ₂ GaN: the method of growing the Mg to suppress the formation Mg-H bond structure or irradiated with ultraviolet light at a low temperature have been proposed, but the like still stable process conditions and process equipment Not specifically presented. Therefore, since most of the nitride semiconductor is formed by p-GaN growth by the conventional MOVCD method and subsequent heat treatment, the above-mentioned problems may reduce yield and deteriorate device characteristics.

As described above, when GaN: Mg is grown at a high temperature by using ammonia as a nitrogen precursor and H ₂ as a carrier gas for growth of conventional p-GaN, Mg formed inside the growth layer by hydrogen generated in a high temperature environment Since the layer is deactivated by -H, in order to activate the layer as p-type, heat treatment is performed at a high temperature for a long time to dissociate Mg-H bond, so that the yield is lowered and Mg is diffused to the outside to activate the efficiency. This lowered the Mg is oxidized during the heat treatment, there is a problem that the bonding properties with the subsequent metal layer is deteriorated.

In view of the above problems, the present invention uses ammonia as a nitrogen precursor and H ₂ as a carrier gas to grow GaN: Mg at high temperature, and then irradiates the layer with an excimer laser having energy above Mg-H dissociation energy. The Mg-H bond generated during the process is cut off to activate the layer as p-type, and if necessary, a protective layer is formed on top of the layer before laser irradiation. It is an object of the present invention to provide a method for manufacturing a nitride semiconductor device capable of preventing the layer from being oxidized.

In order to achieve the above object, the present invention comprises the steps of growing a GaN layer containing Mg as an impurity at a high temperature using ammonia (NH ₃ ) and H ₂ gas on the substrate formed with a predetermined nitride layer; Irradiating the formed GaN: Mg layer with an excimer laser to disconnect the Mg-H formed in the step, thereby activating the layer to a p-type.

The excimer laser is used to have a light energy higher than the dissociation energy of Mg-H, it characterized in that the laser irradiation in a nitrogen atmosphere.

The method may further include depositing a protective layer on the grown GaN: Mg layer before the excimer laser irradiation step and removing the excimer laser irradiation after the excimer laser irradiation is completed.

When described in detail with reference to the accompanying drawings, the present invention as follows.

Figure 1 is a simple cross-sectional view showing a manufacturing process of an embodiment of the present invention, as shown, showing the process of activating the layer by performing a heat treatment with an excimer laser after forming a GaN: Mg layer.

First, FIG. 1A is a cross-sectional view illustrating a state in which a GaN: Mg layer 20 is grown on a substrate 10 on which various nitride semiconductors are formed, as shown in FIG. 1A. By-products are formed, deactivating the layer with insulators.

By-products having the Mg-H structure are released as ammonia is thermally decomposed when the GaN: Mg layer is grown at a high temperature by using ammonia (NH ₃ ) as a nitrogen precursor and H ₂ as a carrier gas, as mentioned above. A large amount of hydrogen and carrier gas (H ₂ ) to be produced by combining with Mg applied as an impurity.

Therefore, this GaN: to dissociate the binding of the Mg-H structure contained immediately after the growth of the Mg layer 20 is supposed to be that only residual Mg, in the present invention, an excimer laser on the N ₂ atmosphere, the GaN: the Mg layer 20 Do this by investigating.

The excimer laser used is a laser that emits a wavelength in the ultraviolet region and generates a high power short wavelength laser light, which is widely used in precision processing and medical fields, and is already used in various applications to obtain a laser device having a desired performance. It has the advantage of being easy.

This excimer laser is a kind of gas laser that puts inert gases into a gas container and provides electrical stimulation thereto. The term excimer comes from a term referring to a specific state that these gases may have. The oscillation wavelength varies according to the gas used. ArF (193 nm) and KrF (248 nm) are the most commonly used gases, and various gases having wavelengths between 200 and 400 nm can be used.

The excimer laser is distinguished by its ability to provide high power ultraviolet light directly due to the fact that it can actively use the short wavelength that the ultraviolet laser can have. The shorter wavelength means that the energy of photons is higher, which means that it is possible to destroy a material without high heat in the case of a polymer material. In addition, such a short wavelength is advantageous in precision processing.

