JPH0512862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for adjusting the resistance value of a semiconductor integrated circuit having a poly-Si resistor whose resistance value is controlled.

[Background of the invention]

In recent years, semiconductor integrated circuits have become more highly integrated and have higher performance. Therefore, a method has come to be used in which the resistance value of a resistor formed within 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 the method commonly used for adjusting thick film or thin film resistors formed on ceramic substrates. That is, as shown in FIG. 1, SiO ₂ is deposited on the Si substrate 1.
A resistor 3 made of tantalum nitride, chromium silicon, nichrome, polysilicon, etc. is insulated by a film 2, etc., and a part of the resistor 3 is removed using a laser beam 4. For example, the resistance value between the electrodes 5 and 5' at both ends of the resistor 3 is adjusted. Alternatively, as shown in Fig. 2, the resistor 3 is subjected to spot processing (processing traces 6), or as shown in Fig. 3, the resistance value 7 is shaped like a ladder step.
A method has been used in which the resistance value between the electrodes 5 and 5' is adjusted by cutting the electrodes 5 and 5'.

However, all of these methods remove a part of the formed resistor and adjust by increasing the initial resistance value, so if the initial resistance value is higher than the required value, It was impossible to adjust it lower. 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 if a part of the resistor is removed, the passivation film is also removed, which is a problem from a reliability standpoint. ,
It was necessary to coat the passivation film again.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for adjusting the resistance value of a semiconductor integrated circuit, which eliminates the above-mentioned drawbacks of the prior art and allows the resistance value to be increased or decreased without damaging the passivation film.

[Summary of the invention]

In the present invention, polysilicon doped with impurities is used as a resistor, and a high resistance region not doped with impurities at all or doped with a small amount of impurities is provided in a part of the resistor so as to cross the direction of current flow. The same type of impurity doped into the polysilicon resistor can be diffused into the high resistance region using laser heating to reduce the resistance value, or a different type of impurity can be diffused into the polysilicon resistor to increase the resistance. By increasing the resistance value, the resistance value is reduced or increased and adjusted to the required (optimal) resistance value.

[Embodiments of the invention]

The present invention will be explained below with reference to the drawings. FIG. 4 shows a resistor formed in a semiconductor integrated circuit illustrating the principle of the present invention. Figure 4a is a plan view, Figure 4b
is a cross-sectional view of the SiO ₂ film 2 on the Si substrate 1.
Poly doped with n-type impurities through
-Si resistor 11 is formed, and both ends thereof are connected to other elements (diodes, transistors, etc.) via Al wirings 12, 12'. On the Poly-Si resistor 11, a Poly-Si layer 14 doped with an n-type impurity and a Poly-Si layer 15 doped with a p-type impurity are formed in an island shape via a SiO ₂ film 13. on which a SiO ₂ layer 16 and a final passivation film 17 are formed.
A film consisting of _two SiO layers, _four Si ₃ N layers, or both is formed.

Generally, the poly-Si resistor 11 is doped with phosphorus as an n-type impurity, has a thickness of 500 to 5000 Å, and has a sheet resistance of several tens of Ω/□ to several 100 KΩ/□. Moreover, the thickness of the SiO ₂ layer 13 is 500~
3000Å, n-type impurity doped Poly
-Si layer 14 has a thickness of 500 to 5000 Å and has an impurity concentration one order of magnitude higher than that of the Poly-Si resistor, and the Poly-Si layer 15 doped with p-type impurities has a thickness of 500 to 5000 Å and -It has an impurity concentration comparable to that of the Si resistor 11. Further, the SiO ₂ layer 16 formed thereon has a thickness of 500 to 3000 Å, and the final passivation film 17 has a thickness of 1000 to 4000 Å.

Here, as a sample, a poly-Si resistor 11 formed of phosphorus-doped poly-Si having a film thickness of 3000 Å, a sheet resistance of 10 KΩ/a width of 5 μm, and a length of 45 μm was used. The poly-Si resistor shown in FIG. 4 is irradiated with a laser using the optical system shown in FIG. That is, the optical system shown in FIG. 5 has a variable slit 22 formed in the resistor 11 and its upper layer by a variable slit 22 that can shape the laser beam 21 oscillated by a laser oscillator (not shown) into any size.
It is formed into a rectangular shape that matches the shape of the irradiation onto the Poly-Si layer 14 or 15.
The resistor 11 is placed at a position where the real image of the variable slit 22 connects, and the Poly-
The structure is such that the Si layer 14 or 15 is irradiated with condensed light that passes through the insulating films 16 and 17 and has a magnitude that is the reciprocal of the magnification of the objective lens 23. Note that the insulating films 16, 17, etc. are omitted in FIG. 5. Furthermore, the laser oscillator uses an N ₂ laser pumped Dye laser, and the laser beam has a wavelength of 60 nm and a pulse width of 6 ns at half maximum.

