JP5549049B2 - Thin film resistor, semiconductor device, and method of manufacturing thin film resistor - Google Patents

Description

  The present invention relates to a thin film resistor of a semiconductor device, and relates to a thin film resistor of a semiconductor device capable of stable laser trimming without being affected by manufacturing variations in the lower layer thickness of the thin film resistor and without affecting the characteristics of the thin film resistor. Is.

  Conventionally, there is a laser trimming technique in which a thin film resistor is irradiated with a laser, only a region irradiated with the laser is trimmed, and a resistance value and product characteristics are adjusted. However, in this laser trimming process, there is a problem that the thin film resistor cannot be trimmed normally due to manufacturing variations in the lower layer thickness of the thin film resistor.

  For example, FIG. 7 shows a cross-sectional view of a thin film resistance region of a conventional semiconductor device, in which a field oxide film 2 and a first interlayer insulating film 3 are formed on a silicon substrate 1, and a conductive terminal is formed thereon. 4, a second interlayer insulating film 5 is further formed thereon, and a thin film resistor 7 and a passivation film 8 are formed thereon. The thin film resistor 7 is electrically connected to the conductive terminal 4 through the through hole 6 and is connected to another device. FIG. 8 shows a simulation result of the laser intensity in the depth direction when a laser beam having a wavelength of 1.3 μm is irradiated from the surface side of the semiconductor device shown in FIG. As a manufacturing variation, the silicon oxide film thickness under the thin film resistor is changed by ± 5%. The film thickness of the thin film resistor is very thin, and most of the laser light is transmitted through the thin film resistor. Therefore, the reflected light intensity at the silicon substrate interface is strong, and the reflected light is irradiated to the thin film resistor again. As a result, interference between incident light and reflected light occurs. Since the phase of the reflected light depends on the lower layer film thickness of the thin film resistor, it can be seen that the effective laser intensity at the thin film resistor varies greatly depending on the manufacturing variation of the lower layer film thickness. As a result, there arises a problem that trimming within the wafer surface / between wafers / between lots cannot be performed stably.

  In order to stably trim the thin film resistor, it is only necessary to increase the laser absorptance. For example, in a thin film resistor using Poly Si, an impurity is implanted at a high concentration in a region irradiated with the laser in advance. There is a method to perform (see FIG. 9). Also proposed are a method of forming a LOCOS step in the lower layer thickness to ensure that there is a region where the laser power is strong, and a method of forming a W heating film on the surface of the thin film resistor (see FIG. 10). Has been.

In addition, a resistor circuit is provided in which a plurality of metal thin film resistors R1, R2, and R3 whose resistance values are adjusted by being cut or altered by irradiation with a laser beam are provided, and the metal thin film resistors R1, R2, and R3 are provided. The resistance value adjustment ranges ΔR1, ΔR2, and ΔR3, the total resistance value adjustment range ΔR0 (= ΔRa + ΔRb + ΔRc), and the resistance value adjustment accuracy R1_step, R2_step, R3_step are ΔR2 ≧ R1_step, ΔR3 ≧ R2_step, R3_step ≦ 0.001 × ΔR0 <R2_step By satisfying the relationship of ≦ 0.01 × ΔR0 <R1_step ≦ 0.1 × ΔR0, a semiconductor device having a resistance circuit in which a plurality of metal thin film resistors are connected in series can be used to accurately resist a wide range of resistance value adjustment. A technique capable of adjusting the value is disclosed (for example, see Patent Document 1).
JP 2007-096174 A

  However, the method of introducing a high-concentration impurity into Poly Si and the method of forming a W heating film on the surface require an additional mask and a process step, which increases the process cost. In order to increase the integration of a high-precision analog integrated circuit, the resistance value of the resistance element is preferably high. To increase the absorption rate of the laser, it is necessary to increase the film thickness of the thin film resistor. On the contrary, there is a problem that the resistance value decreases when the film thickness is increased.

  The present invention has been made in view of such a situation, and the present invention does not affect the manufacturing variation without adding a new mask and a process step, and does not affect the characteristics of the thin film resistor. An object is to enable stable laser trimming.

In order to achieve the above object, one embodiment of the present invention is a thin film resistor which is formed on a semiconductor substrate and is subjected to laser trimming, and has a thickness of 3 to 50 nm which is a target of the laser trimming. A silicon oxide film formed in a thickness of 10 to 30 nm on the upper layer of the first resistor, and a film thickness of 50 nm or more on the upper layer of the silicon oxide film. The second resistor is formed in a laminated structure, and the second resistor is electrically separated from the first resistor by the silicon oxide film. During the laser trimming, the second resistor is electrically separated from the first resistor by the silicon oxide film. It is characterized in that the intensity of transmitted laser light is weakened .

  According to the present invention, it is possible to perform stable laser trimming without adding a new mask and process steps, without affecting manufacturing variations, and without affecting the characteristics of the thin film resistor.

