WO2014007098A1

WO2014007098A1 - Deep ultraviolet laser light source by means of electron beam excitation

Info

Publication number: WO2014007098A1
Application number: PCT/JP2013/067234
Authority: WO
Inventors: 松本　貴裕; 岩山　章
Original assignee: スタンレー電気株式会社
Priority date: 2012-07-02
Filing date: 2013-06-24
Publication date: 2014-01-09
Also published as: JP2014011377A; JP5943738B2

Abstract

This deep ultraviolet laser light source is provided with: a substrate; a wide band gap semiconductor layer which is provided on the substrate; an aluminum metal back layer which is provided on the wide band gap semiconductor layer; and a resonator structure which causes deep ultraviolet light produced from the wide band gap semiconductor layer to resonate. This deep ultraviolet laser light source is configured such that the wide band gap semiconductor layer is excited by electron beam irradiation from the aluminum metal back layer side and laser oscillation of the deep ultraviolet light produced from the wide band gap semiconductor layer is caused by the resonator structure. Consequently, there is achieved a deep ultraviolet laser light source which uses a wide band gap semiconductor layer by means of electron beam excitation.

Description

Deep ultraviolet laser light source by electron beam excitation.

The present invention relates to a deep ultraviolet laser light source having a wavelength range of 200 to 350 nm, which is used as a light source for high density recording, a light source for semiconductor lithography, a light source for processing fine materials, and the like.

There is a gas laser light source as a first conventional deep ultraviolet laser light source, for example, an excimer laser light source represented by an ArF laser light source with a wavelength of 193 nm, an ArCl laser light source with a wavelength of 175 nm, a KrF laser light source with a wavelength of 249 nm, and the wavelength There is a metal vapor ion laser light source represented by a copper vapor ion laser light source of 248.6 nm and a gold vapor ion laser light source of wavelength 226.4 nm.

However, the above-described first conventional deep ultraviolet laser light source has a high manufacturing cost of, for example, about 200 to 300,000 dollars, a large size of, for example, 2 m ³ or more, and a power / laser conversion efficiency of, for example, about 0.1 to 0.01%. For example, it requires frequent gas exchange once a week, for example, about 1000 to 5000 hours, the life of a hot cathode discharge tube (thyratron) is short, and fluorine / chlorine harmful gases are used. There are drawbacks.

There is a solid-state laser light source as a second conventional deep ultraviolet laser light source (see:

Patent Documents

1, 2, and 3). In this solid-state laser light source, for example, a fundamental wave of a YAG laser device having a wavelength of 1064 nm is converted into a high-order harmonic of, for example, a wavelength of 266 nm by a wavelength conversion element and output.

However, the above-described second conventional deep ultraviolet laser light source has a high manufacturing cost of about 200 to 300,000 dollars, for example, a large size of 2 m ³ or more, for example, about 0.1 to 0.01%, depending on the wavelength conversion element. There are drawbacks such as low power / laser conversion efficiency.

As a deep ultraviolet laser light source, a semiconductor laser light source using a wide band gap semiconductor layer, for example, an AlGaN quantum well layer, which is attracting attention in terms of miniaturization, high output, high efficiency, etc. can be considered. However, the development of light-emitting diode (LED) light sources has been limited (

Patent Documents

4 and 5, Non-Patent Document 1).

JP 2012-37813 A JP 2009-31684 A (Patent No. 4826558) JP 2007-86104 A (US / 2007 / 0064750A1) WO2011 / 104969A1 WO2010 / 027016A1

However, when an LED light source using the above-mentioned wide band gap semiconductor layer is applied to a deep ultraviolet laser light source, the LED light source has the following problems.

First, power / light conversion efficiency is low at around 0.1-0.01%.

Second, the luminous efficiency is still insufficient.

Third, since it is difficult to form a p-type layer, an efficient double hetero current injection structure cannot be realized.

Fourth, the lifetime is as short as about 10 hours.

In order to solve the above-described problems, a deep ultraviolet laser light source according to the present invention includes a substrate, a wide band gap semiconductor layer provided on the substrate, and an aluminum metal back layer provided on the wide band gap semiconductor layer. And a resonator structure that resonates deep ultraviolet light generated from the wide band gap semiconductor layer, and irradiates an electron beam from the aluminum metal back layer side to excite the wide band gap semiconductor layer to start from the wide band gap semiconductor layer. The generated deep ultraviolet light is laser-oscillated by a resonator structure. This realizes a deep ultraviolet laser light source using a wide band gap semiconductor layer by electron beam excitation. In addition, the aluminum metal back layer prevents the wide band gap semiconductor layer from being charged and causing dielectric breakdown.

The wide band gap semiconductor layer is an Al _x Ga _1-x N / AlN multiple quantum well layer, and the thickness of the Al _x Ga _1-x N / AlN multiple quantum well layer is about 6 to 60 nm. Thereby, luminous efficiency becomes very high.

Furthermore, an electron emission source composed of a graphite nano needle rod for generating an electron beam is provided. As a result, the vacuum degree of vacuum sealing is lowered, and the electron emission source has a long life.

