Patent Description:
In the related art, as an example of a method for recognizing an in-plane distribution of an activation state of a semiconductor wafer that is subjected to implantation of dopants and activation annealing, measurement of a sheet resistance is performed. The activation state of the dopants may be evaluated from the in-plane distribution of the sheet resistance (see <CIT>).

United States Patent Application <CIT> discloses a method for monitoring sheet resistance of a metal silicide layer in the manufacture of an integrated circuit device, wherein a modulated first laser beam heats the metal silicide layer and wherein a detector is used to gather a second laser beam reflected from the metal silicide layer.

Japanese Patent Document <CIT> discloses a laser anneal apparatus capable of estimating activation rate of a dopant injected into a deep area.

Generally, a four-point probe method is used for measurement of a sheet resistance. The measurement of the sheet resistance based on the four-point probe method is performed by a device different from an activation annealing apparatus after annealing. Accordingly, the measurement of the sheet resistance becomes an off-line operation, which takes time and labor. Further, since probes should be in contact with a semiconductor wafer, the semiconductor wafer is damaged.

It is desirable to provide a laser annealing apparatus capable of reducing time and labor for measurement of a sheet resistance and measuring a sheet resistance in a non-contact manner. Further, it is desirable to provide a sheet resistance calculation apparatus capable of calculating a sheet resistance in a non-contact manner.

The invention is set out in the appended set of claims <NUM>-<NUM>.

It is possible to measure a sheet resistance of a semiconductor wafer in an in-line manner and in a non-contact manner.

A laser annealing apparatus according to an embodiment will be described with reference to <FIG>.

<FIG> is a schematic diagram of a laser annealing apparatus according to an embodiment. The laser annealing apparatus according to this embodiment includes a laser optical system <NUM>, a chamber <NUM>, an infrared detector <NUM>, a processing device <NUM>, a storage device <NUM>, an output device <NUM>, and an input device <NUM>.

The laser optical system <NUM> includes a laser light source <NUM>, a uniformizing optical system <NUM>, and a folding mirror <NUM>. The laser light source <NUM> outputs a laser beam of an infrared region. As the laser light source <NUM>, for example, a laser diode having an oscillation wavelength of <NUM> may be used. The uniformizing optical system <NUM> makes a beam profile of a laser beam output from the laser light source <NUM> uniform. The folding mirror <NUM> reflects a laser beam passed through the uniformizing optical system <NUM> downward.

A window <NUM> through which a laser beam passes is provided on a top plate of a chamber <NUM>, and a stage <NUM> is disposed in the chamber <NUM>. On the stage <NUM>, a semiconductor wafer <NUM> that is an annealing target is retained. Dopants are implanted into a surface layer part of the semiconductor wafer <NUM>. An ion implantation method is used as the implantation of the dopants, for example. Before annealing, the dopants are not activated. As the semiconductor wafer <NUM>, for example, a silicon wafer may be used. As the dopants, for example, phosphorous (P), arsenic (As), boron (B), or the like may be used.

A laser beam output from the laser optical system <NUM> passes through a dichroic mirror <NUM> and the window <NUM>, and is incident onto the semiconductor wafer <NUM> retained on the stage <NUM>. On a path of the laser beam, a mirror, a lens, or the like may be disposed as necessary. A beam spot of the laser beam on a front surface of the semiconductor wafer <NUM> has an elongated shape of a length of about <NUM> to <NUM> and a width of about <NUM> to <NUM>, for example. The stage <NUM> allows movement of the semiconductor wafer <NUM> in a two-dimensional direction parallel to its front surface. By scanning the surface of the semiconductor wafer <NUM> in the width direction of the beam spot, it is possible to perform laser annealing with respect to an approximately whole region of the front surface of the semiconductor wafer <NUM>.

In a case where a laser beam is incident onto the semiconductor wafer <NUM>, the surface layer part at an incidence position is heated, and thus, the dopants are activated. Thermal radiation light is emitted from the heated portion. A part of the thermal radiation light emitted from the semiconductor wafer <NUM> is reflected from the dichroic mirror <NUM> to then be incident onto the infrared detector <NUM>. The dichroic mirror <NUM> transmits light of a wavelength region shorter than <NUM>, and reflects light of a wavelength region longer than <NUM>, for example. On a path of thermal radiation light from the semiconductor wafer <NUM> to the infrared detector <NUM>, a lens, an optical filter, or the like may be disposed, as necessary. In this embodiment, an optical filter is inserted so that thermal radiation light of a wavelength region of <NUM> to <NUM> is incident onto the infrared detector <NUM>.

