JPH05102161A - Manufacture of semiconductor device, and the semiconductor device - Google Patents

Abstract

PURPOSE:To localize a low lifetime layer whose half-width is narrower, to eliminate a need for a heat treatment at a high temperature and to enhance an ON voltage and a switching speed as compared with those by a proton irradiation operation or an electron-beam irradiation operation in conventional cases by a method wherein a prescribed region inside a semiconductor substrate is irradiated with helium ions. CONSTITUTION:This device is provided with a process wherein a prescribed region inside a semiconductor substrate 1 is irradiated with helium ions <3>He<2+>. The accelerating energy of the helium ions is set at 1 to 40MeV, and their dose is set at 1X10<9> to 5X10<13>/cm<2>. In addition, it is preferable that the semiconductor substrate 1 is heated to 300 to 400 deg.C after the helium ions have been irradiated. For example, a P<+> diffusion layer at a depth of d3=10mum is formed on the main face of an N-type silicon substrate 1 (its thickness d1 = about 400mum). Then, the surface side of the substrate 1 is irradiated with helium ions; a low lifetime layer 7 having a half-width of (w) is formed in the position of a depth of d2, and a P<+> N-type switching diode is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device and a semiconductor device manufactured by the manufacturing method, and in particular, a low lifetime layer is provided in a localized region of a semiconductor substrate on which the device is formed. It is used for high speed switching devices.

[0002]

As is well known, when switching from a forward direction to a reverse direction in a switching semiconductor element, it takes a certain amount of time for the excess minority carriers accumulated during the forward direction to disappear, which is an obstacle to speeding up. ing. Therefore, in the conventional technology, gold or platinum is thermally diffused in the device to reduce the lifetime, or electron beams or neutron beams are irradiated to form lattice defects, which act as recombination centers to reduce the lifetime. We are trying to shorten it. Among conventional techniques, there is a proton irradiation technique as a localization technique for the low lifetime layer. This is because when protons stop in the semiconductor substrate,
High level density defects occur near the stop position. By utilizing this phenomenon, the low lifetime layer can be localized.

This conventional example will be described with reference to the drawings. FIG. 6 is a schematic cross-sectional view of a switching P ⁺ N type diode. A P ⁺ diffusion layer 2 is selectively formed on the main surface of the N-type silicon substrate 1. An anode electrode 4 (front surface electrode) is provided in contact with the P ⁺ diffusion layer 2, and a cathode electrode 5 (back surface electrode) is provided in contact with the N-type substrate 1. Reference numeral 3 is an insulating film.

In the switching diode, the on-voltage characteristic and the switching speed are important electrical characteristics.
The on-voltage characteristic is represented by a forward voltage drop V _F between the anode and the cathode of the device (V _{on in a} thyristor or the like) when a specified forward current I _F is passed. In the P ⁺ N type diode of FIG. 6, V _F is mainly determined by the junction and the resistance of the N cathode region 1, and the smaller the element, the better. The switching speed is represented by the reverse recovery time _trr . As for the reverse recovery time, as shown in FIG. 7, a specified forward current I _F is applied to the diode, and a specified reverse voltage V _R is applied at t ₁ ,
When it is reduced at the specified forward current reduction rate (di / dt),
The time from t ₂ to t _{3 at} which the reverse current flows is referred to as t _rr . The reverse current is mainly due to the holes accumulated in the N-type region 1.
Since it is desirable that _rr is as short as possible, it is necessary to shorten the lifetime of minority carriers in the N-type region 1.

Reference numeral 6 in FIG. 6 is a low lifetime layer which is stabilized by irradiating protons from the front surface or the back surface of the semiconductor substrate 1 and then performing heat treatment, and the width w is a half width. The full width at half maximum is the distance between substrate positions where the defect concentration distribution (normally chevron) in the thickness direction of the substrate is half of the maximum value, and is 15 μm in the case of proton irradiation.

In the lifetime control by proton irradiation, unless the irradiation dose is set to about 5 × 10 ¹² atoms / cm ² ,
Compared with the case of platinum diffusion or electron beam irradiation, the on-voltage (V
_F ) and switching speed (t _rr ) do not become higher performance. On the other hand, the proton dose is 5 × 10 ¹² atoms / cm ²
If this happens, the breakdown voltage of the element will deteriorate. FIG. 5 shows the dose dependence of the breakdown voltage of the P ⁺ N-type diode. Curve a is for proton irradiation (1.5 MeV), and curve b is ³ He ^2+.
In the case of irradiation (6 MeV), it shows a decrease in withstand voltage when the irradiation amount is increased. Therefore, after proton irradiation, 40
Heat treatment at 0 ° C. for 10 minutes or more is required. Since the defect level formed as a lifetime killer is also recovered by this heat treatment, in the proton irradiation, as compared with platinum diffusion and electron beam irradiation techniques, as shown in Table 1, the on-voltage (V
Switching speed (t _rr ) with only a slight recovery of _F )
Is hardly seen.

