JPS6245701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a funk which precisely controls a semiconductor device, particularly a semiconductor integrated circuit including a thin film resistive element for trimming, by fusing a portion of the thin film resistive element with a laser beam while measuring the electrical characteristics of the semiconductor integrated circuit. An object of the present invention is to prevent electrical effects on the semiconductor integrated circuit due to laser beam irradiation regarding a semiconductor device to be subjected to side trimming.

Analog-to-digital converter (A/D) as an interface between analog and digital signals
In line with recent advances in LSI technology, all functions of digital-to-analog converters and digital-to-analog converters (D/A converters) have been integrated into monolithic ICs, and they are becoming more accurate and faster. In particular, in order to improve precision, the thin film resistive elements are trimmed one by one in order to correct manufacturing variations in the formed thin film resistive elements. That is, in a high-precision A/D converter, it is necessary to adjust many resistance values with extremely high precision, so it is necessary to melt part of the resistance with a laser beam to delicately adjust the resistance value. Trimming is performed by applying a bias voltage to the semiconductor integrated circuit to put the circuit in an operating state, and by irradiating the semiconductor integrated circuit with a laser beam capable of microfabrication while observing the output voltage or current value. In other words, this so-called resistance value control is function-trimmed.

Conventionally, in a hybrid type in which a thin film resistive element and other functional circuit blocks are formed on separate semiconductor substrates, even if the semiconductor substrate on which the thin film resistive element is formed is irradiated with laser light for processing, the semiconductor substrate is Since they were separate, there was no effect on the active elements. However, due to recent demands for higher precision, higher speed, and reliability in A/D converters and the like, monolithic structures are being implemented in which thin film resistive elements are integrated with other functional circuit blocks on the same semiconductor substrate. In this case, it has been found that irradiating the same semiconductor substrate with processing laser light has a significant electrical effect on functional circuits that are integrated therein, including active elements other than resistors.

In particular, in monolithic A/D converters, in order to form an integrated structure that includes high-speed logic circuits and current switching circuits, the epitaxial layer must be thinned from the conventional 10-odd micrometers to several micrometers, making it possible to create high-speed devices. The current situation is that we are trying to be adaptable. Therefore, the depth of the pn junction of other integrated circuit elements to be formed after this is also shallow, with diffusion of about 1 μm. On the other hand, the diameter of the laser beam for microfabrication is desirably 20 μm or less in view of the relationship between the shape of the thin film resistor element and precision. Therefore, laser light has a wavelength of 1.06 μm.
YAG is used. The bandgap energy of silicon is 1.1ev, but based on its distribution, laser light with a wavelength of 1.06μm is sufficient to excite the bandgap. In addition, the absorption depth of laser light with a wavelength of 1.06 μm from the silicon surface is 0.9 μm.
Since it is before and after, the shallow junction is sufficiently excited as described above.

Therefore, if a laser beam with a wavelength of 1.06 μm and the energy necessary to trim the thin film resistor (1 to 3 J/cm ² based on absorption efficiency) is irradiated onto the semiconductor substrate to which a bias voltage is applied, the thin film resistor will be trimmed. After trimming, it passes through the silicon oxide film and is absorbed into the underlying silicon. the result,
Generates carrier generation of electrons and holes. Most of the carriers generated are recombined, but the bleeding of the laser light excites shallow junctions in transistors and other devices located away from the irradiated point.
Laser light bleed is estimated to have a diameter of several 100 μm, depending on the converging lens system, so to prevent junction excitation, it is necessary to provide a buffer space of several 100 μm around the thin film resistor, which is difficult to achieve with high density. This is extremely disadvantageous. In addition, there is excitation due to the reflection of laser light, and during trimming the IC chip is placed under constant illumination and monitored with a TV camera, so shallow junctions generate leakage current due to light other than laser light.

Further, since a bias is applied to the semiconductor substrate and the circuit is in an operating state, the bias state is momentarily disturbed during the application time of the laser light (for example, about 100 to 200 nsec). This disturbance occurs within the semiconductor substrate as a pulsed noise voltage. This pulsed noise voltage can cause transistor leakage current,
Sometimes an abnormal current of several 100mA flows between the power supply terminal and the common ground terminal. This phenomenon in which abnormal current flows is usually called latch-up, but to stop it, the power must be turned off or lowered, and trimming may become impossible. but,
If this latch-up is left unchecked, it will destroy the transistor junction and cause the aluminum wiring to melt. The cause of the latch-up phenomenon is the generation of pulse noise voltage due to laser light irradiation, which induces secondary causes. Although this depends on the arrangement of each device in the semiconductor integrated circuit, it is often structurally composed of PNP transistors and NPN transistors to form a positive feedback loop between power supply terminals. PNP
A positive feedback loop formed by a transistor and an NPN transistor equivalently becomes a thyristor, and the latch-up phenomenon caused by laser light irradiation is caused by an optical thyristor that triggers the gate of the thyristor with light.

