CN104835858A - Diode - Google Patents

Abstract

The invention relates to a diode, and provides a diode with excellent switching characteristics. The diode (1) comprises a silicon carbide substrate (11), a stopping layer (12), a drifting layer (13), a protection ring (14), a Schottky electrode (15), an ohmic electrode (16), and a surface protection film (17). The product R*Q of the positive conduction resistance of the diode (1) and a response charge Q of the diode (1) meets the relation: R*Q is not greater than 0.25*V<blocking><2> under the measurement temperature of 25 DEG C. A reverse blocking voltage V is defined as a reverse voltage of the diode (1), wherein the reverse voltage can generate a current density Jr which is high as much as 10-5 times of the current density (Jf) of a positive current. The response charge Q is obtained through the testing results of a double-pulse method.

Description

Diode

Technical field

The present invention relates to a kind of diode, and particularly relate to the diode requiring that puncture voltage is high and conducting resistance is low.

Background technology

Usually adopted silicon (Si) as the semi-conducting material manufacturing power semiconductor.But this performance of low-loss, high-breakdown-voltage and high service speed is close to the theoretical limit of silicon semiconductor element.

Semiconductor band gap being greater than silicon is called " wide band gap semiconducter ".Due to wide band gap semiconducter, so expect the performance significantly improving power semiconductor.Such as, the wide band gap semiconducter of such as carborundum (SiC) or gallium nitride (GaN) arouses attention as the material of power semiconductor.Such as, Yoshitomo Hatakeyama, Kazuki Nomoto, Naoki Kaneda, ToshihiroKawano, Tomoyoshi Mishima, Tohru Nakamura, in December, 2011 IEEEELECTON DEVICE LETTERS, Vol.32, " Over 3.0GW/cm in No.12, pp.1674-1676 ²figure-of-Merit GaN p-n Junction Diodes on Free-Standing GaNSubstrates, " in reported the on-resistance characteristics be formed in without the p-n junction diode supported in GaN substrate.

Summary of the invention

About power diode, conducting resistance and puncture voltage are the key properties for assessment of diode.Conducting resistance may be used for the conduction loss assessed during diode operation in diode.But, be difficult to assess the switching loss in diode based on conducting resistance.By the switching characteristic with suitable method assessment diode, the diode with better switching characteristic can be realized.

The object of the present invention is to provide a kind of diode with excellent switching characteristic.

Diode according to an aspect of the present invention includes active layer and the first and second electrodes for applying forward voltage and reverse voltage to this active layer.In the forward current-voltage characteristic of the diode when applying forward voltage via the first and second electrodes to active layer, voltage in the current value corresponding with current density, J f is defined as forward conduction resistance R about the change of electric current, and current density, J f obtains by the conductivityσ (unit: S/mm) of active layer is multiplied by electric field strength 50 (unit: V/mm).In the reverse current-voltage characteristic of the diode when applying reverse voltage via the first and second electrodes to active layer, the voltage corresponding with current density, J r is defined as reverse BV V _block(unit: V), 10 of current density, J r and current density, J f ^-5doubly equally high.Utilize dipulse method, by under the following conditions: (a) reverse voltage Vr:2/3 × V _block(b) turn-off speed (di/dt): the limit of integration of-200 (A/ μ s) and (c) diode current I: from diode current I through 0 time point until diode current I returns to the time point of 10% of reverse current peak value, the electric charge obtained diode current I integration is defined as the response charge Q of diode.Under the measuring tempeature of 25 DEG C, the product RQ of forward conduction resistance R and response charge Q meets RQ≤0.25 × V _block ²relation.Here, the unit of R is the unit of m Ω, Q is nC.

Diode according to another aspect of the present invention includes active layer and the first and second electrodes for applying forward voltage and reverse voltage to this active layer.In the forward current-voltage characteristic of the diode when applying forward voltage via the first and second electrodes to active layer, be 3 (units: A/mm at current density, J f ²) time voltage be defined as forward conduction resistance R about the change of electric current, current density, J f is by obtaining the value of forward current divided by junction interface area.In the reverse current-voltage characteristic of the diode when applying reverse voltage via the first and second electrodes to active layer, the voltage corresponding with density Jr is defined as reverse BV V _block(unit: V), 10 of density Jr and current density, J f ^-5doubly equally high.Utilize dipulse method, by under the following conditions: (a) reverse voltage Vr:2/3 × V _block(b) turn-off speed (di/dt): the limit of integration of-200 (A/ μ s) and (c) diode current I: from diode current I through 0 time point until diode current I returns to the time point of 10% of reverse current peak value, the electric charge obtained diode current I integration is defined as the response charge Q of diode.Under the measuring tempeature of 25 DEG C, the product RQ of forward conduction resistance R and response charge Q meets RQ≤0.25 × V _block ²relation.Here, the unit of R is the unit of m Ω, Q is nC.

According to the present invention, the diode with excellent switching characteristic can be provided.

By reference to the accompanying drawings, from the detailed description below of the present invention, aforesaid and other object, feature, aspect and advantage of the present invention will become more obvious.

Accompanying drawing explanation

Fig. 1 is the sectional view of the structure of the diode schematically shown according to the first embodiment.

Fig. 2 is the figure of an example of forward current-voltage characteristic that diode is shown.

Fig. 3 is the figure of an example of the configuration of the forward current-voltage characteristic illustrated for measuring diode.

Fig. 4 is the figure of an example of the reverse current-voltage characteristic that diode is shown.

Fig. 5 is the figure of an example of the configuration of the reverse current-reverse voltage characteristic illustrated for measuring diode.

Fig. 6 is the figure of the illustrative arrangement of the circuit illustrated for performing dipulse method testing diode.

Fig. 7 is the oscillogram of the reverse recovery characteristic illustrating the diode 1 obtained with the test circuit 520 shown in Fig. 6.

Fig. 8 is the figure of the conducting resistance R-response charge Q characteristic of the five kinds of samples illustrated in each in example 1-1 (600V level blocking voltage device) and example 1-2 (1200V level blocking voltage device).

Fig. 9 is the RQ product-V of the sample illustrated according to example 1-1 and 1-2 _blockthe figure of characteristic.

Figure 10 is the figure of the GR width-reverse BV characteristic illustrated according to the sample of example 1-3 and 1-4.

Figure 11 is the figure of the GR width-response charge Q characteristic illustrated according to the sample of example 1-3 and 1-4.

Figure 12 illustrates RQ product-reverse BV V _blockthe figure of the GR wide dependency of characteristic.

Figure 13 is the figure of the GR wide dependency that the scale factor A shown in Figure 12 is shown.

Figure 14 is the sectional view of the structure of the diode schematically shown according to the second embodiment.

Figure 15 illustrates that the conducting resistance R-according to the sample of example 2-1 (150V level blocking voltage device), example 2-2 (80V level blocking voltage device) and example 2-3 (40V level blocking voltage device) responds the figure of charge Q characteristic.

Figure 16 is the RQ product-V of the sample illustrated according to example 2-1 to 2-3 _blockthe figure of characteristic.

Figure 17 illustrates RQ product-reverse BV V _blockthe figure of the GR wide dependency of characteristic.

Figure 18 is the sectional view of the structure of the diode schematically shown according to the 4th embodiment.

Figure 19 illustrates that the conducting resistance R-according to the sample of example 4-1 (600V level blocking voltage device) and example 4-2 (1200V level blocking voltage device) responds the figure of charge Q characteristic.

Figure 20 is the RQ product-V of the sample illustrated according to example 4-1 and 4-2 _blockthe figure of characteristic.

Figure 21 is the figure of the FP width-reverse BV characteristic illustrated according to the sample of example 5-1 and 5-2.

Figure 22 is the figure of the FP width-response charge Q characteristic illustrated according to the sample of example 5-1 and 5-2.

Figure 23 illustrates RQ product-reverse BV V _blockthe figure of the FP wide dependency of characteristic.

Figure 24 is the figure of the FP wide dependency that the scale factor A shown in Figure 23 is shown.

Embodiment

[description of this inventive embodiment]

First will list and describe embodiments of the invention.