Further, since the full width at half maximum of the low lifetime layer due to proton irradiation is about 15 μm, this technique cannot be used when a localized region of the low lifetime layer having a width of 10 μm or less is required.

[0008]

As described above, there has been a proton irradiation technique as a conventional localization technique for the low lifetime layer. However, when the dose is set to about 5 × 10 ¹² atoms / cm ² , the breakdown voltage is reduced. Since heat treatment at 400 ° C. for 10 minutes or more is required to recover the deterioration, as a result, the on-voltage (V _F ) is slightly improved as compared with the conventional platinum diffusion and electron beam irradiation techniques, and the switching speed is increased. (T _rr ) hardly improves. Further, with the localization technique of the low lifetime layer of proton irradiation, the half width of the low lifetime layer is as wide as 10 μm, and it is not possible to form a low lifetime layer with a narrower half width.

The present invention has been made in view of the above problems, and an object thereof is to enable localization of a narrow lifetime half-width low lifetime layer and to require heat treatment at high temperature after irradiation of charged particles. the non processes and conventional proton irradiation, as compared with electron beam irradiation or the like, the oN voltage (V _F) and the switching speed (t _rr) manufacturing method of a semiconductor device to be improved along with the semiconductor device manufactured by the manufacturing method Is to provide.

[0010]

Means and Actions for Solving the Problems Claim 1 of the present invention
The method of manufacturing a semiconductor device according to claim 3 is characterized in that helium is applied to a predetermined region (for example, in an N type cathode region of a P ⁺ N type switching diode, an optimum region obtained by trial in advance (see FIG. 1)) in a semiconductor substrate. Ion ³ He ²⁺
Is provided.

The breakdown voltage characteristics (see FIG. 5) of the element when the semiconductor device is irradiated with helium ion ³ He ²⁺ and when irradiated with proton ¹ H ⁺ are almost the same. However defect level of the high level position density by irradiation damage in the case of proton irradiation (E _c -0.39), in the case of helium ions ³ the He ²⁺ irradiation (E _c -0.43), and the Helium ion
Towards ³ the He ²⁺ irradiation becomes deep level, helium ions ³ the He ²⁺ was considered valid process for high-speed switching element. Based on such a concept, in the present invention, ³ He ²⁺ irradiation is performed as a localization technique of the low lifetime layer, and the low lifetime layer having a half width w narrower than that of proton irradiation (see FIG. 3). )was gotten. Further, by the above helium ion irradiation, a device having a low on-voltage (V _F ) and a high switching speed (t _rr ) as compared with the prior art was obtained.

A method of manufacturing a semiconductor device according to claim 2 is
2. The method according to claim 1, wherein the helium ion ³ He ^{2+ has} an acceleration energy of 1 MeV to 40 MeV and a dose of 1 × 10 ⁹ atoms / cm ² to 5 × 10 ¹³ atoms.
/ Cm ² . The acceleration energy of helium ions is set to 1 MeV to 40 MeV to indicate an acceleration energy range required for setting a predetermined region by irradiating a desired region in a semiconductor substrate forming a semiconductor device with helium ions. In addition, the dose of 1 × 10 ⁹ atoms / c
m ² is the lower limit value at which the practically useful effect of the present invention is obtained, and the dose of 5 × 10 ¹³ atoms / cm ² can be recovered by heat treatment even if damaged and can function as a single crystal substrate. It is the upper limit.

A method of manufacturing a semiconductor device according to claim 3 is
The manufacturing method according to claim 1 or 2, wherein the semiconductor substrate is heated to 300 ° C to 400 ° C after irradiation with helium ions ³ He ²⁺ . The heat treatment is performed in order to recover the damage to the substrate due to the helium ion irradiation and stabilize the defects. Since the helium ion irradiation is often performed on the wafer before the dicing after the wafer process is completed, the upper limit of the heat treatment temperature (400 ° C.) may cause thermal destruction of the elements formed on the substrate. No temperature and
The lower limit (300 ° C) is the practical heat treatment time (for example, 30
The temperature is set to a temperature at which defects can be stabilized in (min. As heating means, resistance heating, high frequency induction (R
F) It is desirable to use heating or radiant heating.