According to the present invention, it is possible to realize a deep ultraviolet laser light source using a wide band gap semiconductor layer by electron beam excitation. Moreover, the formation of the p-type layer is not required by electron beam excitation.

It is sectional drawing which shows the 1st Example of the deep ultraviolet laser light source which concerns on this invention. It is a graph for demonstrating the thickness of the sapphire (0001) board | substrate of FIG. It is a figure for demonstrating the spreading | diffusion of the electron of an electron beam when the electron beam energy in the deep ultraviolet laser light source of FIG. 1 is 10 keV. It is a figure for demonstrating the spreading | diffusion of an exciton when the electron beam energy in the deep ultraviolet laser light source of FIG. 1 is 10 keV. It is a graph which shows the incident angle dependence of the reflectance of the aluminum metal back layer of FIG. It is a graph which shows the incident angle dependence of the reflectance of the aluminum metal back layer of FIG. It is a flowchart for demonstrating the manufacturing method of the electron emission source of FIG. It is a scanning electron microscope (SEM) photograph which shows the electron emission source before and behind the plasma etching of FIG. It is a graph which shows the electric field / current characteristic of the electron emission source before and behind the plasma etching of FIG. It is a graph which shows the electric field / current density characteristic of the electron emission source after the plasma etching of FIG. 7, and the electric field / current density characteristic of the electron emission source as another comparative example. It is a flowchart which shows the example of a change of FIG. It is sectional drawing which shows the 2nd Example of the deep ultraviolet laser light source which concerns on this invention. It is the fragmentary sectional view which actually assembled the deep ultraviolet laser light source of FIG. 1, FIG. It is a fragmentary sectional view which shows the example of a change of FIG. It is a top view which shows an example of the electron beam irradiation pattern on the aluminum metal back layer obtained when the direct-current voltage for focus of FIG. 13, FIG. 14 is controlled. It is a graph which shows the emission intensity of the deep ultraviolet laser light source of FIG. 14, and the spectrum of a laser oscillation. It is a graph for demonstrating the directivity of the deep ultraviolet laser light source of FIG. It is a graph which shows the optical output characteristic of the deep ultraviolet laser light source of FIG. It is sectional drawing which shows the example of a change of the deep ultraviolet laser light source of FIG. It is sectional drawing which shows the 3rd Example of the deep ultraviolet laser light source which concerns on this invention. It is a graph which shows the lifetime of the deep ultraviolet laser light source of FIG.1, FIG.12, FIG.20.

Examples for carrying out the invention

FIG. 1 is a sectional view showing a first embodiment of a deep ultraviolet laser light source according to the present invention. The deep ultraviolet laser device of FIG. 1 is an end face reflection type.

In FIG. 1, the deep ultraviolet laser light source includes a sapphire (0001) substrate 1, an AlN buffer layer 2 having a thickness of about 600 nm formed on the sapphire (0001) substrate 1, and a thickness of about 2 nm formed on the AlN buffer layer 2. 3 μm grating AlN layer 3, approximately 15 μm thick AlN layer 4 formed on grating AlN layer 3, approximately 3 nm thick Al _0.7 Ga _0.3 N well layer formed on AlN layer 4 and approximately 3 nm thick On the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 and the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 having a thickness of about 6 to 60 nm including 1 to 10 repetition periods with one AlN barrier layer as one period It comprises an aluminum (Al) metal back layer 6 formed and an electron emission source 7 that emits an electron beam EB. Further, both side surfaces of the sapphire (0001) substrate 1, AlN buffer layer 2, grating AlN layer 3, AlN layer 4, Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 and aluminum metal back layer 6 are cut or wall-opened. Two reflection structures RS1 having a reflectance R = 30% or more are formed. In FIG. 1, when the electron beam EB is irradiated from the electron emission source 7, the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is excited and resonated, and the deep ultraviolet laser light DUV is converted into at least one of the reflection structures RS1. Is emitted.

First, the sapphire (0001) substrate 1 will be described in detail.

Black dots B in FIG. 2 indicate the thickness t ₁ of the sapphire (0001) substrate 1 at which leakage X-rays obtained by simulation have legally specified values at the energy E (keV) of each electron beam EB. . By setting the thickness t ₁ of the sapphire (0001) substrate 1 to be equal to or greater than the value indicated by the black point B, the leakage X-ray can be set to a legally prescribed value or less. When this is plotted, a curve like a dotted line is drawn. Therefore, as shown in FIG. 2, the thickness t ₁ of the sapphire (0001) substrate 1 is calculated from the equation representing the plotted dotted line in order to prevent leakage X-rays.
t ₁ ≧ a · E ³
Where E is the energy of the electron beam EB (keV)
a is 1 μm / (keV) ³
It is. That is, the highest energy of X-rays generated by the braking range is the same as the energy E of the electron beam EB. Therefore, for example, when E = 6 keV, the thickness t ₁ of the sapphire (0001) substrate 1 is 216 μm or more, and when E = 10 keV, the thickness t ₁ of the sapphire (0001) substrate ₁ is 1000 μm or more. Thus, by setting the thickness t ₁ of the sapphire (0001) substrate 1 based on the above-described formula, the intensity of the leaked X-ray can be made lower than the legally prescribed value.

