JP2002280573A - Silicon carbide semiconductor element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon carbide semiconductor element such as, a Schottky diode, MOSFET, etc., which is processed to suppress silicon nitride particulates and provide good characteristics. SOLUTION: To prevent a nitrogen gas from residing in a manufacturing apparatus or entering therein from outside, a load lock type epitaxial film forming apparatus is used and repeats purging with an argon gas and 800 deg.C baking, etc., to limit a nitrogen content in an epitaxial layer to 1×10<15> /cm<3> or less. A group Vb element or a group VI element other than nitrogen is also used as an n-type dopant for forming impurity regions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device made of silicon carbide, that is, a silicon carbide semiconductor device.

[0002]

2. Description of the Related Art Silicon carbide has many advantages over silicon as a material for semiconductor devices, and studies for its practical use are being vigorously conducted with the aim of using it for power semiconductors and high-frequency semiconductors. The crystal structure of silicon carbide is 6H type or 4H type,
There is a 3C type, and the single crystal is produced by a sublimation method.
The 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) or performing ion implantation to locally control conductivity. It is made. Also, silicon carbide is
For example, when exposed to a high temperature oxidizing atmosphere of 1100 to 1200 ° C., carbon in silicon carbide is oxidized and carbon dioxide (C
O ₂ ), while the silicon in the silicon carbide is oxidized to form a silicon dioxide (SiO ₂ ) film on the surface. The thermal oxide film can be used as an insulating film of a semiconductor device.

[0003]

The substrate and the epitaxial growth layer formed by the sublimation method tend to exhibit n-type conductivity by taking in the nitrogen gas in the atmosphere remaining or mixed in the manufacturing apparatus. In particular, the shrimp growth step is 150
This is a process at a high temperature of 0 ° C. or more and for a long time.
Also, ion implantation of dopants to improve the activation rate,
Often performed at a high temperature of 1000 ° C. or higher.

During thermal oxidation, carbon in silicon carbide is CO ₂
It becomes gas and is discharged out of the system. At this time, the trapped nitrogen is also exhausted to the outside as a gas, but part of the nitrogen bonds with silicon atoms in the silicon carbide to form ultrafine silicon nitride particles in the silicon carbide near the interface with the mature oxide film. It is formed. For example, when manufacturing a Schottky diode which is a type of rectifier element, 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 is formed. There was a problem that good rectification characteristics could not be obtained because of the presence.

When a MOS field effect transistor (hereinafter referred to as a MOSFET) is manufactured by using a thermal oxide film, a nitride layer is formed on a channel layer formed on a semiconductor layer near an oxide film / semiconductor boundary. Since silicon fine particles are present, there is a problem that carriers moving in the channel layer are scattered by the silicon nitride fine particles, resulting in a low mobility.

In view of these problems, an object of the present invention is to provide a silicon carbide semiconductor device such as a Schottky diode or a MOSFET having excellent characteristics by suppressing the generation of silicon nitride fine particles.

[0007]

According to the present invention, there is provided a silicon carbide semiconductor device having a silicon carbide epitaxial layer grown on a silicon carbide semiconductor substrate, wherein the concentration of nitrogen contained in the silicon carbide epitaxial layer is 1 × 10 It is assumed to be ¹⁵ / cm ³ or less. By suppressing the nitrogen concentration in the silicon carbide epitaxial layer, generation of silicon nitride fine particles can be suppressed.

In particular, when the silicon carbide epitaxial layer is n-type, it is important to use a Vb group element other than nitrogen, such as phosphorus, chromium, or antimony, or a VI group element as a dopant to avoid the incorporation of nitrogen. . The silicon carbide epitaxial layer is made of III such as aluminum or boron.
Element or a group II element, and the concentration of a Vb group element other than nitrogen, or a group VI element, a III element, or a group II element may be 1 × 10 ¹⁵ / cm ³ or more. Of course.

