JP2002050665A - Thickness-measuring element for semiconductor film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thickness-measuring element for a semiconductor film which is capable of easily and electrically measuring the thickness of an SOI layer, rather than introducing facilities, such as high-price film thickness measuring instruments, etc., for measuring the thickness of a silicon film (SOI layer) for forming an active layer on a SOI substrate. SOLUTION: A pair of SOI layers are surrounded with isolation trenches and are connected to an embedded oxide film on an SOI substrate, and one of the SOI layers has a p+-type diffused layer or oxide film formed shallower than the thickness of the SOI layer. The sheet resistance or the diffusion resistance of the pair of SOI layers is measured and simultaneous equations composed of the resistivity, and the effective thickness of the SOI layers are solved to readily obtain the thickness of the SOI layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for measuring the thickness of a semiconductor thin film, and more particularly to an SOI (Silicon).
The present invention relates to a measuring element for electrically measuring the thickness of a semiconductor layer formed of a silicon thin film on an on-insulator substrate.

[0002]

2. Description of the Related Art In recent years, in the field of semiconductor integrated circuits (hereinafter abbreviated as ICs) which incorporate semiconductor elements having a high withstand voltage and a large current used in OA equipment, information communication equipment, lighting equipment and the like, the integration of circuits has been increased. At the same time, a semiconductor device using an SOI substrate that can incorporate a device with high withstand voltage and large current drive has been receiving attention. As an SOI substrate in this field, a bonded substrate in which two single-crystal silicon substrates are bonded via an insulating film and the surface is polished to form a silicon thin film to be an active layer having a desired thickness is often used. You.

When an IC is manufactured using this bonded substrate, a trench isolation groove is formed between the elements to reach an insulating film embedded in the substrate, in order to perform lateral element isolation. A semiconductor element is formed on an active layer (hereinafter, abbreviated as SOI layer) made of an island-like silicon thin film completely buried with an insulator and separated by a dielectric.

[0004]

However, in the SOI substrate described above, a silicon substrate serving as an SOI layer is attached to a silicon substrate serving as a supporting substrate, and the surface of the SOI substrate is formed to a desired thickness (the SOI layer film usually used for ICs). Thickness is several μm to 10
(It is about several μm). However,
Since the thickness of the entire SOI substrate is 500 μm or more, it is difficult to control the thickness of the thin SOI layer with high accuracy, and the variation in the thickness of the SOI layer affects the electrical characteristics such as the breakdown voltage of the semiconductor element. It is important to control the thickness of the SOI layer in the acceptance inspection of the substrate or in the manufacturing process of the semiconductor device.

However, in a conventional ellipsometer using a visible light source or a light interference type film thickness measuring device using a white light source, visible light is absorbed by the SOI layer, and the film thickness cannot be measured.
On the other hand, the measurement can be performed by using a light source in the ultraviolet region, but the measurement cannot be performed accurately unless the film thickness is less than several μm. In particular, when the film thickness is more than 10 μm, the light is absorbed by the SOI layer and cannot be measured. Therefore, in order to measure the thickness of the SOI layer of the SOI substrate in the field of high withstand voltage and large current, an expensive device such as a Fourier transform infrared spectrometer was required.

The present invention solves the above-mentioned problem. Instead of introducing an expensive film thickness measuring device or the like for measuring the thickness of the SOI layer, the thickness of the SOI layer can be simply and electrically measured. It is an object of the present invention to provide a semiconductor thin film thickness measuring element which can be measured dynamically.

[0007]

In order to achieve this object, a semiconductor thin film thickness measuring element according to claim 1 of the present invention comprises a first insulating film separated from a supporting substrate by a buried insulating film.
A pair including a conductive semiconductor film and a first conductive first semiconductor layer and a first conductive second semiconductor layer formed on the semiconductor film and electrically isolated from each other is provided. In the measurement element to be formed, a diffusion layer of a second conductivity type formed shallower than a thickness of the semiconductor film is provided on a surface of the first semiconductor layer.

According to this structure, since the diffusion layer of the second conductivity type is formed in the first semiconductor film by using the diffusion layer forming the semiconductor element, it is necessary to add a new process for forming the film thickness measuring element. There is no.

Next, a semiconductor thin film thickness measuring element according to a second aspect of the present invention is formed on the semiconductor film of the first conductivity type insulated and separated from the supporting substrate by a buried insulating film. A pair of measuring elements comprising a first conductive type first semiconductor layer and a first conductive type second semiconductor layer which are electrically insulated and separated from each other. It has an oxide film formed on the surface.

