Crystalline silicon carbide fiber and method for manufacturing same, and ceramic composite substrate

A method for manufacturing a crystalline silicon carbide fiber, the method comprising:

• a pretreatment step of heating an amorphous silicon carbide fiber containing boron and zirconium to 1550° C. to 1850° C. in an inert gas atmosphere different from nitrogen to obtain a first heating treatment product;
• a calcination step of heating the first heating treatment product to 1900° C. to 2200° C. in an inert gas atmosphere to obtain a second heating treatment product containing SiC crystal grains;
• and
• an annealing step of heating the second heating treatment product to 1800° C. to 2100° C. in an inert gas atmosphere including nitrogen to obtain the crystalline silicon carbide fiber,
• wherein the crystalline silicon carbide fiber contains silicon carbide, boron nitride, and zirconium carbide,
• the crystalline silicon carbide fiber has a content of Si of 64% by weight or more and a content of C of 28% by weight or more, and
• an average particle size of SiC crystal grains is 100 nm to 200 nm wherein a content of Al in a grain boundary phase including amorphous SiC is 0.02 atom % to 0.1 atom % and a content of Zr in a grain boundary phase including amorphous SiC is 0.02 atom % to 0.1 atom %.