Method and associated system for thermally processing a substrate - Patents.com

Abstract

A method of thermally treating a substrate (4) having a surface region (5) and a buried region (6) with a pulsed light beam (13), wherein the substrate exhibits an initial temperature-depth profile and the surface region exhibits an initial surface temperature (T0); b) irradiating the surface area with a preliminary pulse (25) so that it generates a certain amount of heat and reaches a predetermined preliminary surface temperature (T 25 ) and c) After a time interval (Δt), a subsequent pulse (27) is applied to the surface area, which generates a predetermined subsequent surface temperature (T 27 ) and A method comprising: According to the present invention, a time interval is specified such that the surface region reaches a predetermined intermediate surface temperature (Ti) that is higher than the initial surface temperature, whereby during the time interval, heat is diffused to a predetermined depth into the substrate, causing the substrate to exhibit a predetermined intermediate temperature-depth profile.

Description

[Technical field]

[0001] The present invention relates to the thermal processing of semiconductor materials.

[0002] More particularly, the present invention relates to a method for thermally processing a substrate using a pulsed light beam.

[0003] The present invention also relates to a system for thermally processing a substrate using a pulsed light beam. [Background technology]

[0004] In semiconductor manufacturing processes, devices formed on the surface of a substrate, as well as devices buried below the surface, can be highly sensitive and susceptible to temperature dynamics.

[0005] To avoid damaging the device during the heat treatment stage of the manufacturing process, it is important to achieve perfect control over the temperature variations of the substrate.

[0006] Modern thermal processing techniques such as laser annealing can achieve very short times at the melting point, i.e., on the sub-microsecond time scale, and very shallow heat penetration into the substrate, but even with limited heat sources and controlled times, the annealing dynamics are always difficult to control.

[0007] In particular, in nanosecond laser techniques where the surface region of the substrate is exposed to nanosecond laser pulses, the annealing dynamics during one pulse is a competitive phenomenon between thermal excitation of the surface region and relaxation due to thermal diffusion into the buried region of the substrate.

[0008] For example, when nanosecond laser annealing is performed on materials with high thermal conductivity, heat diffusion during the pulse can be important: the surface temperature rises slowly and the anneal penetrates deep into the buried regions of the substrate.

[0009] In the opposite situation, when a thermal insulating material is exposed to a nanosecond laser, thermal diffusion during the pulse is negligible, and therefore localized deep heating and a rapid rise in surface temperature are obtained.

[0010] Furthermore, in many cases the surface region must be annealed at one temperature while the buried region within the substrate must be annealed at another temperature or should not be annealed at all.

[0011] Therefore, temperature changes and heat diffusion during laser processing are traditionally difficult to control due to the indirect consequences of interdependent laser parameters and material / device thermal properties. Control is much more difficult in sub-microsecond systems such as nanosecond pulsed lasers, where pulse duration and repetition rate are generally constant, inflexible, and limited by the laser source.

[0012] Methods for improving temperature control during heat treatment are desirable. Summary of the Invention

[0013] In this regard, the present invention provides a method for thermally treating a substrate with a pulsed light beam, the substrate having a surface region and a buried region, the substrate exhibiting an initial temperature depth profile, the surface temperature of the surface region being at an initial surface temperature; b) irradiating the surface region with a preliminary pulse of the pulsed light beam, the preliminary pulse thereby providing a preliminary amount of energy to the surface region, whereby the surface region generates a preliminary amount of heat such that the surface temperature reaches a predetermined preliminary surface temperature; and c) irradiating the surface region of the substrate with a subsequent pulse of the pulsed light beam after a time interval, the subsequent pulse thereby providing a subsequent amount of energy to the surface region, whereby the surface region generates a subsequent amount of heat, such that the surface temperature reaches a predetermined subsequent surface temperature.

[0014] According to this method, a time interval is specified during which the surface temperature reaches a predetermined intermediate surface temperature, said predetermined intermediate surface temperature being higher than the initial surface temperature, whereby during the time interval an amount of preliminary heat is diffused into the implant region to a predetermined depth of the substrate, whereby the substrate temperature exhibits a predetermined intermediate temperature-depth profile.

[0015] This method allows precise control of the surface temperature of the surface region and the temperature-depth profile of the substrate, ie the variations in temperature dynamics of the substrate.

[0016] In this way, the surface temperature gradually increases over time due to the cumulative effect of the pulses. In fact, the time interval is such that the surface temperature cannot return to the initial temperature between two pulses. Thus, the subsequent heat generated by the surface area is added to the heat that has not yet diffused into the implanted area, and the surface temperature after the subsequent pulse is higher than the surface temperature after the preliminary pulse.

[0017] This is advantageous because the temperature rise of the surface region, and therefore the rate of temperature change over time, can be tailored depending on the substrate material and devices formed in and on the substrate: for example, sensitive devices and substrates can be exposed to a gradual temperature rise, whereas more robust devices and substrates can be exposed to a steeper temperature rise.

[0018] This method also allows for controlled variations in the temperature profile of the implanted region: for pulses providing less energy, less heat is diffused into the implanted region, and the implanted region reaches a lower temperature than for pulses providing more energy, but the cumulative effect still allows the target surface temperature to be reached.

[0019] This is advantageous because the method is thus adaptable to process thermal conductors and insulators.

[0020] This method also allows the substrate to be exposed to a target temperature-depth profile adapted for the thermal processing of a particular electronic structure such as a FINFET or IGBT.

[0021] Another advantageous, non-limiting feature of the method according to the invention includes the steps of b) irradiating the surface region with a preliminary pulse and c) irradiating the surface region with a subsequent pulse, the steps being repeated until the surface temperature reaches the target temperature and the substrate temperature exhibits the target temperature-depth profile.