(1) diode according to an embodiment of the invention includes active layer and the first and second electrodes for applying forward voltage and reverse voltage to this active layer.In the forward current-voltage characteristic of the diode when applying forward voltage via the first and second electrodes to active layer, voltage in the current value corresponding with current density, J f is defined as forward conduction resistance R about the change of electric current, and current density, J f obtains by the conductivityσ (unit: S/mm) of active layer is multiplied by electric field strength 50 (unit: V/mm).In the reverse current-voltage characteristic of the diode when applying reverse voltage via the first and second electrodes to active layer, the voltage corresponding with current density, J r is defined as reverse BV V _block(unit: V), 10 of current density, J r and current density, J f ^-5doubly equally high.Utilize dipulse method, by under the following conditions: (a) reverse voltage Vr:2/3 × V _block(b) turn-off speed (di/dt): the limit of integration of-200 (A/ μ s) and (c) diode current I: from diode current I through 0 time point until diode current I returns to the scope of the time point of 10% of reverse current peak value, the electric charge obtained diode current I integration is defined as the response charge Q of diode.Under the measuring tempeature of 25 DEG C, the product RQ of forward conduction resistance R and response charge Q meets RQ≤0.25 × V _block ²relation.Here, the unit of R is the unit of m Ω, Q is nC.

According to above configuration, the diode with excellent switching characteristic can be provided.RQ product is the good index representing total losses in diode.In addition, RQ product and reverse BV V _{resistance disconnected}square proportional (RQ ∝ V _block ²).By this scale factor is set as 0.25 or less, can realize obtaining the diode reduced the wastage.Therefore, it is possible to realize the diode with excellent switching characteristic.

(2) preferably, product RQ meets RQ≤0.1 × V _block ²relation.

According to above configuration, when the material using silicon (Si) as diode, the diode with excellent switching characteristic can be provided.

(3) semi-conducting material preferably, forming diode is silicon.

According to above configuration, when the material using silicon (Si) as diode, the diode with excellent switching characteristic can be provided.

(4) preferably, product RQ meets RQ≤4.9 × 10 ^-3× V _block ²relation.

According to above configuration, when the material using wide band gap semiconducter as diode, the diode with excellent switching characteristic can be provided.

(5) semi-conducting material more preferably, forming diode is carborundum.

According to above configuration, when the material using carborundum (SiC) as diode, the diode with excellent switching characteristic can be provided.

(6) preferably, product RQ meets RQ≤1.3 × 10 ^-3× V _block ²relation.

According to above configuration, when the material using wide band gap semiconducter as diode, the diode with excellent switching characteristic can be provided.

(7) semi-conducting material more preferably, forming diode is gallium nitride.

According to above configuration, when the material using gallium nitride (GaN) as diode, the diode with excellent switching characteristic can be provided.

(8) preferably, diode comprises the edge termination structure be formed in active layer.This edge termination structure has and is not less than 5 μm and the width being not more than 200 μm.

According to above configuration, the high blocking voltage of diode can be guaranteed when preventing the loss of diode from significantly increasing.

(9) diode according to another embodiment of the invention includes active layer and the first and second electrodes for applying forward voltage and reverse voltage to this active layer.In the forward current-voltage characteristic of the diode when applying forward voltage via the first and second electrodes to active layer, be 3 (units: A/mm at current density, J f ²) time voltage be defined as forward conduction resistance R about the change of electric current, current density, J f is by obtaining the value of forward current divided by junction interface area.In the reverse current-voltage characteristic of the diode when applying reverse voltage via the first and second electrodes to active layer, the voltage corresponding with density Jr is defined as reverse BV V _block(unit: V), 10 of density Jr and current density, J f ^-5doubly equally high.Utilize dipulse method, by under the following conditions: (a) reverse voltage Vr:2/3 × V _block(b) turn-off speed (di/dt): the limit of integration of-200 (A/ μ s) and (c) diode current I: from diode current I through 0 time point until diode current I returns to the scope of the time point of 10% of reverse current peak value, the electric charge obtained diode current I integration is defined as the response charge Q of diode.Under the measuring tempeature of 25 DEG C, the product RQ of forward conduction resistance R and response charge Q meets RQ≤0.25 × V _block ²relation.Here, the unit of R is the unit of m Ω, Q is nC.

According to above configuration, the diode with excellent switching characteristic can be provided.

(10) preferably, product RQ meets RQ≤0.1 × V _block ²relation.

According to above configuration, when the material using silicon (Si) as diode, the diode with excellent switching characteristic can be provided.

(11) semi-conducting material preferably, forming diode is silicon.

According to above configuration, when the material using silicon (Si) as diode, the diode with excellent switching characteristic can be provided.

(12) preferably, product RQ meets RQ≤4.9 × 10 ^-3× V _block ²relation.

According to above configuration, when the material using wide band gap semiconducter as diode, the diode with excellent switching characteristic can be provided.

(13) semi-conducting material more preferably, forming diode is carborundum.

According to above configuration, when the material using carborundum (SiC) as diode, the diode with excellent switching characteristic can be provided.

(14) preferably, product RQ meets RQ≤1.3 × 10 ^-3× V _block ²relation.

According to above configuration, when the material using wide band gap semiconducter as diode, the diode with excellent switching characteristic can be provided.

(15) semi-conducting material more preferably, forming diode is gallium nitride.

According to above configuration, when the material using gallium nitride (GaN) as diode, the diode with excellent switching characteristic can be provided.

(16) preferably, diode comprises the edge termination structure be formed in active layer.This edge termination structure has and is not less than 5 μm and the width being not more than 200 μm.

According to above configuration, the high blocking voltage of diode can be guaranteed when preventing the loss of diode from significantly increasing.

[details of this inventive embodiments]

With reference to accompanying drawing, embodiment of the present invention will be described hereinafter.In accompanying drawing below, identical or corresponding element has the same reference character of specifying and no longer will repeat it and describes.During crystallography in this article represents, single orientation, set orientation, single plane and set plane use [], <> respectively, () and { } illustrates.And crystallographic negative exponent is usually by the numeral being added with "-" above, but negative sign appears at before numeral in this article.

Any one in pn junction diode and Schottky diode can be applied to according to the diode of the embodiment of the present invention.Example according to the diode of the embodiment of the present invention will be described below.But embodiments of the invention are not restricted to diode described below.

[the first embodiment]

< component structure >

It is the Schottky barrier diode (SBD) be made up of carborundum (SiC) according to the diode 1 of the first embodiment.Fig. 1 is the sectional view of the structure of the diode schematically shown according to the first embodiment.

With reference to figure 1, diode 1 comprises silicon carbide substrates 11, stop-layer 12, drift layer 13 (active layer), guard ring 14, Schottky electrode 15, Ohmic electrode 16 and surface protection film 17.

Stop-layer 12 and drift layer 13 are made up of carborundum.Stop-layer 12 is arranged in silicon carbide substrates 11.Drift layer 13 is arranged on stop-layer 12.Guard ring 14 is arranged in drift layer 13 to contact with the surface of drift layer 13.Each in silicon carbide substrates 11, stop-layer 12 and drift layer 13 has the conduction type of such as N-shaped.Guard ring 14 is conduction types contrary with each drift layer 13.Such as, guard ring 14 has p conduction type.

Schottky electrode 15 contacts with the surface 131 of drift layer 13.Suitably select the material of Schottky electrode 15 to realize the schottky junction between Schottky electrode 15 and drift layer 13.Schottky electrode 15 is overlapping with guard ring 14.Schottky electrode 15 corresponds to the anode electrode of diode 1.

Ohmic electrode 16 contacts with the surface 111 of silicon carbide substrates 11.The surface 111 of silicon carbide substrates 11 is positioned at the surface contrary with arranging the surface of stop-layer 12.The material of Ohmic electrode 16 is suitably selected to tie with the ohm realized between Ohmic electrode 16 and silicon carbide substrates 11.Ohmic electrode 16 corresponds to the cathode electrode of diode 1.

Surface protection film 17 covers the part being different from the part that to contact with Schottky electrode 15 on the surface 131 of drift layer 13.Surface protection film 17 is made up of such as polyimides.

< manufacturing process >

(example 1-1:600V level SiC-SBD)

An example for the formation of the condition of the diode 1 shown in Fig. 1 is described.Condition described below is such as the formation of the condition of 600V level SiC-SBD.

