JP2011138993A - Method for manufacturing semiconductor device with thin-film resistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device, capable of forming a thin-film resistor having a small TCR (temperature coefficient of resistance) value and formed of a TaN film ensuring a practically necessary film thickness while preventing TaN film damage in forming a wiring of the resistor. <P>SOLUTION: A first interlayer dielectric is formed on a semiconductor substrate having a semiconductor element formed thereon, and a tantalum nitride film is formed on the first interlayer dielectric by first sputtering at a substrate temperature from a normal temperature to 400°C with a nitride gas partial pressure ratio of 3-10% in a reaction gas. After that, a via hole reaching the tantalum nitride film is formed by wet etching on the second interlayer dielectric formed on the first interlayer dielectric, a metal film is deposited by second sputtering to form the metal film in the via hole, and a via connected to the tantalum nitride film is formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device including a thin film resistor made of a TaN film having good TCR (resistance value temperature coefficient) characteristics, and more particularly to an improvement in a wiring method for a high resistance thin film resistor.

  In an acoustic product such as an audio amplifier, it is well known that the performance of a resistor used in a circuit of an output stage particularly affects sound quality. Conventionally, a polysilicon thin film resistor is used in the semiconductor integrated circuit at the output stage of the amplifier. The performance of the resistor that affects the sound quality includes a TCR value. That is, the TCR value is a temperature coefficient of resistance value, and is a characteristic indicating how much the resistance value changes due to temperature change. The smaller the TCR value (closer to 0), the more the resistance value is the temperature. High sound quality can be obtained without fluctuation. The conventional polysilicon resistor has a TCR value of about ± 100 ppm / ° C in a temperature range of about 25 to 125 ° C., and further reduces the TCR value to about ± 50 ppm / ° C. in order to further improve sound quality. Is desired.

The adjustment of the TCR value is conventionally performed by adjusting the N ₂ partial pressure ratio of the source gas when the resistance film is formed by sputtering. It has also been proposed to obtain a good TCR characteristic close to 0 as a whole by laminating a thin film resistor having a positive TCR characteristic and a thin film resistor having a negative TCR characteristic.

  As a tantalum nitride (TaN) thin film resistor for the purpose of reducing the TCR value, there is one disclosed in Patent Document 1. In this conventional tantalum nitride thin film resistor, an electrode film made of Au is formed on an upper surface of a tantalum nitride thin film through an intermediate film made of Ti, and a combined resistance temperature coefficient of the intermediate film and the electrode film is set to a first resistance. When the temperature coefficient is the temperature coefficient of resistance of the tantalum nitride thin film, the sum of the first and second temperature coefficients is −10 to 0 ppm / ° C.

JP 2004-342705 A

  However, the conventional polysilicon thin film resistor has a high film formation temperature of about 600 ° C. during film formation by low pressure CVD (Chemical Vapor Deposition), and a metal material for wiring such as Al melts. In order to avoid this, a polysilicon thin film resistor cannot be formed after these metal wirings are formed. Therefore, it is necessary to form this polysilicon thin film resistor below the metal wiring, and its formation position is restricted on a LOCOS (Local Oxidation of Silicon) oxide film. For this reason, when polysilicon is used for the thin film resistor, it is necessary to secure a space for disposing the resistor immediately above the LOCOS oxide film while avoiding the transistor region, and it is difficult to reduce the chip area.

  Further, as described above, the polysilicon thin film resistor does not necessarily have a sufficiently low TCR value. For this reason, it is difficult to obtain excellent sound quality even if a polysilicon thin film resistor is used in the semiconductor integrated circuit at the output stage of the audio amplifier.

  On the other hand, the TaN thin film resistor has a low film formation temperature of about 400 ° C. or less during film formation by sputtering. Therefore, even if the TaN thin film resistor is formed after the metal wiring is formed, the metal wiring is not melted. Does not occur. Therefore, the TaN thin film resistor can be formed on the upper layer of the metal wiring, and can be stacked on the interlayer insulating film forming the metal wiring. In particular, since the area occupancy decreases as the distance from the upper wiring layer increases, it is easy to secure a space for forming the TaN resistor, so that there is an advantage that the chip area can be reduced.