[0009] Even when the silicon carbide semiconductor device has a region into which impurity ions are implanted, it is assumed that nitrogen is not taken in and the concentration of nitrogen contained in the ion-implanted region is 1 × 10 ¹⁵ / cm ³ or less. Also for the ion implantation region, in the case of n-type, V other than nitrogen such as phosphorus,
A group b element or a group VI element is used as a dopant to avoid incorporation of nitrogen.

There is no problem when the impurity ions are elements III or II such as aluminum or boron. In the case where the semiconductor element is a Schottky diode having rectification characteristics due to a Schottky barrier formed by a metal / semiconductor interface, a Schottky diode having good interface characteristics can be obtained as described later by suppressing the generation of silicon nitride fine particles. Can be

When the semiconductor element has a thermal oxide film,
In particular, since silicon nitride particles are easily generated in the thermal oxidation process,
It is important to keep the nitrogen concentration in the part to be thermally oxidized low. When the semiconductor element is a MOSFET, a silicon carbide MOSFET having high mobility can be obtained because carriers traveling in the channel layer are not scattered by silicon nitride fine particles as described later.

[0012]

Embodiment 1 FIG. 1 is a sectional view of a silicon carbide Schottky diode (hereinafter referred to as SBD) according to Embodiment 1 of the present invention. An SBD having a size of 3 mm square and an electrode area of 3.14 mm ² manufactured by using an shrimp epitaxial wafer on which an n ⁻ shrimp epitaxial layer 12 is grown on a 4H silicon carbide substrate (hereinafter referred to as a SiC substrate) 11. . 13 the n ^- Ebitakisharu 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), Fifteen
Denotes an oxide film, and 16 denotes a guard ring formed by boron ion implantation and heat treatment.

Hereinafter, the manufacturing method will be described in detail. A 4H-type SiC substrate 11 having a silicon surface (hereinafter referred to as Si surface) inclined by 8 degrees in the (11-20) direction (this angle is referred to as off-angle) and having a diameter of 2 inches was used. The SiC substrate 11 is n-type and has a carrier concentration of 1 × 10 ¹⁸ / cm ³ . However, 6H type or 3C type may be used, and C-plane or (11-20) plane may be used. Or, even if the off-angle direction and angle are different, there is no effect on the application of the present invention.

First, an n ⁺ cathode layer 17 is formed on the rear surface 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 nitrogen gas in the atmosphere remaining or mixed in the manufacturing apparatus, using a load-lock type epitaxial film forming apparatus, purging with argon gas and 800 ° C.
After repeating the baking three times, n phosphorus doped ^- forming the Ebitakisharu layer 12. n ^- Ebitakisharu 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 ).
By the RF heating of the coat using a graphite susceptor, the film formation temperature is 1500 ° C. and the time is 5 hours. During this epitaxial growth, the 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 which is not a load-lock type, unintended nitrogen doping occurs and its concentration is 1 × 10 ¹⁶ / cm ³
Reaches even more.

The guard ring 16 is patterned using a positive type photoresist. Then, add boron
After ion implantation in a box shape at an acceleration voltage of 0 to 180 keV, annealing is performed at 1600 ° C. for 30 minutes to form a guard ring 16 having a depth of about 0.5 μm. 1100
30nm thickness by pyrogenic oxidation for 5 hours
After the oxide film 15 is formed and patterned, Ti is sputter-deposited as the Schottky electrode 13, heat treated at 200 ° C. for 5 minutes, and then Ti / Ni / Au is sputter-deposited as the cathode electrode 14 to form a chip. did.

FIG. 1 (solid line-phosphorus doping) is a reverse current-voltage characteristic diagram of the SBD thus manufactured. The figure also shows, 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. In the nitrogen-doped SBD according to 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 the first embodiment is 1.5 mA / cm ² . It can be seen 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 n ^- Ebitakisharu layer 12 This is probably because silicon nitride particles were hardly generated in the vicinity of the surface 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 / c
It was m ^3.

