JPH0318335B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for connecting wiring within a semiconductor integrated circuit.

By cutting or connecting (short-circuiting) some of the integrated circuit wiring, it is possible to program (circuit change) a fabricated integrated circuit chip. Conventionally, this program has been used, for example, to program a read-only memory (ROM) or, more recently, to repair defective cells in a memory device. The following methods are known as these conventional methods.

(1) Cut specific parts (fuses) of PoLy-Si, AI, Nichrome, etc. wiring using electric current.

(2) Cut specific parts of PoIy-Si, AI, Nichrome, etc. wiring by applying optical energy from the outside using a laser.

These methods all cut part of the wiring, requiring a large amount of energy, and the melted PoIy-Si
or wiring metal can easily damage the nearby SiO ₂ film, and the laser beam can easily damage the substrate. Furthermore, if the wiring part is covered with a passivation film (SiO ₂ , SiN, etc.), part of the passivation film on top of it will be removed when the wiring is cut, so the passivation film must be coated again. There were drawbacks such as:

On the other hand, as a method for eliminating these drawbacks, a method has been proposed in which specific portions of the wiring are connected (short-circuited), as shown in FIG. That is, in FIG. 1A, two N ⁺ type PoIy-Si (polycrystalline Si) layers 3 and 4, which are insulated from the substrate 1 by the SiO ₂ layer 2 deposited on the Si substrate 1, have extremely high resistance (for example, 100KΩ). /more than mouth)
This is a wiring structure in which the wirings face each other with an i-layer 5 formed of a PoIy-Si layer (which does not need to be doped with impurities) interposed therebetween. By irradiating this with a laser spot such as 6 and giving sufficient energy, diffusion is caused from the n ⁺ type layers 3 and 4, and the high resistance layer 5 becomes the low resistance layer 7 as shown in FIG. 1B. It is something that converts. As a result of the above, before laser irradiation, the n ⁺ type layer 3
and 4 were in a non-conducting state, but after irradiation, ⁺ type layer 3
and 4 change to a conductive state, and the wiring connection (short circuit) is completed.

However, in this method, although the laser irradiation power density is lower than in the cutting method, it is necessary to cause impurity diffusion in a short ^time .
The PoIy-Si layers 3, 4 must be heated to a fairly high temperature. On the other hand, if the temperature is too high
This will cause damage to the PoIy-Si layer, and in extreme cases it will be cut off. Therefore, the range of laser conditions (irradiation power density) for connection (short circuit) is extremely narrow. That is, there was a drawback that the yield of connections (short circuits) was low due to variations in laser output.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to improve the performance of ROM (Read Only Memory), PLA
(ProgramabIe Logic Array) program,
Another object of the present invention is to provide a method that can perform wiring connections (short circuits) with high yield, which can be applied to defect relief in semiconductor devices including memory elements.

That is, in order to achieve the above-mentioned object, the present invention has a polycrystalline Si wiring having low resistance parts doped with conductive type impurities to lower the resistance on both sides of a high resistance part in a non-conducting state. Thin, free of impurities
Laser light is applied to the wiring part covered with an insulating film containing impurities of the same conductivity type as the low resistance part through the SiO ₂ film, and to the part of the insulating film covering at least the high resistance part of the polycrystalline Si wiring. , multiple pulses are irradiated at a power density that allows wiring connection, and the impurities contained in the insulating film are diffused from the top surface to almost the entire surface of the high-resistance part through a thin SiO ₂ film that does not contain the impurities, thereby forming a high-resistance part. This is a connection wiring method using a laser, which is characterized in that it easily changes from a non-conductive state to a conductive state and connects polycrystalline Si wiring in a semiconductor device. Furthermore, even if there is some variation in laser output, the present invention
- By irradiating multiple times (preferably 5 or more times) at a low power density that does not cause damage to the Si layer, it is possible to make high-quality connections with a high yield without causing damage to the wiring. This is how it was done.

