CN101424878A - Method for making high W/N ratio T-shaped gate by once electron beam exposure - Google Patents

Abstract

A method for forming a T-shaped grid with a high aspect ratio by one electron beam exposure is characterized in that it comprises the following steps: Step 1: making the layout of the T-shaped grid required for electron beam exposure; Step 2: making the T-shaped grid The substrate is cleaned and dried; Step 3: Apply three layers of electron beam exposure glue on the substrate and dry; Step 4: Electron beam exposure, transfer the required T-shaped grid pattern to the substrate; Step 5: Developing and fixing, forming a T-shaped grid groove on the three-layer electron beam exposure glue; Step 6: Electron beam evaporation grid metal; Step 7: Metal peeling, forming a T-shaped grid structure in the groove.

Description

Method for forming T-shaped grid with high aspect ratio by one electron beam exposure

technical field

The invention relates to a manufacturing method of a T-shaped grid applied to gallium nitride (GaN)-based semiconductor devices, in particular to a manufacturing method for forming a T-shaped grid with a high aspect ratio by one electron beam exposure.

Background technique

Wide bandgap semiconductor materials represented by gallium nitride (GaN) and silicon carbide (SiC) have the characteristics of large bandgap width, high electron drift speed, and high thermal conductivity. Therefore, while they are ideal high-power electronic materials, they also have great potential in the field of ultra-high frequencies. At present, although the growth technology of GaN materials restricts the development of the performance of GaN-based semiconductor devices, GaN-based high electron mobility transistors (HEMTs) with a maximum oscillation frequency (f _max ) of 200 GHz have also come out.

The high-frequency performance of GaN-based semiconductor devices is closely related to the fabrication process of the device gate. The smaller the gate length (L _g ) and the lower the gate resistance (R _g ), the higher the cut-off frequency of the device. However, since the gate length and gate resistance have a relationship as shown below

R _g ∝1/L _g

Therefore, in order to reduce the gate length and gate resistance at the same time, we need to use T-shaped gate technology. In recent years, there are mainly two technologies for making T-shaped grids published in the world: (1) Divide the T-shaped grid pattern into two regions with different doses, and after coating three layers of electron beam exposure glue on the substrate, only Use one electron beam exposure to form a T-shaped grid; (2) deposit a layer of silicon dioxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) on the substrate, and use pattern transfer technology and two electron beam exposures to form a T-shaped grid. Form a T-shaped grid.

The above two methods have their own advantages and disadvantages. Dividing the T-shaped grid pattern into two regions with different doses, the method of forming a T-shaped grid with three layers of glue and one electron beam exposure is better than the process. It is difficult to obtain an ideal shape at the junction, thereby increasing the parasitic capacitance of the gate. At the same time, it is also difficult to obtain a high aspect ratio (the larger the aspect ratio, the smaller the gate resistance when the gate length is constant) . However, the method of pattern transfer and double electron beam exposure overcomes the problems of shape and aspect ratio, but at the same time increases a large number of process steps, which seriously affects the production efficiency.

Contents of the invention

The purpose of the present invention is to provide a method for forming a high aspect ratio T-shaped grid by one-time electron beam exposure, so that it can have the advantages of the above two methods, thereby simplifying the manufacturing process of small grid length, improving the yield and reducing the cost .

The present invention is a method for forming a high-width-narrow-ratio T-shaped grid by one electron beam exposure, which is characterized in that it comprises the following steps:

Step 1: making the layout of the T-shaped grid required for electron beam exposure;

Step 2: cleaning and drying the substrate for making the T-shaped grid;

Step 3: Coating three layers of electron beam exposure glue on the substrate and drying;

Step 4: E-beam exposure, transferring the required T-grid pattern to the substrate;

Step 5: developing and fixing, forming grooves for making T-shaped grids on the three-layer electron beam exposure glue;

Step 6: E-beam evaporation of grid metal;

Step 7: Metal stripping, forming a T-shaped gate structure in the trench.

The substrate is a GaN/GaAl epitaxial wafer with a sapphire substrate.

The materials coated with three layers of electron beam exposure glue on the substrate are PMMA, PMMA-MAA and PMMA respectively.

Wherein the layout of the T-shaped grid described in step 1 is divided into three areas with different exposure doses, and the exposure doses of each area are respectively:

The first zone a is 1140pC/cm;

The second zone b is 100 μC/cm ² ;

The third zone c is 60 μC/cm ² .

Wherein the temperature during drying described in step 2 is 110 degree, and the time is 5 minutes.

