JPH02318A - Lift-off treatment method and equipment therefor - Google Patents

Abstract

PURPOSE:To enable lift-off while foreign material is prevented from re-attaching by jetting lift-off solvent on a semiconductor wafer surface, via a nozzle, while high frequency ultrasonic wave of 0.5-2.0MHz is applied, and utilizing its pulverizing effect. CONSTITUTION:While a spin head 2 is rotated, MEK 4, as solvent, is made to pass an ultrasonic wave oscillation nozzle 5 at a pressure of 0.5kg/cm<2>, and the solvent is jetted on the surface of a wafer. In the ultrasonic oscillation nozzle 5, a resonator to obtain ultrasonic wave oscillation of 0.8MHz and 30W is contained. The MEK 6 passes the resonator and is energized by the ultrasonic wave. As the result, high speed vibration is induced at the molecular level, and the resultant acceleration pulverizes photoresist 14 and a metal film 15. By adding pulverizing effect to the MEK having original capability to melt the photoresist 14, the melting and exfoliating of the photoresist 14 are progressed, and the lift-off of the metal film 15 is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to lift-off processing in the process of manufacturing semiconductor device wafers, and particularly to a processing method and a processing apparatus used therein.

[Conventional technology]

Typical examples of lift-off in semiconductor device manufacturing are shown in Part 9.
This will be explained with reference to the drawings and FIG.

In the simplest case, as shown in FIG. 9(a), a photoresist 14 is patterned on a semiconductor wafer (hereinafter referred to as wafer) 1 using ordinary photolithography technology, and then as shown in FIG. 9(b). A metal film 15 is deposited by vapor deposition. In this case, the thickness of the photoresist 14 is intentionally made thicker than the thickness of the metal film 15 so that the metal film 15 is broken at the pattern edges 24 of the photoresist 14.

In order to ensure that the metal film is cut in 150 steps, an oxide film (
A SiOz film 16 is deposited by the usual CVD method, a photoresist 14 pattern is formed thereon, and this is used as an etching mask to etch the exposed SiO2 film 16 using buffered hydrofluoric acid, for example. SiO2 film 16
The etching is so-called isotropic etching, in which etching occurs not only in the vertical (depth) direction but also in the horizontal direction.
Pattern edge 2゛4. In this case, an undercut 17 of the 5if2 film 16 is formed. Next, as shown in FIG. 7(b), when the metal film 15 is deposited by vapor deposition, the spacer and undercut 17 of the 5in2 film 16 ensure that the metal film 15 is cut in 15 steps at the pattern edge 24 compared to the method shown in FIG. 9 described above. Become something.

Of the metal film 15 deposited in this manner, in order to remove unnecessary metal film 15 (ie, metal film 15 on photoresist) 14, photoresist 14 is used as a solvent in FIGS. 9(C) and 1θ(C). The metal film 15 and the wafer 1 are melted.
As for the 5if2 film 16, the wafer 1 is immersed in a non-corrosive organic solvent such as methyl ethyl ketone (MEK), and the photoresist 14 is dissolved and peeled off from the wafer 1 while being irradiated with ultrasonic waves with a frequency of 20 to 50 KHz. At the same time, the metal film 15 is also peeled off and crushed.

The above process is called lift-off.

Conventionally, as a treatment method for this type of lift-off, specifically, as shown in FIG.
A method of placing water 19 as a vibration medium in a wafer 8 and placing a beaker 2o containing MEK4 therein and irradiating the wafers 1 one by one with ultrasonic waves.As shown in FIG. Carrier 22 containing wafers l
There is a method in which the carrier 22 is immersed in the wafer 1 and the wafer 1 is immersed in the wafer 1, and ultrasonic processing is performed while the carrier 22 is oscillated up and down for several tens of times in order to avoid the influence of the strength (standing waves) of the ultrasonic waves generated in the longitudinal direction of the wafer 1. In both cases, since the frequency of the ultrasonic waves is 20 to 50 KHz, the cavitation effect plays a major role in MEKd, promoting the separation of the photoresist 14 and the metal film 15.