In place of the sapphire (0001) substrate 1, a SiC substrate or an AlN substrate can be used. In this case, the constant “a” in the above formula is a value other than 1.
Further, since the laser oscillation direction of the deep ultraviolet laser beam DUV and the generation direction of the leakage X-ray are different from each other by 90 °, it is possible to take a leakage prevention measure in consideration of this. For example, it is conceivable to take measures such as covering a X-ray leakage location with a heavy metal lid such as lead that has been drilled in the laser oscillation direction of the deep ultraviolet laser beam DUV.

Next, a method of forming the AlN buffer layer 2, the grating AlN layer 3, the AlN layer 4, and the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 on the sapphire (0001) substrate 1 will be described in detail.

The sapphire (0001) substrate 1 is mounted on a metal organic chemical vapor deposition (MOCVD) apparatus, hydrogen (H ₂ ) gas is supplied as a carrier gas, and the substrate temperature is kept at 1200 ° C. for 10 minutes. ) Pretreatment of the surface of the substrate 1 is performed.

Next, in the same MOCVD apparatus, while maintaining the substrate temperature at 800 ° C., trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia (NH ₃ ) are supplied at a flow rate of 10 sccm and 5 slm, respectively. A 50 nm AlN buffer layer 2 is formed.

Next, in the same MOCVD apparatus, the substrate temperature was raised to 1300 ° C., and trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia (NH ₃ ) were supplied at a flow rate of 10 sccm and 5 slm, respectively, to a thickness of about 3 μm. An AlN layer is formed.

Next, in order to reduce the dislocation density and reduce defects when the AlN layer 4 described later is grown by the epitaxial lateral growth method, the surface of the AlN layer having a thickness of about 3 μm has a period of about 3 μm and a depth of about 3 μm. A grating structure having a thickness of about 500 nm is formed to form the grating AlN layer 3. Specifically, a striped resist pattern (not shown) having a width of about 3 μm is formed on the AlN layer by using a photolithography method, and then the above resist pattern is formed by using a reactive ion etching (RIE) process. The AlN layer is etched using as a mask. Next, the resist pattern is removed using an organic solvent or the like. As a result, a groove (unevenness) structure having a line and space period of about 3 μm and a depth of 500 nm is formed. In this embodiment, the grating structure is used. However, it may be an uneven shape. For example, the unevenness may be arranged in a dot shape.

Next, again in the MOCVD apparatus, the substrate temperature is raised to 1300 ° C., and trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia (NH ₃ ) are supplied at a flow rate of 10 sccm and 5 slm, respectively, to a thickness of about 15 μm. An AlN layer 4 is formed. By making the AlN layer 4 as thick as about 15 μm, the film quality of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 to be grown next can be improved.

Next, an Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is formed on the AlN layer 4 in the same MOCVD apparatus. That is, in the MOCVD apparatus, trimethylgallium ((CH ₃ ) ₃ Ga), trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia so that the stoichiometric ratio is Al: Ga: N = 0.7: 0.3: 1. (NH ₃ ) is supplied at flow rates of 20 sccm, 8 sccm, and 7 slm, respectively, and the substrate temperature is set to 1000 ° C. Thereby, an Al _0.7 Ga _0.3 N well layer having a thickness of 3 nm is formed. In the same MOCVD apparatus, trimethylaluminum ((CH ₃ ) ₃ Al) and ammonia (NH ₃ ) are supplied at a flow rate of 10 sccm and 5 slm, respectively, so that the stoichiometric ratio is Al: N = 1: 1. In addition, the substrate temperature is set to 1200 ° C. Thereby, an AlN barrier layer having a thickness of 3 nm is formed. The Al _0.7 Ga _0.3 N-well layer and AlN barrier layer Repeat 1 cycle to 10 cycles as one cycle to form the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 having a thickness of about 6 - 60 nm.

3 shows that the energy E of the electron beam EB is 10 keV, the beam diameter of the electron beam EB is 10 nm, the thickness t ₆ of the Al metal back layer ₆ is 30 nm, and the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is used. FIG. 7 is a diagram showing a Monte Carlo simulation result of the diffusion of incident electrons of the electron beam EB when the thickness t ₅ of the electron beam is 720 nm. That is, the electron beam EB is absorbed almost for example, Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 99%, the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is more thick, the manufacturing cost Wasted in terms. Also, Al _0.7 Ga _0.3 N / AlN multiple Considering uniformity and quality of the quantum well layer 5, the maximum value of the thickness t ₅ of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is Al _0.7 Ga _0.3 N well It is about 60 nm for 10 periods of the layer and the AlN barrier layer.

