JP2611375B2 - Lift-off processing method and processing apparatus - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a lift-off process in the process of manufacturing a semiconductor device wafer, and more particularly, to a processing method therefor and a processing apparatus used therefor.

[Conventional technology]

A typical example of lift-off in the manufacture of a semiconductor device will be described with reference to FIGS. 9 and 10.

As shown in FIG. 9 (a), the simplest is to pattern a photoresist 14 on a semiconductor wafer (hereinafter abbreviated as "wafer") 1 by a usual photolithography technique, and then, as shown in FIG. 9 (b). A metal film 15 is attached by a vapor deposition method. In this case, the thickness of the photoresist 14 is intentionally made larger than the thickness of the metal film 15 and the pattern edge of the photoresist 14 is
At 24, the metal film 15 is cut off. This metal film
Fig. 10 (a) to make the break of step 15 more reliable
As shown in (1), an oxide film (SiO ₂ film) 16 is deposited on the wafer 1 by an ordinary CVD method, a photoresist 14 pattern is formed thereon, and the exposed SiO ₂ film 16 is used as an etching mask. For example, etching is performed using buffered hydrofluoric acid. Since the etching of the SiO ₂ film 16 is so-called isotropic etching in which not only the etching in the vertical (depth) direction but also in the horizontal direction occurs, the undercut 17 of the SiO ₂ film 16 is formed at the pattern edge 24. Next, when deposited in depositing a seventh diagram (b) metal film 15, the pattern edge 24 compared with the method of Figure 9 described above by a spacer undercut 17 of the SiO ₂ film 16
The disconnection of 15 steps of the metal film becomes reliable.

In order to remove the unnecessary metal film 15, that is, the metal film 15 on the photoresist 14 from the metal film 15 thus deposited, the photoresist 14 is used as a solvent in FIGS. 9 (c) and 10 (c). Dissolves but metal film 15, wafer 1 and SiO ₂ film
16 is a non-corrosive material, for example, methyl ethyl ketone (MEK) is immersed in the wafer 1 with an organic solvent, and the photoresist 14 is dissolved and peeled off from the wafer 1 while irradiating ultrasonic waves having a frequency of 20 to 50 KHz in the metal film. 15 also peels and crushes.

 The above process is called lift-off.

Conventionally, as a treatment method of this type of lift-off, specifically, as shown in FIG. 11, water 19 as a vibration medium is placed in a bath 18 in which an ultrasonic vibrator 17 is arranged, and a beaker 20 containing MEK 4 is placed in the water 19. A method of irradiating the placed wafers 1 one by one with ultrasonic waves, and as shown in FIG. 12, a carrier 22 containing a plurality of wafers 1 is immersed in a bath 21 containing MEK4, and the wafers 1 are immersed.
In order to avoid the influence of the strength (standing wave) of ultrasonic waves generated in the vertical direction, there is a method of performing ultrasonic processing while swinging several tens of mm up and down for each carrier 22. In any case, since the frequency of the ultrasonic wave is 20 to 50 KHz, the cavitation effect is mainly used in the MEK 4 to promote the separation of the photoresist 14 and the metal film 15.

[Problems to be solved by the invention]

In any of the conventional lift-off processing methods described above, the metal film 15 that has once been peeled off from the wafer 1 during the ultrasonic processing is easily re-adhered, and the lift-off processing time
Even in the case of single-sheet processing, there is a disadvantage that it takes more than 30 minutes and the throughput is low.

For reattachment, the frequency of solvent (MEK) exchange can be increased to reduce the probability, but if the frequency of exchange is increased,
The amount of solvent used increases, for example, requiring two solutions per wafer, which is not economical. Further, the batch processing type shown in FIG. 12 has a disadvantage that the scraps of the peeled metal film 15 adhere to the carrier 22, which becomes a contamination source.

