JPS59178748A - Laser processing method - Google Patents

Abstract

PURPOSE:To enable to relieve an integrated circuit of defects with high yield by a method wherein the following processing is performed while measuring the characteristic of said circuit, when the wirings at a specific part of said circuit are connected or cut by irradiating this part with a laser, and then the laser processing condition is varied so as to obtain desired characteristic. CONSTITUTION:The characteristic of a chip 11 is measured by making probers 13a and 13b connected to a tester 14 abut against the pads 12a and 12b of the chip low resistant polycrystalline Si wirings 3 and 4, a high resistant polycrystalline Si wiring 5, and the Al electrode pads 12a and 12b are formed. At this time, the laser light 7 from a laser oscillator 15 is passed through a laser light intensity adjuster 18 controlled by a controlling device 16 and then condensed by means of an objective lans 19, resulting in irradiation on the wiring of the light. Thus constructed, the output of the laser light 7 is adjusted by rotating a deflection plate provided in the adjuster 18, and then these wirings are connected or cut so that the resistance value obtained by the tester 14 becomes a desired value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method of processing a semiconductor integrated circuit by irradiating it with laser light. relates to the method of cutting.

By cutting or connecting (short-circuiting) some of the wiring within the integrated circuit, it is possible to program (circuit change) the fabricated integrated circuit chip. Traditionally, this program (
circuit change).

For example, it has been used to repair defective cells in read-only memory (ROM) or, more recently, in memory devices. These conventional methods include (1) applying optical energy from the outside using a laser to cut a specific portion of wiring made of Po1y-5i, At, nichrome, or the like;

(2) A high-resistance part (not doped with any impurity is allowed) and its surroundings is provided in a part of the Po1y-5i wiring (low-resistance part) by applying optical energy from the outside with a laser. The connection is made by irradiating the high resistance part with a laser to lower the resistance.

It has been known.

In either method, in the case of ROM, etc., preset conditions, i.e., constant Processes such as cutting and connecting are performed by irradiating laser power and a certain number of pulses.

However, in general, Po
Wiring made of 1y-5z, AL, nichrome, etc. is Sin, PSG (phosphorus glass), S5N ring S
It is processed while being covered with a passivation film consisting of a single layer of iO or a plurality of these layers, and if necessary, cutting is performed to form a final passivation film. If a laser is irradiated through the passivation film formed on the wiring section, the reflectance will fluctuate sharply due to the interference effect due to variations in the passivation film thickness, and as a result, the laser power input to the wiring section will fluctuate. I end up. Therefore, when cutting, even if the laser is irradiated under certain conditions, the wiring may not be cut or the substrate may be damaged. Also, when making connections, even if the laser is irradiated under certain conditions, the connection may not be made or the wiring may be cut.

There was a problem with low yield. To prevent this,
Efforts have been made to keep the thickness of the scivation film constant, but it is currently extremely difficult.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to
OM (Read Only Memory), P
LA (Pro, q-rama, hlt Logic
It is an object of the present invention to provide a method that can perform high-yield laser processing that can be applied to programs such as arrays or to repair defects in semiconductor integrated circuits including memory devices.

[Summary of the invention]

Even if the required laser conditions differ for each conductor integrated circuit to be processed due to process variations, the present invention enables irradiation by sequentially changing the laser conditions while monitoring the characteristics of the semiconductor integrated circuit to obtain the optimum characteristics. By completing laser irradiation at the point where the measurement has been completed, laser processing of semiconductor integrated circuits can be performed with high quality and high yield.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. First, a case will be described in which the present invention is applied to wiring connection using a laser. Fig. 1 is a diagram showing the structure of a general wiring connection part. f) Two 1-type Po1y-5i (polycrystalline silicon layers) insulated from the substrate 1 by a 5in2 film 2 deposited on the -5i substrate 1. 6°4 has extremely high resistance (for example, 109
0 or more) Poly-5L layers (which may be doped with impurities) have a wiring structure facing each other with two layers 5 interposed therebetween, and an insulating film 8. This is because the insulating film 9° and the insulating film 10 are formed. Here, the n-type layer 3°4 and the 2nd layer 5 have a thickness of 100 to 5 nm. The shaped layers 3 and 4 are made of phosphorus or arsenic, with an impurity concentration of 10'8/c,
It is doped to 7 or higher. Further, the insulating film 8 has a thickness of 2
0-2020-200rL~2000. J) of 5t
The O2 film and the insulating film 9 contain i-11-1Q% phosphorus.
The insulating film 10 has a thickness of sho-40.
00 rLm (0,!5-4 μm), the final insulating film (Final Pa5si
vtuion membrane).

