Method for producing a semiconductor substrate comprising a layer deposited by epitaxy
By forming an oxide layer on the susceptor using a gaseous oxygen mixture, the method addresses the issue of reactive gas deposition on semiconductor substrates, ensuring consistent and high-quality epitaxial layer deposition without complex equipment modifications.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- SOITEC SA
- Filing Date
- 2023-02-07
- Publication Date
- 2026-06-26
Smart Images
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Abstract
Description
Title of the invention: Method for producing a semiconductor substrate comprising a layer deposited by epitaxy. Technical field
[0001] The field of the invention is that of the processes for producing a semiconductor substrate comprising a layer deposited by epitaxy. DESCRIPTION OF THE ASSOCIATED ART
[0002] An epitaxial deposition process on a semiconductor substrate is described, for example, in US patent 7,479,187 B2, which discloses that it is advantageous and often necessary to remove residues from the epitaxial reactor surfaces that have been uncontrolled during the deposition of, for example, silicon onto the semiconductor substrate. This step, called "chamber etching," is performed more or less frequently depending on the degree of contamination and quality requirements. In some cases, it is advantageous to perform chamber etching after the deposition of an epitaxial layer on a semiconductor substrate before a subsequent epitaxial deposition is performed on another semiconductor substrate. In other cases, chamber etching may also occur less frequently, for example, every 2 to 8 epitaxial depositions on semiconductor substrates.
[0003] US patent 7,479,187 B2 also proposes coating the etched surfaces in the epitaxial reactor with a thin silicon film by passing a deposition gas through the epitaxial reactor. The thin silicon film seals the surfaces and prevents contaminants diffusing from the surfaces from penetrating the growing epitaxial layer during subsequent epitaxial deposition. Depositing a thin silicon film onto the surfaces of the epitaxial reactor after chamber etching is called "chamber coating."
[0004] Epitaxial deposition processes employ a susceptor, for example a graphite susceptor, which comprises one or more circular concavities called pockets, for example made of silicon carbide, each formed at a substrate placement position. The passage of reactive gases between a pocket and the back face of a substrate positioned on that pocket can lead to the deposition of reactive gases on the back face of the substrate. Such deposition is likely to degrade the surface condition of the substrate's back face. This degraded surface condition can render the substrate unsuitable for use in an electronic component manufacturing process, particularly CMOS circuit fabrication.
[0005] In order to circumvent this difficulty, it is known, for example from US 7,601,224 B2, to use susceptors with gas passages to allow a stream of gas to be directed towards the back face of the substrate capable of preventing the flow of reactive gases under the substrate, thus inhibiting the undesirable deposition of reactive gases on the back face of the substrate.
[0006] The use of such susceptors is likely to disrupt the flow of reactive gases in the chamber, which may lead to non-uniformity of the epitaxial deposit. Furthermore, this use is complex, costly, and requires significant modification of the equipment. BRIEF DESCRIPTION OF THE INVENTION
[0007] The invention aims to avoid the deposition of reactive gases on the rear face of a substrate during an epitaxial deposition on the front face thereof by overcoming the aforementioned disadvantages of gas-passage susceptors.
[0008] To this end, the invention proposes a method for producing a semiconductor substrate comprising a layer deposited by epitaxy, successively comprising the steps of etching a susceptor of an epitaxial reactor, coating the susceptor, placing a semiconductor substrate on the susceptor, and depositing an epitaxial layer on the semiconductor substrate. The method further comprises, after coating and before deposition, exposing the susceptor to a gaseous mixture containing oxygen. This exposure leads to oxidation of the susceptor, which forms an oxide layer. During the deposition of the epitaxial layer on a front face of the substrate, this oxide layer is intercalated between the susceptor and a back face of the substrate and prevents the deposition of reactive gases on the back face of the substrate.