First, the silicon carbide substrates 11 be made up of the hexagon single-crystal silicon carbide with many types of 4H is prepared.The resistivity of silicon carbide substrates 11 is 20 (m Ω cm).The thickness of silicon carbide substrates 11 is 400 μm.Surface for the silicon carbide substrates 11 of grown epitaxial layer has departs from Si termination surface ((0001) face) towards 8 ° of the inclination of a axle.

The surface of silicon carbide substrates 11 forms N-shaped stop-layer 12 and n-type drift layer 13 via epitaxial growth.Donor concentration in stop-layer 12 is 2 × 10 ¹⁸cm ^-3.The thickness of stop-layer 12 is 0.5 μm.Donor concentration in drift layer 13 is 6 × 10 ¹⁵cm ^-3.The thickness of drift layer 13 is 5 μm.The substrate be made up of silicon carbide substrates 11, stop-layer 12 and drift layer 13 is also called " silicon carbide epitaxy substrate " hereinafter.

In drift layer 13, p-type guard ring 14 is formed by ion implantation.The ion implantation mask be made up of aluminium (Al) is used to be injected in drift layer 13 by boron (B) ion selectivity.By in boron ion implantation to drift layer 13 to make the overall width of guard ring 14 be 50 μm, the total depth of guard ring 14 is 0.5 μm, and the peak concentration in guard ring 14 is about 5 × 10 ¹⁷cm ^-3.

After injecting boron ion, perform the activation annealing of silicon carbide epitaxy substrate.Particularly, in argon (Ar) gas atmosphere, carborundum place is prolonged silicon and reaches 30 minutes to 1600 DEG C.After this, in oxygen atmosphere, make carborundum place prolong substrate and be subject to heat treatment at 1150 DEG C and reach 80 minutes, thus form the sacrifice oxide film of about 40nm on the surface of drift layer 13.By this sacrifice oxide film of hydrofluoric acid etch, thus remove the damage layer being positioned at the surface portion of drift layer 13.

Then, about 0.2 μm of thick nickel (Ni) electrode is formed with the surface 111 (back surface) sputtering at silicon carbide substrates 11 is upper.After this, in Ar gas atmosphere, make silicon carbide epitaxy substrate be subject to heat treatment at 970 DEG C and reach 3 minutes, thus form Ohmic electrode 16.

Then, with titanium (Ti) electrode that formation 0.1 μm on the whole surface sputtering at drift layer 13 is thick, and the thick Al electrode of formation 5 μm is continued.After this, phosphate etchant (H is also used with photoetching ₃pO ₄: CH ₃cOOH:HNO ₃) etching, carry out selective etch Al electrode, and with photoetching and with buffering hydrofluoric acid (BHF) etchant, carry out selective etch Ti electrode.Therefore, as shown in Figure 1, form Schottky electrode 15 to be located thereon across guard ring 14 to make the end of Schottky electrode 15.The width (hereinafter referred to " GR width ") of the part guard ring 14 overlapping with Schottky electrode 15 is 15 μm with regard to design load.

As shown in table 1, five kinds of samples that preparation junction interface area is different.This " junction interface " refers to the region that Schottky electrode 15 directly contacts mutually with drift layer 13.This region is positioned on the inner side of guard ring 14.The region (opening) of the drift layer 13 contacted with Schottky electrode 15 is for square.In order to prevent electric field from concentrating on corner part, make the corner part of the corner part of Schottky electrode 15 and guard ring 14 circular (radius of curvature is set to 20 μm).

Table 1

Then, use polyimides to form surface protection film 17.After this, with EB evaporation, Ohmic electrode 16 forms the back side pad electrode (not shown) be made up of Ti film (having 50nm thick), Pt film (having 100nm thick) and Au film (have 2 μm thick).

Silicon carbide epitaxy substrate is cut into chip.By tube core joint and wire-bonded, this chip is installed in encapsulation.Use Sn-Ag solder to perform tube core at 230 DEG C to engage.Al lead-in wire is used to perform wire-bonded.

(example 1-2:1200V level SiC-SBD)

The situation that some conditions in the manufacturing process of example 1-1 (600V level SiC-SBD) are modified gets off to prepare 1200V level SiC-SBD.Particularly, the donor concentration in stop-layer 12 is set as 2 × 10 ¹⁸cm ^-3, and the thickness of stop-layer 12 is set as 1 μm.Donor concentration in drift layer 13 is set as 4 × 10 ¹⁵cm ^-3, and the thickness of drift layer 13 is set as 10 μm.In addition, GR width is set as 30 μm.

As shown in table 2, prepare five kinds of different samples of junction interface area by the size changing Schottky electrode 15.

Table 2

Because other condition is identical with the condition in the manufacturing process of example 1-1, so the description that will no longer repeat subsequently.

< appraisal procedure >

Measure the conducting resistance R of (assessment) diode 1, reverse BV V in the following method _block, and charge Q.Measuring tempeature in each measurement is set as 25 DEG C.

(1) conducting resistance

Fig. 2 is the figure of an example of forward current-voltage characteristic that diode is shown.With reference to figure 2, in the forward current-voltage characteristic of diode, conducting resistance R is obtained by the slope Δ V/ Δ I of the voltage under given current density Jf relative to current value.Current density, J f is by taking advantage of the conductivityσ of drift layer 13 to obtain with electric field density E=500V/cm=50V/mm.That is, Jf (A/mm is met ²the relation of)=σ (S/mm) × 50 (V/mm).Unit " S " represents Siemens.

Fig. 3 is the figure of an example of the configuration of the forward current-voltage characteristic illustrated for measuring diode.With reference to figure 3, measuring circuit 500 comprises voltage source 501, voltmeter 502 and ammeter 503.The anode electrode of voltage source 501 transdiode 1 and cathode electrode apply forward voltage Vf.Voltage source 501 can change forward voltage Vf.Forward voltage Vf measured by voltmeter 502.Forward current If measured by ammeter 503.

Current density, J f corresponds to the forward current If (If/ junction area) of each junction area.About electronic representation charge carrier, consider that the speed of electric field is (when electric field E is more than 1kV/cm, the speed of Electronic starting is reduced) and the dependence of reason (heat produce cause electron mobility to reduce) of heat, in the semiconductor diode (Si diode, SiC diode and GaN diode) that reality uses, be used in electric field strength from forward current If during about 200 to 1kV/cm.In this scope of electric field strength, the forward I-V characteristic of diode actually appears linear characteristic, wherein electric current and voltage in proportion.

In this example, use E=500 (V/cm)=50 (V/mm) as the typical value of electric field strength.Current density, J f is defined as the current density of the conductivityσ using drift layer 13.In fact, voltage reduction occurs in the position being different from drift layer 13.But, in the calculating of current density, J f, only consider the prevailing drift layer 13 of field effect.

The conductivityσ of drift layer 13 can measure by various known method.Such as, the conductivityσ of drift layer can be obtained by the resistance of the Hall effect of the layer in measurement dielectric substrate or the layer measured in conductive substrates.In other method, the carrier concentration n in drift layer can measure via CV, and conductivity can use the relation σ=n × μ × e of suitable mobility [mu] to obtain (e representation element electric charge) by having.

The current density, J f obtained by above-mentioned definition is at 1 to 6 (A/mm ²) scope in, but it depends on the design of diode slightly.Therefore, conducting resistance R can also define by the current density of itself.Such as, when being 3 (A/mm by forward current value divided by the current density, J f that junction interface area obtains ²) time, can conducting resistance R be obtained based on this relation R=Δ V/ Δ I.

(2) reverse BV

Fig. 4 is the figure of an example of the reverse current-voltage characteristic that diode is shown.With reference to figure 4, in this example, when causing according to forward current density Jf defined above 1/10 ⁵reverse current density Jr (the Jr=Jf/10 of size ⁵) time reverse voltage, be defined as reverse BV V _block.

Fig. 5 is the figure of an example of the configuration of the reverse current-voltage characteristic illustrated for measuring diode.With reference to figure 5, measuring circuit 510 comprises voltage source 511, voltmeter 512 and ammeter 513.The anode electrode of voltage source 511 transdiode 1 and cathode electrode apply reverse voltage Vr.Voltage source 511 can change reverse voltage Vr.Reverse voltage Vr measured by voltmeter 512.Reverse current Ir measured by ammeter 513.