The coating and drying of three layers of electron beam exposure glue described in step 3 means that the electron beam exposure glue is dried once every time the electron beam exposure glue is applied.

Wherein step 4 is to use the electron beam to fully expose three regions with different doses on the layout at one time.

Wherein the developing and fixing time described in step 5 are both 30 seconds.

Wherein the gate metal evaporated by the electron beam in step 6 is nickel/gold, and its thickness is 30/330nm.

Description of drawings

In order to further illustrate the specific technical content of the present invention, below in conjunction with embodiment and accompanying drawing detailed description as follows, wherein:

Fig. 1 is the schematic sectional view of three layers of electron beam exposure adhesives required for making T-shaped grids in the present invention;

FIG. 2 is a schematic layout diagram of a T-shaped grid required for electron beam exposure used in the present invention.

Detailed ways

In order to achieve this purpose, on the premise that only one electron beam exposure is still used, it is realized through a special layout design. FIG. 2 is a schematic diagram of the electron beam exposure layout of the T-shaped grid used in the present invention. In this layout design, the proximity effect of electron beam exposure is fully considered and utilized, and the supposedly complete T-shaped grid layout is divided into three independent regions with different doses (the traditional one is only divided into two regions). The regions with different doses) are respectively identified as the first region a, the second region b and the third region c. By changing the distance between the first area a and the second area b, the size of the top wide part and the bottom narrow part of the T-shaped grid can be changed, and then through the dose compensation of the third area c, the T-shaped grid can be adjusted during exposure. The tops are connected in one piece, so that a high aspect ratio can be achieved (the aspect ratio can be greater than 8); in addition, by changing the distance between the third zone c and the first zone a, and optimizing the dose of the third zone c, it can effectively improve Morphology of the T-shaped grid.

Please refer to Fig. 1 and Fig. 2, the manufacturing method of forming a high aspect ratio T-shaped grid by one electron beam exposure of the present invention comprises the following steps:

Step 1: Make the layout of the T-shaped grid required for electron beam exposure. The layout of the T-shaped grid is divided into three areas with different exposure doses. The exposure doses of each area are:

The first zone a is 1140pC/cm

The second zone b is 100 μC/cm ² ;

The third zone c is 60 μC/cm ² . ;

Step 2: Clean and dry the substrate 10 on which the T-shaped gate is made. The substrate 10 is a gallium nitride/gallium aluminum nitride epitaxial wafer on a sapphire substrate, and the drying temperature is 110 degrees. , the time is 5 minutes;

Step 3: Apply three layers of electron beam exposure adhesives 20, 30, 40 on the substrate 10, and dry. The materials of the three layers of electron beam exposure adhesives 20, 30, and 40 are respectively PMMA, PMMA-MAA, and PMMA. The above-mentioned drying refers to drying once every time the electron beam exposure glue is applied;

Step 4: Electron beam exposure, transferring the layout of the required T-shaped grid to the substrate 10. The electron beam exposure is to use electron beams to fully expose three regions with different doses on the layout at one time;

Step 5: Developing and fixing, forming a groove 50 for making a T-shaped grid on the three layers of electron beam exposure glue 20, 30, 40, and the time for developing and fixing is 30 seconds;

Step 6: Electron beam evaporation of the grid metal, the evaporated grid metal is nickel/gold with a thickness of 30/330nm;

Step 7: Metal stripping, forming a T-shaped gate 60 structure in the trench 50 .

See also shown in Fig. 1 and Fig. 2 again, detailed steps of the present invention are:

Making the layout of the T-shaped grid required for electron beam exposure, the doses of the first region a, the second region b and the third region c in the layout are 1140pC/cm, 100μC/cm ² and 60μC/cm ² respectively;

For samples that have completed device isolation and source-drain electrodes, rinse them repeatedly with acetone, ethanol, and deionized water, and dry them with a nitrogen gun before drying them in an oven at 110 degrees for 5 minutes;

Apply the lower layer of electron beam exposure glue 20 (PMMA glue), the required thickness is 180nm; immediately put it on a hot plate at 180 degrees for 5 minutes after coating;

After the sample is cooled, apply the middle layer of electron beam exposure glue 30 (PMMA-MAA glue), the required thickness is 300nm; immediately put it on a hot plate at 150 degrees to bake for 15 minutes;

After the sample is cooled, apply a layer of electron beam exposure glue 40 (PMMA glue), the required thickness is 100nm; immediately put it on a hot plate at 180 degrees for 10 minutes after coating;

