KR100676288B1 - Ultraviolet rays sensor - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultraviolet sensing semiconductor device, wherein Al _x Ga _{1 - x} N (0≤x) formed on the substrate 10 to improve the characteristics of the Schottky junction and the ohmic junction and at the same time improve the optical reactivity and reliability. The layer ≤1) is used as the light absorbing layer 13, and a capping layer is formed on the Al _y Ga _{1 - y} N (0≤y≤x) layer having a smaller aluminum (Al) composition than the light absorbing layer 13 and having a very thin layer. (17), a transparent Schottky bonding layer 15 is formed thereon, and the ohmic bonding layer 16 is formed on the capping layer 17 or on the light absorbing layer 13.

UV, Semiconductor, Schottky, Capping, Light Reactivity, Reliability, Yield

Description

Ultraviolet Sensing Semiconductor Device {Ultraviolet rays sensor}

1 is a cross-sectional view of a ultraviolet sensing semiconductor device according to the prior art,

2 is a plan view of the semiconductor device illustrated in FIG. 1;

3 is a cross-sectional view of an ultraviolet sensing semiconductor device according to another conventional technology;

4 is a plan view of the semiconductor device illustrated in FIG. 3;

5 is a cross-sectional view showing a first embodiment of the present invention;

6 is a plan view of the semiconductor device illustrated in FIG. 5;

7 is a cross-sectional view showing a second embodiment of the present invention;

8 is a plan view of the semiconductor device illustrated in FIG. 7;

9 is a cross-sectional view showing a third embodiment of the present invention;

10 is a plan view of the semiconductor device illustrated in FIG. 9;

11 is a graph comparing current-voltage characteristics of devices according to the related art and the present invention;

12 is a yield graph of a conventional device,

13 is a yield graph of the device according to the present invention.

10 substrate 11 low temperature buffer layer

12 high temperature buffer layer 13 light absorbing layer

14: Schottky bonding layer 15: Schottky pad layer

16: ohmic bonding layer 17: capping layer

18: middle buffer layer

The present invention relates to ultraviolet light-sensing semiconductor device, specifically less than the Al composition of the light absorption layer on the _{Al x Ga 1-x N (} 0≤x≤1) of the light absorption layer is very thin _{Al y Ga 1 - y N (} 0 An ultraviolet sensing semiconductor device capable of improving the characteristics of the Schottky junction and the ohmic junction and at the same time improving the optical reactivity and reliability by forming a Schottky junction layer on the ≤y≤x) layer and then forming a Schottky junction layer thereon. It is about.

Ultraviolet rays with a wavelength of 400 nm or less are divided into several bands for each wavelength. The UV-A region is 320 nm-400 nm, and more than 98% of the sunlight reaching the earth's surface is the UV-A region. UV-A has the effect of blackening or skin aging on human skin. The UV-B area is 280nm-320nm, and only about 2% of sunlight reaches the surface of the earth. It has a very serious effect on the human body such as skin cancer, cataracts and erythema. UV-B is mostly absorbed by the ozone layer, but recently, the amount reaching the surface of the earth due to the destruction of the ozone layer is increasing and the area is increasing, which is a serious environmental problem. UV-C is between 200nm and 280nm, and everything coming from sunlight is absorbed into the atmosphere and hardly reaches the earth's surface. This area is widely used for sterilization. One of the quantified effects of ultraviolet rays on the human body is the UV Index defined by the amount of UV-B incident.

Ultraviolet rays can be detected by using a photo multiplier tube (PMT) or a semiconductor device. Since semiconductor devices are cheaper and smaller than PMT, most of them use a lot of semiconductor devices in recent years. In the semiconductor devices, GaN, SiC, etc., in which the energy band gap is suitable for ultraviolet detection, and the energy band gap are small, but Si is widely used. Among the devices based on GaN, Schottky junction type, MSM (metal-semiconductor-metal) type and PIN type devices are mainly used. Schottky junction type devices are preferred because of their simple process. .