4 shows that the energy E of the electron beam EB is 10 keV, the beam diameter of the electron beam EB is 10 nm, the thickness t ₆ of the Al metal back layer ₆ is 30 nm, and the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is used. FIG. 6 is a diagram showing a Monte Carlo simulation result of diffusion of incident electrons of an electron beam EB when the thickness t ₅ of the film is 60 nm. Also in this case, excitons are formed through the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 and in which electron-hole pairs are coupled by electron beam excitation within the diffusion length D of the AlN layer 4. In general, excitons generated in the AlN layer 4 diffuse into the exciton diffusion region DE of the AlN layer 4 and contribute to light emission of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. Absent. However, the present inventors succeeded in obtaining an interesting experimental fact here. It, Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 toward the potential of efficiently Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 by the diffusion phenomenon as shown excitons generated in the AlN layer 4 is by a dotted line arrow The effect is that it contributes to the re-excitation of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. By using this effect, it is possible to reduce the thickness of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 with respect to the energy E of the electron beam EB, high quality and defect less Al _0.7 Ga _0.3 N / AlN multiple quantum well layers can be efficiently excited with an electron beam, and deep ultraviolet laser light DUV can be oscillated at a low threshold. The reason for this is that the thinner Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 can be formed, which is more uniform and has fewer defects.

In FIGS. 3 and 4, the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is shown as vertical stripes, but this is for convenience, and in practice, Al _0.7 Ga _0.3 N / AlN multiple layers are shown. The Al _0.7 Ga _0.3 N well layer and the AlN barrier layer of the quantum well layer 5 are stacked in the lateral direction.

Then, Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 on the formed aluminum metal back layer 6 charge when Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is charged by the irradiation of the electron beam EB This prevents the dielectric breakdown of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5, but the thickness t ₆ of the aluminum metal back layer ₆ is important and will be described in detail.

As described above, since the thickness t ₅ of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is as small as about 6 to 60 nm, the electron beam EB excites the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. In view of luminous efficiency, the energy E of the electron beam EB should be small. Further, in order to avoid the influence of leaked X-rays, the energy E of the electron beam EB should be small. Accordingly, the energy E of the electron beam EB is as small as 10 keV or less, in other words, the electrons of the electron beam EB are slow. For slow electrons is transmitted through the aluminum metal back layer 6, the thickness t ₆ of the aluminum metal back layer 6 is better small. When the thickness t ₆ of the aluminum metal back layer is large, the electron beam EB is absorbed by the aluminum metal back layer 6 and the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 cannot be sufficiently excited, and the light emission is still caused. Efficiency is reduced. Such terms, the thickness t ₆ of the aluminum metal back layer 6 should preferably be as small as possible.

On the other hand, when the deep ultraviolet laser light DUV generated from the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 reaches the aluminum metal back layer 6, the aluminum metal back layer 6 receives as much deep ultraviolet laser light DUV as possible. The light emission efficiency can be increased by reflecting the light back to the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. The thickness t ₆ of the aluminum metal back layer 6 from this point it is as large as possible. However, when the thickness t ₆ of the aluminum metal back layer 6 is in the range of 30 nm or more, the reflectivity of the aluminum metal back layer 6 becomes large regardless of the incident angle θ to the aluminum metal back layer 6. That is, as shown in FIG. 5A, when the thickness t6 of the aluminum metal back layer ₆ is 10 nm, sufficient reflectance cannot be obtained. Further, as shown in FIG. 5B, when the thickness t6 of the aluminum metal back layer ₆ is 21 nm, surface plasmon absorption becomes remarkable, and sufficient reflectance cannot be obtained. Further, as shown in FIG. 6A, when the thickness t6 of the aluminum metal back layer ₆ is 30 nm, the surface plasmon absorption becomes small, and a further sufficient reflectance is obtained. Furthermore, as shown in FIG. 6B, when the thickness t6 of the aluminum metal back layer ₆ is 60 nm, surface plasmon absorption is eliminated and sufficient reflectance is obtained. 5 and 6 are total reflection attenuation (ATR) signal spectrum diagrams when the light is incident on the aluminum metal back layer 6 from the sapphire (0001) substrate 1 through the AlN layers 2, 3 and 4 at an incident angle θ. As a simulation software, Winspall (trade name) developed by Max Planck Institute was used. The conditions for the base of the deep ultraviolet laser beam DUV having the wavelength λ = 240 nm are as follows.
About the sapphire (0001) substrate 1
n ₁ = 1.84
k ₁ = 0
Where n ₁ is the refractive index of the sapphire (0001) substrate 1,
k ₁ is an extinction coefficient of the sapphire (0001) substrate 1.
For AlN layers 2, 3, and 4,
n ₂ = 1.87
k ₂ = 0
Where n ₂ is the refractive index of the AlN layers 2, 3 and 4,
k ₂ is the extinction coefficient of the AlN layers 2, 3 and 4.
For the aluminum metal back layer 6,
n ₆ = 0.172
k ₆ = 2.79
Where n ₆ is the refractive index of the aluminum metal back layer 6,
k ₆ is an extinction coefficient of the aluminum metal back layer 6.