Embodiments of the present invention will be described below with reference to the drawings.
Figure 2 shows that two n ⁺ type PoIy-Si (polycrystalline silicon) layers 3 and 4, which are insulated from the substrate 1 by a SiO ₂ layer 2 deposited on the Si substrate 1, have extremely high resistance (e.g.
10 ⁹ Ω/port or more) It has a wiring structure that faces each other with an i-layer 5 made of a PoIy-si layer (which does not need to be doped with impurities) interposed therebetween, and an insulating film 8 and an insulating film on top of them. 9 and an insulating film 10 are formed thereon. Here, the n ⁺ type layers 3 and 4 and the i layer 5 have a thickness of 100 to 500 nm, and the n ⁺ type layers 3 and 4 are doped with phosphorus or arsenic to an impurity concentration of 10 ¹⁸ /cm ³ or more. Also, the thickness of the insulating film 8 is 20
~200 nm SiO ₂ film, insulating film 9 is 100 to 1000 nm (0.1 to 1 μm) phosphorus glass film (PSG film) containing 1 to 10 moI% phosphorus, and insulating film 10 is 500 to 4000 nm thick.
The final insulating film (FinaI) consists of SiO ₂ or SiN or two layers of
Passivation membrane).

The wiring connection portion shown in FIG. 2 is irradiated with a laser using the optical system shown in FIG. That is, the third
In the optical system shown in the figure, a laser beam 11 oscillated by a laser oscillator (not shown) is formed into a rectangular shape that matches the wiring shape by a variable slit 12 that can be changed to any size, and a real image of the variable slit 12 is formed by an objective lens 13. (As shown in Figure ₂ , the wiring connection part is placed at the ^position where the The light is transmitted through the insulating films 8, 9, and 10 onto the layer 5), and is focused and irradiated with a magnitude that is the reciprocal of the magnification of the objective lens 13. Insulating film 8,
The total thickness of 9 and 10 is 0.5 to 3 μm, and it is transparent to wavelengths in the visible region, and absorption loss can be almost ignored.

PoIy-Si wirings 3, 4, 5 (wiring width 2 μm, length of i-layer 5 4 μm) using the optical system shown in Figure 3.
A laser beam was irradiated onto an area of 2 μm x 10 μm. In this case, since the length of the i-layer 5 is 4 μm,
The n ⁺ -type PoIy-Si layers (low resistance layers) on both sides are also irradiated with the laser by 3 μm each.

Figure 4 shows the irradiation results using a laser with a pulse width of 7 ns and a wavelength of 510 nm. Relative power density on vertical axis,
The horizontal axis represents the irradiation power density, and shows the state of the wiring connection section when the laser is irradiated under these conditions. That is, under the conditions above curve 15, the energy of the irradiated laser is excessive, so that the wiring is severely damaged and is in a state of being disconnected or close to disconnection. Furthermore, under the conditions below curve 16, the energy of the irradiated laser was too low, so the wiring was in a non-conductive state, that is, not connected. curve 15
Connection was possible within the condition range between and 16 (shaded area). Here, connected state means high resistance
This refers to a state in which the resistance value of the PoIy-Si layer 5 (i-layer) has decreased to 10 ⁵ Ω or less. This is compared to the resistance value of 10 ⁹ Ω or more of the high resistance PoIy-Si layer 5 before laser irradiation.
This is a change of 10 ⁴ or more and can be considered a complete short circuit. The reason why the high-resistance PoIy-Si layer (i-layer) 5 decreases in resistance by laser irradiation is that () the i-layer 5 and the n ⁺ type PoIy-Si layers 3 and 4 on both sides of it are heated to high temperature by the laser beam, and the n ⁺ type
The impurity (phosphorus) in PoIy-Si layers 3 and 4 is in the i layer 5.
The i-layer 5 changes into an n-layer.

() The i-layer 5 and the n ⁺ type PoIy-Si layers 3 and 4 on both sides thereof become high in temperature due to the laser beam, and the insulating films 8 and 9 in contact with them also become high in temperature, and the phosphorus in the insulating film 9 is heated. It diffuses into the i layer 5 below it and i
Layer 5 changes to an n layer.