To prevent latch-up, it is possible to change the wavelength of the laser beam or lower the energy, but the former makes microfabrication impossible and high integration impossible, and the latter makes it impossible to trim the resistive element.

Furthermore, conventional problems will be considered according to FIGS. 1a and 1b. In FIG. 1a, 1 is the thin film resistor, and 2 is a metal film such as Al, which is in contact with the thin film resistor. 3 and 4 are other circuit blocks connected to the resistor, respectively. In this figure, 1 is, for example, a resistance element of a ladder resistance network of an A/D converter, or a weighting resistance. Reference numeral 5 indicates a light spot A of light or laser light during trimming, and in a laser trimming device that currently has an output of about 1 J (joule)/cm ² , the minimum dimension is about 10 μm.

B shows the blurring of light around spot A, which is affected by the performance of the Q switch, the type of lens, etc., and is much more spread out than spot A.

In Figure 1a, the distance between the thin film resistive elements 1 on the semiconductor substrate is usually several tens of micrometers, but this is due to the fact that the bleeding of such spots is quite large, and this prevents the thin film from being trimmed in unnecessary areas. This is to prevent it.

Further, the explanation will be given again with reference to FIG. 1b, which is a cross section of the integrated circuit. In FIG. 1b, 6 indicates a bipolar transistor substrate, which is made of a P-type silicon substrate. 7 is an n-type epitaxial layer;
Reference numeral 8 denotes a separation diffusion part formed of p ⁺ (high concentration p-type part), 9 a base part, 10 an emitter part, 11 a collector part 12 is a CVDSiO ₂ film. During trimming, the light (hν) is irradiated between the thin film resistor parts 1 together with the spot A or its blur B, so the irradiated photons generate pairs of electrons and holes in the semiconductor substrate, and the electrons and holes are Inside each hole, some are quickly recombined, while some flow due to drifting fields or by diffusion, thereby creating a potential gradient. In particular, the distance between the thin film resistors is shorter than the part where there is a thin film resistor to the substrate, and the difference is not noticeable at a wavelength of 10.6 μm such as with a CO ₂ laser, but with a YAG laser (wavelength of 1.06 μm), Argon laser (0.5-0.6μm)
etc., the penetration depth of light is short, so the effect on the substrate is extremely large compared to the case where there is a thin film resistor.

Now let's try to roughly estimate the photovoltaic force. Now the laser source is YAG and its peak power is about 80KW
be. The pulse width is 150ns. The energy released by one irradiation was 80KW x 150ns = 1.2 x 10 ^-2 J, which means that about 12mJ was released. Now, assuming that the loss of light energy due to diffuse reflection, condensing system, etc. and the conversion efficiency from light to electricity are approximately 0.4%, and comparing it with the electrical charge accumulated in the capacitor (1000PF), it is 1.2%. ×10 ^-2 (J) × 0.004 = 1/2 × 1000 × 10 ^-12 ×V ^2Here , V is the voltage stored in the capacitor. V will be approximately 300V.

Laser irradiation in this manner instantaneously amounts to the same amount of charge as accumulating a potential of 300V in a 1000FF capacitor. Normally, in reliability tests, etc., a semiconductor integrated circuit terminal receives several 100V at 1000PF.
It has been observed that applying a charge of In this case, melting of the Al wiring of the circuit block attached to the terminal is observed.

The present invention was made in view of the above-mentioned problems.The present invention is based on the observation of the electrical characteristics of the functional blocks of the semiconductor substrate using light or laser light, and the measurement of the resistance portion formed on the semiconductor substrate. The purpose is to prevent thermal or electrical effects caused by light or laser light during functional trimming in functional trimming, which precisely controls the resistance value by fusing.

The structure of a semiconductor device according to an embodiment of the present invention will be explained with reference to FIG. Figure 2 a is Figure 1 a
21 is a thin film resistor made of polySi, nickel chrome, silicon chrome, etc.
23 and 24 are circuit blocks each connected to a resistor. 25 is a laser beam spot, and the broken line indicates its blur. Here, 26 is a metal coating made of Al, Mo, etc. according to the present invention, and serves as a laser beam reflecting part.