  However, the TaN thin film resistor described in Patent Document 1 forms a TaN film as a laminated film with a multilayer (Ti film + Au film) metal film, and the TCR value of the multilayer metal film and the TCR value of the TaN film The total TCR value as the sum of the values is brought close to zero. In such a laminated film with a metal film, it is difficult to control the resistance value because the resistance value of the metal film is extremely small, and the formation cost of the Ti film and Au film is high, and the multilayer metal film and TaN There is a problem that the patterning process of the film is complicated.

  Further, the conventional TaN film has a low resistivity, and in order to obtain a sheet resistance of 100 to 300Ω, it is necessary to form the TaN film with a very thin film thickness of 200 to 300 mm. Such a thin resistive film is difficult to form. In addition, an interlayer insulating film is formed on the resistance film, a via hole is formed in the interlayer insulating film, and a metal such as aluminum is buried in the via hole to form a via, thereby forming wiring and resistance formed on the interlayer insulating film. When the film is electrically connected, the thin TaN film may be removed by etching during the formation of the via hole, and the film may not function as a resistance film.

  The present invention has been made in view of such problems, and is a thin film resistor made of a TaN film that is optimal for an audio signal processing circuit, has a small TCR value, and can ensure a practically required film thickness. An object of the present invention is to provide a method of manufacturing a semiconductor device that can be formed while preventing damage to the TaN film during wiring formation.

A method for manufacturing a semiconductor device provided with a thin film resistor according to the present invention includes:
Forming a semiconductor element on a semiconductor substrate;
Forming a first interlayer insulating film on the semiconductor substrate;
Forming a tantalum nitride film on the first interlayer insulating film by first sputtering, setting the substrate temperature from room temperature to 400 ° C., setting the nitrogen gas partial pressure ratio in the reaction gas to 3 to 10%, and ,
Forming a second interlayer insulating film on the first interlayer insulating film including the tantalum nitride film;
Forming a via hole penetrating through the second interlayer insulating film and reaching the tantalum nitride film by wet etching;
Depositing a metal film by second sputtering to form a metal film in the via hole, and providing a via connected to the tantalum nitride film;
It is characterized by having.

  In the present invention, since the via hole is formed by wet etching, it is possible to suppress damage to the tantalum nitride film under the second interlayer insulating film when the via hole is formed. Further, the resistance temperature coefficient TCR of the obtained tantalum nitride film can be controlled to −50 to +50 ppm / ° C. by adjusting the substrate temperature and the nitrogen gas partial pressure ratio when forming the tantalum nitride film.

  In the first sputtering step, the sheet resistance of the tantalum nitride film can be set to 100Ω / □ or more by setting the power during sputtering to 2.5 kW or less. Thereby, even if the thickness of the tantalum nitride film is increased to 1000 mm or more, a sufficiently high resistance value can be obtained.

  Further, in the first sputtering, when the substrate temperature during sputtering is T and the nitrogen gas partial pressure ratio is m, the substrate temperature T and the nitrogen gas partial pressure ratio m are (1/165) T + (95/33) It is preferable to determine so as to satisfy ≦ m ≦ (1/66) T + (155/33). Thereby, the resistance value temperature coefficient TCR of the tantalum nitride film can be set to −50 to +50 ppm / ° C. and the thickness can be set to 1000 mm or more.

  According to the present invention, when the tantalum nitride (TaN) film is formed by sputtering, the nitrogen gas partial pressure ratio is adjusted to 3 to 10%, and the substrate temperature is adjusted to a range from room temperature to 400 ° C. The TCR can be controlled to -50 to +50 ppm / ° C. Since the via hole reaching the tantalum nitride film is formed by wet etching with respect to the second interlayer insulating film, the tantalum nitride film is prevented from being damaged when the via hole is dug. Moreover, when the power during sputtering is 2.5 kW or less, the deposition rate of the TaN film is slowed down, whereby a TaN film having a high sheet resistance can be obtained.