From the above, it is preferable that the thickness t ₆ of the aluminum metal back layer 6 that minimizes the absorption loss of the electron beam EB and maximizes the reflectivity of the deep ultraviolet laser beam DUV is about 30 to 100 nm.

In addition to aluminum, silver (Ag) is also conceivable as a metal back layer that efficiently reflects the deep ultraviolet laser beam DUV. However, heavy metals such as silver have a high electron beam blocking ability, so they absorb the electron beam EB. Thus, the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 cannot be sufficiently excited, that is, cannot emit light. In the end, aluminum, which is a light metal and has good controllability and can be deposited, is optimal as the metal back layer.

Next, two reflecting structures RS1 are formed as resonator structures for causing laser oscillation in the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 formed as described above. In the reflection structure RS1, the two sidewalls of the structure of FIG. 1 including the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 have a cleavage reflectance R of about 30% so that the resonator length L is about 0.1 to 1 mm. A reflecting mirror, that is, two reflecting structures RS1 are realized. The reflective structure RS1 can also be realized by cutting by a dry etching method or laser scribing method and then polishing.

The electron emission source 7 in FIG. 1 is composed of a graphite nano needle rod.

The above-mentioned graphite nano needle rod is formed by the manufacturing method shown in FIG.

That is, in step 701, a graphite substrate having a graphite rod surface shown in FIG. 8A is etched by a plasma etching method using hydrogen gas, and the nano-ordered graphite nanoneedle shown in FIG. Get a rod. The plasma etching conditions are, for example, as follows.
RF power: 100-1000W
Pressure: 133-13300Pa (1-100Torr)
Hydrogen flow rate: 5-500sccm
Etching time: 1-100 minutes

Note that the plasma etching method in step 701 may be any of an electron cyclotron resonance (ECR) etching method, a reactive ion etching (RIE) method, an atmospheric pressure plasma etching method, and the like, and the processing gas is other than H ₂ gas. Ar gas, N ₂ gas, O ₂ gas, CF ₄ gas, etc. may be used.

The graphite nanoneedle rod substrate obtained by performing the plasma etching described above exhibits good electron emission characteristics as shown in FIG.

As shown in FIG. 10, the graphite nanoneedle rod according to the present invention has a higher emission current density than other materials such as carbon nanotube (CNT) and graphite nanofiber (GNF). Therefore, if the graphite nano needle rod according to the present invention is configured integrally with the conductive cathode base material, the adhesion of the graphite nano needle rod, the voltage drop at the interface between the graphite nano needle rod and the base material, and thus It can solve the problem of cathode breakdown due to degradation of electron emission characteristics (current saturation) and interface electric field concentration.

FIG. 11 shows a modified example of the flow of FIG. 7. In step 1101 before the plasma etching step 701 of FIG. 7, irregular micron (submicron) mechanical uneven structure processing by mechanical surface polishing such as sandblasting is performed. I do. Further, in step 1102 after the plasma etching step 701 in FIG. 7, irregular micron (submicron) laser irradiation uneven structure processing by surface polishing by high power laser irradiation such as CO ₂ laser, YAG laser, and excimer laser is performed. Do. Note that both steps 1101 and 1102 may be performed, but only one of them may be performed. In this case, it is preferable to perform step 1101 because small nano-order irregularities are more fragile. As a result, a concavo-convex structure having an irregular period such as a micron order or a submicron order is formed. Accordingly, the surface area of the graphite substrate is increased and more electrons are emitted.

In addition, in the irregular period micron (submicron) mechanical uneven structure processing step 1101 in FIG. 11, the surface area is increased by forming many irregular period micron or submicron order dents on the surface of the graphite substrate. You may let them. For example, a resist layer is applied, and then a pattern of the resist layer is formed by photolithography using a photomask having an irregular periodic pattern, and the graphite substrate is formed with H ₂ gas and O ₂ using the resist layer pattern. Plasma etching using gas, for example, RIE process is performed, and then the pattern of the resist layer is removed. Further, the surface area can be increased by forming an irregular periodic micron order or submicron order sword mountain type concavo-convex structure by a cutting method using a mechanical ruling engine or the like. This sword mountain-type uneven structure can also be formed by forming a reverse sword mountain mold by etching and pouring a liquid graphite material, such as carbon black, into it. The electron emission source 7 may be one that can change the energy E of the electron beam EB to be emitted, or may be one that is fixed. The thickness t ₁ of the sapphire (0001) substrate 1 is set in accordance with the electron emission source 7 to be used. For example, if the energy E of the electron beam EB is fixed at E = 6 keV, a thickness of 216 nm or more is selected, and if it is fixed at E = 10 keV, a thickness of 1000 nm or more is selected. If the energy E of the electron beam EB of the electron emission source 7 is variable, the thickness t _{1 of the} sapphire (0001) substrate ₁ is determined in accordance with the assumed upper limit of the use range, and if the upper limit is 10 keV or more, the thickness is 1000 nm. It is selected from the above range.

