JPH0426219B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of adjusting the resistance value of a resistor formed in a semiconductor integrated circuit using a laser.

[Background of the invention]

In recent years, there has been a demand for higher integration and higher performance for semiconductor integrated circuits. For this reason, a method has come to be used in which the resistance value of a resistor formed in a semiconductor integrated circuit is adjusted while measuring the overall characteristics after the semiconductor integrated circuit is completed. A laser is used to adjust this resistance value. This method is similar to methods commonly used to tune thick film or thin film resistors formed on ceramic substrates. That is, as shown in FIG. 1, a part of a resistor 3 formed of tantalum nitride, chromium silicon, polycrystalline silicon, etc. on a Si substrate 1 and insulated by a SiO ₂ film 2 is exposed to a laser beam. 4 and adjust the resistance value between the electrodes 5A and 5B, or perform spot processing (machining marks 6) on the resistor 3 as shown in FIG. 2 and adjust the resistance value, or As shown in FIG. 3, a method has been used in which the resistance value between electrodes 5A and 5B is adjusted by cutting the ladder-like resistor 7.

However, these methods all involve removing a part of the formed resistor, and adjustment is made by increasing the resistance value from the original value.
If the resistance value was higher than the required value, adjustment was not possible. In addition, since the resistance value is adjusted after the semiconductor integrated circuit is completed, the entire circuit is coated with a passivation film, and the passivation film is also removed in the laser removal section, so from the standpoint of reliability, that part must be repassivated. It was necessary to coat it with a film.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to make it possible not only to increase but also to decrease the resistance value created in advance, and to provide a resistor in a semiconductor integrated circuit that does not damage the passivation film. It is an object of the present invention to provide a method for adjusting the resistance value of the body.

[Summary of the invention]

In order to achieve the above object, the present invention provides a method for adjusting the resistance value of a resistor in a semiconductor integrated circuit, which is formed in a semiconductor integrated circuit, doped with a first conductivity type impurity to a concentration close to a predetermined value, and a film containing impurities of a first conductivity type in the vicinity of the polycrystalline silicon resistor covered with the film;
A film containing impurities of a second conductivity type opposite to the conductivity type is provided, and through the passivation film,
When it is desired to lower the resistance value of the resistor, a predetermined region of the film containing the impurity of the first conductivity type is used, and when it is desired to increase the resistance value, a predetermined region of the film containing the impurity of the second conductivity type is diffusing the impurity from the impurity-containing film toward the resistor by irradiating the region with a laser beam and heating it;
The gist is to reduce or increase the above resistance value. That is, the present invention uses polycrystalline silicon doped with impurities as a resistor, and further diffuses impurities of the same conductivity type as the impurities doped into the polycrystalline silicon resistor by laser heating to reduce the resistance value. Alternatively, by diffusing impurities of opposite conductivity type to increase the resistance value, the resistance value is reduced or increased, and the resistance value is adjusted to the required value.

The resistance value of the resistor can be determined by irradiating a fixed area on the resistor and changing the amount of irradiation.
This can also be done by keeping the irradiation amount per unit area constant and changing the irradiation area. To change the irradiation amount, it is convenient to change the irradiation time or the number of pulses.

Hereinafter, the present invention will be explained in more detail using examples with reference to the drawings, but these are merely illustrative and it is understood that various modifications and improvements may be made without going beyond the scope of the present invention. Of course.

[Embodiments of the invention]

FIG. 4 shows a resistor formed on a semiconductor integrated circuit to which the resistance value adjustment method of the present invention is applied. FIG. 4a is a plan view, and FIG. 4b is a sectional view thereof. A polycrystalline silicone resistor 11 doped with an n-conductivity type impurity is formed on a Si substrate 1 via a SiO ₂ film 2, and both ends thereof are connected to Al wiring 12A.
and 12B to other elements (for example, diodes and transistors). On the _{polycrystalline} silicon resistor 11, there is a p
A polycrystalline silicon layer 14 doped with a conductive type impurity at a high concentration is formed in the form of an island, and SiO ₂
Layer 15, phosphor glass layer 16, SiO ₂ layer or Si ₃ N ₄
A final passivation film 17 consisting of one or both layers is formed.

