JPH118224A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the charge-up damage generated by plasma by a method, wherein the electron temperature of plasma for plasma etching is made spatially uniform on a semiconductor substrate. SOLUTION: A desired plasma state can be obtained by changing the current value of two pairs of solenoid coils 5. The plasma state is diagnosed by a Langmuir probe 8. After confirmation of the plasma state, a metal wiring is formed by dry-etching the aluminum alloy of a damage measuring semiconductor device, using a resist mask. The resist mask which has become unnecessary is ashed off by the mixed gas plasma of oxygen ad water. Subsequently, the amount of charge-up damage is estimated by checking electrical characteristics using a transistor characteristic measuring instrument. As a result, charge-up damage can be suppressed. Since the intensity of electric field, generated between a gate electrode and a semiconductor substrate can be suppressed, the yield of production can be drastically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device when a semiconductor substrate is etched using a plasma etching apparatus, particularly when metal wiring is etched.

[0001]

2. Description of the Related Art As the thickness of a gate oxide film is reduced with the miniaturization of LSIs, the destruction of the gate oxide film due to charging during plasma processing, especially during plasma etching, has become a serious problem. In particular, charging damage tends to be remarkable during metal wiring etching after transistor formation. Therefore, it is necessary to develop an etching apparatus with less charging damage and to find an index that can be used to avoid charging damage. One example of such an apparatus is proposed in Japanese Patent Laid-Open No. 8-255787. This etching apparatus transmits a 13.56 MHz high frequency signal to a substrate bias electrode side on which etching is performed at a frequency of 600 to 80 having a duty ratio of 50/50%.
An object of the present invention is to apply a high-frequency power modulated by a 0 kHz pulse signal (hereinafter, referred to as a pulse bias method) to reduce a potential difference on a surface of a semiconductor substrate exposed to plasma and reduce charge-up.

Further, a positive ion saturation current density distribution in plasma is frequently used as an index of plasma with little charge-up damage, ie, uniform plasma. It has been described that when performing plasma etching, plasma damage can be avoided by setting control parameters during discharge so that the ion current density distribution becomes uniform. This ion saturation current density distribution can be easily measured using the Langmuir probe method. For example, Gab
riel et al. (J. Vac. Sci. Technol. B
12 p454, 1994) uses an inductively coupled plasma discharge etching apparatus to measure the uniformity of the ion current density and the plasma potential using the above-described probe method. It has gained. It is reported that by applying this plasma to etching, etching with less damage was realized.

[0003]

However, according to the pulse bias method disclosed in Japanese Patent Application Laid-Open No. 8-255787, the duty ratio of 50/50% and the pulse frequency of 600 to 800 kHz can always be optimized depending on the type of etching gas. Absent. This is because the impedance of the plasma greatly differs depending on the type of gas (a rare gas such as a rare gas such as He or Ar or a halogen gas). Therefore,
There is no guarantee that the potential difference on the surface of the semiconductor substrate exposed to plasma can be kept small. Further, Japanese Patent Application Laid-Open No.
The measurement of the surface potential distribution shown in 255787 is an effective method as a means for monitoring the uniformity of plasma, but cannot be said to be a simple method as a measuring means. The simplest method is the measurement of various plasma quantities using the above-described Langmuir probe method.

[0004] However, it has been clarified by experiments of the present inventor that the ion saturation current density distribution described above is not always an index of low charge-up damage.
Specific examples are shown below.

FIG. 3 shows an ion saturation current density distribution on a semiconductor substrate having a diameter of 150 mm under three types of discharge conditions. These discharge conditions can be broadly classified into those giving an extremely uniform current density distribution and those giving an extremely non-uniform distribution (discharge conditions in which the uniformity of the ion saturation current density distribution is ± 4.6%). Is referred to as condition 1, similarly, a discharge condition of ± 7.1% is referred to as condition 2, and a discharge condition of ± 40.4% is referred to as condition 3). Therefore, according to the conventional determination of the plasma uniformity using the ion saturation current density, the plasma uniformity of the conditions 1 and 2 is much better than that of the condition 3;
Therefore, the charge-up damage is expected to be the lowest. On the other hand, condition 3 should cause the most damage.
However, it was found that damage occurred in conditions 1 and 2, and that condition 3 caused the least damage.