FIG. 12 is a cross-sectional view showing a second embodiment of the deep ultraviolet laser light source according to the present invention. The deep ultraviolet laser light source of FIG. 12 is also an end face reflection type.

In FIG. 12, a reflective structure RS2 made of a dielectric multilayer mirror is provided instead of the reflective structure RS1 that becomes the reflective mirror of FIG. Dielectric multilayer mirror is a combination of two dielectric multilayer films with different refractive indexes such as LaF ₃ / Na ₃ AlF ₆ , Al ₂ O ₃ / SiO ₂ , Y ₂ O ₃ / SiO ₂ , HfO ₂ / SiO _2, etc. It is configured by laminating about 2 to 100 thin films. The thickness of each layer is appropriately selected depending on the oscillation laser wavelength. At this time, for example, if the reflectance R of one reflective structure RS2 is 100% and the reflectance R of the other reflective structure RS2 is 90%, laser output can be obtained from only one direction.

In FIG. 12, a photonic crystal structure may be used instead of the dielectric multilayer mirror as the reflective structure RS2. The photonic crystal structure has a higher reflectance R than the dielectric multilayer mirror.

FIG. 13 is a partial sectional view in which the deep ultraviolet laser light source of FIGS. 1 and 12 is actually assembled.

In FIG. 13, a laminate S, an aluminum metal back layer 6, and graphite composed of a sapphire (0001) substrate 1, an AlN buffer layer 2, a grating AlN layer 3, an AlN layer 4, an Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. The electron emission source 7 made of nano needle rods is vacuum sealed to the glass tube 8 and the anode electrode 9 using a stem pin (vacuum introduction terminal or the like) (not shown). In this case, the anode electrode 9 has a metal structure in which a suitable metal plate is perforated or a structure in which the electrode can be obtained by metal deposition on the glass tube 8. Next, the aluminum metal back layer 6 is closely attached to the anode electrode 9 so as to cover the opening of the glass tube 8 so as to maintain a vacuum using an indium (In) seal or the like. What is used for adhesion is not limited to an indium seal, but any conductive material may be used. There is an aluminum metal back layer 6 between the stacked body S and the anode electrode 9, and in use, electric charges can be released from the aluminum metal back layer 6 to the anode electrode 9 through a conductive material. Further, the glass tube 8 and the anode electrode 9 are welded. At this time, glass is easily welded to each other, but in the case of a metal structure in which the anode electrode 9 is perforated, a step-sealed glass that gradually changes from glass to metal is prepared. On the cathode side of the glass tube 8, an electron emission source 7 made of a graphite nano needle rod and an electrostatic lens 10 made of a cylindrical metal are attached using a stem pin or the like. The electrostatic lens 10 is for focusing the electron beam EB of the electron emission source 7 on the stacked body S. A stem pin to which the electron emission source 7 and the electrostatic lens 10 are attached is welded and vacuum sealed. When a graphite nano needle rod is used as the electron emission source 7, its tip is installed perpendicularly to the plane of the laminate S, and because it saves space, the glass tube 8 can be made smaller, and the entire apparatus can be made compact. Can be At this time, since the glass tube 8 performs a so-called bipolar operation, the above-described stem pin is welded so that the distance between the electron emission source 7 on the cathode side and the anode electrode 9 becomes a predetermined value. Specifically, the distance is set to a predetermined value of about 0.5 mm / kV with respect to the voltage (kV) between the electron emission source 7 and the anode electrode 9.

The DC power source 11 is between the anode electrode 9 and the electron emission source 7 and applies a DC voltage V ₁ to the anode electrode 9 so that the anode electrode 9 has a low potential when viewed from the electrons, whereas the DC power source 12 is an electron. A focusing DC voltage V ₂ is applied to the electrostatic lens 10 so that the electrostatic lens 10 is at a high potential when viewed from the electrons between the emission source 7 and the electrostatic lens 10.

FIG. 14 is a partial cross-sectional view showing a modified example of FIG. In FIG. 14, an extraction electrode 13 is added in the vicinity of the electron emission source 7 to the components of FIG. 13, and a DC voltage V ₃ is applied to the extraction electrode 13 by a DC power source 14 independently of the voltage of the anode electrode 9. The current I _EB of the electron beam EB flowing between the electron emission source 7 and the anode electrode 9 is controlled independently. As a result, the glass tube 8 performs a so-called triode operation.
In the above description, the DC power source is described as an example of the

power sources

11, 12, and 14. However, the electron beam EB can be temporally modulated by appropriately using an AC power source and a pulse power source. Thus, the laser beam of the deep ultraviolet laser beam DUV can perform not only continuous oscillation but also pulse oscillation according to the modulation of the electron beam EB.