Insulating film 8.9.1
The laser beam 7 with a wavelength sufficiently transparent to 0 is rL+ type P.
When the o1y-5i layers 3, 4 and the T layer 5 are irradiated, under appropriate laser conditions, phosphorus diffuses into the L layer 5 from either the n-type layers 3, 4 or PSGS2O2, or both. becomes low resistance. At this time, insulating films 8, 9, 10
causes almost no damage. Here, appropriate laser conditions are, for example, using the second harmonic of a Q-switched YAG laser, 1 to 2 pulses, x T P o l y-5i
The condition is to irradiate several pulses and several ten pulses at a power density of 1/2 of the power density that causes the wiring part to break.

In addition, here, the state of connection due to low resistance means that the resistance value of the high resistance Poly-5i layer (L layer) 5 is 105
This refers to the state in which the resistance has decreased below Ω. This is a change of 104 or more compared to the resistance value of 10[Omega] or more of the high-resistance Po1y-5i layer (L layer) 5 before laser irradiation, and can be regarded as a completely short-circuited state, that is, a connected state.

However, in the process of manufacturing semiconductor chips,
Insulating films 8, 9. It is extremely difficult to keep the IQ film thickness constant. Here, the insulating film 8.9. A case where the IQ film thickness changes will be described. If the insulating film 10 is a single layer film of SL O2, the wavelength of all insulating films 8, 9, and 10 is 532.
4,4 (second harmonic of YAG laser), it can be safely assumed that the refractive index is 1.45, and absorption can be ignored.
The insulating films 8, 9 and 10 can be considered as one insulating film as a whole. At this time, changes in the film thickness and reflectance of the insulating film when the second harmonic of the YAG laser is incident perpendicularly to the above structure are shown in FIG. 2, assuming that the refractive index of Si is 43. As you can see from this figure, 2n = '836. The reflectance changes in the range of about 11% to 39% with a cycle of 'i. (λ is the wavelength of the incident light, and L is the refractive index of the insulating film.) In other words, when irradiating the laser 7 with a part of the output power, the Po1y-5i layers 3 and 4 are effectively
．． 5 shows that the absorbed laser fist energy varies in the range of 61% to 89% with respect to the irradiation energy.

Next, a case will be described in which a single layer film of silicon nitride film is used as the insulating film 1o. The refractive index for 532 islands of silicon nitride is approximately 20. As mentioned above, the insulating film 8 and the insulating film 9 have a film thickness of 20 to 200 rLm and 110 rLm, respectively.
0-10007L, T alka optically? -1ff tear, 120 to 1200nm, it can be considered as an insulating film. In addition, the insulating film 10 is 500 to 4ooorLrIL
It is.

Here, the total of the insulating film 8.9 is 6 A Onm - the insulating film 1° is 1400 lumen. Insulating films 8 and 9 are shown at 640 in Figure 3.
The insulating film 10 is fixed at 120 nm (1-1600 nm).
When the insulating film 10 is changed in the range of 140 m as shown in FIG.
Fixed to 01Lm, insulating film 8.9 is 400 to 8007
It shows the change in reflectance when changing within the range of Lm. Each.

It varies in the range of 12% to 61% and 0.4% to 61%.

The relationship between these film thicknesses and reflectance is 1. For example, see "Thin Films (Applied Physics Selection 3)", co-authored by Kinko Shokabo and Fujiwara, JP
, 227. ff[I, insulating film 8°9.10
The reflectance varies from 1% or less to 61% depending on the film thickness. This means that even if the laser output is constant, -Po1y-5i
Effective laser input into layers 3, 4.5 is 39%-99%
For example, even if a constant laser output of 1 μJ is applied, the Po1y-8i layers 3, 4.5
The energy absorbed by this varies in the range of 039 μJ to 099 μJ. This means that even if the laser output is always constant,
Because the absorbed energy is small, resistance may not be lowered.