[0009] Some preferred, but not limiting, aspects of the present process are as follows:
[0010] - the gas mixture containing oxygen is a mixture of hydrogen and argon comprising between 0.1% and 10% O2
[0011] - O2 is introduced into the epitaxial reactor at a flow rate between 0.1 and 10 sim
[0012] - exposure of the susceptor to a gaseous mixture containing oxygen is carried out after said coating and before said installation;
[0013] - exposure of the susceptor to the gaseous mixture containing oxygen forms an oxide layer less than 10Å thick on the surface of the susceptor;
[0014] - the steps of placing a semiconductor substrate on the susceptor and of the deposition of an epitaxial layer on the semiconductor substrate are repeated for at least one other semiconductor substrate without in the meantime etching, coating and oxidizing the susceptor;
[0015] - exposure of the susceptor to a gaseous mixture containing oxygen is carried out after said implementation and before said filing;
[0016] - exposure of the susceptor to a gaseous mixture containing oxygen is carried out while increasing the temperature of the epitaxial reactor to an epitaxial deposition temperature;
[0017] - the steps for placing a semiconductor substrate on the susceptor, exposure of the susceptor to a gaseous mixture containing oxygen and deposition of an epitaxial layer on the semiconductor substrate are repeated for at least one other semiconductor substrate without etching and coating the susceptor in the meantime;
[0018] - it further comprises, after the semiconductor substrate has been placed on the susceptor and before the deposition of the epitaxial layer on the semiconductor substrate, a baking step of the semiconductor substrate, which removes, except on the underside of the semiconductor substrate, the oxide layer formed by the exposure of the susceptor to a gaseous mixture containing oxygen. Brief description of the drawings
[0019] Other aspects, objectives, advantages and features of the invention will become more apparent upon reading the following detailed description of its preferred embodiments, provided by way of non-limiting example, and made with reference to the accompanying drawings, in which:
[0020] - Fig. 1 is a schematic representation of the temperature evolution at the interior of an epitaxial reactor during an epitaxial deposition process according to the prior art;
[0021] - [Fig.2] is a schematic representation of the temperature evolution at the interior of an epitaxial reactor during an epitaxial deposition process according to a first embodiment of the invention;
[0022] - [Fig. 3] is a schematic representation of the temperature evolution at the interior of an epitaxial reactor during an epitaxial deposition process according to a second embodiment of the invention;
[0023] - [Fig. 4] is a schematic representation of the steps in a deposition process epitaxial according to a first embodiment of the invention;
[0024] - [Fig. 5] is a schematic representation of the steps in a deposition process epitaxial according to a second embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION
[0025] The invention relates to a method for producing a semiconductor substrate comprising a layer deposited by epitaxy, which includes exposing a susceptor of an epitaxy reactor to a gaseous mixture containing oxygen.
[0026] The invention thus utilizes an epitaxial reactor into which a gaseous mixture containing oxygen can be introduced so as to expose the materials placed therein to the gaseous mixture containing oxygen, thereby achieving oxidation. situ of these materials. This in situ oxidation forms an oxide layer which, when the epitaxial layer is deposited on a front face of the substrate, is intercalated between the susceptor and a back face of the substrate and prevents the deposition of reactive gases on the back face of the substrate.
[0027] As mentioned below, the susceptor is exposed to a gas mixture containing oxygen after the "chamber coating" and before the formation of the epitaxial layer. For example, the susceptor may be exposed to a gas mixture containing oxygen after the "chamber coating," before the semiconductor substrate on which the epitaxial layer is to be deposited is placed on the susceptor, or after the semiconductor substrate has been placed on the susceptor before the epitaxial deposition is performed on the semiconductor substrate.
[0028] Figure 1 is a schematic representation of the evolution over time t of the temperature T inside an epitaxial reactor during a prior art epitaxial deposition process. As shown in Figure 1, after one or more epitaxial EPI depositions on semiconductor substrates, carried out in the epitaxial reactor (four epitaxial EPI depositions in the illustrated example), the susceptor is etched in an ETCH chamber etching step and coated with a silicon layer in a CO AT chamber coating step. After this, one or more additional epitaxial EPI depositions can be performed before repeating the ETCH chamber etching and CO AT chamber coating.