According to this structure, since the oxide film is formed on the first semiconductor film using the oxide film forming the semiconductor element, it is not necessary to add a new process for forming the film thickness measuring element.

Next, according to a third aspect of the present invention, there is provided a semiconductor thin film thickness measuring element, wherein a pair of measuring elements measures the sheet resistance of the first semiconductor layer and the second semiconductor layer. hand,
It is a four-terminal square sheet resistance pattern configured to calculate the thickness of the semiconductor layer from the measured value.

With this configuration, the sheet resistance of the first semiconductor layer and the second semiconductor layer can be measured, and the thickness of the semiconductor layer can be easily obtained from the measured values.

Next, in a semiconductor thin film thickness measuring element according to a fourth aspect of the present invention, a pair of measuring elements measures a diffusion resistance value of the first semiconductor layer and the second semiconductor layer. And a two-terminal rectangular diffusion resistance pattern configured to calculate the thickness of the semiconductor layer from the measured value.

With this configuration, the diffusion resistance values of the first semiconductor layer and the second semiconductor layer can be measured, and the thickness of the semiconductor layer can be easily obtained from the measured values.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a semiconductor thin film thickness measuring element according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along line AA 'of the pair of film thickness measuring elements shown in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB' of one film thickness measuring element shown in FIG. In each of the figures, reference numeral 2 denotes a trench isolation trench in which the inside of the trench is buried with an insulating film such as a silicon oxide film, and 3 denotes an n ⁻ -type first SOI surrounded by the trench isolation trench 2 and completely separated by a dielectric. Layer, 4 is first
N ⁻ -type second SOI layer forming a pair with the SOI layer 3 of FIG.
5 is an n ⁺ type diffusion layer serving as a contact layer, 6 is a p ⁺ type diffusion layer, 7 to 14 are electrodes connected to the respective contact layers 5, 15 is a p ⁻ type silicon support substrate, 16 is a buried oxide film, 17 is an n ⁻ type silicon thin film, and 21 is a field oxide film.

As shown in FIG. 1, a pair of first SO
Two pairs of contact layers 5 are arranged opposite to each other on the I layer 3 and the second SOI layer 4, and a p ⁺ -type diffusion layer 6 is formed in a region excluding the contact layer 5 from the first SOI layer 3. Is formed. As shown in FIG. 2, the SOI substrate has a multilayer structure including a support substrate 15, a buried oxide film 16, and a silicon thin film 17, and the elements are island-shaped SOI layers 3, 4 made of a silicon thin film 17. Formed in In addition,
The SOI substrate used here has a buried oxide film thickness of about 1 μm.
m, and the thickness of the SOI layer is about several μm to several tens μm.

As shown in FIG. 3, the p ⁺ type diffusion layer 6 is formed to be shallower than the thickness of the first SOI layer 3, and the trench isolation trench 2 is formed in a region excluding the contact layer 5.
Is in contact with Further, electrodes 7-14 connected to the respective contact layers 5 through contact windows provided in the field oxide film 21 are provided. Note that the embodiment of the present invention includes a protective film and the like, but is omitted in FIGS. 2 and 3.

In the semiconductor thin film thickness measuring device according to the first embodiment having such a configuration, when a current of several tens of μA to several hundreds of μA is applied from the electrode 11 formed on the second SOI layer 4 to the electrode 12. , SOI layer 4 flows current I2 [A]. At this time, since a voltage difference V2 [V] is generated between the opposing electrodes 13 and 14, Vande
The sheet resistance value Rs2 [Ω] of the second SOI layer 4 can be calculated by Expression 1 by the r Pauw method.

Rs2 = (π / ln2) × (V2 / I2) Formula 1 And the specific resistance ρSOI [Ω · c of the second SOI layer 4
m] is the sheet resistance value Rs2 [Ω] and the film thickness tSOI [μ].
m], and can be expressed by Equation 2.

ΡSOI = Rs2 × tSOI / 10000 Equation 2 Next, from the electrode 7 formed on the first SOI layer 3 to the electrode 8
When a current is applied to the, p ⁺ -type SOI directly under the diffusion layer 6 of
A current I1 flows through the layer. At that time, a voltage difference V1 [V] is generated between the opposing electrode 9 and the electrode 10, and therefore, the equation 1
Similarly, the sheet resistance value Rs1 of the first SOI layer 3
Can also be calculated by Equation 3.

