KR101683470B1 - Reducing Method for Gate Leakage Current of AlGaN/GaN HEMTs - Google Patents

Abstract

The present invention relates to a method of reducing gate leakage current of an AlGaN / GaN HEMT device, and more particularly, to an AlGaN / GaN HEMT by applying an SF ₆ plasma treatment to improve gate leakage current, characteristics below a threshold voltage, .
The present invention relates to a method for reducing the gate leakage current of an AlGaN / GaN HEMT device by etching the SiN _x pre-passivation layer to protect the GaN surface during the high temperature ohmic annealing, through etching of the SF ₆ plasma process, And after the GaN surface is treated, the SiN _x passivation layer is re-deposited after the in-situ N ₂ plasma pretreatment using ICP-CVD.

Description

(Reducing Method for Gate Leakage Current of AlGaN / GaN HEMTs)

The present invention relates to a method of reducing gate leakage current of an AlGaN / GaN HEMT device, and more particularly, to an AlGaN / GaN HEMT by applying an SF ₆ plasma treatment to improve gate leakage current, characteristics below a threshold voltage, .

Gallium nitride (GaN) -based high electron mobility transistors (HEMTs) have shown great potential as promising candidates for next generation high frequency, high power applications.

However, surface-related problems such as large reverse-voltage gate leakage currents or current decay through Schottky contacts still need a better solution.

Wherein the gate leakage current is an important characteristic for determining reliability and a breakdown voltage.

Subthreshold characteristics are also an important factor for achieving good power dissipation and good pinch-off of AlGaN / GaN HEMT devices.

In order to reduce the gate leakage current and improve the characteristics below the threshold voltage, various methods such as plasma processing, removal of sidewall leakage current, metal insertion with a high work function and appropriate heat treatment have been applied. The intermediate plasma treatment process is a process involved in etching the SiN _x passivation layer in GaN device fabrication.

In order to reduce the gate leakage current, CF ₄ plasma has been mainly used. However, the CF ₄ plasma treatment has a problem that the plasma is damaged due to the strong treatment of the bias voltage of about 100V.

It also leaves unintentional impurities such as carbon (C) on the surface, causing deep-level traps in the interface or bulk of the GaN-deposited dielectrics.

On the other hand, although there is a good result that the gate leakage current is reduced by using the O ₂ plasma treatment, if the oxide is present on the surface, the gate leakage current and the trapping characteristics are easily deteriorated.

Korean Patent Publication No. 10-2011-0088460 (published on August 03, 2011)

The present invention been made in view of solving the problems described above, SF ₆ plasma sikimyeo treatment to remove the SiN _x advance (pre) passivation layer to and enhance the GaN surface, SF ₆ plasma processing time prior to re-deposit the SiN _x passivation layer It is possible to reduce the gate leakage current of the AlGaN / GaN HEMT device, which can reduce the gate leakage current by a factor of 1000, obtain a characteristic with a slope lower than the threshold voltage, and improve the current decay phenomenon. The purpose is to provide.

Another object of the present invention is to apply a soft SF ₆ plasma process with little damage caused by low power and to optimize the application of the exposure time, thereby reducing the damage caused by the plasma, And a method of reducing gate leakage current of an AlGaN / GaN HEMT device.

AlGaN / GaN HEMT gate leakage current reduction method of the device according to an embodiment of the present invention for achieving the above object is, SF ₆ through the etching of the plasma treatment, vapor deposition for protecting during the high-temperature heat treatment ohmic a GaN surface Removing the SiN _x pre-passivation layer after the ohmic process, and treating the GaN surface.

Also, the SiN _x passivation layer is removed and then the SiN _x passivation layer is re-deposited after the in-situ N ₂ plasma pretreatment using ICP-CVD.

Further, the SF ₆ plasma treatment time is 1 to 5 minutes.

Further, the SiN _x passivation layer is etched by an SF ₆ plasma process to form a gate region in the SiN _x passivation layer, followed by depositing a gate metal.

The gate metal is Ni / Au, which is a Schottky gate metal.

The method for reducing gate leakage current of an AlGaN / GaN HEMT device is characterized in that the SF ₆ plasma process is performed under a soft plasma condition in which a DC bias value is applied to an SF ₆ plasma etching equipment.

Then, SiN _x is further deposited on the second passivation layer by using ICP-CVD after the gate metal is deposited, and PGA is performed at 400 ° C.

According to the solving means of the above problems, the GaN surface prior to the formation of the SiNx passivation layer to the place of SF ₆ plasma treatment of the hard (hard) plasma conditions reported are applied to the SF ₆ plasma treatment of soft (soft) plasma conditions A gate leakage current, a subthreshold slope, an on / off drain current ratio, and a pulse current-voltage characteristic can be improved.