[0029] Figures 2 and 3 are schematic representations of the evolution over time t of the temperature T inside an epitaxial reactor during an epitaxial deposition process according to embodiments of the invention. As these figures show, the process of the invention comprises a step designated ISO of exposing the susceptor to a gas mixture containing oxygen, this ISO step being carried out after coating in a CO₂ AT chamber and before performing an epitaxial EPI deposition.
[0030] Figure 4 illustrates steps in a process for producing a semiconductor substrate comprising a layer deposited by epitaxy according to a first embodiment of the invention. This process uses a susceptor S of an epitaxial reactor, for example a graphite susceptor, which includes one or more circular concavities P called pockets, for example made of silicon carbide, each formed at a substrate placement position.
[0031] In step (a), the susceptor is subjected to a chamber etching step, for example in H2 and HCl. H2 can be introduced into the epitaxial reactor at a flow rate of 3 to 100 sim (standard liters per minute), while HCl can be introduced into the epitaxial reactor at a flow rate of 5 to 20 sim. The chamber etching step can be carried out at a temperature between 1050°C and 1200°C for a duration between 20 seconds and 400 seconds.
[0032] In step (b), the susceptor is subjected to a chamber coating step to form a silicon film on it, for example, polycrystalline silicon. The chamber coating step may include the introduction of a mixture of H2 and TCS (trichlorosilane) into the epitaxial reactor. The H2 may be introduced into the epitaxial reactor at a flow rate of 3 to 100 sim (standard liters per minute), while the TCS may be introduced into the epitaxial reactor at a flow rate of 10 to 19 sim. The chamber coating step may be carried out at a temperature between 1000°C and 1150°C for a duration of between 10 and 100 seconds.
[0033] In step (c), the coated susceptor is exposed to a gas mixture containing oxygen. This exposure forms an oxide layer 20 on the surface of the susceptor. The thickness of this oxide layer is, for example, less than 10 Å. More specifically, as mentioned above, this step (c) performs an in situ oxidation of the susceptor, the oxygen-containing gas mixture introduced into the epitaxial reactor reacting in situ with the coated susceptor to form the oxide layer 20. In [Fig. 2], these three steps (a), (b), and (c) are respectively designated ETCH, COAT, and ISO.
[0034] The step of exposing the susceptor to the oxygen-containing gas mixture can be carried out at a temperature between 900°C and 1100°C for a duration between 5 and 100 seconds. The oxygen-containing gas mixture to which the susceptor is exposed during in situ oxidation can comprise hydrogen as the carrier gas and argon containing between 0.1% and 10% O2. In one possible embodiment, the in situ oxidation comprises introducing oxygen into the epitaxial reactor at a flow rate between 0.1 and 10⁻¹¹ sim with H2 carrier gas at a flow rate between 5 and 100 sim.
[0035] The process continues with a step (d) of placing one or more semiconductor substrates 30 onto the oxide layer 20 of the susceptor S (more precisely at the substrate placement position(s) corresponding to the pocket(s)). The oxide layer 20 is thus intercalated between the susceptor and the back face of each of the substrate(s), thereby preventing the diffusion of reactive gases between the susceptor and the back face of the substrate(s) during subsequent steps.
[0036] The process then comprises a step (e) of baking the semiconductor substrate(s) 30 on the susceptor S, which removes the oxide layer 20 except on the underside of the semiconductor substrate(s) 30 (i.e., the oxide layer remains between the back face of the substrate(s) and the susceptor), and a step (f) of depositing an epitaxial layer 30 on the front face of each of the semiconductor substrate(s) 30. In [Fig. 2], these two steps (e) and (f) are respectively designated BAKE and EPI. As illustrated in [Fig. 2], baking is generally performed after a temperature ramp-up, and epitaxial deposition is performed after baking and followed by a temperature ramp-down. For simplicity, the BAKE baking step is shown only once in [Fig. 2], but it is understood that such a baking step precedes each EPI epitaxial deposition.