[Problem to be solved by the invention]

In all of the conventional lift-off processing methods described above, the metal film 15 once peeled off from the wafer 1 during ultrasonic treatment is likely to re-attach, and the lift-off processing time is short.
- Even in the case of sheet processing, it takes more than 30 minutes and the throughput is low.

Regarding redeposition, it is possible to reduce the probability of re-deposition by increasing the frequency of replacing the solvent (MEK), but increasing the replacement frequency
The amount of solvent used increases, for example, 21 parts of solvent are required per wafer, which is uneconomical. In addition, in the batch processing type shown in FIG. 12, the metal film 1 peeled off on the carrier 22 is
There is a disadvantage that the debris of No. 5 adheres and becomes a source of contamination.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a lift-off processing method and a lift-off processing apparatus in which re-deposition of foreign substances such as a metal layer after lift-off is prevented and contamination by foreign substances is prevented.

[Means to solve the problem]

According to the present invention, a sample to be lifted off, which is a semiconductor wafer having a metal layer to be removed on a photoresist pattern, is rotated, and a solvent containing ultrasonic waves with a frequency of 0.5 to 2.0 MHz is applied to the sample to be lifted off. This solvent irradiation is carried out at the same time as the first irradiation, in which the irradiation trajectory passes through the rotation axis of the lift-off sample and scans in the concentric direction, and the second irradiation, in which only the outer periphery of the lift-off sample is irradiated. Obtain a lift-off processing method. It is more effective if the surface to be lifted off is soaked in a solvent prior to this lift-off treatment method.

Further, according to the present invention, in 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 spraying a solvent for dissolving the photoresist pattern toward the surface of the semiconductor wafer; A lift-off processing apparatus is obtained, which includes an ultrasonic wave applying means for applying ultrasonic waves of 5 to 2.0 MHz to the solvent injected from the nozzle, and a driving means for rotating the semiconductor wafer.

[Effect]

In the present invention, a solvent is injected from a nozzle toward a semiconductor wafer, and an ultrasonic wave applying means applies ultrasonic waves of 0.5 to 1.0 MHz to the solvent.

In this manner, when a solvent to which high-frequency ultrasonic waves are applied is injected onto the surface of a semiconductor wafer, the photoresist is removed due to its crushing effect, and the metal layer on the photoresist is lifted off.

〔Example〕

Next, the present invention will be explained 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 Figure 1(a),
The wafer 1 is set on the spin head 2 with the side to be lifted off facing up using vacuum suction or a mechanical chuck (vacuum suction shown).

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 5 kg/- to irradiate the surface of the wafer 1 which is rotating at high speed. The ultrasonic oscillation nozzle 5 has a frequency of 0.8MH.
There is a built-in vibrator that generates ultrasonic vibrations with an output of 30 W, and the MEK6 that passes through this and emits ultrasonic waves causes high-speed vibration at the molecular level, and the resulting acceleration crushes the photoresist 14 and metal film 15. It has the effect of

Therefore, MEK originally has the ability to dissolve photoresist 14.
By adding the crushing effect of ultra-high frequency ultrasonic waves to 4, the photoresist 14 is dissolved and peeled off, and the metal film 15 can be lifted off.

Furthermore, megahertz band ultrasonic waves are highly directional, so once they hit the Ever-1 surface, they attenuate rapidly.
MEK6 irradiation is planned for wafer 1 and it is necessary to increase the number of irradiations. For this purpose, in addition to the rotation (rotation) of the wafer 1, the ultrasonic oscillation nozzle 5 is caused to scan in the concentric direction of the wafer 1. FIG. 1(b) shows a trajectory 9 of MEK6 irradiation on the wafer 1. Since this is an oscillating nozzle, the trajectory 9 is arcuate, but it may be a straight trajectory. What is important is that the trajectory 9 always passes through the rotation axis (that is, the center of the wafer 1). In this way, the scraps of the peeled metal film 15 and the solvent are spun out, received by the cup 7 and discharged through the drain 8, and can be lifted off without any metal scraps being reattached.