It is sectional drawing which shows the resistive film which concerns on embodiment of this invention. It is a graph which shows correlation with substrate temperature T and nitrogen partial pressure ratio. It is a graph which shows the relationship between VCR and TCR. It is sectional drawing which shows the resistive film which concerns on other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing a semiconductor device in which a high resistance resistance film according to an embodiment of the present invention is formed. In this semiconductor device, first, various transistors and the like are formed on a substrate 1 such as a silicon substrate. At this time, the first interlayer insulating film 10 is formed on the surface of the substrate 1, and the first wiring layer 21 is formed on the first interlayer insulating film 10 from aluminum or copper. The first wiring layer 21 is formed by forming a layer of aluminum or copper on the first interlayer insulating film 10 by a normal film forming technique, and then forming this layer into a desired wiring pattern by a patterning method using a normal resist. It is formed by patterning.

  Next, a second interlayer insulating film 11 is formed on the first interlayer insulating film 10 including these first wiring layers 21, and a second wiring layer 22 is formed on the second interlayer insulating film 11. Then, the third interlayer insulating film 12 is formed on the entire surface including the second wiring layer 22, the third wiring layer 23 is formed on the third interlayer insulating film 12, and the third interlayer including the third wiring layer 23 is formed. A fourth interlayer insulating film 13 is formed on the insulating film 12.

  The fourth interlayer insulating film 13 is formed in two layers of a lower insulating film 13a and an upper insulating film 13b. Then, after forming the lower insulating film 13a, before forming the upper insulating film 13b, a pattern is formed on the lower insulating film 13a so that the tantalum nitride (TaN) film 2 has a predetermined size and shape. The TaN film 2 can be formed as follows. That is, after forming a resist pattern (not shown) having an opening in the region where the TaN film 2 is to be formed on the lower insulating film 13a, using this resist pattern as a mask, using a Ta target, a nitrogen gas is introduced into the Ar gas. By sputtering (first sputtering) with a reaction gas added at a predetermined partial pressure ratio, TaN is deposited on the entire surface. Thereafter, the TaN film 2 can be formed by removing the resist and lifting off the TaN film 2 on the resist. Alternatively, the TaN film 2 can be formed by the following method. That is, a TaN film is formed on the entire surface of the lower insulating film 13a by sputtering, a resist pattern is formed on the TaN film, and then the TaN film is etched using the resist pattern as a mask. The TaN film 2 can also be formed by this method.

  After the TaN film 2 is formed, an upper insulating film 13b is formed on the entire surface of the lower insulating film 13a including the TaN film 2, and then a fourth wiring layer 24c is formed on the fourth interlayer insulating film 13. Each wiring layer is connected by a via provided by forming a conductive material in a via hole formed in the interlayer insulating film. For example, the fourth wiring layer 24 c and the second wiring layer 22 are connected by the via 4. That is, in the step of forming the third interlayer insulating film 12 and the fourth interlayer insulating film 13, the third interlayer insulating film 12 and the fourth interlayer insulating film 13 are wet using the via holes penetrating these films and the resist film as a mask. The via 4 is formed by etching or dry etching, and then sputtering a metal material such as aluminum or depositing it by CVD (Chemical Vapor Deposition) and forming the metal material in the via hole. Then, a wiring 23 and a wiring 24 c are formed on the third interlayer insulating film 12 and the fourth interlayer insulating film 13 so as to be connected to the via 4. For example, vias and wirings can be formed by depositing W in the via hole by CVD, etching back this W to form a W plug, and sputtering Al.

  On the other hand, regarding the formation of wiring for the TaN film 2, after the TaN film 2 is formed, an upper insulating film 13b is formed on the entire surface of the lower insulating film 13a including the TaN film 2, and reaches the TaN film 2 on the upper insulating film 13b. Two via holes are formed. This via hole is formed by wet etching (wet etching). In the case of wet etching, the TaN film on the bottom of the via hole due to overetching can be suppressed compared to dry etching. As a result, the processing margin is improved, and the resistance can be increased by further reducing the thickness of the TaN film 2.

  Then, a metal film such as aluminum or copper is deposited in these via holes by the second sputtering to form vias 3a and 3b. Thereafter, fourth wiring layers 24a and 24b are formed on the upper insulating film 13b so as to be connected to the vias 3a and 3b, respectively. By the fourth wiring layers 24a and 24b, the TaN film 2 is connected as a thin film resistor provided in a path through which an output current flows in the circuit of the output stage of the amplifier.