[0037] The BAKE cooking step can be carried out in H2 introduced at a flow rate of between 3 and 100 sim. It can be carried out at a temperature of between 950°C and 1200°C for a duration of between 5 and 100 seconds.
[0038] The epitaxial deposition (EPI) step is carried out in H2 using a reactive gas for epitaxial deposition, such as TCS. The TCS can be introduced at a flow rate of between 5 and 50 sim, while the carrier gas H2 can be introduced at a flow rate of between 3 and 100 sim. The epitaxial deposition (EPI) step can be carried out at a temperature of between 950°C and 1200°C for a duration of between 10 and 1000 seconds.
[0039] According to a possible variant of this first embodiment, the steps of placing a semiconductor substrate on the susceptor, baking the semiconductor substrate, and depositing an epitaxial layer on the semiconductor substrate are repeated for at least one other semiconductor substrate without intervening to etch, coat, and in situ oxidize the susceptor. By way of example, four to six epitaxial deposits can be made before exposing the susceptor to a new sequence of etch, coat, and in situ oxidation. In [Fig. 2], four epitaxial EPI deposits are made between two sequences of etch, coat, and in situ oxidation of the susceptor.
[0040] Figure 5 illustrates the steps of a process for producing a semiconductor substrate comprising a layer deposited by epitaxy according to a second embodiment of the invention. Steps (a) and (b) are respectively a chamber etching step and a chamber coating step similar to those mentioned above in relation to Figure 4. After coating, the process includes a step (c) of placing one or more semiconductor substrates 30 onto the susceptor S (more precisely, at the substrate placement position(s) corresponding to the pocket(s)). As schematically illustrated in Figure 5, the semiconductor substrate 30 may exhibit degraded local flatness values in its edge region.
[0041] The exposure of the coated susceptor to a gaseous mixture containing oxygen then takes place in step (d), by an in situ oxidation during which the gaseous mixture containing oxygen introduced into the epitaxy reactor reacts in situ with the coated susceptor to form an oxide layer 25 located both on the front face of the semiconductor substrate and on the back face of the semiconductor substrate, between the semiconductor substrate and the coated susceptor. The thickness of this oxide layer is, for example, less than 10 Å. In [Fig. 3], this in situ oxidation is designated by ISO.
[0042] The oxygen-containing gas mixture to which the susceptor is exposed during in situ oxidation may comprise hydrogen as a carrier gas and argon comprising between 0.1% and 10% O2. In one possible embodiment, the in situ oxidation comprises the introduction of oxygen into the epitaxial reactor at a flow rate greater than 0.1 sim while carrier gas H2 is introduced at a flow rate between 5 and 100 sim so as to ensure contact of the layer on the coated susceptor.
[0043] The in situ oxidation of the susceptor is followed by a step (e) of baking one or more semiconductor substrates 30 onto the susceptor S, which removes the oxide layer 25 except on the underside of the semiconductor substrate(s) 30 (i.e., it remains present between the back face of the substrate(s) and the susceptor), and a step (f) of deposition of an epitaxial layer 40 onto each of the semiconductor substrate(s) 30. In [Fig. 3], these two steps (e) and (f) are respectively designated BAKE and EPI. As illustrated in [Fig. 3], the baking is generally carried out after a temperature ramp-up, and the epitaxial deposition is carried out after baking and is followed by a temperature ramp-down. To simplify the illustration, the BAKE baking step is shown only once on [Fig.3], but it is understood that a baking step of this type precedes each epitaxial EPI deposition.