Po1y-5i layer 3. absorbs a lot of energy. d, 5 may be damaged, resulting in a problem of low connection yield. Moreover, the changes shown in Figures 3 and 4 are the characteristics when one film thickness is kept constant, but in reality, both film thicknesses change simultaneously, so each has a 1or
There are cases where the reflectance changes significantly just by changing Lm. In addition, considering the impurity concentration of the n+ type Po1y-5i layers 3 and 4, the phosphorus concentration in the PSG 9, the length of the layer 5, etc., variations in chip manufacturing, and variations in laser output, the yield decreases significantly.

A laser processing method according to an embodiment of the present invention is shown in FIG.

In Fig. 5, 1 step 11 is shown to simplify the explanation.
A case is shown in which one wiring connection portion is formed on the top. That is, on the chip 11 there is a low resistance Po1y-5i 3
, 4 and high resistance Po1y-5i5
y-5i wiring is formed.

At both ends thereof, At electrodes (buds) 12 are provided.

These Al-electrodes 12a, 12b and Ic are in contact with each other, and the resistance value between the At electrodes can be measured with the tester 14.The wiring connection in FIG. The structure is the same as that shown in FIG. 1, but for the sake of simplicity, the parts such as the wafer and the scivation film are omitted from the illustration.

Further, the laser beam 7 oscillated from the laser oscillator 15 passes through a laser beam intensity adjuster 18 driven by a control device 16, and is focused by an objective lens 19.
5i wiring is irradiated. Here, the tester 14 always applies a constant voltage and measures the resistance value from the current flowing through the -Poly-5i wiring sections 3 and 4.5. The laser oscillator 15 is one that generates the second harmonic of a Q-switched YAG laser, for example, and the laser light intensity adjuster 18 is a glass circular type that continuously changes transmittance by rotating a polarizing plate. It is possible to use a method in which the thickness is continuously changed using a metal vapor deposited film that is continuously changed in the circumferential direction on a plate, or a modulator using an electro-optic effect.

First, in a state where the transmittance of the laser beam intensity adjuster 18 is sufficiently low, that is, with a sufficiently weak laser output, a portion of the wiring connection portion is irradiated by the Barne number.

After irradiation, the tester 14 measures the resistance value, and if the set resistance value is not reached, the control device 16 slightly increases the transmittance of the laser beam intensity regulator 18, that is, -Po1y-5i.
The laser power irradiated onto the wiring section is increased and irradiated with a fixed number of pulses. The resistance value is measured again by the tester 14, and if it does not decrease to the set resistance value, Po1 is further measured.
Irradiation is repeated with a constant number of pulses while increasing the laser output irradiated to the y-5i wiring section.

Laser irradiation may be stopped when the resistance value decreases to the set resistance value. As a result of the experiment, the relationship between the cumulative number of irradiation pulses, the laser output (relative value), and the resistance value after irradiation is as shown in FIG. In the characteristic diagram of Figure 6, A
indicates the laser output, and B indicates the resistance value.

This shows that first, the relative laser output was set to o5 and 2° pulse irradiation was performed, and the resistance value measured immediately after was 1090, which was unchanged from before the irradiation. Next, set the relative laser output to 1
．． The relative laser output was set to 0 for 20 pulses, the relative laser output was set to 1.5 for 20 pulses, the relative laser output was increased by 0.5, and the moth was irradiated with 20 pulses at a time, but the relative laser output was 3. No change was observed until the O1 cumulative irradiation pulse number reached 120 pulses.

However, when irradiating 20 pulses (cumulative irradiation pulse number 140 pulses) with a relative laser output of 3.5, the resistance value is 1011
01, and the laser output was fixed at 65 from then on.
When irradiation was continued, the cumulative number of irradiation pulses was 280, and the resistance decreased to about 103Ω (1XΩ).