(3) electric charge is responded

The response charge Q of diode 1 can obtain by dipulse method.Fig. 6 illustrates the figure carrying out the illustrative arrangement of the circuit of test diode for performing dipulse method.

With reference to figure 6, test circuit 520 comprises DC power supply 521, load inductor 523, transistor 524, grid impulse circuit 525 and grid resistor 527.The total inductance of the inductance that load inductor 523 can be used as in the encapsulation of inductance in the encapsulation of the inductance of the circuit in test circuit 520, diode 1 and transistor 524 replaces.

Fig. 6 shows the igbt (IGBT) as an instantiation of transistor 524.But transistor 524 is not restricted to IGBT, such as mos field effect transistor (MOSFET) can also be used.

Following execution dipulse method.Series-connected diodes 1 and transistor 524.DC power supply 521 applies voltage Vr to diode 1 and transistor 524.Reverse voltage is applied to diode 1.

Grid impulse circuit 525 applies voltage Vg to the grid of transistor 524.First, turn-on transistor 524 be fed to electric current to load inductor 523 and in load inductor stored energy.Then, transistor 524 turns off to make forward current be fed to diode 1 from load inductor 523.After this, the reverse recovery characteristic (turn-off characteristic) of the diode 1 of the performance when second time turn-on transistor 524 is measured.Based on resistance value adjustment turn-off speed (di/dt) of grid resistor 527.

Fig. 7 is the oscillogram of the reverse recovery characteristic illustrating the diode 1 obtained with the test circuit 520 shown in Fig. 6.As shown in Figure 7, the response charge Q of diode 1 equals the time integral (∫ I (t) dt) of the electric current I flowing through diode 1.

Calculate the response charge Q of diode 1 under the following conditions:

(a) reverse voltage Vr:2/3 × V _block,

(b) diode current I:If,

(c) turn-off speed (di/dt) :-200 (A/ μ s), and

The limit of integration of (d) electric current I: pass the time point (t0) of 0 (A) until diode current 1 returns to the scope of the time point (trr) of 10% of reverse current peak value (irp) from diode current I.

< assessment result >

(1) R-Q characteristic

Fig. 8 is the figure of the conducting resistance R-response charge Q characteristic of the five kinds of samples illustrated in each in example 1-1 (600V level blocking voltage device) and example 1-2 (1200V level blocking voltage device).With reference to figure 8, according to the sample in each example, conducting resistance R and response charge Q meet substantially each other in inversely proportional relation.That is, y=ax is obtained ^bthe relation of (a represents constant, b ≈-1), wherein y represents charge Q and x represents conducting resistance R.The product (y × x) of conducting resistance R and charge Q can be seen as and be substantially equal to constant a.The product RQ of conducting resistance R and charge Q is also called as " RQ product " hereinafter.

Can by as follows for R-Q behavioral illustrations.First, the conducting resistance R of diode 1 can be expressed as expression formula (1) below:

R＝Rd+Rs+Rsub+Rc (1)

Wherein Rd represents drift layer resistance, and Rs represents stop-layer resistance, and Rsub represents resistance substrate, and Rc represents Ohmic electrode resistance.

Usually, stop-layer resistance Rs and Ohmic electrode resistance Rc is extremely lower than drift layer resistance Rd.Therefore, stop-layer resistance Rs and Ohmic electrode resistance Rc can be ignored.In addition, drift layer resistance Rd more occupies an leading position than resistance substrate Rsub.Therefore, as shown in expression formula (2), conducting resistance R can be made close to drift layer resistance Rd.

R～Rd (2)

The resistance Rd of drift layer can be expressed as expression formula (3):

Rd＝ρ·d/A (3)

Wherein ρ represents drift layer conductivity, and d represents the thickness of drift layer, and A represents junction area.Expression (3) can be transformed to expression formula (4) below:

Rd＝1/(n·μ·q)·d/A (4)

Wherein n represents drift layer carrier concentration, and μ represents drift layer mobility.

Then, the phenomenon of Reverse recovery response is considered.Forward current is made to flow through diode by applying forward bias voltage.Then, reverse bias voltage is applied to diode.Charge carrier (electronics) pulled out drift layer and therefore form depletion layer.Assuming that drift layer is completely depleted.

Response charge Q refers to this change of the state at diode.Therefore, response charge Q is expressed as expression formula (5) below.

Q＝A·q·n·d (5)

From expression formula (4) and expression formula (5), response charge Q is expressed as expression formula (6) below.

R·Q＝d ²/μ (6)

Expression formula (6) represents when not relying on junction area A, by drift layer thickness d and the mobility [mu] determination conducting resistance R of drift layer and the product RQ of response charge Q.

On the other hand, when applying reverse bias voltage to diode, drift layer may not be completely depleted yet.In this case, when applying reverse bias voltage to diode, the thickness of the depletion layer of formation in drift layer is used for d' and represents.Response charge Q ' be expressed as expression formula below (5').

Q'＝A·q·n·d' (5')

From expression formula (4) and expression formula (5') respond charge Q ' be expressed as below expression formula (6').

R·Q'＝d·d'/μ (6')

As expression formula (6) and expression formula (6') shown in, when the situation that drift layer is completely depleted and drift layer are by part depletion, RQ product does not rely on junction area A.Fig. 8 shows the RQ product (6') represented by expression formula (6) and expression formula.

(2) RQ product-V _blockcharacteristic

Fig. 9 is the RQ product-V of the sample illustrated according to example 1-1 and example 1-2 _blockthe figure of characteristic.Substantially reverse BV V is used with reference to figure 9, RQ product _blockvalue determine.

Can by RQ sum of products reverse BV V _blockbetween relation explain be described as follows.The critical electric field strength of semi-conducting material is represented by Ec, and the thickness of drift layer is represented by d.Can by the avalanche breakdown voltage V of diode _puncturebe expressed as expression formula (7) below.

V _puncture=Ecd/2 (7)

From expression formula (7) and expression formula (6), can be expression formula (8) by RQ product representation.

RQ=4/ (μ Ec ²) V _puncture ²(8)

Think reverse BV V _blockwith avalanche breakdown voltage V _punctureproportional.Therefore, as shown in expression formula (9), think RQ product and reverse BV V _blocksquare proportional.

RQ ∝ V _block ²(9)

With regard to shown in Fig. 9 according to regard to the sample of example 1-1 and 1-2, RQ product also with reverse BV V _blocksquare proportional.From the RQ sum of products reverse BV V each sample _block, the relational expression obtaining below with least square fitting (LSM).

RQ=3.4 × 10 ^-3(m Ω nC/V ²) V _block ²

The loss of diode is the summation of conduction loss and switching loss.Conduction loss is made up of the loss (logical loss) of the conducting state of diode and the loss (breakdown consumption) of off state.But in conduction loss, logical loss is occupied an leading position.As shown in expression formula (10), logical loss Lon and conducting resistance R becomes larger pro rata.α represents proportionality constant.

Lon＝αR (10)

Switching loss is made up of conduction loss and turn-off power loss.But in switching loss, turn-off power loss is occupied an leading position.As shown in expression formula (11), turn-off power loss Ltf and charge Q proportional.β represents proportionality constant.

Ltf＝βQ (11)

The total losses Lt of diode is expressed as the summation of logical loss Lon and turn-off power loss Ltf.Therefore, total losses Lt can be expressed as expression formula (12).Here, C represents constant.

Lt＝Lon+Ltf＝αR+βQ＝αR+βC/R (12)

When conducting resistance R being set as R*=(beta/alpha C) ^1/2and response charge Q is set as Q*=(α/β C) ^1/2time, total losses Lt reaches minimum value Lt*.Minimum value Lt* can be expressed as expression formula (13) below.

Lt*＝2(α·β·R*·Q*) ^1/2(13)

That is, the minimum value of total losses Lt and the square root of RQ product proportional.This shows that RQ product is the good index of the total losses representing diode.

In addition, will consider that RQ product is to the dependence of material based on expression formula (8).With regard to Si material, SiC material and GaN material, the material limits of RQ product ratio can be expressed as expression formula (14).