In order to stably operate the electron emission source 7 made of graphite nano needle rods and extend the life of the deep ultraviolet laser light source, the degree of vacuum in the glass tube 8 may be increased. However, a normal field emission type electron emission source requires a vacuum degree of 10 ⁻⁷ Pa or more, whereas in the case of the electron emission source 7 composed of the graphite nano needle rod according to the present invention, about 10 ⁻⁶ Pa. The degree of vacuum is sufficient. Therefore, the vacuum sealing time can be greatly shortened, and as a result, the tact time can be shortened and a cheaper deep ultraviolet laser light source can be provided in the manufacture of the deep ultraviolet laser light source. In order to maintain the established degree of vacuum for a long time, a getter or the like (not shown) may be enclosed in the glass tube 8.

FIG. 15 is a plan view showing an example of an electron beam irradiation pattern P having a width of about 1 μm on the aluminum metal back layer 6 obtained when the direct current for focusing voltage V ₂ shown in FIGS. 13 and 14 is controlled. When such an electron beam irradiation pattern P is obtained, the transverse mode (TEM ₀₀ ) pattern and the laser oscillation frequency are stabilized.

FIG. 16 shows emission intensity and laser oscillation obtained by applying 5 kV as the DC voltage V ₁ to the deep ultraviolet laser light source of FIG. 14 and applying the DC voltage V ₃ to the current I _EB of the electron beam EB of 1 μA, 2 μA, and 30 μA. An intensity spectrum is shown. The thickness t ₅ of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer ₅ is 60 nm.

In FIG. 16, AlN emits light from defects in the AlN layer 4, QW 1 emits light from the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5, and QW 2 represents a deep quasi of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. Emission from the position, QW3, indicates the laser intensity from the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5. As described above, when the current I _EB of the electron beam EB is increased to 30 μA based on the DC voltage V ₁ = 5 kV, the excitation density increases, the loss of the resonance structures RS1 and RS2 is overcome, and an inversion distribution is formed. Cause laser oscillation.

FIG. 17 is a graph for explaining the directivity of the deep ultraviolet laser light source of FIG.

As shown in FIG. 17, in the case of simple light emission before laser oscillation with a DC voltage V ₁ = 5 kV and an electron beam EB current I _EB = 1 μA, the half-value width of the far-field image is as large as 30 ° to 40 °. On the other hand, in the case of laser oscillation where the DC voltage V ₁ after laser oscillation is V ₁ = 5 kV and the current I _EB = 30 μA of the electron beam EB, the half-value width of the far-field image is as small as about 5 °.

FIG. 18 is a graph showing the light output characteristics of the deep ultraviolet laser light source of FIG.

As shown in FIG. 18, when the density of the current I _EB of the electron beam EB is 0 to 30 A / cm ² , and the threshold value 30 A / cm ² is exceeded from the simple deep ultraviolet emission, the light output increases rapidly. It turns out that it becomes a laser oscillation state.

Thus, according to the above-described embodiment, the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 can obtain good laser oscillation characteristics by electron beam excitation. Further, when it is desired to improve the laser oscillation characteristics, as shown in FIG. 19, the AlN / AlGaN superlattice cladding layer 21 and the AlN light guide layer 22 are formed under the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 in FIG. At least one is provided, and at least one of the AlN light guide layer 23 and the AlN / AlGaN superlattice cladding layer 24 is provided on the upper layer of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5, thereby improving the optical confinement efficiency. Improve. The configuration of FIG. 19 can also be applied to the deep ultraviolet laser light source of FIG. When considering the optical confinement efficiency of the deep ultraviolet laser device of FIGS. 1 and 12 when an AlN / AlGaN superlattice cladding layer and / or an AlN optical guide layer is used as the optical confinement means as shown in FIG. The optical confinement light intensity of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 with respect to the total light intensity of the laser device is
Γ = 1-exp (-C · Δn · t ₅ )
However, C is a constant according to the semiconductor material, and in the case of AlGaAl, 2.5 × 10 ⁻³ Å ⁻¹ ,
Δn is the refractive index difference 0.3 between the refractive index n _AlGaN = 2.6 of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 and the refractive index n _AlN = 2.3 of the AlN / AlGaN superlattice cladding layer and / or AlN light guide layer,
It can be expressed as For example, if the thickness t ₅ of the Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 5 is 60 nm, Γ = 0.36, which is larger than Γ = 0.01, which is a standard for normal laser oscillation, and is very high. Light confinement efficiency can be realized.

FIG. 20 is a sectional view showing a third embodiment of the deep ultraviolet laser light source according to the present invention. The deep ultraviolet laser device of FIG. 20 is a surface emitting type.