In Figure 6, up to 300 pulses are irradiated to examine the characteristics of low resistance, but in reality, the connection can be considered complete when a resistance of 104Ω or less is obtained, so the cumulative number of irradiation pulses is 180. At this point, the irradiation can be finished. Note that although the experimental results shown in Figure 6 start with a sufficiently low relative laser output, a reduction in resistance occurs when considering variations in reflectance due to variations in passivation film thickness and variations in process. Just start with the lowest possible laser power. Further, it is desirable that the setting interval of the laser output is sufficiently small, but from the viewpoint of processing time, the interval between the optimum laser output and the laser output that causes damage to the wiring portion may be divided into 3 to 4.

In addition, in FIG. 6, after 20 pulses were irradiated with a relative laser output of 35, the resistance value decreased by 1050 mm.

Irradiation continues without changing the relative laser output, but
Even if the relative laser output was changed to 440 and irradiation was performed, back-filling occurred.

Next, we will introduce the processing method of the present invention as a semiconductor memory redundancy technique (
FIG. 7 shows a specific configuration example of the case where the present invention is applied to the repair of defective bits. That is, as shown in FIG. 7, a probe 23 from a probe card 22 is pressed against a bump (electrode made of At or the like) provided on a semiconductor memory chip 20, and a memory tester 24 presses a probe 23 from a probe card 22. The memory chip 20 is tested.

Normally, the wafer is mounted on an X-Y stage or the like and inspected one chip at a time using a probe card 22, but only one chip is shown in the figure. When a defect is found based on the inspection result of the memory tester 24, a laser is irradiated to a specific wiring connection portion to remedy the defect. The laser oscillator 15 is composed of, for example, a Q-switched YAG laser and a second harmonic generator.
-f[7id- The laser beam is focused by the objective lens 19 at an intensity arbitrarily set by the laser beam intensity adjuster 18, and is irradiated onto the chip 20. Further, the control device 25 is configured to control the transmittance adjustment of the laser light intensity adjuster 18 and to control the on/off of the laser oscillator 15 based on the results of the memory tester 24.

In FIG. 7, the memory tester 24 is first tested and a defect is found on the chip.

The chip (or wafer) is positioned at the wiring connection part for repairing the defect using an X-Y nutage on which it is mounted, or a laser beam scanning device such as a galvanometer (not shown). Here, the control device 25
As a result, a part of the wiring connection portion is irradiated with a transmission signal of the laser beam intensity adjuster 18 at a sufficiently low power density, that is, a Parnu number of 1, for example, 20 pulses.

After the laser irradiation, the memory tester 24 performs an inspection again to check whether the defective part has been repaired or not. If the defective part has not been repaired, the control device 25 performs an inspection.

The settings of the laser beam intensity adjuster 1B are changed so that the transmittance increases, and the same spot is again irradiated with a partial number of pulses. After irradiation, an inspection is performed to repair the defective part 1, and the control device 2
4, the transmittance setting of the laser light intensity adjuster 18 is increased sequentially.

That is, the irradiation and inspection are repeated while sequentially increasing the laser energy irradiated to the wiring connection portion. According to Yokokura's results using Memory Tester 2A, when the defective part is repaired, the laser irradiation to that chip ends, in the case of a wafer, the -XY stage is moved by one chip, and in the case of a chip, a new chip is placed. Replace and repeat the procedure from inspection. Here, to remedy one defect.

If multiple locations need to be connected, it is a good idea to repeat the inspection and irradiation procedure to all required locations.

Next, another example will be described. For example, as shown in Figure 2, if the change in reflectance is relatively small and the variation in the chip manufacturing process is also small, the irradiation pulse Just change the numbers.

Figure 8 shows the relationship between the number of irradiation pulses and the resistance value when the laser output is fixed. Curve A shows the case where the reflectance is low enough and it is easy to connect. 8 curves. According to experiments, when connection is easy, 6
The resistance starts to decrease at 0 pulses and decreases to 1 after 80 pulses.
It has decreased to below 040. After this, when irradiation was continued at a rate of 20 pulses, damage occurred when the cumulative number of irradiation pulses was 220<rus. On the other hand, if it is difficult to connect,
A decrease was seen at 0 pulses, and decreased to 1040 at 340 pulses. In other words, the laser output is irradiated with a fixed number of pulses up to a constant level of 1, and the resistance value after irradiation or the characteristics of the entire circuit are used to determine whether the desired connection has been made. By further repeating irradiation with a fixed number of pulses and measurement or inspection, the same effect as the method described in FIG. 5 or FIG. 7 can be obtained.