RQ material limits ratio (Si): RQ material limits ratio (SiC): RQ material limits ratio (GaN)=about 100: about 3:1 (14)

Therefore, the material limits of total losses ratio can be expressed as expression formula (15).

Total losses material limits ratio (Si): total losses material limits ratio (SiC): total losses material limits ratio (GaN)=10 (Si): 2 (SiC): 1 (GaN) (15)

(example 1-3:600V level SiC-SBD)

The sample according to example 1-3 is made by the method identical according to the method for the sample of example 1-1 with making.The structure of epitaxial loayer is identical with the structure in example 1-1.Junction interface area be set as constant and make GR width different.Particularly, junction interface area is set as the 0.75mm identical with the junction interface area of the sample 1 according to example 1-1 ².As shown in table 3, preparation GR width is changed to the sample of 800 μm from 0 (not having guard ring).In the sample 5-9 with large GR width, specify total GR width to meet the relation of (total GR width)=(GR width)+30 μm.

Table 3

(example 1-4:1200V level SiC-SBD)

The sample according to example 1-4 is made by the method identical according to the method for the sample of example 1-2 with making.The structure of epitaxial loayer is identical with the structure in example 1-2.Junction interface area be set as constant and make GR width different.Particularly, junction interface area is set as the 0.75mm identical with the junction interface area of the sample 1 according to example 1-2 ².As shown in table 4, preparation GR width is changed to the sample of 800 μm from 0 (not having guard ring).In the sample 5-9 with large GR width, specify total GR width to meet the relation of (total GR width)=(GR width)+30 μm.

Table 4

< appraisal procedure >

Conducting resistance R, the reverse BV V of the sample according to example 1-3 and 1-4 is measured by the method identical according to the method for the sample of example 1-1 with 1-2 with assessment _blockwith response charge Q.Therefore, by the details of no longer repeat assessment method.

< assessment result >

Figure 10 is the figure of the GR width-reverse BV characteristic illustrated according to the sample of example 1-3 and 1-4.With reference to Figure 10, there is no the sample of the guard ring GR width of 0 (have be) and having in the sample of GR width of 3 μm, reverse BV V _blockreduce.Abscissa in the chart of Figure 10 represents logarithm.This logarithm can not be expressed as the GR width of 0.In Figure 10 (with figure subsequently), but, be conveniently 0 by GR width means when not having guard ring.

When example 1-3, be not less than in the sample of 5 μm at GR width, reverse BV V _blockbe about 600V, and obtain good result.Similarly in example 1-4, be not less than in the sample of 5 μm at GR width, reverse BV V _blockbe about 1200V and obtain good result.

When GR width is not more than 3 μm, relax the concentrated decreased effectiveness of electric field by guard ring structure, think that leakage current increases and reverse BV V _blockreduce.

In addition, as shown in table 5, in any one in example 1-3 and 1-4, conducting resistance R changes according to GR width hardly.

Table 5

Figure 11 is the figure of the GR width-response charge Q characteristic illustrated according to the sample of example 1-3 and 1-4.With reference to Figure 11, in two of example 1-3 and 1-4, have from the sample of the GR width of 0 to 50 μm, response charge Q is constant substantially.When GR width is set as 100 μm, response charge Q increases slightly.The increment rate of response charge Q is about 20%.When GR width is not less than 100 μm, response charge Q significantly increases.Think, when GR width is large, compared with the electric charge produced by Schottky electrode region, the electric charge produced by guard ring region is very important, and therefore total electrical charge adds.

Figure 12 illustrates RQ product-reverse BV V _blockthe figure of the GR wide dependency of characteristic.In the relation that expression formula (9) illustrates, RQ product and reverse BV V _blocksquare precedent.Figure 13 is the figure of the GR wide dependency that the scale factor A shown in Figure 12 is shown.With reference to Figure 13, when GR width is not more than 3 μm, reverse BV V _blockreduce and A increase.In other words, RQ product-reverse BV V _blockdeterioration in characteristics.When in the scope of GR width at 5 to 200 μm, A substantially reaches minimum value and it is substantially constant.When GR width is more than 200 μm, RQ product starts to increase also therefore RQ product-reverse BV V _blockdeterioration in characteristics.

Use according to the sample of example 1-3 as the sample of GR width with 15 μm.Use according to the sample of example 1-4 as the sample of GR width with 30 μm.As mentioned above, from the scope of the GR width of 15 to 30 μm, RQ product reaches minimum value.Based on the data of these two samples, be plotted in the value being used for factors A when GR width being set as 20 μm in fig. 13.

From expression formula (13), the total losses Lt of diode and the square root of RQ product proportional.When GR width is not more than 200 μm, the increase of total losses Lt can be suppressed to 20% or lower.From foregoing teachings, the optimum range for GR width is not less than 5 μm and is not more than 200 μm.Expression formula (16) below RQ product representation can be by this.

RQ≤4.9 × 10 ^-3(m Ω nC/V ²) V _block ²(16)

More than discuss the edge termination structure being also applicable to be different from guard ring.The proper range of the length of this edge termination structure is be not less than 5 μm and be not more than 200 μm equally.

In switching circuit, need to reduce loss.Loss in switching circuit mainly comprises conduction loss and switching loss.

Conduction loss is the product of electric current in the conducting state of switch element and voltage.Switching loss produces at switching elements conductive with when turning off.Switching loss increases with switching frequency proportional.

Therefore, in power diode, two kinds of losses of conducting resistance loss and switching loss should be considered.

According to the first embodiment, the index of product RQ (RQ product) as the performance of diode of the conducting resistance R of diode and the response charge Q of diode can be used.Particularly, RQ product can be used as the index of the total losses of diode.

According to the first embodiment, by using SiC as the material of diode and the structure of optimized epitaxial layer and device architecture, minimum RQ product can be obtained.Therefore, according to the first embodiment, the diode with excellent switching characteristic can be provided.

[the second embodiment]

< component structure >

It is the Schottky barrier diode be made up of silicon (Si) according to the diode of the second embodiment.Figure 14 is the sectional view of the structure of the diode schematically shown according to the second embodiment.

With reference to Figure 14, diode 2 comprises silicon substrate 21, stop-layer 22, drift layer 23, guard ring 24, Schottky electrode 25, Ohmic electrode 26 and surface protection film 27.

Because the structure shown in Figure 14 is substantially identical with the structure shown in Fig. 1, so will no longer repeat to describe in detail.Different from the diode 1 according to the first embodiment in semi-conducting material according to the diode 2 of the second embodiment.

< manufacturing process >

(example 2-1:150V level Si-SBD)

An example for the formation of the condition of the diode 2 shown in Figure 14 is described.Condition described below is such as the formation of the condition of 150V level Si-SBD.

First, preparation has resistivity is 2 × 10 ^-3the silicon substrate 21 of the N-shaped of (Ω cm).With epitaxy method formed on silicon substrate 21 0.5 μm thick, wherein donor concentration be 2 × 10 ¹⁸cm ^-3n-shaped stop-layer 22, then formed on stop-layer 22 10 μm thick, wherein donor concentration be 8 × 10 ¹⁴cm ^-3n-type drift layer 23.The substrate be made up of silicon substrate 21, stop-layer 22 and drift layer 23 is also called " silicon epitaxy substrate " hereinafter.

On the surface of drift layer 23, oxidation film is formed by the heat treatment in oxygen atmosphere.This oxidation film corresponds to the surface protection film 27 in Figure 14.Heat treated temperature will be used for and be set as 1100 DEG C.Then, one after the other photoetching and the etching with BHF etchant is performed.Therefore, the oxidation film in the part forming guard ring region removed and form the window being used for p-type diffusion.In oxygen atmosphere, oxidation film is used to be diffused in silicon epitaxy substrate by boron (B) as mask.Therefore guard ring 24 is formed.Guard ring 24 is that to have surface concentration be 1 × 10 ¹⁹cm ^-3and there are 2 μm of dark p-type area.Total GR width is 50 μm.

Ohmic electrode 26 is formed with EB evaporation.Ohmic electrode 26 is the films with the three-decker be made up of Ti film/Ni film/Au film.

Then, the window of Schottky electrode 25 is used for by photoetching with the formation in oxidation film (surface protection film) that is etched in of BHF.Form Schottky electrode 25 to make the end of Schottky electrode 25 across guard ring 24 side of being located thereon (designs of overlapping 20 μm).As the first embodiment, make and finish three kinds of different samples of interfacial area (with reference to table 6).

