JPS6267834A - Laser processing - Google Patents

Abstract

PURPOSE:To produce a semiconductor memory with high reliability enabling a wire to be cut off without cracking at all by a method wherein a wavelength to be absorbed into a passivation film is selected for the laser beams for laser processing to remove the passivation film from the surface successively downward finally to cut off the wiring. CONSTITUTION:When a chip with an Si film 7 showing the characteristics of a curve 29 is irradiated with the third higher harmonics 12b of YAG laser, the ultraviolet laser beams are absorbed into the SiN film 7 to be removed successively downward to the perfect removal of SiN film 7 limited to the part irradiated with the laser beams. When the chip is further irradiated with the laser beams 12b, the laser beams 12b are transmitted by phosphorus glass layer 4 but absorbed into a poly-Si layer 3 to be explosively diffused simultaneously removing the phosphorus glass layer 4. When an irradiated region is set up using a rectangular slit on a sample with an SiO2 film 4 on the poly-Si wiring 3 and another SiO2 film on the SiO2 film 4 to be irradiated with the third higher harmonics of YAG laser, the SiN film can be almost perfectly removed at the third pulse while the poly-Si wiring can be cut off at the fourth pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of laser processing a semiconductor integrated circuit, and particularly to a laser processing method suitable for application to redundancy technology for large-capacity semiconductor memories.

[Background of the invention]

By cutting part of the wiring within a semiconductor integrated circuit,
Programs (circuit changes) can be made to the integrated circuit chip in the production tube. Recently, it has been used particularly to repair defective cells in semiconductor memory devices. A laser is used to cut this wiring. Regarding this technology, for example,
Proceedings of the National Electron
Conference (Proceeding of Nat.
ionalElectron Conference
) No. 56 (published in 1982), pp. 385-589.

That is, as shown in FIG. 6(α), Si is deposited on the Si substrate 1.

A poly-8i wiring 6 insulated through the film 2 is formed, insulated by a phosphorus glass layer 4, and a poly-8i wiring 3
Pulsed light 6 from an Nd-doped YAG laser (wavelength t064μ) is irradiated onto a link portion having a structure in which both ends are connected to the AJ wiring 5. At this time, as shown in FIG. 6(b), the laser beam 6 is transmitted through the phosphor glass layer 4, but the poly-8
i5, poly-3i3 is rapidly heated, explosively scattered, and cut. Therefore, the phosphor glass 4 above the cut portion is also scattered and removed at the same time. Then, in order to prevent contamination from entering through the opening, a SiN film 7 is formed as shown in FIG. 6(C). The second harmonic of a YAG laser has also been used as a laser.

However, in this method, the laser treatment is performed midway through the sea urchin fly, so poly-! Particles of 9i and phosphorus glass adhere to the surrounding area, and before laser processing, a probe is placed on the probe and an inspection is performed using a tester, so the traces of the needle on the final SiN film may have an adverse effect on the finished chip. There are drawbacks that reduce reliability.

On the other hand, in the state shown in Fig. 6 (α), without laser treatment, after forming the SiN film, holes are made in the SiN film in the areas that may be irradiated with laser. Another method is to irradiate the areas with a laser beam.

However, in this method, all links that do not require laser processing remain open, so reliability problems remain due to breakage due to moisture intrusion or contamination intrusion.

Therefore, there is a method of forming a SiN film after processing again, but in this case, there are problems in that extra steps are required and costs increase.

Furthermore, as shown in FIG. 7(α), after forming the SiN film 7, without raising the window, the poly-8i wiring 3
However, as shown in Figure 7(b), the SiN film around the laser irradiation area was largely peeled off and cracks 8 appeared, which caused a major problem in terms of chip reliability. Understood.

This is due to the thick passivation film thickness and the S
This is presumed to be because the iN film 7 is made of a material with high mechanical strength. Note that phosphorus glass (PS) is used as the passivation film.
When using G), sufficient thickness is required, but
As stated in page 461 of the Proceedings of the 61st Applied Physics Association Lectures, Spring 1981, if PSG is thick, po
There also arises a problem that the cutting yield of ly-8t is reduced.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, an object of the present invention is to provide a laser processing method that can be applied to redundancy technology for manufacturing a highly reliable semiconductor memory without increasing the number of man-hours.

[Summary of the invention]

That is, in order to achieve the above object, the present invention selects a wavelength that is absorbed by the passivation film as the laser light used for laser processing, performs removal processing sequentially from the passivation surface, and finally cuts the wiring. All interconnections (links) of the chip (perfectly good product), which enables crack-free cutting and does not require laser treatment, are protected by passivation, ensuring sufficient reliability.
It is characterized in that no extra steps are required.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to the drawings.

First, FIG. 5 shows the configuration of an optical system of an apparatus suitable for carrying out the present invention. The infrared laser beam 12 (Z) oscillated from the laser oscillator 11 is converted by the third harmonic generator 16 into ultraviolet laser beam 12b (wavelength 0.355 μrIL) with a wavelength of T, and the mirror 14 and dichroic mirror 15 It is combined with the reference light 16. See.

