JP2011138983A - Integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an integrated circuit which improves a sound quality compared with a conventional product, and incorporates a circuit for analog sound signal processing. <P>SOLUTION: In the integrated circuit 10, analog sound signals input from input terminals 12, 14 are voltage-divided by a resistor network 20 composed of resistance elements R1, R2 and input to a non-inverting input terminal of an operational amplifier 22. An output signal from the operational amplifier 22 is voltage-divided by a resistor network 24 composed of resistance elements R3, R4 and fed back to an inverting input terminal of the operational amplifier 22. Signals from both the ends of the resistance elements R3, R4 are output from output terminals 16, 18. Each of the resistance elements R1 to R4 composing respective resistor networks 20, 24 is composed of a two-layer lamination structure of a tantalum nitride layer 30 and a tantalum layer 28. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an integrated circuit incorporating a circuit for processing an analog audio signal, and has improved sound quality as compared with the conventional circuit.

  Conventionally, a resistance element built in an integrated circuit is generally composed of polysilicon. As an integrated circuit in which the resistance element is made of polysilicon, for example, there is one described in Patent Document 1 below.

JP2000-022077

  Using an integrated circuit with a built-in analog audio signal processing circuit with a resistive element made of polysilicon, the audio signal was amplified by power and played back with headphones, and it was found that there was a problem with sound quality. .

  The present invention has been made in view of the above points, and an object of the present invention is to provide an integrated circuit having improved sound quality as compared with the conventional one.

  In the integrated circuit of the present invention, a resistance element disposed in a circuit through which an analog audio signal flows is configured by a two-layer laminated structure of a tantalum nitride layer and a tantalum layer. According to the integrated circuit of the present invention, as a result of the trial listening evaluation, better sound quality evaluation was obtained as compared with the case where the resistive element was made of other materials.

  The integrated circuit of the present invention is effective when applied to a circuit portion that has a great influence on the sound quality, particularly the resistance element. An example of such a circuit portion is a resistor network that divides (divides) an analog audio signal. That is, in the resistive network constituting the dividing circuit, the gain of the circuit varies depending on the dividing ratio (voltage dividing ratio), so it is important that the dividing ratio does not vary with temperature and voltage. An example of the resistor network is a resistor network of a power amplifier circuit.

  In the integrated circuit of the present invention, only a part of all the resistance elements having a large influence on the sound quality is constituted by a two-layer laminated structure of a tantalum nitride layer and a tantalum layer, and the other resistance elements are made of other materials (for example, poly In addition, the total resistance element can be composed of a two-layer laminated structure of a tantalum nitride layer and a tantalum layer. If the entire resistance element is formed of a two-layer laminated structure of a tantalum nitride layer and a tantalum layer, a resistance layer made of another material can be dispensed with separately, so that the manufacturing process can be simplified.

It is sectional drawing which shows an example of the laminated structure of the part in which resistance element R1-R4 in the integrated circuit 10 of FIG. 2 was comprised. 1 is a circuit diagram of an integrated circuit according to an embodiment of the present invention. It is a block diagram of the integrated circuit which performed the audition evaluation test.

  FIG. 2 shows a circuit diagram of an integrated circuit according to the embodiment of the present invention. The integrated circuit 10 is configured as a circuit that amplifies an analog audio signal input from the input terminals 12 and 14 by voltage / power amplification and outputs it from the output terminals 16 and 18. That is, the analog audio signal input from the input terminals 12 and 14 is divided by the resistor network 20 including the resistor elements R1 and R2 and input to the non-inverting input terminal of the operational amplifier 22. If the voltage of the input signal is x, the voltage of the signal input to the non-inverting input terminal of the operational amplifier 22 is x · R2 / (R1 + R2). The output signal of the operational amplifier 22 is divided by a resistance network 24 composed of resistance elements R3 and R4 and fed back to the inverting input terminal of the operational amplifier 22. As a result, the voltage gain of the operational amplifier 22 becomes (R3 + R4) / R4. Signals at both ends of the resistance elements R3 and R4 connected in series are output from the output terminals 16 and 18. Terminals 14 and 18 are at the same potential.

  The resistive elements R1 to R4 constituting the resistive networks 20 and 24 are each configured by a two-layer laminated structure in which a tantalum nitride layer and a tantalum layer are laminated. An example of a laminated structure of a portion where the resistance elements R1 to R4 in the integrated circuit 10 are configured is shown in FIG. An appropriate lower layer 25 is formed on the surface of a wafer (not shown), and an insulating layer 26 is laminated thereon. On the insulating layer 26, a resistance layer 31 is formed in which a tantalum layer 28 and a tantalum nitride layer 30 are sequentially stacked. An insulating layer 32 is laminated on the resistance layer 31. Via holes 32 a and 32 b are formed in the insulating layer 32. On the insulating layer 32, a metal layer (conductive layer) 34 constituting a wiring is laminated. The metal layer 34 is divided into left and right regions 34a and 34b by etching. The left and right metal layers 34a and 34b are also deposited in the via holes 32a and 32b, and are electrically connected to the resistance layer 31, respectively. Thus, the portion of the resistance layer 31 between the via holes 32a and 32b constitutes one of the resistance elements R1 to R4, and the left and right metal layers 34a and 34b are connected to both ends of the resistance element. A conducting wire (wiring) is formed. Resistive elements R1 to R4 having such a laminated structure are formed in the integrated circuit 10, respectively. An insulating and protective layer 36 is laminated on the metal layer 34.