Table 6

After this, with EB evaporation, the Schottky electrode 25 be made up of molybdenum (Mo) film and Al film is formed.Schottky electrode 25 is formed with stripping.After this, above form at the back surface (surface 211 of silicon substrate 21) of silicon epitaxy substrate the Ohmic electrode 26 be made up of Ti film/Ni film/Au film.

Above-mentioned silicon epitaxy substrate is cut into chip.By tube core joint and wire-bonded, this chip is arranged in encapsulation.Use Sn-Ag solder to perform tube core at 230 DEG C to engage.Al lead-in wire is used to perform wire-bonded.

(example 2-2:80-level Si-SBD)

The situation that some conditions in the manufacturing process of example 2-1 (80V level SiC-SBD) are modified gets off to prepare 80V level SiC-SBD.Particularly, the donor concentration in drift layer 23 is set as 1.5 × 10 ¹⁵cm ^-3, and the thickness of drift layer 23 is set as 5 μm.In addition, as shown in table 7, prepare three kinds of different samples of junction interface area by the size changing Schottky electrode 25.

Table 7

Because other condition is identical with the condition in the manufacturing process of example 2-1, so no longer repeat description subsequently.

(example 2-3:40V level Si-SBD)

The situation that some conditions in the manufacturing process of example 2-1 (150V level SiC-SBD) are modified gets off to prepare 40V level SiC-SBD.Particularly, the donor concentration in drift layer 23 is set as 3 × 10 ¹⁵cm ^-3, and the thickness of drift layer 23 is set as 3 μm.In addition, as shown in table 8, prepare three kinds of different samples of junction interface area by the size changing Schottky electrode 25.

Table 8

Because other condition is identical with the condition of the manufacturing process of example 2-1, so no longer repeat description subsequently.

< appraisal procedure >

Conducting resistance R, reverse BV and response charge Q is measured with the appraisal procedure identical according to the method for the first embodiment.Therefore, by the details of no longer repeat assessment method.

The result > of < assessment

(1) R-Q characteristic

Figure 15 illustrates that the conducting resistance R-according to the sample of example 2-1 (150V level blocking voltage device), example 2-2 (80V level blocking voltage device) and example 2-3 (40V level blocking voltage device) responds the figure of charge Q characteristic.With reference to Figure 15, according to the sample in each example, conducting resistance R and response charge Q meet relation substantially inversely proportional each other.(6') this relation can be understood from expression formula (6) and expression formula.

(2) RQ product-V _blockcharacteristic

Figure 16 is the RQ product-V of the sample illustrated according to example 2-1 to 2-3 _blockthe figure of characteristic.Substantially reverse BV V is used with reference to Figure 16, RQ product _blockvalue determine.By making the measured value of RQ product through least square fitting according to expression formula (9), obtain relational expression below.

RQ=7.9 × 10 ^-2(m Ω nC/V ²) V _block ²

Value according to the RQ product of above-mentioned expression formula is the value that structure or edge termination structure by optimizing silicon epitaxy layer (drift layer 23 and stop-layer 22) obtain.The change illustrated about the RQ product of these values will be explained with reference to next embodiment.

[the 3rd embodiment]

It is the Schottky barrier diode be made up of silicon (Si) according to the diode of the 3rd embodiment.Because the configuration of the diode according to the 3rd embodiment is identical with the structure shown in Figure 14, so the description that will no longer repeat subsequently.Different from according to the diode of the second embodiment in the structural change of silicon epitaxy layer (drift layer 23 and stop-layer 22) and the overlapping widths between guard ring 24 and Schottky electrode 25 according to the diode of the 3rd embodiment.

As shown in table 9, prepare sample 1 to 7.Sample 1 is the diode formed when identical with the condition of the diode according to the second embodiment.That is, in sample 1, thickness and the GR width optimization of drift layer 23 is made.Sample 2 to 4 is different from sample 1 in the thickness d of drift layer.Sample 5 to 7 is different from sample 1 at overlapping widths (in other words, the GR width) aspect of guard ring 24.

Table 9

Sample 6 and sample 7 have large GR width.For sample 6 and sample 7, design total GR width and be set as GR width+30 μm to make total GR width.Because other condition is identical with the condition of the manufacturing process of example 2-1 with 2-2, so no longer repeat description subsequently.

< appraisal procedure >

Conducting resistance R, reverse BV and response charge Q is measured with the appraisal procedure identical according to the method for the first embodiment.Therefore, by the details of no longer repeat assessment method.

The result > of < assessment

Figure 17 illustrates RQ product-reverse BV V _blockcharacteristic is to the dependent figure of GR width.With reference to Figure 17, sample 2 and sample 3 are poorer than sample 1 in RQ characteristic.Particularly, for identical reverse BV V _block, compared with the RQ product of sample 1, the RQ product of sample 2 or sample 3 increases.

As shown in table 9, sample 2 and sample 3 are greater than sample 1 in the thickness of drift layer.Compared with the RQ product of sample 1, the reason that sample 2 and each RQ product of sample 3 increase is, because the thickness of drift layer 23 increases, even if so reverse BV V compared with optimal thickness _blockkeep identical but conducting resistance R increase.

Reverse BV V _blockcharge Q is each represents reverse bias characteristics with responding.Reverse BV V _blockdepend on the electric field strength at the interface at Schottky electrode.Response charge Q depends on the width of the depletion layer formed in drift layer.When drift layer has the thickness being greater than optimum thickness, the electric field strength of interface and the width of depletion layer be not by the impact of the thickness of drift layer.On the other hand, along with the thickness increase conducting resistance of drift layer also increases.

Sample 4 is less than sample 1 in the thickness of drift layer.Compared with the blocking voltage of sample 1, the blocking voltage of sample 4 reduces.Compare with conducting resistance R with the response charge Q of sample 1, the response charge Q of sample 4 and conducting resistance R reduce.So, the RQ product-reverse BV V of sample 4 _blockcharacteristic is slightly worse than the RQ product-reverse BV V of sample 1 _blockcharacteristic.RQ product substantially with reverse BV V _blockproportional (with reference to expression formula (9)).Therefore, based on RQ/V _block ², i.e. scale factor A, makes sample 4 and sample 1 mutually compare.Along with scale factor A diminishes, RQ product-reverse BV V _blockcharacteristic improves.

Sample 5 has the GR width of 5 μm.Sample 5 in blocking voltage lower than sample 1.In addition, the response electric charge that the response charge Q of sample 5 compares sample 1 reduces slightly.So, the RQ product-reverse BV V of sample 5 _blockcharacteristic is slightly worse than the RQ product-reverse BV V of sample 1 _blockcharacteristic.

Sample 6 has the GR width of 100 μm.The value of the scale factor A of sample 6 is substantially the same with sample 1.Sample 7 has the GR width of 300 μm.Compared with sample 1, sample 7 has the response charge Q significantly increased.So scale factor A is 0.12 (=1.2 × 10 ^-1).This value represents add about 40% compared with the value of the scale factor A of sample 1.That is, the RQ product-reverse BV V of sample 7 _blockcharacteristic is than the RQ product-reverse BV V of sample 1 _blockcharacteristic is poor.

The maximum of the scale factor A in sample 1 to sample 7 is 2.5 × 10 ^-1(sample 3).Therefore, the lower relation of plane of RQ product is obtained thus.

RQ/V _block ²=A≤2.5 × 10 ^-1

That is, RQ≤0.25 × V is met _block ²relation.

Therefore, can find out, the condition optimizing RQ product is present in thickness (structure of epitaxial loayer) and the GR width of drift layer.It is the element formed in such optimised conditions according to the diode of the second embodiment.By optimizing thickness (structure of epitaxial loayer) and the GR width of drift layer, the increment rate of RQ product can be controlled 44% or lower.In other words, the increment rate of the total losses Lt of diode can be suppressed 20% or lower.This relation can represent by expression formula (17) below.

RQ≤0.1 × V _block ²(17)

As mentioned above, according to second and the 3rd embodiment, by using Si as the material of diode and the structure of optimized epitaxial layer and device architecture, minimum RQ product can be obtained.Therefore, according to second and the 3rd embodiment, the diode with excellent switching characteristic as the first embodiment can be provided.