  In the present embodiment, the TaN film 2 as a high resistance resistor is formed by sputtering, and the TCR of the TaN film 2 is controlled by adjusting the substrate temperature and the nitrogen gas partial pressure ratio at the time of sputtering. . Further, by setting the power during sputtering to 2.5 kW or less, the sheet resistance of the TaN film 2 is increased to 100Ω / □ or more.

  That is, by lowering the sputtering power of the TaN film 2 to 2.5 kW or less, the deposition speed of the TaN film 2 is reduced, and the film quality of the formed TaN film 2 is high in resistivity ρ. In other words, the TaN film 2 having a sufficiently high sheet resistance Rs is obtained even if the film thickness t is increased. That is, by lowering the power at the time of sputtering, the TaN film 2 having a high film quality with a sheet resistance Rs of 100Ω / □ or more can be obtained even if the film thickness t is 1000 mm or more.

  However, when the film quality is high in resistivity ρ, the absolute value of the TCR also increases. When the TCR is negative, the TCR shifts to the more negative side, and when the TCR is positive, the TCR shifts to the more positive side. . Therefore, the TCR is controlled to a value close to 0, that is, −50 to +50 ppm / ° C. by adjusting the substrate temperature and / or the nitrogen gas partial pressure ratio during sputtering as follows. Alternatively, by adjusting the substrate temperature and / or nitrogen gas partial pressure ratio during sputtering as described below, the TCR is controlled to a value close to 0, that is, −50 to +50 ppm / ° C., and then the power during sputtering. The TaN film 2 having a high resistivity ρ and sheet resistance Rs may be obtained. Due to the power reduction at this time, the resistivity ρ increases and the absolute value of the TCR also increases, but in this case, the value of the TCR is small by adjusting the substrate temperature and / or the nitrogen gas partial pressure ratio during sputtering in advance. Therefore, even if the resistivity is increased, the TCR can be kept in the range of −50 to +50 ppm / ° C.

  Next, a method for adjusting the TCR will be described. The TaN film 2 is formed by sputtering with the substrate temperature set to room temperature to 350 ° C. and the nitrogen gas partial pressure ratio set to 3 to 10%. Within this temperature condition range and nitrogen gas partial pressure ratio condition range, the substrate temperature and the nitrogen gas partial pressure ratio are determined so that the TCR value is −50 to +50 ppm / ° C.

  When the substrate temperature is raised, the TCR value of the obtained TaN film 2 changes more in the positive (+) direction. Further, when the nitrogen gas partial pressure ratio is increased, the TCR value of the obtained TaN film 2 changes more in the negative (-) direction. The substrate temperature and the nitrogen gas partial pressure ratio are determined in a balanced manner so that the TCR value is close to zero.

  In this case, it is preferable that the nitrogen gas partial pressure ratio is relatively low when the substrate temperature is low, and the nitrogen gas partial pressure ratio is relatively high when the substrate temperature is high. That is, when the substrate temperature is normal temperature (20 ° C.), the nitrogen gas partial pressure ratio is preferably 3 to 5%, and when the substrate temperature is 350 ° C., the nitrogen gas partial pressure ratio is preferably 5 to 10%. In the middle of the temperature range from room temperature to 350 ° C., the upper limit value and lower limit value of the nitrogen gas partial pressure ratio may be proportionally distributed with respect to the temperature. That is, when the substrate temperature is T, the lower limit value of the preferable nitrogen gas partial pressure ratio at this time is m1, and the upper limit value is m2, the following formulas 1 and 2 are established.

As for the TaN film formation conditions, the substrate temperature is in the range from room temperature to 350 ° C., but the sputtering gas pressure is, for example, 5 mTorr. The flow rate of the sputtering gas, such as Ar gas is 67sccm, _{N 2} gas is 8 sccm _{(N 2} gas partial pressure ratio of 10%). The supply power is, for example, 0.5 to 3 kW.

これらの数式から、下記数式３，４が成立する。

From these mathematical expressions, the following mathematical expressions 3 and 4 are established.