As described above, FIG. 4 shows the relationship between lift-off time and wafer rotation speed when lift-off processing is performed. In the figure, the solid line represents the boundary of lift-off, and there is metal remaining in the hatched area, meaning that lift-off has not been completed. As the rotational speed of the wafer I increases, the time required for lift-off becomes shorter, and when the rotational speed is 400 rpm or more, the lift-off is completed in about 30 seconds, which shows that the required time is significantly shortened compared to the above-mentioned conventional technology. This data confirms that increasing the rotation speed increases the number of irradiations, and as a result, the peelability of the metal film increases.
The rotational speed of 0 to 5000 rpm is within the range of machine capabilities of ordinary spinners and poses no problem in practical use.

FIG. 5 shows a second embodiment of the present invention.
) is a state in which a photoresist is patterned on a wafer 1 using a reduction projection exposure method and a metal film is deposited on the wafer 1. One to several chips of elements are exposed in a field 11, and the exposure of the entire wafer is performed by step-and-repeat. and buttering. When high-precision pattern alignment is required, chip alignment (or die, pie,
Since the dial-a-main method is adopted, the outer peripheral region 12 of the wafer 1, where part of the field is missing and the a-la-main mark is missing, is not exposed (in particular, the GaA
s substrate with poor surface flatness). Therefore, when a positive resist is used, the photoresist remains in this outer peripheral region 12 and a metal film is deposited on it, resulting in several
The above-mentioned lift-off region is generated. When a wafer 1 having a wide area to be lifted off in the outer circumferential area 12 is processed in the embodiment shown in FIG. occurs, and irradiation for at least 2 minutes is required to remove it. Another reason why the metal residue 13 is likely to occur is the difference in angular velocity between the center and the outer periphery of the wafer 1.
This is because the effective ultrasonic irradiation time becomes shorter as one goes toward the outer circumference.

FIG. 2(a) shows the method of FIG. 2 for dealing with the case wafer 1 described above as a second embodiment of the third embodiment of the invention.
This is based on the embodiment shown in FIG. 1, and one ultrasonic oscillation nozzle 4 is added to irradiate the outer periphery of the wafer 10 as shown in FIG. 2(b), thereby eliminating the influence of angular velocity. As a result of processing this method under the conditions of irradiation for 30 seconds at a wafer rotation speed of 500 rpm, there is no remaining metal 13 in the outer circumferential region 12 of the wafer 1, as shown in FIG. 5(c).

Next, as a fourth embodiment of the present invention, as shown in FIG. 3(a), about 10 mu of MEK4 is dropped onto the surface of the wafer 1 before ultrasonic irradiation, and the MEK4 is stopped on the wafer 1 using surface tension. The surface dip treatment was carried out for 5 minutes in this manner, and then ultrasonic waves were irradiated as in the second embodiment as shown in FIG. 3(b). By performing the surface dip treatment, the etching of the photoresist 14 pattern and the dissolution of the groove 24 proceed, so that 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 (MEK 4 ) used per sheet is approximately 120 rall, which is 10% or less of the amount consumed in the prior art (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. 5 is a sectional view showing a first example of the lift-off processing apparatus of the present invention. The spin head 111 vacuum-chucks the wafer 101 in the same way as a typical resist coater, developer, or water jet scrubber.

This spin head 111 is fixed on a rotating shaft 112 and rotates about its center at a rotation speed of 500 to 3000 rpm. Around the spin head 111,
A cup 113 is disposed to surround the wafer 101 vacuum-adsorbed by the spin head 111. A drain 114 is attached to the bottom of this cup 113. The solvent in the cup 113 is collected into the collection tank through the drain 114.

Above the spin head 111 is a lift-off solvent ME.
A nozzle 115 is provided for spraying K onto the wafer 101 adsorbed by the spin head 111. Nozzle 11
5 has a built-in ultrasonic oscillation plate (not shown) that oscillates ultrasonic waves at a frequency of 0.8 MHz, for example, and when MEK, which is a lift-off solvent, is supplied to this nozzle 115, the ultrasonic oscillation Ultrasonic vibrations are applied to the MEK by the plate, and the MEK 116 tinged with ultrasonic waves passes through the nozzle 11.
5 onto the surface of the rotating wafer 101.