FIG. 4 is a graph showing Qbd (a unit area up to the dielectric breakdown, estimated from the time required to pass a constant current through the gate insulating film to the breakdown, which is an index of the breakdown voltage of the gate insulating film in the semiconductor device). FIG. 4 shows the dependence of the amount of charge passing therethrough on the antenna ratio (the value obtained by dividing the area of a wiring electrically connected to the gate electrode by the area of the gate electrode). This is one of the generally well-known damage evaluation methods.
There are S capacitors and MOS transistors. The effect of the charge-up damage appears as a reduction in the breakdown voltage of the gate insulating film. That is, as the antenna ratio increases, Qbd
Deteriorates (decreases). In each of the above conditions, conditions 1, 2, and 3 are obtained by arranging Qbd in a descending order of the degree of deterioration. That is, the higher the uniformity of the ion saturation current density is, the more severe the charge-up damage is.

Therefore, it is understood that the ion saturation current density distribution is not always sufficient to be used as an index of plasma uniformity with less charge-up damage.

An object of the present invention is to reduce charge-up damage caused by plasma in a method of manufacturing a semiconductor device, and to provide a method which can be easily manufactured with high reliability and productivity. It is.

[0009]

A method of manufacturing a semiconductor device according to the present invention is characterized in that a plasma electron temperature for plasma etching is made spatially uniform on a semiconductor substrate.

Further, the variation in electron temperature is 0.5e
V or less.

The operation of the present invention will be described. In a dry etching process of a silicon semiconductor device, it is necessary to suppress a potential difference or an electric field generated between a gate electrode of the device and a silicon substrate as much as possible. As a guide, it is said that the electric field strength at which an intrinsic breakdown of a gate insulating film made of a silicon oxide film occurs is 8 MV / cm. When dry etching a silicon semiconductor device, the gate electrode of the silicon semiconductor device is in an electrically floating state. Therefore, the potential of the gate electrode becomes equal to the floating potential (hereinafter referred to as Vf) given by the plasma generated in the dry etching apparatus. Further, the potential of the silicon substrate is also determined by this Vf. The reason is that the edge of the silicon semiconductor substrate irradiated with the plasma (hereinafter referred to as silicon substrate) is also directly exposed to the plasma. In addition, the silicon substrate is placed on the bias electrode and is in a DC floating state. Therefore, it becomes equal to Vf, similarly to the potential of the gate electrode. Generally, Vf is determined by a DC self-bias voltage (hereinafter referred to as Vdc) generated when an RF high frequency is applied to a bias electrode and a plasma potential (hereinafter referred to as Vp) which is a reference potential of plasma. Vdc is determined by the electron temperature of the plasma (hereinafter, referred to as Te), the mass (M) of the process gas element, the electron mass (m), and the RF high-frequency voltage (Vrf) applied to the bias electrode. Assuming that the Boltzmann constant is k and the elementary charge is e, the relational expression is as follows.

Vdc = Vrf + (1/2) (kTe / e)
{In (M / 2πm) -ln (2πeVrf / kTe)} Vf−Vp = Vdc Further, Vp and Te are Vp = Te / 2, so if Te is spatially uniform, Vf will also be spatially uniform. This is clear from the above two equations. For example,
In dry etching using chlorine gas, assuming that the variation of Te is 0.5 eV and the electric field strength leading to intrinsic breakdown is 8 MV / cm as described above, the 2.9 nm gate insulating film can withstand charge-up damage in principle. It will be.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 of the present invention will be described below in detail. FIG. 1 is a configuration diagram of a dry etching apparatus used in an embodiment of the present invention. Reference numeral 1 denotes a vacuum device for generating plasma, having a diameter of 357 mm and a height of 125.
It comprises a metal container 2 having a height of 60 mm and a quartz bell jar 3 having a height of 60 mm and a diameter of 100 mm. The vacuum device at the time of etching is maintained at about 10 mTorr. Plasma used for etching is generated by a helicon wave excited in the plasma. Helicon waves are 13.56 MH
It is excited by a static magnetic field generated from an RF antenna 4 to which a high frequency of z is applied and two pairs of solenoid coils 5. The directions of the magnetic fields generated from the inner and outer solenoid coils are opposite to each other, with the inside facing downward and the outside facing upward. Reference numeral 6 denotes a bias electrode, and the semiconductor substrate 7 is provided on the bias electrode 6. A high frequency of 13.56 MHz is applied to the bias electrode 6 and has a role of controlling the energy when ions in the plasma enter the semiconductor substrate 7.