The structure of a conventional Schottky junction ultraviolet sensing element is shown in FIGS. 1 and 2. As shown in FIG. 1 and FIG. 2, the conventional Schottky junction UV sensing device first grows a GaN and SiC layer on the substrate 10 using MOCVD or MBE. In the substrate 10 to be used, sapphire is most often used for GaN layer growth, Si, GaAs, SiC, etc. are used, and glass is rarely used.

In the case of a sapphire substrate is grown on the (0001) plane, if the growth immediately due to the lattice constant difference between GaN and sapphire cracks (crack) occurs, the layer does not grow properly. Therefore, the low temperature buffer layer 11 is grown at a temperature lower than the normal growth temperature, and then the growth temperature is raised to grow a layer required for the device. The low temperature buffer layer 11 mainly grows GaN or AlN and has a thickness of 0.1 μm or less. After the low temperature buffer layer 11 is grown, the high temperature buffer layer 12 is grown thereon, and a GaN layer is mainly grown. Generally, about 0.5 to 2 μm needs to be grown to prevent defects caused by the substrate 10 and the low temperature buffer layer 11. By reducing the influence, the crystallinity of the layer becomes better. The high temperature buffer layer 12 may grow an AlGaN layer when the light absorbing layer is an AlGaN layer. The high temperature buffer layer 12 may be artificially doped with a dopant such as Si to maintain the doping concentration of the layer as n-type.

The growth of the light absorbing layer 13 after the growth of the high temperature buffer layer 12 is made by varying the composition of the layer according to the wavelength of light to be absorbed. For example, to detect a UV-B region, an AlGaN layer containing about 20% of Al is grown, and an AlGaN layer containing about 45% of Al is grown to detect a UV-C area.

In the case where the high temperature buffer layer 12 is GaN and the light absorbing layer 13 is AlGaN, if the Al composition is high, cracks may occur during or after the growth due to the lattice constant difference, and thus the device does not operate. The high temperature buffer layer 12 and the light absorbing layer 13 Another intermediate buffer layer (not shown) may be inserted between the lines. The interposed intermediate buffer layer grows the AlGaN or AlN layer to lower the growth temperature or to grow a thin layer (<0.1um) having a larger Al composition than the light absorbing layer 13. The doping concentration of the light absorbing layer 13 is maintained at n-type while the doping concentration is low, so the efficiency is large, so it is maintained at 1E17cm ^{- 3} or less as possible. In the case of the AlGaN layer, the doping concentration may also be 1E18cm- ³ . The thickness of the light absorbing layer 13 grows in various ways depending on the structure of the device from 0.1um to 2um.

After the MOCVD growth, the wafer is first formed with an ohmic junction layer 16, which may be formed directly on the light absorbing layer 13 as shown in FIGS. 1 and 2, or as shown in FIGS. 3 and 4. The absorber layer 13 may be etched and formed on the high temperature buffer layer 12. When the ohmic junction is formed in the high temperature buffer layer 12, the high temperature buffer layer 12 is formed to have a higher doping concentration than the light absorbing layer 13, and the ohmic bonding characteristic is good, and the light absorbing layer 13 is AlGaN. If it is difficult to secure, an AlGaN layer having a lower Al composition than the GaN or light absorbing layer 13 may be formed in the high temperature buffer layer 12, and the ohmic bonding layer 16 may be formed thereon. As the metal for forming the ohmic junction, Ti / Al and Cr / Ni / Au are mainly used. In the case of Ti / Al, Ti (<500Å) / Al (> 3000Å) thickness is formed, and metal is deposited, followed by heat treatment at a temperature of> 400 ° C. for a suitable time in a mixed gas atmosphere containing nitrogen or nitrogen to form an ohmic junction. Form.

After the ohmic junction layer 16 is formed, the Schottky junction layer 14 is formed on the light absorbing layer 13, and the mainly used metals are Ni, Pt, Ru, Au, and the like.