[0022] Another advantageous, non-limiting feature of the method according to the invention includes the buried region of the substrate comprising a region implanted with a dopant element having a predetermined dopant element concentration-depth profile, and the target temperature-depth profile is adapted to activate the dopant element in the implanted region.

[0023] Other advantageous, non-limiting features of the method according to the invention include: the implanted region is at a depth of more than 500 nanometers from the surface region and has a thickness of less than 50 micrometers; the dopant element is adapted to generate one type of unipolar carrier in the implanted region; the dopant element is adapted to generate two types of unipolar carriers in the implanted region; the substrate is a semiconductor material selected from the group comprising silicon, silicon carbide, silicon germanium, germanium, gallium nitride, gallium arsenide, diamond;

[0024] Other advantageous, non-limiting features of the method according to the invention include: the pre-pulse and the subsequent pulse each have a duration equal to or less than 1 nanosecond, which is advantageous because a pulse of less than 1 nanosecond produces a rapid temperature rise during the pulse, while not being very diffuse, thus allowing precise control of the surface peak temperature.

[0025] Other advantageous, non-limiting features of the method according to the invention include: the pulsed light beam has a wavelength equal to or less than 532 nanometers. This is advantageous because light having a wavelength equal to or less than 532 nanometers is better absorbed by the substrate than light having a wavelength longer than 532 nm. Thus, the energy provided by the pulse is limited within a shallow region of the substrate.

[0026] Other advantageous, non-limiting features of the method according to the invention include: - the time interval between the pre-pulse and the subsequent pulse is equal to or less than 25 nanoseconds; the pulsed light beam has a wavelength less than or equal to 532 nanometers; - the energy density of the pulsed light beam is greater than 1 millijoule per square centimeter per pulse; the method further comprising the steps of: a) identifying values ​​of parameters related to the pulsed light beam to reach the predetermined preliminary surface temperature, the predetermined intermediate surface temperature, and the predetermined subsequent temperature-depth profile, the parameters related to the pulsed light beam being selected from the group comprising: a time interval, an energy density of the pulsed light beam, a shape of a light spot formed on the surface region by the pulsed light beam; the method further comprises the step of d) scanning the pulsed light beam over the surface area, wherein during step a) the set of parameters relating to the pulsed light beam further comprises a scanning speed of the pulsed light beam; - the amount of preliminary energy delivered by the preliminary pulse is different from the amount of subsequent energy delivered by the subsequent pulse; - the amount of energy delivered by each of the pre-pulse and the subsequent pulse is less than the amount of energy required for the surface region to reach the melting point of the surface region of the substrate; The target temperature is the melting point of the surface region.

[0027] The present invention also relates to a system for thermally treating a substrate with a pulsed light beam, the substrate having a surface region and a buried region, the substrate temperature of the substrate exhibiting an initial temperature-depth profile, the surface temperature of the surface region being an initial surface temperature, the system comprising: a light source adapted to emit a light beam; a beam control system configured to generate a pulsed light beam from an emitted light beam, the system being adapted to generate a preliminary pulse and a subsequent pulse; Including, - said preliminary pulse of the pulsed light beam is irradiated onto a surface region of a substrate, the preliminary pulse thereby providing a preliminary amount of energy to said surface region, whereby the surface region generates a preliminary amount of heat, such that the surface temperature reaches a predetermined preliminary surface temperature; The subsequent pulse of the pulsed light beam is irradiated onto the surface region of the substrate after a time interval, the subsequent pulse thereby providing a subsequent amount of energy to the surface region, whereby the surface region generates a subsequent amount of heat, such that the surface temperature reaches a predetermined subsequent surface temperature.

[0028] According to the invention, the system is adapted to generate the subsequent pulse after the time interval, the time interval being specified such that during the time interval the surface temperature reaches a predetermined intermediate surface temperature, the predetermined intermediate surface temperature being higher than the initial surface temperature, whereby during the time interval an amount of preliminary heat is diffused into the implant region to a predetermined depth of the substrate, whereby the substrate temperature exhibits a predetermined intermediate temperature-depth profile.

[0029] Other advantageous, non-limiting features of the method according to the invention include: the system being configured to repeat the irradiating of the surface region with a pre-pulse and the irradiating of the surface region with a subsequent pulse until the surface temperature reaches a target temperature and the substrate temperature exhibits a target temperature-depth profile; the buried region of the substrate includes a region implanted with a dopant element having a predetermined dopant element concentration-depth profile, and the target temperature-depth profile is adapted to activate the dopant element in the implanted region; each of the pre-pulse and the follow-up pulse has a duration equal to or less than 1 nanosecond; the pulsed light beam has a wavelength less than or equal to 532 nanometers; - the time interval between the pre-pulse and the subsequent pulse is equal to or less than 25 nanoseconds; - the energy density of the pulsed light beam is greater than 1 millijoule per square centimeter; - the beam control system is configured to identify values ​​of parameters related to the pulsed light beam to reach a predetermined preliminary surface temperature, a predetermined intermediate surface temperature, and a predetermined subsequent temperature-depth profile, the parameters related to the pulsed light beam being selected from the group including time interval, energy density of the pulsed light beam, and shape of a light spot formed on the surface region by the pulsed light beam.