Next, the operation of the lift-off processing apparatus configured as described above will be explained. First, the semiconductor wafer 101 is vacuum-adsorbed by the spin head 111.

Then, MEK 116 is injected from the nozzle 115 toward the surface of the wafer 101 while rotating the spin head 111 at a predetermined rotational speed to cause the wafer 101 to rotate. In this case, the ultrasonic oscillation plate in the nozzle 115
Adds high frequency ultrasonic vibration to EK.

Normally, when the frequency exceeds 0.4 MHz, the cavitation effect does not occur with the solvent (MEK in this case) A, as it does with low frequencies (several tens of KHz), but due to the acceleration of the solvent liquid molecules when they vibrate at high speed. The crushing effect is mainly used to remove stains from resist or metal. Therefore, the above-mentioned crushing effect is added to MEK, which originally has resist-dissolving power, so that the resist on the surface of the wafer 101 progresses in dissolution and peeling, and the metal layer is lifted off. Since such high-frequency ultrasonic waves have strong directivity, they rapidly attenuate once they are irradiated onto the Ever surface, so that the MEK irradiation is spread over the entire surface of the wafer 101.

By rotating the wafer 101 and sliding the ultrasonic oscillation nozzle 115 in the direction of the center of the wafer 112, the peeled metal debris is spun out from the surface of the wafer 101. This prevents the release layer from re-adhering. This spun out metal scrap and solvent ME
K is received in a cup 113 and discharged to a drain 114.

Next, a second example of the lift-off processing apparatus used in the lift-off processing of the present invention will be described with reference to FIGS. 7(a) and 7(b). This device example is suitable for highly efficient lift-off by reducing the amount of solvent used, or for cases where the metal layer is made of highly malleable Au and is difficult to lift-off. In FIGS. 7(a) and 7(b), the same parts as those in FIG. 6 are given the same reference numerals and their explanations will be omitted. This device example differs from the first device example in that a MEK dripping nozzle 116 is disposed near the ultrasonic oscillation nozzle 115.

In this device, first, as shown in FIG.
A drop of 0 ml was dropped on the surface of the wafer 101, and the MEK 119 was held in a raised state on the wafer 101 due to surface tension, and left for 1 minute. During this time, the resist at the pattern edge 24 continues to dissolve, resulting in an undercut.

Next, as shown in FIG. 7(b), the spin head rad 111
rotate to shake off the MEK 119 on the wafer 101. If necessary, after repeating dropping, leaving, and shaking off several times, the supply of MEK is switched from the dropping nozzle 118 to the ultrasonic oscillation nozzle 115 in the same force in the pipe 113, and processing is performed in the same manner as in FIG. 6. . In this case, since the undercut treatment is performed in advance, lift-off is completed with MEK 116 irradiation for a shorter time than in the case of the first device example, and the amount of solvent MEK used can be reduced.

Next, a third example of the device used for lift-off of the present invention will be described with reference to FIGS. 8(a) to 8(c). This device example is for performing LSI level lift-off processing. Figures 8(a) and (b) are respectively Figure 7(a)
, (b) shows an apparatus similar to that shown in FIG. 7, and performs a process similar to that shown in FIG.

FIG. 8(c) shows a spin head 111a placed in another cup 113a, to which spin.

The door 1lla also rotates around the rotating shaft 112a. A jet nozzle 20 for ejecting high-pressure MEK 116 is provided above the spin rad 111a.

In this device example, as shown in FIG. 8(b), the ME
After spraying K116 onto the surface of the semiconductor wafer 101,
As shown in Figure 8(c), 50 to 150 kg/cf
MEK 16 pressurized to lf is injected onto the wafer 101 from the jet nozzle 120 to remove metal debris and resist caught in the fine pattern on the surface of the semiconductor wafer 101.

〔Effect of the invention〕

As explained above, according to the present invention, a lift-off solvent is injected onto the surface of a semiconductor wafer 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. Since the wafer is rotated and this lift-off effect is uniformly spread over the entire wafer surface, lift-off can be performed while preventing foreign matter from re-adhering. In addition, according to the present invention, the basic configuration uses the spinner device that has been widely used as is, and a nozzle with a built-in ultrasonic oscillation plate is newly installed, so that the nozzle that sprays the solvent and the The device can be easily constructed by simply adding a means for applying sound waves, and it can also be easily automated.