In the case of the Schottky junction UV sensing element, since the light must pass through the Schottky junction layer 14 and enter the light absorbing layer 13, the ultraviolet ray transmittance of the Schottky junction layer 14 is an important item. Therefore, most of the metal thickness is formed by depositing less than 500Å. Also, in order to improve electrical and reliability characteristics, an oxide may be formed by heat treatment after metal deposition. In other words, many improved properties such as NiO _x and RuO _x have been reported. The heat treatment temperature is variously processed by the metal and the process, and is mainly performed at about 300 ° C.

ITO is mainly used to further form a light transmissive conductive layer on the Schottky bonding layer 14 to improve electrical properties. After the Schottky bonding layer 14 is formed, Au is thickly deposited on the Schottky bonding layer 14 for wire connection with an external electrode to form the Schottky pad layer 15.

The schottky pad layer 15 mainly uses Ni / Au or Cr / Ni / Au, and may be formed separately on the ohmic junction layer 16. Since the region in which the schottky pad layer 15 is formed does not transmit light and thus does not function as the schottky bonding layer 14, the region of the schottky pad layer 15 should be reduced to a minimum space for the bonding wire. After the formation of the schottky pad layer 15, the back surface of the substrate 10 is wrapped / polished to a total thickness of about 100 μm, and then separated into individual devices through a scribing / breaking process.

The separated individual device is mounted in a TO-CAN type package or an SMD type package to operate as a sensing device.

In the case of the conventional Schottky junction sensing device, a Schottky junction layer is heat-treated to improve ultraviolet transmittance and improve reliability. In other words, when the metal is deposited and then heat-treated in an oxygen-containing atmosphere to form an oxide, UV transmittance at short wavelength is increased and reliability is improved. However, in spite of the improvement effect, when Schottky junction layer is formed directly on the AlGaN light absorbing layer, the high resistance of AlGaN does not provide uniform Schottky bonding characteristics, and at the same time the bonding force between the light absorbing layer and the Schottky junction interface is weak. Over time, there exists a problem of a photoreactivity fall and reliability fall.

The present invention has been made to solve the above-mentioned shortcomings of the conventional Schottky junction UV sensing semiconductor device, and an object of the present invention is to provide a light absorbing layer over an Al _x Ga _{1 - x} N (0≤x≤1) layer. By using a thin Al _y Ga _{1 - y} N (0≤y≤x) layer with a low Al composition as a capping layer, a Schottky junction layer is formed thereon, thereby improving the characteristics of the Schottky junction and the ohmic junction. At the same time, to provide an ultraviolet sensing semiconductor device suitable for improving the light reactivity and reliability.

Hereinafter, with reference to the accompanying drawings, preferred embodiments that do not limit the present invention will be described in detail.

In the structure of the present invention, Al _y Ga _{1 - y} having a lower Al composition than the light absorbing layer on the Al _x Ga _1-x N (0 ≦ _x ≦ 1) light absorbing layer in a structure in which a Schottky bonding layer is formed on the conventional light absorbing layer. The N (0≤y≤x) layer is used as a capping layer, and a Schottky junction layer is formed thereon, thereby improving the structure of the Schottky junction and the ohmic junction while improving the optical reactivity and reliability. It is.

5 and 6 illustrate an ultraviolet sensing semiconductor device according to a first embodiment of the present invention. Reference numerals in the drawings used the same reference numerals for the same components or parts as those used in the prior art drawings.

The semiconductor device according to the first embodiment is almost the same as the conventional ultraviolet sensing semiconductor device shown in Figs. 1 to 4, but unlike the conventional structure in which the Schottky bonding layer 14 is formed on the light absorbing layer 13, the light absorbing layer is After the capping layer 17 is formed on (13), there is a difference that the Schottky bonding layer 14 is formed on the capping layer 17.