Here, the Poyh-Si resistor shown in Figure 4 is doped with n-type impurities.
A partial laser beam having a length of 15 μm was irradiated onto the Poly-Si antibody body 11 separately through the Poly-Si layer 14 and the Poly-Si layer 15 doped with a p-type impurity. The relationship between the number of laser irradiation pulses and the resistance value at this time is shown in the sixth table. Approximately before laser irradiation
When the n-layer 14 is irradiated, the resistance value, which was 90KΩ, decreases with the number of irradiation pulses as shown by ○.
It becomes constant at 61KΩ after about 50 pulses, and when the P layer 15 is irradiated, it becomes about 70KΩ as shown in
It became constant at 150KΩ. ) In Figure 6, the resistance value is plotted every 10 pulses. ) From this, by selecting the position to irradiate the laser, irradiating the laser while measuring the resistance value, and stopping the irradiation when the predetermined resistance value is obtained, the resistance value, which was originally 90KΩ, can be reduced. 61KΩ～
This means that it can be adjusted to any resistance value between 150KΩ (although it changes stepwise rather than continuously due to pulse irradiation). At this time, the irradiation laser power density was 1 to 2 pulses, and the poly-Si resistor 1
Although the power density was set at 1/3 of the power density that can perform removal processing on 1 (in the case where there is no Poly-Si layer 14 or 15 on top), there was no damage or trace on the passivation film 17 even after irradiation with 100 pulses. I couldn't find it either.

In the explanation of the principle of the present invention described above,
The adjustment range of resistance value is -32% to +66 relative to the initial value.
% range, but this adjustment range is
It is clear that the n-type and p-type impurities covering the resistor 11 can be varied by changing the areas of the doped poly-Si layers 14 and 15. That is, by increasing the area of the n-type Poly-Si layer 14 in the upper layer of the Poly-Si resistor 11, the range in which the resistance value decreases is widened, and the p-type
By increasing the area of the Poly-Si layer 15,
It is clear that the range of increase in resistance value is expanded.

Furthermore, in explaining the principles of the present invention,
Although Poly-Si doped with n-type impurities was used as the poly-Si resistor 11, it is also possible to use poly-Si doped with p-type impurities as the resistor.

In addition, when using an n-type Poly-Si resistor, a PSG (phosphorus glass) layer may be formed in place of the n-type Poly-Si layer 14 in the upper layer, or a PSG (phosphorus glass) layer may be formed.
When using a type Poly-Si resistor, by forming a BSG (boron glass) layer instead of the p-type Poly-Si layer 15, the resistance value can be increased or decreased as desired in exactly the same way. is clear.

Furthermore, in the explanation of the principle of the present invention, an _N2 laser excitation Dye laser is used as the laser beam 21, but the invention is not limited to this.
At the wavelength that passes through the passivation films 16 and 17
Continuous oscillation, as long as it can heat Poly-Si
It is clear that the invention is applicable regardless of pulse oscillation.

Next, another example showing the principle of the present invention will be explained. As shown in Figure 7, Poly-
With respect to the Si resistor 11, the length of the laser irradiation area 25 is 2 μm, and the laser irradiation conditions described above are n
Type Poly-Si layer 14 or p-type Poly-
The process of irradiating 70 pulses through the Si layer 15k, then moving 2 μm and irradiating the laser irradiation area 25' with 70 pulses was repeated. This allows n-type Poly
When irradiating through the -Si layer 14, the resistance value decreased stepwise, and when irradiating through the p-type Poly-Si layer 15, it increased stepwise. In other words, as shown in Figure 8, the initial value of 90KΩ changes with the number of irradiations (70 pulses irradiated to the laser irradiation area is considered to be one time).
- When irradiated through the Si layer 14, it decreases by about 4KΩ as shown by ○, and after 7 times of irradiation (the length of the irradiation area is 14μm), it decreases to 62KΩ, and the p-type
When irradiation was performed through the Poly-Si layer 15, the resistance increased by about 8KΩ as shown by ●, and changed to 146KΩ after 7 irradiation times (the length of the irradiation area was 14 μm).

From this, by selecting the irradiation position for the Poly-Si resistor shown in FIG. 4, the initial resistance value can be increased or decreased as desired.