Send the glued sample to the electron beam exposure, and complete the exposure according to the dosage requirements;

Developing: The developing solution is MIBK:IPA=1:3, and the developing time is 30 seconds;

Fixing: The fixing solution is IPA, and the fixing time is 30 seconds;

Immediately after the fixing is completed, the sample is blown dry with a nitrogen gun to form a groove 50 for making a T-shaped grid, and the glue pattern shown in FIG. 1 can be obtained at this time;

Electron beam evaporation grid metal, the material of grid metal is nickel/gold=30/300nm;

Submerge the sample in acetone to complete the metal lift-off to form a T-shaped grid 60 .

Beneficial effects of this method

In this method, under the premise of fully considering and utilizing the proximity effect of electron beam exposure, when designing the layout, the layout is divided into three regions with different doses instead of the previous method of only dividing the layout into two regions with different doses. method, and use three layers of glue to make a T-shaped grid by one electron beam exposure. In this way, a T-shaped gate structure with high aspect ratio and good morphology can be obtained without increasing the process steps. The specific advantages are as follows:

Using the proximity effect, increase the distance between the first area a and the second area b during layout design to increase the size of the top wide part of the T-shaped grid, and then through the dose compensation of the third area c, the T-shaped grid will be adjusted during exposure The tops are connected into one piece, so that a T-shaped grid 60 with a high aspect ratio can be obtained;

changing the distance between the first region a and the third region c and optimizing the dose of the third region c to improve the shape of the T-shaped gate 60;

Only one electron beam exposure makes the process simple and controllable, has good repeatability and is conducive to improving the yield and reducing the cost of mass production;

The PMMA glue is easy to peel off, and it is convenient to form a good T-shaped grid 60 after evaporating the metal.

Examples of implementation effects

On a sapphire substrate, an n-type GaN field effect transistor is fabricated. After the isolation of the device and the fabrication of the source and drain electrodes are completed, the gate is fabricated by the method described in the present invention. Thus, a T-shaped gate with a gate length of 180nm and an aspect ratio of 10 (that is, the width part is 1800nm) is obtained, and the performance of the entire field effect transistor is good.

The method for forming a high-aspect-ratio T-shaped grid by one electron beam exposure of the present invention is highly controllable, and the electron beam exposure adhesives used are all mature commercial adhesives, and the chemical used in cleaning, developing and fixing Reagents are also conventional reagents. Each step involved in the method has the characteristics of simplicity, practicality, strong operability, and good practical effect.

Claims (9)

1, a kind of once electron beam exposure forms the method for making of high W/N ratio T-shaped gate, it is characterized in that, comprises the steps:

Step 1: make the domain that carries out the required T shape grid of electron beam exposure;

Step 2: the substrate of making T shape grid is cleaned oven dry;

Step 3: on substrate, be coated with three layers of electron beam exposure glue, oven dry;

Step 4: electron beam exposure, the domain of required T shape grid is transferred on the substrate;

Step 5: develop and photographic fixing, on three layers of electron beam exposure glue, form the groove of making T shape grid;

Step 6: electron beam evaporation gate metal;

Step 7: metal-stripping, the structure of formation T shape grid in groove.

2, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that wherein substrate is the gallium nitride/aluminum gallium nitride epitaxial wafer of Sapphire Substrate.

3, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that the material that wherein is coated with three layers of electron beam exposure glue on substrate is respectively PMMA, PMMA-MAA, PMMA.

4, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that wherein the domain of the described T shape of step 1 grid is divided into the zone that three exposure doses have nothing in common with each other, and each regional exposure dose is respectively:

The first district a is 1140pC/cm;

The second district b is 100 μ C/cm ²

The 3rd district c is 60 μ C/cm ²

5, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that, wherein the temperature the during oven dry described in the step 2 is 110 degree, and the time is 5 minutes.

6, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that, wherein step 3 is described is coated with three layers of electron beam exposure glue, oven dry, is meant whenever to be coated with the oven dry of once electron beam exposure glue once.

7, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that wherein step 4 is with three zones that dosage has nothing in common with each other on burn-out domain of electron beam.

8, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that wherein the time of described development of step 5 and photographic fixing is 30 seconds.

9, once electron beam exposure according to claim 1 forms the method for making of high W/N ratio T-shaped gate, it is characterized in that wherein the gate metal of the described electron beam evaporation of step 6 is nickel/gold, and its thickness is 30/330nm.

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