[0030] This description is given for non-limiting illustrative purposes and will be better understood with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of a system for thermally processing a region of a substrate in accordance with the present invention. [Diagram 2] 4 is a graph of the change in surface temperature over time for a surface area of ​​a substrate undergoing a thermal treatment according to the present invention. [Diagram 3] 2 is a schematic representation of method steps for heat treating an area of ​​a substrate according to the present invention. [Figure 4] 4 is a graph of temperature change over time at different depths in a substrate undergoing a thermal treatment according to the present invention. [Diagram 5] 1 is a schematic representation of a semiconductor structure undergoing a thermal treatment in accordance with the present invention; [Figure 6] 5a and 5b are graphs of temperature variation over time at different depths in the semiconductor structure of FIGS. 5a and 5b subjected to a thermal treatment according to the present invention. [Figure 7]1 is a graph of multiple surface temperature dynamics obtained by exposing a substrate to multiple pulse trains having different energies and frequencies. [Figure 8] 4 shows a temperature curve illustrating a typical surface temperature rise and the corresponding pulse train. [Figure 9] 1 is a graph of temperature variation with depth in a substrate exposed to different combinations of parameters for a pulsed beam and a dopant implantation profile for a substrate implanted with one dopant element. [Figure 10] 1 is a graph of temperature variation with depth in a substrate exposed to different combinations of parameters for a pulsed beam and a dopant implantation profile for a substrate implanted with two dopant elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] FIG. 1 illustrates a system 1 for thermally processing a substrate 4 .

[0033] The substrate 4 is made of a semiconductor material, for example, a Si (silicon) material or a SiGe (silicon-germanium) material.

[0034] Electronic devices such as transistors, resistors, or their metal interconnects are formed on a surface region 5 of the substrate 4 .

[0035] The surface region 5 has a surface melting point Tm that depends on the substrate material and on the electronics formed on the surface region 5.

[0036] Beneath the surface region 5, the substrate 4 exhibits buried regions 6. The buried regions 6 may also include buried layers 41 of the electronic device. Each buried layer 41 has a depth Dl measured along a first axis (0z). The first axis (0z) is perpendicular to the surface region 5 and has an origin 0, which is on the surface region 5. The first axis (0z) is oriented towards the bulk semiconductor material 3. Each buried layer 41 has a respective melting point Tblm.

[0037] The buried region 6 exhibits a temperature-depth profile 8. The temperature-depth profile 8 corresponds to the variation of temperature with respect to the depth of the buried region 6.

[0038] The system 1 includes a light source 7 and a beam control system 9 .

[0039] The light source 7 emits a light beam 11, for example a laser beam 11. The light source 7 is for example a short wavelength laser with an emission wavelength equal to or shorter than 1.06 micrometers. The light source 7 is preferably a laser with an emission wavelength equal to or shorter than 532 nanometers. The light source 7 is preferably an ultraviolet laser with an emission wavelength equal to or shorter than 355 nanometers.

[0040] The light source 7 is preferably a pulsed laser, preferably a quasi-continuous wave laser operating at a very high repetition rate, for example greater than 40 megahertz.

[0041] A beam control system 9 modulates the outgoing light beam 11 to produce a pulsed light beam 13 adapted to thermally treat the substrate 4 .

[0042] The beam control system 9 controls the change in the surface temperature of the surface region 5 and the change in the temperature-depth profile of the buried region 6 by controlling the parameters of the pulsed light beam 13. The parameters of the pulsed light beam 13 include the energy density E of the pulsed light beam, the pulse duration t p , the pulse frequency, the inter-pulse time interval Δt which is equal to the inverse of the pulse frequency, the total exposure time of the pulsed light beam, and the number of pulses during the thermal treatment.

[0043] To this end, the beam control system 9 includes components such as a cavity, lenses, attenuators 15, mirrors 17, a beam shaper 19, a beam scanner 21, and a control unit 23.

[0044] For example, the beam control system 9 controls the pulse energy density Ed by passing the emitted light beam 11 through an attenuator 15, which may comprise, for example, an attenuating plate, and varying the transmittance of the attenuator. Alternatively or additionally, the beam control system 9 controls the pulse energy density Ed by varying an internal parameter of the light source 7, such as the pumping power of the light source 7.

[0045] For example, the beam control system 9 controls, by adapted components, the frequency of the pulsed light beam 13. For example, the frequency of the pulsed light beam 13 can be adjusted by externally controlling an oscillator of the light source 7. Alternatively, the frequency of the pulsed light beam 13 can be controlled by using an electro-optical module, for example a "pulse picker", which deflects specific pulses in a pulse train.

[0046] For example, the beam control system 9 controls the shape and size of a light spot 20 formed on the surface area 5 by the pulsed light beam 13 via a beam shaper 19 .

[0047] For example, the beam control system 9 controls the number of pulses that the surface area 5 receives during thermal treatment by the beam scanner 21. The scanning speed is specified to irradiate the surface area 5 with the desired number of pulses. The accumulated pulses at any irradiation point on the surface area 5 are equal to the light pulse magnitude multiplied by the frequency of the pulsed light beam 13 divided by the scanning speed.

[0048] The beam control system 9 includes a control unit 23. The control unit 23 includes, for example, a microprocessor and a memory. The memory of the control unit 23 stores a computer program that, when executed by the microprocessor, is adapted to implement a method for thermally treating the substrate 4. Furthermore, the control unit 23 is configured to send instructions to the other components 15, 17, 19, 21 of the beam control system 9 and to the light source 7 in order to control parameters related to the pulsed light beam 13.

[0049] Figure 2 shows some of the parameters of the pulsed light beam 13. The pulsed light beam 13 comprises a pulse train 24, where the pulse train 24 comprises six pulses 25, 27, also referred to as six cycles.

[0050] The duration t of one pulse 25, 27 of the pulsed light beam 13 p is, for example, equal to or less than 100 nanoseconds. The duration t p The duration t of one pulse 25, 27 is preferably equal to or less than 10 nanoseconds. p is preferably equal to or less than 1 nanosecond.