In view of the process technology, the substrate 10 mainly uses sapphire, but SiC, Si, GaAs, glass, and the like may also be used. In the case of a 2 inch diameter sapphire substrate, the thickness is 300 to 450 um, and a (0001) plane is mainly used as a growth plane. A tilted substrate is also used to improve the surface of the light absorbing layer. As a device for growing on the substrate 10, mainly MOCVD, MBE, HVPE and the like are used. In the case of MOCVD, after the substrate 10 is mounted, the temperature is raised to 1,000 ° C. or more to perform a thermal cleaning process to remove impurities on the surface of the substrate 10, and then grow. First, the low temperature buffer layer 11 is grown. That is, after lowering the growth temperature of the MOCVD to 500 ~ 600 ℃, to grow the low temperature buffer layer 11 to 200 ~ 500 하는데 thickness GaN or AlN is grown. The reason for growing the low temperature buffer layer 11 is to solve this problem because the lattice constant between the substrate 10 and the growing layer is different. After the low temperature buffer layer 11 is grown, the growth temperature is increased to 1,000 ° C. or higher, and the high temperature buffer layer 12 is grown. The high temperature buffer layer 12 mainly grows a GaN layer, and generally has a thickness of 0.5 to 3 μm and is n-type doped, whether or not artificially doped. Doping concentration was mid. Keep E16 ~ low E18 cm ^-3 . On the high temperature buffer layer 12 is grown a light absorbing layer 13 that absorbs ultraviolet light and generates a current. The light absorbing layer 13 is grown to have a low doping concentration as much as possible to grow the GaN or AlGaN layer to a thickness of about 0.1 ~ 2um.

In the case where the light absorbing layer 13 is AlGaN and the high temperature buffer layer 12 is GaN, cracks occur when the thickness is thick due to the lattice constant difference, so that the thickness of the AlGaN layer is limited. For example, AlGaN having 20% Al composition. In the case of layers, cracks occur when they are grown to 0.1um or more. Therefore, in order to prevent this, an intermediate buffer layer 18 may be inserted between the high temperature buffer layer 12 and the light absorbing layer 13, which is illustrated in the third embodiment of FIG. 9. As the intermediate buffer layer 18, mainly an AlN or AlGaN layer is grown, and the thickness is formed to be 500 Å or less. The growth temperature may be at a low temperature of 500 ~ 600 ℃ or at a high temperature of 900 ~ 1,100 ℃. After the light absorbing layer 13 grows, the capping layer 17 is grown. An Al _y Ga _1-y N (0 ≦ _y ≦ x) layer of 10 nm or less may be used as the capping layer. The capping layer 17 is formed of a layer having a lower Al composition than the light absorbing layer 13, and the growth temperature of the capping layer 17 may be grown between 500 and 1200 ° C. The thickness of the capping layer 17 should be at least 1/10 smaller than the thickness of the space charge region (SCR) region formed in the light absorbing layer 13 to have an effect of 10% or less on the light reactivity of the light absorbing layer 13. Will be given. In addition, the doping concentration should be formed to be equal to or lower than the light absorbing layer (13). After the growth up to the capping layer 17, the grown sample is taken out of the growth apparatus, washed with HF solution, and then proceeds to a chip manufacturing process. First, a pattern is formed on the capping layer 17 using a photoresist, a Ti / Al metal is deposited using an electron beam (e-beam) or a thermal evaporator, and then the photoresist is removed to form an ohmic junction layer ( 16). Metals mainly used to form ohmic junctions in N-type GaN or AlGaN layers include Ti / Al, Cr / Ni / Au, and the deposition thickness is about Ti (100 to 500Å) for Al (5,000 ~). 10,000Å) is deposited. The deposited ohmic bonding layer 16 undergoes a heat treatment process to secure ohmic bonding characteristics, and is generally heat treated for several minutes in a nitrogen or general air atmosphere at a temperature of about 500 ° C. Some metals, such as Cr / Ni / Au, can secure ohmic bonding properties even without heat treatment. Although the ohmic bonding layer 16 is formed on the capping layer 17 as in the embodiments shown in FIGS. 5 and 6, when the ohmic bonding characteristics are difficult to obtain in the capping layer, the second embodiment of FIGS. As described above, the capping layer 17 and the light absorbing layer 13 may be etched and formed on the high temperature buffer layer 12. Etching mainly uses a dry etching method using an inductively coupled plasma generator (ICP).