The present invention has been made in view of such a problem, and provides a lift-off processing method and a lift-off processing apparatus in which foreign substances such as a metal layer after lift-off are prevented from reattaching and contamination by foreign substances is prevented. The purpose is to:

[Means for solving the problem]

According to the present invention, a lift-off sample, which is a semiconductor wafer having a metal layer to be removed on a photoresist pattern, is rotated, and a solvent with an ultrasonic wave having a frequency of 0.5 to 2.0 MHz is irradiated on the lift-off surface of the lift-off sample. A lift-off process in which the solvent irradiation is simultaneously performed with first irradiation in which the irradiation trajectory passes through the rotation axis of the lift-off sample and scans in the direction of the center of the circle, and second irradiation in which only the outer periphery of the sample to be lifted-off is irradiated. Get the way. It is more effective to immerse the lift-off surface in a solvent prior to this lift-off treatment method.

Further, according to the present invention, in a lift-off processing apparatus that lifts off a metal layer deposited on a photoresist pattern on a semiconductor wafer surface, a nozzle that jets a solvent that dissolves the photoresist pattern toward the semiconductor wafer surface, A lift-off apparatus having an ultrasonic wave applying unit for applying ultrasonic waves of 2.0 MHz to the solvent jetted from the nozzle and a driving unit for rotating the semiconductor wafer on its own axis is obtained.

[Action]

In the present invention, a solvent is sprayed from a nozzle toward a semiconductor wafer, and an ultrasonic wave of 0.5 to 1.0 MHz is applied to the solvent by an ultrasonic wave applying unit.

As described above, when the solvent to which the high frequency ultrasonic wave is applied is jetted onto the surface of the semiconductor wafer, the photoresist is removed by the crushing effect, and the metal film on the photoresist is lifted off.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment which is the most basic embodiment of the present invention. As shown in FIG. 1 (a), the wafer 1 is set on the spin head 2 by vacuum suction or a mechanical chuck (vacuum suction in the figure) with the surface to be lifted off facing up. Note that the center of the wafer 1 is aligned with the rotation axis 3 of the spin head 2. While rotating the spin head 2, MEK as a solvent is passed through the ultrasonic oscillation nozzle 5 at a pressure of 0.5 kg / cm ² to irradiate the surface of the wafer 1 rotating at high speed. The ultrasonic oscillation nozzle 5 has a built-in vibrator for obtaining ultrasonic vibration of frequency 0.8 MHz and output 30 W, and the MEK 6 which has passed and passed the ultrasonic wave generated high-speed vibration at the molecular level and was generated. There is an effect that the photoresist 14 and the metal film 15 are crushed by the acceleration. Therefore,
Originally, photoresist 14 was added to MEK4, which has the ability to dissolve, by adding the crushing effect of ultra-high frequency ultrasonic waves.
Dissolution and peeling of 14 progress, and lift-off of the metal film 15 can be achieved.

Since the ultrasonic wave in the megahertz band has a strong directivity, and once it hits the surface of the wafer 1, it is rapidly attenuated. Therefore, it is necessary to irradiate the MEK 6 onto the entire wafer 1 and increase the number of times of irradiation. Therefore, in addition to the rotation (rotation) of the wafer 1, the ultrasonic oscillation nozzle 5 is caused to scan in the direction of the center of the wafer 1. FIG. 1B shows a trajectory 9 of the MEK6 irradiation on the wafer 1. This is an arc-shaped locus 9 because it is a swing type nozzle, but may be a linear locus. What is important is that the trajectory 9 always passes through the rotation axis (that is, the center of the wafer 1). Thus, the peeled metal film 15
The dust and the solvent are spun out, received by the cup 7 and discharged through the drain 8 and can be lifted off without reattachment of the metal dust.

As described above, FIG. 4 shows the relationship between the lift-off time and the wafer rotation speed when the lift-off process is performed. In the figure, the line shown by the solid line represents the boundary of the lift-off, which means that the hatched area metal remains and the lift-off is not completed. As the number of rotations of the wafer 1 is increased, the time required for lift-off becomes shorter, and when the number of rotations is 4000 rpm or more, the lift-off is completed in about 30 seconds. This data confirms that the number of irradiations was increased by increasing the number of rotations, and as a result, the metal film peeling property was increased.
The rotation speed of m is within the range of the machine capacity of a normal spinner, and there is no practical problem.