[0051] Energy density E of one pulse 25, 27 d is between 1 microjoule / centimeter squared and 30 millijoules / centimeter squared.

[0052] In FIG. 2, it can be seen that the pulsed laser beam 13 has two energy states: an "on state" in which the energy delivered by the pulses 25, 27 is non-zero, and an "off state" in which the energy delivered by the pulses 25, 27 is equal to zero.

[0053] The duration of the time interval Δt between the pre-pulse 25 and the subsequent pulse 27 is equal to or less than 1 millisecond. The duration of the time interval Δt between the pre-pulse 25 and the subsequent pulse 27 is equal to or less than 1 microsecond. The duration of the time interval Δt between the pre-pulse 25 and the subsequent pulse 27 is equal to or less than 1 nanosecond. In other words, the frequency of the pulsed light beam 13 is in the range of 10 megahertz to 1 gigahertz.

[0054] The total exposure time of the surface area 5, including the total time between pulses, is equal to or less than 1 millisecond. The total exposure time of the surface area 5 is preferably equal to or less than 10 microseconds.

[0055] By controlling the time interval Δt, the pulsed light beam energy density Ed, the pulsed light beam frequency, the scan speed and the beam shape, the system 1 provides complete control of the process conditions.

[0056] In figure 2, a first curve 29 represents the variation over time of the surface temperature Ts of the surface area 5. In figure 2, it can be seen that the surface temperature Ts has a cyclical behaviour, where one temperature cycle is achieved when the surface temperature cycles from one temperature extreme to the next same temperature extreme, for example between two successive minima or two successive maxima.

[0057] When the surface region 5 is irradiated with the preliminary pulse 25, the surface temperature Ts increases to a predetermined preliminary surface temperature T 25 If the surface area 5 is not irradiated, the surface temperature reaches a predetermined intermediate surface temperature T i to reach.

[0058] Here, the surface temperature Ts drops when the surface area 5 is not irradiated, so that the surface temperature Ts is a predetermined preliminary surface temperature T 25 is the maximum temperature.

[0059] In this example, the surface area 5 is irradiated with a pulse train 24 of six pulses, so that the first curve 29 shows six temperature cycles.

[0060] During the subsequent pulse 27, the surface temperature Ts increases to a predetermined subsequent surface temperature T 27 to reach.

[0061] FIG. 2 also shows the envelope of the surface temperature, which has an upper envelope portion 31 through which passes the temperature maximum reached after the pulse, and a lower envelope portion 33 through which passes the temperature minimum reached after the pulse.

[0062] 2 also shows the temperature gradient 35, or in other words the rate of temperature change over time. The temperature gradient 35 is specified based on parameters related to the pulsed light beam 13.

[0063] In one example, light source 7 includes a quasi continuous wave (QCW) laser, such as Coherent's Paladin laser model.

[0064] The emission wavelength of the Paladin laser is 355 nm.

[0065] Pulse duration t of one pulse p is 15 picoseconds.

[0066] The Paladin laser has a constant pulse frequency equal to 80 MHz, in other words the duration of the interpulse time interval Δt is 12.5 ns.

[0067] The power of the Paladin laser is 16 W. The energy of one pulse of the emitted beam is 0.2 microjoules.

[0068] The beam control system 9 shapes the pulsed light beam 13 into a Gaussian light spot of approximately 30 micrometers to produce an energy density E of 28 microjoules per square centimeter. d Reach.

[0069] The scanning speed is, for example, 1 meter / s. For a light spot size of 30 micrometers at a frequency of 80 MHz, the processing time is 30 microseconds, which corresponds to 2400 pulses.

[0070] In another example, the light source 7 includes another quasi-continuous wave laser with a tunable frequency, which allows the inter-pulse time interval to be modulated.

[0071] 3, the method for thermally treating a substrate 4 with a pulsed light beam 13 comprises a phase a) of determining values ​​of parameters related to the pulsed light beam 13. The parameters related to the pulsed light beam are the duration of the time interval Δt between two pulses 25, 27, the energy density Ed of the pulses 25, 27, the scanning speed of the pulsed light beam over the surface area 5, the shape of the pulsed light beam, the pulse duration t p , 25, 27 pulses.

[0072] The amount of energy delivered by each pulse 25, 27 is less than the amount of energy required for the surface region 5 to reach its melting temperature Tm.

[0073] The parameter values ​​for the pulsed light beam 13 are determined based on at least one thermal treatment parameter, which may include a target surface temperature, a predetermined preliminary surface temperature, a predetermined subsequent surface temperature T 27 , a predetermined temperature ramp, a time at and / or over a predetermined temperature, a predetermined temperature-depth profile 8 of the substrate 4, a predetermined depth.

[0074] The predetermined depth is a depth below which the temperature of the substrate 4 should not exceed a certain temperature in order to avoid damaging devices embedded deeper within the substrate 4. The certain temperature is, for example, 400°C.

[0075] FIG. 4 is a graph of the change in temperature in region 3 with respect to time during the thermal process.

[0076] 4 shows a second temperature curve 37 corresponding to the change in the surface temperature of the surface region 5. 41 3 shows a third temperature curve 39 corresponding to another temperature change of the buried layer 41 at a depth D 41 is, for example, about 1 micrometer.

[0077] At the start of the thermal treatment, the substrate 4 has an initial temperature-depth profile and the surface temperature Ts of the surface region 5 is an initial surface temperature T0. For example, the substrate 4 is at room temperature.

[0078] During step b), a preliminary pulse 25 of the pulsed light beam 13 is irradiated onto the surface area 5. The preliminary pulse 25 thereby provides a preliminary energy amount E 25 to the surface area 5, heat is generated locally by the surface area 5, and the surface temperature Ts is increased to a predetermined preliminary surface temperature T 25 The local heating, also called the thermal equilibration phase, reaches 1×10 -10 It happens faster than a second.