Generally, the polycrystalline silicon resistor 11 is doped with phosphorus as an n-conductivity type impurity, has a thickness of 50 to 500 nm, and has a sheet resistance value of several tens of Ω/□ to 100 Ω.
Formed as Ω/□. Furthermore, the _SiO2 layers 13 and 15 each have a thickness of 50 to 300 nm, and the polycrystalline silicon layer 14 doped with p conductivity type impurities has a thickness of 50 to 300 nm.
The phosphorus glass film 16 has an impurity concentration of 50 to 500 nm, which is about the same as that of the resistor 11, and the phosphorus concentration of the phosphorus glass film 16 is 1 to 10 nm.
The final passivation film 17 has a thickness of 100 to 4000 nm in terms of mole %.

Here, as a sample, polycrystalline silicon resistor 1
1 is polycrystalline silicon doped with phosphorus, and the film thickness is
300nm, sheet resistance 10kΩ/□, width 5μm, length
The SiO ₂ films 13 and 15 each have a film thickness of 70 nm, the phosphorous glass film 16 has a film thickness of 4 mol % and a film thickness of 400 nm, and the passivation film 1 has a film thickness of 400 nm.
For No. 7, a single layer film of Si ₃ N ₄ with a thickness of 1000 nm was used.

A predetermined region of the polycrystalline silicon resistor shown in FIG. 4 is irradiated with a laser beam using the optical system shown in FIG. That is, the optical system shown in FIG.
A variable slit 2 that can shape a laser beam 21 emitted from a laser oscillator (not shown) into any size.
2, the objective lens 23 is formed into a rectangular shape that matches the shape of the irradiation onto the resistor 11, and the objective lens 23 is formed through the variable slit 22.
The light is transmitted through insulating films 17, 16, 15, and 13, and is focused at a magnitude that is the reciprocal of the magnification of the objective lens 23, and is projected onto a resistor 11 placed at a position where a real image is formed. . Note that in FIG. 5, the layer formed on the resistor 11 is omitted. The laser oscillator is also an _N2 laser pumped die.
The wavelength of the laser light is 510 nm, and the pulse width is 6 ns at half maximum.

Here, with respect to the polycrystalline silicon resistor 11 shown in FIG.
That is, a laser beam was projected through the SiO ₂ films 13 and 15 to a length of 10 μm in the portion where the phosphor glass film 16 was present. The relationship between the number of irradiated laser pulses and the resistance value at this time is shown in FIG. The resistance value, which was approximately 60kΩ before laser irradiation, decreased with the number of irradiation pulses and reached 10kΩ.
It showed a relatively rapid change at ~30 pulses, and had a constant value of 41 kΩ after 50 pulses, with almost no change. Therefore, by irradiating with a laser beam while measuring the resistance value, and stopping the irradiation when the predetermined resistance value is obtained, it is possible to
It can be adjusted to any resistance value between Ω (although it changes stepwise rather than continuously due to pulse irradiation).

Next, the polycrystalline silicon resistor 11 shown in FIG.
Laser radiation is applied within a 5 μm length area through the SiO ₂ film 15, phosphorous glass film 16, and passivation film 17.
Irradiated with a beam. The relationship between the number of irradiated laser pulses and the resistance value at this time is shown in FIG. The resistance value, which was about 60 kΩ before laser irradiation, showed a relatively rapid change between 30 and 60 pulses, and after 70 pulses, it had a constant value of 84 kΩ and hardly changed. From this, by stopping laser irradiation when a predetermined resistance value is obtained, the resistance value can be adjusted to any value between 60kΩ and 84kΩ (although it changes stepwise rather than continuously due to pulsed irradiation). can do. That is, by selecting the laser irradiation position for the polycrystalline silicon resistor shown in Fig. 4, the initial value can be determined.
Starting from 60kΩ, the resistance value can be adjusted to any value between 41 and 84kΩ. The irradiation laser power density at this time was set to 1/3 of the power density that can perform removal processing on the polycrystalline silicon resistor 11 with 1 to 2 pulses, but even after 100 pulses irradiation,
No damage or traces were found on the passivation film 17.

