JPH02205281A - Wafer marking device - Google Patents

Abstract

PURPOSE:To obtain a wafer marking device in which the roundness of a dot shape at the time of dot-marking on a wafer is improved by providing a light attenuator to be variably linked into an optical system in order to regulate output light, while the device is oscillated as a laser oscillator in the most stable area. CONSTITUTION:When a marking mode set by an input part 18 is normal, a marker controller 16 controls respective elements 2, 5, 7, 12 and 13 so as to mark dots at depths approximately 1.5 to 2.5mum on a wafer 15, and a single Q switching pulse marks a single dot. In this case, the regulation of the depth is determined manually or by a control signal from a marker controller 16 in an attenuator 12 beforehand. Further numbers of pulses A and B in a diesel mark mode and a soft mark mode are controlled by a computer, and they can be made freely variable by the software with the controller 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention improves the circularity of dot shapes when marking dots on wafers, reduces variations in size and depth, and further improves the dot shape by reducing the dots to zero. This invention relates to a technique for soft marking with a depth of 5 to 1.0 μm.

[Conventional technology]

Conventionally, in this type of marking device, when controlling the depth of the dot, the output of the YAG laser beam was adjusted by varying the lamp current.

[Problem to be solved by the invention]

In the conventional method of varying the lamp current described above, when the lamp current is changed, the amount of heat generated within the laser head changes, which changes the thermal equilibrium state in each part of the laser resonator, causing light As a result, the optimal 7 alignments that maintain the resonator most stably are destroyed, and the stability of the laser pulse is deteriorated. In particular, the degree of thermal lens effect in the YAG laser rod causes a subtle change in the alignment of the optical resonator even in response to a weak lamp current change (~0.5 A). For this reason, when attempting to change the laser power, changing the lamp current causes instability of the laser output light, resulting in variations in the size, depth, etc. of the marking dots.

In addition, in the conventional marking device, the laser 0N10FF of the laser oscillator activates the ultrasonic Q-switch element.
This is done by setting the FF to 10N, but as a result, even without changing the lamp current, the dots at the beginning of characters become unstable.

In other words, the first factor is a phenomenon peculiar to lasers such as YAG lasers that operate with a Q-switch, and once the laser oscillation is stopped for a time longer than the relaxation time of the upper laser level of Nd"+, which is the active medium, the The first Q-switch pulse oscillated after the pause is larger than the pulse leading value during continuous oscillation.On the contrary, the second Q-switch pulse
The leading value of the switch pulse becomes small. In this way, sporadic pulses become very unstable.

The second vA factor is that after marking characters on several wafers, if you do not mark for a long time due to changing wafer lots or for other reasons, when you start marking, the Laser output may become unstable. This is because the temperature of the quartz crystal of the ultrasonic Q-switch element, the output mirror, etc. decreased in proportion to the time the laser oscillator was stopped, resulting in a slight change in the actual resonator length, resulting in a misalignment. It depends. Generally, the stability of the leading value of the Q-switch pulse required for laser marking of wafers must be ±0.5% or less, and even a slight change in temperature is sufficient to prevent this. It had become a thing.

Another capability that has recently been increasingly demanded of wafer marking devices is a processing method called soft marking that does not scatter the wafer material during dot marking. This is possible by making very shallow markings with a dot depth of about 0.5 μm to 1.0 μm. However, in order to make this marking possible, the leading value of the Q switch pulse and the pulse energy must be adjusted by ±0.1.
It is necessary to stably control it to about %.

If the pulse energy is even a little small, it will be 0.1 to 0.2
On the other hand, if the dot is even slightly larger, it becomes a deep dot of 1.0 μm or more. This phenomenon involves complex nonlinear physical phenomena; for example, the dependence of the reflectance on the wafer surface on the laser output intensity is extremely large;
AG laser Q-switch pulse width 75ns to 100ns
This is thought to be caused by the fact that the thermal diffusion length exceeds 1 μm.

In this way, the stability and usage of the Q-switched laser pulse of conventional wafer marking equipment is limited to 0.5 μm to 1 μm.
．． It was impossible to stably mark dots with a depth of 0 μm.

[Means to solve the problem]

The wafer marking device of the present invention allows the laser to oscillate in the most stable region as a laser oscillator, and has a continuously variable optical attenuator in the optical system in order to adjust the output light. Furthermore, in order to enable laser oscillation even when marking is not being performed, an external shutter is provided outside the optical resonator. controlled.