[0079] During this "on state" of the pulsed light beam 13, the surface temperature Ts increases to a predetermined preliminary surface temperature T 25 , for example, to about 240°C.

[0080] The pulsed light beam 13 is then in an "off state". During the "off state", which corresponds to the time interval Δt between two pulses, the surface area 5 is not irradiated with the pulsed light beam 13. As a result, the surface temperature Ts decreases and reaches a predetermined intermediate surface temperature Ti.

[0081] The duration of the time interval Δt is specified in step a) such that the surface area 5 is only partially relaxed. The surface area 5 relaxes in proportion to the time interval Δt. In other words, the surface temperature Ts does not return to the initial value T0. In other words, the predetermined intermediate surface temperature Ti is higher than the initial value T0.

[0082] Furthermore, during the time interval Δt, the other temperature 37 of the buried layer increases as the heat generated by the surface region 5 diffuses towards the buried region 6. During step a), the values ​​of the parameters for the pulsed light beam 13 were specified such that the generated preliminary heat quantity diffuses to a predefined diffusion depth to obtain a predefined temperature-depth profile of the substrate 4.

[0083] During step c), after a time interval Δt a subsequent pulse 27 is irradiated onto the surface area 5. The subsequent pulse 27 thereby generates a subsequent energy amount E 27 is provided to the surface region 5. The surface region 5 generates a subsequent heat quantity, and the surface temperature Ts is a predetermined subsequent surface temperature T 27 Then, a cumulative effect is observed, i.e., at a given intermediate surface temperature T i is higher than the initial surface temperature T0, the subsequent surface temperature T 27 is the predetermined preliminary surface temperature T 25 In this example, all pulses 25, 27 provide the same amount of energy.

[0084] Step b) of irradiating the surface region 5 with a preliminary pulse 25 and step c) of irradiating the surface region 5 with a subsequent pulse 27 are repeated until the surface temperature Ts of the surface region 5 reaches the target surface temperature and the substrate temperature reaches the target temperature-depth profile.

[0085] Optionally, if the surface area 5 to be heat-treated is larger than the light spot 20, during step d) the pulsed light beam 13 is scanned over the surface area 5. In this case, a first part of the surface area 5 is irradiated with a pre-pulse 25 and a second part of the surface area 5 is irradiated with a subsequent pulse 27.

[0086] In figure 4, 41 cycles corresponding to 41 pulses are seen. It can be seen that the surface temperature Ts exhibits a periodic variation, changing rapidly between a surface temperature maximum reached during the "on state", corresponding to the preliminary and subsequent temperatures, and a surface temperature minimum reached during the "off state".

[0087] In contrast, the third temperature curve 39 of the buried layer 41 has a smooth profile. The buried layer 41 is not subjected to cyclic temperature changes.

[0088] 5a and 5b show examples of structures that can be treated with the thermal treatment of the present invention.

[0089] Figures 5a and 5b show a silicon FINFET structure 43. The fins 45 are separated by a distance d, for example equal to 50 nanometers.

[0090] In FIG. 5 a , the pulsed laser beam 13 is in the “on state” and a pulse of the pulsed light beam 13 is directed onto the surface area 5 .

[0091] The pulsed light beam 13 is not strictly limited to the surface region 5. The pulsed light beam 13 penetrates a few nanometers into the FINFET structure 43. For example, for an ultraviolet laser, the pulsed light beam penetrates 1 nanometer into germanium material, 3 nanometer into silicon-germanium material, and 7 nanometer into silicon material. For example, for an ultraviolet laser, the pulsed light beam penetrates up to 10 nanometers into common semiconductors. For example, for an ultraviolet laser, the pulsed light beam penetrates up to 200 nanometers into metals and other wide-gap materials such as silicon carbide (SiC) or gallium nitride (GaN).

[0092] The FINFET structure 43 receives an amount of energy from the pulse, causing localized heating (thermal equilibration) in areas 47 of the FINFET structure 43 .

[0093] In Figure 5b, the pulsed laser beam 13 is in the "off state" and the surface region 5 is not irradiated. Heat diffuses into the FINFET structure 43, over area 47. Arrows 49 indicate the direction of heat diffusion.

[0094] FIG. 6 is a graph of temperature variation at various depths in the FINFET structure 43.

[0095] In this example, the temperature of silicon surface region 5 of FINFET structure 43 should withstand gradual annealing up to or above a target temperature, here equal to the melting point of 1415° C. Substrate 4 has a buried layer at a depth of 10 micrometers below surface region 5, which should not be annealed to temperatures higher than 500° C. to prevent damage.

[0096] Values ​​of parameters for the pulsed light beam 13 are specified to meet the temperature requirements mentioned above. The following values ​​of parameters have been specified to meet the temperature requirements: -Pulse duration = 0.9 nanoseconds -Time interval = 10 nanoseconds -Repetition rate = 100 MHz -Energy / pulse = 10 millijoules / square centimeter -Peak temperature = 272.98℃

[0097] After the substrate 4 is subjected to a heat treatment, the surface temperature is above 1420° C., in other words above the melting point. The time at that temperature is 7.4 microseconds.

[0098] 6, the fourth temperature curve 51 corresponds to the higher part of the surface temperature envelope and the fifth temperature curve 53 corresponds to the lower part of the envelope. After 5 microseconds of heat treatment, the fourth temperature curve 51 has reached the target temperature.