A semiconductor device according to a fourth aspect is a semiconductor device manufactured by the manufacturing method according to any one of the first to third aspects.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a P ⁺ N type switching diode used in carrying out the present invention. N-type silicon substrate 1 (thickness d ₁ = about 400 μm)
A P ⁺ diffusion layer 2 having a depth d ₃ = 10 μm is formed on the main surface of. Helium ions are irradiated from the front surface side of the substrate to form a low lifetime layer 7 having a half width w at the position of depth d ₂ . For example, helium ion ³ He ²⁺ is accelerated energy 6
When irradiation is performed with MeV at a dose of 1 × 10 ¹² atoms / cm ² , d ₂ = 40 μm and w = 3 μm.

Next, a typical trial example performed using the P ⁺ N type diode shown in FIG. 1 will be described with reference to FIG. Irradiation dose 1 × 10 with acceleration energy 6 MeV
¹⁰ atoms / cm ² (A ₁ ), 5 × 10 ¹¹ atoms / cm ² (A 1
₂ ) 1 × 10 ¹² atoms / cm ² (A ₃ ), 1 × 10 ¹³ a
Irradiate with ³ He ²⁺ of toms / cm ² (A ₄ ), 300 ° C. 10
Performs minute thermal treatment, for each element, I _F = 2A in (anode voltage between the cathode when the forward current I _F 15A) and switching speed t _rr (7 ON voltage V _F, di / dt = 50 μA / sec, V _R = 3
0V) is calculated. In FIG. 2, the horizontal axis represents the ON voltage V _F (V),
The vertical axis represents the switching speed _trr (nsec), and the measurement results in the cases of A ₁ to A ₄ with different irradiation doses are marked with a circle. As a comparative sample, the acceleration energy was 1.5 MeV and the dose was 1 × 10 ¹² atoms / cm ² (B
₁ ), 5 × 10 ¹² atoms / cm ² (B ₂ ), 1 × 10 ¹³ a
Irradiated with protons of toms / cm ² (B ₃ ), 400 ° C. 10
And the acceleration energy of 10Me
V, an element (C ₁ ) in which a sample in which platinum was diffused was irradiated with electrons with a dose of 5 × 10 ¹³ atoms / cm ²
The on-voltage V _F and the switching speed _trr were measured respectively, and the results are plotted in FIG. 2 with Δ marks and □ marks to compare the relationship between the on-voltage and the switching speed. The mark ● indicates the measured value of an unirradiated sample.

As shown in FIG. 2, it is understood that the irradiation with ³ He ²⁺ improves both the on-voltage and the switching speed as compared with the conventional proton irradiation or electron beam irradiation + platinum diffusion. The curve a passing through the point A ₁ to the point A ₄ shows a relation between the switching speed t _rr and the ON voltage V _F when changing the irradiation amount of ³ He ^{2+, 3} He
The dose of ²⁺ is 1 × 10 ⁹ atoms / cm ² to 5 × 10
¹³ atoms / cm ² is desirable.

Although the heat treatment is performed by resistance heating in the above embodiment, RF heating or radiant heating may be used. Also, similar results can be obtained by treating with electron beam heating or laser heating.

In FIG. 3, helium ion ³ He ²⁺ is added to P ⁺ with an acceleration energy of 6 MeV and a dose of 1 × 10 ¹² atoms / cm ^2.
The depth from the substrate surface and the crystal defect density (relative value) at each depth when the N-type diode is irradiated are shown. DLTS (deep level transient spectroscopy)
) Method. The low lifetime layer has a depth of about 4
A half width w = 3 μm is formed at a position of 0 μm. In the case of conventional proton irradiation, the half-width of the low lifetime layer is about 15 μm, and in the case of helium ion,
5 is extremely narrow. Therefore, the low lifetime layer can be localized in a region having a width of 10 μm or less.

Next, an example of trials carried out for obtaining an appropriate value of heat treatment conditions will be described. P ⁺ N type diode (Fig. 1
Helium ion ³ He ²⁺ as acceleration energy 6M
A plurality of samples irradiated with eV and a dose of 1 × 10 ¹² atoms / cm ² are prepared. The heat treatment is performed to stabilize the crystal defects generated by the ion irradiation. In this trial example, the leakage current when a reverse bias is applied to the device is stabilized by the heat treatment as the evaluation criterion for the heat treatment effect. .. Heat treatment temperature conditions are 400 ° C (○ mark), 385 ° C
(△ mark), 350 ℃ (□ mark) and 300 ℃ (× mark) 4
As a condition, it was examined how the leak current (reverse bias voltage 100 V) of the device decreases (stabilizes) with the elapse of the heat treatment time (min) for each condition. The result is shown in FIG.
It can be seen from the figure that when the heat treatment temperature condition is 300 ° C. or less, it takes too long for the leak current to stabilize, and when it is 400 ° C. or more, it stabilizes in a short time, but there is a risk of thermal destruction of the element.