For confirmation, in the step of forming the epitaxial layer 12, the purge conditions and bake conditions in the load-lock type epitaxial film forming apparatus were changed to change the SBD having different nitrogen concentrations.
Was fabricated, and its reverse characteristics were measured. The sum of the nitrogen concentration and the phosphorus concentration was 1 × 10 ¹⁶ / cm ³ . FIG.
FIG. 9 is a characteristic diagram showing the nitrogen concentration dependency of the leakage current at 00V.

If the nitrogen concentration is 1 × 10 ¹⁵ / cm ³ or less,
Although the leakage current can be suppressed to 3mA / cm ² or less, 1 × 10 ¹⁵ / c
current leakage and Kosu the m ³ is rapidly increasing. Therefore, it is important to keep the nitrogen concentration at 1 × 10 ¹⁵ cm ⁻³ or less. still,
The ion-implanted species may be any Vb element other than nitrogen. In the case of a p-type epitaxial wafer, similar results can be obtained even when aluminum is used.

[Embodiment 2] FIG. 4 shows a SiC according to Embodiment 2 of the present invention.
It is sectional drawing of MOSFET. The same type of 4H type as in Example 1
The SiC substrate 21 was used. P-doped aluminum using trimethylaluminum on the SiC substrate 21 ^- was grown Ebitakisharu 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 formed Ebitakisharu layer 22.

After patterning using a positive type photoresist, phosphorus is ion-implanted in the form of a box at an accelerating voltage of 30 to 180 keV, annealing is performed at 1600 ° C. for 30 minutes, and n is about 0.5 μm deep. ⁺ Source area
27 and an n ⁺ drain region 28 are formed. 1100 ° C,
After forming and patterning a gate oxide film 25 having a thickness of 30 nm by pyrogenic oxidation for 5 hours, Ti / Ni / Au
Was formed by sputtering and patterned to form a source electrode 24, a drain electrode 23, a gate electrode 26, and a substrate electrode 29, and formed into chips.

The carrier mobility in the channel of the MOSFET fabricated as described above was measured to be 115 cm.
It showed about 20-fold or more the value of the mobility 5 cm ² / Vs but was formed Ebitakisharu layer ^- p by a method which does not avoid the ² / Vs and conventional nitrogen pollution. This is, above p ^- Ebitakisharu layer
It is probable that silicon nitride fine particles near the surface were hardly generated due to the method of avoiding the nitrogen contamination in the atmosphere remaining or mixed in the manufacturing apparatus in the forming step 22. P ^- epitaxial layer 22 by SIMS analysis
Was 2 × 10 ¹⁴ / cm ³ .

For confirmation, in the step of forming the p ^- epitaxial layer 22, MOSFETs having different nitrogen concentrations were manufactured by changing the ratio of the doping gas, and their 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 the nitrogen concentration dependency of the carrier mobility. If the nitrogen concentration is 1 × 10 ¹⁵ / cm ³ or less, the carrier mobility is 100 cm ² / Vs or more, but 1 × 10 ¹⁵ / cm ³
After that, it drops rapidly. Therefore, the nitrogen concentration is 1 ×
It is important to keep it below 10 ¹⁵ cm ^-3 .

For the purpose of improving channel mobility due to Coulomb scattering at the MOS interface, n ⁺ source regions 27 and n ⁺
A counter-doped region 30 was formed between the ⁺ drain region 28 and the implantation of phosphorus ions. Accelerating voltage, 30 kV, the dose was ² × 10 ¹¹ / cm 2. For comparison, a counter-doped region was formed by implanting nitrogen ions. As a result of comparison between the two, the channel mobility was 100 cm ² / Vs in nitrogen counter doping, but was significantly improved to 150 cm ² / Vs in phosphorus doping.

[0025]

As described above, according to the present invention, nitrogen is prevented from being mixed in the epitaxial layer growth step and the concentration of nitrogen contained in the silicon carbide epitaxial layer is reduced to 1 × 10 ¹⁵
By suppressing the density to / cm ³ or less, the effect of the generation of silicon nitride fine particles was avoided, and the characteristics of the Schottky diode and the MOSFET could be improved.