In contrast to the conventional wafer marking device described above, in the present invention, the lamp current is not changed for the purpose of varying the laser output, and even when not marking, the repetition frequency in the laser resonator is the same as that during actual marking. The difference is that it oscillates at a certain frequency. A further difference in soft marking is that the number of shots is set in advance, and stabilized Q-switch pulses are overprinted on the same dot, rather than using one Q-switch pulse.

〔Example〕

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

FIG. 1 is a block diagram of a first embodiment of a wafer marking apparatus system according to the present invention.

In the figure, 1 is a total reflection mirror, 2 is an ultrasonic Q-switch element, 3 is an internal aperture (mode selector), 4 is a lamp house, 5 is an internal shutter, and 6 is an output mirror, which are arranged on the same axis. It constitutes a YAG laser oscillator 17. Also, 7 is an external shutter, 8 is an aperture, 9 is a leveling mirror, 10 is an expander (Galilean type), 11 is an aperture, 12 is an attenuator (light attenuator), 13 is a galvanic mirror 14 is an f-θ lens, and 15 is a Wafer (workpiece), 16 is a marker controller.

The Q-switch YAG laser oscillator 17 is aligned and adjusted in advance at a lamp current that provides the most stable Q-switch pulse, and the lamp current is fixed.

The marker controller 16 includes each element (reference numbers 2 and 5).
, 7, 12, and 13) are controlled as shown in FIG.

Next, the present invention will be explained in detail along with FIG. 2 and FIG. 1 as well. First, character input and marking mode for printing on the wafer are set using the input unit 18. When the set marking mode is the normal mode, the marker controller 16 controls each element 2.5.7 to mark a dot with a depth of about 1.5 to 2.5 μm on the wafer 15.
．． 12.13 is controlled to mark one dot with one Q-switch pulse. The depth adjustment is determined in advance manually by the attenuator 12 or by a control signal from the marker controller 16.

If the marking mode is deep mark mode, 2.
Make deep markings of 5 μm or more. In this mode, the marker controller 16 sets the Q switch pulse number in advance to the pulse number A corresponding to the depth in the normal mode, and
The Q-switch pulse from A is applied to the two dots one after the other.

1.0 if marking mode is soft mark mode
In this mode, in which dot marking is performed at a shallow depth of .mu.m or less, the attenuator 12 is set manually or by a control signal from the marker controller 16 in accordance with the low power for soft marking. In order to vary the depth of 0.5 μm to 1.0 μm required for soft marking, the number of pulses B corresponding to the depth is set in advance, and the Q switch from B is applied to each dot. Repeat the pulses. Here, the values of A and B in the deep mark mode and soft mark mode are controlled by a computer. It can be freely varied by software using the Y-ca controller 16.

FIG. 3 is a front view of a portion of a second embodiment of the invention. In this embodiment, only the expander 10 and the 7x tenator 12 of the embodiment shown in FIG. 1 are changed, so only these parts are shown.

In the figure, 18 is an expander (Kevlar type);
19 is a 7 pertier as a spatial filter, 20 is an attenuator [variable neutral density filter (
ND filter)]. The expander 18 is a Kevlar type expander, and the spatial filter 19 is
By inserting it as a condensing lens, the f-theta lens 14 (the first
(Figure) can deliver laser light with a very clean Gaussian distribution. This has the advantage that the roundness of the spot diameter during condensation is greatly improved and it becomes possible to narrow down the spot diameter to a smaller spot diameter. In the embodiment shown in FIG. 1, the laser beam emitted from the Q-switched YAG laser oscillator 17 rotates the polarizing plate by utilizing the polarization component determined by the quartz crystal of the ultrasonic Q-switched element. In contrast to the laser beam passing through the polarizing plate, the 7-tensioner 20 of the second embodiment has an ND filter (neutral density filter) whose transmittance changes continuously and gradually on the disk. ing. When a polarizing plate is used as a 7T tenator, the optical path shifts by an amount proportional to the thickness of the polarizing plate, so if you try to adjust the light intensity while marking, the marking position on the wafer will shift slightly.However, using an ND filter This drawback is overcome by using

As described above, each embodiment of the present invention maintains the highest stability of the laser oscillator over a wide laser power range by providing an attenuator external to the laser oscillator that can be continuously attenuated. Can be done. In particular, by improving the stability at low power, which was previously very unstable, it has become possible to greatly reduce the variation in dots during shallow marking. Further 0.5 μm ~ 1
．． Regarding so-called soft marking at a depth of 0 μm, it has been difficult to perform it stably due to physical factors no matter how much the laser output stability is improved. 115 to 1 with attenuator
By using two or more consecutive Q-switched pulses weakened to /10 and irradiating the same dot in a superimposed manner, it has become possible to perform soft marking without scattering the board at all.