  FIG. 2 shows the relationship between the upper limit m2 and lower limit m1 of the nitrogen gas partial pressure ratio and the substrate temperature T (formulas 3 and 4), with the substrate temperature T on the horizontal axis and the nitrogen gas partial pressure ratio on the vertical axis. FIG. According to the substrate temperature T, m1 and m2 are obtained, a nitrogen gas partial pressure ratio is selected in the range of m1 to m2, and the nitrogen gas partial pressure ratio is adjusted so that the TCR falls within the range of −50 to +50 ppm / ° C. Alternatively, a nitrogen gas partial pressure ratio is selected in the region between the line segment m2 and the line segment m1 in FIG. 2 and the substrate temperature is 20 to 350 ° C., and then the substrate temperature T May be adjusted so that the TCR falls within the range of −50 to +50 ppm / ° C. At this time, as described above, when the substrate temperature T is raised, the TCR changes in a more positive (+) direction, and when the substrate temperature is lowered, the TCR changes in a more negative (−) direction. The TCR value can be controlled to fall within the range of −50 to +50 ppm / ° C. Also, for example, once the nitrogen gas partial pressure ratio or the substrate temperature, which is one factor, is determined, and then the TCR value is changed by changing the substrate temperature or the nitrogen gas partial pressure ratio, which are the other factors, as described above. Even if the TCR value is adjusted by changing the factor in three or more stages, such as changing the nitrogen gas partial pressure ratio or the substrate temperature, which is one of the factors, and adjusting the factor in three or more stages. Good.

  Eventually, in sputtering, when the substrate temperature is T and the nitrogen gas partial pressure ratio is m, m should satisfy m1 ≦ m ≦ m2, and therefore m satisfies the following equation 5 from equations 3 and 4. Is preferred.

  In this way, the substrate temperature T and the nitrogen gas partial pressure ratio m, which are film formation conditions during film formation by sputtering, are raised within a range where the substrate temperature T and the nitrogen gas partial pressure ratio m satisfy the above-described Expression 5. And the TCR value of the TaN film 2 is adjusted as appropriate based on the criteria that the TCR changes in the positive (+) direction and the TCR changes in the negative (-) direction when the nitrogen gas partial pressure ratio is increased. The range of −50 to +50 ppm / ° C. can be controlled. Therefore, in the embodiment of the present invention, the resistance value of the TaN film 2 as the thin film resistor is high, and the resistance value at this time is almost constant regardless of the temperature change. Therefore, the change in the output current of the amplifier output stage due to the temperature change is small. This effect can be obtained in a temperature range in which the sputtering temperature exceeds 350 ° C. and reaches 400 ° C. Therefore, in the present invention, the sputtering temperature of the TaN film is from room temperature to 400 ° C.

  In the present invention, since the sputtering temperature of the TaN film is at most 400 ° C., the aluminum wiring or the like is not melted. Therefore, the TaN film 2 as the resistor is formed relatively late in the semiconductor device manufacturing process. It can be formed in the upper layer of the interlayer insulating film. Therefore, a TaN film resistive film can be disposed on the aluminum wiring layer, and the chip area can be reduced. In addition, since the TaN film of the present invention may have a low sputtering temperature, it can be easily incorporated in an LSI (Large Scale Integrated Circuit) instead of a single resistor, thereby providing a resistor having a small TCR value. It is possible to easily obtain a circuit to perform.

  Thus, the TaN film has a correlation between TCR (resistance temperature characteristics) and VCR (resistance voltage characteristics). That is, as shown in FIG. 3, the inventors of the present invention decrease the TCR between the TCR (x) and the VCR (y), and the VCR decreases proportionally, and y = 2.83x. It was experimentally found that the relational expression holds. However, the units of TCR and VCR are ppm / ° C. and ppm / V, respectively.

  In an integrated circuit including a general audio amplifier, a resistance film used in the circuit has a unique VCR characteristic in which an absolute value of the resistance changes according to an applied voltage. In an integrated circuit including an audio amplifier using a resistor having such a VCR characteristic, the voltage amplitude of an electric signal flowing in the circuit varies greatly depending on the audio signal (volume). When the absolute value of the resistance value used in the circuit changes with respect to this voltage amplitude, the audio signal that is finally output from this amplifier is reproduced as a distorted sound with the distortion of the resistance value change. Will be. On the other hand, the smaller the VCR of the resistor used in the circuit, the smaller the change in the absolute value of the resistance value with respect to the voltage amplitude of the electric signal, so the distortion of the audio signal finally output from this amplifier is less. The audio characteristics of the amplifier are improved.