[the 4th embodiment]

< component structure >

It is the Schottky barrier diode be made up of gallium nitride (GaN) according to the diode of the 4th embodiment.Figure 18 is the sectional view of the structure of the diode schematically shown according to the 4th embodiment.

With reference to Figure 18, diode 4 comprises GaN substrate 41, stop-layer 42, drift layer 43, Schottky electrode 45, Ohmic electrode 46 and surface protection film 47.Basic structure due to diode 4 is identical with the structure of the diode 1 according to the first embodiment, so the description that will no longer repeat subsequently.

< manufacturing process >

(example 4-1:600V level GaN-SBD)

An example for the formation of the condition of the diode 4 shown in Figure 18 is described.Condition described below is such as the formation of the condition of 600V level GaN-SBD.

First, preparation has the GaN substrate 41 of the N-shaped in C-face.GaN substrate 41 has the diameter of 4 inches (1 inch approximates 2.5cm).GaN substrate 41 has the resistivity of 8 (m Ω cm) and the thickness of 500 μm.

Via epitaxial growth, on the C face of GaN substrate 41, form N-shaped stop-layer 42 and n-type drift layer 43 with metal organic vapor (MOVPE).Donor concentration in stop-layer 42 is 2 × 10 ¹⁸cm ^-3.The thickness of stop-layer 42 is 0.5 μm.Donor concentration in drift layer 43 is 7 × 10 ¹⁵cm ^-3.The thickness of drift layer 43 is 5 μm.Growth temperature during epitaxial growth is set as 1050 DEG C.As the source material for GaN, use trimethyl gallium (TMG) and NH ₃gas.Use SiH ₄(silane) is as n-type dopant.The substrate be made up of GaN substrate 41, stop-layer 42 and drift layer 43 is also called " GaN epitaxy substrate " hereinafter.

The surface 431 of drift layer 43 forms surface protection film 47.Surface protection film 47 is the dielectric films for field plate (FP) as edge termination structure.Particularly, SiH is used ₄and NH ₃as source material, formed with plasma CVD and there is 0.5 μm of thick SiNx film.

After this, use rapid thermal annealing (RTA) equipment at N ₂gaN epitaxy substrate is made to be subject to heat treatment in atmosphere.It is 600 DEG C and 3 minutes for heat treated condition.Then, use up and form opening in the photoresist quarter.The SiNx film in opening is removed with etching.Therefore the opening being used for field plate is formed.In an etching step, with the hydrofluoric acid (HF of the 50 % by weight and NH of 40 % by weight of buffering ₄f) etch GaN epitaxy substrate and reach 15 minutes.

The area of opening equals the area of the junction interface in the region that Schottky electrode 45 and drift layer 43 are in direct contact with one another.As shown in table 10, four kinds of samples that preparation junction interface area is different.This opening has square.In order to prevent electric field from concentrating on corner part, make the corner part of opening circular (radius of curvature is set as 20 μm).

Table 10

After removing photoresist, form etchant resist with photoetching.With EB evaporation, formed and there is the thick Ni layer of 50nm and there is the thick Au layer of 300nm.With the stripping in acetone, form Schottky electrode 45.The length (FP width) of part Schottky electrode 45 and surface protection film 47 (SiN film) overlapped each other is set as 15 μm.

Then, with photoetching and EB evaporation, on Schottky electrode 45, pad electrode is formed with stripping.This pad electrode is the electrode of the three-decker with Ti film/Pt film/Au film, and Ti film, Pt film and Au film have the thickness of 50nm, 100nm and 3 μm respectively.After this, there is the electrode of the three-decker of Al film/Ti film/Au film as Ohmic electrode 46 in the upper formation of whole surperficial 411 (back surfaces) of GaN substrate 41.Al film, Ti film and Au film have the thickness of 200nm, 50nm and 500nm respectively.In addition, Ohmic electrode 46 forms back side pad electrode.This back side pad electrode is the electrode of the three-decker with Ti film/Pt film/Au film, and Ti film, Pt film and Au film have the thickness of 50nm, 100nm and 1 μm respectively.

Above-mentioned GaN epitaxy substrate is cut into chip.By tube core joint and wire-bonded, this chip is installed in encapsulation.Use Sn-Ag solder to perform tube core at 230 DEG C to engage.Al lead-in wire is used to perform wire-bonded.

(example 4-2:1200V level GaN-SBD)

The situation that some conditions in the manufacturing process of example 4-1 (600V level GaN-SBD) are modified gets off to prepare 1200V level GaN-SBD.Particularly, the donor concentration in stop-layer 42 is set as 2 × 10 ¹⁸cm ^-3and the thickness of stop-layer 42 is set as 1 μm.Donor concentration in drift layer 43 is set as 5 × 10 ¹⁵cm ^-3and the thickness of drift layer 43 is set as 10 μm.The thickness of surface protection film 47 (SiN film) is set as 1 μm.In addition, FP width is set as 30 μm.

As shown in table 11, prepare four kinds of different samples of junction interface area by the size changing Schottky electrode 45.

Table 11

Because other condition is identical with the condition in the manufacturing process of example 4-1, so the description that will no longer repeat subsequently.

< appraisal procedure >

Conducting resistance R, reverse BV and response charge Q is measured with the appraisal procedure identical according to the method for the first embodiment.Therefore by the details of no longer repeat assessment method.

The result > of < assessment

(1) R-Q characteristic

Figure 19 illustrates that the conducting resistance R-according to the sample of example 4-1 (600V level blocking voltage device) and example 4-2 (1200V level blocking voltage device) responds the figure of charge Q characteristic.With reference to Figure 19, according to the sample of each example, conducting resistance R and response charge Q meet relation substantially inversely proportional each other.(6') this relation can be understood from expression formula (6) and expression formula.

(2) RQ product-V _blockcharacteristic

Figure 20 is the RQ product-V of the sample illustrated according to example 4-1 and example 4-2 _blockthe figure of characteristic.With reference to Figure 20, RQ product substantially by reverse BV V _blockvalue determine.By providing the measured value of the RQ product about least square fitting according to expression formula (9), obtain relational expression below.

RQ=9.6 × 10 ^-4(m Ω nC/V ²) V _block ²

Value according to the RQ product of above-mentioned expression formula is the value that structure or FP structure by optimizing GaN epitaxial layer (drift layer 43 and stop-layer 42) obtain.The change illustrated about the RQ product of these values is explained with reference to next embodiment.

[the 5th embodiment]

< component structure >

It is the Schottky barrier diode be made up of gallium nitride (GaN) according to the diode of the 5th embodiment.Because the configuration of the diode according to the 5th embodiment is identical with the structure shown in Figure 18, so the description that will no longer repeat subsequently.Different from according to the diode of the 4th embodiment in FP change width according to the diode of the 5th embodiment.

< manufacturing process >

(example 5-1:600V level GaN-SBD)

The sample according to example 5-1 is made by the method identical according to the method for the sample of example 4-1 with making.The structure of epitaxial loayer is identical with the structure in example 4-1.Junction interface area be set as constant and make FP width different.Particularly, junction interface area is set as the 0.75mm identical with the junction interface area of the sample 3 according to example 4-1 ².As shown in table 12, preparation FP width is changed to the sample of 800 μm from 0 (not having FP structure).The thickness of surface protection film 47 (SiN film) is set as 0.5 μm.

Table 12

(example 5-1:1200V level GaN-SBD)

The sample according to example 5-2 is made by the method identical according to the method for the sample of example 4-2 with making.The structure of epitaxial loayer is identical with the structure in example 4-2.Junction interface area be set as constant and make FP width different.Particularly, junction interface area is set as the 0.75mm identical with the junction interface area of the sample 3 according to example 4-2 ².As shown in table 13, preparation FP width is changed to the sample of 800 μm from 0 (not having FP structure).The thickness of surface protection film 47 (SiN film) is set as 1 μm.

Table 13

< appraisal procedure >

Conducting resistance R, reverse BV and response charge Q is measured with the appraisal procedure identical according to the method for the first embodiment.Therefore, by the details of no longer repeat assessment method.

