JP4574293B2 - Crystallinity evaluation method - Google Patents

Description

  The present invention evaluates the crystallinity of a substrate or thin film by applying a depth direction element distribution measurement method that measures the depth direction distribution of an element contained in a solid using sputter etching generated by ion beam irradiation. It relates to the improvement of the method of performing.

  Generally, in order to grasp the crystallinity change in the depth direction of a crystal, a transmission electron microscope (TEM) or Rutherford back scattering (RBS) method is used.

  However, in order to perform TEM observation, it takes a lot of time and labor to prepare a sample, and in order to carry out the RBS method, special equipment for generating a high-energy ion beam used for backscattering is necessary. It is a means that is hardly practical in terms of simplicity and speed.

  In the present invention, the depth of damage caused by, for example, ion implantation can be measured easily and quickly as compared with TEM and RBS.

  Generally, an analytical method that measures the distribution in the depth direction of elements contained in a solid by detecting secondary ions emitted from the surface of the solid by performing sputter etching by ion beam irradiation (primary ions). Is known as a secondary ion mass spectrometry (SIMS) method.

  The SIMS method is widely used mainly in the field of semiconductor materials and semiconductor devices, and is the most frequently used physical analysis method when measuring the depth distribution of elements existing in a substrate or thin film.

  Therefore, if an analysis based on the SIMS method is performed and not only the distribution of elements but also the change in crystallinity can be known at the same time, it is possible to perform a process evaluation relating to a substrate or a thin film very easily and quickly.

  For example, when evaluating an ion implantation process, information on the substrate or thin film made amorphous by ion implantation can be acquired simultaneously with the concentration distribution in the depth direction of the implanted element. It is possible to evaluate the pros and cons of the process.

In crystalline evaluation method according to the present invention, the solid surface is irradiated with ion beams, while generating an insulator or a semi-insulating material on the solid surface continues to sputter etching, this time, are released from the solid surface in an intensity change with respect to the etching time of the secondary ions are measured in a method of assessing the crystallinity of the single crystal or amorphous solid sample that, in the depth direction by applying a certain offset voltage to the solid sample It is characterized in that it comprises measuring the intensity change of secondary ions accompanying the crystallinity change.

  By adopting the above means, for example, the measurement of the distribution in the depth direction of the ion-implanted element and the measurement of the damaged region caused by the ion implantation can be performed at the same time. In comparison, it is possible to carry out the damage area evaluation simply and quickly, and therefore, the results can be immediately fed back to correct the process conditions, for example, and contribute to the manufacture of a high-quality semiconductor device.

  As an embodiment, an example in which the present invention is applied to a sample in which boron (B) is ion-implanted at high concentration and low energy into silicon (Si) will be described.

FIG. 1 is a photograph showing a transmission electron microscope image (TEM image) of a Si substrate into which B ⁺ ions are implanted. In this case, B ⁺ ion implantation conditions are an acceleration voltage of 1 [keV] and a B ⁺ concentration of 1 ×. 10 ¹⁵ cm ⁻² .

  In the Si substrate shown in FIG. 1, a damaged region due to ion implantation from the outermost surface is clearly shown, and it is considered that the Si single crystal is in an amorphous state in this damaged region. It can be seen that the damaged area is composed of two areas having different degrees of damage, that is, an area A and an area B.

FIG. 2 is a diagram showing the relationship between the offset voltage and the secondary ion ( ³⁰ Si ⁺ ) intensity in the regions A, B and C (C is a single crystal region) seen in FIG. For example, depending on the offset voltage, a difference in secondary ion intensity occurs in each of the regions A, B, and C, and it is observed that the difference is most noticeable in the vicinity of −20V. In order to obtain this data, 0.5 keV O ₂ ⁺ was irradiated perpendicularly to the sample surface.

FIG. 3 is a diagram showing the relationship between the change in offset voltage and the change in secondary ion ( ³⁰ Si ⁺ ) intensity in the same sample as described with reference to FIG. This is a result of detecting ³⁰ Si ⁺ while irradiating an ion beam under the same conditions as in the case of 1 and continuing etching, and the offset voltage was changed to 0, −5, −10, −20 V at the time of detection. .