  FIG. 1 shows a cross-sectional view of a semiconductor device including the thin film resistor according to the first embodiment of the present invention. This structure has a structure in which a silicon oxide film 9 is formed on an upper layer of the conventional first thin film resistor 7 shown in FIG. 7, and a second thin film resistor 10 is further stacked thereon. By forming the thin film resistor into a two-layer structure and forming a silicon oxide film 9 as an insulating film between the thin film resistors, the upper layer and the lower layer thin film resistors are electrically separated from each other. The required resistance value characteristic is determined by the characteristic of the first thin film resistor 7 in the lower layer as in the past, and the second thin film resistor 10 in the upper layer independently sets the film thickness necessary for absorbing the laser. It becomes possible.

  FIG. 2 is a diagram showing a simulation result of the thickness direction distribution of the upper thin film resistor 10 and the laser intensity in the depth direction. From FIG. 2, it can be seen that the intensity of the laser beam transmitted through the first thin film resistor 7 decreases as the thickness of the second thin film resistor 10 in the upper layer increases. Using this simulation result, FIG. 3 shows the relationship between the amplitude width of the laser in the interlayer insulating film under the first thin film resistor 7 and the film thickness of the second thin film resistor 10 in the upper layer. As shown in FIG. 3, the transmission laser intensity of the thin film resistor is saturated when the film thickness of the second thin film resistor 10 is 50 nm or more, and the film thickness of the second thin film resistor 10 is formed to be 50 nm or more. The upper second thin film resistor 10 absorbs the laser beam, and at the same time, as shown in FIG. 2, the energy of the transmitted laser beam is reduced, so that the optical interference effect is suppressed, and the effective variation in laser power due to manufacturing variation. Therefore, stable trimming can be easily realized.

  Hereinafter, with reference to FIG. 4, the manufacturing method of a semiconductor device provided with the thin film resistor of 1st Embodiment is demonstrated. First, a field oxide film 2, an interlayer insulating film 3, and a conductive film 12 such as Al-SiCu are formed on a silicon substrate 1 by a known semiconductor manufacturing method (a).

  Subsequently, the conductive film 12 is patterned by the known photolithography and dry etching methods of the semiconductor manufacturing method to form the conductive terminals 4 (b).

  Similarly, an interlayer insulating film such as NSG, BPSG, or TEOS film is formed by a known semiconductor manufacturing method, and the first thin film resistor 7, the conductive terminal 4, and the like are formed by a photolithography process and a dry etching method. Through holes 6 are formed to electrically connect the two (c).

  Next, the first thin film resistor 7 is formed to a thickness of 3 to 50 nm by, for example, sputtering using a SiCr target, and the upper layer is formed by plasma CVD using a mixed gas of SiH 4 / N 2 O. Then, the silicon oxide film 9 is formed into a thickness of 10 to 20 nm, and the second thin film resistor 10 is formed into an upper layer again by the same method as the first thin film resistor 7 in the lower layer (d).

Subsequently, by a known photolithography process, the resist 13 is left only in the region where the thin film resistor 7 is to be formed (e), and silicon oxide is formed between the upper and lower thin film resistors using a mixed gas of Ar / SF ₆ / He. The film is etched simultaneously to form a thin film resistor pattern, and a passivation film 8 made of, for example, a silicon nitride film is formed by a general plasma CVD method to complete (f). At that time, since the selection ratio of the silicon oxide film is about 1, there is no problem even if the silicon oxide film is formed therebetween.

  FIG. 5 shows a cross-sectional view of a semiconductor device including the thin film resistor according to the second embodiment of the present invention. This structure is different from the structure of the first embodiment in that the resistance value of the upper third thin film resistor 11 is lower than that of the lower first thin film resistor 11 instead of forming the silicon oxide film 9 between the upper and lower thin film resistors. The resistance value of the thin film resistor 7 is 10 times or more. By omitting the formation of the silicon oxide film, the process can be simplified and the process cost can be reduced. Further, by increasing the resistance value, it is possible to suppress the characteristic variation to the resistance value of the first thin film resistor 7 in the lower layer. If the ratio of the resistance values is 10 times, the characteristic fluctuation is about 10%. However, if the analog trimming technique is used, it is an allowable range. However, in a more accurate product, it is preferably 100 times or more in order to reduce the influence. For example, a thin film resistor having a resistance value of 10 kΩ / □ can be formed by forming the first thin film resistor 7 to a thickness of 5 nm by sputtering using a target having a Si / Cr composition ratio of 70/30. As the thin film resistor 11 of No. 3, a 130 k / □ thin film resistor is formed by introducing 11 sccm of nitrogen into the sputtering chamber and forming a film of 50 nm using a target having a Si / Cr composition ratio of 82/18. Can do.

  As described above, in the thin film resistor using SiCr, the resistance value of the thin film resistor can be controlled by using a Si / Cr target composition of the sputtering apparatus with a high Si concentration target or introducing nitrogen during sputtering. Can be easily controlled.

  Further, in the method of manufacturing a semiconductor device including the thin film resistor according to the second embodiment, the silicon oxide film forming step of the manufacturing method according to the first embodiment is omitted, and the film forming conditions of the third thin film resistor 11 are changed. This is possible only by doing. Specifically, as shown in FIG. 6, a field oxide film 2, an interlayer insulating film 3, and a conductive film 12 such as Al—SiCu are formed on the silicon substrate 1 by a known semiconductor manufacturing method (a).