The infrared detector <NUM> has a sensitivity in an infrared wavelength region, and outputs a signal (voltage) having a size based on the intensity of incident thermal radiation light. The output signal (output voltage) of the infrared detector <NUM> is input to the processing device <NUM>. The processing device <NUM> controls the laser light source <NUM> so that a pulse laser beam is output from the laser light source <NUM>. Further, the processing device <NUM> controls the stage <NUM> so that the semiconductor wafer <NUM> is moved in a two-dimensional direction, to thereby repeat main scanning and sub-scanning.

The processing device <NUM> acquires a size (output value) of a signal output from the infrared detector <NUM> in synchronization with each shot of pulse laser beams. Further, the processing device <NUM> stores the acquired output value in the storage device <NUM> in association with an in-plane position of the semiconductor wafer <NUM>. For example, for each shot of the pulse laser beams, a temporal waveform of the output value is obtained in accordance with a temporal change of the intensity of the thermal radiation light. The output value accumulated in the storage device <NUM> is a peak value of the temporal waveform or an integrated value of the temporal waveform for each shot of the pulse laser beams, for example.

A variety of commands for instructing operations of the laser annealing apparatus and data are input to the processing device <NUM> through the input device <NUM>. The processing device <NUM> outputs a sheet resistance calculation result to the output device <NUM>.

<FIG> is a graph showing an example of a schematic waveform of a pulse laser beam output from the laser light source <NUM> and an output signal waveform of the infrared detector <NUM>. In a case where a laser pulse rises at a time point t1, an output value of the infrared detector <NUM> gradually increases in accordance with a temperature increase of a surface layer part of the semiconductor wafer <NUM>. In a case where the laser pulse falls at a time point t2, the output value of the infrared detector <NUM> gradually decreases in accordance with a temperature decrease of the surface layer part of the semiconductor wafer <NUM>. An output peak value Vp of the output of the infrared detector <NUM> or an integrated value Vi of a temporal waveform based on the laser pulse from the time point t1 to the time point t2 is accumulated in the storage device <NUM>.

<FIG> is a schematic diagram showing relational data <NUM> indicating a relationship between an output of the infrared detector <NUM> and a sheet resistance in a graph form. The relational data <NUM> is prepared for each type of the semiconductor wafer <NUM>. The processing device <NUM> (<FIG>) calculates a sheet resistance from an output value of the infrared detector <NUM> using the relational data <NUM>. For example, the intensity of thermal radiation light from the surface layer part of the semiconductor wafer <NUM> becomes large due to laser irradiation. That is, the intensity of thermal radiation light becomes larger as an annealing temperature becomes higher, and consequently, the output value of the infrared detector <NUM> becomes larger. Accordingly, as the output value of the infrared detector <NUM> becomes larger, the sheet resistance tends to become smaller.

Further, the sheet resistance depends on the type or concentration of dopants implanted to the semiconductor wafer <NUM>, the thickness of the semiconductor wafer <NUM>, or the like. Accordingly, the relational data <NUM> is prepared for each type (product type) of the semiconductor wafer <NUM>. The relational data <NUM> may be obtained by laser-annealing an evaluation semiconductor wafer having the same structure as an actual product using laser beams having various fluencies and measuring a sheet resistance.

<FIG> is a flowchart showing a procedure for performing laser annealing of the semiconductor wafer <NUM> using the laser annealing apparatus according to this embodiment.

First, the semiconductor wafer <NUM> (<FIG>) in which dopants are ion-implanted is retained on the stage <NUM> (<FIG>) (step S1). For example, this procedure is performed by a robot arm, or the like, for example. The stage <NUM> fixes the semiconductor wafer <NUM> using a vacuum chuck, for example. The type of the semiconductor wafer <NUM> that flows in a manufacturing line is stored in the storage device <NUM> in advance. The processing device <NUM> may acquire the type of the semiconductor wafer <NUM> by reading an identification mark or the like recorded on the semiconductor wafer <NUM>.

After the semiconductor wafer <NUM> is retained on the stage <NUM>, output of a pulse laser beam from the laser light source <NUM> and movement of the stage <NUM> are started (step S2). While the semiconductor wafer <NUM> is being scanned using the pulse laser beam, the intensity of thermal radiation light from the semiconductor wafer <NUM> is measured by the infrared detector <NUM> (step S3). The processing device <NUM> acquires an output value of the infrared detector <NUM>.

The processing device <NUM> stores an in-plane position of the semiconductor wafer <NUM> on which the laser beam is incident and the output value of the infrared detector <NUM> in the storage device <NUM> in association with each other (step S4). The processes of step S3 and step S4 are repeated until an approximately whole region of a front surface of the semiconductor wafer <NUM> is annealed (step S5).