[0099] A sixth temperature curve 55 corresponds to the temperature change of the layer at a depth of 1 micrometer. A seventh temperature curve 57 corresponds to the temperature change of the layer at a depth of 2 micrometers. An eighth temperature curve 59 corresponds to the temperature change of the layer at a depth of 5 micrometers. A ninth temperature curve 61 corresponds to the temperature change of the layer at a depth of 10 micrometers.

[0100] In FIG. 6 it can be seen that the temperature decreases with depth.

[0101] It can also be seen that after 5 microseconds of heat treatment, the temperature of the layer buried at a depth of 10 micrometers reaches about 420°C, which is lower than the desired 500°C.

[0102] FIG. 7 shows the different surface temperature dynamics obtained with different values ​​of the parameters for the pulsed light beam 13 .

[0103] A tenth temperature curve 63 is obtained by irradiating the surface region 3 with a tenth pulse train 65. The tenth temperature curve 63 corresponds to a long-term thermal treatment with a smooth temperature gradient and a relatively uniform depth. The thermal treatment achieved with the tenth pulse train 65 is similar to classical equilibrium annealing, also called millisecond rapid thermal annealing (RTP).

[0104] An eleventh temperature curve 67 is obtained by irradiating the surface region 3 with an eleventh pulse train 69. The pulses of the eleventh pulse train 69 provide a higher energy to the surface region 5 compared to the pulses of the tenth pulse train 65. The thermal treatment achieved with the eleventh pulse train 69 is similar to classical steps and repeating nanosecond processes.

[0105] A twelfth temperature curve 71 is obtained by irradiating the surface region 5 with a twelfth pulse train 73. The thermal treatment realized with the twelfth pulse train 73 is an intermediate solution with significant selectivity and high peak temperatures, but with a temperature gradient that is less steep than that of classical pulsed laser treatments, and therefore less aggressive and with less risk of damaging the devices in the surface region 5 and the devices embedded in the substrate 4.

[0106] 8a, 8b and 8c show yet another possibility to control the surface envelope by controlling the energy delivered by each pulse of the pulse train.

[0107] 8a shows a thirteenth temperature curve 75, which shows a standard surface temperature rise. In this example, the surface region 5 is subjected to a thirteenth pulse train 77 having pulses of equal energy and uncontrolled cooling at the end of the pulse train.

[0108] FIG. 8b shows a fourteenth temperature curve 79, which shows the stabilization of the envelope at a temperature obtained by a standard temperature increase and then a corresponding decrease in the energy per pulse of the fourteenth pulse train 81.

[0109] FIG. 8c shows a fifteenth temperature curve 83, which shows a standard temperature rise followed by a controlled cooling achieved by gradually decreasing the energy provided by each pulse of the fifteenth pulse train 85.

[0110] According to other examples, other combinations of parameters for the pulsed light beam 13 can be used, for example varying both the time interval Δt and the energy delivered by each pulse during the thermal treatment.

[0111] According to another example, the method can be applied to a substrate 4 whose implanted region comprises a region 87 implanted with a dopant element having a predetermined dopant element concentration-depth profile. In this case, the steps b) of irradiating the surface region 5 with a pre-pulse 25 and c) of irradiating the surface region 5 with a subsequent pulse 27 are repeated until the substrate temperature exhibits a target temperature-depth profile. The target temperature-depth profile is adapted to activate the dopant element in the implanted region 87.

[0112] For example, the methods are applicable to the formation of deep junction devices, such as silicon insulated gate bipolar transistors (IGBTs).

[0113] To fabricate silicon IGBT devices, dopant elements are implanted into a silicon substrate by bombarding a surface region, here the backside, of the silicon substrate with dopant elements. For example, the implanted area of ​​the substrate is 1×10 13 It is possible to have dopant element concentrations higher than atoms per square centimeter.

[0114] Dopant elements modulate the electrical properties of the substrate by generating unipolar carriers: acceptor-type dopant elements generate positive unipolar carriers, and donor-type dopant elements generate negative unipolar carriers.

[0115] 9 shows a substrate 4 including an implanted region 87. In this example, the implanted region 87 is implanted with one dopant species, here phosphorus (Ph). The phosphorus dopant element is adapted to generate one type of unipolar carriers.

[0116] FIG. 9 represents a predetermined implantation profile of phosphorus 89 in the substrate 4 as a function of the depth of the substrate, in other words a predetermined dopant element concentration-depth profile 89 of the substrate 4 .

[0117] Implant energies between 700 keV and 2 MeV are used to obtain deep implant profiles reaching depths of 1 micrometer to 5 micrometers.

[0118] The implanted region 87 is at a depth greater than the surface region, for example 5-500 nanometers, in a buried region of the substrate. The implanted region 87 has a thickness, for example equal to or less than 500 nanometers.

[0119] In this example, to activate the phosphorus dopants implanted at a depth of 2 micrometers, the temperature at the 2 micrometer depth of the implantation region 87 should be higher than or equal to the activation temperature Ta. The activation temperature Ta is, for example, higher than or equal to 700° C. However, the temperature of the surface opposite to the implantation surface of the substrate 4 cannot be heated to a temperature above 400° C. to prevent damage. Preferably, the opposite surface should not be heated to a temperature above 100° C.

[0120] 9, the activation temperature Ta is represented by a horizontal dashed line 90. Regions of the substrate 4 that are at a temperature higher than the activation temperature Ta are activated. Regions of the substrate 4 that are at a temperature lower than the activation temperature Ta are not activated.

[0121] 9 also shows a series of temperature-depth profiles 91, 93, 95, 97, 99, 101, 103, 105 of the substrate 4. Each of the temperature-depth profiles 91-105 is obtained when the substrate 4 is subjected to the method of the present invention. Each of the temperature-depth profiles 91-105 corresponds to a different combination of parameter values ​​for the pulsed light beam. In this example, each temperature-depth profile 91-105 is obtained with a different combination of energy density and number of pulses.