The result > of < assessment

Figure 21 is the figure of the FP width-reverse BV characteristic of the sample illustrated according to example 5-1 and example 5-2.With reference to Figure 21, there is no the sample of the FP structure FP width of 0 (have be) and having in the sample of FP width of 3 μm, reverse BV V _blockreduce.

In example 5-1, the sample with the FP width being not less than 5 μm has the reverse BV V of about 600V _blockand achieve good result.Similarly in example 5-2, the sample with the FP width of not little 5 μm has the reverse BV V from about 1100 to 1200V _blockand achieve good result.

Think, when FP width is not more than 3 μm, relax the concentrated decreased effectiveness of electric field by FP structure, so leakage current increases and reverse BV V _blockreduce.

In addition, as shown in table 14, example 5-1 and 5-2 any one in, conducting resistance R changes according to FP width hardly.

Table 14

Figure 22 is the figure of the FP width-response charge Q characteristic illustrated according to the sample of example 5-1 and 5-2.With reference to Figure 22, in two examples of example 5-1 and 5-2, have from the sample of the FP width of 0 to 50 μm, response charge Q is constant substantially.When FP width is set as 100 μm, response charge Q increases slightly.The increment rate of response charge Q is about 20%.When FP width is not less than 100 μm, response charge Q significantly increases.Think, when FP width is large, compared with the electric charge produced by Schottky electrode region, the electric charge produced by FP region is very important, and therefore total electrical charge adds.

Figure 23 illustrates RQ product-reverse BV V _blockcharacteristic is to the dependent figure of FP width.In the relation that expression formula (9) illustrates, RQ product and reverse BV V _blocksquare proportional.Figure 24 illustrates the dependent figure of the scale factor A shown in Figure 23 to FP width.With reference to Figure 24, when FP width is not more than 3 μm, reverse BV V _blockreduce and A increase.In other words, RQ product-reverse BV V _blockdeterioration in characteristics.When in the scope of FP width at 5 to 200 μm, A substantially reaches minimum value and it is substantially constant.When FP width is more than 200 μm, RQ product starts to increase also therefore RQ product-reverse BV V _blockdeterioration in characteristics.

Use according to the sample of example 5-1 as the sample of FP width with 15 μm.Use according to the sample of example 5-2 as the sample of FP width with 30 μm.As mentioned above, from the scope of the FP width of 15 to 30 μm, RQ product reaches minimum value.Based on the data of these two samples, be plotted in the value being used for factors A when FP width being set as 20 μm in fig. 24.

From expression formula (13), the total losses Lt of diode and the square root of RQ product proportional.When FP width is not more than 200 μm, the increase of total losses Lt can be suppressed to 20% or lower.From foregoing teachings, the optimum range for FP width is not less than 5 μm and is not more than 200 μm.Expression formula (18) below RQ product representation can be by this.

RQ≤1.3 × 10 ^-3(m Ω nC/V ²) V _block ²(18)

According to the 4th and the 5th embodiment, minimum RQ product can by use GaN as the material of diode and the structure of optimized epitaxial layer and device architecture obtain.Therefore, according to the 5th embodiment, the diode with excellent switching characteristic as first to fourth embodiment can be obtained.

More than discuss the edge termination structure be also applicable to except field plate.The proper range of the length of this edge termination structure is be not less than 5 μm and be not more than 200 μm equally.

As mentioned above, according to the 4th and the 5th embodiment, by using GaN as the material of diode and the structure of optimized epitaxial layer and device architecture, minimum RQ product can be obtained.Therefore, according to the 4th and the 5th embodiment, the diode with excellent switching characteristic as the first to the 3rd embodiment can be obtained.

Although describe in detail and illustrate the present invention, should be expressly understood that it is only the mode of example and example and does not adopt the mode of restriction, scope of the present invention is explained by the item of claims.

Claims (16)

1. a diode, comprising:

Active layer; With

First and second electrodes, described first and second electrodes are used for applying forward voltage and reverse voltage to described active layer,

In the forward current-voltage characteristic of the described diode when applying described forward voltage via described first and second electrodes to described active layer, voltage is defined as forward conduction resistance R about the change of electric current, the current value of described electric current is corresponding with current density, J f, described current density, J f obtains by the conductivityσ of described active layer is multiplied by electric field strength 50V/mm, wherein, the unit of described forward conduction resistance R is m Ω, and the unit of described conductivityσ is S/mm

In the reverse current-voltage characteristic of the described diode when applying described reverse voltage via described first and second electrodes to described active layer, the voltage corresponding with current density, J r is defined as reverse BV V _block, 10 of described current density, J r and described current density, J f ^-5doubly equally high, wherein, described reverse BV V _blockunit be V, and

Utilize dipulse method, be defined as the response charge Q of described diode by the electric charge obtained diode current I integration under the following conditions, wherein, the unit of described response charge Q is nC, and described condition is:

(a) reverse voltage Vr:2/3 × V _block,

(b) turn-off speed di/dt:-200A/ μ s, and

The limit of integration of (c) described diode current I: pass the time point of 0 until described diode current I returns to the scope of the time point of 10% of reverse current peak value from described diode current I,

Under the measuring tempeature of 25 DEG C, the product RQ of described forward conduction resistance R and described response charge Q meets RQ≤0.25 × V _block ²relation.

2. diode according to claim 1, wherein

Described product RQ meets RQ≤0.1 × V _block ²relation.

3. diode according to claim 2, wherein

The semi-conducting material forming described diode is silicon.

4. diode according to claim 1, wherein

Described product RQ meets RQ≤4.9 × 10 ^-3× V _block ²relation.

5. diode according to claim 4, wherein

The semi-conducting material forming described diode is carborundum.

6. diode according to claim 1, wherein

Described product RQ meets RQ≤1.3 × 10 ^-3× V _block ²relation.

7. diode according to claim 6, wherein

The semi-conducting material forming described diode is gallium nitride.

8. the diode according to any one in claim 4 to 7, wherein

Described diode comprises the edge termination structure be formed in described active layer, and described edge termination structure has and is not less than 5 μm and the width being not more than 200 μm.

9. a diode, comprises

Active layer; With

First and second electrodes, described first and second electrodes are used for applying forward voltage and reverse voltage to described active layer,

In the forward current-voltage characteristic of the described diode when applying described forward voltage via described first and second electrodes to described active layer, when current density, J f is 3A/mm ²time voltage be defined as forward conduction resistance R about the change of electric current, described current density, J f is by the value of forward current being obtained divided by junction interface area, and wherein, the unit of described forward conduction resistance R is m Ω,

In the reverse current-voltage characteristic of the described diode when applying described reverse voltage via described first and second electrodes to described active layer, the voltage corresponding with current density, J r is defined as reverse BV V _block, 10 of described current density, J r and described current density, J f ^-5doubly equally high, wherein, described reverse BV V _blockunit be V, and

Utilize dipulse method, be defined as the response charge Q of described diode by the electric charge obtained diode current I integration under the following conditions, wherein, the unit of described response charge Q is nC, and described condition is:

(a) reverse voltage Vr:2/3 × V _block,

(b) turn-off speed di/dt:-200A/ μ s, and

The limit of integration of (c) described diode current I: pass the time point of 0 until described diode current I returns to the scope of the time point of 10% of reverse current peak value from described diode current I,

Under the measuring tempeature of 25 DEG C, the product RQ of described forward conduction resistance R and described response charge Q meets RQ≤0.25 × V _block ²relation.

10. diode according to claim 9, wherein

Described product RQ meets RQ≤0.1 × V _block ²relation.

11. diodes according to claim 10, wherein

The semi-conducting material forming described diode is silicon.

12. diodes according to claim 9, wherein

Described product RQ meets RQ≤4.9 × 10 ^-3× V _block ²relation.

13. diodes according to claim 12, wherein

The semi-conducting material forming described diode is carborundum.

14. diodes according to claim 9, wherein

Described product RQ meets RQ≤1.3 × 10 ^-3× V _block ²relation.

15. diodes according to claim 14, wherein

The semi-conducting material forming described diode is gallium nitride.

16. according to claim 12 to the diode described in any one in 15, wherein

Described diode comprises the edge termination structure be formed in described active layer, and described edge termination structure has and is not less than 5 μm and the width being not more than 200 μm.