It is conceivable that both are occurring. However, i-layer 5
The length of the i-layer 5 is as long as 4 μm, compared to 20 μm.
Since it is in close proximity to the insulating film (PSG film) 9 containing phosphorus through the SiO ₂ film 8 with a thickness of ~200 nm, when irradiated with laser light, the phosphorus in the insulating film 9 is
It is clear that the reason why the i-layer 5 is almost uniformly diffused into the layer 5 and changes into the n-layer is mainly due to the factor (ii) above.

As is clear from FIG. 4, connection could not be established with one pulse irradiation. That is, at a relative power density of 1 or more, the PoIy-Si layer is cut, and at a relative power density of 1 or less, sufficient diffusion of phosphorus does not occur. Relative power density for 2-pulse irradiation
Although we were able to connect at 0.9, the laser pulse output generally varies by about ±5% even when it is stable, so the PoIy-Si layer may be cut or not connected, resulting in a low connection yield. In 5-pulse irradiation, by setting the relative power density to 0.72, connections could be made with a high yield. Furthermore, if the number of irradiation pulses is increased, connections can be made with lower relative power densities, and a wider range of laser pulse variations can be tolerated. Generally, in a pulsed laser, the variation between pulses is about ±10% or more, and temporal changes are also added to this. Further, process variations, ie, variations in various film thicknesses and impurity concentrations from wafer to wafer or from lot to lot, produce the same effect as a relatively greater variation in laser pulse output. Therefore, a more stable connection can be achieved by setting the relative power density low and irradiating a large number of pulses. For example, at 1/2 of the lowest power density that can cut the PoIy-Si layer with one pulse, that is, at a relative power density of 0.5,
When irradiating 20 pulses, the laser pulse is ±
Even if there is a variation of 30% or more, the connection can be established reliably. Furthermore, when the relative power density is 0.4 and 100 pulses are irradiated, a variation of ±50% or more is allowed.

As mentioned above, the results shown in Figure 4 are i
This is for the case where the width of the layer 5 is 2 μm and the length is 4 μm. As the length of the i-layer becomes longer, a larger power density or a larger number of pulses is required, and the curve 16 in FIG. 4 shifts to the upper right. On the other hand, if the thickness and width of the i-layer do not change, the curve 15 will remain unchanged, and as a result, the range of conditions under which connection can be made will be narrowed.
However, even when the length of the i-layer 5 is 10 μm, sufficient connection can be achieved with a relative power density of 0.4 and irradiation with 200 pulses, and the variation in laser pulses is ±20%.
was allowed until Further, when the thickness of the i-layer 5 changes, the curve 15 shifts. That is, as the thickness increases, the curve 15 shifts to the upper right, and as the thickness decreases, the curve 15 shifts to the lower left. However, the thickness of i-layer 5 is 100 nm
If it is above this level, a sufficient connection can be made.

The embodiments described above are based on the case where the optical system shown in FIG. Although laser irradiation can be prevented, the present invention is not limited to this optical system. A second example will be shown below. Figure 5 shows n ⁺ type PoIy-Si layers 3 and 4.
and a plan view of a wiring connection portion consisting of an i-layer 5 sandwiched therebetween (insulating films 8, 9, 10 are
(omitted), a method is usually used in which a laser beam is focused on a minute spot 17 using an objective lens and irradiated thereon. In this method as well, the center of the light condensing spot 15 and the center of the i-layer 5 are made to substantially coincide, and the light condensing spot 17 is at least n ⁺
Connection can be made by irradiating the PoIy-Si layers 3 and 4 so as to overlap them. In this case, the range in which a good connection can be made is narrower than the condition range shown in FIG. That is, the power density distribution at the condensing spot 17 is a Gaussian distribution, and the average power density is higher at the center and lower at the periphery, so the curve 15
is shifted to the lower left, and curve 16 is shifted to the upper right. However, if a laser beam focused to a spot diameter of approximately 10 μm is used for 50 pulses at an average power density (relative value) of 0.4,
Sufficient connection was achieved by irradiating 100 pulses with an average power density (relative value) of 0.3.