In addition, the soft SF ₆ plasma process, which is less susceptible to damage, is applied to remove the SiN _x pre-paved layer and to improve the GaN surface, and the SF ₆ plasma treatment time before the re-deposition of the SiN _x passivation layer The gate leakage current can be reduced by 1/1000 times to obtain 67nA / mm at the gate voltage of -100V (the smallest value of the recently reported gate leakage current in AlGaN / GaN HEMT) and 63mV / dec, and the current decay phenomenon can also be improved.

FIG. 1 is a flowchart showing a manufacturing process of an AlGaN / GaN HEMT device after an ohmic forming process according to an embodiment of the present invention.
FIGS. 2A and 2B are graphs showing a reverse voltage gate leakage current characteristic and a forward voltage gate current characteristic of an AlGaN / GaN HEMT device to which an embodiment of the present invention is applied, in comparison with the related art.
FIG. 3 is a graph showing drain current and gate current characteristics of an AlGaN / GaN HEMT device to which the embodiment of the present invention is applied, in comparison with the conventional case.
4A to 4C are graphs showing pulse voltage-current characteristics of an AlGaN / GaN HEMT device according to respective processing conditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

It is to be noted that the same components of the drawings are denoted by the same reference numerals and symbols as possible even if they are shown in different drawings.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Also, when a part is referred to as "including " an element, it does not exclude other elements unless specifically stated otherwise.

FIG. 1 is a flowchart showing a manufacturing process of an AlGaN / GaN HEMT device after an ohmic forming process according to an embodiment of the present invention.

The hard plasma condition and the soft plasma condition are referred to as a hard plasma condition when the DC bias applied to the etching equipment using the SF ₆ plasma is high, and a soft plasma condition when the numerical value is low.

In the present invention, a 10 nm SiN _x pre-passivation layer is deposited after the ohmic process is completed to protect the GaN surface that has been cleaned during the high-temperature ohmic annealing, The SF ₆ plasma treatment is performed under the soft plasma condition.

1, the removal of the SiN _x pre-passivation layer of 10 nm and the GaN surface treatment are carried out simultaneously (successively) with the SF ₆ plasma (see (a) to (b) _x passivation layer is redeposited (see (c)).

The environment of the SF ₆ plasma treatment is performed with an SF ₆ gas flow rate of 50 to 100 sccm, a chamber pressure of 100 mTorr, an RF power of 10 W, and a plasma treatment time of 1, 2, 3 and 5 minutes.

Since the processing time includes the SiN _x etching time of 10 nm (the etching rate of SiN _x is 20 nm / min), the time when the plasma treatment is actually performed on the pure GaN surface is 30 seconds shorter than the above processing time.

On the other hand, the reference sample is treated with buffered oxide etchant (BOE) (1: 7) for 2 minutes to remove the 10 nm SiN _x pre-passivation layer.

The SiN _x pre-passivation layer having a thickness of 10 nm was removed by the SF ₆ plasma treatment and then subjected to in-situ N ₂ plasma pretreatment at 350 ° C. using inductively coupled plasma (ICP) -chemical vapor deposition (CVD) Then, a 120 nm SiN _x passivation layer is redeposited.

Next, the SiN _x passivation layer is etched under soft SF ₆ plasma conditions to form a gate region in the SiN _x passivation layer and then evaporated to a Schottky gate metal of Ni / Au (20/180 nm) d)).

Then, a second passivation layer is formed by further depositing SiN _x 30 nm at 250 ° C using ICP-CVD, followed by 400 ° C post-gate annealing (PGA).

The 400 ° C PGA stabilizes the device characteristics and confirms that it does not degrade when heated and maintains a small gate leakage.

On the other hand, in GaN-based materials, the surface is very sensitive and the surface treatment greatly affects the surface potential.

According to the present invention, the soft SF ₆ plasma treatment cleans the sensitive GaN surface by reducing the amount of carbon or oxygen impurities, nitrogen vacancies, and other adsorbates.

In addition, the Ga-S or NS bond formed on the GaN surface can prevent the native oxide from forming on the surface, and the GaN surface can be kept clean, similar to the effect of (NH ₄ ) ₂ S treatment .

This improves the quality of the SiN _x / GaN interface and improves the gate leakage current, slope below the gate voltage, on / off drain current ratio, and pulse IV characteristics as shown in Table 1 below.

Table 1 will be described with reference to FIG. 2 and subsequent drawings.