Furthermore, it has been shown that it is effective to use an element other than nitrogen as an n-type dopant in forming an impurity region. According to the present invention, a silicon carbide semiconductor device having excellent characteristics other than the Schottky diode and the MOSFET can be manufactured with high reproducibility.

[Brief description of the drawings]

FIG. 1 is a diagram showing currents of a SiCSBD of Example 1 of the present invention and a comparative example.
Voltage characteristic diagram

FIG. 2 is a cross-sectional view of the SiCSBD according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a nitrogen concentration dependency of a leakage current of SiCSBD.

FIG. 4 is a cross-sectional view of a SiCMOSFET according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram showing the nitrogen concentration dependence of the carrier mobility of a SiCMOSFET.

[Explanation of symbols]

11 and 21 SiC substrate 12 n ^- Ebitakisharu layer 13 Schottky electrode 14 cathode electrode 15 the silicon dioxide film 16 guard rings 22 p ^- Ebitakisharu layer 23 source electrode 24 drain electrode 25 a gate oxide film 26 gate electrode 27 n ⁺ source region 28 n ⁺ drain region 29 substrate electrode 30 counter-doped region

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI theme Court Bu (reference) H01L 29/861 H01L 29/91 D F term (reference) 4K030 AA05 AA06 AA09 BA37 BB02 CA04 FA10 LA14 4M104 AA03 BB14 CC01 CC03 CC05 DD23 DD37 DD63 DD78 DD83 DD90 FF02 FF13 FF17 GG03 GG09 GG10 GG14 5F045 AA03 AB06 AC01 AC07 AC19 AD18 CA05 DA60 5F140 AA01 BA02 BA17 BB15 BE07 BF07 BF15 BF21 BF25 BG30 BJ07 BF21 BF21 BF21

Claims (10)

[Claims] In a silicon carbide semiconductor device having a silicon carbide epitaxial layer grown on a silicon carbide semiconductor substrate, the concentration of nitrogen contained in the silicon carbide epitaxial layer is 1 × 10 ¹⁵
/ cm ³ or less. 2. The method according to claim 1, wherein the silicon carbide epitaxial layer is made of a Vb element other than nitrogen, such as phosphorus, arsenic or antimony, or V
The silicon carbide semiconductor device according to claim 1, comprising a Group I element. 3. The silicon carbide semiconductor device according to claim 1, wherein the silicon carbide epitaxial layer contains a III element such as aluminum or boron, or a group II element. 4. The silicon carbide epitaxial layer has a concentration of a Vb group element other than nitrogen, or a group VI, III, or II element, of 1 × 10 ¹⁵ / cm ³ or more. 4. The silicon carbide semiconductor device according to 2 or 3. 5. The silicon carbide according to claim 4, further comprising a region into which impurity ions are implanted, wherein the concentration of nitrogen contained in the ion-implanted region is 1 × 10 ¹⁵ / cm ³ or less. Semiconductor element. 6. The silicon carbide semiconductor device according to claim 5, wherein the impurity ions are Vb group elements other than nitrogen, such as phosphorus, arsenic or antimony, or group VI elements. 7. The silicon carbide semiconductor device according to claim 5, wherein the impurity ions are an element such as aluminum or boron, or a group II element. 8. The silicon carbide semiconductor device according to claim 1, wherein the semiconductor device is a Schottky barrier diode having rectification characteristics due to a Schottky barrier formed by a metal / semiconductor interface. 9. An MO having a metal-thermal oxide film-semiconductor structure.
The silicon carbide semiconductor device according to any one of claims 1 to 7, further comprising an S-type gate, wherein the oxide film is formed of a thermal oxide film. 10. The silicon carbide semiconductor device according to claim 9, wherein the semiconductor device is a field effect transistor.