The illumination 16 is a light from a light source 17, and a specific visible wavelength is selected by an interference filter 18. The reference light 16 is shaped into a rectangle of arbitrary dimensions by a rectangular opening slit 19, bent by a mirror 20, focused and imaged by an objective lens 21, and placed on a stage 22 movable in X-Y-Z-〇. The wafer 23 placed thereon is irradiated with light.

At this time, the image of the rectangular aperture slit 19 on the wafer 23 is converted to the reciprocal of the objective lens magnification, that is, the magnification M by the objective lens 21.
Then, it is placed at a position that is reduced and projected onto M. In the case of manual operation, the operator simultaneously observes the slit image by the reference light 16 and the surface/surface using the observation optical system consisting of the observation light source 24, the eyepiece 25, etc., or in the case of automatic operation, the operator applies turn recognition. Then, the wiring portion to be cut and the slit image are aligned, and then the ultraviolet laser beam 12b is oscillated. At this time, the laser beam 12b is focused on the same position and dimension as the slit image formed by the reference beam 16, and processing is performed.

Here, as shown in FIG. 7(α), the link portion to which the laser is irradiated is formed with a SiN film 7 as the final passivation. Although the absorption edge of the SiN film 7 differs depending on the film formation process, it has spectral transmission characteristics as shown in FIG. 5, for example. The solid line (curve 27), the dashed line (curve 28), and the dashed line (curve 29) have absorption edges of 2000X and zsoo, respectively.
A. In the case of 2,700 people.

Here, when the third harmonic wave 12b of the YAG laser is irradiated to the chip on which the SiN film 7 exhibiting the characteristic of curve 29 is formed, the ultraviolet laser light is absorbed by the SiN film 7 as shown in FIG. 1 (α). The removal process proceeds in order from the top, as shown in Figure 1(b).
As shown in the figure, 5iN7 is completely removed only in the laser irradiated area. When the laser beam 12b is further irradiated, the phosphor glass layer 4 transmits the laser beam, but the poly-8i
Absorbed in layer 5.

It scatters explosively, and the phosphor glass layer 4 is also removed at the same time.

5ft on poly-Si wiring 3 with thickness zooooA and width 2-.

For a sample in which the film 4 was zsooX and a 1 μm thick SiN film was formed on it, an irradiation area of 5 μm was set using a rectangular slit, and the YAG was adjusted to have a power density of 8 x 10” W/cd. The third harmonic of the laser (pulsed light with a pulse width of 15 ns) was irradiated.The first pulse formed a 5 μm groove in the SiN film, the second pulse increased the depth, and the third pulse almost completely covered the SiN film. It was completely removed, and the poly-8i wiring was cut with the fourth pulse.The cutting was extremely good, with no cracks in the surrounding SiN film, and no damage to the underlying 5iO1 film or Si substrate. I couldn't see it.

In addition, a 5 μm irradiation area was set for the same sample, and the third harmonic of a YAG laser (pulse width 15 ns) was adjusted to have a power density of 4 × 10' W/-.
pulsed light) was irradiated. As a result, due to variations in processing speed caused by variations in laser output, the SiN film was removed in 5 to 7 pulses, and the poly-8 film was removed in the next pulse.
i Wiring is disconnected, then 2 to 4 more pulses (10 pulses in total)
Even after irradiation, good cutting was obtained without any damage to the underlying layer or the surrounding area.

In addition, an irradiation area of 10 μm was set for the same sample, and the third harmonic pulsed light (pulse width 15 ns) of the same YAG laser was adjusted so that the power density was l×10′V−. 2 on the SiN film on the i-wiring.
Pulse irradiation was performed. As a result, Si in the area of 10μ
The N film was almost completely removed. This shape was the same as that obtained when a window was formed in the SiN film by photo-etching technology. Then, the irradiation area was reset to 5 μm, and the power density was adjusted to 4×10′ W/−. As a result, good cutting was obtained. Also, the third harmonic of YAG laser is 10μ7110.1x1o'W/y
, After opening a window in the SiN film at 2 bus A/s, YA
Pulsed light (pulse width 40 ns) of the fundamental wave (wavelength 1.06 μm) of a G laser was focused on a Gaussian spot, and cutting was performed with one pulse. Good cutting was obtained with a spot diameter (processing diameter) of 6μ and a noxious energy of 2μJ.

Next, another example will be shown. FIG. 4 shows the optical system of an apparatus suitable for carrying out the method. The YAG laser oscillator 11 oscillates the laser beam, the fifth harmonic generator 16 converts it into an ultraviolet 2 ultraviolet laser 12b, and the objective lens 51 focuses and irradiates the wafer 23 placed on the x-y-z-θ stage 22. be done. At this time, the wafer 26 is placed in a position that matches the focal point of the objective lens 51. In this case, the focused laser beam has a Gaussian power density distribution at the focal point, so the second
As shown in the figure, the removal process is deep at the center and shallow at the periphery. The depth increases with each pulse, and the S
When the S tQt film 4 is exposed from the removed portion of the iN film 7, the poly-8i wiring 3 is explosively scattered by the next pulse, and the 3i0.4 is also removed at the same time, as shown in FIG. 2(C). As a result, a good cut can be obtained.