Next, another example will be shown. FIG. 6, like FIG. 5, is a plan view of a wiring connection section consisting of n ⁺ type PoIy-Si layers 3 and 4 and an i layer 5 sandwiched between them, and shows a laser beam that is finely divided by an objective lens. The light is focused on a spot 18 and irradiated. In this case, the light condensing spot 18
is approximately the same as the width of the wiring section, that is, a dimension that takes into consideration the width of the wiring section and positioning accuracy. In this example, the wiring width is 2μm, and the positioning accuracy is ±1μm.
m is possible, so the spot diameter should be 3 to 4μ.
mφ is optimal. This condensing spot 18 is scanned relatively from the n ⁺ type PoIy-Si layer 3 to the n ⁺ type PoIy-Si layer 4 through the i layer 5, for example, as shown in FIG. The scanning means includes movement of an X-Y stage on which a wafer (or chip state) is placed;
Alternatively, laser beam scanning may be performed using a galvanometer mirror, a rotating polygon mirror, or the like. The second harmonic (wavelength) of the Q-switch YAG laser as a laser
532 nm, pulse width 30 ns), the light was focused on a spot of approximately 4 μmφ at an average power density (relative value) of 0.4, and scanned at a repetition rate of 1 KHz so that the spot spacing (pitch) was 1 μm. 6μ scanning distance
When the length of the i-layer 5 was 4 μm, a good connection was obtained by scanning three times or more. Almost similar results were obtained not only when scanning in a fixed direction but also when irradiating back and forth (one round trip is considered as two scans). i
If the length of the layer 5 is long, it is possible to connect by increasing the power density or increasing the number of scans, and when the length of the i-layer 5 is 10 μm, the average power density (relative value) 0.5, 6 scans were enough to establish a connection.

In this embodiment, as in the first embodiment, the wiring connection part is irradiated with almost uniform laser power, and it also has the effect of preventing the laser from being irradiated to parts other than the wiring connection part. be.

In the embodiments described above, n ⁺ type PoIy
−Si−i layer −n ⁺ type PoIy − Although we have only explained the structure of the Si layer (n ⁺ −i−n ⁺ ), P ⁺ type PoIy−
Si layer - i layer - P ⁺ type - PoIy - Si layer (P ⁺ -i-P ⁺ )
Exactly the same effect can be obtained with this configuration. However, in this case, it is more desirable to use a boron glass film (BSG film) as the insulating film 9. The object can also be achieved by forming a P-n diode with a configuration of P ⁺ type PoIy-Si layer-i layer-n ⁺ type PoIy-Si layer (P ⁺ -i-n ⁺ ). In this case, the insulating film 9 may be made of either phosphorus glass or boron glass. As described above, it is clear that by irradiating the laser beam, impurities such as phosphorus or boron from the insulating film 9 are almost uniformly diffused into the i-layer, and the resistance of the i-layer is reduced.

Furthermore, we have explained the case where the second harmonic of the n2 laser pumped Dye laser or the Q-switched YAG laser is used as the laser, but the second harmonic of the Q-switched YAG laser has a pulse width of 200 ns.
Front and rear, or fundamental wave of Q-switched pulsed YAG laser, Xe laser, metal vapor laser, excimer laser, ruby laser, cavity damping pulsed Ar or Kr laser, various pulsed laser excitation or flash lamp excitation Dye laser, etc., insulation It is clear that similar benefits can be obtained by using transparent lasers for the membranes 8, 9, 10.