FIG. 5 shows a second embodiment of the present invention. FIG. 5A shows a state in which a photoresist is patterned on a wafer 1 by a reduced projection exposure method and a metal film is applied.
One to several chips of elements are exposed in the field 11, and the entire surface of the wafer is patterned by performing step-and-repeat. When a high-precision pattern alaminate is required, since the chip aramite (or die-by-diaraminate) method is used, a part of the field is missing and an alaminate mark is lost. No exposure is performed (especially those with poor surface flatness such as GaAs substrates). Therefore, when a positive resist is used, the photoresist 12 remains in the outer peripheral region 12 as it is, and a metal film is deposited thereon, and a lift-off region of several mm or more occurs. Such a wafer 1
When an object having a wide range of lift-off portions in the outer peripheral area 12 is processed in the embodiment of FIG. 1, a short time processing of about 30 seconds produces a metal residue 13 as shown in FIG. Removal requires at least two minutes of irradiation.
Another cause of metal residue 13 is wafer 1
This is the difference in angular velocity between the central part and the outer peripheral part, because the effective ultrasonic irradiation time becomes shorter in the outer peripheral direction.

As a second embodiment of the third embodiment of the present invention, the method of FIG. 2 is shown to deal with the case wafer 1 described above. FIG. 2 (a) shows an ultrasonic oscillation nozzle based on the embodiment of FIG. 4 and the wafer 1 as shown in FIG.
Irradiation 10 is applied to the outer periphery of the lens to eliminate the influence of the angular velocity. As shown in FIG. 5 (c), as a result of processing under the conditions of 5,000 rpm for one revolution of the wafer and irradiation for 30 seconds by this method, there is no metal residue 13 in the outer peripheral area 12 of the wafer 1.

Next, as a fourth embodiment of the present invention, about 10 ml of MEK4 is dropped on the surface of the wafer 1 before ultrasonic irradiation in FIG. 3 (a), and the MEK4 is retained on the wafer 1 using surface tension. The surface dip treatment is performed for 5 minutes in this manner, and then, as shown in FIG. 3B, ultrasonic irradiation is performed in the same manner as in the second embodiment. By performing the surface dip treatment, the dissolution of the edge portion 24 of the photoresist 14 pattern proceeds, so that the lift-off is completed in only 5 seconds at 5000 rpm, for example, as shown by the broken line curve in FIG. At this time, the amount of solvent (MEK4) used per sheet is about 120 ml, and it is possible to consume less than 10% of the conventional technology (FIG. 11).

Next, some examples of the lift-off processing apparatus of the present invention will be described with reference to the accompanying drawings. FIG. 6 is a sectional view showing a first example of the lift-off processing apparatus of the present invention.
The spin head 111 vacuum-adsorbs the wafer 101 in the same manner as an ordinary resist coating machine, developing machine or water jet scrubber. The spin head 111 is fixed on a rotation shaft 112, and rotates around its center at a rotation speed of 500 to 3000 rpm. A cup 113 is provided around the spin head 111 so as to surround the wafer 101 that has been vacuum-adsorbed to the spin head 111. A drain 114 is attached to the bottom of the cup 113. This drain 114
The solvent in the cup 113 is collected in the collection tank via the.

Above the spin head 111, a nozzle 115 for jetting MEK of the lift-off solvent onto the wafer 101 adsorbed by the spin head 111 is provided. For example, an ultrasonic oscillation plate (not shown) that oscillates an ultrasonic wave having a frequency of 0.8 MHz is built in the nozzle 115. When MEK that is a lift-off solvent is provided to the nozzle 115, the ultrasonic oscillation Ultrasonic vibration is applied to the MEK by the plate, and the MEK 116 bearing the ultrasonic waves is jetted from the nozzle 115 onto the surface of the wafer 101 which is rotating.