FIG. 2b shows a cross section of a predetermined part of the semiconductor device in FIG. 2, where 27 is a p-type substrate, 28 is an n
29 shows a p ⁺ isolation region, 30 a base portion of a bipolar transistor, 31 an emitter portion, and 32 a collector portion. 33 is a base, emitter, and collector electrode formed in the same process as the reflecting plate 26, and 34 is a
It is a _CVDSiO2 film. Note that 26 is a metal reflective film shown in FIG. 2a.

Now, as shown in 25, when a laser beam for trimming is irradiated, in the present invention, by placing a reflective film 26 adjacent to the resistor part 21, the beam spot 25 or its The blurred light is reflected by the metal reflective film 26. Usually metal reflective film 26 such as cu, Al etc.
It can be seen that those formed by vacuum evaporation have a reflectance of over 99%, meaning that most of the laser beam is reflected.

Further, a major feature of the present invention is that this metal reflective film 2
6 does not require any new effort. That is, in the manufacturing process of semiconductor integrated circuits, a metal film is usually used for connections between elements, and this is done by depositing a metal film on the entire surface and then opening holes in predetermined areas. The reflective film of the present invention has the great advantage that it is achieved by leaving the metal coating between the resistor parts intact during this process, which can be achieved without adding any new process.

The results of fabricating a prototype semiconductor integrated circuit according to the present invention and measuring its characteristics are shown below. The YAG laser spot shown at 25 in Figure 2a is 10
When the electrical output signal was observed using a sampling oscilloscope at other points on the semiconductor integrated circuit (not shown), it was found that the conventional structure
A peak voltage of 100V was observed. However, in the case where the reflective film according to the present invention was inserted, the peak voltage was 100V or less. Further, according to the present invention, even in integrated circuits that are prone to latch-up, latch-up can be prevented by providing such a reflective film.

In addition, there was no problem with the manufacturing method, and the resistor 21
It is also possible to change the distance between the reflective film 26 and the reflective film 26 from 2.5 μm to 10 μm.

Next, a semiconductor device according to another embodiment of the present invention will be explained with reference to FIG. In this embodiment, a metal coating is formed directly under the thin film resistor element and in its periphery so that the laser beam is not transmitted or absorbed by the semiconductor substrate. Third
This will be explained along the diagram. 101 indicates a p-type semiconductor substrate. Reference numeral 102 denotes an n-type semiconductor layer, which is composed of an epitaxial layer, etc., and is reverse biased with respect to the substrate 1, and is a collector layer of a transistor. 103 is a p-type semiconductor base layer, and 104 is an n-type semiconductor emitter layer. 1
05 indicates an oxide film formed at the stage of forming a transistor structure. Reference numeral 108 denotes a thin film resistor formed on the oxide film 105, and a metal that reflects laser light, such as Al, Au, etc., is placed directly below and around it.
A patterned reflective layer 106 is formed by depositing Cu, W, Mo, or the like. The element 108 is formed after the insulating layer 107 is formed by a CVD method or the like to provide insulation between the reflective layer 106 and the thin film resistive element 108. 109, 110, 111, 112, 11
3 indicates aluminum for electrode wiring, especially 11
1, 112, 113 are transistor collectors,
Compatible with base and emitter electrodes.

As explained above, the thin film resistance element 108 with the laser reflective layer 106 is formed on the same semiconductor substrate 10.
1 along with other transistors 102 without changing the conventional manufacturing process.

According to the structure shown in Fig. 3, even if a laser beam is irradiated for trimming a thin film resistor element onto a semiconductor integrated circuit to which a bias voltage is applied, the laser beam is prevented by the reflective layer provided directly below and around the laser beam. Light is not absorbed by the semiconductor substrate. This prevents the generation of carriers due to excitation and prevents the latch and
It can prevent bumps. To prevent latch-up,
In particular, the accuracy of trimming a semiconductor integrated circuit can be observed simultaneously with laser light irradiation, and highly accurate A/D and D/A converters can be obtained.

Further, another embodiment of the present invention will be described with reference to FIG. In this embodiment, a functional circuit section including active elements other than the thin film resistive element to be trimmed is shielded from light in order to prevent excitation of shallow junctions by light and laser light. 201 is a p-type semiconductor substrate, and 202 is an n-type semiconductor layer, which is used with a reverse bias to 201. Diffusion layers 203 and 204 formed within 202 represent the base and emitter layers of the transistor. Reference numeral 205 indicates an isolation diffusion layer of each element. 206 is a transistor structure 202, 20
The oxide film formed at the stage of forming No. 3,204 is shown. 207, 208, 209, 210, 21
Reference numeral 1 denotes a metal film for wiring that connects each element, 212 a thin film resistance element, 213 an insulating film in which holes are formed at least for external wiring pads and the thin film resistance element, and 214 a metal film formed on the insulating film. , a metal coating that reflects light or laser light, such as Al, Au,
It is formed by vapor depositing Cu, W, Mo, etc. Diameter 20μ
The laser beam focused to about m is reflected by the coating 214 and does not directly hit the insulating coating 213. Note that instead of the two-layer structure of the insulating film 213 and the metal film 214, a resin film may be used as the insulating film 213 and the metal film 214 may not be used.