Rs1 = (π / ln2) × (V1 / I1) Equation 3 Here, the sheet resistance value Rs1 is the squeeze resistance of the SOI layer immediately below the p ⁺ type diffusion layer 6. Since the diffusion length tp [μm] of the p ⁺ type diffusion layer 6 is a value measured and controlled in advance in the diffusion step, the specific resistance ρSOI of the SOI layer can be expressed by Expression 4 in the same manner as Expression 2.

ΡSOI = Rs1 × (tSOI−tp) / 10000 (Equation 4) By solving the simultaneous equations of Equations 2 and 4, S
The thickness tSOI of the OI layer can be obtained by Expression 5.

TSOI = (Rs1 × tp) / (Rs1−Rs2) (Equation 5) As described above, in the semiconductor thin film thickness measuring element according to the first embodiment of the present invention, the first and the third equations are used. By measuring the sheet resistance values of the second SOI layer 4 and the first SOI layer 3 and using the results, the thickness of the SOI layer can be easily obtained by equation (5). Since the p ⁺ -type diffusion layer 6 formed in the first SOI layer 3 is formed using a diffusion layer constituting an element built in the IC, a new process is added to measure the film thickness. No need. The thickness of the SOI layer is more than 10 μm.
Even in the case described above, the measurement can be made relatively accurately by selecting a deep diffusion layer as the p ⁺ type diffusion layer 6.

The diffusion length of the p ⁺ -type diffusion layer 6 is a value measured and managed in advance by a spreading resistance measurement or SIMS analysis in the diffusion step.

[Second Embodiment] FIG. 4 is a plan view of a semiconductor thin film thickness measuring element according to a second embodiment of the present invention.
The cross-sectional view taken along line AA ′ of the pair of film thickness measuring elements shown in FIG. 4 is the same as FIG. 2, and the cross-sectional view taken along line BB ′ of one film thickness measuring element shown in FIG. It is omitted because it is the same. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 4, a pair of first SO
A pair of contact layers 5 are arranged to face each of the I layer 3 and the second SOI layer 4, and a p ⁺ -type diffusion layer 6 is formed in a region excluding the contact layer 5 from the first SOI layer 3. Is formed. The p ⁺ -type diffusion layer 6 is a contact layer 5
Are in contact with the trench isolation trenches 2 in the region excluding. Further, the electrodes 8, 9, 12, 1 connected to each contact layer 5
3 are provided. The first SO thus formed
Both the I layer 3 and the second SOI layer 4 have a resistance length L [μm].
Thus, a diffusion resistance having a resistance width W [μm] is obtained.

In the semiconductor thin film thickness measuring device according to the second embodiment having such a configuration, when a current of several tens μA to several hundred μA is applied from the electrode 12 formed on the second SOI layer 4 to the electrode 13. , An electric current I4 [A] flows through the SOI layer 17, and a potential difference V4 [V] is generated between the electrodes at both ends.
The sheet resistance Rs2 [Ω] of the layer 4 can be calculated by Expression 6.

Rs2 = R2 × (W / L) Equation 6 Similarly to the first embodiment, the specific resistance ρSOI of the SOI layer can be expressed by Equation 2.

Next, when a current is applied from the electrode 8 formed on the first SOI layer 3 to the electrode 9, a current I3 flows in the SOI layer immediately below the p ⁺ -type diffusion layer 6, and both ends of the electrode Since the potential difference V3 is generated, the first SO
The sheet resistance value Rs1 of the I layer 3 can also be calculated by Expression 7.

Rs1 = R1 × (W / L) (7) Here, the sheet resistance value R is calculated in the same manner as in the first embodiment.
Since s1 is the squeeze resistance of the SOI layer immediately below the p ⁺ type diffusion layer 6, the specific resistance ρSOI of the SOI layer can be expressed by Expression 4.

Here, the sheet resistance value Rs1 is the squeeze resistance of the SOI layer immediately below the p ⁺ type diffusion layer 6. Since the diffusion length tp [μm] of the p ⁺ -type diffusion layer 6 is a value measured and controlled in advance in the diffusion process, S
The specific resistance ρSOI of the OI layer can be expressed by Expression 4. Therefore, similarly to the first embodiment, the thickness t of the SOI layer
The SOI can be obtained by Expression 5.

As described above, in the semiconductor thin film thickness measuring element according to the second embodiment of the present invention, similarly to the first embodiment, the second SOI layer 4 and the first SO
By measuring the sheet resistance value of the I layer 3 and using the result, the thickness of the SOI layer can be easily obtained by the equation (5). In addition to the effects of the first embodiment, by measuring the SOI layer as a diffusion resistance value, the number of probes required for the measurement is reduced by half, and a highly accurate voltmeter for measuring the potential difference is provided. Not required. Further, the number of electrodes required for measuring the sheet resistance value is halved, and the area for forming the measuring element can be reduced.