Next, the operation of the lift-off processing apparatus thus configured will be described. First, the semiconductor wafer 101 is vacuum-adsorbed to the spin head 111. And spin head 1
While rotating the wafer 101 at a predetermined rotation speed to rotate the wafer 101, the MEK 116 is jetted from the nozzle 115 toward the surface of the wafer 101. In this case, high-frequency ultrasonic vibration is applied to the MEK by the ultrasonic oscillation plate in the nozzle 115.

Normally, when the frequency exceeds 0.4 MHz, the cavitation effect does not occur as in the case of the solvent (MEK in this case) A and low frequency (several tens of KHz). The effect mainly removes stains such as resist or metal. Therefore, the above-described crushing effect is added to MEK, which originally has a resist dissolving power, and the wafer 1
Dissolution and peeling of the resist on the surface of 01 progress, and the metal layer is lifted off. Since such high-frequency ultrasonic waves have a strong directivity, once irradiated onto the wafer surface, they rapidly attenuate.Therefore, the wafer 101 is rotated so that the MEK irradiation reaches the entire surface of the wafer 101, and the ultrasonic oscillation is performed. By sliding the nozzle 115 in the direction of the center of the wafer 112, the separated metal dust is spun out from the surface of the wafer 101. This prevents reattachment of the debris. The spun metal scrap and the solvent MEK are received by the cup 113 and discharged to the drain 114.

Next, a second example of the lift-off processing apparatus used for the lift-off processing of the present invention will be described with reference to FIGS. 7 (a) and 7 (b). This example of the apparatus is suitable when lift-off is performed with high efficiency by reducing the amount of solvent used, or when lift-off is difficult when the metal layer is made of highly extensible Au. 7 (a) and 7 (b), the same components as those in FIG. 6 are denoted by the first reference numerals and description thereof is omitted. In this example of the apparatus, the MEK drop nozzle 116 is located near the ultrasonic oscillation nozzle 115.
Is different from the first device example.

In this apparatus, first, as shown in FIG. 7 (a), a dripping nozzle 118 drops MEK 119, for example, about 10 ml on the surface of the wafer 101, and the MEK 119 is raised on the wafer 101 by surface tension. And leave for 1 minute. During this time, the dissolution of the resist at the pattern edge 24 progresses, so that the pattern is undercut.

Next, as shown in FIG.
Is rotated to shake off MEK 119 on the wafer 101. If necessary, the dripping, leaving, and shaking off are repeated a plurality of times, and then the supply of MEK is switched from the dripping nozzle 118 to the ultrasonic oscillation nozzle 115 in the same cup 113, and the processing is performed in the same manner as in FIG. In this case, since the undercut processing has been performed in advance, the MEK1 has a shorter time than the case of the first apparatus example.
The lift-off is completed by the irradiation of 16, and the usage amount of the solvent MEK can be reduced.

Next, with reference to FIGS. 8A to 8C, a third example of the apparatus used for lift-off according to the present invention will be described. This apparatus example is for performing lift-off processing at an LSI level. FIGS. 8 (a) and (b) show FIGS. 7 (a) and
The same apparatus as that shown in FIG. 7B is shown, and the same steps as those in FIG. 7 are performed.

FIG. 8 (c) shows a spin head 111a arranged in another cup 113a, and this spin head 111a also has a rotating shaft 112a.
To rotate. Above the spin head 111a, a jet nozzle 20 for jetting high-pressure MEK 116 is provided.

In this example of the apparatus, as shown in FIG.
MEK11 with ultrasonic vibration added from ultrasonic oscillation nozzle 115
After jetting 6 onto the surface of the semiconductor wafer 101, MEK pressurized to 50 to 150 kg / cm ² as shown in FIG.
16 is jetted from the jet nozzle 120 onto the wafer 101 to remove the metal dust and the resist caught on the fine pattern on the surface of the semiconductor wafer 101.