In the embodiment described above, the adjustment range of the resistance value is about ±30% of the initial value, but this adjustment range is variable depending on the configuration of the polycrystalline silicon resistor 11 and its surroundings. it is obvious. That is, the length of the island-shaped polycrystalline silicon layer 14 doped with p-conductivity type impurities formed on the polycrystalline silicon resistor 11 to cover the polycrystalline silicon resistor 11 (in the direction connecting electrodes 5A and 5B) ),
In addition, by increasing the length of laser irradiation or by increasing the impurity concentration of the island-shaped polycrystalline silicon layer 14 doped with p conductivity type impurities, the resistance value can be adjusted to a higher value. The resistance value can be adjusted to a lower value by increasing the portion (length) that is not covered by the island-shaped polycrystalline silicon layer 14 doped with conductive type impurities and by increasing the length over which the laser is projected. becomes.

Furthermore, in this embodiment, polycrystalline silicon doped with n-conductivity type impurities was used as the polycrystalline silicon resistor 11, but polycrystalline silicon doped with p-conductivity type impurities was used as the resistor. By using an island-shaped polycrystalline silicon layer doped with an n-conductivity type impurity and forming boron glass instead of phosphorous glass, the resistance value can be increased or decreased in the same way. It is clear that this can be done.

In the above embodiment, a film containing an impurity of the same conductivity type as the polycrystalline silicon resistor 14 (FIG. 4b)
Although the phosphorous glass layer 16) and the film containing impurities of the opposite conductivity type (the polycrystalline silicon film 14 in FIG. 4b) are provided on the polycrystalline silicon resistor 14, these films are not necessarily used as resistors 14 and when heated by the laser beam,
The impurities contained in the insulating film surrounding the resistor 14 (in FIG. 4b, the SiO ₂ film 13,
Alternatively, as long as it is close enough to diffuse through the SiO ₂ films 13 and 15 to the polycrystalline silicon resistor, it is of course possible to place it on the side or below.

In addition, in this embodiment, as the laser beam 21, N ₂
A laser-excited dye laser is used, but is not limited to this, and can heat polycrystalline silicon with a wavelength that passes through the passivation film 17, phosphor glass film 16, and SiO ₂ films 15 and 13. If so, regardless of continuous oscillation or pulse oscillation,
The applicability is clear. When the passivation film 17 is SiO ₂ , the films 15, 16, 1
7 is all SiO ₂ and is transparent to wavelengths from 300 nm to 2 μm. Passivation film 17
When using Si ₃ N ₄ , the thickness of films 15, 16, and 17 is 400 nm ~
Transparent to a wavelength of 2 μm. If the laser light is not transparent to the films 15, 16, and 17, the laser light will be absorbed by those films, which will not only increase the temperature of those films and cause damage, but also cause polycrystalline damage. The energy necessary for heating the silicon layer cannot be supplied. When the wavelength is 1.1 μm or more, the laser light passes through Si and does not heat the polycrystalline silicon layer, so the wavelength of the laser light used must be between 400 nm and 1.1 μm.

The SiO ₂ films 13 and 15, which are intermediate permeable layers, are turned into phosphorus silicates or borosilicate, and pinholes are formed in these films, but pinholes are formed in the final passivation film 17, and the pinholes are removed. As long as this is not the case, it will not be a problem for the integrated circuit as a whole.

FIG. 8 is a plan view for explaining a method for adjusting the resistance value of a resistor in a semiconductor integrated circuit according to a second embodiment of the present invention. As shown in FIG. 8, the length of the laser irradiation area 24A on the polycrystalline silicon resistor 11 shown in FIG. Move the area by 2 μm to create the laser irradiation area 24.
Irradiate B with 50 pulses. By repeating this step by step, the resistance value decreased step by step. In other words, as shown in Figure 9, the initial value of approximately 60 kΩ decreases by approximately 3.8 kΩ as the number of irradiations increases (50 pulses of irradiation in each laser irradiation area is considered to be one time), and the number of irradiations decreases to 7. It decreased to 33kΩ. The length of the irradiation area at this time was 14 μm.