[Third Embodiment] FIG. 5 is a plan view of a semiconductor thin film thickness measuring device according to a third embodiment of the present invention.
FIG. 6 is a cross-sectional view taken along line CC 'of the pair of film thickness measuring elements shown in FIG. 5, and FIG.
It is sectional drawing by the -D 'line. In each of the drawings, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 5, a pair of first SO
Two pairs of contact layers 5 are arranged to face the I layer 3 and the second SOI layer 4, respectively. As shown in FIGS. 6 and 7, the surface of the region excluding the contact layer 5 from the first SOI layer 3 is covered with a silicon oxide film (hereinafter abbreviated as LOCOS oxide film) 22 by a selective oxidation method. For,
The effective SOI film thickness is smaller than the film thickness of the second SOI layer 4. Further, similarly to FIGS. 1 to 3, electrodes 7-14 connected to each contact layer 5 are provided. In the embodiment of the present invention, a protective film and the like are provided, but are omitted in FIGS. 6 and 7.

In the semiconductor thin film thickness measuring device according to the third embodiment, the sheet resistance value Rs2 and the specific resistance ρSOI of the second SOI layer 4 are set in the same manner as in the first embodiment. , Can be represented by Equations 1 and 2, respectively. Further, the sheet resistance value Rs1 of the first SOI layer 3
Similarly, can be expressed by Equation 3. Here, the first
Since the LOCOS oxide film 22 is formed on the SOI layer 3, the effective SOI layer becomes thinner. Generally, when oxidizing a silicon crystal, 45% of the entire oxide film thickness to [μm] can be formed below the original surface, and thus the effective SOI film thickness is a film thickness obtained by subtracting to × 0.45. Therefore,
The specific resistance ρSOI of the first SOI layer 3 can be expressed by Expression 8.

ΡSOI = Rs1 × (tSOI−to × 0.45) / 10000 Equation 8 Therefore, by solving the simultaneous equations of Equations 2 and 8, S
The thickness tSOI of the OI layer can be obtained by Expression 9.

TSOI = (Rs1 × to × 0.45) / (Rs1−Rs2) Equation 9 As described above, in the semiconductor thin film thickness measuring element according to the third embodiment of the present invention, the first embodiment Similarly to the embodiment, the sheet resistance values of the second SOI layer 4 and the first SOI layer 3 are measured by Equations 1 and 3, and the results are used to easily determine the film thickness of the SOI layer by Equation 9. You can ask. And the first S
Since the LOCOS oxide film 22 formed on the OI layer 3 can be formed using the same process as the LOCOS oxide film for isolating elements built in the IC, there is no need to add a new process. Further, in the first embodiment, the first
Since the p ⁺ type diffusion layer 6 is formed in the SOI layer 3 of FIG.
Since it is affected by the depletion layer extending from the PN junction and the leakage current of the PN junction, it causes a variation in the measured value of the squeeze resistance. However, when the LOCOS oxide film 22 is used, these can be avoided. Also, LOCO is smaller than the diffusion length of the p ⁺ type diffusion layer.
Since the thickness of the S oxide film has good controllability and there is little variation within the wafer surface, between wafers, and between batches, the thickness of the SOI layer can be measured more accurately.

As the thickness of the LOCOS oxide film 22, a value previously measured and controlled by an ellipsometer or the like in the oxidation step is used.

[Fourth Embodiment] FIG. 8 is a plan view of a semiconductor thin film thickness measuring element according to a fourth embodiment of the present invention.
A cross-sectional view of the pair of film thickness measurement elements shown in FIG. 8 taken along line CC ′ is the same as FIG. 6, and a cross-sectional view of one film thickness measurement element shown in FIG. 8 taken along line DD ′ is FIG. It is omitted because it is the same. The same components as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 8, a pair of first SO
A pair of contact layers 5 are arranged to face each of the I layer 3 and the second SOI layer 4, and the surface of the region excluding the contact layer 5 from the first SOI layer 3 is covered with a LOCOS oxide film 22. Covering. The LOCOS oxide film 22 is in contact with the trench isolation trench 2 in a region except for the contact layer 5. Further, electrodes 8 connected to each contact layer 5,
9, 12, and 13 are provided. The first SOI layer 3 and the second SOI layer 4 thus formed are both diffusion resistances having a resistance length L and a resistance width W, as in the second embodiment.