As shown in FIG. 4, a semiconductor integrated circuit including a thin film resistor element with a coating that reflects or shields laser light includes a conventional transistor, a diffused resistor (a diffused layer 203 connected by electrode wirings 207 and 210)
can be integrated without any changes to the manufacturing process. As described above, by forming a film that reflects or shields light or laser light on the parts other than the thin-film resistor element and bonding pad parts, the shallow junctions are prevented from being excited by light energy and the generation of leakage current is prevented. By eliminating this, highly accurate trimming is possible. In particular, in the monolithic structure of an A/D converter that requires high speed performance, the n-type epitaxial layer 202 is as thin as several μm in order to improve the high frequency characteristics of the transistor and obtain a high switching speed. Therefore, the junctions 203 and 204 formed are shallow, about 0.7 to 1.1 μm from the silicon surface, and leakage current of the transistor increases when irradiated with ordinary light other than laser light, such as light from a microscope. Therefore, eliminating this leakage current during trimming, which is performed to control accuracy at a few nanoamps, is
High-speed, high-precision A/D converter monolithic IC
This makes it possible to

FIG. 5 shows yet another embodiment of the invention. 3
01 is a p-type semiconductor substrate, and 302 is an n-type epitaxial layer semiconductor layer, which is biased in the opposite direction to 301. Diffusion layer 303,3 formed in 302
04 indicates the base and emitter layers of the transistor. Reference numeral 305 indicates an isolation diffusion layer of each element. 306
shows an oxide film formed in the step of forming transistor structures 302, 303, and 304. 30
Reference numerals 7, 308, 309, 310, and 311 indicate wiring metal films that connect each element. 312 indicates a thin film resistance element. Reference numeral 313 indicates an insulating film in which holes are formed at least in the external wiring pad portion and the thin film resistance element portion. 314 is formed on an insulating film,
A metal coating that reflects light or laser light.
Formed by vapor deposition of Al, Au, Cu, W, Mo, etc. 315 is a metal film formed on the oxide film 306 directly under the thin film resistance element 312, and is made of Al, Au,
It is formed by vapor depositing Cu, W, Mo, etc. Reference numeral 316 indicates an insulating film, which prevents electrical contact between the thin film resistive element 312 and the metal film 315.

According to the structure shown in FIG. 5, it is possible to prevent the laser beam from entering the transistor portion and under the resistor element on the same side, and almost completely prevent the adverse effects of the laser beam.

As described above, according to the present invention, it is possible to eliminate the influence of trimming light such as laser light,
A high-precision, high-density semiconductor device can be realized, and it is particularly suitable for function trimming.

[Brief explanation of the drawing]

FIG. 1a is a schematic plan view of a semiconductor integrated circuit board on which a conventional thin film resistance element is formed, FIG. 1b is a partial sectional view of FIG. FIG. 2B is a partial cross-sectional view of the substrate shown in FIG. 21... Thin film resistor section, 25... Laser beam spot, 26... Metal coating, 27... P-type substrate, 28... N-type epitaxial layer, 101, 2
01,301...p-type semiconductor substrate, 102,20
2,302...n-type epitaxial layer, 108,
212,312... Thin film resistor, 106... Reflective layer, 213,313,316... Insulating coating, 2
14,315...metal coating.

Claims (1)

[Scope of Claims] 1. A semiconductor integrated circuit element is formed within a semiconductor substrate, a resistor element that is trimmed by light irradiation is provided on the substrate, and a resistor element is provided on the semiconductor substrate outside the resistor element. A semiconductor device characterized by forming a film that blocks transmission of the light. 2. The semiconductor device according to claim 1, wherein a plurality of resistive elements are formed, and a film is formed between the resistive elements. 3. The semiconductor device according to claim 1 or 2, wherein the light is a laser beam and the coating is a metal film serving as a light reflector. 4 A semiconductor integrated circuit element is formed in a semiconductor substrate, a resistive element that is trimmed by light irradiation is provided on the substrate, and an insulating film is provided under the resistive element to block the transmission of the light. A semiconductor device characterized by forming a film. 5. The semiconductor device according to claim 4, wherein the light is a laser beam and the coating is a metal film serving as a light reflector.