Next, FIG. 9 shows a first embodiment of a resistor according to the present invention that can increase or decrease the resistance value.

A poly-Si resistor 27 doped with n-type impurities is formed between the Al electrodes 12 and 12'. The n-type Poly-Si resistor 27 has a so-called "ladder step" shape in which multiple resistors are arranged in parallel. A high-resistance portion 30 is formed in a part of the region. This high-resistance portion 30 is made of Poly-Si (doped with no impurity) having a resistance value sufficiently greater than that of the Poly-Si resistor 27. Furthermore, the high resistance section 30
The _upper layer of the
A PSG film (not shown) is formed. on the other hand,
The lower half Poly-Si resistor 27' in FIG. 9 similarly has a ladder-like shape, and except for the longest part of the resistor, the upper layer of the ladder-like resistor has the following shapes: A poly-Si layer 31 doped with p-type impurities is formed in an island shape with a SiO ₂ layer (not shown) interposed therebetween. The resistance value of this resistor is mainly determined by the longest distance in the ladder step provided with the high resistance part 30, and the shortest distance in the ladder step provided with the poly-Si layer 31 doped with p-type impurities. It can be thought that only the parts form a resistor. (To be exact, the low antibodies in the form of ladder steps are connected in parallel, and the resistance value is determined as the reciprocal of the sum of the reciprocals of their respective resistance values.) First, let us consider the ladder step section where the high resistance section 30 is provided. Then, when the laser is irradiated using the optical system shown in FIG. 5 so as to sufficiently overlap the high resistance part 30 and the resistor 27 at both ends thereof, the PSG film formed on the upper layer of the resistors 27 and 30 (Fig. (not shown), phosphorus diffuses into the high resistance part 30, and the high resistance part 30
The resistance value drops sufficiently and a short circuit occurs. That is, the high resistance part 3 on the side where the distance of the resistor 27 is the longest
By sequentially irradiating the laser beam starting from 0, the resistance value between 12 and 12' decreases in stages.

In addition, polystyrene doped with p-type impurities
When a laser beam is irradiated onto the step part of the ladder having the -Si layer 31 so as to sufficiently overlap it in the width direction of the resistor 27, the p-type impurity is diffused and the resistance value of the laser irradiated part increases. When the impurity concentration of the Poly-Si layer 31 was set to a level that balanced the impurity concentration of the resistor 27 after laser irradiation, the laser irradiated part obtained an extremely high resistance value, and the laser irradiated part changed into an insulating layer. It can also be considered as That is,
The resistance between the electrodes 12 and 12' is reduced by irradiating the poly-Si layer doped with a p-type impurity and the resistor 27 below it with a laser, starting from the side with the shortest distance between the resistors 27. The value increases step by step. From the above, by selecting the laser and the position to be irradiated, the resistance value between the electrodes 12 and 12' can be increased or decreased as desired. Next, FIG. 10 shows a second embodiment of the resistor according to the present invention, which can increase or decrease the resistance value.

A poly-Si resistor 32 doped with n-type impurities is formed between the Al electrodes 12 and 12'. Of the n-type Poly-Si resistor 32,
The resistance value adjustment section is rectangular, and a high resistance section 33 having a constant width is formed in a direction perpendicular to the path through which the current flows, except for a portion thereof. This high resistance part 33 is made of Poly-
Poly with a sufficiently larger resistance value than the Si resistor 32
-Si (doped with impurities is not required). Furthermore, in the upper layer of the high resistance section 33,
PSG film (not shown) through SiO ₂ layer (not shown)
is formed. In addition, p-type impurities were doped into the upper layer of the resistor 32 at a position sufficiently away from the high-resistance portion 33 and parallel to the high-resistance portion 33.
The Poly-Si layer 34 has an island shape, and the SiO ₂ layer (not shown in the figure)
It is formed with the exception of a part. The resistance value of this resistor is mainly determined by the shape excluding the high resistance portion 33.

First, from the side where the resistor 32 remains so as to sufficiently overlap the high resistance part 33 and the resistor 32 around it, a certain condition (for example, a power that can remove the resistor 32) is applied. By increasing the laser irradiation area while irradiating the laser with a power density of 1/3 (100 pulses),
Phosphorus diffuses into the high resistance part 33 from the PSG film (not shown) formed on the upper layer of the resistor 32 via the SiO ₂ film, and the high resistance part becomes resistant.
The resistance value between the Al electrodes 12 and 12' decreases.

