JP4042336B2 - Silicon carbide semiconductor element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor element made of silicon carbide, that is, a silicon carbide semiconductor element.
[0002]
[Prior art]
Silicon carbide has many advantages over silicon as a material for semiconductor elements, and research for practical application has been vigorously conducted with the aim of using it for power semiconductors and high-frequency semiconductors.
There are 6H type, 4H type, and 3C type crystal structures of silicon carbide, and the single crystal is produced by the sublimation method. A silicon carbide semiconductor element is formed by forming an epitaxial growth layer having a predetermined carrier concentration on a single crystal substrate by CVD (chemical vapor deposition method), or by performing ion implantation for locally controlling conductivity. Produced. Further, when silicon carbide is exposed to a high temperature oxidizing atmosphere of, for example, 1100 to 1200 ° C., carbon in silicon carbide is oxidized to carbon dioxide (CO ₂ ), while silicon in silicon carbide is oxidized to form a surface. Then, a silicon dioxide (SiO ₂ ) film is formed. The thermal oxide film can be used as an insulating film of a semiconductor element.
[0003]
[Problems to be solved by the invention]
Substrates and epitaxial growth layers by the sublimation method tend to exhibit n-type conductivity by taking in atmospheric nitrogen gas remaining or mixed in the manufacturing apparatus. In particular, the epitaxial growth process is a process that takes a long time at a high temperature of 1500 ° C. or higher. Also, dopant ion implantation is often performed at a high temperature of 1000 ° C. or higher in order to improve the activation rate.
[0004]
During thermal oxidation, carbon in silicon carbide becomes CO ₂ gas and is discharged out of the system. At that time, the taken-in nitrogen is also discharged to the outside as a gas, but a part of the nitrogen is bonded to silicon atoms in the silicon carbide to form ultrafine silicon nitride particles in the silicon carbide near the interface with the thermal oxide film. It is formed. For example, when a Schottky diode that is a seed of a rectifying element is manufactured, even if the thermal oxide film is removed and a Schottky electrode is formed on the surface, a layer in which fine particles of silicon nitride are dispersed at the metal / semiconductor interface. Due to the existence, there was a problem that good rectification characteristics could not be obtained.
[0005]
When a MOS field effect transistor (hereinafter referred to as a MOSFET) is manufactured using a thermal oxide film, silicon nitride particles are formed on the channel layer formed in the semiconductor layer close to the oxide film / semiconductor boundary. Therefore, there is a problem that the carriers moving through the channel layer are scattered by the silicon nitride fine particles and the mobility is lowered.
[0006]
In view of these problems, an object of the present invention is to provide silicon carbide semiconductor elements such as Schottky diodes and MOSFETs which suppress generation of silicon nitride fine particles and have good characteristics.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a silicon carbide semiconductor element having a silicon carbide epitaxial layer grown on a silicon carbide semiconductor substrate, wherein the nitrogen concentration contained in the silicon carbide epitaxial layer is 2 × 10 ¹⁴ / cm ³ or more and 1 × 10 ^15. / cm ³ or less, the silicon carbide epitaxial layer comprises a V b group element or VI-group element, other than nitrogen, V b group elements other than nitrogen or the concentration of the VI group elements,, 1 × 10 ¹⁵ / It shall be cm ³ or more .
By suppressing the nitrogen concentration in the silicon carbide epitaxial layer, the generation of silicon nitride fine particles can be suppressed.
[0008]
In particular, when the silicon carbide epitaxial layer is n-type, it is important to avoid incorporation of nitrogen by using a Vb group element other than nitrogen, such as phosphorus, chlorine or antimony, or a group VI element as a dopant. Silicon carbide epitaxial layer, also contain a group III element of the aluminum or boron arsenide or Group II element, and, Vb group elements other than those nitrogen or VI group elements, Group III elements, the concentration of the II-group element Of course, it may be 1 × 10 ¹⁵ / cm ³ or more.
[0009]
Even when the silicon carbide semiconductor element has a region into which impurity ions are implanted, it is assumed that the nitrogen concentration contained in the ion implantation region is 1 × 10 ¹⁵ / cm ³ or less, avoiding nitrogen uptake.
As for the ion implantation region, in the case of n-type, the incorporation of nitrogen is avoided by using a Vb group element other than nitrogen, such as phosphorus, chlorine or antimony, or a group VI element as a dopant.