After the ohmic junction layer 16 is formed, a pattern is formed in the region where the Schottky junction layer 14 is to be formed by using a photoresist, and Ni, Pt, Pd, and the like are formed by using an e-beam or a thermal evaporator. After thin deposition of Au or the like, the photoresist is removed to form the Schottky bonding layer 14. The thickness of the Schottky metal to be deposited is 100 kPa or less in consideration of the transmittance. After the Schottky metal is deposited, the heat treatment is performed, and the temperature is lower than the temperature at which the ohmic junction layer 16 is formed. When Ni is deposited, NiOx is formed by heat treatment in an oxygen atmosphere. Thus, the Schottky junction is improved in transmittance at shorter wavelengths and improves reliability of the device than Ni which is not heat-treated. After the Schottky bonding layer 14 is formed, a pattern is formed with a photoresist to form the Schottky pad layer 15, and Ni / Au, Pt / Au, etc. are deposited using an electron beam or a thermal evaporator, and then the photoresist is removed. The schottky pad layer 15 is formed. The deposition thickness is about Ni, Pt (<500Å), Au (> 5,000Å) and no additional heat treatment. When the schottky pad layer 15 is formed, a thickness corresponding to the wavelength may be deposited using SiO ₂ to prevent reflection of incident ultraviolet rays. Then, by inspecting the characteristics of the device in the wafer state, the good and bad devices are distinguished by ink marks, and then the back surface of the substrate 10 is ground / wrapped / polished to form a total thickness of about 100 μm, followed by scribing ( The package process is performed by dividing into individual chips through the scribe / brake process.

In the packaging process, die-bonding chips manufactured in a TO-CAN type or SMD type package are used, and the Schottky pad layer 15 and the ohmic junction layer 16 are respectively packaged with anode and cathode electrodes. And wire bonding using Au or Al wire. The final assembly is then encapsultant or glass to completely separate the chip from the external environment.

7 and 8 illustrate a case in which the ohmic bonding layer 16 is formed on the high temperature buffer layer 12 without being formed on the capping layer 17. This case is formed when the band gap of the capping layer 17 is high or when it is difficult to obtain ohmic bonding characteristics for other reasons.

9 and 10, the intermediate buffer layer 18 is formed between the high temperature buffer layer 12 and the light absorbing layer 13. When the light absorbing layer 13 is formed of AlGaN, the high temperature buffer layer 12 is formed. When GaN and the lattice constant is large, there is a problem that cracks occur. To solve this problem, an AlN or AlGaN layer or a superlattice layer in which two materials having different compositions are alternately grown is inserted into the intermediate buffer layer 18. In the case of the super lattice layer, GaN / AlN, GaN / AlGaN, AlGaN / AlN, etc. are used so that each layer does not exceed 200Å.

The ultraviolet-sensing semiconductor device of the present invention configured as described above is separated into individual chips to be packaged and operated in TO-CAN type or SMD type. When the bias is reversed or zero biased between the anode and cathode electrodes, the incident ultraviolet rays penetrate the Schottky junction layer 14 to be absorbed in the depletion layer formed on the capped layer 17 and the light absorbing layer 13. They generate electrons and holes, and they move to the cathode and anode electrodes, respectively, to sense the amount of incident light. Changing the composition of the light absorbing layer 13 can adjust the wavelength of the ultraviolet rays to be detected. That is, when the AlGaN layer having 20% Al composition is formed as the light absorbing layer 13, only the wavelength of 320 nm or less is absorbed by the band gap, so that only the UV-B and UV-C regions can be detected. If it is formed in%, only the wavelength below 280nm is absorbed and only the UV-C region can be detected. In addition, when the coating having a filter function on the glass used in the package may have various wavelength control functions. That is, when the light absorbing layer 13 is formed of GaN, all wavelengths of 370 nm or less are sensed, but if the glass only transmits 280-320 nm, only the UV-B region can be detected even if the light absorbing layer 13 is formed of GaN. have.