As explained above, according to the present invention, polycrystalline
A laser beam is applied to the wiring part on the Si wiring, which is covered with an insulating film containing impurities of the same conductivity type as the low resistance part, through a thin SiO ₂ film that does not contain impurities that suppress diffusion of impurities during heat treatment. The impurities contained in the above insulating film are removed by irradiation of
By diffusing almost the entire surface of the high-resistance area from the top surface through the SiO ₂ film, the high-resistance area can be easily changed from a non-conductive state to a conductive state, and interconnection of polycrystalline Si wiring can be performed. This has the effect of realizing wiring connections applicable to defect relief in semiconductor devices at a high yield. Further, according to the present invention,
Even if the output of the laser oscillator varies to some extent, the wiring connection can be performed with high quality and high yield without causing damage to the wiring part.

[Brief explanation of drawings]

Fig. 1 is an explanation F of a conventional technique for connecting specific parts of wiring, Fig. 2 is a diagram showing a general configuration of a wiring connection part in which the present invention is implemented, and Fig. 3 is a diagram showing a general configuration of a wiring connection part in which the present invention is implemented. FIG. 4 is a diagram showing the optical system, FIG. 4 is a diagram showing an appropriate condition range, and FIGS. 5 and 6 are explanatory diagrams showing other embodiments of the present invention. 1...Si substrate, 2...SiO ₂ layer, 3, 4...n ⁺
Type PoIy-Si layer, 5... High resistance layer (i layer), 6...
Laser beam, 8...SiO ₂ film, 9...PSG film,
10...Final insulation film (FinaI Passivation)
membrane), 12... variable rectangular slit, 13... objective lens.

Claims (1)

[Claims] 1. A thin SiO layer containing no impurities is placed on a polycrystalline Si wiring having low resistance parts doped with conductive type impurities to reduce resistance on both sides of a high resistance part in a non-conductive state. _{A laser} beam is applied to a portion of the insulating film that covers at least the high resistance portion of the polycrystalline Si wiring, with respect to the wiring portion covered with an insulating film containing an impurity of the same conductivity type as the low resistance portion through two films. Multiple pulses are irradiated at a power density that allows wiring connection, and the impurities contained in the insulating film are diffused from the top surface to almost the entire surface of the high-resistance part through the thin SiO ₂ film that does not contain the impurities, thereby easily forming the high-resistance part. 1. A connection wiring method using a laser, characterized in that polycrystalline Si wiring in a semiconductor device is connected by changing from a non-conductive state to a conductive state. 2. The connection wiring method using a laser according to claim 1, wherein the insulating film containing impurities is formed of a phosphorus glass film or a boron glass film. 3. The connection wiring method using a laser according to claim 1, wherein the laser beam is a reduced image of a variable rectangular slit that can be formed to any size. 4. A connection wiring method using a laser according to claim 1, wherein the laser beam is relatively scanned at a pitch smaller than the spot diameter. 5. The above is applied via a thin SiO ₂ film that does not contain impurities onto a polycrystalline Si wiring that has low resistance parts doped with conductive type impurities to reduce resistance on both sides of a high resistance part that is in a non-conductive state. For a wiring part covered with an insulating film containing impurities of the same conductivity type as the low-resistance part, a single pulse of laser light is applied to the part of the insulating film covering at least the high-resistance part of the polycrystalline Si wiring. Multiple pulses are irradiated at a power density that is 3/4 or less of the power density required to cut the wiring, and the impurities contained in the above insulating film are removed into a thin SiO ₂ film that does not contain the above impurities.
The polycrystalline silicon in the semiconductor device is diffused from the upper surface to almost the entire surface of the high resistance area through the film to easily change the high resistance area from a non-conductive state to a conductive state.
A connection wiring method using a laser, which is characterized in that wiring is connected. 6. The connection wiring method using a laser according to claim 5, wherein the insulating film containing impurities is formed of a phosphorus glass film or a boron glass film. 7. The connection wiring method using a laser according to claim 5, wherein the laser beam is a reduced image of a variable rectangular slit that can be formed to any size. 8. The connection wiring method using a laser according to claim 5, wherein the laser beam is relatively scanned at a pitch smaller than the spot diameter.