[0010]
There is no problem when the impurity ions are group III elements such as aluminum or boron, or group II elements.
In the case where the semiconductor element is a Schottky diode having a rectifying characteristic due to a Schottky barrier formed by a metal / semiconductor interface, a Schottky diode having good interface characteristics as described later can be obtained by suppressing the formation of silicon nitride fine particles. It is done.
[0011]
When the semiconductor element has a thermal oxide film, particularly a silicon nitride particles tends to occur in the thermal oxidation process, the nitrogen concentration of the portion to be thermally oxidized kept low by and the location wolfberry is important.
In the case where the semiconductor element is a MOSFET, a silicon carbide MOSFET having a high mobility can be obtained because carriers traveling in the channel layer are not scattered by the silicon nitride fine particles as will be described later.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
[Example 1]
FIG. 2 is a cross-sectional view of a silicon carbide Schottky diode (hereinafter referred to as SBD) of Example 1 of the present invention. (And referred hereinafter SiC substrate) on 11 4H-type silicon carbide substrate, n ^- and fabricated using et pin Taki interstitial wafer grown et pin Takisharu layer 12, 3 mm square, the electrode area of 3.14 mm ² SBD It is. 13 the n ^- d peak Takisharu layer 12 and the Schottky electrode of titanium to form a Schottky junction (Ti), titanium 14 provided on the back surface of the SiC substrate 11, a nickel, a cathode electrode of gold (Ti / Ni / Au) , 15 is an oxide film, and 16 is a guard ring formed by boron ion implantation and heat treatment.
[0013]
The manufacturing method will be described in detail below. A SiC substrate 11 having a diameter of 2 inches and having a silicon surface (hereinafter referred to as Si surface) tilted 8 degrees in the (11-20) direction (this angle is referred to as an off-angle) was used. The SiC substrate 11 is n-type and has a carrier concentration of 1 × 10 ¹⁸ / cm ³ . However, the 6H type or 3C type may be used, or the C surface or (11-20) surface may be used. Or even if the off-angle direction and angle are different, the application of the present invention is not affected.
[0014]
First, an n ⁺ cathode layer 17 is formed on the back side of the SiC substrate 11 by ion implantation of phosphorus ions. The acceleration voltage is 50 kV and the dose is 5 × 10 ¹⁴ / cm ² . Next, in order to avoid atmospheric nitrogen gas remaining or mixed in the manufacturing apparatus, a purge with argon gas and baking at 800 ° C. were repeated three times using a load-lock type epitaxial film forming apparatus, the n ^- deposited et pin Takisharu layer 12. n ^- d peak Takisharu layer 12, n-type with a thickness of 10 [mu] m, the carrier concentration of 1 × 10 ¹⁶ / cm ^3. The source gases are monosilane (SiH ₄ ), propane (C ₃ H ₈ ) and phosphine (PH ₃ ). The film formation temperature is 1500 ° C. and the time is 5 hours by RF heating using a SiC-coated graphite susceptor. is there. During this epitaxial growth, phosphorus ions implanted into the n ⁺ cathode layer 17 on the back surface are heat-treated and activated. In the case of an epitaxial film forming apparatus that is not a load lock type, unintended nitrogen doping occurs, and the concentration reaches 1 × 10 ¹⁶ / cm ³ or more.
[0015]
The patterning of the guard ring 16 using the positive type photoresist.
Subsequently, boron is ion-implanted in a box shape at an acceleration voltage of 30 to 180 keV, and then annealed at 1600 ° C. for 30 minutes to form a guard ring 16 having a depth of about 0.5 μm.
After forming and patterning an oxide film 15 having a thickness of 30 nm by pyrogenic oxidation at 1100 ° C. for 5 hours, Ti is sputter-deposited as a Schottky electrode 13, heat-treated at 200 ° C. for 5 minutes, and then the cathode electrode 14 Ti / Ni / Au was sputter-deposited into chips.
[0016]
FIG. 1 (solid line-phosphorus dope) is a reverse current-voltage characteristic diagram of the SBD produced in this way.
As a comparative example, the reverse current-voltage characteristics of an SBD (broken line-nitrogen doped) having a nitrogen-doped epitaxial layer according to a conventional manufacturing method are also shown in FIG.