In Table 1, the present invention can be seen that the gate leakage current (I _G ^l), BOE-treated reference to SF ₆ plasma in 57uA / mm of the element as a 67nA / mm handle 2 minutes to reduce about 3 degree (order) have.

This is the smallest of the recently reported gate leakage currents in AlGaN / GaN HEMTs.

In order to find the cause of the decrease in the gate leakage current, the forward voltage gate current characteristics of the SF ₆ plasma-treated device and the non-SF ₆ plasma-treated device were measured and shown in FIG.

FIGS. 2A and 2B are graphs showing a reverse voltage gate leakage current characteristic and a forward voltage gate current characteristic of an AlGaN / GaN HEMT device to which an embodiment of the present invention is applied, in comparison with the related art.

The Schottky barrier height (SBH) and the ideality factor (IF) were extracted from the forward gate current. The ideal coefficients were SF ₆ plasma treatment without BO ₆ treatment and SF ₆ plasma treatment 1.28 and 1.29, while the Schottky barrier height increased from 0.71 eV to 1.09 eV with SF ₆ plasma treatment.

When the SF ₆ plasma treatment was performed for a long time (5 minutes), the ideal coefficient to be close to 1 slightly increased to 1.39, indicating that plasma damage could be induced.

FIG. 3 is a graph showing the drain current and gate current characteristics of an AlGaN / GaN HEMT device to which the embodiment of the present invention is applied, with and without SF ₆ plasma treatment at V _DS = 5 V The drain current is represented by a symbol line and the gate current is represented by a dashed line.

As shown in FIG. 3, the reduction of the gate leakage current improves the subthreshold slope (SS) and the on / off drain current ratio.

This is because when the device is pinch off, both the drain leakage current and the slope (SS) below the threshold voltage are dominated by the reverse voltage gate leakage current.

The maximum on / off drain current ratio is expressed by the current in the ON state (indicated by I _{D , ON} , when V _GS = 1V), the current in the OFF state (I _{D ,} marked _OFF , was defined as the ratio of the current _{(minimum I D, oFF))} , the maximum oN / oFF drain current ratio when 2 minutes treatment with SF ₆ plasma is 3.5 × 0 ^7, the slope (SS) of less than a threshold voltage is 63mV / dec Can be obtained.

The slope SS below the threshold voltage has a theoretical limit value of 60 mV / dec at room temperature, but the present invention achieves a value similar to this.

To further explore the interface and surface related properties, a pulse IV measurement is shown in Figure 4 with increasing quiescent drain bias point (V _DSQ ).

Figures 4a to 4c are AlGaN / pulse voltage of the GaN HEMT device according to each of the processing conditions, if a graph showing the characteristics of electric current, Figure 4a is not treated SF ₆ plasma, Figure 4b 2 minutes SF ₆ plasma processing FIG. 4C is a graph showing the case where SF ₆ plasma treatment is performed for 5 minutes.

As shown in FIG. 4B, the drain current attenuation phenomenon is improved by the SF ₆ plasma two-minute treatment.

However, SF ₆ in Figure 4c When the plasma is exposed for a long time, the current discrepancy is increased due to the plasma damage.

It is known that the gate edge rather than the gate edge further affects the IV dispersion. In the present invention, the soft SF ₆ plasma treatment is performed at the gate edge (gate-source, gate-drain ), It is possible to eliminate impurities near the gate edge and to re-distribute the IV dispersion.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. In addition, it is a matter of course that various modifications and variations are possible without departing from the scope of the technical idea of the present invention by anyone having ordinary skill in the art.

Claims (7)

The SiN _x pre-passivation layer deposited to protect the GaN surface during the high temperature ohmic annealing, through the etching of the SF ₆ plasma treatment for 1 to 5 minutes, is removed after the ohmic process and the GaN surface is removed Lt; / RTI >
After removing the SiN _x pre-passivation layer and then performing in-situ N ₂ plasma pretreatment at 350 ° C using ICP-CVD, the SiN _x passivation layer was redeposited,
Wherein the SF ₆ plasma process is performed under a soft plasma condition in which the DC bias value applied to the SF ₆ plasma etching equipment is low. delete delete The method according to claim 1,
Wherein the SiN _x passivation layer is etched by an SF ₆ plasma process to form a gate region in the SiN _x passivation layer, followed by depositing a gate metal. 5. The method of claim 4,
Wherein the gate metal is a Schottky gate metal, Ni / Au. ≪ RTI ID = 0.0 > 8. < / RTI > delete 5. The method of claim 4,
Wherein the gate metal is deposited, and then SiN _x is further deposited on the second passivation layer by ICP-CVD, followed by performing a PGA at 400 ° C. The gate leakage current of the AlGaN / GaN HEMT device is reduced.

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