Above, we have described the case in which the present invention is applied to wiring connection for the purpose of writing to ROM or relieving defective cells in semiconductor memory, but when it is applied to cutting wiring for the same purpose You can get exactly the same effect.

That is, if the reflectance is too high, the effective h laser φ energy to the cutting part will be low (and the cutting will not be possible).

If the reflectance is too low, the effective energy applied to the cut will be too high and may damage the substrate. However, by applying the present invention, one pulse is irradiated with a laser energy that does not cause damage to the substrate, and measurement and inspection are performed while increasing the laser energy sequentially based on the success or failure of disconnection or judgment from the overall characteristics. By repeating laser irradiation,
It is clear that wiring can be cut reliably without damage to the board.

In addition, in this embodiment, a Q switch Y is used as a laser.
Although we have discussed the case of using the second harmonic of an AG laser, it is not limited to this, and pulse oscillation, C
It is clear that the same effect can be obtained regardless of the wavelength, regardless of the 'lF (continuous) oscillation.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, while measuring the characteristics of a semiconductor integrated circuit, the laser irradiation conditions are sequentially changed and the laser irradiation is completed when the optimum processing is obtained. This process produces semiconductor integrated circuits with the desired characteristics, so high quality is always achieved under optimal conditions.

The effect is that laser processing can be performed with high yield.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a wiring connection part of a semiconductor integrated circuit to which the present invention is applied, FIGS. 2 to 4 are diagrams showing changes in reflectance when the film thickness of the semiconductor integrated circuit changes, and FIG. FIG. 5 is a diagram showing a specific device configuration for explaining the present invention in detail, FIG. 6 is a diagram showing the relationship between cumulative irradiation pulse number, laser output, and resistance value, and FIG. 7 is a diagram showing another embodiment of the present invention. The apparatus configuration diagram, FIG. 8, is a diagram showing the relationship between the number of irradiation pulses and the resistance value when the laser output is kept constant. 1-5i substrate 2 ・5in2 film 3, 4
・・n+ type Po1y-5i layer 5-・i layer 8.9.1
0... Insulating film 7... Laser light 13.23...
-Gloves 1A, 2A...Tester 15...Laser oscillator 18...Laser light intensity adjuster 19 -Objective lens 17 (Second insulating film thickness penalty) Figure 3! Thickness of hand U quadrant 1o (Tsume) No. 47 Seasonal membranous membrane 890 Gouji Shishi thickness (7L m) S section No. 6 Figure 1 300 40
0 plan yes! l! 'A size λ less wa missing,

Claims (1)

[Scope of Claims] (1) A semiconductor integrated circuit having arbitrary characteristics whose characteristics are changed by irradiating a specific portion of the semiconductor integrated circuit with a laser and cutting or disconnecting wiring in the irradiated portion of the semiconductor integrated circuit. A laser processing method for obtaining a semiconductor integrated circuit, characterized in that while measuring the characteristics of the semiconductor integrated circuit, laser irradiation is performed while sequentially changing laser processing conditions until the desired characteristics of the semiconductor integrated circuit are obtained. . 2) The laser processing method according to claim 1, wherein the characteristic measurement of the semiconductor integrated circuit is a characteristic measurement of the entire semiconductor integrated circuit. (3) The characteristic measurement of the semiconductor integrated circuit is characterized in that the characteristic measurement of the laser irradiation part is performed.(4) The laser beam 2. The laser processing method according to claim 1, wherein the irradiation condition is that the irradiation laser energy is sequentially increased from a sufficiently low value and irradiation is performed in increments of a certain number of pulses (or for a certain period of time). (5) The laser processing method according to claim 1, wherein the laser irradiation condition is such that cumulative irradiation and <number of ruses (or cumulative irradiation time) are sequentially increased.