The plasma measurement is performed using the Langmuir probe 8
Was performed using The probe 8 is connected to the 25 of the semiconductor substrate 7.
mm. The tip of the probe 8 is a cylindrical needle made of tungsten and has a surface area of 0.05 cm @ 2. A direct current voltage is swept from -50 V to 70 V on tungsten at the probe tip 8, and charged particles in the plasma are taken in along with the current. The current-voltage characteristic causes the electron temperature, plasma potential, floating potential, ion saturation current density, etc. Plasma quantities can be estimated.

Next, the semiconductor device used for damage measurement and dry etching conditions according to the present invention will be described. The damage measuring semiconductor device comprises an N-channel MOSFET group formed on a P-type silicon substrate having a diameter of 150 mm. The design rules for the transistor are as follows: the gate insulating film is 6.0 nm, the gate length is 0.35 μm, and the gate width is 10 μm.
m. The gate electrode was electrically connected to a metal wiring (antenna) made of an aluminum alloy, and the antenna ratio was changed from 53 times to 26000 times. As an etching gas, a mixed gas of chlorine and boron trichloride was used. The total gas flow rate was 100 sccm, the high frequency power for exciting the helicon wave was 1000 W, and the substrate bias power for controlling the ion incident energy was 140 W.

The procedure up to the damage measurement will be described.
A desired plasma state is generated by changing the current values of the two pairs of solenoid coils. The plasma state is diagnosed with a Langmuir probe. After confirming the plasma state, a metal wiring is formed by dry-etching the aluminum alloy of the semiconductor device for damage measurement according to a resist mask. The unnecessary resist mask is ashed and removed by a mixed gas plasma of oxygen and water. Thereafter, the amount of charge-up damage is estimated by examining the electrical characteristics with a transistor characteristic measuring device.

FIG. 2 is a drawing showing an electron temperature distribution on a semiconductor substrate. The current value of the inner solenoid coil is 50A,
Assuming that the outer current value is 30 A, the damage measuring semiconductor device having a diameter of 150 mm has a mountain-shaped distribution, and a maximum temperature variation of 6 eV occurs. Next, the inner coil current value is set to 40
A, if the outside current value is 25 A, the temperature variation is 3e
V. Further, assuming that the inner coil current value is 10 A and the outer current value is 10 A, the temperature variation is 0.5 e.
V. Thus, it is understood that the plasma state can be arbitrarily changed by changing the coil current value. Now, as described in the above-mentioned [Problems to be Solved by the Invention], the conditions 1, 2 and 3 shown in FIG. 4 satisfy the above-mentioned inner and outer solenoid current values 50A / 30A and 40A / 25.
A, 10A / 10A respectively. In other words, it can be concluded that etching in the plasma state in which the variation in the electron temperature is minimum (in the present embodiment, plasma in which the inner and outer solenoid current values are discharged at 10 A / 10 A) causes the least damage. On the other hand, the degree of damage increases as the variation in electron temperature increases.

Although the above embodiment has been described with respect to a helicon wave plasma etcher, the present invention relates to an electron cyclotron resonance plasma (ECR plasma) apparatus, an inductively coupled plasma apparatus, a capacitively coupled plasma apparatus, and the like. Even if it is used, it is needless to say that charge-up damage can be suppressed by using plasma having a uniform electron temperature distribution.

[0019]

The effect is that charge-up damage can be suppressed. Thereby, the production yield is dramatically improved. This is because the electric field intensity generated between the gate electrode and the semiconductor substrate was suppressed because a method of performing dry etching with plasma in which the variation in electron temperature of plasma was minimized was selected.

[Brief description of the drawings]

FIG. 1 shows a dry etching apparatus used in an embodiment of the present invention.

FIG. 2 shows an electron temperature distribution obtained in an example of the present invention.

FIG. 3 shows an ion saturation current density distribution for describing a problem to be solved by the present invention.

FIG. 4 shows Qbd as an index of the gate insulating film breakdown voltage of the semiconductor device obtained in the example of the present invention. The results of the examples of the present invention are also used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum apparatus 2 Metal container 3 Quartz bell jar 4 RF antenna 5 Solenoid coil 6 Bias electrode 7 Semiconductor substrate 8 Langmuir probe

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device, comprising: making a plasma electron temperature for plasma etching spatially uniform on a semiconductor substrate. 2. The method according to claim 1, wherein the variation in the electron temperature is 0.5 eV or less.