The resistance layer 31 can be formed by sputtering, for example. An example of the process will be described. It is assumed that the wafer and the tantalum (Ta) target that have been completed up to the step immediately before the formation of the resistance layer 31 are arranged in the vacuum chamber of the sputtering apparatus. First, a tantalum target is sputtered for a predetermined time while introducing an argon (Ar) gas into the vacuum chamber to form a tantalum layer 28 having a predetermined thickness. Subsequently, argon gas and nitrogen (N ₂ ) gas are introduced into the vacuum chamber at a predetermined partial pressure ratio, and a tantalum target is sputtered for a predetermined time, and a tantalum nitride layer (TaN _x , x has a value of 0.03). ≦ x ≦ 0.25, preferably 0.05 ≦ x ≦ 0.20. As an example, a case where x = 0.16 is aimed is shown in the following embodiment) 30 is formed. In this way, the resistance layer 31 in which the tantalum layer 28 and the tantalum nitride layer 30 are sequentially stacked is formed. The tantalum nitride layer 30 is adjusted by adjusting the amount of nitrogen gas during sputtering (partial pressure ratio with respect to argon gas), so that the resistance temperature coefficient TCR (coefficient indicating the variation in resistance value with temperature) and the resistance voltage coefficient VCR (resistance due to voltage) It is produced so that the coefficient indicating the fluctuation of the value becomes small.

"Example"
By the above process, the tantalum layer 28 was first formed, and then the tantalum nitride layer 30 was formed to produce the resistance layer 31. The film formation conditions at that time were as follows.

<Deposition conditions for tantalum layer 28>
・ Argon gas flow: 75sccm
・ Gas pressure: 5mTorr
・ Input power: 3.0kW
-Substrate temperature: 350 ° C
・ Sputtering time: 1.5 seconds

<Deposition conditions for tantalum nitride layer 30>
・ Gas flow rate: Argon gas = 63sccm, Nitrogen gas = 12sccm
・ Total gas pressure: 5mTorr
・ Partial pressure ratio of nitrogen gas: 16% (nitrogen gas partial pressure = 0.8 mTorr)
・ Input power: 3.0kW
-Substrate temperature: 350 ° C
・ Sputtering time: 1.5 seconds

When the film was formed under the above film formation conditions, the tantalum layer 28 was formed to a thickness of 25 nm, and the tantalum nitride layer 30 was formed to a thickness of 25 nm. The tantalum nitride layer 30 was TaN _x in an amorphous state, and the dispersion state of nitrogen in the film was almost uniform. Further, the sheet resistance of the entire resistance layer 31 composed of the tantalum layer 28 and the tantalum nitride layer 30 was 69Ω / □ (the sheet resistance ratio of the tantalum layer 28 and the tantalum nitride layer 30 = 1: 1). The resistance element made of the resistance layer 31 has a length of 50 μm and a width of 1 μm (type A), a length of 50 μm and a width of 5 μm (type B), a length of 300 μm and a width of 1 μm. Thing (type C). Two samples (types 1 and 2, total 6 samples) were made for each of types A, B, and C. First, the resistance temperature coefficient TCR was measured for four types A and B samples. The measurement was performed at the center of the wafer. The measurement results were as follows.

<Resistance temperature coefficient TCR (ppm / ℃)>
Type A Type B
Sample 1 16.0 1.6
Sample 2 3.0 3.8

Next, the resistance voltage coefficient VCR was measured for two samples of type C. The measurement was performed by changing the voltage within a range of ± 5 V at the center of the wafer. The measurement results were as follows.

<Resistance voltage coefficient VCR (ppm / V)>
Type C
Sample 1-1.3
Sample 2-2.1

In the case of a polysilicon resistor, the resistance temperature coefficient TCR is about 150 ppm / ° C. and the resistance voltage coefficient VCR is about 200 ppm / V. Therefore, according to the manufactured resistance layer 31, both the resistance temperature coefficient and the resistance voltage coefficient are small. You can see that it is within the value. Note that heat treatment (600 ° C. to 950 ° C.) may be performed by lamp annealing after forming the tantalum nitride layer 30 or after forming an interlayer oxide film on the tantalum nitride layer 30. In this way, the surface of the TaN _x film is slightly oxidized, but the crystallinity is improved and a more stable film quality can be obtained. In other words, a TaN _x (x is 0.10 to 0.25) single layer film having a surface oxidized and a more uniform film quality due to re-diffusion of nitrogen in the film can be obtained.