FIG. 5 shows the P ⁺ N type diode (see FIG. 1) irradiated with protons having an acceleration energy of 1.5 MeV (curve a) and with helium ions ³ He ²⁺ having an acceleration energy of 6 MeV. (Curve b) is a curve showing the relationship between each breakdown voltage (vertical axis) and the irradiation amount (horizontal axis). The tendency for the breakdown voltage to decrease with increasing irradiation dose is
Almost the same for proton and helium ion. On the other hand, with helium ion irradiation, even if the irradiation amount is the same as that of protons, defects larger than those of proton irradiation are created. In order to generate the same defect density, helium ion irradiation can reduce the irradiation amount as compared with proton irradiation, and as shown in FIG.

[0022]

[Table 1]

Table 1 is a comparison table for comparing representative data of low lifetime layer formation. That is, as the treatment method, (a) in the case of non-irradiation, (b) the substrate on which the electron beam was platinum-diffused, the acceleration energy was 5 MeV, and the dose was 5 ×
When irradiated with 10 ¹³ atoms / cm ² , (c) ¹ proton
H ⁺ , acceleration energy 1.5 MeV, irradiation dose 5 × 10
^When heat treatment is performed at 400 ° C. for 10 minutes after irradiation with ¹² atoms / cm ² , (d) helium ion ³ He ²⁺ is irradiated with an acceleration energy of 6 MeV and a dose of 1 × 10 ¹² atoms / cm ² , It is classified into four cases when heat treatment is performed at 300 ° C. for 10 minutes. Create a plurality of samples for each treatment method, to measure the switching speed t _rr and the ON voltage V _F, the average value. The measurement conditions are the same as in the trial example shown in FIG. Further, in order to facilitate the comparison, the value of _trr or V _F of the unirradiated element is set to 1, and the relative value of _trr or V _F of the element by another processing method is calculated. Table 1 summarizes these data. As shown in Table 1, in the case of helium ion ³ He ²⁺ irradiation, the switching speed _trr is 12% that of the unirradiated element, and the on-voltage V _F is 1.2 times, which is faster and lower on-state than the conventional technology. Voltage conversion is achieved.

Although the above embodiment describes the P ⁺ N type switching diode, the present invention can be applied to power transistors, thyristors (including GTO etc.) and other power control semiconductor devices.

[0025]

As described above, in the present invention, since the low lifetime layer is formed by irradiating the helium ion ³ He ²⁺ , the half lifetime is narrower than that of the prior art. The on-state voltage V is higher than that of conventional proton irradiation, electron beam irradiation, etc. by the process that enables localization of the layer and does not require high temperature heat treatment.
_F (or V _on ) and switching speed t _rr (or t
It was possible to provide a method for manufacturing a semiconductor device in which both _off ) are improved and a semiconductor device manufactured by the manufacturing method.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device (an example) to which the present invention is applied.

FIG. 2 is a characteristic diagram showing a relationship between a switching speed and an ON voltage of a semiconductor device according to the methods of the present invention and the related art.

FIG. 3 is a characteristic diagram showing the depth from the substrate surface and the relative defect density of the semiconductor device according to the method of the present invention.

FIG. 4 is a characteristic diagram showing the relationship between the leak current and the heat treatment time when the heat treatment temperature of the semiconductor device according to the method of the present invention is used as a parameter.

FIG. 5 is a characteristic diagram showing the relationship between the withstand voltage and the dose of semiconductor devices of the present invention and the prior art.

FIG. 6 is a cross-sectional view of a semiconductor device to which a conventional technique is applied.

7 is a diagram showing a current waveform when the semiconductor device shown in FIG. 1 or 6 is turned off.

[Explanation of symbols]

1 N-type semiconductor substrate 2 P ⁺ diffusion layer 6 Low lifetime layer (conventional) 7 Low lifetime layer (present invention) t _rr Switching speed V _F ON voltage w Half-width of low lifetime layer

Claims (4)

[Claims] 1. A method of manufacturing a semiconductor device, comprising the step of irradiating a predetermined region in a semiconductor substrate with helium ions ³ He ²⁺ . 2. The helium ion ³ He ²⁺ acceleration energy is 1 MeV to 40 MeV, and the irradiation dose is 1 × 1.
The method for manufacturing a semiconductor device according to claim 1, wherein the amount is set to 0 ⁹ atoms / cm ² to 5 × 10 ¹³ atoms / cm ² . 3. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor substrate is heated to 300 ° C. to 400 ° C. after irradiation with helium ions ³ He ²⁺ . 4. A semiconductor device manufactured by the manufacturing method according to claim 1, claim 2, or claim 3.