[0122] For example, the temperature-depth profile 91 corresponds to a pulse sequence having a higher energy density and a lower number of pulses than the other temperature-depth profiles 93-105. In comparison with the other temperature-depth profiles 93-105, it can be seen that the temperature of the substrate 4 is higher at shallower depths and drops to lower temperatures faster at deeper depths than the other temperature-depth profiles 93-105.

[0123] When the surface region 5 is exposed to a pulse sequence with a high energy density and low pulse number, the heat generated is confined to the vicinity of the surface region, and therefore the substrate temperature near the surface region 5 is high and the substrate temperature near the deeper depths is low.

[0124] The temperature-depth profile 105 corresponds to a pulse sequence having a lower energy density and a higher number of pulses than the other temperature-depth profiles 91 to 103. It can be seen that the temperature change near the surface and at the deepest depth is small compared to the other temperature-depth profiles 91 to 103.

[0125] When the surface region 5 is exposed to a pulse sequence with a lower energy density and a higher pulse number, the heat dissipates deeper into the substrate, so that the substrate temperature near the surface region 5 and at the deepest depth are close.

[0126] Temperature-depth profiles 93-103 between the steepest temperature-depth profile 91 and the flattest temperature-depth profile 103 correspond to other different combinations of parameter values ​​for the pulsed light beam, with the steeper profiles having higher energy densities and fewer pulse numbers than the flatter profiles.

[0127] 9, it can be seen that not all temperature-depth profiles are adapted to activate the dopant element at a depth of 2 micrometers. Here, only the temperature-depth profiles 99-105 are adapted, because the substrate temperature at a depth of 2 micrometers is higher than the activation temperature Ta. Therefore, the target temperature-depth profile adapted to activate the phosphorus dopant element may be selected from any of the temperature-depth profiles 99-105.

[0128] One of the temperature-depth profiles 99-105 can be obtained, for example, by irradiating a surface area with 500 pulses of less than 1 nanosecond duration, each pulse having an energy density of 19 millijoules per square centimeter and a time interval Δt of 12 nanoseconds.

[0129] Another of the temperature-depth profiles 99-105 can be obtained by irradiating a surface region with, for example, 1000 pulses of less than 1 nanosecond duration, each pulse having an energy density of 15 millijoules per square centimeter and a time interval Δt of 12 nanoseconds. In this second example energy profile, the longer the diffusion time, the deeper the effects.

[0130] Figure 10 shows another example, where the substrate 4 is implanted with two dopant elements, where the two dopant elements include phosphorus and boron. In the silicon substrate, the boron dopant element acts as an acceptor. In other words, the boron dopant element is adapted to generate other types of unipolar carriers, more precisely holes.

[0131] Thus, in this example, the substrate is implanted with dopant elements adapted to generate two types of unipolar carriers.

[0132] Phosphorus atoms may be implanted, for example, as in the previous examples, and boron atoms may be implanted, for example, with an energy of 1 to 100 kiloelectron volts.

[0133] Figure 10 shows the same curves as in Figure 9. In addition, Figure 10 also shows the boron implantation profile (107) of the substrate 4 as a function of the substrate depth, in other words the other dopant element concentration-depth profile 107 of the substrate 4.

[0134] The different temperature-depth profiles 91 - 105 can be used to select a target temperature-depth profile and, therefore, a combination of energy density and number of pulses for activating the dopant elements implanted in the substrate 4 .

[0135] The method is applicable to substrates made of semiconductor materials selected from the group including silicon carbide, silicon germanium, germanium, gallium nitride, gallium arsenide, diamond.

[0136] Depending on the application, the dopant elements are selected from the group including boron, phosphorus, arsenic, aluminum, gallium, indium, thallium, antimony, and bismuth.

Claims

1. A method for heat treating a substrate (4) with a pulsed light beam (13), the substrate (4) having a surface region (5) and a buried region (6) including a region (87) implanted with a dopant element having a predetermined dopant element concentration-depth profile (89, 107), the substrate temperature of the substrate (4) exhibits an initial temperature-depth profile, and the surface temperature (Ts) of the surface region (5) is an initial surface temperature (T0); b) irradiating said surface area (5) with a preliminary pulse (25) of said pulsed light beam (13), said preliminary pulse (25) thereby providing said surface area (5) with a preliminary amount of energy, whereby said surface area (5) generates a preliminary amount of heat, and said surface temperature (Ts) increases to a predetermined preliminary surface temperature (T ２５ ) and c) irradiating said surface area (5) of said substrate (4) after a time interval (Δt) with a subsequent pulse (27) of said pulsed light beam (13), said subsequent pulse (27) thereby providing a subsequent amount of energy to said surface area (5), which causes said surface area (5) to generate a subsequent amount of heat, such that said surface temperature (Ts) increases to a predetermined subsequent surface temperature (T ２７ and wherein the time interval (Δt) is specified such that during the time interval (Δt) the surface temperature (Ts) reaches a predetermined intermediate surface temperature (Ti), the predetermined intermediate surface temperature (Ti) being higher than the initial surface temperature (T0), whereby During said time interval (Δt), said reserve heat quantity is diffused into said implant region (6) to a predetermined depth of said substrate (4) such that said substrate temperature exhibits a predetermined intermediate temperature-depth profile; a) determining values ​​of a parameter for said pulsed light beam (13) to reach said predetermined preliminary surface temperature (T 25 ), said predetermined intermediate surface temperature (Ti) and said predetermined subsequent temperature-depth profile, said parameter for said pulsed light beam (13) being selected from the group comprising: number of pulses.