Moreover, on the island-shaped polycrystalline silicon layer 14 provided on the polycrystalline silicon resistor 11 and doped with an impurity different from the impurity doped into the polycrystalline silicon resistor, the By irradiating each laser irradiation area with 70 pulses, the resistance value increased stepwise. That is, the fourth
By selecting the irradiation position for the polycrystalline silicon resistor shown in the figure (or FIG. 8), the initial resistance value can be increased or decreased as desired.

Furthermore, in this example, we have explained the case of laser irradiation using the optical system shown in FIG. It is clear that exactly the same effect can be obtained by repeating the procedure of irradiating 70 pulses, moving the irradiation position, and irradiating the laser further.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to arbitrarily increase or decrease the resistance value of a resistor in a semiconductor integrated circuit without damaging the passivation film, thereby achieving high performance and highly reliable semiconductor integrated circuits. The effect is that circuits can be manufactured with high yield.

[Brief explanation of drawings]

FIGS. 1 to 3 are perspective views for explaining three different conventional methods for adjusting the resistance value of a resistor in a semiconductor integrated circuit, and FIGS. 4a and 4b are perspective views to which the resistance value adjustment method of the present invention is applied. 5 is a plan view and a sectional view of a resistor formed on a semiconductor integrated circuit, respectively. FIG. 5 is a perspective view of a laser optical system for carrying out the resistance value adjustment method according to the present invention. FIGS. Figure 7 is a diagram showing the relationship between the number of irradiation pulses and the resistance value of the resistor when a region of the opposite conductivity type and a region of the same conductivity type as the resistor are irradiated with a laser beam, respectively, and Figure 8 is a diagram showing the relationship between the number of irradiation pulses and the resistance value of the resistor. FIG. 9, which is a plan view for explaining the resistance value adjustment method according to another embodiment, is a diagram showing the relationship between the number of irradiations and the resistance value of the resistor in the embodiment shown in FIG. DESCRIPTION OF SYMBOLS 1...Si substrate, 2... _SiO2 film, 11...n-type polycrystalline silicon resistor, 12A, 12B...electrode, 13, 15... _SiO2 film, 14...p-type polycrystalline silicon layer, 16... Phosphorous glass film, 17... Final passivation film, 21... Laser light, 22
...Variable slit, 23...Objective lens, 24
A, 24B...Laser irradiation area.

Claims (1)

[Scope of Claims] 1. A first conductive layer formed in a semiconductor integrated circuit, doped with a first conductive type impurity to a concentration close to a predetermined value, and provided in the vicinity of a polycrystalline silicon resistor covered with a passivation film. When it is desired to lower the resistance value of the resistor through the passivation film by providing a film containing an impurity of a type impurity and a film containing an impurity of a second conductivity type opposite to the first conductivity type, the first When it is desired to increase the resistance value of a predetermined region of the film containing conductive type impurities, the second
A predetermined area of the film containing conductive impurities is irradiated with a laser beam.
A resistor of a resistor in a semiconductor integrated circuit, characterized in that the impurity is diffused from the impurity-containing film toward the resistor by irradiation with a beam and heating, thereby reducing or increasing the resistance value. Value adjustment method. 2. Claim 1, characterized in that the irradiation is performed over a constant area of the resistor, and the resistance value of the resistor is controlled by controlling the degree of diffusion. A method for adjusting the resistance value of a resistor in a semiconductor integrated circuit. 3. The resistance value of the resistor in the semiconductor integrated circuit according to claim 2, wherein the degree of diffusion of the impurity is controlled by controlling the irradiation time or the number of pulses of the laser. Adjustment method. 4. Resistance value adjustment of a resistor in a semiconductor integrated circuit according to claim 1, wherein the resistance value of the resistor is controlled by controlling the area irradiated with a laser beam. Method.