Therefore, as shown in the drawing, the excimer laser having a short wavelength is pulse-driven for a very short irradiation time (several ns), and when the repetition speed, the number of irradiation, and the energy density of the laser are precisely adjusted, Accurate heat treatment for localized areas is possible. That is, since the desired light energy can be applied to a desired object to a desired depth, the light energy can be dissociated from Mg-H bonds by providing light energy with an appropriate energy density according to the thickness of the GaN: Mg layer 20. Will be.

In general, the theoretical dissociation energy of Mg-H is 1.5 eV, so the light energy provided by the excimer laser should have an energy density of more than 1.5 eV. Since the energy density of a commercially available KrF (248 nm) excimer laser is about 5 eV, it is sufficiently applicable to dissociate Mg-H. In addition, as described above, if the irradiation is carried out with the desired thickness and the desired energy through proper adjustment, the GaN: Mg is rapidly activated by p-type by heat-treating only the desired local area without exposing the whole element to high temperature. You can.

Pulse laser annealing (PLA) by the excimer laser can activate the p-GaN layer 25 as shown in FIG. 1B. If the area of the layer is large, the excimer laser is scanned in all areas while the PLA is scanned. The method of investigating can be applied.

However, when activating the layer by directly irradiating the excimer laser to the GaN: Mg layer 20 thus generated, Mg, which is mainly located on the surface of the concentration distribution, is diffused to the outside during the laser heat treatment process so that the concentration of Mg becomes insufficient. It can be a problem that the activation efficiency is lowered, Mg may combine with the oxygen of the ambient atmosphere during the heat treatment process to form a compound. Such oxides can inhibit ohmic properties by increasing contact resistance in subsequent ohmic metal formation. Therefore, a protective layer may be additionally used as shown in FIG. 2 to prevent the loss of Mg.

FIG. 2A illustrates a case in which a GaN: Mg layer 20 is grown and then further formed with a TiN protective layer 30 by chemical vapor deposition or sputtering, and then irradiated with an excimer laser. Since the excimer laser uses light, the excimer laser is transmitted to the TiN protective layer 30 of the thin film and applied to the GaN: Mg layer 20 under the thin film.

The GaN: Mg layer 20 may not lose Mg even during the laser heat treatment process by the TiN protective layer 30 formed as described above.

Subsequently, when the GaN layer 25 is activated to be p-type, the TiN protective layer 30 is etched and removed to increase the activation efficiency of the P-GaN layer 25.

As described above, in the method of manufacturing a nitride semiconductor device of the present invention, GaN: Mg is grown at a high temperature using ammonia as a nitrogen precursor and H ₂ as a carrier gas, and then a protective film is formed thereon, and Mg-H dissociation energy is formed. By irradiating the GaN: Mg layer with the excimer laser having the above optical energy, the Mg-H bond generated during the growth process is cut off to activate the layer as p-type, and the protective film is removed, thereby minimizing the loss of Mg at low temperature. The p-type GaN layer can be activated quickly and accurately, resulting in higher yields and improved properties.

Claims (5)

Growing a GaN layer including Mg as an impurity at a high temperature by using ammonia (NH ₃ ) and H ₂ gas on the substrate on which the nitride layers are formed; Depositing a protective layer on top of the grown GaN: Mg layer; And irradiating the formed GaN: Mg layer with the excimer laser through the protective layer to break the Mg-H bond formed in the step to activate the p-type nitride semiconductor device. The method according to claim 1, wherein the excimer laser has a light energy higher than the dissociation energy of Mg-H, and laser irradiation is performed in a nitrogen atmosphere. The method of claim 1, wherein the excimer laser emits a GaN: Mg layer in all regions by a pulsed irradiation and a scanning irradiation by a scanning method. The method of claim 1, further comprising removing the protective layer after the excimer laser irradiation is completed. The method of claim 1, wherein the excimer laser has a light output exceeding 1.5 eV using a gas having a wavelength between 200 and 400 nm.

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