In the semiconductor thin film thickness measuring element according to the fourth embodiment having the above-described structure, the second SOI layer 4 and the first SOI layer 4 are expressed by the equations 6 and 7 in the same manner as in the second embodiment.
Then, the sheet resistance value of the SOI layer 3 is measured, and the thickness of the SOI layer can be easily obtained by Expression 9 using the result.

As described above, in the semiconductor thin film thickness measuring element according to the fourth embodiment of the present invention, in addition to the effect according to the third embodiment, the sheet thickness is measured in the same manner as the effect according to the second embodiment. The number of electrodes required for measuring the resistance value is reduced by half, and the formation area of the measurement element can be reduced.

In the first and second embodiments, the SOI layer to be measured is of the n ⁻ type and the diffusion layer for forming the squeeze resistance is of the p ⁺ type. The thickness of the SOI layer can be measured in the same manner even when the layer is p ⁻ type and the diffusion layer for forming the squeeze resistance is n ⁺ type. However, at this time, it is necessary to reverse the polarity of the applied current in order to bring the PN junction formed by the p ⁻ type SOI layer and the n ⁺ type diffusion layer into a reverse bias state.

[0045]

As described above, the element for measuring the thickness of a semiconductor thin film of the present invention can be formed by using components (diffusion layer, oxide film, etc.) for forming a semiconductor element incorporated in an IC. It is not necessary to add a new step to measure the thickness of the SOI layer. Then, the sheet resistance value or the diffusion resistance value of the SOI layer is measured by an electrical characteristic evaluation performed during or after the manufacturing process, and the thickness of the SOI layer can be easily obtained from the measured value. Furthermore, it is possible to manage the variation in the thickness of the SOI layer of the SOI substrate and the variation in the characteristics in the manufacturing process by observing the correlation between the thickness of the SOI layer which affects the breakdown voltage of the semiconductor element and the electrical characteristics of the element. it can.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a semiconductor thin film thickness measuring element according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of the semiconductor thin film thickness measuring element taken along line AA ′ in FIG. 1;

FIG. 3 is a cross-sectional view of the semiconductor thin film thickness measuring element taken along line BB ′ in FIG. 1;

FIG. 4 is a schematic plan view of a semiconductor thin film thickness measuring element according to a second embodiment of the present invention.

FIG. 5 is a schematic plan view of a semiconductor thin film thickness measuring element according to a third embodiment of the present invention.

6 is a cross-sectional view of the semiconductor thin film thickness measuring element taken along the line CC ′ in FIG. 5;

7 is a cross-sectional view of the semiconductor thin film thickness measuring element taken along line DD ′ in FIG. 5;

FIG. 8 is a schematic plan view of a semiconductor thin film thickness measuring element according to a fourth embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 2 trench isolation trench 3 first SOI layer (semiconductor layer) 4 second SOI layer (semiconductor layer) 5 n ⁺ type diffusion layer serving as contact layer 6 p ⁺ type diffusion layer 7-14 electrode 15 p ⁻ type Silicon support substrate 16 buried oxide film 17 n ^- type silicon thin film (semiconductor film) 21 field oxide film 22 LOCOS oxide film

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01L 27/12

Claims (4)

[Claims] 1. A semiconductor film of a first conductivity type, which is insulated and separated from a supporting substrate by a buried insulating film, and a first semiconductor of a first conductivity type, which is formed on the semiconductor film and is electrically insulated and separated. A pair of measuring elements comprising a first semiconductor layer and a second semiconductor layer of the first conductivity type, wherein the diffusion of the second conductivity type formed shallower than the thickness of the semiconductor film on the surface of the first semiconductor layer. An element for measuring the thickness of a semiconductor thin film, comprising a layer. 2. A semiconductor film of a first conductivity type, which is insulated and separated from a supporting substrate by a buried insulating film, and a first semiconductor of a first conductivity type, which is formed on the semiconductor film and is electrically insulated and separated. A pair of measuring elements comprising a first semiconductor layer and a second semiconductor layer of a first conductivity type, comprising: an oxide film formed on a surface of the first semiconductor layer; Measuring element. 3. A pair of measuring elements are configured to measure sheet resistance values of a first semiconductor layer and a second semiconductor layer and calculate a film thickness of the semiconductor layer from the measured values. 3. The semiconductor thin film thickness measuring element according to claim 1, wherein the element has a square sheet resistance pattern with four terminals. 4. A pair of measuring elements are configured to measure the diffusion resistance values of the first semiconductor layer and the second semiconductor layer and calculate the thickness of the semiconductor layer from the measured values. 3. The semiconductor thin film thickness measuring element according to claim 1, wherein the element has a rectangular diffusion resistance pattern with two terminals.