In the nitrogen-doped SBD by the conventional manufacturing method, for example, the leakage current at a reverse voltage of 400 V is about 30 mA / cm ² , whereas the leakage current of the SBD of Example 1 is 1.5 mA / cm ² . Yes, you can see that it is 1/20.
[0017]
That is, in the step of forming the epitaxial layer 12 above, using an epitaxial deposition apparatus of the load lock, do to avoid nitrogen gas in the well production apparatus, the phosphorous doped the n ^- d peak Takisharu layer 12 formed This is probably because silicon nitride fine particles in the vicinity of the surface were hardly generated due to the film formation. When the nitrogen concentration of the epitaxial layer 12 was measured by the SiMS analysis method, it was 2 × 10 ¹⁴ / cm ³ .
[0018]
For confirmation, SBDs with different nitrogen concentrations were produced by changing the purge conditions and baking conditions in the load-lock type epitaxial film forming apparatus in the film forming process of the epitaxial layer 12, and the reverse characteristics were measured. The sum of the nitrogen concentration and the phosphorus concentration was 1 × 10 ¹⁶ / cm ³ .
FIG. 3 is a characteristic diagram showing the nitrogen concentration dependence of the leakage current at a reverse voltage of 400V.
[0019]
If the nitrogen concentration is 1 × 10 ¹⁵ / cm ³ or less, the leakage current can be suppressed to 3 mA / cm ² or less, but the current rapidly increases beyond 1 × 10 ¹⁵ / cm ³ . Therefore, it is important to keep the nitrogen concentration below 1 × 10 ¹⁵ cm ⁻³ . The ion-implanted species may be any Vb group element other than nitrogen. In the case of a p-type epitaxial wafer, the same result can be obtained even if aluminum is used.
[0020]
[Embodiment 2] FIG. 4 is a sectional view of a SiC MOSFET according to Embodiment 2 of the present invention. A 4H type SiC substrate 21 of the same type as in Example 1 was used. Using trimethylaluminum on the SiC substrate 21 doped with aluminum p ^- the growth of the error peak Takisharu layer 22. At this time, in the same manner as in Example 1, using an epitaxial deposition apparatus Rodorotsuku type, and purge with argon gas, it was repeated three times and 800 ° C. bake, p ^- was deposited et pin Takisharu layer 22.
[0021]
After the patterning using the positive type photoresist, phosphorus is ion-implanted into a box shape at an acceleration voltage of 30～180KeV, annealing is carried out for 30 minutes at 1600 ° C., a depth of about 0.5 [mu] m n ⁺ source region 27 and n ⁺ drain region 28 are formed.
After forming and patterning a gate oxide film 25 having a thickness of 30 nm by pyrogenic oxidation at 1100 ° C. for 5 hours, Ti / Ni / Au is sputter-deposited and patterned to form a source electrode 24, a drain electrode 23, and a Kate electrode 26. Then, the substrate electrode 29 was formed into a chip.
[0022]
In this manner was measured carrier mobility in the channel of a MOSFET fabricated by methods that do not avoid the conventional nitrogen pollution and 115cm ² / Vs p ^- mobility 5 cm ² / Vs but to form a et pin Takisharu layer The value was about 20 times or more.
This, p above ^- with d peak Takisharu layer 22 formation step, by taking the method to avoid nitrogen contamination in the air remaining or mixed in the manufacturing apparatus, hardly occurs silicon nitride particles near the surface This is probably because When the nitrogen concentration of the p ⁻ epitaxial layer 22 was measured by SIMS analysis, it was 2 × 10 ¹⁴ / cm ³ .
[0023]
For confirmation, MOSFETs with different nitrogen concentrations were produced in the step of forming the p ⁻ epitaxial layer 22 by changing the ratio of the dope gas, and the mobility characteristics were measured. The sum of the nitrogen concentration and the phosphorus concentration was 1 × 10 ¹⁶ / cm ³ .
FIG. 5 is a characteristic diagram showing dependency of carrier mobility on nitrogen concentration. When the nitrogen concentration is 1 × 10 ¹⁵ / cm ³ or less, the carrier mobility is 100 cm ² / Vs or more, but when it exceeds 1 × 10 ¹⁵ / cm ³ , it rapidly decreases. Therefore, it is important to keep the nitrogen concentration below 1 × 10 ¹⁵ cm ⁻³ .