[Brief explanation of the drawing]

FIG. 1(a) shows the first treatment using the lift-off treatment method of the present invention.
FIG. 2(b) is a cross-sectional view showing one step of the embodiment, FIG. 2(b) is a diagram showing the trajectory of the sprayed solvent, and FIG. Figure 3 (b) is a cross-sectional view showing the trajectory of the sprayed solvent, Figure 3 (
a) and (b) are cross-sectional views showing a fourth embodiment of the lift-off processing method of the present invention; FIG. 4 is a graph showing the relationship between wafer rotation speed and lift-off processing time in the lift-off processing method of the present invention; Figure 5 (a), (b), (c)
FIG. 6 is a cross-sectional view showing a first example of the processing apparatus used for the lift-off processing of the present invention; FIG. 7(a) , (b) is a cross-sectional view showing a second example of the processing apparatus used for the lift-off processing of the present invention for each processing step, and FIGS. FIGS. 9(a) and 9(b) are cross-sectional views showing a third example of the processing apparatus used for each processing step. (C) is a sectional view showing the first conventional example of lift-off processing in the order of steps; FIGS. 10(a), (b) and (c) are sectional views showing the second conventional example of lift-off processing in order of steps; 11
The figure is a 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 a lift-off processing apparatus. 1.101...Wafer 2,111...
... Spin head, 3 ... Rotating shaft, 4,116
,119...MEK,5,115...
Ultrasonic oscillation nozzle, 6...ME tinged with ultrasonic waves
K, 7,113...Cup, 8,114...
...Drain, 9. River...Trajectory, 10...Peripheral irradiation, 11...Field, 12...
・Outer area, 13...Metal remaining, 14...
...Photoresist, 15...Metal film, 16.
Old...5iCh membrane, 17...Ultrasonic transducer, 1
8...Bathtub, 19.Old...Water, 20,1...
... Beaker, 21... Bathtub, 22 Old...
Carrier, 23... Rocking, 24 Old... Pattern edge, 118... Dripping nozzle, 120...
...Jet nozzle agent Patent attorney Uchihara Oto (a) (I)) $ 1 time (a) (J,) Kaya 3 z Ca) Kaya 2 Ishicha 4WI (b) Cha 7 Kuni (al (Mu) 2 (C) (C) (CI 茅閏过It) 鏏(＾) 茅閏茅 协视Proceedings procedural amendment (method) 6. ``Brief explanation of the drawings'' column of the specification to be amended

Claims (5)

[Claims] (1) In a lift-off processing method in which a metal film is deposited on a photoresist pattern formed on the surface of a semiconductor wafer and only the metal film on this photoresist pattern is removed by a lift-off method, a solvent for dissolving the photoresist is heated at a high frequency. The ultrasonic wave is irradiated onto the surface of the semiconductor wafer to be lifted off while the semiconductor wafer is rotated at a rotation speed of 1000 to 8000 rpm through a dispensing nozzle containing a built-in vibrator that oscillates ultrasonic waves of 0.5 to 2.0 MHz. lift-off processing method. (2) The lift-off processing method according to claim 1, wherein the solvent irradiated from the dispense nozzle passes through the rotation axis of the semiconductor wafer and scans in a circular direction. (3) The lift-off processing method according to claim 2, characterized in that the solvent is irradiated only onto the outer periphery of the semiconductor wafer from another dispense nozzle. (4) The lift-off processing method according to claim 1, wherein the surface of the semiconductor wafer to be lifted off is immersed in the solvent before irradiating the solvent. (5) In 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 spraying a solvent that dissolves the photoresist pattern toward the semiconductor wafer;
A lift-off processing apparatus comprising: ultrasonic wave applying means for applying ultrasonic waves of 2.0 MHz to 2.0 MHz to the solvent sprayed from the nozzle; and driving means for rotating the semiconductor wafer.