20, the deep ultraviolet laser light source includes a sapphire (0001) substrate 31, an AlN buffer layer 32 formed on the sapphire (0001) substrate 31, a grating AlN layer 33 formed on the AlN buffer layer 32, and a grating AlN layer. A reflective structure RS31 formed of a dielectric multilayer mirror formed on 33, an AlN resonant layer 34 formed on the reflective structure RS31, and an Al _0.7 Ga _0.3 N well having a thickness of about 3 nm formed on the AlN resonant layer 34 Al _0.7 Ga _0.3 N / AlN multiple quantum well layer 35, Al _0.7 Ga _0.3 N / AlN multiple layer having a thickness of about 6 to 60 nm including 1 to 10 repetition periods, with an AlN barrier layer having a thickness of about 3 nm and one period as a cycle A reflective structure RS32 comprising an AlN resonant layer 36 formed on the quantum well layer 35, a dielectric multilayer mirror formed on the AlN resonant layer 36, and an aluminum (Al) metal back layer 37 formed on the reflective structure RS32. And an electron emission source 38 that emits an electron beam EB It becomes. In this case, the reflectance R of the reflecting structure RS31 is small, and on the other hand, the reflectance R of the reflecting structure 32 is large. Thus, when the electron beam EB is irradiated from the electron emission source 38, Al _0.7 Ga _0.3 N The / AlN multiple quantum well layer 35 is excited and resonates in the direction perpendicular to the growth surface, and the deep ultraviolet laser beam DUV is emitted from the reflective structure RS31 side.

The deep ultraviolet laser light source shown in FIG. 20 eliminates the need for a current confinement structure for realizing surface emission, thereby simplifying the epitaxial growth process. In addition, since the reflecting structures RS31 and RS32 are formed on the entire surface, the manufacture becomes easy. Further, since laser oscillation occurs from the electron beam irradiation position, the geometrical light emission pattern of the surface emitting laser can be freely changed.

FIG. 21 is a timing diagram showing the laser intensity for explaining the lifetime of the deep ultraviolet laser light source of FIGS.

As shown in FIG. 21, stable laser intensity is maintained even after 4000 hours. Therefore, the lifetime is expected to exceed 40,000 hours from the exponential lifetime prediction, and the lifetime is longer than that of the conventional deep ultraviolet laser light source, and the high emission intensity and the high emission efficiency are expected.

In the above-described embodiment, an Al _0.7 Ga _0.3 N / AlN multiple quantum well layer is used as the wide band gap semiconductor, but Al _x Ga _1-x N / AlN (0.1 ≦ x ≦ 0.9) A multiple quantum well layer may be used. In this case, the wavelength of the laser light becomes shorter as x becomes larger. In addition, other wide band gap semiconductors such as ZnMgO, BN, and diamond semiconductor can be used.

1, 31: Sapphire (0001) substrate 2, 32: AlN buffer layer 3, 33: Grating AlN layer 4: AlN layer _{_{5,35: Al 0.7 Ga 0.3 N /}} AlN multiple quantum well layer 6,37: aluminum metal back layer 7, 38: Electron emission source 8: Glass tube 9: Anode electrode 10: Electrostatic lens 11, 12: DC power supply 13: Extraction electrode 14: DC power supply 34, 36: AlN resonance layer
EB: Electron beam
DUV: deep ultraviolet laser light
RS1, RS2, RS31, RS32: Reflective structure

Claims

A substrate,
A wide band gap semiconductor layer provided on the substrate;
An aluminum metal back layer provided on the wide band gap semiconductor layer;
Comprising a resonator structure for resonating deep ultraviolet light generated from the wide band gap semiconductor layer;
An electron beam is irradiated from the aluminum metal back layer side to excite the wide band gap semiconductor layer so that deep ultraviolet light generated from the excited wide band gap semiconductor layer is laser-resonated by the resonator structure. Deep ultraviolet laser light source.
The wide band gap semiconductor layer comprises an Al x Ga 1-x N / AlN multiple quantum well layer comprising an Al x Ga 1-x N well layer (0.1 ≦ x ≦ 0.9) and an AlN barrier layer. Deep UV laser light source.
The deep ultraviolet laser device according to claim 2, wherein the Al x Ga 1-x N / AlN multiple quantum well layer has a thickness of about 6 nm to 60 nm.
The deep ultraviolet laser light source according to claim 1, wherein the thickness of the aluminum metal back layer is about 30 to 100 nm.
The deep ultraviolet laser light source according to claim 1, further comprising an electron beam source for irradiating the aluminum metal back layer with the electron beam.
The deep ultraviolet laser light source according to claim 5, wherein the electron beam source is composed of a graphite nano needle rod.
The thickness t 1 of the substrate is
t 1 ≧ a · E 3
Where E is the energy of the electron beam,
The deep ultraviolet laser light source according to claim 1, wherein “a” is a constant determined by a material of the substrate.
The deep ultraviolet laser light source according to claim 1, further comprising an electrostatic lens for focusing the electron beam on the wide band gap semiconductor layer.
The deep ultraviolet laser light source according to claim 1, further comprising an extraction electrode for controlling the current of the electron beam in the vicinity of the electron beam source.
Furthermore, it comprises a glass tube whose inside is a vacuum,
The electron beam source is installed in the glass tube,
6. The deep ultraviolet laser light source according to claim 5, wherein the aluminum metal back layer is in close contact with the glass tube.
The deep ultraviolet laser light source according to claim 1, wherein the reflection structure is an end face reflection type provided on both sides of a wide band gap semiconductor layer.
The deep ultraviolet laser light source according to claim 1, wherein the reflection structure is a surface-emitting type provided above and below the wide band gap semiconductor layer.