FIG. 11 is a graph comparing the current-voltage characteristics of the device according to the present invention shown in FIGS. 1 to 4 with the present invention. The conventional device is turned on as an ohmic junction is formed in an AlGaN layer. ) The current flow is limited due to high voltage and large resistance, but the device according to the present invention has a thin aluminum composition and a very thin Al _y Ga _1-y N (0≤y≤x) layer than the light absorbing layer. The Schottky bonding layer is formed thereon, and the ohmic bonding layer is formed on the capping layer or on the light absorbing layer, which shows that the current flow is greatly improved.

12 is a graph showing the yield of the conventional ultraviolet sensing semiconductor device shown in FIGS. 1 to 4, and shows a distribution diagram in the wafer of the dark current ld and the photocurrent lph, and the conventional device is a dark current ld. Yield decrease by, but the yield decrease by the photocurrent (lph) is so large that the 14% yield is recorded because the depletion region due to Schottky junction is not properly formed due to poor metal adhesion. On the other hand, as can be seen in the graph of Figure 13, the yield of the ultraviolet-sensing semiconductor device according to the present invention has been shown to improve the yield to 67% by solving this disadvantage.

As described above, the conventional technique consists of a Schottky junction on the light absorbing layer. When the AlGaN layer is used as the light absorbing layer, it is difficult to form an ohmic junction directly on the AlGaN layer because of high resistance at an Al composition of 15% or more. It becomes difficult to obtain uniform Schottky characteristics. In addition, a problem arises in that the adhesion between the light absorbing layer and the Schottky bonding layer is weak. Therefore, in the present invention, when the light absorbing layer is Al _x Ga _{1 - x} N (0≤x≤1), the cap is applied by applying the Al _y Ga _{1 - y} N (0≤y≤x) capping layer having a smaller Al composition than the light absorbing layer. Omic bonding and Schottky bonding can be simultaneously performed on the ping layer, and uniform Schottky bonding characteristics can be obtained from the Schottky bonding layer formed on the capping layer. In addition, AlGaN layer with high Al composition does not have good adhesion with metal, which causes chip manufacturing yield or reliability to be reduced due to this reason. It has a useful effect to improve the yield and improve the reliability.

Claims (7)

 In the ultraviolet sensing semiconductor light receiving device having a structure consisting of a buffer layer, a light absorbing layer, a Schottky bonding layer, an ohmic bonding layer on a substrate, The buffer layer is composed of an n-type Al _x Ga _{1 - x} N (0≤x≤1) layer, and the light absorbing layer is an n-type Al _x Ga _{1 - x} N (0≤x≤1) layer. A capping layer formed of an Al _y Ga _{1 - y} N (0 ≦ _y ≦ x) layer is formed on the light absorbing layer, and an ohmic junction layer is formed on a portion of the buffer layer or the capping layer. An ultraviolet sensing semiconductor device, characterized in that a Schottky junction layer is formed. The method according to claim 1, The substrate is ultraviolet sensing semiconductor device, characterized in that the substrate is selected from the group consisting of sapphire, SiC, Si, GaAs, glass. The method according to claim 1, Ultraviolet-sensing semiconductor device, characterized in that the buffer layer is composed of several layers of different Al composition and doping concentration. The method according to claim 1, The thickness of the light absorbing layer is a semiconductor device for ultraviolet sensing, characterized in that 0.1 ~ 2um. The method according to claim 1, The thickness of the capping layer is a semiconductor device for ultraviolet sensing, characterized in that made of 10nm or less. The method according to claim 1, Ultraviolet-sensing semiconductor device, characterized in that the ohmic junction layer made of a metal containing Au or Al. The method according to claim 1, The Schottky bonding layer is a semiconductor device for ultraviolet sensing, characterized in that made of a conductive oxide containing Ni, Pt, Pd.

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