  Subsequently, the conductive film 12 is patterned by the known photolithography and dry etching methods of the semiconductor manufacturing method to form the conductive terminals 4 (b).

  Similarly, an interlayer insulating film such as NSG, BPSG, or TEOS film is formed by a known semiconductor manufacturing method, and the first thin film resistor 7, the conductive terminal 4, and the like are formed by a photolithography process and a dry etching method. Through holes 6 are formed to electrically connect the two (c).

  Next, for example, the first thin film resistor 7 is formed with a thickness of 3 to 50 nm by sputtering using a SiCr target having a composition ratio of 70/30, and the third thin film resistor 11 is formed thereon. Using a target having a Si / Cr composition ratio of 82/18, 11 sccm of nitrogen is introduced to form a film of 50 nm by the same sputtering method (d).

Subsequently, the resist 13 is left only in the region where the thin film resistor 7 is to be formed by a known photolithography process (e), and the upper and lower thin film resistors are etched by using a mixed gas of Ar / SF ₆ / He. A resistor pattern is formed, and a passivation film 8 made of, for example, a silicon nitride film is formed and completed by a general plasma CVD method (f).

  The thin film resistor has a two-layer structure, and the resistance value of the upper layer thin film resistor is 10 times or more that of the lower layer thin film resistor element, thereby suppressing the influence of the upper layer resistance value characteristic and absorbing the laser beam. An efficient thin film resistor can be formed, and stable trimming can be realized.

  The semiconductor device including the thin film resistor according to the third embodiment of the present invention is characterized in that phosphorus or boron is introduced into the silicon oxide film 9 shown in FIG. By introducing phosphorus or boron impurities into the silicon oxide film, the melting point of the silicon oxide film is lowered, and chemical reactions and physical changes with the thin film resistor during laser irradiation are likely to occur, so that more stable trimming can be performed. Is possible.

Phosphorus or boron is introduced into the silicon oxide film by plasma CVD using a PH ₃ or B ₂ H ₆ gas as in known semiconductor processes.

  Each of the above-described embodiments is a preferred embodiment of the present invention, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing of a semiconductor device provided with the thin film resistor of the 1st Embodiment of this invention. It is a simulation result of the laser intensity of the depth direction of this invention. It is a figure which shows the relationship between the 2nd thin film resistor film thickness, and the laser intensity which permeate | transmits a resistor. It is a figure explaining the manufacturing method of the 1st Embodiment of this invention. It is sectional drawing of a semiconductor device provided with the thin film resistor of the 2nd Embodiment of this invention. It is a figure explaining the manufacturing method of the 2nd Embodiment of this invention. It is sectional drawing of the semiconductor device of a prior art example. It is a figure which shows the simulation result of the laser intensity of the depth direction of a prior art example. It is explanatory drawing of an example of the semiconductor device of a prior art example. It is explanatory drawing of an example of the semiconductor device of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Field oxide film 3 1st interlayer insulation film 4 Conductive terminal 5 2nd interlayer insulation film 6 Through hole 7 1st thin film resistor 8 Passivation film 9 Silicon oxide film 10 2nd thin film resistor 11 1st 3 Thin film resistor 12 Conductive film 13 Resist 14 Heat generating conductive film 15 High light absorption region 16 Low light absorption region 17 Diffusion layer

Claims (7)

A thin film resistor formed on a semiconductor substrate and subjected to laser trimming,
A first resistor formed with a thickness of 3 to 50 nm, which is an object of the laser trimming ;
A silicon oxide film formed in a thickness of 10 to 30 nm on an upper layer of the first resistor;
A second resistor formed in a thickness of 50 nm or more on the upper layer of the silicon oxide film in a laminated structure;
The thin film resistor, wherein the second resistor is electrically separated from the first resistor by the silicon oxide film, and weakens the intensity of the laser beam transmitted during the laser trimming. . 2. The thin film resistor according to claim 1, wherein SiCr is used as a material for the first resistor and the second resistor. 3. The thin film resistor according to claim 1, wherein phosphorus or boron is introduced into the silicon oxide film.   A semiconductor device comprising the thin film resistor according to claim 1. A method of manufacturing a thin film resistor formed on a semiconductor substrate and subjected to laser trimming,
Forming the first resistor to be laser trimmed with a thickness of 3 to 50 nm;
Forming a silicon oxide film on the first resistor in a thickness of 10 to 30 nm;
The silicon oxide film is electrically isolated from the first resistor, and a second resistor that weakens the intensity of the laser beam that is transmitted during the laser trimming has a thickness above the silicon oxide film. Forming a thin film resistor having a film thickness of 50 nm or more.   6. The method of manufacturing a thin film resistor according to claim 5, wherein SiCr is used as a material for the first resistor and the second resistor. 7. The method of manufacturing a thin film resistor according to claim 5, wherein phosphorus or boron is introduced into the silicon oxide film.

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