2. 2. The method of claim 1, wherein the steps b) of irradiating the surface area (5) with the preliminary pulse (25) and c) of irradiating the surface area (5) with the subsequent pulse (27) are repeated until the surface temperature (Ts) reaches a target surface temperature and the substrate temperature exhibits a target temperature-depth profile.

3. The method of claim 2, wherein the target temperature-depth profile is adapted to activate the dopant element in the implantation region (87).

4. 4. The method of claim 3, wherein the implanted region (87) is at a depth greater than 500 nanometers from the surface region (5) and has a thickness less than 50 micrometers.

5. 5. The method according to claim 3 or 4, wherein the dopant elements are adapted to generate one type of unipolar carriers in the implantation region (87).

6. 5. The method according to claim 3 or 4, wherein the dopant elements are adapted to generate two types of unipolar carriers in the implantation region (87).

7. The method according to any one of claims 2 to 6, wherein the substrate (4) is a semiconductor material selected from the group comprising silicon carbide, silicon germanium, germanium, gallium nitride, gallium arsenide, diamond.

8. The method according to any one of claims 2 to 7, wherein the target surface temperature is the melting point (Tm) of the surface region (5).

9. The method according to any one of claims 1 to 8, further comprising a step d) of scanning the pulsed light beam (13) over the surface area (5), wherein during step a) the set of parameters relating to the pulsed light beam further comprises a scanning speed of the pulsed light beam (13).

10. The method according to any one of claims 1 to 9, wherein the amount of preliminary energy delivered by the preliminary pulse (25) is different from the amount of subsequent energy delivered by the subsequent pulse (27).

11. The method according to any one of claims 1 to 10, wherein the amount of preliminary energy and the amount of subsequent energy are less than the amount of energy required for the surface region (5) to reach a melting point (Tm) of the surface region (5) of the substrate (4).

12. The method according to any one of the preceding claims, wherein each of the pre-pulse (25) and the post-pulse (27) has a duration equal to or less than 1 nanosecond.

13. The method according to any one of the preceding claims, wherein the time interval (Δt) between the pre-pulse (25) and the subsequent pulse (27) is equal to or less than 25 nanoseconds.

14. The method according to any one of the preceding claims, wherein said pulsed light beam (13) has a wavelength equal to or shorter than 532 nanometers.

15. The method according to any one of the preceding claims, wherein the energy density of the pulsed light beam (13) is higher than 1 millijoule per square centimeter.

16. A system (1) for thermally treating a substrate (4) with a pulsed light beam (13), the substrate (4) having a surface region (5) and a buried region (6) including a region (87) implanted with a dopant element having a predetermined dopant element concentration-depth profile (89, 107), the substrate temperature of the substrate (4) exhibits an initial temperature-depth profile, the surface temperature (Ts) of the surface region (5) is an initial surface temperature (T0), the system (1) comprising: a light source (7) adapted to emit a light beam (11); - a beam control system (9) configured to generate said pulsed light beam (13) from said luminous beam (11), the system being adapted to generate a preliminary pulse (25) and a subsequent pulse (27); Including, - the preliminary pulse (25) of the pulsed light beam (13) is irradiated onto the surface area (5) of the substrate (4), the preliminary pulse thereby providing the surface area (5) with a preliminary amount of energy, whereby the surface area (5) generates a preliminary amount of heat, and the surface temperature (Ts) is increased to a predetermined preliminary surface temperature (T ２５ ) and - the subsequent pulse (27) of the pulsed light beam (13) is irradiated onto the surface area (5) of the substrate (4) after a time interval (Δt), the subsequent pulse (27) thereby providing a subsequent amount of energy to the surface area (5), whereby the surface area (5) generates a subsequent amount of heat, and the surface temperature (Ts) increases to a predetermined subsequent surface temperature (T ２７ ) and the system is adapted to generate the subsequent pulse (27) after a time interval (Δt), the time interval (Δt) being specified such that during the time interval (Δt) the surface temperature (Ts) reaches a predetermined intermediate surface temperature (Ti), the predetermined intermediate surface temperature (Ti) being higher than the initial surface temperature (T0); whereby during said time interval (Δt) said reserve heat quantity is diffused into said implant region (6) to a predetermined depth of said substrate (4), whereby said substrate temperature exhibits a predetermined intermediate temperature-depth profile; The system (1), wherein the beam control system (9) is configured to determine values ​​of parameters for the pulsed light beam (13) in order to reach the predetermined preliminary surface temperature (T25), the predetermined intermediate surface temperature (Ti), and a predetermined subsequent temperature-depth profile, the parameters for the pulsed light beam (13) being selected from the group comprising: a number of pulses.

17. The system (1) of claim 16, configured to repeat the irradiation of the surface region (5) with the preliminary pulse (25) and the irradiation of the surface region (5) with the subsequent pulse (27) until the surface temperature (Ts) reaches a target temperature and the substrate temperature exhibits a target temperature-depth profile.

18. The system of claim 17, wherein the target temperature-depth profile is adapted to activate the dopant element in the region (87) where the dopant element is implanted.

19. Each of the pre-pulse (25) and the subsequent pulse (27) has a duration (t ｐ The system according to any one of claims 16 to 18, further comprising:

20. The system according to any one of claims 16 to 19, wherein the pulsed light beam (13) has a wavelength equal to or shorter than 532 nanometers.

21. A system according to any one of claims 16 to 20, wherein the time interval (Δt) between the pre-pulse (25) and the subsequent pulse (27) is equal to or less than 25 nanoseconds.

22. The system according to any one of claims 16 to 21, wherein the energy density of the pulsed light beam (13) is higher than 1 millijoule per square centimeter.

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