[0044] According to this second embodiment, the in situ oxidation of the ISO susceptor can be carried out during the temperature ramp-up, that is, during the increase in the temperature of the epitaxial reactor until an epitaxial deposition temperature is reached. By way of example, the in situ oxidation of the ISO susceptor is carried out during the temperature ramp-up at a rate of 3 to 10 °C / s, up to a temperature between 600 °C and 1100 °C. Its duration can be between 5 and 200 seconds.
[0045] The BAKE step can be carried out in H2 introduced at a flow rate of between 3 and 100 sim. It can be carried out at a temperature of between 950°C and 1200°C for a duration of between 5 and 100 seconds. The EPI epitaxial deposition step is carried out in H2 using a reactive gas for epitaxial deposition, such as TCS. The TCS can be introduced at a flow rate of between 5 and 50 sim, while the carrier gas H2 can be introduced at a flow rate of between 3 and 100 sim. The EPI epitaxial deposition step can be carried out at a temperature of between 950°C and 1200°C for a duration of between 10 and 1000 seconds.
[0046] According to a possible variant of this second embodiment, the implementation steps The process of placing a semiconductor substrate on the susceptor, exposing the susceptor to an oxygen-containing gas mixture, baking the semiconductor substrate, and depositing an epitaxial layer onto the semiconductor substrate is repeated for at least one other semiconductor substrate without etching and coating the susceptor in between. For example, four to six epitaxial depositions can be performed before exposing the susceptor to a new ETCH etching and COAT coating sequence. In [Fig. 3], four such epitaxial EPI depositions are performed between two ETCH etching and COAT coating sequences of the susceptor, each EPI deposition being preceded by in situ oxidation (ISO) of the susceptor.
Claims
Demands
1. A method for producing a semiconductor substrate comprising a layer deposited by epitaxy, comprising successively the following steps: - etching (ETCH) of a susceptor (S) of an epitaxial reactor; - coating (COAT) of the susceptor; - placement of a semiconductor substrate (30) on the susceptor; - deposition (EPI) of an epitaxial layer (40) on the semiconductor substrate (30); and furthermore, after coating and before deposition, the exposure (ISO) of the susceptor to a gaseous mixture containing oxygen, said exposure leading to an oxidation of the susceptor which forms an oxide layer (20, 25) on the surface of the susceptor, said oxide layer (20, 25) being found, during the deposition of the epitaxial layer on a front face of the semiconductor substrate, intercalated between the susceptor and a back face of the semiconductor substrate;and furthermore, after placement and before deposition (EPI), a baking (BAKE) of the semiconductor substrate which removes said oxide layer (20, 25) except on the underside of the semiconductor substrate (30).
2. A method according to claim 1, wherein the gas mixture comprising oxygen is a mixture of hydrogen and argon comprising between 0.1% and 10% O2.
3. Method according to claim 2, wherein O2 is introduced into the epitaxial reactor at a flow rate between 0.1 and 10 sim.
4. A method according to any one of claims 1 to 3, wherein the oxide layer (20, 25) formed by the exposure (ISO) of the susceptor to the oxygen-containing gas mixture has a thickness of less than 10Å.
5. A method according to any one of claims 1 to 4, wherein said exposure (ISO) is carried out after coating (COAT) and before said placement.
6. A method according to claim 5, wherein the steps of placing a semiconductor substrate on the susceptor and depositing an epitaxial layer on the semiconductor substrate are repeated for at least one other semiconductor substrate without in the meantime etching, coating, and exposing the susceptor to a gaseous mixture containing oxygen.
7. A method according to any one of claims 1 to 4, wherein said exposure (ISO) is carried out after said placement and before said deposit.
8. Method according to claim 7, wherein said exposure is carried out while increasing a temperature of the epitaxial reactor to an epitaxial deposition temperature.
9. A method according to any one of claims 7 and 8, wherein the steps of placing a semiconductor substrate on the susceptor, exposing the susceptor and depositing an epitaxial layer on the semiconductor substrate are repeated for at least one other semiconductor substrate without in the meantime etching and coating the susceptor.