[0024]
Further, for the purpose of improving channel mobility due to Coulomb scattering at the MOS interface, a counter-doped region 30 is formed by implanting phosphorus ions between the n ⁺ source region 27 and the n ⁺ drain region 28. The acceleration voltage was 30 kV and the dose was 2 × 10 ¹¹ / cm ² . For comparison, a device in which a counter-doped region was formed by nitrogen ion implantation was also produced. As a result of comparison between the two, the channel mobility was 100 cm ² / Vs with nitrogen counter-doping, but it was significantly improved to 150 cm ² / Vs with phosphorous doping.
[0025]
【The invention's effect】
As described above, according to the present invention, nitrogen contamination in the epitaxial layer growth step is avoided, and the nitrogen concentration contained in the silicon carbide epitaxial layer is suppressed to 2 × 10 ¹⁴ / cm ³ or more and 1 × 10 ¹⁵ / cm ³ or less. As a result, the influence of generation of silicon nitride fine particles was avoided, and the characteristics of the Schottky die auto and the MOSFET could be improved.
[0026]
Furthermore, it has been shown that it is effective to use an element other than nitrogen as an n-type dopant when forming an impurity region.
According to the present invention, it is possible to manufacture a silicon carbide semiconductor element having excellent characteristics other than Schottky die auto and MOSFET with good reproducibility.
[Brief description of the drawings]
1 is a current-voltage characteristic diagram of SiCSBD of Example 1 of the present invention and a comparative example. FIG. 2 is a cross-sectional view of SiCSBD of Example 1 of the present invention. FIG. 3 is a characteristic showing the nitrogen concentration dependence of leakage current of SiCSBD. [Fig. 4] Cross-sectional view of SiCMOSFET of Example 2 of the present invention [Fig. 5] Characteristic diagram showing nitrogen concentration dependence of carrier mobility of SiCMOSFET [Explanation of symbols]
11, 21 SiC substrate
12 n ^- d peak Takisharu layer
13 Schottky electrode
14 Cathode electrode
15 Silicon dioxide film
16 Guard ring
22 p ^- d peak Takisharu layer
23 Source electrode
24 Drain electrode
25 Gate oxide film
26 Gate electrode
27 n ⁺ source region
28 n ⁺ drain region
29 Substrate electrode
30 Counter-dope region

Claims (5)

In the silicon carbide semiconductor device grown silicon carbide epitaxial layer on a silicon carbide semiconductor substrate, the nitrogen concentration in the silicon carbide epitaxial layer has a 1 × 10 ¹⁵ / cm ³ or less 2 × 10 ¹⁴ / cm ³ or more, carbon reduction silicon epitaxial layer comprises a V b group element or VI-group element, other than nitrogen, V b group elements other than nitrogen or the concentration of the group VI element, and characterized in that 1 × 10 ¹⁵ / cm ³ or more A silicon carbide semiconductor element. In the silicon carbide semiconductor device grown silicon carbide epitaxial layer on a silicon carbide semiconductor substrate, the nitrogen concentration in the silicon carbide epitaxial layer has a 1 × 10 ¹⁵ / cm ³ or less 2 × 10 ¹⁴ / cm ³ or more, carbon reduction A silicon carbide semiconductor element, wherein the silicon epitaxial layer contains a group III element or a group II element, and the concentration of the group III element or group II element is 1 × 10 ¹⁵ / cm ³ or more . The silicon carbide epitaxial layer has a region in which impurity ions of a group Vb element other than nitrogen, a group VI element, a group III element, or a group II element are implanted, and a nitrogen concentration contained in the ion implanted region is 2 × 10 ^{3. The} silicon carbide semiconductor element according to claim 1, wherein the silicon carbide semiconductor element is ¹⁴ / cm ³ or more and 1 × 10 ¹⁵ / cm ³ or less. 2. The silicon carbide semiconductor element according to claim 1 , wherein the semiconductor element is a Schottky barrier diode having a rectifying characteristic by a Schottky barrier formed by the silicon carbide epitaxial layer and a metal . 4. The silicon carbide semiconductor device according to claim 3 , further comprising a MOS gate having a metal-thermal oxide film-semiconductor structure, wherein the ion implantation region is a source region and a drain region .

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