In a case where the annealing of the approximately whole region of the front surface of the semiconductor wafer <NUM> is terminated, the processing device <NUM> calculates a sheet resistance of the semiconductor wafer <NUM> on the basis of the output value of the infrared detector <NUM> (step S6). The processing device <NUM> calculates the sheet resistance using the output value of the infrared detector <NUM> and, for example, the relational data shown in <FIG>. Then, the processing device <NUM> outputs the calculation value of the sheet resistance to the output device <NUM> (<FIG>) in association with the in-plane position of the semiconductor wafer <NUM>. For example, a distribution of the in-plane sheet resistance of the semiconductor wafer <NUM> may be displayed as a figure.

<FIG> is a diagram showing an in-plane distribution of a sheet resistance calculated using the laser annealing apparatus according to this embodiment, and <FIG> is a diagram showing an in-plane distribution of the sheet resistance calculated by the four-point probe method in the related art with respect to the same sample as in <FIG>. In <FIG>, sizes of sheet resistances are indicated by shades of gray. In a measurement result shown in <FIG>, a striped pattern parallel to a main scanning direction of a pulse laser beam is shown. Focusing on one band-like region of the striped pattern, there is a tendency that a sheet resistance on an upper stream side in a scanning direction is higher than a sheet resistance on a downstream side. A cycle of stripes in the striped pattern corresponds to a moving distance in one-time sub-scanning of the pulse laser beam. In the four-point probe method, sheet resistances at <NUM> points in a plane of the semiconductor wafer <NUM> are measured.

<FIG> is a diagram the distribution of the sheet resistances shown in <FIG> and an isopleth of the sheet resistance obtained by measurement using the four-point probe method in an overlapping manner. It can be understood that there is a relationship between the distribution of the sheet resistances obtained by the method according to this embodiment and the distribution of the sheet resistances measured by the four-point probe method. Consequently, it can be understood that the method for calculating the sheet resistances using the laser annealing apparatus according to this embodiment may be employed as an alternative of the method for measuring the sheet resistances using the four-point probe method.

Next, excellent effects of the laser annealing apparatus according to this embodiment will be described.

In the laser annealing apparatus according to this embodiment, basic information (output value of the infrared detector <NUM>) for calculating a sheet resistance is acquired during laser annealing. Thus, it is possible to obtain a sheet resistance without measuring the sheet resistance in an off-line manner after laser annealing.

Further, using the laser annealing apparatus according to this embodiment, it is possible to calculate a sheet resistance without causing the semiconductor wafer <NUM> to be in contact with a probe or the like. Thus, it is possible to calculate a sheet resistance without damaging the semiconductor wafer <NUM> due to the contact with the probe or the like.

A spatial resolution in a case where a sheet resistance is measured by the four-point probe method depends on an inter-probe distance. For example, a distance between probes at opposite ends is about <NUM>. It is difficult to obtain a sheet resistance by a spatial resolution higher than the distance between the probes. On the other hand, in the method according to this embodiment, it is possible to make a spatial resolution high to the extent of the size of a beam spot of a laser beam.

The sheet resistance capable of being measured by the four-point probe method is a sheet resistance in a very shallow surface layer part having a depth of about <NUM> from a front surface of the semiconductor wafer <NUM>. On the other hand, in this embodiment, thermal radiation light emitted from a region having a deeper depth, for example, a region having a depth of <NUM> to <NUM> may also pass through the semiconductor wafer <NUM> to be detected by the infrared detector <NUM>. Thus, it is possible to estimate a sheet resistance in consideration of the depth of <NUM> to <NUM> in the method according to this embodiment.

Next, various modification examples of this embodiment will be described. In the above-described embodiment, a configuration in which silicon is used as the semiconductor wafer <NUM> is shown, but a configuration in which a wafer is formed of a different semiconductor material may be used. Further, in the above-described embodiment, a configuration in which the relational data <NUM> (<FIG>) indicating the relationship between the output of the infrared detector <NUM> and the sheet resistance is prepared for each type of the semiconductor wafer <NUM> is shown. Instead, a configuration in which the relational data <NUM> is prepared for each of various parameters such as a material of the semiconductor wafer <NUM>, a thickness thereof, a type of dopants, a dose, or an implantation depth may be used.

In the above-described embodiment, the laser annealing apparatus having a function for calculating a sheet resistance has been described. A configuration in which functions relating to sheet resistance calculation, of the processing device <NUM>, the storage device <NUM> and the output device <NUM>, and the infrared detector <NUM> are extracted from the laser annealing apparatus according to this embodiment to realize those components as a sheet resistance calculation apparatus are provided.

Claim 1:
A sheet resistance calculation apparatus comprising:
a detector (<NUM>) onto which thermal radiation light from a semiconductor wafer (<NUM>) that is an annealing target is incident, and which outputs a signal based on the intensity of the thermal radiation light; and
a processing device (<NUM>) to which an output value of the detector (<NUM>) is input, and which calculates a sheet resistance of the semiconductor wafer (<NUM>) on the basis of the output value of the detector (<NUM>) and outputs a calculation value of the sheetresistance, characterised in that the detector is an infrared detector.