《Evaluation Test for Audition》
For YDA158, which is an integrated circuit manufactured by the applicant company, a feedback resistor network of a built-in headphone amplifier was made of various materials, a music signal was input, and an output signal was reproduced by headphones to make a comparative audition. A block diagram of this integrated circuit is shown in FIG. An integrated circuit 40 (YDA158) is mounted on a mobile phone, and a music signal is amplified by a headphone amplifier 42 and reproduced by a headphone (not shown) inserted into a headphone jack 38, and a ringtone is a class D amplifier. A function of amplifying at 52 and sounding at the speaker 50 is provided. The headphone amplifier 42 includes operational amplifiers 44 and 46 for the left and right channels. The operational amplifiers 44 and 46 are connected to a resistor network (feedback resistor network) 48 including a total of four resistor elements R11, R12, R13, and R14 for each of two channels. The resistance elements R11 to R14 of the feedback resistor network 48 were made of the following materials and evaluated for listening.

<Material of resistance elements R11 to R14>
-Polysilicon layer (material used in actual products)
-Tantalum layer-Tantalum nitride layer-Tantalum nitride / tantalum bilayer ("/" means that the material indicated on the front side constitutes the upper layer, and the material indicated on the rear side constitutes the lower layer. The same applies hereinafter)
・ Tantalum nitride / titanium (Ti) bilayer (thickness ratio is 1: 1)
・ Tantalum nitride / titanium bilayer (thickness ratio 1: 3)

The trial evaluation was conducted by five semiconductor engineers listening to the same music source using headphones. Evaluation was based on absolute impression evaluation rather than score evaluation. The evaluation results were as follows.

<Results of audition evaluation>
-Polysilicon layer: The sound field is narrow and the stereo effect is poor. There is little music harmony.
・ Tantalum layer: The sound is light and quiet. The highs are a bit metallic and not a good impression.
・ Tantalum nitride layer: The bass is clear and the sound is beautiful.
-Tantalum nitride / tantalum double layer: The piano is moist and rich and the music is comfortable.
-Tantalum nitride / titanium bilayer (thickness ratio is 1: 1): The piano sound is less moist. The sound feels metallic.
-Tantalum nitride / titanium bilayer (thickness ratio 1: 3): good balance of bass and treble, bright sound but thin.

  According to the above audition evaluation, good sound quality evaluation was obtained in the tantalum nitride single layer and the tantalum nitride / tantalum bilayer.

  In the trial evaluation test, only the resistance elements of the feedback resistor network 48 of the operational amplifiers 44 and 46 that have a great influence on the sound quality among all the resistance elements of the integrated circuit are composed of tantalum nitride / tantalum two layers. / Tantalum bilayer can also be used. By doing so, the manufacturing process can be simplified as compared with the case where the material of the resistance element is properly used according to the circuit portion. For example, the integrated circuit 40 of FIG. 3 includes a resistor network (feedback resistor network) 48 of a headphone amplifier 42 and a resistor circuit network (feedback resistor network) 54 of a class D amplifier 52 for ringing a ring tone. The resistor elements R15 and R16 constituting the resistor and the resistor elements R17 and R18 constituting the resistor network (feedback resistor network) 56 can be simultaneously made of a tantalum nitride / tantalum bilayer film. In the above embodiment, the tantalum layer is laminated as the lower layer and the tantalum nitride layer as the upper layer, but conversely, the tantalum nitride layer can be laminated as the lower layer and the tantalum layer as the upper layer.

  DESCRIPTION OF SYMBOLS 10,40 ... Integrated circuit, 12, 14 ... Input terminal, 16, 18 ... Output terminal, 20, 24, 48, 54, 56 ... Resistor network, 22, 44, 46 ... Operational amplifier, 25 ... Lower layer, 26 ... Insulation Layers 28, tantalum layer, 30 ... tantalum nitride layer, 31 ... resistance layer, 32 ... insulating layer, 32a, 32b ... via hole, 34 ... metal layer, 34a, 34b ... left and right regions of metal layer, 36 ... insulation and Protective layer, 38 ... headphone jack, 42 ... headphone amplifier, 50 ... speaker, 52 ... class D amplifier, R1, R2, R3, R4, R11, R12, R13, R14, R15, R16, R17, R18 ... resistance elements

Claims (4)

  An integrated circuit in which a resistance element arranged in a circuit through which an analog audio signal flows has a two-layer structure of a tantalum nitride layer and a tantalum layer.   The integrated circuit according to claim 1, wherein the resistance element is a resistance element constituting a resistance network that divides the analog audio signal.   The integrated circuit according to claim 2, wherein the resistor network is a resistor network of a power amplifier circuit.   4. The integrated circuit according to claim 1, wherein all of the resistance elements are configured by a two-layer laminated structure of a tantalum nitride layer and a tantalum layer.

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