〔The invention's effect〕

As described above, according to the present invention, a lift-off solvent is sprayed onto a semiconductor wafer surface through a nozzle while applying high-frequency ultrasonic waves of 0.5 to 2.0 MHz, and lift-off is performed using the crushing effect, and the wafer is lifted off. Since the lift-off effect is uniformly applied to the entire surface of the wafer by being rotated, lift-off can be performed while preventing re-adhesion of foreign matter. Further, according to the present invention, the basic configuration uses a spinner device that has been widely used in the past as it is,
The apparatus can be easily configured simply by adding a nozzle for injecting a solvent and a means for applying an ultrasonic wave to the solvent, such as providing a new nozzle having a built-in ultrasonic oscillation plate, and can be easily automated.

[Brief description of the drawings]

FIG. 1A shows a first example of the lift-off processing method according to the present invention.
FIG. 2B is a cross-sectional view showing one step of the embodiment, FIG. 2B is a view showing the locus of the propellant, and FIG. 2A is a view showing one step of the third embodiment according to the lift-off processing method of the present invention. Sectional view,
FIG. 3B is a view showing the locus of the propellant, FIGS. 3A and 3B are cross-sectional views showing a fourth embodiment according to the lift-off processing method of the present invention, and FIG. FIG. 5 is a graph showing the relationship between the number of rotations of the wafer and the lift-off processing time in the lift-off processing method. FIG. 5 is a diagram showing the difference in the lift-off processing state depending on the number of nozzles in the lift-off processing method of the present invention. FIG. 7 (a) and 7 (b) are cross-sectional views showing, for each processing step, a second example of a processing apparatus used for lift-off processing according to the present invention. FIG. 8 (a), (b),
FIG. 9C is a sectional view showing a third example of the processing apparatus used for the lift-off processing of the present invention for each processing step.
(B) and (c) are cross-sectional views showing a first conventional example of the lift-off processing in the order of steps, and FIGS. 10 (a), (b) and (c) show a second conventional example of the lift-off processing in the order of steps. Cross section, eleventh
The figure is a cross-sectional view showing a first conventional example of a lift-off processing device,
FIG. 12 is a sectional view showing a second conventional example of the lift-off processing apparatus. 1,101 Wafer, 2,111 Spin head, 3 ... Rotating shaft, 4,116,119 MEK, 5,115 Ultrasonic oscillation nozzle 6, Ultrasonic MEK, 7,113 Cup, 8,11
4… drain, 9… locus, 10… perimeter irradiation, 11…
Field, 12 ... Peripheral area, 13 ... Metal remaining, 14 ...
... photoresist, 15 ... metal film, 16 ... SiO ₂ film, 17 ...
Ultrasonic vibrator, 18 ... Bathtub, 19 ... Water, 20, 1 ... Beaker, 21 ... Bathtub, 22 ... Carrier, 23 ... Swing, 24 ...
Pattern edge, 118 ... Drip nozzle, 120 ... Jet nozzle.

Claims (5)

(57) [Claims] 1. A lift-off method for removing a metal film on a photoresist pattern formed on the surface of a semiconductor wafer by a lift-off method after depositing a metal film on the photoresist pattern. Through a dispensing nozzle with a built-in oscillator that oscillates ultrasonic waves with a frequency of 0.5 to 2.0 MHz, while rotating the semiconductor wafer at a rotation speed of 1000 to 8000 rpm,
A lift-off processing method comprising irradiating a lift-off surface of the semiconductor wafer. 2. The lift-off processing method according to claim 1, wherein said solvent radiated from said dispense nozzle passes through a rotation axis of said semiconductor wafer and scans in a circular center direction. 3. The lift-off processing method according to claim 2, wherein said solvent is irradiated from another dispensing nozzle only to the outer periphery of said semiconductor wafer. 4. The lift-off processing method according to claim 1, wherein a surface of said semiconductor wafer to be lifted off is immersed in said solvent before irradiating said solvent. 5. A lift-off processing apparatus for lifting off a metal layer deposited on a photoresist pattern on a surface of a semiconductor wafer, a nozzle for jetting a solvent for dissolving the photoresist pattern toward the semiconductor wafer,
A lift-off processing apparatus comprising: an ultrasonic wave applying unit that applies an ultrasonic wave of 0.5 to 2.0 MHz to a solvent ejected from the nozzle; and a driving unit that rotates the semiconductor wafer.