In addition, Polymer doped with p-type impurities
- By sequentially increasing the laser irradiation area under the above conditions from the side opposite to the side where the resistor 32 remains on the part having the Si layer 34,
Since p-type impurities diffuse into the resistor 32 and the resistance value of the laser irradiated part increases, the Al electrode 12
and 12' increases. From the above, by selecting the laser irradiation position, the resistance value between the electrodes 12 and 12' can be increased arbitrarily.
can be reduced. Moreover, in the case of the resistor shown in FIG. 9, the resistance value changed stepwise, but in the case of this example, by making the movement pitch of the laser irradiation position sufficiently fine, the resistance value changes almost continuously. The resistance value can be changed to

In the embodiment shown in FIGS. 9 and 10, the resistor 2
7 and 32 show cases where a Paly-Si layer doped with n-type Poly-Si, PSG as the n-type impurity source, and p-type impurity doped as the P-type impurity source, but the present invention is not limited to this. It's not something you can do. For n-type Poly-Si resistor,
As an n-type impurity source, an n-type impurity-doped Si layer (Poly
- or doped with a metal film that serves as an n-type impurity (not limited to Si), a BSG film as a p-type impurity source, or a metal film that serves as a p-type impurity, and a p-type impurity as a resistor. It is clear that exactly the same effect can be obtained using Poly-Si.

Furthermore, although the impurity source was formed in the upper layer of the resistor in this example, the impurity source is not limited to this.
For example, it may be formed in the lower layer of the resistor (via a SiO ₂ film serving as a barrier), which is particularly suitable when a metal film is used as an impurity source.

Furthermore, in this embodiment, a case has been described in which laser irradiation is performed using the optical system shown in FIG. 5, but the invention is not limited to this. The same effect can be obtained by irradiating a focused spot.

〔Effect of the invention〕

According to the present invention, by providing a high resistance portion in a part of the resistor, the resistance value of the resistor can be significantly reduced easily and with high precision. Furthermore, as mentioned above, the resistance value of the resistor in the semiconductor integrated circuit can be increased or decreased arbitrarily without damaging the buffering film, making it possible to manufacture high-performance, highly reliable semiconductor integrated circuits at high yields. It has the effect of being able to be manufactured.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams explaining the conventional resistance value adjustment method, Figure 4 is a diagram showing the structure of a resistor to explain the principle of the present invention, and Figure 5 is a diagram showing the resistance of the resistor of the present invention. Explanatory diagram of the laser optical system most suitable for value adjustment, Part 6
The figure shows the number of laser irradiation pulses and the change in resistance value in explaining the principle of the present invention, Figure 7 shows the laser irradiation method in explaining the principle of the present invention, and Figure 8 shows the principle of the present invention. FIG. 9 is a diagram showing the first embodiment of the resistor of the present invention, and FIG. 10 is a diagram showing the second embodiment of the resistor of the present invention. FIG. Explanation of symbols, 1...Si substrate, 2...SiO ₂ film,
3, 11, 27, 32...Resistor, 5, 12...
Electrode (pad), 13... SiO ₂ film, 14... Poly-Si doped with n-type impurity, 15, 3
1...Poly-Si doped with p-type impurities,
16, 17...Insulating film (passivation film),
30, 33...High resistance part.

Claims (1)

[Scope of Claims] 1. In a semiconductor integrated circuit having a resistor doped with a conductive impurity, a part of the resistor is provided with a high-low resistance part, and another part of the resistor is provided with a resistance part of the resistor. A region for adjusting the resistance value is provided, a first layer containing the same conductive impurity as the impurity doped in the resistor is provided in the upper layer of the high resistance portion, and further, a region for adjusting the resistance value is provided. A second layer containing a conductive impurity opposite to the impurity doped in the resistor is provided in the upper layer, and the first layer is irradiated with a laser beam to remove the conductive impurity in the first layer. or by irradiating the second layer with laser light to remove the impurities of the opposite conductivity from the second layer. A method for adjusting a resistance value of a semiconductor integrated circuit, characterized in that the resistance value of the resistor is adjusted by diffusing into a region where the resistance value is to be adjusted and increasing the resistance value in the region where the resistance value is to be adjusted. 2. The resistance value adjustment of a semiconductor integrated circuit according to claim 1, wherein the high resistance portion is provided in an elongated shape substantially perpendicular to the direction of the current flowing through the resistor. Method. 3. Claim 1, wherein the concentration of impurities contained in the first layer and the concentration of impurities contained in the second layer are higher than the concentration of impurities doped into the resistor. A method for adjusting the resistance value of a semiconductor integrated circuit as described in .