  For example, when considering the case of an audio amplifier driven with a power supply voltage of 6 V, if the VCR is set to 150 ppm / V, the distortion rate due to the resistance component is 0.09%. In general, even at such a large volume, if the distortion rate is 0.1% or less, it is considered that the amplifier has a distortion rate that is sufficiently small for general users. Therefore, a resistor having such a small VCR is used as an audio device. By using the amplifier, it is possible to sufficiently reduce the distortion rate required for the audio amplifier.

  As described above, a TaN film having a VCR characteristic smaller than 150 ppm / V can be referred to as a high-quality sound resistance film. When this is converted into a TCR value using FIG. 3, it becomes 53 ppm / ° C. As described above, when the nitrogen gas partial pressure ratio between m1 and m2 in FIG. 2 has the substrate temperature characteristic, since the TCR is within the range of ± 50 ppm / ° C., the VCR is also ± 150 ppm / V. Within the range, it becomes a high-quality audio resistive film.

  The TaN film 2 is not limited to being formed in the uppermost interlayer insulating film (fourth interlayer insulating film 13) as in the above-described embodiment, but as shown in FIG. 21 may be formed in the first interlayer insulating film 10 below 21. In this case, the wiring layers 24 a and 24 b connected to the TaN film 2 through the vias 3 a and 3 b are formed in the same layer as the first wiring layer 21. As described above, the interlayer insulating film on which the TaN film 2 is to be disposed is arbitrary and is not limited to the uppermost layer. However, in terms of the margin of selection of the arrangement position, the inside of the uppermost interlayer insulating film is advantageous.

  According to the manufacturing method of the present invention, a thin film resistor made of a TaN film having a small TCR can be obtained by adjusting the substrate temperature and the nitrogen gas partial pressure ratio, and the thin film made of the TaN film can be obtained by lowering the sputtering power. The resistance of the resistor can be increased, and a via hole for wiring is formed by wet etching, so that damage due to etching of the TaN film can be prevented. Therefore, the present invention is useful for manufacturing a semiconductor integrated circuit that requires a high resistance film having a small TCR. Furthermore, since the sputtering temperature for forming the TaN film is low, it can be easily incorporated later in the manufacturing process of the semiconductor integrated circuit. Therefore, the TaN film has a high resistance resistance film having a small TCR value. This is useful for reducing the chip area.

1: silicon substrate, 2: tantalum nitride (TaN) film, 3a, 3b, 4: via, 10: first interlayer insulating film, 11: second interlayer insulating film, 12: third interlayer insulating film, 13: fourth Interlayer insulating film, 13a: lower insulating film, 13b: upper insulating film, 21: first wiring layer, 22: second wiring layer, 23: third wiring layer, 24a, 24b, 24c: fourth wiring layer

Claims (3)

Forming a semiconductor element on a semiconductor substrate;
Forming a first interlayer insulating film on the semiconductor substrate;
Forming a tantalum nitride film on the first interlayer insulating film by first sputtering, setting the substrate temperature from room temperature to 400 ° C., setting the nitrogen gas partial pressure ratio in the reaction gas to 3 to 10%, and ,
Forming a second interlayer insulating film on the first interlayer insulating film including the tantalum nitride film;
Forming a via hole penetrating through the second interlayer insulating film and reaching the tantalum nitride film by wet etching;
Depositing a metal film by second sputtering to form a metal film in the via hole, and providing a via connected to the tantalum nitride film;
A method of manufacturing a semiconductor device comprising a thin film resistor, comprising: 2. The method of manufacturing a semiconductor device having a thin film resistor according to claim 1, wherein power in sputtering is 2.5 kW or less in the first sputtering step. In the first sputtering, when the substrate temperature during sputtering is T and the nitrogen gas partial pressure ratio is m, the substrate temperature T and the nitrogen gas partial pressure ratio m are (1/165) T + (95/33) ≦ m 3. The method of manufacturing a semiconductor device having a thin film resistor according to claim 1, wherein it is determined so as to satisfy ≦ (1/66) T + (155/33).

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