In order to reduce variations in each dot in soft marking, the dots are marked with a laser beam having a repetition frequency of 1 KHz or less under the control of the marker controller 16. This is because by suppressing the frequency to 1 KHz or less, the first dot, the so-called first pulse, which is struck once marking has stopped and after the dot marking frequency has changed, has the same leading value, so there is less variation in dots. This is to become. Furthermore, by marking the same dot by superimposing n Q-switch pulses after the first pulse described above at a repetition frequency of 2 to 5 KHz, the cross-sectional shape of the dot is very smooth and the dot's roundness is also very good. Make marking possible. This is as shown in Figure 4.
By superimposing the pulses from the second note onwards with the Q-switch pulse of the first note, which have only about 60% of the initial value, the pulse of the first note is After processing to a depth of about 0.2 μm, the second and subsequent pulses dig dots at a rate of 0.025 μm to 0.05 μm per pulse, gradually melting the surface of the dots. Even if the laser beam shape at the time of condensation is not a perfect circle, the roundness of the processed dots will be good. That is, by adopting this method, the burden on the optical system that serves to make the laser beam close to the Gaussian beam is greatly reduced. Furthermore, considering variations in the dot depth, or in other words, the dot diameter, the number of pulses after the second shot is approximately 0.8 μm (in the case of a bare silicon substrate).
Approximately 20 total culm degrees are required to achieve this, but even if the leading values of these 20 laser pulses vary to some extent, 20
As a result of being averaged by the start, the variation becomes very small.

In addition, the repetition frequency of the second and subsequent pulses should be set to 2 to 5KH.
The reason why it is set to 2 is that the YAG laser oscillator 17 has the highest stability of the leading value of the Q-switch pulse in this frequency range. Also, as a result of experiments, the best ratio between the leading value of the first pulse and the second and subsequent pulses is about 0.6 to 0.8, but if the frequency is increased beyond this, this ratio will drop to 0.
．． Fall below 5. Pulse trains with ratios below 0.5 (
When overlapping is performed using pulse train), the number of pulses for overlapping increases, the time required to process one dot increases, and the overall marking speed decreases.

Not only this, but as this ratio becomes smaller, it enters a non-linear region where it is impossible to obtain a dot depth proportional to the number of pulses, and it becomes difficult to control the dot depth with the number of pulses. For this reason, with the leading value of the first Q-switch pulse, adjust the 7T tenator to an intensity that does not penetrate a depth of more than 1 μm with one pulse, and overlap as few pulses as possible at a frequency of about 2 to 5 KHz to mark. It is best to do so.

FIG. 5 shows the number of superimposed pulses and the depth of dots in soft marking obtained as a result of an actual experiment.

Next, after adjusting the 7T tenator or 20 so that it has a leading value that covers a depth of about 1.5 μm with one Q-switch pulse, the second and subsequent pulses have a magnitude of 60 to 80% of this pulse. By superimposing the pulses of 5 on the same dot,
It is also possible to make date markings with a depth of ~10 μm. In particular, the Q switch pulse of the first sales outlet is 1.0~
When the marking is 1.5 μm without scattering, it is possible to make a marking with a depth of 5 to 10 μm without scattering. While the shutter 7 provided outside the oscillator is closed, that is, even when not marking, the oscillator 17 outputs laser light at the Q-switch frequency used for marking at all times. It is also possible to completely eliminate variations in the marking dots.

The wafer marking device of the present invention includes an attenuator 12
(20) The marker controller 16 controls all the signals to the ultrasonic Q-switch element 2, and the marking mode selection 2, dot depth designation, etc. can be freely set by the software program. It goes without saying that this system has an excellent feature in that it can be made into a highly flexible system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a flowchart showing the operation of the first embodiment of the present invention, FIG. 3 is a front view showing a part of the second embodiment of the present invention,
FIG. 4 is a diagram showing the laser output pulse waveform in the embodiment of the present invention, and FIG. 5 is a diagram showing the relationship between the number of shots and the marking depth in the embodiment of the invention. Agent: Susumu Uchihara, Patent Attorney

Claims (1)

[Claims] In wafer marking equipment that uses a Q-switched YAG laser as a light source to mark characters and symbols made of dots on the surface of a wafer such as Si, there is a shutter to block the light emitted from the laser oscillator, and a shutter to continuously transmit the light. The repetition frequency of the YAG laser pulse that irradiates each dot is 1 KHz or less, and furthermore, the YAG laser pulse that irradiates each dot within the above-mentioned repetition frequency range is provided with an attenuator for attenuating the laser pulse. A wafer marking device characterized by marking while superimposing a finite number of laser pulses at a high repetition frequency of 2 to 5 KHz.