In FIG. 3, the etching time is shown converted into depth using a known etching rate, but as the offset voltage decreases, the change in ³⁰ Si ⁺ intensity becomes noticeable up to a depth of about 30 nm. By changing the voltage to −20 V specified in the measurement of FIG. 1, it is possible to clearly know the change in crystallinity. This changed region of ³⁰ Si ⁺ intensity is considered to be a damaged region due to ion implantation, which is consistent with the TEM image shown in FIG.

FIG. 4 is a diagram obtained by measuring the depth direction distribution of B, which is an ion-implanted element, using the same sample as that used in FIGS. 1 to 3, and at the time of ¹¹ B ⁺ detection, −5 V, ³⁰ Si ⁺ detection Sometimes, an offset voltage of -20V is applied.

  As is apparent from FIGS. 2 and 3, the offset voltage of −5 V does not significantly affect the secondary ion intensity, but the offset voltage of −20 V has a great influence on the secondary ion intensity. Therefore, by applying different offset voltages for the secondary ions of the ion-implanted element and the secondary ions of the base material element, the depth distribution of the desired ion-implanted element and the measurement of the damaged region can be performed simultaneously. it can.

  When performing the measurement, it is important that the surface of the sample be an insulator or a semi-insulator. The charging effect of the insulating surface is a secondary effect as the offset voltage changes as shown in FIG. There is a change in ionic strength.

  In order to form an insulator or semi-insulator on the sample surface, it is easiest to oxidize or nitride the sample surface. As a method for this, an ion beam of oxygen or nitrogen is directly irradiated on the sample surface. It is easy. Alternatively, a method of performing sputter etching while introducing oxygen gas or nitrogen gas into the sample surface without using an ion beam of oxygen or nitrogen may be employed.

  In either method, in order to oxidize or nitride the sample surface, the amount of oxygen or nitrogen injected or adsorbed must be sufficient to produce an oxide film or nitride film in the steady state of sputtering. In order to do this, it is essential to control the acceleration energy of the irradiated ions and the incident angle on the sample surface.

It is a photograph showing the transmission electron microscope image (TEM image) of the Si substrate which ion-implanted B ^<+> . It is a diagram showing the relationship between an offset voltage and secondary ion intensity. It is a diagram showing the relationship between the change of an offset voltage and the change of secondary ion intensity. It is a diagram showing the depth direction distribution of B in Si, and a damage area | region.

Claims (5)

Sputter etching is continued while irradiating the solid surface with an ion beam and generating an insulator or semi-insulator on the solid surface. At that time, the intensity change with respect to the etching time of the secondary ions released from the solid surface is measured. Te in the method of evaluating the crystallinity of the single crystal or amorphous solid sample, a certain offset voltage measuring changes in the intensity of the secondary ions with the crystalline changes in the depth direction is applied to the solid sample A method for evaluating crystallinity, comprising: When applying the offset voltage, the relationship between the offset voltage change and the secondary ion intensity change is obtained in advance, and the offset voltage at which the change in the secondary ion intensity due to the crystallinity change becomes noticeable is included as the specific offset voltage. The crystallinity evaluation method according to claim 1, wherein: 2. When specifying an offset voltage, an offset voltage at which a change in secondary ion intensity accompanying a change in crystallinity does not appear significantly is also specified, and obtained by applying the specified offset voltage together with the measurement of crystallinity evaluation according to claim 1. A method for evaluating crystallinity, comprising measuring a change in element concentration distribution simultaneously with crystallinity by measuring a change in secondary ion intensity. 2. The crystal according to claim 1, wherein the formation of the insulator or semi-insulator includes using an ion beam of oxygen or nitrogen to control the acceleration energy of ions and the incident angle to the sample surface. Sex assessment method. When forming an insulator or semi-insulator, an ion beam that does not contain oxygen and nitrogen is used. When ion beam irradiation is performed, oxygen gas or nitrogen gas is blown onto the solid surface, and the acceleration energy of the irradiated ions and the incident angle on the sample surface 2. The crystallinity evaluation method according to claim 1, further comprising controlling

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