The sample described above was irradiated with the third harmonic of a YAG laser adjusted to have a pulse energy of 2 μJ using an objective lens capable of obtaining a spot diameter of 5 μmφ. As a result, the SiN film was removed with three pulses, and the poly-Si wiring was cut with the fourth pulse. The SiN film was removed in a circular shape with almost vertical sides, and no cracks were observed in the surrounding SiN film, nor was any damage to the underlying 5iOxi/Si substrate.

In the detailed description of the present invention, a case has been described in which a SiN film is used as a base film, and the poly-Si wiring underneath is cut using the third harmonic of a YAG laser. However, the present invention is not limited thereto.

For example, for a SiN film with a shorter absorption edge wavelength, use N, laser (wavelength 337 nm), fourth harmonic of YAG laser (266 nm), XeC1-1-ximer laser (
308M).

KrF excimer laser (249nu) * KrC
l Excimer laser (222 nm) * By using an ArF excimer laser (ed. 195), it is possible to remove the SiN film only in the laser irradiated area and cut the underlying wiring. In addition, when a SiOg-based material such as phosphorous glass is used as the passivation film, YAG
V-the. No. Harmonic (266n,), KrFxv
-'/-zV-f (249 nm), Kr (J excimer laser (222 nm → l ArF excimer laser (19
53m), it is possible to remove the only film in the laser irradiated area and cut the underlying wiring.

Also, the wiring to be cut is poly-8i
I have explained the wiring, MoSi, WSi.

Mo, W, AA! It is clear that the present invention can also be applied to wiring made of metals such as metals, metal silicides, or multiple layers thereof.

Furthermore, although the configuration of the optical system is shown in FIGS. 3 and 4 as an apparatus suitable for carrying out the present invention, the present invention is not limited thereto. In the embodiment, a transmission/refraction type lens is used as the objective lens, but a reflection type objective lens may also be used. Also, use the X-Y-Z-〇 stage to adjust the laser irradiation position!
However, it is clear that movement of the optical system including the objective lens, scanning by a galvanometer mirror, etc., or a combination thereof can be used.

Although the present invention has been described above based on Examples, the present invention can be summarized as follows.

Si is used as a final passivation film on the wiring to be cut.
If N is formed, remove the SiN by irradiating the SiN surface with a pulsed laser of the fifth harmonic (355 nm) of a YAG laser or a shorter wavelength.The pulse width is from 10038 to The shorter the length, the better from the viewpoint of thermal effects on the surrounding area.

The irradiation laser power density varies depending on the absorption rate for the SiN film thickness wavelength, but it is generally 1 x 10" or more, and it is desirable to remove by irradiating multiple pulses. A value that allows removal processing, for example 1 x 10" /i, and from the viewpoint of processing speed, it is desirable to irradiate with 1 to several tens of pulses, but the number is not particularly limited to these.

In addition, when 5iOt is formed as the final passivation film, the fourth harmonic (266
nm → or a shorter wavelength) (a Luth laser is used).

After removing the final passivation film or the layer immediately above the wiring layer, the wiring is further irradiated with laser light to cut the wiring. In this case, any wavelength that can be absorbed by the wiring as a laser is sufficient, and generally any of infrared, visible, and ultraviolet wavelengths are possible.

However, when using lasers with multiple wavelengths, the optical system (especially the characteristics of the reflecting mirror, chromatic aberration of the objective lens, adjustment of laser output, etc.) becomes complicated, so from a practical standpoint, it is necessary to remove the passivation film. It is most appropriate to use the same laser as is, and it is desirable to cut with one pulse of irradiation.

As described above, the present invention does not require extra steps such as opening a window on a wafer on which a final passivation film has been formed, and allows wiring that requires cutting to be processed (cutting) without damaging the surrounding area. ), and has the effect of ensuring sufficient reliability for chips that do not require cutting.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to process the wafer after the manufacturing process has been completed, and it is only necessary to process the minimum necessary portion, so a highly reliable semiconductor memory can be produced with a reduced number of manufacturing steps. There are effects that can be obtained without increasing.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing a portion to be treated by the processing method according to the present invention, FIG. The figure is a spectral transmission characteristic diagram of SiN according to the present invention, and Figures 1 and 7 are cross-sectional views showing a portion to be processed according to the prior art. 1...Si substrate, 2...5ift film, 5
...poly-8i wiring, 4...phosphorus glass film, 5...M wiring, 6...laser light, 7
-=SiN M, 11... YAG laser oscillator, 13... Third harmonic generator, 19... Rectangular aperture slit, 21... Objective lens, 23... Ueno rod.叉-m-

Claims (1)

[Claims] 1. Remove the passivation film by irradiating a desired portion of the wiring in the semiconductor device on which the final passivation film is formed with laser light of a wavelength that is absorbed by the passivation film, and then remove the passivation film under the passivation film. A laser processing method characterized by cutting formed wiring.